quantum physics essay topics

What Is Quantum Physics?

This article was reviewed by a member of Caltech's Faculty .

Quantum physics is the study of matter and energy at the most fundamental level. It aims to uncover the properties and behaviors of the very building blocks of nature.

While many quantum experiments examine very small objects, such as electrons and photons, quantum phenomena are all around us, acting on every scale. However, we may not be able to detect them easily in larger objects. This may give the wrong impression that quantum phenomena are bizarre or otherworldly. In fact, quantum science closes gaps in our knowledge of physics to give us a more complete picture of our everyday lives.

Quantum discoveries have been incorporated into our foundational understanding of materials, chemistry, biology, and astronomy. These discoveries are a valuable resource for innovation, giving rise to devices such as lasers and transistors, and enabling real progress on technologies once considered purely speculative, such as quantum computers . Physicists are exploring the potential of quantum science to transform our view of gravity and its connection to space and time. Quantum science may even reveal how everything in the universe (or in multiple universes) is connected to everything else through higher dimensions that our senses cannot comprehend.

The Origins of Quantum Physics

The field of quantum physics arose in the late 1800s and early 1900s from a series of experimental observations of atoms that didn't make intuitive sense in the context of classical physics. Among the basic discoveries was the realization that matter and energy can be thought of as discrete packets, or quanta, that have a minimum value associated with them. For example, light of a fixed frequency will deliver energy in quanta called "photons." Each photon at this frequency will have the same amount of energy, and this energy can't be broken down into smaller units. In fact, the word "quantum" has Latin roots and means "how much."

Knowledge of quantum principles transformed our conceptualization of the atom, which consists of a nucleus surrounded by electrons. Early models depicted electrons as particles that orbited the nucleus, much like the way satellites orbit Earth. Modern quantum physics instead understands electrons as being distributed within orbitals, mathematical descriptions that represent the probability of the electrons' existence in more than one location within a given range at any given time. Electrons can jump from one orbital to another as they gain or lose energy, but they cannot be found between orbitals.

Other central concepts helped to establish the foundations of quantum physics:

• Wave-particle duality: This principle dates back to the earliest days of quantum science. It describes the outcomes of experiments that showed that light and matter had the properties of particles or waves, depending on how they were measured. Today, we understand that these different forms of energy are actually neither particle nor wave. They are distinct quantum objects that we cannot easily conceptualize.
• Superposition : This is a term used to describe an object as a combination of multiple possible states at the same time. A superposed object is analogous to a ripple on the surface of a pond that is a combination of two waves overlapping. In a mathematical sense, an object in superposition can be represented by an equation that has more than one solution or outcome.
• Uncertainty principle : This is a mathematical concept that represents a trade-off between complementary points of view. In physics, this means that two properties of an object, such as its position and velocity, cannot both be precisely known at the same time. If we precisely measure the position of an electron, for example, we will be limited in how precisely we can know its speed.
• Entanglement : This is a phenomenon that occurs when two or more objects are connected in such a way that they can be thought of as a single system, even if they are very far apart. The state of one object in that system can't be fully described without information on the state of the other object. Likewise, learning information about one object automatically tells you something about the other and vice versa.

Mathematics and the Probabilistic Nature of Quantum Objects

Because many of the concepts of quantum physics are difficult if not impossible for us to visualize, mathematics is essential to the field. Equations are used to describe or help predict quantum objects and phenomena in ways that are more exact than what our imaginations can conjure.

Mathematics is also necessary to represent the probabilistic nature of quantum phenomena. For example, the position of an electron may not be known exactly. Instead, it may be described as being in a range of possible locations (such as within an orbital), with each location associated with a probability of finding the electron there.

Given their probabilistic nature, quantum objects are often described using mathematical "wave functions," which are solutions to what is known as the Schrödinger equation . Waves in water can be characterized by the changing height of the water as the wave moves past a set point. Similarly, sound waves can be characterized by the changing compression or expansion of air molecules as they move past a point. Wave functions don't track with a physical property in this way. The solutions to the wave functions provide the likelihoods of where an observer might find a particular object over a range of potential options. However, just as a ripple in a pond or a note played on a trumpet are spread out and not confined to one location, quantum objects can also be in multiple places—and take on different states, as in the case of superposition—at once.

Observation of Quantum Objects

The act of observation is a topic of considerable discussion in quantum physics. Early in the field, scientists were baffled to find that simply observing an experiment influenced the outcome. For example, an electron acted like a wave when not observed, but the act of observing it caused the wave to collapse (or, more accurately, "decohere") and the electron to behave instead like a particle. Scientists now appreciate that the term "observation" is misleading in this context, suggesting that consciousness is involved. Instead, "measurement" better describes the effect, in which a change in outcome may be caused by the interaction between the quantum phenomenon and the external environment, including the device used to measure the phenomenon. Even this connection has caveats, though, and a full understanding of the relationship between measurement and outcome is still needed.

The Double-Slit Experiment

Perhaps the most definitive experiment in the field of quantum physics is the double-slit experiment . This experiment, which involves shooting particles such as photons or electrons through a barrier with two slits, was originally used in 1801 to show that light is made up of waves. Since then, numerous incarnations of the experiment have been used to demonstrate that matter can also behave like a wave and to demonstrate the principles of superposition, entanglement, and the observer effect.

The field of quantum science may seem mysterious or illogical, but it describes everything around us, whether we realize it or not. Harnessing the power of quantum physics gives rise to new technologies, both for applications we use today and for those that may be available in the future .

Dive Deeper

Why Are Soap Bubbles So Colorful? Iridescence explained by wave theory and quantum electrodynamics

Charlie Marcus Knows That Quantum Facts Aren't Complicated

The Biggest Ideas in the Universe: Sean Carroll

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Philosophical Issues in Quantum Theory

This article is an overview of the philosophical issues raised by quantum theory, intended as a pointer to the more in-depth treatments of other entries in the Stanford Encyclopedia of Philosophy.

1. Introduction

2.1 quantum states and classical states, 2.2 quantum mechanics and quantum field theory, 2.3 quantum state evolution, 3. entanglement, nonlocality, and nonseparability, 4.1 the measurement problem formulated, 4.2 approaches to the measurement problem, 4.3 extended wigner’s friend scenarios as a source of no-go theorems, 4.4 the role of decoherence, 4.5 comparison of approaches to the measurement problem, 5.1 the question of quantum state realism., 5.2 ontological category of quantum states, 6. quantum computing and quantum information theory, 7. reconstructions of quantum mechanics and beyond, other internet resources, related entries.

Despite its status as a core part of contemporary physics, there is no consensus among physicists or philosophers of physics on the question of what, if anything, the empirical success of quantum theory is telling us about the physical world. This gives rise to the collection of philosophical issues known as “the interpretation of quantum mechanics”. One should not be misled by this terminology into thinking that what we have is an uninterpreted mathematical formalism with no connection to the physical world. Rather, there is a common operational core that consists of recipes for calculating probabilities of outcomes of experiments performed on systems subjected to certain state preparation procedures. What are often referred to as different “interpretations” of quantum mechanics differ on what, if anything, is added to the common core. Two of the major approaches, hidden-variables theories and collapse theories, involve formulation of physical theories distinct from standard quantum mechanics; this renders the terminology of “interpretation” even more inappropriate.

Much of the philosophical literature connected with quantum theory centers on the problem of whether we should construe the theory, or a suitable extension or revision of it, in realist terms, and, if so, how this should be done. Various approaches to what is called the “Measurement Problem” propose differing answers to these questions. There are, however, other questions of philosophical interest. These include the bearing of quantum nonlocality on our understanding of spacetime structure and causality, the question of the ontological character of quantum states, the implications of quantum mechanics for information theory, and the task of situating quantum theory with respect to other theories, both actual and hypothetical. In what follows, we will touch on each of these topics, with the main goal being to provide an entry into the relevant literature, including the Stanford Encyclopedia entries on these topics. Contemporary perspectives on many of the issues touched on in this entry can be found in The Routledge Companion to Philosophy of Physics (Knox and Wilson, eds., 2021); The Oxford Handbook of the History of Quantum Interpretations (Freire, et al. eds., 2022) contains essays on the history of discussions of these issues.

2. Quantum Theory

In this section we present a brief introduction to quantum theory; see the entry on quantum mechanics for a more detailed introduction.

In classical physics, with any physical system is associated a state space, which represents the totality of possible ways of assigning values to the dynamical variables that characterize the state of the system. For systems of a great many degrees of freedom, a complete specification of the state of the system may be unavailable or unwieldy; classical statistical mechanics deals with such a situation by invoking a probability distribution over the state space of the system. A probability distribution that assigns any probability other than one or zero to some physical quantities is regarded as an incomplete specification of the state of the system. In quantum mechanics, things are different. There are no quantum states that assign definite values to all physical quantities, and probabilities are built into the standard formulation of the theory.

In formulating a quantum theory of some system, one usually begins with the Hamiltonian or Lagrangian formulation of the classical mechanical theory of that system. In the Hamiltonian formulation of classical mechanics, the configuration of a system is represented by a set of coordinates. These could be, for example, the positions of each of a set of point particles, but one can also consider more general cases, such as angular coordinates that specify the orientation of a rigid body. For every coordinate there is an associated conjugate momentum . If the coordinate indicates the position of some object, the momentum conjugate to that coordinate may be what we usually call “momentum,” that is, the velocity of the body multiplied by its mass. If the coordinate is an angle, the momentum conjugate to it is an angular momentum.

Construction of a quantum theory of a physical system proceeds by first associating the dynamical degrees of freedom with operators . These are mathematical objects on which operations of multiplication and addition are defined, as well as multiplication by real and complex numbers. Another way of saying this is that the set of operators forms an algebra . Typically, it is said that an operator represents an observable , and the result of an experiment on a system is said to yield a value for some observable. Two or more observables are said to be compatible if there is some possible experiment that simultaneously yields values for all of them. Others require mutually exclusive experiments; these are said to be incompatible .

Of course, in a classical theory, the dynamical quantities that define a state also form an algebra also, as they can be multiplied and added, and multiplied by real or complex numbers. Quantum mechanics differs from classical mechanics in that the order of multiplication of operators can make a difference. That is, for some operators \(A\),\(B\), the product \(AB\) is not equal to the product \(BA.\) If \(AB = BA,\) the operators are said to commute .

The recipe for constructing a quantum theory of a given physical systems prescribes algebraic relations between the operators representing the dynamical variables of the system. Compatible observables are associated with operators that commute with each other. Operators representing conjugate variables are required to satisfy what are called the canonical commutation relations . If \(q\) is some coordinate, and \(p\) its conjugate momentum, the operators \(Q\) and \(P\) representing them are required to not commute. Instead, the difference between \(PQ\) and \(QP\) is required to be a multiple of the identity operator (that is, the operator \(I\) that satisfies, for all operators \(A\), \(IA = AI).\)

A quantum state is a specification, for every experiment that can be performed on the system, of probabilities for the possible outcomes of that experiment. These can be summed up as an assignment of an expectation value to each observable. These states are required to be linear . This means that, if an operator \(C\), corresponding to some observable, is the sum of operators \(A\) and \(B\), corresponding to other observables, then the expectation value that a quantum state assigns to \(C\) must be the sum of the expectation values assigned to \(A\) and \(B\). This is a nontrivial constraint, as it is required to hold whether or not the observables represented are compatible. A quantum state, therefore, relates expectation values for quantities yielded by incompatible experiments.

Incompatible observables, represented by noncommuting operators, give rise to uncertainty relations; see the entry on the uncertainty principle . These relations entail that there are no quantum states that assign definite values to the observables that satisfy them, and place bounds on how close they can come to be simultaneously well-defined in any quantum state.

For any two distinct quantum states, \(\rho\), \(\omega\), and any real number between 0 and 1, there is a corresponding mixed state . The probability assigned to any experimental outcome by this mixed state is \(p\) times the probability it is assigned by \(\rho\) plus \(1-p\) times the probability assigned to it by \(\omega\). One way to physically realize the preparation of a mixed state is to employ a randomizing device, for example, a coin with probability \(p\) of landing heads and probability \(1-p\) of landing tails, and to use it to choose between preparing state \(\rho\) and preparing state \(\omega\). We will see another way to prepare a mixed state after we have discussed entanglement, in section 3. A state that is not a mixture of any two distinct states is called a pure state .

It is both useful and customary, though not strictly necessary, to employ a Hilbert space representation of a quantum theory. In such a representation, the operators corresponding to observables are represented as acting on elements of an appropriately constructed Hilbert space (see the entry on quantum mechanics for details). Usually, the Hilbert space representation is constructed in such a way that vectors in the space represent pure states; such a representation is called an irreducible representation . Irreducible representations, in which mixed states are also represented by vectors, are also possible.

A Hilbert space is a vector space. This means that, for any two vectors \(|\psi\rangle\), \(|\phi\rangle\) , in the space, representing pure states, and any complex numbers \(a\), \(b\), there is another vector, \(a |\psi\rangle + b |\phi\rangle\), that also represents a pure state. This is called a superposition of the states represented by \(|\psi\rangle\) and \(|\phi\rangle\) . Any vector in a Hilbert space can be written as a superposition of other vectors in infinitely many ways. Sometimes, in discussing the foundations of quantum mechanics, authors fall into talking as if some state are superpositions and others are not. This is simply an error. Usually what is meant is that some states yield definite values for macroscopic observables, and others cannot be written in any way that is not a superposition of macroscopically distinct states.

The noncontroversial operational core of quantum theory consists of rules for identifying, for any given system, appropriate operators representing its dynamical quantities. In addition, there are prescriptions for evolving the state of system when it is acted upon by specified external fields or subjected to various manipulations (see section 1.3 ). Application of quantum theory typically involves a distinction between the system under study, which is treated quantum mechanically, and experimental apparatus, which is not. This division is sometimes known as the Heisenberg cut .

Whether or not we can expect to be able to go beyond the noncontroversial operational core of quantum theory, and take it to be more than a means for calculating probabilities of outcomes of experiments, remains a topic of contemporary philosophical discussion.

Quantum mechanics is usually taken to refer to the quantized version of a theory of classical mechanics, involving systems with a fixed, finite number of degrees of freedom. Classically, a field, such as, for example, an electromagnetic field, is a system endowed with infinitely many degrees of freedom. Quantization of a field theory gives rise to a quantum field theory . The chief philosophical issues raised by quantum mechanics remain when the transition is made to a quantum field theory; in addition, new interpretational issues arise. There are interesting differences, both technical and interpretational, between quantum mechanical theories and quantum field theories; for an overview, see the entries on quantum field theory and quantum theory: von Neumann vs. Dirac .

The standard model of quantum field theory, successful as it is, does not yet incorporate gravitation. The attempt to develop a theory that does justice both the quantum phenomena and to gravitational phenomena gives rise to serious conceptual issues (see the entry on quantum gravity ).

2.3.1 Schrödinger and Heisenberg pictures

When constructing a Hilbert space representation of a quantum theory of a system that evolves over time, there are some choices to be made. One needs to have, for each time t , a Hilbert space representation of the system, which involves assigning operators to observables pertaining to time t . An element of convention comes in when deciding how the operators representing observables at different times are to be related.

For concreteness, suppose that have a system whose observables include a position, \(x\), and momentum, \(p\), with respect to some frame of reference. There is a sense in which, for two distinct times, \(t\) and \(t'\), position at time \(t\) and position at time \(t'\) are distinct observables, and also a sense in which they are values, at different times, of the same observable. Once we have settled on operators \(\hat{X}\) and \(\hat{P}\) to represent position and momentum at time \(t\), we still have a choice of which operators represent the corresponding quantities at time \(t.\) On the Schrödinger picture , the same operators \(\hat{X}\) and \(\hat{P}\) are used to represent position and momentum, whatever time is considered. As the probabilities for results of experiments involving these quantities may be changing with time, different vectors must be used to represent the state at different times.

The equation of motion obeyed by a quantum state vector is the Schrödinger equation. It is constructed by first forming the operator \(\hat{H}\)corresponding to the Hamiltonian of the system, which represents the total energy of the system. The rate of change of a state vector is proportional to the result of operating on the vector with the Hamiltonian operator \(\hat{H}\).

There is an operator that takes a state at time 0 into a state at time \(t\); it is given by

This operator is a linear operator that implements a one-one mapping of the Hilbert space to itself that preserves the inner product of any two vectors; operators with these properties are called unitary operators , and, for this reason, evolution according to the Schrödinger equation is called unitary evolution.

For our purposes, the most important features of this equation is that it is deterministic and linear . The state vector at any time, together with the equation, uniquely determines the state vector at any other time. Linearity means that, if two vectors \(\ket{\psi_1(0)}\) and \(\ket{\psi_2(0)}\) evolve into vectors \(\ket{\psi_1(t) }\) and \(\ket{\psi_2(t)}\), respectively, then, if the state at time 0 is a linear combination of these two, the state at any time \(t\) will be the corresponding linear combination of \(\ket{\psi_1(t)}\) and \(\ket{\psi_2(t)}\).

\[ a\ket{\psi_{1}(0)} + b\ket{\psi_{2}(0)} \rightarrow a\ket{\psi_{1}(t)} + b\ket{\psi_{2}(t)} . \]

The Heisenberg picture, on the other hand, employs different operators \(\hat{X}(t)\), \(\hat{X}(t')\) for position, depending on the time considered (and similarly for momentum and other observables). If \(\hat{A}(t)\)is a family of Heisenberg picture operators representing some observable at different times, the members of the family satisfy the Heisenberg equation of motion,

One sometimes hears it said that, on the Heisenberg picture, the state of the system is unchanging. This is incorrect. It is true that there are not different state vectors corresponding to different times, but that is because a single state vector serves for computing probabilities for all observables pertaining to all times. These probabilities do change with time.

2.3.2. The collapse postulate

As mentioned, standard applications of quantum theory involve a division of the world into a system that is treated within quantum theory, and the remainder, typically including the experimental apparatus, that is not treated within the theory. Associated with this division is a postulate about how to assign a state vector after an experiment that yields a value for an observable, according to which, after an experiment, one replaces the quantum state with an eigenstate corresponding to the value obtained. Unlike the unitary evolution applied otherwise, this is a discontinuous change of the quantum state, sometimes referred to as collapse of the state vector , or state vector reduction . There are two interpretations of the postulate about collapse, corresponding to two different conceptions of quantum states. If a quantum state represents nothing more than knowledge about the system, then the collapse of the state to one corresponding to an observed result can be thought of as mere updating of knowledge. If, however, quantum states represent physical reality, in such a way that distinct pure states always represent distinct physical states of affairs, then the collapse postulate entails an abrupt, perhaps discontinuous, change of the physical state of the system. Considerable confusion can arise if the two interpretations are conflated.

The collapse postulate occurs already in the general discussion at the fifth Solvay Conference in 1927 (see Bacciagaluppi and Valentini, 2009, 437–450). It is also found in Heisenberg’s The Physical Principles of the Quantum Theory , based on lectures presented in 1929 (Heisenberg, 1930a, 27; 1930b, 36). Von Neumann, in his reformulation of quantum theory a few years later, distinguished between two types of processes: Process 1:, which occurs upon performance of an experiment, and Process 2:, the unitary evolution that takes place as long as no measurement is made (von Neumann, 1932; 1955, §V.I). He does not take this distinction to be a difference between two physically distinct processes. Rather, the invocation of one process or the other depends on a somewhat arbitrary division of the world into an observing part and an observed part (see von Neumann,1932, 224; 1955, 420).

The collapse postulate does not appear in the first edition (1930) of Dirac’s Principles of Quantum Mechanics ; it is introduced in the second edition (1935). Dirac formulates it as follows.

When we measure a real dynamical variable \(\xi\), the disturbance involved in the act of measurement causes a jump in the state of the dynamical system. From physical continuity, if we make a second measurement of the same dynamical variable \(\xi\) immediately after the first, the result of the second measurement must be the same as that of the first. Thus after the first measurement has been made, there is no indeterminacy in the result of the second. Hence, after the first measurement has been made, the system is in an eigenstate of the dynamical variable \(\xi\), the eigenvalue it belongs to being equal to the result of the first measurement. This conclusion must still hold if the second measurement is not actually made. In this way we see that a measurement always causes the system to jump into an eigenstate of the dynamical variable that is being measured, the eigenvalue this eigenstate belongs to being equal to the result of the measurement (Dirac 1935: 36).

Unlike von Neumann and Heisenberg, Dirac is treating the “jump” as a physical process.

Neither von Neumann nor Dirac take awareness of the result by a conscious observer to be a necessary condition for collapse. For von Neumann, the location of the cut between the “observed” system and the “observer”is somewhat arbitrary. It may be placed between the system under study and the experimental apparatus. On the other hand, we could include the experimental apparatus in the quantum description, and place the cut at the moment when light indicating the result hits the observer’s retina. We could also go even further, and include the retina and relevant parts of the observer’s nervous system in the quantum system. That the cut may be pushed arbitrarily far into the perceptual apparatus of the observer is required, according to von Neumann, by the principle of psycho-physical parallelism .

A formulation of a version of the collapse postulate according to which a measurement is not completed until the result is observed is found in London and Bauer (1939). For them, as for Heisenberg, this is a matter of an increase of knowledge on the part of the observer.

Wigner (1961) combined elements of the two interpretations. Like those who take the collapse to be a matter of updating of belief in light of information newly acquired by an observer, he takes collapse to take place when a conscious observer becomes aware of an experimental result. However, like Dirac, he takes it to be a real physical process. His conclusion is that consciousness has an influence on the physical world not captured by the laws of quantum mechanics. This involves a rejection of von Neumann’s principle of psycho-physical parallelism, according to which it must be possible to treat the process of subjective perception as if it were a physical process like any other.

There is a persistent misconception that, for von Neumann, collapse is to be invoked only when a conscious observer becomes aware of the result. As noted, this is the opposite of his view, as the cut may be placed between the observed system and the experimental apparatus, and it is for him an important point that the location of the cut be somewhat arbitrary. In spite of this, von Neumann’s position is sometimes conflated with Wigner’s speculative proposal, and Wigner’s proposal is sometimes erroneously referred to as the von Neumann-Wigner interpretation .

None of the standard formulations are precise about when the collapse postulate is to be applied; there is some lee-way as to what is to count as an experiment, or (for versions that require reference to an observer) what is to count as an observer. Some, including von Neumann and Heisenberg, have taken it to be a matter of principle that there be some arbitrariness in where to apply the postulate. It is common wisdom that, in practice, this arbitrariness is innocuous. The rule of thumb that seems to be applied, in practice, in setting the split between the parts of the world treated quantum-mechanically and things treated as classical objects has been formulated by J. S. Bell as, “[w]hen in doubt enlarge the quantum system,” to the point at which including more in the quantum system makes negligible difference to practical predictions (Bell 1986, 362; Bell 2004, 189). If anything is to be counted as “standard” quantum mechanics, it is the operational core we have discussed, supplemented by a heuristic rule of application of this sort. Standard quantum mechanics works very well. If, however, one seeks a theory that is capable of describing all systems, including macroscopic ones, and can yield an account of the process by which macroscopic events, including experimental outcomes, come about, this gives rise to the so-called “measurement problem”, which we will discuss after we have introduced the notion of entanglement (see section 3 ).

2.3.3. Wave functions

Among the Hilbert-space representations of a quantum theory are wave-function representations.

Associated with any observable is its spectrum , the range of possible values that the observable can take on. Given any physical system and any observable for that system, one can always form a Hilbert-space representation for the quantum theory of that system by considering complex-valued functions on the spectrum of that observable. The set of such functions form a vector space. Given a measure on the spectrum of the observable, we can form a Hilbert space out of the set of complex-valued square-integrable functions on the spectrum by treating functions that differ only on a set of zero measure as equivalent (that is, the elements of our Hilbert space are really equivalence classes of functions), and by using the measure to define an inner product (see entry on Quantum Mechanics if this terminology is unfamiliar).

If the spectrum of the chosen observable is a continuum (as it is, for example, for position or momentum), a Hilbert-space representation of this sort is called a wave function representation, and the functions that represent quantum states, wave functions (also “wave-functions,” or “wavefunctions”). The most familiar representations of this form are position-space wave functions, which are functions on the set of possible configurations of the system, and momentum-space wave functions, which are functions of the momenta of the systems involved.

Given two disjoint physical systems, \(A\) and \(B\), with which we associate Hilbert spaces \(H_{A}\) and \(H_{B}\), the Hilbert space associated with the composite system is the tensor product space, denoted \(H_{A} \otimes H_{B}\).

When the two systems are independently prepared in pure states \(\ket{\psi}\) and \(\ket{\phi}\), the state of the composite system is the product state \(\ket{\psi} \otimes \ket{\phi}\) (sometimes written with the cross, \(\otimes\), omitted).

In addition to the product states, the tensor product space contains linear combinations of product states, that is, state vectors of the form

The tensor product space can be defined as the smallest Hilbert space containing all of the product states. Any pure state represented by a state vector that is not a product vector is an entangled state .

The state of the composite system assigns probabilities to outcomes of all experiments that can be performed on the composite system. We can also consider a restriction to experiments performed on system \(A\), or a restriction to experiments performed to \(B\). Such restrictions yields states of \(A\) and \(B\), respectively, called the reduced states of the systems. When the state of the composite system \(AB\) is an entangled state, then the reduced states of \(A\) and \(B\) are mixed states. To see this, suppose that in the above state the vectors \(\ket{\phi_{1}}\) and \(\ket{\phi_{2}}\) represent distinguishable states. If one confines one’s attention to experiments performed on \(A\), it makes no difference whether an experiment is also performed on \(B\). An experiment performed on \(B\) that distinguishes \(\ket{\phi_{1}}\) and \(\ket{\phi_{2}}\) projects the state of \(A\) into either \(\ket{\psi_{1}}\) or \(\ket{\psi_{2}}\), with probabilities \(\abs{a}^{2}\) and \(\abs{b}^{2}\), respectively, and probabilities for outcomes of experiments performed on \(A\) are the corresponding averages of probabilities for states \(\ket{\psi_{1}}\) and \(\ket{\psi_{2}}\). These probabilities, as mentioned, are the same as those for the situation in which no experiment is performed on \(B\). Thus, even if no experiment is performed on \(B\), the probabilities of outcomes of experiments on \(A\) are exactly as if system \(A\) is either in the state represented by \(\ket{\psi_{1}}\) or the state represented by \(\ket{\psi_{2}}\), with probabilities \(\abs{a}^{2}\) and \(\abs{b}^{2}\), respectively.

In general, any state, pure or mixed, that is neither a product state nor a mixture of product states, is called an entangled state.

The existence of pure entangled states means that, if we consider a composite system consisting of spatially separated parts, then, even when the state of the system is a pure state, the state is not determined by the reduced states of its component parts. Thus, quantum states exhibit a form of nonseparability . See the entry on holism and nonseparability in physics for more information.

Quantum entanglement results in a form of nonlocality that is alien to classical physics. Even if we assume that the reduced states of \(A\) and \(B\) do not completely characterize their physical states, but must be supplemented by some further variables, there are quantum correlations that cannot be reduced to correlations between states of \(A\) and \(B\); see the entries on Bell’s Theorem and action at a distance in quantum mechanics .

4. The measurement problem

If quantum theory is meant to be (in principle) a universal theory, it should be applicable, in principle, to all physical systems, including systems as large and complicated as our experimental apparatus. It is easy to show that linear evolution of quantum states, when applied to macroscopic objects, will routinely lead to superpositions of macroscopically distinct states. Among the circumstances in which this will happen are experimental set-ups, and much of the early discussions focussed on how to construe the process of measurement in quantum-mechanical terms. For this reason, the interpretational issues have come to be referred to as the measurement problem . In the first decades of discussion of the foundations of quantum mechanics, it was commonly referred to as the problem of observation .

Consider a schematized experiment. Suppose we have a quantum system that can be prepared in at least two distinguishable states, \(\ket{0} _{S}\) and \(\ket{1} _{S}\). Let \(\ket{R} _{A}\) be a ready state of the apparatus, that is, a state in which the apparatus is ready to make a measurement.

If the apparatus is working properly, and if the measurement is a minimally disturbing one, the coupling of the system \(S\) with the apparatus \(A\) should result in an evolution that predictably yields results of the form

where \(\ket{“0” } _{A}\) and \(\ket{“1”} _{A}\) are apparatus states indicating results 0 and 1, respectively.

Now suppose that the system \(S\) is prepared in a superposition of the states \(\ket{0} _{S}\) and \(\ket{1}_{S}\).

where \(a\) and \(b\) are both nonzero. If the evolution that leads from the pre-experimental state to the post-experimental state is linear Schrödinger evolution, then we will have

This is not an eigenstate of the instrument reading variable, but is, rather, a state in which the reading variable and the system variable are entangled with each other. The eigenstate-eigenvalue link, applied to a state like this, does not yield a definite result for the instrument reading. The problem of what to make of this is called the “measurement problem” which is discussed in more detail below.

If quantum state evolution proceeds via the Schrödinger equation or some other linear equation, then, as we have seen in the previous section, typical experiments will lead to quantum states that are superpositions of terms corresponding to distinct experimental outcomes. It is sometimes said that this conflicts with our experience, according to which experimental outcome variables, such as pointer readings, always have definite values. This is a misleading way of putting the issue, as it is not immediately clear how to interpret states of this sort as physical states of a system that includes experimental apparatus, and, if we can’t say what it would be like to observe the apparatus to be in such a state, it makes no sense to say that we never observe it to be in a state like that.

Nonetheless, we are faced with an interpretational problem. If we take the quantum state to be a complete description of the system, then the state is, contrary to what would antecedently expect, not a state corresponding to a unique, definite outcome. This is what led J.S. Bell to remark, “Either the wavefunction, as given by the Schrödinger equation, is not everything, or it is not right” (Bell 1987: 41, 2004: 201). This gives us a ( prima facie ) tidy way of classifying approaches to the measurement problem:

• There are approaches that involve a denial that a quantum wave function (or any other way of representing a quantum state) yields a complete description of a physical system.
• There are approaches that involve modification of the dynamics to produce a collapse of the quantum state in appropriate circumstances.
• There are approaches that reject both horns of Bell’s dilemma, and hold that quantum states undergo unitary evolution at all times and that a quantum state-description is, in principle, complete.

We include in the first category approaches that deny that a quantum state should be thought of as representing anything in reality at all. These include variants of the Copenhagen interpretation, as well as pragmatic and other anti-realist approaches. Also in the first category are approaches that seek a completion of the quantum state description. These include hidden-variables approaches and modal interpretations. The second category of interpretation motivates a research programme of finding suitable indeterministic modifications of the quantum dynamics. Approaches that reject both horns of Bell’s dilemma are typified by Everettian, or “many-worlds” interpretations.

4.2.1 The “Copenhagen interpretation”

Since the mid-1950’s, the term “Copenhagen interpretation” has been commonly used for whatever it is that the person employing the term takes to be the ‘orthodox’ viewpoint regarding the philosophical issues raised by quantum mechanics. According to Howard (2004), the phrase was first used by Heisenberg (1955, 1958), and is intended to suggest a commonality of views among Bohr and his associates, included Born and Heisenberg himself. Recent historiography has emphasized diversity of viewpoints among the figures associated with the Copenhagen interpretation; see the entry on Copenhagen interpretation of quantum mechanics , and references therein. Readers should be aware that the term is not univocal, and that different authors might mean different things when speaking of the“Copenhagen interpretation.”

4.2.2 Non-realist and pragmatist approaches to quantum mechanics

From the early days of quantum mechanics, there has been a strain of thought that holds that the proper attitude to take towards quantum mechanics is an instrumentalist or pragmatic one. On such a view, quantum mechanics is a tool for coordinating our experience and for forming expectations about the outcomes of experiments. Variants of this view include some versions of the Copenhagen interpretation. More recently, views of this sort have been advocated by physicists, including QBists, who hold that quantum states represent subjective or epistemic probabilities (see Fuchs et al. , 2014). The philosopher Richard Healey defends a related view on which quantum states, though objective, are not to be taken as representational (see Healey 2012, 2017a, 2020). For more on these approaches, see entry on Quantum-Bayesian and pragmatist views of quantum theory .

4.2.2 Hidden-variables and modal interpretations

Theories whose structure include the quantum state but include additional structure, with an aim of circumventing the measurement problem, have traditionally been called “hidden-variables theories”. That a quantum state description cannot be regarded as a complete description of physical reality was argued for in a famous paper by Einstein, Podolsky and Rosen (EPR) and by Einstein in subsequent publications (Einstein 1936, 1948, 1949). See the entry on the Einstein-Podolsky-Rosen argument in quantum theory .

There are a number of theorems that circumscribe the scope of possible hidden-variables theories. The most natural thought would be to seek a theory that assigns to all quantum observables definite values that are merely revealed upon measurement, in such a way that any experimental procedure that, in conventional quantum mechanics, would count as a “measurement” of an observable yields the definite value assigned to the observable. Theories of this sort are called noncontextual hidden-variables theory. It was shown by Bell (1966) and Kochen and Specker (1967) that there are no such theories for any system whose Hilbert space dimension is greater than three (see the entry on the Kochen-Specker theorem ).

The Bell-Kochen-Specker Theorem does not rule out hidden-variables theories tout court . The simplest way to circumvent it is to pick as always-definite some observable or compatible set of observables that suffices to guarantee determinate outcomes of experiments; other observables are not assigned definite values and experiments thought of as “measurements” of these observables do not reveal pre-existing values.

The most thoroughly worked-out theory of this type is the pilot wave theory developed by de Broglie and presented by him at the Fifth Solvay Conference held in Brussels in 1927, revived by David Bohm in 1952, and currently an active area of research by a small group of physicists and philosophers. According to this theory, there are particles with definite trajectories, that are guided by the quantum wave function. For the history of the de Broglie theory, see the introductory chapters of Bacciagaluppi and Valentini (2009). For an overview of the de Broglie-Bohm theory and philosophical issues associated with it see the entry on Bohmian mechanics .

There have been other proposals for supplementing the quantum state with additional structure; these have come to be called modal interpretations ; see the entry on modal interpretations of quantum mechanics .

4.2.3 Dynamical Collapse Theories

As already mentioned, Dirac wrote as if the collapse of the quantum state vector precipitated by an experimental intervention on the system is a genuine physical change, distinct from the usual unitary evolution. If collapse is to be taken as a genuine physical process, then something more needs to be said about the circumstances under which it occurs than merely that it happens when an experiment is performed. This gives rise to a research programme of formulating a precisely defined dynamics for the quantum state that approximates the linear, unitary Schrödinger evolution in situations for which this is well-confirmed, and produces collapse to an eigenstate of the outcome variable in typical experimental set-ups, or, failing that, a close approximation to an eigenstate. The only promising collapse theories are stochastic in nature; indeed, it can be shown that a deterministic collapse theory would permit superluminal signalling. See the entry on collapse theories for an overview, and Gao, ed. (2018) for a snapshot of contemporary discussions.

Prima facie , a dynamical collapse theory of this type can be a quantum state monist theory, one on which, in Bell’s words, “the wave function is everything”. In recent years, this has been disputed; it has been argued that collapse theories require “primitive ontology” in addition to the quantum state. See Allori et al. (2008), Allori (2013), and also the entry on collapse theories , and references therein. Reservations about this approach have been expressed by Egg (2017, 2021), Myrvold (2018), and Wallace (2020).

4.2.4 Everettian, or “many worlds” theories

In his doctoral dissertation of 1957 (reprinted in Everett 2012), Hugh Everett III proposed that quantum mechanics be taken as it is, without a collapse postulate and without any “hidden variables”. The resulting interpretation he called the relative state interpretation.

The basic idea is this. After an experiment, the quantum state of the system plus apparatus is typically a superposition of terms corresponding to distinct outcomes. As the apparatus interacts with its environment, which may include observers, these systems become entangled with the apparatus and quantum system, the net result of which is a quantum state involving, for each of the possible experimental outcomes, a term in which the apparatus reading corresponds to that outcome, there are records of that outcome in the environment, observers observe that outcome, etc. . Everett proposed that each of these terms be taken to be equally real. From a God’s-eye-view, there is no unique experimental outcome, but one can also focus on a particular determinate state of one subsystem, say, the experimental apparatus, and attribute to the other systems participating in the entangled state a relative state , relative to that state of the apparatus. That is, relative to the apparatus reading ‘+’ is a state of the environment recording that result and states of observers observing that result (see the entry on Everett’s relative-state formulation of quantum mechanics , for more detail on Everett’s views).

Everett’s work has inspired a family of views that go by the name of “Many Worlds” interpretations; the idea is that each of the terms of the superposition corresponds to a coherent world, and all of these worlds are equally real. As time goes on, there is a proliferation of these worlds, as situations arise that give rise to a further multiplicity of outcomes (see the entry many-worlds interpretation of quantum mechanics , and Saunders 2007, for overviews of recent discussions; Wallace 2012 is an extended defense of an Everettian interpretation of quantum mechanics).

There is a family of distinct, but related views, that go by the name of “Relational Quantum Mechanics”. These views agree with Everett in attributing to a system definite values of dynamical variables only relative to the states of other systems; they differ in that, unlike Everett, they do not take the quantum state as their basic ontology (see the entry on relational quantum mechanics for more detail).

As mentioned, quantum theory, as standardly formulated, employs a division of the world into a part that is treated with the theory, and a part that is not. Both von Neumann and Heisenberg emphasized an element of arbitrariness in the location of the division. In some formulations, the division was thought of as a distinction between observer and observed, and it became common to say that quantum mechanics requires reference to an observer for its formulation.

The founders of quantum mechanics tended to assume implicitly that, though the “cut” is somewhat moveable, in any given analysis a division would be settled on, and one would not attempt to combine distinct choices of the cut in one analysis of an experiment. If, however, one thinks of the cut as marking the distinction between observer and observed, one is led to ask about situations involving multiple observers. Is each observer permitted to treat the other as a quantum system?

The consideration of such scenarios was initiated by Wigner (1961). Wigner considered a hypothetical scenario in which a friend conducts an observation, and he himself treats the joint system, consisting of the friend and the system experimented upon, as a quantum system. For this reason, scenarios of this sort have come to be known as “Wigner’s friend” scenarios. Wigner was led by consideration of such scenarious to hypothesize that conscious observers cannot be in a superposition of states corresponding to distinct perceptions; the introduction of conscious observers initiates a physical collapse of the quantum state; this involves, according to Wigner, “a violation of physical laws where consciousness plays a role” (Wigner 1961, 294 ;167, 181).

Frauchiger and Renner (2018) initiated the discussion of scenarios of this sort involving more than two observers, which have come to be called “extended Wigner’s friend” scenarios. Further results along these lines include Brukner (2018), Bong et al. (2020), and Guérin et al. (2021). The strategy of these investigations is to present some set of plausible-seeming assumptions (a different set, for each of the works cited), and to show, via consideration of a hypothetical situation involving multiple observers, the inconsistency of that set of assumptions. The theorems are, therefore, no-go theorems for approaches to the measurement problem that would seek to satisfy all of the members of the set of assumptions that has been shown to be inconsistent.

An assumption common to all of these investigations is that it is always permissible for one observer to treat systems containing other observers within quantum mechanics and to employ unitary evolution for those systems. This means that collapse is not regarded as a physical process. It is also assumed that each observer always perceives a unique outcome for any experiment performed by that observer; this excludes Everettian interpretations. Where the works cited vary is in the other assumptions made.

It should be noted that each of the major avenues of approach to the measurement problem is capable of giving an account of goings-on in any physical scenario, including the ones considered in these works. Each of them, therefore, must violate some member of the set of assumptions shown to be inconsistent. These results do not pose problems for existing approaches to the measurement problem; rather, they are no-go theorems for approaches that might seek to satisfy all of the set of assumptions shown to be inconsistent. As the assumptions considered include both unitary evolution and unique outcomes of experiments, and the scenarios considered involved situations involving superpositions of distinct experimental outcomes, these results concern theories on which the quantum state, as given by the Schrödinger equation, is not a complete description of reality, as it fails to determine the unique outcomes perceived by the observers. These preceptions could be thought of as supervening on brain states, in which case there is physical structure not included in the quantum state, or as attributes of immaterial minds. On either interpretation, the sorts of theories ruled out fall under the first horn of Bell’s dilemma, mentioned in section 4.2, and these no-go results in part reproduce, and in part extend, no-go results for certain sorts of modal interpretations (see entry on modal interpretations of quantum mechanics ).

These results involving extended Wigner’s friend scenarios have engendered considerable philosophical discussion; see Sudbery (2017, 2019), Healey (2018, 2020), Dieks (2019), Losada et al. (2019), Dascal (2020), Evans (2020), Fortin and Lombardi (2020), Kastner (2020), Muciño & Okon (2020), Bub (2020, 2021), Cavalcanti (2021), Cavalcanti and Wiseman (2021), and Żukowski and Markiewicz (2021).

A quantum state that is a superposition of two distinct terms, such as

where \(\ket{\psi_{1}}\) and \(\ket{\psi_{2}}\) are distinguishable states, is not the same state as a mixture of \(\ket{\psi_{1}}\) and \(\ket{\psi_{2}}\), which would be appropriate for a situation in which the state prepared was either \(\ket{\psi_{1}}\) or \(\ket{\psi_{2}}\), but we don’t know which. The difference between a coherent superposition of two terms and a mixture has empirical consequences. To see this, consider the double-slit experiment, in which a beam of particles (such as electrons, neutrons, or photons) passes through two narrow slits and then impinges on a screen, where the particles are detected. Take \(\ket{\psi_{1}}\) to be a state in which a particle passes through the top slit, and \(\ket{\psi_{2}}\), a state in which it passes through the bottom slit. The fact that the state is a superposition of these two alternatives is exhibited in interference fringes at the screen, alternating bands of high and low rates of absorption.

This is often expressed in terms of a difference between classical and quantum probabilities. If the particles were classical particles, the probability of detection at some point \(p\) of the screen would simply be a weighted average of two conditional probabilities: the probability of detection at \(p\), given that the particle passed through the top slit, and the probability of detection at \(p\), given that the particle passed through the bottom slit. The appearance of interference is an index of nonclassicality.

Suppose, now, that the electrons interact with something else (call it the environment ) on the way to the screen, that could serve as a “which-way” detector; that is, the state of this auxiliary system becomes entangled with the state of the electron in such a way that its state is correlated with \(\ket{\psi_{1}}\) and \(\ket{\psi_{2}}\). Then the state of the quantum system, \(s\), and its environment, \(e\), is

If the environment states \(\ket{\phi_{1}} _{e}\) are \(\ket{\phi_{2}}_{e}\) are distinguishable states, then this completely destroys the interference fringes: the particles interact with the screen as if they determinately went through one slit or the other, and the pattern that emerges is the result of overlaying the two single-slit patterns. That is, we can treat the particles as if they followed (approximately) definite trajectories, and apply probabilities in a classical manner.

Now, macroscopic objects are typically in interaction with a large and complex environment—they are constantly being bombarded with air molecules, photons, and the like. As a result, the reduced state of such a system quickly becomes a mixture of quasi-classical states, a phenomenon known as decoherence .

A generalization of decoherence lies at the heart of an approach to the interpretation of quantum mechanics that goes by the name of decoherent histories approach (see the entry on the consistent histories approach to quantum mechanics for an overview).

Decoherence plays important roles in the other approaches to quantum mechanics, though the role it plays varies with approach; see the entry on the role of decoherence in quantum mechanics for information on this.

Most of the above approaches take it that the goal is to provide an account of events in the world that recovers, at least in some approximation, something like our familiar world of ordinary objects behaving classically. None of the mainstream approaches accord any special physical role to conscious observers. There have, however, been proposals in that direction (see the entry on quantum approaches to consciousness for discussion).

All of the above-mentioned approaches are consistent with observation. Mere consistency, however, is not enough; the rules for connecting quantum theory with experimental results typically involve nontrivial (that is, not equal to zero or one) probabilities assigned to experimental outcomes. These calculated probabilities are confronted with empirical evidence in the form of statistical data from repeated experiments. Extant hidden-variables theories reproduce the quantum probabilities, and collapse theories have the intriguing feature of reproducing very close approximations to quantum probabilities for all experiments that have been performed so far but departing from the quantum probabilities for other conceivable experiments. This permits, in principle, an empirical discrimination between such theories and no-collapse theories.

A criticism that has been raised against Everettian theories is that it is not clear whether they can even make sense of statistical testing of this kind, as it does not, in any straightforward way, make sense to talk of the probability of obtaining, say, a ‘+” outcome of a given experiment when it is certain that all possible outcomes will occur on some branch of the wavefunction. This has been called the “Everettian evidential problem”. It has been the subject of much recent work on Everettian theories; see Saunders (2007) for an introduction and overview.

If one accepts that Everettians have a solution to the evidential problem, then, among the major lines of approach, none is favored in a straightforward way by the empirical evidence. There will not be space here to give an in-depth overview of these ongoing discussions, but a few considerations can be mentioned, to give the reader a flavor of the discussions; see entries on particular approaches for more detail.

Everettians take, as a virtue of the approach, the fact that it does not involve an extension or modification of the quantum formalism. Bohmians claim, in favor of the Bohmian approach, that a theory on these lines provides the most straightforward picture of events; ontological issues are less clear-cut when it comes to Everettian theories or collapse theories.

Another consideration is compatibility with relativistic causal structure. See Myrvold (2021) for an overview of relavistic constraints on approaches to the measurement problem.The de Broglie-Bohm theory requires a distinguished relation of distant simultaneity for its formulation, and, it can be argued, this is an ineliminable feature of any hidden-variables theory of this sort, that selects some observable to always have definite values (see Berndl et al. 1996; Myrvold 2002, 2021). On the other hand, there are collapse models that are fully relativistic. On such models, collapses are localized events. Though probabilities of collapses at spacelike separation from each other are not independent, this probabilistic dependence does not require us to single one out as earlier and the other later. Thus, such theories do not require a distinguished relation of distant simultaneity. There remains, however, some discussion of how to equip such theories with beables (or “elements of reality”). See the entry on collapse theories and references therein; see also, for some recent contributions to the discussion, Fleming (2016), Maudlin (2016), and Myrvold (2016). In the case of Everettian theories, one must first think about how to formulate the question of relativistic locality. Several authors have approached this issue in somewhat different ways, with a common conclusion that Everettian quantum mechanics is, indeed, local. (See Vaidman 1994; Bacciagaluppi 2002; Chapter 8 of Wallace 2012; Tipler 2014; Vaidman 2016; and Brown and Timpson 2016.)

5. Ontological Issues

As mentioned, a central question of interpretation of quantum mechanics concerns whether quantum states should be regarded as representing anything in physical reality. If this is answered in the affirmative, this gives rise to new questions, namely, what sort of physical reality is represented by the quantum state, and whether a quantum state could in principle give an exhaustive account of physical reality.

Harrigan and Spekkens (2010) have introduced a framework for discussing these issues. In their terminology, a complete specification of the physical properties is given by the ontic state of a system. An ontological model posits a space of ontic states and associates, with any preparation procedure, a probability distribution over ontic states. A model is said to be \(\psi\)- ontic if the ontic state uniquely determines the quantum state; that is, if there is a function from ontic states to quantum states (this includes both cases in which the quantum state also completely determines the physical state, and cases, such as hidden-variables theories, in which the quantum state does not completely determine the physical state). In their terminology, models that are not \(\psi\)-ontic are called \(\psi\) -epistemic . If a model is not \(\psi\)-ontic, this means that it is possible for some ontic states to be the result of two or more preparations that lead to different assignments of pure quantum states; that is, the same ontic state may be compatible with distinct quantum states.

This gives a nice way of posing the question of quantum state realism: are there preparations corresponding to distinct pure quantum states that can give rise to the same ontic state, or, conversely, are there ontic states compatible with distinct quantum states? Pusey, Barrett, and Rudolph (2012) showed that, if one adopts a seemingly natural independence assumption about state preparations—namely, the assumption that it is possible to prepare a pair of systems in such a way that the probabilities for ontic states of the two systems are effectively independent—then the answer is negative; any ontological model that reproduces quantum predictions and satisfies this Preparation Independence assumption must be a \(\psi\)-ontic model.

The Pusey, Barrett and Rudolph (PBR) theorem does not close off all options for anti-realism about quantum states; an anti-realist about quantum states could reject the Preparation Independence assumption, or reject the framework within which the theorem is set; see discussion in Spekkens (2015): 92–93. See Leifer (2014) for a careful and thorough overview of theorems relevant to quantum state realism, and Myrvold (2020) for a presentation of a case for quantum state realism based on theorems of this sort.

The major realist approaches to the measurement problem are all, in some sense, realist about quantum states. Merely saying this is insufficient to give an account of the ontology of a given interpretation. Among the questions to be addressed are: if quantum states represent something physically real, what sort of thing is it? This is the question of the ontological construal of quantum states. Another question is the EPR question, whether a description in terms of quantum states can be taken as, in principle, complete, or whether it must be supplemented by different ontology.

De Broglie’s original conception of the “pilot wave” was that it would be a field, analogous to an electromagnetic field. The original conception was that each particle would have its own guiding wave. However, in quantum mechanics as it was developed at the hands of Schrödinger, for a system of two or more particles there are not individual wave functions for each particle, but, rather, a single wave function that is defined on \(n\)-tuples of points in space, where \(n\) is the number of particles. This was taken, by de Broglie, Schrödinger and others, to militate against the conception of quantum wave functions as fields. If quantum states represent something in physical reality, they are unlike anything familiar in classical physics.

One response that has been taken is to insist that quantum wave functions are fields nonetheless, albeit fields on a space of enormously high dimension, namely, \(3n\), where \(n\) is the number of elementary particles in the universe. On this view, this high-dimensional space is thought of as more fundamental than the familiar three-dimensional space (or four-dimensional spacetime) that is usually taken to be the arena of physical events. See Albert (1996, 2013), for the classic statement of the view; other proponents include Loewer (1996), Lewis (2004), Ney (2012, 2013a,b, 2021), and North (2013). Most of the discussion of this proposal has taken place within the context of nonrelativistic quantum mechanics, which is not a fundamental theory. It has been argued that considerations of how the wave functions of nonrelativistic quantum mechanics arise from a quantum field theory undermines the idea that wave functions are relevantly like fields on configuration space, and also the idea that configuration spaces can be thought of as more fundamental than ordinary spacetime (Myrvold 2015).

A view that takes a wave function as a field on a high-dimensional space must be distinguished from a view that takes it to be what Belot (2012) has called a multi-field , which assigns properties to \(n\)-tuples of points of ordinary three-dimensional space. These are distinct views; proponents of the \(3n\)-dimensional conception make much of the fact that it restores Separability: on this view, a complete specification of the way the world is, at some time, is given by specification of local states of affairs at each address in the fundamental (\(3n\)-dimensional) space. Taking a wave function to be a multi-field, on the other hand, involves accepting nonseparability. Another difference between taking wave-functions as multi-fields on ordinary space and taking them to be fields on a high-dimensional space is that, on the multi-field view, there is no question about the relation of ordinary three-dimensional space to some more fundamental space.­ Hubert and Romano (2018) argue that wave-functions are naturally and straightforwardly construed as multi-fields.

It has been argued that, on the de Broglie-Bohm pilot wave theory and related pilot wave theories, the quantum state plays a role more similar to that of a law in classical mechanics; its role is to provide dynamics for the Bohmian corpuscles, which, according to the theory, compose ordinary objects. See Dürr, Goldstein, and Zanghì (1997), Allori et al. (2008), Allori (2021).

Dürr, Goldstein, and Zanghì (1992) introduced the term “primitive ontology” for what, according to a physical theory, makes up ordinary physical objects; on the de Broglie-Bohm theory, this is the Bohmian corpuscles. The conception is extended to interpretations of collapse theories by Allori et al. (2008). Primitive ontology is to be distinguished from other ontology, such as the quantum state, that is introduced into the theory to account for the behavior of the primitive ontology. The distinction is meant to be a guide as to how to conceive of the nonprimitive ontology of the theory.

Quantum mechanics has not only given rise to interpretational conundrums; it has given rise to new concepts in computing and in information theory. Quantum information theory is the study of the possibilities for information processing and transmission opened up by quantum theory. This has given rise to a different perspective on quantum theory, one on which, as Bub (2000, 597) put it, “the puzzling features of quantum mechanics are seen as a resource to be developed rather than a problem to be solved” (see the entries on quantum computing and quantum entanglement and information ).

Another area of active research in the foundations of quantum mechanics is the attempt to gain deeper insight into the structure of the theory, and the ways in which it differs from both classical physics and other theories that one might construct, by characterizing the structure of the theory in terms of very general principles, often with an information-theoretic flavour.

This project has its roots in early work of Mackey (1957, 1963), Ludwig (1964), and Piron (1964) aiming to characterize quantum mechanics in operational terms. This has led to the development of a framework of generalized probabilistic model. It also has connections with the investigations into quantum logic initiated by Birkhoff and von Neumann (1936) (see the entry quantum logic and probability theory for an overview).

Interest in the project of deriving quantum theory from axioms with clear operational content was revived by the work of Hardy (2001 [2008], Other Internet Resources). Significant results along these lines include the axiomatizations of Masanes and Müller (2011) and Chiribella, D’Ariano, and Perinotti (2011). See Chiribella and Spekkens (2015) for an overview of this burgeoning research area.

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How to cite this entry . Preview the PDF version of this entry at the Friends of the SEP Society . Look up topics and thinkers related to this entry at the Internet Philosophy Ontology Project (InPhO). Enhanced bibliography for this entry at PhilPapers , with links to its database.

• Feynman, R., Lectures on Physics . These are introductory lectures aimed at physics undergraduates.
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Articles on Quantum physics

Displaying 1 - 20 of 65 articles.

How long before quantum computers can benefit society? That’s Google’s US$5 million question

Adam Lowe , Aston University

Gravity experiments on the kitchen table: why a tiny, tiny measurement may be a big leap forward for physics

Sam Baron , The University of Melbourne

What is quantum advantage? A quantum computing scientist explains an approaching milestone marking the arrival of extremely powerful computers

Daniel Lidar , University of Southern California

New technique uses near-miss particle physics to peer into quantum world − two physicists explain how they are measuring wobbling tau particles

Jesse Liu , University of Cambridge and Dennis V. Perepelitsa , University of Colorado Boulder

Before he developed the atomic bomb, J. Robert Oppenheimer’s early work revolutionized the field of quantum chemistry – and his theory is still used today

Aaron W. Harrison , Austin College

Quantum physics proposes a new way to study biology – and the results could revolutionize our understanding of how life works

Clarice D. Aiello , University of California, Los Angeles

Physicists have used entanglement to ‘stretch’ the uncertainty principle, improving quantum measurements

Lorcan Conlon , Australian National University and Syed Assad , Australian National University

What quantum technology means for Canada’s future

Stephanie Simmons , Simon Fraser University

The magic of touch: how deafblind people taught us to ‘see’ the world differently during COVID

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Nobel-winning quantum weirdness undergirds an emerging high-tech industry, promising better ways of encrypting communications and imaging your body

Nicholas Peters , University of Tennessee

This Australian experiment is on the hunt for an elusive particle that could help unlock the mystery of dark matter

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Quantum physics offers insights about leadership in the 21st century

Randall Carolissen , University of Johannesburg

Quantum entanglement: what it is, and why physicists want to harness it

Nicholas Bornman , University of the Witwatersrand

Is space infinite? We asked 5 experts

Noor Gillani , The Conversation

Can consciousness be explained by quantum physics? My research takes us a step closer to finding out

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Curious Kids: is light a wave or a particle?

Sam Baron , Australian Catholic University

Can the laws of physics disprove God?

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New postage stamp honors Chien-Shiung Wu, trailblazing nuclear physicist

Xuejian Wu , Rutgers University - Newark

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10 mind-boggling things you should know about quantum physics

From the multiverse to black holes, here’s your cheat sheet to the spooky side of the universe.

1. The quantum world is lumpy

The quantum world has a lot in common with shoes. You can’t just go to a shop and pick out sneakers that are an exact match for your feet. Instead, you’re forced to choose between pairs that come in predetermined sizes.

The subatomic world is similar. Albert Einstein won a Nobel Prize for proving that energy is quantized. Just as you can only buy shoes in multiples of half a size, so energy only comes in multiples of the same "quanta" — hence the name quantum physics.

The quanta here is the Planck constant , named after Max Planck, the godfather of quantum physics. He was trying to solve a problem with our understanding of hot objects like the sun. Our best theories couldn’t match the observations of the energy they kick out. By proposing that energy is quantized, he was able to bring theory neatly into line with experiment.

2. Something can be both wave and particle

J. J. Thomson won the Nobel Prize in 1906 for his discovery that electrons are particles. Yet his son George won the Nobel Prize in 1937 for showing that electrons are waves. Who was right? The answer is both of them. This so-called wave-particle duality is a cornerstone of quantum physics. It applies to light as well as electrons. Sometimes it pays to think about light as an electromagnetic wave, but at other times it’s more useful to picture it in the form of particles called photons. 

A telescope can focus light waves from distant stars, and also acts as a giant light bucket for collecting photons. It also means that light can exert pressure as photons slam into an object. This is something we already use to propel spacecraft with solar sails, and it may be possible to exploit it in order to maneuver a dangerous asteroid off a collision course with Earth , according to Rusty Schweickart, chairman of the B612 Foundation.

3. Objects can be in two places at once

Wave-particle duality is an example of superposition . That is, a quantum object existing in multiple states at once. An electron, for example, is both ‘here’ and ‘there’ simultaneously. It’s only once we do an experiment to find out where it is that it settles down into one or the other. 

This makes quantum physics all about probabilities. We can only say which state an object is most likely to be in once we look. These odds are encapsulated into a mathematical entity called the wave function. Making an observation is said to ‘collapse’ the wave function, destroying the superposition and forcing the object into just one of its many possible states.

This idea is behind the famous Schrödinger’s cat thought experiment. A cat in a sealed box has its fate linked to a quantum device. As the device exists in both states until a measurement is made, the cat is simultaneously alive and dead until we look.

4. It may lead us towards a multiverse

The idea that observation collapses the wave function and forces a quantum ‘choice’ is known as the Copenhagen interpretation of quantum physics. However, it’s not the only option on the table. Advocates of the ‘many worlds’ interpretation argue that there is no choice involved at all. Instead, at the moment the measurement is made, reality fractures into two copies of itself: one in which we experience outcome A, and another where we see outcome B unfold. It gets around the thorny issue of needing an observer to make stuff happen — does a dog count as an observer, or a robot?

Instead, as far as a quantum particle is concerned, there’s just one very weird reality consisting of many tangled-up layers. As we zoom out towards the larger scales that we experience day to day, those layers untangle into the worlds of the many worlds theory. Physicists call this process decoherence.

5. It helps us characterize stars

Danish physicist Niels Bohr showed us that the orbits of electrons inside atoms are also quantized. They come in predetermined sizes called energy levels. When an electron drops from a higher energy level to a lower energy level, it spits out a photon with an energy equal to the size of the gap. Equally, an electron can absorb a particle of light and use its energy to leap up to a higher energy level.

Astronomers use this effect all the time. We know what stars are made of because when we break up their light into a rainbow-like spectrum, we see colors that are missing. Different chemical elements have different energy level spacings, so we can work out the constituents of the sun and other stars from the precise colors that are absent.

6. Without it the sun wouldn’t shine

The sun makes its energy through a process called nuclear fusion. It involves two protons — the positively charged particles in an atom — sticking together. However, their identical charges make them repel each other, just like two north poles of a magnet. Physicists call this the Coulomb barrier, and it’s like a wall between the two protons. 

Think of protons as particles and they just collide with the wall and move apart: No fusion, no sunlight. Yet think of them as waves, and it’s a different story. When the wave’s crest reaches the wall, the leading edge has already made it through. The wave’s height represents where the proton is most likely to be. So although it is unlikely to be where the leading edge is, it is there sometimes. It’s as if the proton has burrowed through the barrier, and fusion occurs. Physicists call this effect "quantum tunneling".

7. It stops dead stars collapsing

Eventually fusion in the sun will stop and our star will die. Gravity will win and the sun will collapse, but not indefinitely. The smaller it gets, the more material is crammed together. Eventually a rule of quantum physics called the Pauli exclusion principle comes into play. This says that it is forbidden for certain kinds of particles — such as electrons — to exist in the same quantum state. As gravity tries to do just that, it encounters a resistance that astronomers call degeneracy pressure. The collapse stops, and a new Earth-sized object called a white dwarf forms. 

Degeneracy pressure can only put up so much resistance, however. If a white dwarf grows and approaches a mass equal to 1.4 suns, it triggers a wave of fusion that blasts it to bits. Astronomers call this explosion a Type Ia supernova , and it’s bright enough to outshine an entire galaxy.

8. It causes black holes to evaporate

A quantum rule called the Heisenberg uncertainty principle says that it’s impossible to perfectly know two properties of a system simultaneously. The more accurately you know one, the less precisely you know the other. This applies to momentum and position, and separately to energy and time.

It’s a bit like taking out a loan. You can borrow a lot of money for a short amount of time, or a little cash for longer. This leads us to virtual particles. If enough energy is ‘borrowed’ from nature then a pair of particles can fleetingly pop into existence, before rapidly disappearing so as not to default on the loan.

Stephen Hawking imagined this process occurring at the boundary of a black hole, where one particle escapes (as Hawking radiation), but the other is swallowed. Over time the black hole slowly evaporates, as it’s not paying back the full amount it has borrowed. 

9. It explains the universe’s large-scale structure

Our best theory of the universe’s origin is the Big Bang . Yet it was modified in the 1980s to include another theory called inflation . In the first trillionth of a trillionth of a trillionth of a second, the cosmos ballooned from smaller than an atom to about the size of a grapefruit. That’s a whopping 10^78 times bigger. Inflating a red blood cell by the same amount would make it larger than the entire observable universe today.

As it was initially smaller than an atom, the infant universe would have been dominated by quantum fluctuations linked to the Heisenberg uncertainty principle. Inflation caused the universe to grow rapidly before these fluctuations had a chance to fade away. This concentrated energy into some areas rather than others — something astronomers believe acted as seeds around which material could gather to form the clusters of galaxies we observe now.

10. It is more than a little ‘spooky’

As well as helping to prove that light is quantum, Einstein argued in favor of another effect that he dubbed ‘spooky action at distance’. Today we know that this ‘quantum entanglement’ is real, but we still don’t fully understand what’s going on. Let’s say that we bring two particles together in such a way that their quantum states are inexorably bound, or entangled. One is in state A, and the other in state B.

The Pauli exclusion principle says that they can’t both be in the same state. If we change one, the other instantly changes to compensate. This happens even if we separate the two particles from each other on opposite sides of the universe. It’s as if information about the change we’ve made has traveled between them faster than the speed of light, something Einstein said was impossible.

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Unit 17: Quantum Physics

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• Published: 28 April 2023

Fresh perspectives on the foundations of quantum physics

• Eric G. Cavalcanti 1 ,
• Rafael Chaves 2 ,
• Flaminia Giacomini 3 &
• Yeong-Cherng Liang 4  

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• Quantum physics

As we are at the beginning of the second century of quantum physics, we asked four researchers to share their views on new research directions trying to answer old, yet still open, questions in the foundations of quantum theory.

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Acknowledgements

E.G.C. acknowledges L. del Rio, N. Tischler, H. Wiseman, W. Zeng and participants of the Towards Experimental Wigner’s Friends workshop in San Francisco for useful discussions on the LF experimental programme, as well as support from grant no. FQXi-RFP-CPW-2019 from the Foundational Questions Institute and Fetzer Franklin Fund. R.C. acknowledges support from the Serrapilheira Institute (grant no. Serra – 1708-15763) and the Simons Foundation (grant no. 1023171, RC). F.G. would like to thank R. Renner for helpful comments on a first draft of her contribution, and acknowledges support from the Swiss National Science Foundation via the Ambizione Grant PZ00P2-208885. Y.-C.L. is grateful to N. Gisin for the many inspiring discussions on quantum foundations and for introducing to him the exciting topic of entangled measurements, and acknowledges support from the National Science and Technology Council and the National Center for Theoretical Sciences, Taiwan.

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Centre for Quantum Dynamics, Griffith University, Gold Coast, QLD, Australia

Eric G. Cavalcanti

International Institute of Physics, IIP-UFRN, Natal, Brazil

Rafael Chaves

Institute for Theoretical Physics, ETH Zürich, Zürich, Switzerland

Flaminia Giacomini

Department of Physics and Center for Quantum Frontiers of Research and Technology (QFort), National Cheng Kung University, Tainan, Taiwan

Yeong-Cherng Liang

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Correspondence to Eric G. Cavalcanti , Rafael Chaves , Flaminia Giacomini or Yeong-Cherng Liang .

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The contributors

Eric Cavalcanti is an Associate Professor at Griffith University in Queensland, Australia. He has also worked at the University of Sydney and University of Oxford, after a PhD in Physics from the University of Queensland. His research focus is on quantum foundations and quantum information theory, and he has also made contributions to a wide range of fields including philosophy of science, quantum atom-optics and experimental atomic collisions.

Rafael Chaves is a research leader at the International Institute of Physics in Natal, Brazil. Previously, he worked in ICFO and the Universities of Freiburg and Cologne as a postdoctoral researcher. His contributions include quantum computation, communication and machine learning. The focus of his research is on the interface between quantum information and causal inference, developing new tools and concepts to investigate the emergence of non-classical features in quantum networks.

Flaminia Giacomini is an SNSF Ambizione Fellow at ETH Zurich. She received her PhD from the University of Vienna and then held a postdoctoral fellowship at Perimeter Institute for Theoretical Physics. Her research uses quantum information tools to answer fundamental questions at the interface between quantum theory and general relativity. Her research interests span from conceptual consequences of the lack of a classical spacetime, such as quantum time, quantum reference frames and indefinite causality, to the study of the observational implications of the quantum nature of gravity in table-top experiments.

Yeong-Cherng Liang is a professor of physics and a research group leader based at the National Cheng Kung University (NCKU), Taiwan. He received his PhD from the University of Queensland, Australia, in 2008. He then did postdoctoral research at the University of Sydney, the University of Geneva and ETH Zürich, before taking up a faculty position at NCKU in 2015. His expertise is in quantum foundations, especially quantum nonlocality, quantum entanglement and their applications in quantum information.

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Cavalcanti, E.G., Chaves, R., Giacomini, F. et al. Fresh perspectives on the foundations of quantum physics. Nat Rev Phys 5 , 323–325 (2023). https://doi.org/10.1038/s42254-023-00586-z

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Essay on Quantum Physics

Students are often asked to write an essay on Quantum Physics in their schools and colleges. And if you’re also looking for the same, we have created 100-word, 250-word, and 500-word essays on the topic.

Let’s take a look…

100 Words Essay on Quantum Physics

Introduction to quantum physics.

Quantum physics, also known as quantum mechanics, is a branch of physics that deals with phenomena on a very small scale, like molecules, atoms, and subatomic particles.

Quantum Particles

In the quantum world, particles can exist in multiple places at once. This is called superposition. Particles can also be linked across space, known as entanglement.

Wave-Particle Duality

Quantum physics suggests that particles can behave both like particles and waves. This is known as wave-particle duality.

Uncertainty Principle

The Heisenberg Uncertainty Principle states that it is impossible to accurately measure both the position and momentum of a particle at the same time.

250 Words Essay on Quantum Physics

Quantum physics, also known as quantum mechanics, is a fundamental theory in physics that describes nature at the smallest scales of energy levels of atoms and subatomic particles. It departs from classical mechanics primarily at the quantum realm of atomic and subatomic length scales.

Quantum Superposition and Entanglement

Two of the most intriguing principles in quantum physics are superposition and entanglement. Superposition refers to the quantum phenomenon where a particle can exist in multiple states at once, only collapsing into one state when observed. This is best exemplified by the famous Schrödinger’s cat thought experiment.

Quantum entanglement, on the other hand, describes the inexplicable interconnectedness of particles regardless of distance. If two particles are entangled, the state of one immediately influences the state of the other, even if they are light-years apart.

Quantum Physics and Reality

Quantum physics challenges our perception of reality. The Copenhagen interpretation, one of the earliest and most commonly taught interpretations of quantum mechanics, suggests that a quantum particle doesn’t exist in one state or another, but in all of its possible states at once. It’s only when we observe its state that a quantum particle is essentially forced to choose one probability, and that’s the state that we observe.

Quantum physics, while complex and counterintuitive, provides a more accurate description of the universe at microscopic scales. It has revolutionized our understanding of the physical world and continues to inspire new technologies, from quantum computing to quantum teleportation.

500 Words Essay on Quantum Physics

Quantum physics, also known as quantum mechanics, is a branch of physics that deals with phenomena on a very small scale, such as molecules, atoms, and even smaller particles. It is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles.

The Birth of Quantum Mechanics

Quantum mechanics was developed in the early 20th century as a response to problems that could not be solved by classical physics. The theory of classical physics, based on the principles laid down by Isaac Newton, worked well for macroscopic objects but failed at the atomic and subatomic levels. Quantum mechanics was born out of the need to explain behaviors that did not fit into the classical framework, such as the photoelectric effect and blackbody radiation.

Key Principles of Quantum Physics

One of the most intriguing aspects of quantum physics is the principle of superposition, which holds that a physical system—such as an electron—can exist in multiple states simultaneously. This principle is illustrated by the famous Schrödinger’s cat thought experiment.

Another fundamental principle in quantum physics is wave-particle duality. This concept suggests that all particles also have properties of waves. It’s an idea that was first introduced by Louis de Broglie in 1924.

Quantum entanglement, another key concept, describes a phenomenon where particles become interconnected and the state of one can instantly affect the state of the other, no matter the distance between them. This phenomenon was famously referred to as “spooky action at a distance” by Albert Einstein.

Quantum Physics and the Modern World

Quantum physics has been instrumental in the development of many technologies that we use today. Semiconductors, the building blocks of modern electronics, function due to principles of quantum mechanics. The field has also given rise to technologies like lasers and magnetic resonance imaging (MRI). More recently, quantum physics has become essential in the developing field of quantum computing, which has the potential to revolutionize technology.

Challenges and Future Directions

Despite its successes, quantum mechanics also presents several philosophical and practical challenges. The interpretation of quantum mechanics remains a contentious issue among physicists. Additionally, the unification of quantum mechanics with general relativity, to create a single theory that can describe all of the fundamental forces in nature, remains an unsolved problem in theoretical physics.

In conclusion, quantum physics is a fascinating and complex field that has revolutionized our understanding of the universe. It has led to numerous technological advancements and continues to be an active area of research with promising future applications. Despite its complexities and unresolved questions, the study of quantum physics offers a glimpse into the fundamental workings of our universe.

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Physical Review Letters

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Essay: Quantum Sensing with Atomic, Molecular, and Optical Platforms for Fundamental Physics

Jun ye and peter zoller, phys. rev. lett. 132 , 190001 – published 7 may 2024.

• No Citing Articles
• Introduction.—
• Emerging quantum technologies based on…
• Connections and application to…
• Connection and applications to condensed…
• Connection and applications to…
• Theory connections between quantum…
• Concluding remarks.—
• ACKNOWLEDGMENTS

Atomic, molecular, and optical (AMO) physics has been at the forefront of the development of quantum science while laying the foundation for modern technology. With the growing capabilities of quantum control of many atoms for engineered many-body states and quantum entanglement, a key question emerges: what critical impact will the second quantum revolution with ubiquitous applications of entanglement bring to bear on fundamental physics? In this Essay, we argue that a compelling long-term vision for fundamental physics and novel applications is to harness the rapid development of quantum information science to define and advance the frontiers of measurement physics, with strong potential for fundamental discoveries. As quantum technologies, such as fault-tolerant quantum computing and entangled quantum sensor networks, become much more advanced than today’s realization, we wonder what doors of basic science can these tools unlock. We anticipate that some of the most intriguing and challenging problems, such as quantum aspects of gravity, fundamental symmetries, or new physics beyond the minimal standard model, will be tackled at the emerging quantum measurement frontier.

Part of a series of Essays which concisely present author visions for the future of their field .

• Received 28 March 2024

DOI: https://doi.org/10.1103/PhysRevLett.132.190001

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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• JILA, National Institute of Standards and Technology, and Department of Physics, University of Colorado, Boulder, Colorado 80309, USA
• Institute for Theoretical Physics, University of Innsbruck, 6020 Innsbruck, Austria and Institute for Quantum Optics and Quantum Information, Austrian Academy of Sciences, 6020 Innsbruck, Austria

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Vol. 132, Iss. 19 — 10 May 2024

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Quantum system design and engineering to open new frontiers for quantum sensing. (a) A quantum network that links individual clocks in space with enhanced performance and security based on their entangled quantum states. The optimal use of global resources and quantum-enabled precision and accuracy also represent a unique long-baseline observatory for fundamental physics [ 6 ]. (b) A Wannier-Stark optical lattice where clock (spin) and atom interferometer (motion) are integrated into a single quantum platform [ 7 ]. Cavity-QED-based entanglement generation will further enhance the probing of clock frequency, coherence, and gravity [ 8 ]. (c) A new monolithic ion trap configuration allows a two-dimensional arrangement of laser-cooled ions for quantum simulations of spin models and increased sensing capabilities [ 9 ]. (d) A tweezer array of neutral atoms that enable any-to-any connectivity among hundreds of atomic qubits with universal local single-qubit rotations and high-fidelity two-qubit Rydberg gates. Fast midcircuit readout and feedforward can be implemented together with parallel transport in reconfigurable array architecture [ 10, 11 ]. (e) The generation of GHZ entangled states for enhanced interferometric sensitivity in clock operation, reaching the Heisenberg limit where the phase sensitivity scales with the inverse of particle number N . This is the best possible outcome defined by quantum physics [ 11, 12 ].

Peter Zoller

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Revision notes for IB Physics

Topic 12: quantum and nuclear physics (hl).

See the guide for this topic.

12.1 – The interaction of matter with radiation

• Einstein proposed that light consists of particles called photons.
• Quantum refers to the smallest discrete amount of something. A photon is a quantum of electromagnetic radiation (light).
• Photons exhibit wave properties under refraction or interference.
• Photons exhibit wave properties under its emission or absorption.
• A photon’s energy (E) is proportional to its frequency (f) and is given by

where h is Planck’s constant, c is the speed of light, and λ is its wavelength (electromagnetic wave).

The photoelectric effect

• Photoelectric effect refers to the emission of electrons from a metal surface as a result of the absorption of electromagnetic wave energy.

• An example of the photoelectric effect on a sample metal surface.

Incident electromagnetic waves with lower frequency have a smaller chance of inducing the photoelectric effect.

• Why does the intensity of light affect the number of ejected electrons?

The number of photons per unit time in the incident light is proportional to the light intensity.

An increase in the intensity of the incident light allows a higher number of photon-electron interactions. Therefore, more electrons are ejected.

• Why is there a minimum frequency below which no electrons are ejected?

There exists a minimum energy below which electrons would not be ejected from the metal. This minimum energy level depends on the metal in use and is called the work function (φ).

Since E=hf, φ=hf0 where f0 is called the threshold frequency.

• How does the frequency of the incident light affect the maximum kinetic energy of the ejected electrons?

The work function corresponds to the potential energy which binds the electron to the nucleus.

Since total energy = potential energy + kinetic energy,

which may be represented on graph by the following

Matter waves

• The De Broglie hypothesis suggests that all matter exhibits wave-like properties. In particular, the momentum of a particle is related to its wavelength where the De Broglie wavelength may be deduced by the following formula

where p is momentum, h is Planck’s constant, λ is wavelength, m is mass, and v is velocity.

• The term “wave-particle duality” refers to matter acting as both waves and particles.

Pair production and pair annihilation

All matters have their antimatter counterparts which resemble their corresponding matter in every way except for the sign of their charge and the direction of their spin.

Pair production

When a high energy photon collides with a nucleus, it makes a pair of electron and positron (electron antimatter) and gives kinetic energy to each particle.

Pair annihilation

When matter collides with its corresponding antimatter, they annihilate one another with the conservation of energy, momentum, and charge.

The positron (+e) collides with the electron (-e), annihilating each other into two photons with exactly opposite directions and the same amount of momentum.

Quantization of angular momentum in the Bohr model for hydrogen

• Bohr developed a model for hydrogen that was able to explain the emission and absorption spectra of hydrogen.
• His model assumed discrete orbital paths in which electrons orbit the nucleus through, the same way planets orbit stars.
• The orbits were quantized in terms of their allowable angular momentum (rotational momentum).

• Therefore, the orbital radii and energies are also quantized.
• The energy of the orbit is the energy required to ionize (remove) an electron and can be given through the following equation in relation to the order of orbit (n)

• When the electrons are excited, they jump to higher energy orbits and eventually drop back down to a more stable orbit by releasing excess energy by the form of light. The energy of the light released is therefore equal to the difference in energy of the two orbits.

The wave function

By quantum physics, all particles do not have a defined position until they are observed. Instead, all particles are described as “a wave function”.

TL;DR : The wave function gives the probability of finding a particle at a given point which is given by the square of the amplitude of the wave function at that location.

The uncertainty principle for energy and time and position and momentum

The Heisenberg uncertainty principle states that

• If the energy state only lasts for a brief period of time, its energy is uncertain.
• Position and momentum cannot be measured simultaneously with precision. The more precisely the position is determined, the less precisely the momentum is known, and vice versa.

Tunnelling, potential barrier and factors affecting tunnelling probability

• Imagine throwing a ball at a wall and having it disappear the instant before making contact and appearing on the other side. The wall remains intact and the ball did not break through it. Believe it or not, there is a finite (if extremely small) probability that this even would occur. This phenomenon is called quantum tunnelling.

• The position of a particle is described as a wave function (see previous section).
• From the graph above, the observable particle is most likely to be at the position where its wave function has the largest amplitude. However, although the amplitude of the wave function will decay exponentially, since the wave function does not reach an amplitude of zero, the wave function can exit the barrier. Once the wave function exits the barrier, its amplitude no longer decays. This means that a particle has a certain probability of bouncing off a barrier and a certain probability of passing through the other side.
• This explains how tunnelling is frequent in nanoscale but negligible at the macroscopic level.

12.2 – Nuclear physics

Rutherford scattering and nuclear radius.

Rutherford’s undergraduate students, Geiger and Marsden, bombarded a sheet of gold foil by alpha particles.

The alpha particles passed through the gold foil in most cases, a small percentage of alpha particles were deflected by small angles of deflection, and an even smaller percentage of alpha particles were deflected by large angles of deflection.

Rutherford thus deduced that the atom consists of a small compact positive nucleus (where alpha particles deflect by large angles) with a majority of volume existing as empty space (where alpha particles pass right through).

Nuclear energy levels

• In the same way electrons can move between discrete energy levels, the nucleus of an atom can too.
• Atoms that decay through gamma decay emit distinct frequencies of gamma rays which correspond to distinct energy levels.

The neutrino

• A neutrino is a type of lepton. Since they have no electrical charge or strong charge, most neutrinos do not react with other particles and pass right through earth with no interaction.
• Neutrinos are produced in many particle decays, such as in beta decay. When a neutron at rest (zero momentum) decays by releasing a proton and an electron, because of the law of conservation of momentum, the resultant products of decay must have a total momentum of zero, which the observed proton and electron clearly does not portray. Therefore, we suggest the presence of another particle to balance the momentum – by the release of an antineutrino (neutrino antimatter). This was confirmed by experimentation.

• Neutrinos were produced in great abundance in the early universe and rarely interact with matter. This may suggest that neutrinos contribute to the total mass of the universe and affects its expansion.

The law of radioactive decay and the decay constant

Apart from half-lives (see topic 7), the activity of radioactive decay can also be shown exponentially by the law of radioactive decay.

• The decay constant (λ) represents the probability of decay of a nucleus per unit time and is dependent on the type of element.

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Quantum Physics

Title: quantum sensing with atomic, molecular, and optical platforms for fundamental physics.

Abstract: Atomic, molecular, and optical (AMO) physics has been at the forefront of the development of quantum science while laying the foundation for modern technology. With the growing capabilities of quantum control of many atoms for engineered many-body states and quantum entanglement, a key question emerges: what critical impact will the second quantum revolution with ubiquitous applications of entanglement bring to bear on fundamental physics? In this Essay, we argue that a compelling long-term vision for fundamental physics and novel applications is to harness the rapid development of quantum information science to define and advance the frontiers of measurement physics, with strong potential for fundamental discoveries. As quantum technologies, such as fault-tolerant quantum computing and entangled quantum sensor networks, become much more advanced than today's realization, we wonder what doors of basic science can these tools unlock? We anticipate that some of the most intriguing and challenging problems, such as quantum aspects of gravity, fundamental symmetries, or new physics beyond the minimal standard model, will be tackled at the emerging quantum measurement frontier.

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A List of 240 Physics Topics & Questions to Research

Plates break when you drop them. Glasses help you see better. Have you ever wondered why?

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Physics has the answer. It studies the observable as well as invisible aspects of nature. An essential part of this is examining the structure and interactions of matter.

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🔝 Top 10 Physics Research Topics

✅ branches of physics.

• ⭐ Top 10 Physics Topics
• ⚙️ Mechanics
• 🌡️ Thermodynamics
• ⚡ Electromagnetism
• 🔊 Sounds & Waves
• ☢️ Modern Physics
• 🔋 Physics Project Topics
• 🔭 Astrophysics
• 🌎 Physical Geography
• 🤔 Theoretical Physics
• ⚛️ Quantum Physics

🔍 References

• Modern vs. classical physics
• Gravity method in geophysics
• Why can’t the multiverse be real?
• Nuclear physics vs. quantum physics
• Photonics’ relationship to other fields
• Is electromagnetism the strongest force?
• What would extra dimensions look like?
• The importance of kinematics in real life
• Is string theory a generalization of quantum field theory?
• The difference between liquid pressure and air pressure

Now: before writing about physics you should know about its main branches. These are classical and modern . Let’s take a closer look:

• Mechanics , which is concerned with motion. Two of its essential aspects are kinematics and dynamics.
• Optics helps us understand the properties of light.
• Another branch investigates waves and sound . It studies the way they travel and how they are produced.
• Thermodynamics deals with heat and motion. One of its key concepts is entropy.
• Electromagnetism studies the interactions between charged particles. It also deals with the forces and fields that surround them.
• Finally, physical geographers observe our Earth’s physical features. These include environmental processes and patterns.
• Atomic physics , which examines the structure and behavior of atoms.
• Nuclear physics investigates the nucleus of atoms. This branch often deals with radioactivity.
• Scientists working in quantum physics concentrate on the erratic behavior of waves and particles.
• Relativity can be general and special. Special relativity deals with time and motion. General relativity describes gravity as an alteration of spacetime caused by massive objects.
• Cosmology and astrophysics explore the properties of celestial bodies. Cosmologists strive to comprehend the universe on a larger scale.
• Mesoscopic physics covers the scale between macroscopic and microscopic.

You can talk about any of these branches in your essay. Keep in mind that this division is a basic outline. Strictly speaking, everything that happens around you is physics! Now, we’re all set to move on to our physics paper topics.

Just in 1 hour! We will write you a plagiarism-free paper in hardly more than 1 hour

⭐ Top 10 Physics Topics 2024

• Biophysics vs. biochemistry
• The future of nano-physics
• The use of perturbation theory
• Possible cause of baryogenesis
• Solid-state vs. condensed matter physics
• Why is the quark model introduced?
• The importance of plasma in physics
• Statistical mechanics vs. statistical physics
• Ways to calculate electronic structure
• Difference between matter and dark matter

🧲 Classical Physics Topics to Write About

Classical physics deals with energy, force, and motion. You encounter this kind of physics in everyday life. Below, we’ve compiled a list with compelling prompts you’ll recognize from your physics class:

⚙️ Mechanics Essay Topics

• What does Newton’s laws of motion state?
• How do ships stay afloat?
• Equipartition: for what systems does it not hold?
• What does Bernoulli’s principle state about fluids?
• Surface tension: what causes it?
• How does buoyancy work?
• An overview of the molecular origins of viscosity.
• The equipartition theorem: how does it connect a system’s temperature to its energies?
• The benefits of the continuum assumption.
• Contrast the different types of forces.
• Explain the term “momentum.”
• Kinematics: describing the relationships of objects in constrained motion.
• What causes objects to oscillate?

🌡️ Thermodynamics Paper Topics

• Thermodynamics as a kinetic theory of matter.
• What is entropy?
• Describe the three types of thermodynamic processes.
• The Carnot heat engine as part of a thermodynamic cycle.

• Perpetual motion: is it possible or not?
• Investigate fire in terms of chemistry and thermodynamics.

⚡ Electromagnetism Topics to Research

• Examine the connection between electric potential and electric field.
• What makes an excellent conduit?
• How does a dielectric impact a capacitor?
• Contrast current, resistance, and power.
• How do magnetic fields relate to electricity?
• Explain inductance. What causes it?
• How do induction stoves work?

🔊 Essay Topics on Sounds & Waves

• Sound waves: how do they travel?
• Describe the two types of mechanical waves.
• What are electromagnetic waves used for?
• The difference between interference and diffraction.
• Music and vibrations: the properties of sound.

👓 Optics Topics to Write About

• How does reflection work?
• What happens when an object absorbs light?
• Why does light break into a rainbow?
• Lasers: what do we use them for?
• What causes Aurora Borealis?
• Photography: what happens when you change the aperture?
• Explain what influences the colors of sunsets.
• Fata Morgana mirages: where do they originate from?
• What is the Novaya Zemlya effect?

☢️ Modern Physics Topics for a Paper

The world of modern physics shifts away from its more tangible origins. It deals with atoms and even smaller particles. Nuclear, atomic, and quantum physics belong to this category. One of the central problems of modern physics is redefining the concept of gravity.

• Relativity: a discovery that turned our understanding of physics upside down.
• An overview of 20th century physics.
• The ultraviolet catastrophe and how it was solved.
• What happens to the energy entering an ideal blackbody?
• The photoelectric effect: creating current with light.
• Why did the classical lightwave model become outdated?
• How do night vision devices work?
• The production of x-rays.
• Explain why the charge of electrons is quantized.
• How does the kinetic energy of an electron relate to the light’s frequency and intensity?
• Describe the photon model of the Compton Scattering.
• How do you identify an element using its line spectra?
• Cold Fusion: how likely is it?
• Explain the Pauli Exclusion Principle.
• Electron shells and atomic orbitals: properties of electrons.
• What causes peaks in the x-ray spectrum?
• How do you calculate radioactive decay?
• Carbon dating: how accurate is it?
• The discovery of radioactivity.
• What holds electronic nuclei together?
• Nuclear Fusion: will it ever be possible?
• Describe the types of elemental transmutation.
• Applications of nuclear fission.
• Virtual particles: how do they come into existence?

• Nucleosynthesis: creating atomic nuclei.
• How do you dope a semiconductor using ion implantation?
• What are the magic numbers?
• Superheavy primordial elements: the history of unbihexium.
• Predictions surrounding the island of stability.
• How does a computer tomography work?

🔋 Physics Project Topics for a Science Fair

What’s the most fun part of every natural science? If you said “experiments,” you guessed it! Everybody can enjoy creating rainbows or exploring the effects of magnets. Your next physics project will be as fascinating as you want it to be with these exciting ideas!

• Build a kaleidoscope and learn how it works.
• Investigate the centripetal force with the help of gelatin and marbles.
• Make a potato battery.
• Construct an elevator system.
• Prove Newton’s laws of motion by placing objects of different weights in a moving elevator.
• Learn how a telescope works. Then build one from scratch.
• Levitate small objects using ultrasound.
• Measure how fast a body in free fall accelerates.
• Find out what causes a capacitor to charge and discharge over time.
• Measure how light intensity changes through several polarizing filters.
• Observe how sound waves change under altered atmospheric conditions.
• Find out how a superheated object is affected by its container.
• Determine the mathematics behind a piece of classical music.
• Replicate an oil spill and search for the best way to clean it up.
• What makes a circular toy easy to spin? Experiment by spinning hula hoops of different sizes.
• Make DNA visible. What happens if you use different sources of plant-based DNA?
• Charge your phone with a handmade solar cell.
• Find out what properties an object needs to stay afloat.
• Create music by rubbing your finger against the rim of a glass. Experiment with several glasses filled with different amounts of water.
• Compare the free-fall speed of a Lego figure using various parachutes.
• Experiment with BEC to understand quantum mechanics.
• Make a windmill and describe how it works.
• Build an automatic light circuit using a laser.
• How do concave and convex mirrors affect your reflection?
• Investigate how pressure and temperature influence the air volume.
• Determine the conductivity of different fluids.
• Learn about the evolution of the universe by measuring electromagnetic radiation.
• Capture charged particles in an ion trap.
• Build a rocket car using a balloon.
• Experiment with pendulums and double pendulums. How do they work?

🔭 Astrophysics Topics for a Research Paper

Astrophysicists, astronomers, and cosmologists observe what happens in space. Astronomy examines celestial bodies, while astrophysics describes their mechanics. At the same time, cosmology attempts to comprehend the universe as a whole.

• Explain when a celestial body is called a planet.
• Dark energy and dark matter: how do they affect the expansion of the universe?
• The cosmic microwave background: investigating the birth of the universe.
• What are the possible explanations for the expansion of the universe?
• Evidence for the existence of dark matter.
• The discovery of gravitational waves: consequences and implications.
• Explore the history of LIGO.
• How did scientists observe a black hole?
• The origins of light.
• Compare the types of stars.
• Radioactivity in space: what is it made of?
• What do we know about stellar evolution?
• Rotations of the Milky Way.
• Write an overview of recent developments in astrophysics.
• Investigate the origin of moons.
• How do we choose names for constellations?
• What are black holes?
• How does radiative transfer work in space?
• What does our solar system consist of?
• Describe the properties of a star vs. a moon.

• What makes binary stars special?
• Gamma-ray bursts: how much energy do they produce?
• What causes supernovae?
• Compare the types of galaxies.
• Neutron stars and pulsars: how do they differ?
• The connection between stars and their colors.
• What are quasars?
• Curved space: is there enough evidence to support the theory?
• What produces x-rays in space?
• Exoplanets: what do we know about them?

🌎 Physical Geography Topics to Write About

Physical geographers explore the beauty of our Earth. Their physical knowledge helps them explain how nature works. What causes climate change? Where do our seasons come from? What happens in the ocean? These are the questions physical geographers seek to answer.

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• What creates rainbows?
• How do glaciers form?
• The geographical properties of capes.
• What causes landslides?
• An overview of the types of erosion.
• What makes Oceania’s flora unique?
• Reefs: why are they important?
• Why is there a desert in the middle of Siberia?
• The geography of the Namibian desert.
• Explain the water cycle.
• How do you measure the length of a river?
• The Gulf Stream and its influence on the European climate.
• Why is the sky blue?
• What creates waves?
• How do marshes form?
• Investigate the causes of riptides.
• The Three Gorges Dam: how was it built?
• Explain the phenomenon of Green Sahara.
• The consequences of freshwater pollution.
• What are the properties of coastal plains?
• Why is the Atacama Desert the driest place on Earth?
• How does a high altitude affect vegetation?
• Atmospheric changes over the past 100 years.
• Predicting earthquakes: a comparison of different methods.
• What causes avalanches?
• Seasons: where do they come from?
• The Baltic and the Northern Seas meeting phenomenon.
• The geographical properties of the Altai Mountains.
• How do the steppes form?
• Why are some water bodies saltier than others?

🤔 Theoretical Physics Topics to Research

Math fans, this section is for you. Theoretical physics is all about equations. Research in this area goes into the development of mathematical and computer models. Plus, theoretical physicists try to construct theories for phenomena that currently can’t be explained experimentally.

• What does the Feynman diagram describe?
• How is QFT used to model quasiparticles?
• String theory: is it a theory of everything?
• The paradoxical effects of time travel.
• Monstrous moonshine: how does it connect to string theory?
• Mirror symmetry and Calabi-Yau manifolds: how are they used in physics?
• Understanding the relationship between gravity and BF theories.
• Compare the types of Gauge theories.

• Applications of TQFT in condensed matter physics.
• Examine the properties of fields with arbitrary spin.
• How do quarks and gluons interact with each other?
• What predictions does quantum field theory make for curved spacetime?
• How do technicolor theories explain electroweak gauge symmetry breaking?
• Quantum gravity: a comparison of approaches.
• How does LQG address the structure of space?
• An introduction into the motivation behind the eigenstate thermalization hypothesis.
• What does the M-theory state?
• What does the Ising model say about ferromagnetism?
• Compare the thermodynamic Debye model with the Einstein model.
• How does the kinetic theory describe the macroscopic properties of gases?
• Understanding the behavior of waves and particles: scattering theory.
• What was the luminiferous aether assumption needed for?
• The Standard Model of particles: why is it not a full theory of fundamental interactions?
• Investigate supersymmetry.
• Physical cosmology: measuring the universe.
• Describe the black hole thermodynamics.
• Pancomputationalism: what is it about?
• Skepticism concerning the E8 theory.
• Explain the conservation of angular momentum.
• What does the dynamo theory say about celestial bodies?

⚛️ Quantum Physics Topics for Essays & Papers

First and foremost, quantum physics is very confusing. In quantum physics, an object is not just in a specific place. It merely has the probability to be in one place or another. Light travels in particles, and matter can be a wave. Throw physics as you know it overboard. In this world, you can never be sure what and where things really are.

• How did the Schrödinger Equation advance quantum physics?
• Describe the six types of quarks.
• Contrast the four quantum numbers.
• What kinds of elementary particles exist?
• Probability density: finding electrons.
• How do you split an atom using quantum mechanics?
• When is an energy level degenerate?
• Quantum entanglement: how does it affect particles?
• The double-slit experiment: what does it prove?
• What causes a wave function to collapse?
• Explore the history of quantum mechanics.
• What are quasiparticles?
• The Higgs mechanism: explaining the mass of bosons.
• Quantum mechanical implications of the EPR paradox.
• What causes explicit vs. spontaneous symmetry breaking?
• Discuss the importance of the observer.
• What makes gravity a complicated subject?
• Can quantum mechanical theories accurately depict the real world?
• Describe the four types of exchange particles.
• What are the major problems surrounding quantum physics?
• What does Bell’s theorem prove?
• How do bubble chambers work?
• Understanding quantum mechanics: the Copenhagen interpretation.
• Will teleportation ever be possible on a large scale?
• The applications of Heisenberg’s uncertainty principle.
• Wave packets: how do you localize them?
• How do you process quantum information?
• What does the Fourier transform do?
• The importance of Planck’s constant.
• Matter as waves: the Heisenberg-Schrödinger atom model.

We hope you’ve found a great topic for your best physics paper. Good luck with your assignment!

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Essays on Quantum Physics

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Example Of Quantum Computer And Security Research Paper

Introduction

Good Essay On Physics In Everyday Life

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Comparison between the cultural impact of Quantum physics to the reaction to the Theory of Natural Selection

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Home — Essay Samples — Science — Physics — Quantum Mechanics

Essays on Quantum Mechanics

Quantum mechanics is a fundamental theory in physics that describes the behavior of matter and energy at the smallest scales. It has revolutionized our understanding of the universe, challenging the classical laws of physics and opening up new possibilities for technology and scientific exploration. In this essay, we will explore a wide range of topics in quantum mechanics, from the foundational principles to cutting-edge research and applications.

Importance of the Topic

Advice on choosing a topic.

When choosing a topic for your quantum mechanics essay, consider your interests and the latest advancements in the field. You may want to explore a specific experiment, theory, or application of quantum mechanics, or delve into the philosophical implications of quantum phenomena. It's important to select a topic that you are passionate about and that allows you to engage with the complex and fascinating concepts of quantum mechanics. Additionally, consider the availability of research material and sources to support your chosen topic.

Quantum Mechanics Essay Topics

• The Double-Slit Experiment: An Exploration of Wave-Particle Duality
• The Uncertainty Principle: Understanding Heisenberg's Groundbreaking Theory
• Quantum Entanglement: The Spooky Action at a Distance
• Schrödinger's Cat: A Thought Experiment in Quantum Superposition
• Quantum Tunneling: Breaking the Laws of Classical Physics
• Quantum Computing: The Future of Information Processing
• The Many-Worlds Interpretation: Exploring the Multiverse
• Bell's Theorem: Testing the Limits of Quantum Mechanics
• Quantum Teleportation: The Science of Instantaneous Communication
• Quantum Cryptography: Securing Information with Quantum Principles
• Quantum Chaos: Unraveling the Complex Dynamics of Quantum Systems
• Quantum Gravity: Bridging the Gap Between Quantum Mechanics and General Relativity
• Quantum Biology: Investigating Quantum Effects in Biological Systems
• Quantum Cosmology: Understanding the Origins of the Universe through Quantum Mechanics
• Quantum Field Theory: Describing Elementary Particles and Forces through Quantum Principles
• Quantum Simulation: Using Quantum Systems to Model Complex Phenomena
• Decoherence: Exploring the Loss of Quantum Coherence in Macroscopic Systems
• Quantum Optics: Harnessing Quantum Effects for Advanced Optical Technologies
• Quantum Information Theory: The Study of Quantum Information Processing
• Quantum Mechanics in Everyday Life: Applications and Implications

Quantum mechanics offers a vast array of topics for exploration and study, ranging from foundational principles to cutting-edge research and applications. By delving into these topics, we can gain a deeper understanding of the fundamental nature of the universe and the potential for groundbreaking technological advancements. Whether you are interested in the theoretical aspects of quantum mechanics or its practical applications, there is no shortage of intriguing and thought-provoking topics to explore in this captivating field of physics.

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MyScienceProject.org > Blog > Interesting Topics in Physics for Extended Essays

Interesting Topics in Physics for Extended Essays

Extended essays are an essential component of the International Baccalaureate (IB) program, providing students with an opportunity to explore a subject of their choice in-depth. In physics, an extended essay can help students develop their research and analytical skills, while also allowing them to delve deeper into a topic that interests them.

Choosing a killer physics topic for your extended essay? It’s like finding the golden ticket in a maze. With the physics world changing faster than you can say “Eureka!”, nailing down a topic that’s both fresh and mind-blowing is no walk in the park.

In this article, we’re spilling the beans on how to pick the crème de la crème of physics topics for your extended essay in 2024. We’ll dish out the secret sauce on what makes a topic tick and throw you a hotlist of potential topics that’ll make your essay shine brighter than a shooting star. Buckle up, ’cause we’re about to guide you through the maze of selecting a physics topic that’ll knock everyone’s socks off!

Criteria for Choosing a Good Physics Topic

Choosing a good physics topic for an extended essay requires careful consideration of various criteria. The following are some important factors to keep in mind when selecting a topic:

• Relevance to current issues in physics – A good physics topic should be relevant to current issues in the field. This means selecting a topic that has significant implications for the future of physics and is likely to spark interest among readers.
• Availability of resources and data – A good physics topic should have access to the necessary resources and data needed for research. This includes access to published articles, databases, and other relevant materials that will help in the writing and analysis of the extended essay.
• Feasibility of research – A good physics topic should be feasible in terms of research. This means selecting a topic that can be studied within the time constraints of the extended essay and is within the scope of the student’s academic abilities.

By considering these criteria, students can identify a physics topic that is both relevant and interesting while also ensuring that they have access to the resources and data needed for research. The next section of this article will discuss some potential physics topics for extended essays in 2024 that meet these criteria.

Top 20 Physics Topics for Extended Essays

Here are 20 potential physics topics for extended essays:

• Quantum Computing and its Applications
• Dark Matter and Dark Energy
• Artificial Intelligence in Physics
• Renewable Energy and its Efficiency
• Advancements in Nanotechnology
• The Physics of Sports
• The Physics of Music and Sound
• The Physics of Medical Imaging
• The Physics of Climate Change
• Gravitational Waves and their Detection
• Black Holes and their Properties
• The Higgs Boson and its Implications
• The Role of Symmetry in Physics
• The Theory of Everything and its Challenges
• The Physics of Superconductivity
• The Quantum Hall Effect and Topological Insulators
• The Physics of Fusion Energy
• The Physics of Fluid Dynamics and Turbulence
• The Physics of Optics and Photonics
• The Physics of Quantum Entanglement

These topics are not exhaustive, but they provide a starting point for students to explore different areas of physics that may interest them. When choosing a physics topic for an extended essay, it’s essential to keep in mind the criteria discussed in the previous section and select a topic that aligns with the student’s interests and academic abilities.

Other Possible Physics Topics for Extended Essays

Here are 10 additional potential physics topics for extended essays:

• The Physics of Magnetic Resonance Imaging (MRI)
• The Physics of Climate Modeling and Prediction
• The Physics of Materials Science and Engineering
• The Physics of Quantum Cryptography
• The Physics of Cosmology and the Big Bang Theory
• The Physics of Particle Accelerators and their Applications
• The Physics of Renewable Energy Storage
• The Physics of Quantum Computing Algorithms
• The Physics of Optoelectronics and their Applications
• The Physics of Atomic, Molecular and Optical (AMO) Physics

These topics offer a diverse range of areas for students to explore, each with their unique challenges and opportunities for research. As with the previous section, it’s essential to consider the criteria for selecting a good physics topic and choose a topic that aligns with the student’s interests and academic abilities.

What Can We Conclude

Selecting a good physics topic for an extended essay can be challenging, but by considering the criteria we’ve discussed in this article, students can identify a topic that aligns with their interests and academic abilities. We have provided a list of 30 potential physics topics for extended essays in 2024, covering a broad range of topics in physics.

We hope that this guide has been helpful in providing students and educators with a starting point for selecting a physics topic for an extended essay. Remember that choosing a topic that interests you and that aligns with your strengths and abilities is key to a successful extended essay. If you can’t choose the best topic or need help with your physics homework, don’t hesitate to contact us.

Hey, future physics champs! Don’t be shy about getting some backup from your teachers or tapping into the resources in your school or hood. With a dash of commitment and a dollop of elbow grease, you’ll whip up an extended essay that’ll blow minds and showcase your physics prowess.

To all the budding researchers out there, dive deep, keep those peepers peeled for guidance, and roll up your sleeves for some hard graft. You’ve got this! Here’s to cracking the code on your extended essay and showing off your physics superpowers. Go get ’em!

Delving into science and education is my passion! I’m all about unraveling mysteries through research, mixing that with my love for American lit. I whip up engaging content that’s easy to digest, sharing the scoop on cutting-edge discoveries. Beyond work, I’m nose-deep in scientific journals, always thirsty for knowledge.

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Quantum physics may help lasers see through fog, aid in surveillance

Military surveillance and communication can be hampered by adverse conditions such as fog, extreme temperatures or long distances. An engineer in the McKelvey School of Engineering at Washington University in St. Louis is implementing quantum technology to develop ways that lasers can operate effectively in these challenging environments.

Jung-Tsung Shen , an associate professor in the Preston M. Green Department of Electrical & Systems Engineering, is developing a prototype of a quantum photonic-dimer laser with a two-year $1 million grant from the Defense Advanced Research Projects Agency (DARPA) of the U.S. Department of Defense. With the funding, Shen will implement his lab’s two-color photonic dimer laser technology, in which carefully controlled pairs of light particles, or photonic dimers, are used to generate a powerful and concentrated beam of light, or laser. Quantum photonic-dimer lasers take advantage of quantum effects to bind two photons together, increasing their energy and efficiency.

Photons, or particles that represent a quantum of light, travel very quickly and don’t carry a charge, so it is difficult to get them to interact with each other and to manipulate them. Shen’s lab found that when he “glued” two photons of different colors together to form a photonic dimer using the power of quantum mechanics, they took on the behavior of a blue photon. The entanglement between the two photons within the dimer may revolutionize applications in communication and imaging, offering unprecedented capabilities, Shen said.

“Photons encode information when they travel, but the travel through the atmosphere is very damaging to them,” Shen said. “When two photons are bound together, they still suffer the effects of the atmosphere, but they can protect each other so that some phase information can still be preserved.”

These two-color dimers can be tailored to the atmosphere or to the fog through a unique property of quantum mechanics known as quantum entanglement, Shen said.

“Quantum entanglement is a correlation between photons,” he said. “We are trying to exploit the property of entanglement to do something innovative. The entanglement can do many things that we can only dream of — this is just the tip of the iceberg.”

Shen previously received funding from the Chan Zuckerberg Initiative to develop the technology for deep brain imaging. Researchers can implant fluorescent molecules in the brain and use photons to excite them, which allows the photons to collect information about the brain’s structure.

Now, Shen is exploring more of that vast iceberg to move toward the realization of applications in telecommunications, quantum computing and more, in addition to the military applications supported by DARPA.

Shen’s team, which includes graduate student Qihang Liu and collaborators from Texas A&M University’s Institute for Quantum Science & Engineering , will introduce the quantum photonic-dimer laser methods that will allow them to create different states of two-color dimers at a rate of 1 million pairs per second — a rate that has never been seen before.

“The unique thing about this project is its dual focus on generating these novel strongly correlated quantum photonic states and developing the theoretical framework and advanced algorithms for their efficient detection, potentially revolutionizing quantum imaging and communication,” Shen said.

Shawn Ballard contributed to this story.

Originally published on the McKelvey School of Engineering website.

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Novel hybrid scheme speeds the way to simulating nuclear reactions on quantum computers

by US Department of Energy

The nuclear reactions that power the stars and forge the elements emerge from the interactions of the quantum mechanical particles, protons and neutrons. Explaining these processes is one of the most challenging unsolved problems in computational physics.

As the mass of the colliding nuclei grows, the resources required to model them outpace even the most powerful conventional computers. Quantum computers could perform the necessary computations. However, they currently fall short of the required number of reliable and long-lived quantum bits.

Research, published in Physical Review A , combined conventional computers and quantum computers to significantly accelerate the prospects of solving this problem.

The researchers successfully used the hybrid computing scheme to simulate the scattering of two neutrons. This opens a path to computing nuclear reaction rates that are difficult or impossible to measure in a laboratory. These include reaction rates that play a role in astrophysics and national security.

The hybrid scheme will also aid in simulating the properties of other quantum mechanical systems. For example, it could help researchers study the scattering of electrons with quantized atomic vibrations known as phonons, a process that underlies superconductivity.

A team of scientists at the University of Washington, the University of Trento, the Advanced Quantum Testbed (AQT), and Lawrence Livermore National Laboratory proposed a hybrid algorithm for the simulation of the (real time) dynamics of quantum mechanical systems of particles.

In this hybrid approach, the time evolution of the particles' spatial coordinates is carried out on a classical processor, while the evolution of their spin variables is carried out on quantum hardware. The researchers demonstrated this hybrid scheme by simulating the scattering of two neutrons at the AQT.

The demonstration validated the principle of the proposed co-processing scheme after implementing error mitigation strategies to improve the accuracy of the algorithm and adopting theoretical and experimental methods to elucidate the loss of quantum coherence.

Even with the simplicity of the demonstration system this project studied, the results suggest that a generalization of the present hybrid scheme may provide a promising pathway for simulating quantum scattering experiments with a quantum computer .

Leveraging future quantum platforms with longer coherence times and higher quantum gate fidelities, the hybrid algorithm would enable the robust computation of complex nuclear reactions important for astrophysics and technological applications of nuclear science.

Journal information: Physical Review A

Provided by US Department of Energy

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IB Physics Extended Essay Topics for IB

Table of contents

• Writing Metier

What’s up, IB scholars? You’re about to start writing your IB Physics Extended Essay, and I know you’re searching for that killer topic that’s going to stand out. Well, guess what? I’ve got over 100 extended essay topics and research questions ready for you. 

You do not need to thank me; you better say thank you to our IB writers at Writing Metier , who have invented and forwarded this awesome list to me for submission.

This isn’t just about getting it done; it’s about crushing it with something you’re passionate about.  So let’s get straight to the point and find you Physics EE ideas that will make some noise and show what you’ve got!

100+ Physics Extended Essay Topics

I’m breaking the list into ten categories for IB Physics extended essay topics, each with three subcategories for easier navigation:

• Projectile Motion (e.g., trajectory analysis, range equations, effects of air resistance)
• Circular Motion (e.g., centripetal force in different systems, banking angles, conical pendulums)
• Dynamics of Rigid Bodies (e.g., rotational inertia, torque, angular momentum conservation)
• Thermodynamics
• Heat Transfer (e.g., efficiency of different materials as insulators, rate of cooling, Newton’s law of cooling)
• Gas Laws (e.g., pressure-volume relationship, temperature effects, real vs. ideal gases)
• Phase Changes (e.g., specific heat capacities, latent heat, cooling curves)
• Waves and Oscillations
• Harmonic Motion (e.g., pendulums, mass-spring systems, resonance)
• Wave Properties (e.g., speed of sound in various media, diffraction patterns, polarization)
• Sound and Acoustics (e.g., Doppler effect, sound intensity, acoustic properties of materials)
• Electricity and Magnetism
• Circuit Analysis (e.g., Ohm’s law, series vs. parallel circuits, Kirchhoff’s laws)
• Electromagnetism (e.g., Faraday’s law, magnetic fields around conductors, applications of electromagnets)
• Capacitance and Inductance (e.g., time constants, LC circuits, energy storage)
• Modern Physics
• Quantum Phenomena (e.g., photoelectric effect, electron diffraction, energy levels in atoms)
• Nuclear Physics (e.g., radioactive decay, half-life, nuclear reactions)
• Special Relativity (e.g., time dilation, length contraction, mass-energy equivalence)
• Energy and Power
• Renewable Energy Sources (e.g., efficiency of solar panels, wind turbine performance, biofuels)
• Energy Conversion (e.g., internal combustion engines, thermal power plants, regenerative braking)
• Power Transmission (e.g., electrical grid efficiency, power loss, superconductors)
• Fluid Dynamics
• Aerodynamics (e.g., lift and drag forces, Bernoulli’s principle, airfoil shapes)
• Hydrodynamics (e.g., flow rate, viscosity effects, Reynolds number)
• Buoyancy and Density (e.g., Archimedes’ principle, floating and sinking, density stratification)
• Astrophysics and Cosmology
• Stellar Physics (e.g., Hertzsprung-Russell diagram, star classifications, blackbody radiation)
• Cosmological Models (e.g., Big Bang theory, cosmic microwave background, dark matter)
• Orbital Mechanics (e.g., Kepler’s laws, satellite motion, escape velocity)
• Optics and Light
• Reflection and Refraction (e.g., Snell’s law, critical angle, optical fibers)
• Lens and Mirror Optics (e.g., image formation, focal length, magnification)
• Interference and Diffraction (e.g., double-slit experiment, diffraction gratings, holography)
• Electromagnetic Waves
• Radio and Microwave Radiation (e.g., antenna design, signal propagation, communication systems)
• Infrared and Ultraviolet Light (e.g., thermal imaging, UV radiation effects, spectroscopy)
• X-rays and Gamma Rays (e.g., medical imaging, radiation therapy, nuclear gamma spectroscopy)

Each of these categories and subcategories can be explored through experiments, data analysis, or theoretical investigation, offering a wide range of possibilities for IB students to develop their IB Physics EE topics.

Mechanics Topics and Research Questions

Projectile Motion

Topic:  The effect of launch angle on the range of a projectile.

Research Question:  How does changing the launch angle affect the horizontal distance traveled by a projectile?

Topic:  The impact of air resistance on the trajectory of a projectile.

Research Question:  To what extent does air resistance alter the trajectory of a projectile compared to the idealized motion?

Topic:  The accuracy of range equations in predicting projectile motion.

Research Question:  How accurately do standard range equations predict the motion of a projectile in a controlled environment?

Circular Motion

Topic:  Measuring centripetal force in a rotating system.

Research Question:  How does the centripetal force required for circular motion change with the radius and speed of the rotating object?

Topic:  The physics of banking angles in road design.

Research Question:  What is the optimal banking angle for a curve on a road to maximize friction and safety at a given speed?

Topic:  Investigating the period of a conical pendulum.

Research Question:  How does the length of the string affect the period of oscillation of a conical pendulum?

Dynamics of Rigid Bodies

Topic:  The relationship between rotational inertia and angular acceleration.

Research Question:  How does changing the distribution of mass affect the rotational inertia and angular acceleration of a rigid body?

Topic:  The conservation of angular momentum in a closed system.

Research Question:  How does the angular momentum of a system change when the moment of inertia is altered?

Topic:  The effect of torque on rotational motion.

Research Question:  How does the application of torque affect the rotational motion of a rigid body with a fixed axis?

Mechanics shows us how things move and what affects them, but when we start talking about thermodynamics, we’re dealing with heat and energy. 

It’s like going from watching a ball roll down a hill to understanding why it feels warm to the touch on a sunny day.

Thermodynamics Topics and Research Questions

Heat Transfer

Topic:  Comparing the thermal insulation properties of various materials.

Research Question:  Which material provides the best thermal insulation for a given application, and why?

Topic:  The rate of cooling of a liquid in different environments.

Research Question:  How does the rate of cooling of a hot liquid differ between various environmental conditions?

Topic:  Investigating Newton’s law of cooling.

Research Question:  How closely does the cooling of a warm object follow Newton’s law of cooling in a real-world setting?

Topic:  The pressure-volume relationship of a gas at constant temperature.

Research Question:  How does the volume of a gas change with pressure at a constant temperature, and does it align with Boyle’s law?

Topic:  Temperature effects on the pressure of an enclosed gas.

Research Question:  How does the pressure of a fixed amount of gas change with temperature in a sealed container?

Topic:  Real vs. ideal gases under different conditions.

Research Question:  How do the behaviors of real gases deviate from the predictions of the ideal gas law under high-pressure conditions?

Phase Changes

Topic:  Measuring specific heat capacities of different substances.

Research Question:  How do the specific heat capacities of different substances compare, and what implications does this have for their use in heat storage?

Topic:  The energy involved in the phase change of materials.

Research Question:  How much energy is absorbed or released during the phase change of a substance, and how does this relate to its latent heat?

Topic:  Analyzing cooling curves of substances.

Research Question:  What can the cooling curve of a substance tell us about its phase change properties and purity?

After getting a grip on how heat works, it’s pretty cool to see how that energy gets around. Waves are all about energy transfer, whether it’s the sound from your speakers or the ripples on a pond when you toss a stone.

Waves and Oscillations Topics and Research Questions

Harmonic Motion

Topic:  The period of a simple pendulum.

Research Question:  How does the length of a pendulum affect its period, and does this confirm the theoretical model?

Topic:  The behavior of mass-spring systems.

Research Question:  How do different spring constants affect the oscillation of a mass-spring system?

Topic:  Resonance frequencies in mechanical systems.

Research Question:  At what frequencies do various mechanical systems resonate, and what factors influence this?

Wave Properties

Topic:  Measuring the speed of sound in different media.

Research Question:  How does the speed of sound compare in various gases, and what does this tell us about the properties of those gases?

Topic:  Investigating diffraction patterns through different apertures.

Research Question:  How do diffraction patterns change with the shape and size of apertures?

Topic:  Polarization of light by various materials.

Research Question:  How effectively can different materials polarize light, and what does this indicate about their structure?

Sound and Acoustics

Topic:  The Doppler effect and moving sources.

Research Question:  How does the frequency of a sound wave change as the source moves relative to an observer?

Topic:  Sound intensity levels at different distances.

Research Question:  How does the intensity of sound change with distance from the source, and is it consistent with the inverse square law?

Topic:  Acoustic properties of materials in soundproofing.

Research Question:  Which materials are most effective at soundproofing a room, and how do their acoustic properties contribute to this effectiveness?

Each of these topics can be tailored to fit the requirements of an IB Physics extended essay, with the research question guiding the experimental design, data collection, and analysis.

If you are interested, we also have a list of potential  Physics IA topic ideas  for you. Make sure to check them out as well.

Once you’ve got a handle on waves, you’re ready to see how they relate to electricity and magnetism. It’s like connecting the dots between the vibrations in the air and the current in the wires of your headphones.

Electricity and Magnetism Topics and Research Questions

Circuit Analysis

Topic:  The resistance of series and parallel circuits.

Research Question:  How does the total resistance in a circuit vary with the arrangement of resistors in series and parallel configurations?

Topic:  Verification of Kirchhoff’s laws in complex circuits.

Research Question:  How accurately do Kirchhoff’s laws predict the current and voltage distribution in a multi-loop circuit?

Topic:  The temperature dependence of resistivity in conductors.

Research Question:  How does the resistivity of a metallic conductor change with temperature, and what does this imply about electron scattering?

Electromagnetism

Topic:  Faraday’s law of electromagnetic induction.

Research Question:  How does the rate of change of magnetic flux influence the induced EMF in a coil?

Topic:  The magnetic field patterns around different conductor configurations.

Research Question:  How do the configurations of conductors affect the shape and strength of the magnetic fields they produce?

Topic:  The efficiency of electromagnets.

Research Question:  What factors determine the lifting power of an electromagnet, and how can its efficiency be maximized?

Capacitance and Inductance

Topic:  Time constants in RC circuits.

Research Question:  How does the capacitance and resistance in an RC circuit affect its charging and discharging time constants?

Topic:  Resonance in LC circuits.

Research Question:  At what conditions does resonance occur in an LC circuit, and how does this affect the circuit’s impedance?

Topic:  Energy storage in capacitors and inductors.

Research Question:  How do capacitors and inductors store energy, and what factors affect their energy storage capacity?

Electricity and magnetism are pretty easy to see in action, but modern physics? That’s where things get wild. You’re not just looking at what’s in front of you anymore; you’re considering what’s happening on a scale so small or so huge that it bends your mind a bit.

Modern Physics Topics and Research Questions

Quantum Phenomena

Topic:  The photoelectric effect and Planck’s constant.

Research Question:  How can the photoelectric effect be used to determine Planck’s constant, and what does this reveal about the nature of light?

Topic:  Electron diffraction and crystal structure.

Research Question:  How does electron diffraction provide evidence for the wave nature of electrons and the structure of crystals?

Topic:  Energy levels in hydrogen atoms.

Research Question:  How do the observed spectral lines of hydrogen correspond to the theoretical energy levels predicted by quantum mechanics?

Nuclear Physics

Topic:  Radioactive decay series.

Research Question:  How does the decay series of a radioactive isotope correspond to theoretical predictions of half-life and decay pathways?

Topic:  The effect of shielding on radiation intensity.

Research Question:  How effective are different materials at shielding against various types of radioactive emissions?

Topic:  Nuclear reaction energy calculations.

Research Question:  How does the measured energy released in a nuclear reaction compare to the values predicted by the mass-energy equivalence principle?

Special Relativity

Topic:  Time dilation observed in cosmic muons.

Research Question:  How does the observed decay rate of cosmic muons provide evidence for time dilation effects predicted by special relativity?

Topic:  Length contraction and high-speed particles.

Research Question:  How can length contraction be demonstrated or inferred from high-speed particle interactions?

Topic:  Mass-energy equivalence in particle physics.

Research Question:  How does the increase in mass of particles at high velocities provide evidence for the mass-energy equivalence principle?

But even with all that mind-bending stuff, physics isn’t just about theory. It’s also about practical stuff, like how we use energy. From solar panels on your roof to the battery in your phone, it’s all about getting the power we need to do what we want.

Energy and Power Topics and Research Questions

Renewable Energy Sources

Topic:  The efficiency of photovoltaic cells under different conditions.

Research Question:  How do factors such as light intensity, wavelength, and temperature affect the efficiency of solar panels?

Topic:  Performance analysis of wind turbines.

Research Question:  How does blade design affect the efficiency and power output of a wind turbine?

Topic:  The viability of biofuels compared to fossil fuels.

Research Question:  How do the energy outputs and carbon footprints of biofuels compare to those of traditional fossil fuels?

Energy Conversion

Topic:  The efficiency of internal combustion engines.

Research Question:  How do variables such as fuel type and engine temperature affect the efficiency of an internal combustion engine?

Topic:  Thermal efficiency of power plants.

Research Question:  What are the main factors that limit the thermal efficiency of modern thermal power plants?

Topic:  The effectiveness of regenerative braking systems.

Research Question:  How much energy can regenerative braking systems realistically recover during vehicle deceleration?

Power Transmission

Topic:  Electrical grid efficiency and power loss.

Research Question:  How does the distance and cross-sectional area of transmission lines affect power loss in an electrical grid?

Topic:  The potential of superconductors in power transmission.

Research Question:  What are the challenges and potential benefits of using superconductors for power transmission?

Topic:  The impact of load balancing on power grid stability.

Research Question:  How does load balancing affect the stability and efficiency of a power grid?

These topics and research questions are designed to inspire a range of investigations for the Physics Extended Essay, allowing students to delve into both experimental and theoretical aspects of physics.

And speaking of practical, fluid dynamics is all about understanding how liquids and gases move. It’s like figuring out why blowing over a hot soup cools it down or how an airplane stays up in the sky.

Fluid Dynamics Topics and Research Questions

Aerodynamics

Topic:  The effect of airfoil shape on lift generation.

Research Question:  How does altering the curvature and angle of an airfoil affect its lift and drag forces?

Topic:  Application of Bernoulli’s principle to various wing designs.

Research Question:  How do different wing designs in aircraft utilize Bernoulli’s principle to achieve lift?

Topic:  Drag force comparison on streamlined vs. bluff bodies.

Research Question:  How does the shape of an object affect the drag force experienced at different flow velocities?

Hydrodynamics

Topic:  The relationship between flow rate and pipe diameter in fluid dynamics.

Research Question:  How does changing the diameter of a pipe affect the flow rate of a fluid within it, given a constant pressure difference?

Topic:  Viscosity effects on fluid flow in channels.

Research Question:  How does the viscosity of a fluid influence its flow characteristics in narrow channels?

Topic:  Analysis of Reynolds number in predicting fluid flow regimes.

Research Question:  How does the Reynolds number determine the transition from laminar to turbulent flow in a pipe?

Buoyancy and Density

Topic:  Investigating Archimedes’ principle for irregularly shaped objects.

Research Question:  How accurately does Archimedes’ principle predict the buoyant force on objects with complex shapes?

Topic:  The stability of floating bodies and the concept of metacentric height.

Research Question:  How does the distribution of mass affect the stability of a floating vessel?

Topic:  Density stratification in fluids and its impact on layered flow.

Research Question:  How does density stratification affect the movement and mixing of different fluid layers?

From there, it’s a big leap to astrophysics and cosmology—literally. You go from studying the flow of air around a plane to the flow of galaxies in space. It’s about seeing the bigger picture and our place in it.

If you need Physics paper writing help , we have a separate team of experts who can handle almost any tasks.

Astrophysics and Cosmology Topics and Research Questions

Stellar Physics

Topic:  Analyzing the Hertzsprung-Russell diagram for star clusters.

Research Question:  What can the Hertzsprung-Russell diagram reveal about the age and composition of a star cluster?

Topic:  Classification and analysis of star spectra.

Research Question:  How does the classification of stellar spectra correlate with a star’s temperature, luminosity, and lifecycle stage?

Topic:  Investigating blackbody radiation in stars.

Research Question:  How well does the blackbody radiation model fit the observed spectral energy distribution of stars?

Cosmological Models

Topic:  Evidence for the Big Bang theory from cosmic microwave background radiation.

Research Question:  What does the cosmic microwave background radiation tell us about the origins and evolution of the universe?

Topic:  The role of dark matter in galaxy formation and rotation.

Research Question:  How does the presence of dark matter influence the rotational speeds of galaxies?

Topic:  Verifying Kepler’s laws through observation of planetary motion.

Research Question:  How accurately do Kepler’s laws describe the motion of bodies in the solar system?

Orbital Mechanics

Topic:  The energy requirements for satellite launch and achieving escape velocity.

Research Question:  What are the energy considerations and optimal conditions for a satellite to achieve escape velocity from Earth?

Topic:  The effects of orbital perturbations on satellite stability.

Research Question:  How do factors such as atmospheric drag and gravitational influences affect the stability of satellite orbits?

Topic:  Analysis of gravitational slingshot maneuvers in space missions.

Research Question:  How can gravitational assist maneuvers be optimized to increase spacecraft velocity?

But even with our heads in the stars, we can’t forget about light. Optics brings it back down to earth, showing us how light works, whether it’s bending through a lens or bouncing off a mirror.

Optics and Light Topics and Research Questions

Reflection and Refraction

Topic:  The efficiency of optical fibers in transmitting light.

Research Question:  How do imperfections in optical fibers affect the total internal reflection and efficiency of light transmission?

Topic:  Investigating Snell’s law at various interfaces.

Research Question:  How accurately does Snell’s law predict the angle of refraction for different transparent materials?

Topic:  The critical angle for total internal reflection in various media.

Research Question:  How does the critical angle for total internal reflection change with the refractive index of different materials?

Lens and Mirror Optics

Topic:  The formation of images by converging lenses under various conditions.

Research Question:  How does the focal length of a lens affect the properties of the image it forms?

Topic:  The magnification power of compound microscope systems.

Research Question:  How do the focal lengths of the objective and eyepiece lenses in a microscope affect its overall magnification?

Topic:  The aberrations in images formed by lenses and mirrors.

Research Question:  What types of optical aberrations are most prevalent in simple lens systems, and how can they be minimized?

Interference and Diffraction

Topic:  The double-slit experiment and wave-particle duality.

Research Question:  How does the double-slit experiment provide evidence for the wave-particle duality of light?

Topic:  Measuring the wavelength of light using diffraction gratings.

Research Question:  How can diffraction gratings be used to accurately measure the wavelength of light?

Topic:  The application of holography in image storage and retrieval.

Research Question:  How does holography utilize the principles of interference and diffraction to store and reconstruct images?

And light’s just one piece of the whole world of Physics. Electromagnetic waves are everywhere, from the microwave that heats your lunch to the X-rays at the dentist. It’s all part of the same big family that keeps our world connected and our lives running.

Electromagnetic Waves Topics and Research Questions

Radio and Microwave Radiation

Topic:  The design and optimization of antennas for radio communication.

Research Question:  How does the geometry of an antenna affect its radiation pattern and signal reception?

Topic:  Signal propagation in different atmospheric conditions.

Research Question:  How do atmospheric conditions affect the propagation of radio and microwave signals?

Topic:  The effectiveness of microwave radiation in communication systems.

Research Question:  What are the advantages and limitations of using microwave radiation in satellite communications?

Infrared and Ultraviolet Light

Topic:  Thermal imaging and the emissivity of different materials.

Research Question:  How does the emissivity of a material affect its detection in thermal imaging?

Topic:  The effects of UV radiation on various substances.

Research Question:  How does exposure to ultraviolet light affect the chemical structure and properties of different materials?

Topic:  Spectroscopy and the identification of chemical compounds.

Research Question:  How can infrared and ultraviolet spectroscopy be used to identify and analyze different chemical compounds?

X-rays and Gamma Rays

Topic:  The application of X-ray imaging in medical diagnostics.

Research Question:  How do different tissues and materials affect the absorption and transmission of X-rays in medical imaging?

Topic:  Radiation therapy and the optimization of gamma ray dosage.

Research Question:  How can the dosage and targeting of gamma rays in radiation therapy be optimized for cancer treatment?

Topic:  Nuclear gamma spectroscopy and nuclear structure.

Research Question:  What can gamma-ray spectra reveal about the structure and energy states of atomic nuclei?

These topics and research questions are designed to guide students in their exploration of advanced concepts in physics, providing a foundation for a thorough and insightful Extended Essay.

Creating an engaging and contemporary Physics Extended Essay can be particularly rewarding when the topic is relevant to modern situations and challenges. 

Fresh Breath Ideas for Physics IB EE in 2023/2024

Here are 12 topics that connect to current events or recent advancements in technology, along with a brief explanation of their relevance:

The Physics of Electric Vehicles

Investigate the efficiency of regenerative braking systems in electric cars and how they contribute to the overall energy efficiency of the vehicle.

Renewable Energy Harvesting

Analyze the potential of piezoelectric materials in converting mechanical stress from human activities into electrical energy, contributing to sustainable power generation.

Smartphone Sensors

Explore the use of gyroscopes and accelerometers in smartphones for navigation and gaming, and how these sensors rely on principles of mechanics and material science.

Wireless Charging Technologies

Examine the electromagnetic principles behind wireless charging pads and the efficiency of energy transfer at various distances and alignments.

Solar Panel Coatings

Research the effectiveness of anti-reflective coatings on solar panels and their role in enhancing the absorption of light and overall energy conversion efficiency.

Aerodynamics of Drones

Study the impact of drone design on flight stability and energy consumption, which is critical for extending their use in delivery systems and aerial photography.

Physics in Sports Equipment

Investigate the materials and design features that contribute to the performance and safety of modern sports helmets, from bicycles to football.

Thermal Imaging and Disease Detection

Explore the use of thermal imaging in detecting fevers and its potential application in managing pandemics by early identification of symptomatic individuals.

Nanomaterials in Electronics

Analyze the electrical conductivity and properties of graphene and other nanomaterials that are revolutionizing the electronics industry.

Physics of Modern Building Design

Investigate how principles of thermodynamics are applied in the design of eco-friendly and energy-efficient buildings.

Quantum Computing

Study the basic principles of quantum computing and the challenges in maintaining quantum coherence in qubits, which are the fundamental building blocks of quantum computers.

SpaceX and Reusable Rockets

Research the physics behind the reusability of rockets, focusing on the landing mechanisms employed by companies like SpaceX and how they conserve momentum and energy.

Each of these topics is not only grounded in physics principles but also has a wealth of information available due to their current relevance and the ongoing research in these areas. 

They offer a chance to combine theoretical physics with practical application in the modern world, which can be particularly engaging for an Extended Essay.

Need a Hand with Your Physics IB EE?

Hey there, IB students! If you’re stuck on coming up with a topic or diving into writing your Physics IB Extended Essay, don’t sweat it. Our team of IB experts at Writing Metier is here to help you write a custom IB EE on this exciting subject . 

Whether you need a spark of inspiration for your topic or you want a custom-written EE following the word count , rubric and criteria that hits all the right notes, we’ve got your back. 

Reach out to us at Writing Metier extended essay writing service and have a rest while experts are working on your task.

So, that’s the rundown. Physics isn’t just about equations and lab coats; it’s the stuff all around us, from the smallest particles to the vastness of space. It’s about getting to the heart of how things work, from the every day to the extraordinary. 

And the more you learn, the more you see how everything’s linked together in one big, amazing picture.

Free topic suggestions

Vasy kafidoff.

Vasyl Kafidoff is a co-founder and CEO at WritingMetier. He is interested in education and how modern technology makes it more accessible. He wants to bring awareness about new learning possibilities as an educational specialist. When Vasy is not working, he’s found behind a drum kit.

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