hypothesis the universe is expanding

Webb & Hubble confirm Universe’s expansion rate

Webb measurements shed new light on a decade-long mystery.

The rate at which the Universe is expanding, known as the Hubble constant, is one of the fundamental parameters for understanding the evolution and ultimate fate of the cosmos. However, a persistent difference, called the Hubble Tension, is seen between the value of the constant measured with a wide range of independent distance indicators and its value predicted from the afterglow of the Big Bang. The NASA/ESA/CSA James Webb Space Telescope has confirmed that the Hubble Space Telescope’s keen eye was right all along, erasing any lingering doubt about Hubble’s measurements.

One of the scientific justifications for building the NASA/ESA Hubble Space Telescope was to use its observing power to provide an exact value for the expansion rate of the Universe. Prior to Hubble’s launch in 1990, observations from ground-based telescopes yielded huge uncertainties. Depending on the values deduced for the expansion rate, the Universe could be anywhere between 10 and 20 billion years old. Over the past 34 years Hubble has shrunk this measurement to an accuracy of less than one percent, splitting the difference with an age value of 13.8 billion years. This has been accomplished by refining the so-called ‘cosmic distance ladder’ by measuring important milepost markers known as Cepheid variable stars.

However, the Hubble value does not agree with other measurements that imply that the Universe was expanding faster after the Big Bang. These observations were made by the ESA Planck satellite’s mapping of the cosmic microwave background radiation – a blueprint for how the Universe would evolve structure after it cooled down from the Big Bang.

The simple solution to the dilemma would be to say that maybe the Hubble observations are wrong, as a result of some inaccuracy creeping into its measurements of the deep-space yardsticks. Then along came the James Webb Space Telescope , enabling astronomers to crosscheck Hubble’s results. Webb’s infrared views of Cepheids agreed with Hubble’s optical-light data. Webb confirmed that the Hubble telescope’s keen eye was right all along, erasing any lingering doubt about Hubble’s measurements.

The bottom line is that the so-called Hubble Tension between what happens in the nearby Universe compared to the early Universe’s expansion remains a nagging puzzle for cosmologists. There may be something woven into the fabric of space that we don’t yet understand.

Does resolving this discrepancy require new physics? Or is it a result of measurement errors between the two different methods used to determine the rate of expansion of space?

Hubble and Webb have now tag-teamed to produce definitive measurements, furthering the case that something else – not measurement errors – is influencing the expansion rate.

“With measurement errors negated, what remains is the real and exciting possibility that we have misunderstood the Universe,” said Adam Riess, a physicist at Johns Hopkins University in Baltimore. Adam holds a Nobel Prize for co-discovering the fact that the Universe’s expansion is accelerating, owing to a mysterious phenomenon now called ‘dark energy’.

As a crosscheck, an initial Webb observation in 2023 confirmed that Hubble’s measurements of the expanding Universe were accurate. However, hoping to relieve the Hubble Tension, some scientists speculated that unseen errors in the measurement may grow and become visible as we look deeper into the Universe. In particular, stellar crowding could affect brightness measurements of more distant stars in a systematic way.

The SH0ES (Supernova H0 for the Equation of State of Dark Energy) team, led by Adam, obtained additional observations with Webb of objects that are critical cosmic milepost markers, known as Cepheid variable stars, which can now be correlated with the Hubble data.

“We’ve now spanned the whole range of what Hubble observed, and we can rule out a measurement error as the cause of the Hubble Tension with very high confidence,” Adam said.

The team’s first few Webb observations in 2023 were successful in showing Hubble was on the right track in firmly establishing the fidelity of the first rungs of the so-called cosmic distance ladder.

Astronomers use various methods to measure relative distances in the Universe, depending upon the object being observed. Collectively these techniques are known as the cosmic distance ladder – each rung or measurement technique relies upon the previous step for calibration.

But some astronomers suggested that, moving outward along the ‘second rung’, the cosmic distance ladder might get shaky if the Cepheid measurements become less accurate with distance. Such inaccuracies could occur because the light of a Cepheid could blend with that of an adjacent star – an effect that could become more pronounced with distance as stars crowd together on the sky and become harder to distinguish from one another.

The observational challenge is that past Hubble images of these more distant Cepheid variables look more huddled and overlapping with neighbouring stars at ever greater distances between us and their host galaxies, requiring careful accounting for this effect. Intervening dust further complicates the certainty of the measurements in visible light. Webb slices through the dust and naturally isolates the Cepheids from neighbouring stars because its vision is sharper than Hubble’s at infrared wavelengths.

“Combining Webb and Hubble gives us the best of both worlds. We find that the Hubble measurements remain reliable as we climb farther along the cosmic distance ladder,” said Adam.

The new Webb observations include five host galaxies of eight Type Ia supernovae containing a total of 1000 Cepheids, and reach out to the farthest galaxy where Cepheids have been well measured – NGC 5468, at a distance of 130 million light-years. “This spans the full range where we made measurements with Hubble. So, we’ve gone to the end of the second rung of the cosmic distance ladder,” said co-author Gagandeep Anand of the Space Telescope Science Institute in Baltimore, which operates the Webb and Hubble Telescopes for NASA.

Together, Hubble’s and Webb’s confirmation of the Hubble Tension sets up other observatories to possibly settle the mystery, including NASA’s upcoming Nancy Grace Roman Space Telescope and ESA’s recently launched  Euclid  mission.

At present it’s as though the distance ladder observed by Hubble and Webb has firmly set an anchor point on one shoreline of a river, and the afterglow of the Big Bang observed by Planck from the beginning of the Universe is set firmly on the other side. How the Universe’s expansion was changing in the billions of years between these two endpoints has yet to be directly observed. “We need to find out if we are missing something on how to connect the beginning of the Universe and the present day,” said Adam.

These findings were published in the 6 February 2024 issue of  The Astrophysical Journal Letters .

More information Webb  is the largest, most powerful telescope ever launched into space. Under an international collaboration agreement, ESA provided the telescope’s launch service, using the Ariane 5 launch vehicle. Working with partners, ESA was responsible for the development and qualification of Ariane 5 adaptations for the Webb mission and for the procurement of the launch service by Arianespace. ESA also provided the workhorse spectrograph  NIRSpec  and 50% of the mid-infrared instrument  MIRI , which was designed and built by a consortium of nationally funded European Institutes (The MIRI European Consortium) in partnership with JPL and the University of Arizona.

Webb is an international partnership between NASA, ESA and the Canadian Space Agency (CSA).

Release on esawebb.org

Contact: ESA Media relations [email protected]

Thank you for liking

You have already liked this page, you can only like it once!

Our expanding universe: Age, history & other facts

The evolution and content of our ballooning universe

The Big Bang

Expanding universe, additional resources, bibliography.

The universe was born with the Big Bang as an unimaginably hot, dense point. When the universe was just 10 -34 of a second or so old — that is, a hundredth of a billionth of a trillionth of a trillionth of a second in age — it experienced an incredible burst of expansion known as inflation, in which space itself expanded faster than the speed of light. During this period, the universe doubled in size at least 90 times, going from subatomic-sized to golf-ball-sized almost instantaneously.

The work that goes into understanding the expanding universe comes from a combination of theoretical physics and direct observations by astronomers. However, in some cases astronomers have not been able to see direct evidence — such as the case of gravitational waves associated with the cosmic microwave background , the leftover radiation from the Big Bang. A preliminary announcement about finding these waves in 2014 was quickly retracted, after astronomers found the signal detected could be explained by dust in the Milky Way .

According to NASA, after inflation the growth of the universe continued, but at a slower rate . As space expanded, the universe cooled and matter formed. One second after the Big Bang, the universe was filled with neutrons, protons, electrons , anti-electrons, photons and neutrinos.

During the first three minutes of the universe, the light elements were born during a process known as Big Bang nucleosynthesis. Temperatures cooled from 100 nonillion (10 32 ) Kelvin to 1 billion (10 9 ) Kelvin, and protons and neutrons collided to make deuterium, an isotope of hydrogen . Most of the deuterium combined to make helium , and trace amounts of lithium were also generated.

For the first 380,000 years or so, the universe was essentially too hot for light to shine, according to France's National Center of Space Research (Centre National d'Etudes Spatiales, or CNES). The heat of creation smashed atoms together with enough force to break them up into a dense plasma, an opaque soup of protons, neutrons and electrons that scattered light like fog.

What is the coldest place in the universe?

Geocentric model: The Earth-centered view of the universe

Do parallel universes exist?

Dark stars: The first stars in the universe

Was there a bang at the end of the universe?

Roughly 380,000 years after the Big Bang, matter cooled enough for atoms to form during the era of recombination, resulting in a transparent, electrically neutral gas, according to NASA . This set loose the initial flash of light created during the Big Bang, which is detectable today as cosmic microwave background radiation . However, after this point, the universe was plunged into darkness, since no stars or any other bright objects had formed yet.

About 400 million years after the Big Bang, the universe began to emerge from the cosmic dark ages during the epoch of reionization. During this time, which lasted more than a half-billion years, clumps of gas collapsed enough to form the first stars and galaxies, whose energetic ultraviolet light ionized and destroyed most of the neutral hydrogen.

Although the expansion of the universe gradually slowed down as the matter in the universe pulled on itself via gravity, about 5 or 6 billion years after the Big Bang, according to NASA , a mysterious force now called dark energy began speeding up the expansion of the universe again, a phenomenon that continues today.

A little after 9 billion years after the Big Bang, our solar system was born.

The Big Bang did not occur as an explosion in the usual way one think about such things, despite one might gather from its name. The universe did not expand into space, as space did not exist before the universe, according to NASA . Instead, it is better to think of the Big Bang as the simultaneous appearance of space everywhere in the universe . The universe has not expanded from any one spot since the Big Bang — rather, space itself has been stretching, and carrying matter with it.

Since the universe by its definition encompasses all of space and time as we know it, NASA says it is beyond the model of the Big Bang to say what the universe is expanding into or what gave rise to the Big Bang. Although there are models that speculate about these questions, none of them have made realistically testable predictions as of yet.

In 2014, scientists from the Harvard-Smithsonian Center for Astrophysics announced that they had found a faint signal in the cosmic microwave background that could be the first direct evidence of gravitational waves, themselves considered a " smoking gun " for the Big Bang. The findings were hotly debated , and astronomers soon retracted their results when they realized dust in the Milky Way could explain their findings. 

How old is the universe?

The universe is currently estimated at roughly 13.8 billion years old , give or take 130 million years. In comparison, the solar system is only about 4.6 billion years old.

This estimate came from measuring the composition of matter and energy density in the universe. This allowed researchers to compute how fast the universe expanded in the past. With that knowledge, they could turn the clock back and extrapolate when the Big Bang happened . The time between then and now is the age of the universe.

How is it structured?

Scientists think that in the earliest moments of the universe, there was no structure to it to speak of, with matter and energy distributed nearly uniformly throughout. According to NASA , the gravitational pull of small fluctuations in the density of matter back then gave rise to the vast web-like structure of stars and emptiness seen today. Dense regions pulled in more and more matter through gravity, and the more massive they became, the more matter they could pull in through gravity, forming stars , galaxies and larger structures known as clusters, superclusters, filaments and walls , with "great walls" of thousands of galaxies reaching more than a billion light years in length. Less dense regions did not grow, evolving into area of seemingly empty space called voids.

Contents of the universe

Until a few decades ago, astronomers thought that the universe was composed almost entirely of ordinary atoms, or "baryonic matter," according to NASA . However, recently there has been ever more evidence that suggests most of the ingredients making up the universe come in forms that we cannot see.

It turns out that atoms only make up 4.6 percent of the universe. Of the remainder, 23 percent is made up of dark matter , which is likely composed of one or more species of subatomic particles that interact very weakly with ordinary matter, and 72 percent is made of dark energy, which apparently is driving the accelerating expansion of the universe.

When it comes to the atoms we are familiar with, hydrogen makes up about 75 percent, while helium makes up about 25 percent, with heavier elements making up only a tiny fraction of the universe's atoms, according to NASA .

What shape is it?

The shape of the universe and whether or not it is finite or infinite in extent depends on the struggle between the rate of its expansion and the pull of gravity. The strength of the pull in question depends in part on the density of the matter in the universe.

If the density of the universe exceeds a specific critical value, then the universe is " closed " and "positive curved" like the surface of a sphere. This means light beams that are initially parallel will converge slowly, eventually cross and return back to their starting point, if the universe lasts long enough. If so, according to NASA , the universe is not infinite but has no end, just as the area on the surface of a sphere is not infinite but has no beginning or end to speak of. The universe will eventually stop expanding and start collapsing in on itself, the so-called "Big Crunch."

If the density of the universe is less than this critical density, then the geometry of space is " open " and "negatively curved" like the surface of a saddle. If so, the universe has no bounds, and will expand forever .

If the density of the universe exactly equals the critical density, then the geometry of the universe is "flat" with zero curvature like a sheet of paper, according to NASA . If so, the universe has no bounds and will expand forever, but the rate of expansion will gradually approach zero after an infinite amount of time. Recent measurements suggest that the universe is flat with only a 0.4 percent margin of error, according to NASA.

It is possible that the universe has a more complicated shape overall while seeming to possess a different curvature. For instance, the universe could have the shape of a torus, or doughnut .

In the 1920s, astronomer Edwin Hubble discovered the universe was not static . Rather, it was expanding; a find that revealed the universe was apparently born in a Big Bang.

After that, it was long thought the gravity of matter in the universe was certain to slow the expansion of the universe . Then, in 1998, the Hubble Space Telescope 's observations of very distant supernovae revealed that a long time ago, the universe was expanding more slowly than it is today. In other words, the expansion of the universe was not slowing due to gravity, but instead inexplicably was accelerating. The name for the unknown force driving this accelerating expansion is dark energy, and it remains one of the greatest mysteries in science.

Want to explore the universe for yourself? You can roam the Milky Way's stars and galaxies virtually using NASA's Hubble Skymap . Additionally, you can read 10 wild theories about the universe in this article by Live Science.

"The first stars in the Universe". Monthly Notices of the Royal Astronomical Society: Letters, Volume 373, Issue 1 (2006). https://academic.oup.com/mnrasl/article/373/1/L98/989035?login=true

"The molecular universe". Reviews of Modern Physics (2013). https://journals.aps.org/rmp/abstract/10.1103/RevModPhys.85.1021

"Hubble’s Law and the expanding universe". Proceedings of the National Academy of Sciences of the United States of America (2015). https://www.pnas.org/content/112/11/3173.short

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: [email protected].

Get the Space.com Newsletter

Breaking space news, the latest updates on rocket launches, skywatching events and more!

Charles Q. Choi is a contributing writer for Space.com and Live Science. He covers all things human origins and astronomy as well as physics, animals and general science topics. Charles has a Master of Arts degree from the University of Missouri-Columbia, School of Journalism and a Bachelor of Arts degree from the University of South Florida. Charles has visited every continent on Earth, drinking rancid yak butter tea in Lhasa, snorkeling with sea lions in the Galapagos and even climbing an iceberg in Antarctica. Visit him at http://www.sciwriter.us

Euclid telescope: A scientist tells us of his quest to understand the nature of dark matter and dark energy

Does a cosmic 'glitch' in gravity challenge Albert Einstein's greatest theory?

Houston, we have an encore: ISS virtual reality experience 'The Infinite' returns

Most Popular

• 2 Total solar eclipse 2027: A complete guide to the 'eclipse of the century'
• 3 This Week In Space podcast: Episode 110 — Voyager 1's Brush with Silence
• 4 DARPA's autonomous 'Manta Ray' drone can glide through ocean depths undetected
• 5 'World's purest silicon' could lead to 1st million-qubit quantum computing chips

Mystery of the Universe’s Expansion Rate Widens With New Hubble Data

Astronomers using NASA's Hubble Space Telescope say they have crossed an important threshold in revealing a discrepancy between the two key techniques for measuring the universe's expansion rate. The recent study strengthens the case that new theories may be needed to explain the forces that have shaped the cosmos.

A brief recap: The universe is getting bigger every second. The space between galaxies is stretching, like dough rising in the oven. But how fast is the universe expanding? As Hubble and other telescopes seek to answer this question, they have run into an intriguing difference between what scientists predict and what they observe.

Hubble measurements suggest a faster expansion rate in the modern universe than expected, based on how the universe appeared more than 13 billion years ago. These measurements of the early universe come from the European Space Agency's Planck satellite. This discrepancy has been identified in scientific papers over the last several years, but it has been unclear whether differences in measurement techniques are to blame, or whether the difference could result from unlucky measurements.

The latest Hubble data lower the possibility that the discrepancy is only a fluke to 1 in 100,000. This is a significant gain from an earlier estimate, less than a year ago, of a chance of 1 in 3,000.

These most precise Hubble measurements to date bolster the idea that new physics may be needed to explain the mismatch.

"The Hubble tension between the early and late universe may be the most exciting development in cosmology in decades," said lead researcher and Nobel laureate Adam Riess of the Space Telescope Science Institute (STScI) and Johns Hopkins University, in Baltimore, Maryland. "This mismatch has been growing and has now reached a point that is really impossible to dismiss as a fluke. This disparity could not plausibly occur just by chance."

Tightening the bolts on the 'cosmic distance ladder'

Scientists use a "cosmic distance ladder" to determine how far away things are in the universe. This method depends on making accurate measurements of distances to nearby galaxies and then moving to galaxies farther and farther away, using their stars as milepost markers. Astronomers use these values, along with other measurements of the galaxies' light that reddens as it passes through a stretching universe, to calculate how fast the cosmos expands with time, a value known as the Hubble constant. Riess and his SH0ES (Supernovae H0 for the Equation of State) team have been on a quest since 2005 to refine those distance measurements with Hubble and fine-tune the Hubble constant.

In this new study, astronomers used Hubble to observe 70 pulsating stars called Cepheid variables in the Large Magellanic Cloud. The observations helped the astronomers "rebuild" the distance ladder by improving the comparison between those Cepheids and their more distant cousins in the galactic hosts of supernovas. Riess's team reduced the uncertainty in their Hubble constant value to 1.9% from an earlier estimate of 2.2%.

As the team's measurements have become more precise, their calculation of the Hubble constant has remained at odds with the expected value derived from observations of the early universe's expansion. Those measurements were made by Planck, which maps the cosmic microwave background, a relic afterglow from 380,000 years after the big bang.

The measurements have been thoroughly vetted, so astronomers cannot currently dismiss the gap between the two results as due to an error in any single measurement or method. Both values have been tested multiple ways.

"This is not just two experiments disagreeing," Riess explained. "We are measuring something fundamentally different. One is a measurement of how fast the universe is expanding today, as we see it. The other is a prediction based on the physics of the early universe and on measurements of how fast it ought to be expanding. If these values don't agree, there becomes a very strong likelihood that we're missing something in the cosmological model that connects the two eras."

How the new study was done

Astronomers have been using Cepheid variables as cosmic yardsticks to gauge nearby intergalactic distances for more than a century. But trying to harvest a bunch of these stars was so time-consuming as to be nearly unachievable. So, the team employed a clever new method, called DASH (Drift And Shift), using Hubble as a "point-and-shoot" camera to snap quick images of the extremely bright pulsating stars, which eliminates the time-consuming need for precise pointing.

"When Hubble uses precise pointing by locking onto guide stars, it can only observe one Cepheid per each 90-minute Hubble orbit around Earth. So, it would be very costly for the telescope to observe each Cepheid," explained team member Stefano Casertano, also of STScI and Johns Hopkins. "Instead, we searched for groups of Cepheids close enough to each other that we could move between them without recalibrating the telescope pointing. These Cepheids are so bright, we only need to observe them for two seconds. This technique is allowing us to observe a dozen Cepheids for the duration of one orbit. So, we stay on gyroscope control and keep 'DASHing' around very fast."

The Hubble astronomers then combined their result with another set of observations, made by the Araucaria Project, a collaboration between astronomers from institutions in Chile, the U.S., and Europe. This group made distance measurements to the Large Magellanic Cloud by observing the dimming of light as one star passes in front of its partner in eclipsing binary-star systems.

The combined measurements helped the SH0ES Team refine the Cepheids' true brightness. With this more accurate result, the team could then "tighten the bolts" of the rest of the distance ladder that extends deeper into space.

The new estimate of the Hubble constant is 74 kilometers (46 miles) per second per megaparsec. This means that for every 3.3 million light-years farther away a galaxy is from us, it appears to be moving 74 kilometers (46 miles) per second faster, as a result of the expansion of the universe. The number indicates that the universe is expanding at a 9% faster rate than the prediction of 67 kilometers (41.6 miles) per second per megaparsec, which comes from Planck's observations of the early universe, coupled with our present understanding of the universe.

So, what could explain this discrepancy?

One explanation for the mismatch involves an unexpected appearance of dark energy in the young universe, which is thought to now comprise 70% of the universe's contents. Proposed by astronomers at Johns Hopkins, the theory is dubbed "early dark energy," and suggests that the universe evolved like a three-act play.

Astronomers have already hypothesized that dark energy existed during the first seconds after the big bang and pushed matter throughout space, starting the initial expansion. Dark energy may also be the reason for the universe's accelerated expansion today. The new theory suggests that there was a third dark-energy episode not long after the big bang, which expanded the universe faster than astronomers had predicted. The existence of this "early dark energy" could account for the tension between the two Hubble constant values, Riess said.

Another idea is that the universe contains a new subatomic particle that travels close to the speed of light. Such speedy particles are collectively called "dark radiation" and include previously known particles like neutrinos, which are created in nuclear reactions and radioactive decays.

Yet another attractive possibility is that dark matter (an invisible form of matter not made up of protons, neutrons, and electrons) interacts more strongly with normal matter or radiation than previously assumed.

But the true explanation is still a mystery.

Riess doesn't have an answer to this vexing problem, but his team will continue to use Hubble to reduce the uncertainties in the Hubble constant. Their goal is to decrease the uncertainty to 1%, which should help astronomers identify the cause of the discrepancy.

The team's results have been accepted for publication in The Astrophysical Journal .

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.

Media Contacts :

Claire Andreoli NASA's Goddard Space Flight Center, Greenbelt, Md. 301-286-1940 [email protected]

Donna Weaver / Ray Villard Space Telescope Science Institute, Baltimore, Md. 410-338-4493 / 410-338-4514 [email protected]  /  [email protected]

Science Contact :

Adam Riess Space Telescope Science Institute, Baltimore, Md. and Johns Hopkins University, Baltimore, Md. 410-338-6707 [email protected]

Related Terms

• Astrophysics
• Goddard Space Flight Center
• Hubble Space Telescope

Explore More

Hubble Celebrates the 15th Anniversary of Servicing Mission 4

Hubble Glimpses a Star-Forming Factory

NASA Images Help Explain Eating Habits of Massive Black Hole

Data from NASA’s retired Spitzer Space Telescope has given scientists new insights into why some supermassive black holes shine differently than others. In images from NASA’s retired Spitzer Space Telescope, streams of dust thousands of light-years long flow toward the supermassive black hole at the heart of the Andromeda galaxy. It turns out these streams […]

Discover More Topics From NASA

James Webb Space Telescope

Perseverance Rover

Parker Solar Probe

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

• View all journals
• Explore content
• About the journal
• Publish with us
• Sign up for alerts
• 16 July 2019

How fast is the Universe expanding? Cosmologists just got more confused

• Davide Castelvecchi

You can also search for this author in PubMed   Google Scholar

For much of this decade, the two most precise gauges of the Universe’s rate of expansion have been in glaring disagreement. Now, a highly anticipated independent technique that cosmologists hoped would solve the conundrum is instead adding to the confusion.

Access options

Access Nature and 54 other Nature Portfolio journals

Get Nature+, our best-value online-access subscription

24,99 € / 30 days

cancel any time

Subscribe to this journal

Receive 51 print issues and online access

185,98 € per year

only 3,65 € per issue

Rent or buy this article

Prices vary by article type

Prices may be subject to local taxes which are calculated during checkout

Nature 571 , 458-459 (2019)

doi: https://doi.org/10.1038/d41586-019-02198-z

Freedman, W. L. et al. Astrophys. J. (in the press).

Riess, A. G. et al . Preprint at https://arxiv.org/abs/1903.07603 (2019).

Download references

Reprints and permissions

Dark energy is tearing the Universe apart. What if the force is weakening?

News Feature 03 MAY 24

Could JWST solve cosmology’s big mystery? Physicists debate Universe-expansion data

News 15 APR 24

‘Best view ever’: observatory will map Big Bang’s afterglow in new detail

News 22 MAR 24

Recruitment of Principal Investigators by the School of Life Sciences, Peking University

The School of Life Sciences at Peking University is actively seeking talents, with an emphasis on bioinformatics/computational biology/AI/RNA biology.

Beijing (CN)

School of Life Sciences, Peking University

2024 Recruitment notice Shenzhen Institute of Synthetic Biology: Shenzhen, China

The wide-ranging expertise drawing from technical, engineering or science professions...

Shenzhen,China

Shenzhen Institute of Synthetic Biology

Head of Operational Excellence

In this key position, you’ll be responsible for ensuring efficiency and quality in journal workflows through continuous improvement and innovation.

United States (US) - Remote

American Physical Society

Rowland Fellowship

The Rowland Institute at Harvard seeks outstanding early-career experimentalists in all fields of science and engineering.

Cambridge, Massachusetts

Rowland Institute at Harvard

Postdoctoral Fellowship: Chemical and Cell Biology

The 2-year fellowship within a project that will combine biochemical, cell biological and chemical genetic approaches to elucidate migrasome biology

Umeå, Sweden

Umeå University

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Quick links

• Explore articles by subject
• Guide to authors
• Editorial policies

The expansion of the universe could be a mirage, new theoretical study suggests

New research looking at the cosmological constant problem suggests the expansion of the universe could be an illusion.

The expansion of the universe could be a mirage, a potentially controversial new study suggests. This rethinking of the cosmos also suggests solutions for the puzzles of dark energy and dark matter, which scientists believe account for around 95% of the universe's total energy and matter but remain shrouded in mystery.

The novel new approach is detailed in a paper published June 2 in the journal Classical and Quantum Gravity , by University of Geneva professor of theoretical physics Lucas Lombriser . 

Related: Dark energy could lead to a second (and third, and fourth) Big Bang, new research suggests

Scientists know the universe is expanding because of redshift, the stretching of light's wavelength towards the redder end of the spectrum as the object emitting it moves away from us. Distant galaxies have a higher redshift than those nearer to us, suggesting those galaxies are moving ever further from Earth. 

More recently, scientists have found evidence that the universe's expansion isn't fixed, but is actually accelerating faster and faster. This accelerating expansion is captured by a term known as the cosmological constant , or lambda.

The cosmological constant has been a headache for cosmologists because predictions of its value made by particle physics differ from actual observations by 120 orders of magnitude . The cosmological constant has therefore been described as "the worst prediction in the history of physics." 

Cosmologists often try to resolve the discrepancy between the different values of lambda by proposing new particles or physical forces but Lombriser tackles it by reconceptualizing what's already there..

Sign up for the Live Science daily newsletter now

Get the world’s most fascinating discoveries delivered straight to your inbox.

"In this work, we put on a new pair of glasses to look at the cosmos and its unsolved puzzles by performing a mathematical transformation of the physical laws that govern it," Lombriser told Live Science via email.

In Lombriser's mathematical interpretation, the universe isn't expanding but is flat and static, as Einstein once believed. The effects we observe that point to expansion are instead explained by the evolution of the masses of particles — such as protons and electrons — over time.

In this picture, these particles arise from a field that permeates space-time. The cosmological constant is set by the field's mass and because this field fluctuates, the masses of the particles it gives birth to also fluctuate. The cosmological constant still varies with time, but in this model that variation is due to changing particle mass over time, not the expansion of the universe. 

In the model, these field fluctuations result in larger redshifts for distant galaxy clusters than traditional cosmological models predict. And so, the cosmological constant remains true to the model's predictions.

"I was surprised that the cosmological constant problem simply seems to disappear in this new perspective on the cosmos," Lombriser said. 

A recipe for the dark universe

Lombriser's new framework also tackles some of cosmology's other pressing problems, including the nature of dark matter. This invisible material outnumbers ordinary matter particles by a ratio of 5 to 1, but remains mysterious because it doesn't interact with light.

Lombriser suggested that fluctuations in the field could also behave like a so-called axion field, with axions being hypothetical particles that are one of the suggested candidates for dark matter. 

These fluctuations could also do away with dark energy, the hypothetical force stretching the fabric of space and thus driving galaxies apart faster and faster. In this model, the effect of dark energy, according to Lombriser, would be explained by particle masses taking a different evolutionary path at later times in the universe.

In this picture "there is, in principle, no need for dark energy," Lombriser added.

— Something is wrong with Einstein's theory of gravity

— Da Vinci understood key aspect of gravity centuries before Einstein, lost sketches reveal

— Are black holes wormholes?

Post-doctoral researcher at the Universidad ECCI, Bogotá, Colombia, Luz Ángela García , was impressed with Lombriser's new interpretation and how many problems it resolves. 

"The paper is pretty interesting, and it provides an unusual outcome for multiple problems in cosmology," García, who was not involved in the research, told Live Science. "The theory provides an outlet for the current tensions in cosmology."

However, García urged caution in assessing the paper's findings, saying it contains elements in its theoretical model that likely can't be tested observationally, at least in the near future.

Editor's note: This article was corrected at 1:30 p.m. ET on June 20, to reflect that redshift is evidence of cosmic expansion, but not evidence of  accelerated cosmic expansion.

Robert Lea is a science journalist in the U.K. who specializes in science, space, physics, astronomy, astrophysics, cosmology, quantum mechanics and technology. Rob's articles have been published in Physics World, New Scientist, Astronomy Magazine, All About Space and ZME Science. He also writes about science communication for Elsevier and the European Journal of Physics. Rob holds a bachelor of science degree in physics and astronomy from the U.K.’s Open University

32 of the most colorful birds on Earth

Meta just stuck its AI somewhere you didn't expect it — a pair of Ray-Ban smart glasses

Sarcastic fringehead: The angry little fish that engages in mouth-to-mouth combat

Most Popular

• 2 'The most critically harmful fungi to humans': How the rise of C. auris was inevitable
• 3 2,500-year-old Illyrian helmet found in burial mound likely caused 'awe in the enemy'
• 4 Japan captures 1st image of space debris from orbit, and it's spookily stunning
• 5 32 of the most colorful birds on Earth
• 2 Roman-era skeletons buried in embrace, on top of a horse, weren't lovers, DNA analysis shows
• 3 Papua New Guineans, genetically isolated for 50,000 years, carry Denisovan genes that help their immune system, study suggests
• 4 'The most critically harmful fungi to humans': How the rise of C. auris was inevitable

We have completed maintenance on Astronomy.com and action may be required on your account. Learn More

• Login/Register
• Solar System
• Exotic Objects
• Upcoming Events
• Deep-Sky Objects
• Observing Basics
• Telescopes and Equipment
• Astrophotography
• Space Exploration
• Human Spaceflight
• Robotic Spaceflight
• The Magazine

Why is the universe expanding faster than predicted? A cosmologist explains what we know

Astronomers have known for decades that the universe is expanding. When they use telescopes to observe faraway galaxies, they see that these  galaxies are moving away  from Earth.

To astronomers, the wavelength of light a galaxy emits is longer the faster the galaxy is moving away from us. The farther away the galaxy is, the more its light has shifted toward the longer wavelengths on the red side of the spectrum – so the higher the “redshift.”

Because the speed of light is finite, fast, but not infinitely fast, seeing something far away means we’re looking at the thing how it looked in the past. With distant, high-redshift galaxies, we’re  seeing the galaxy  when the universe was in a younger state. So “high redshift” corresponds to the early times in the universe, and “low redshift” corresponds to the late times in the universe.

But as astronomers have studied these distances, they’ve learned that the universe is not just expanding – its rate of expansion is accelerating. And that expansion rate is even faster than the leading theory predicts it should be, leaving  cosmologists like me  puzzled and looking for new explanations.

Dark energy and a cosmological constant

Scientists call the source of this acceleration  dark energy . We’re not quite sure what drives dark energy or how it works, but we think its behavior could be explained by  a cosmological constant , which is a  property of spacetime  that contributes to the expansion of the universe.

Albert Einstein originally came up with this constant – he marked it with a lambda in his theory of  general relativity . With a  cosmological constant , as the universe expands, the energy density of the cosmological constant stays the same.

Imagine a box full of particles. If the volume of the box increases, the density of particles would decrease as they spread out to take up all the space in the box. Now imagine the same box, but as the volume increases, the density of the particles stays the same.

It doesn’t seem intuitive, right? That the energy density of the cosmological constant does not decrease as the universe expands is, of course, very weird, but this property helps explain the accelerating universe.

A standard model of cosmology

Right now, the leading theory, or standard model, of cosmology is  called “Lambda CDM .” Lambda denotes the cosmological constant describing dark energy, and CDM stands for cold dark matter. This model describes both the acceleration of the universe in its late stages as well as the expansion rate in its early days.

Specifically, the Lambda CDM explains observations of the cosmic microwave background, which is the afterglow of microwave radiation from when the universe  was in a “hot, dense state ” about 300,000 years after the Big Bang. Observations using the  Planck satellite , which measures the  cosmic microwave background , led scientists to create the Lambda CDM model.

Fitting the Lambda CDM model to the cosmic microwave background allows physicists to predict the value of the  Hubble constant , which isn’t actually a constant but a measurement describing the universe’s current expansion rate.

But the Lambda CDM model isn’t perfect. The expansion rate scientists have calculated by measuring distances to galaxies, and the expansion rate as described in Lambda CDM using  observations of the cosmic microwave background , don’t line up. Astrophysicists call that disagreement the Hubble tension.

The Hubble tension

Over the past few years, I’ve been  researching ways  to explain this Hubble tension. The tension may be indicating that the Lambda CDM model is incomplete and physicists should modify their model, or it could indicate that it’s time for researchers to come up with new ideas about how the universe works. And new ideas are always the most exciting things for a physicist.

One way to explain the Hubble tension is to modify the Lambda CDM model by changing the expansion rate at low redshift, at late times in the universe. Modifying the model like this can help physicists predict what sort of physical phenomena might be causing the Hubble tension.

For instance, maybe dark energy is not a cosmological constant but instead the result of gravity working in new ways. If this is the case, dark energy would evolve as the universe expands – and the cosmic microwave background, which shows what the universe looked like only a few years after its creation, would have a different prediction for the Hubble constant.

But,  my team’s latest research  has found that physicists can’t explain the Hubble tension just by changing the expansion rate in the late universe – this whole class of solutions falls short.

Developing new models

To study what types of solutions could explain the Hubble tension, we  developed statistical tools  that enabled us to test the viability of the entire class of models that change the expansion rate in the late universe. These statistical tools are very flexible, and we used them to match or mimic different models that could potentially fit observations of the universe’s expansion rate and might offer a solution to the Hubble tension.

The models we tested include evolving dark energy models, where dark energy acts differently at different times in the universe. We also tested interacting dark energy-dark matter models, where dark energy interacts with dark matter, and modified gravity models, where gravity acts differently at different times in the universe.

But none of these could fully explain the Hubble tension. These results suggest that physicists should study the early universe to understand the source of the tension.

This article first appeared on The Conversation . You can read the original here .

An expert explains the psychedelic rainbow colors of the aurora

Fall into the Whirlpool Galaxy: This Week in Astronomy with Dave Eicher

Could we find Planet Nine using JWST?

A visit to the cutting-edge Southwest Research Institute

Could you survive falling into a black hole it depends..

2024 Full Moon calendar: Dates, times, types, and names

The northern lights: A history of aurora sightings

How to see the northern lights and what they looked like this weekend.

What is an aurora, and why do they come in different shapes and colors?

Astronomers use various observations to determine the universe is expanding. Image adapted from: Caleb Steele

• Space & time

How do astronomers know the universe is expanding?

Studying the wavelengths of light emitted by stars to see how far away they are and how fast they move

All known elements emit and absorb particular wavelengths of light, which is part of the electromagnetic spectrum. By studying the wavelengths of light (as indicated by ‘lines’ within the electromagnetic spectrum) emitted by an object in space, astronomers can get a range of information. One thing they examine is the change in position of lines in the spectrum from a star—this can tell astronomers how far away the star is, whether it is moving towards or away from us and how fast it is moving.

When looking at the radiation emitted by distant stars or galaxies, scientists see emission spectra ‘shifted’ towards the red end of the electromagnetic spectrum—the observed wavelengths are longer than expected. Something causes the wavelength of the radiation to ‘stretch’. But rather than an actual change in the wavelength, this phenomenon was something similar to the Doppler effect—they only appear stretched relative to the observer. The further away an object is, the greater the shift.

The Doppler effect

The noise of a siren or a car speeding past sounds higher in pitch the closer it gets to you and lower as it moves away. This is called the Doppler effect, where waves, in this case sound waves, change in frequency and wavelength as the source moves towards you (higher frequency, shorter wavelength) or away from you (lower frequency, longer wavelength). There is no actual change in sound; the car isn’t making a different noise. It just sounds different due to the car’s movement relative to you.

Doppler shift

This apparent change in wavelength can also be observed for the visible light emitted by stars or galaxies. So, if a star is moving towards Earth, it appears to emit light that is shorter in wavelength compared to a source of light that isn’t moving. Because shorter wavelengths correspond to a shift towards the blue end of the spectrum, this is called blueshift. In contrast, the light from a star moving away from us seems to shift towards longer wavelengths. As this is towards the red end of the spectrum, astronomers call it redshift.

The degree of shift can also give astronomers information about how fast the object is moving relative to us. A faster-moving object has a greater shift in wavelength.

Using various measures to establish how far away the galaxies were, Edwin Hubble (and those that followed him) found that their velocity was always proportional to their distance. The ratio of the two became the famous ‘Hubble constant’ and represents the expansion rate of the universe. But is the expansion rate really constant? Apparently not … and that’s where dark energy comes in.

February 5, 2007

Where is the universe expanding to?

Astrophysicist Alexander Kashlinsky of the NASA Goddard Space Flight Center tackles this question.

The evolution of the universe is described by the physics of general relativity, which was discovered by Albert Einstein in the early 20th century. When compared to Newtonian physics, this theory provides a radically different framework for the physical description of the gravitational force.

In the Newtonian interpretation (where celestial bodies move according to the laws of Newton), space and time are absolute, with time no more than a parameter in the equations of motion. Meanwhile, gravity plays the role of a mysterious force of attraction between massive bodies.

On supporting science journalism

If you're enjoying this article, consider supporting our award-winning journalism by subscribing . By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.

The physics of general relativity is conceptually distinct--even if its equations of motion can be reduced to Newtonian equations in many practical cases, such as with respect to the motion of the moon, or, as we will see shortly, the overall evolution of the universe.

In general relativity, space and time are merged into one four-dimensional grid, whose properties are uniquely specified (via gravity) by the bodies inhabiting them. Gravity curves the spacetime grid, so general relativity thus describes gravitational interactions as manifestations of the spacetime curvature. Objects "fall under gravity" from less curved parts of spacetime to more curved parts of the spacetime. (When spacetime becomes infinitely curved, as in the case of black holes, the gravitational force is so strong that spacetime closes on itself, creating what is called a singularity in the fabric of the underlying spacetime continuum. Nothing can escape such objects.)

According to Einstein's general relativity equations, the spacetime containing matter cannot remain stationary and must either expand or contract. Galaxies and other sources, then, are not strictly expanding away from each other but rather are attached to the fixed grid on the expanding fabric of spacetime. Thus, the galaxies give us the impression of moving away from each other. Imagine the surface of a balloon, on which you put dots. Then start inflating the balloon. The distances between the dots will increase, so if you live in one of these dots, you will interpret this as the dots--which represent galaxies in this example--moving away from each other. In reality, of course, they remain in the same positions, with respect to latitudes and longitudes on the balloon, and it is the fabric of the balloon that is actually expanding.

In Newtonian physics, one can construct a mathematical analogy to the expansion of the universe by defining a system that is expanding or contracting under its own gravity, such as a galaxy made of stars or the solar system. In this framework, however, this expansion is not linked to stretching the fabric of any spacetime. Instead, space is some abstract absolute and fixed entity that all objects move through without affecting it. Thus one can ask not only "Where is the universe expanding to?" in the Newtonian framework, but also "What happened before the initial push?"

In the framework of general relativity, however, both of these questions become meaningless. Asking the question, "Where is the universe expanding to?" implies some other coordinate grid outside spacetime. But since spacetime is linked to matter, there is no outside to the surface of the balloon. Rather, it is all the spacetime that is available.

A widely held theory about the universe expanding has just been contradicted

New NASA data presents a challenge to a fundamental principle of cosmology.

Less than a second after the Big Bang , the universe suddenly blew up from nothing to a hot, dense sea of neutrons and electrons stretching across billions of lightyears.

And, 13.8 billion years later, the universe is still expanding, albeit at a much slower rate.

The prevailing theory, known as the isotropy hypothesis , argues that the universe is not only expanding but doing so at the same rate in all directions. But a new study suggests that may not be the case at all.

In a study published Wednesday in the journal Astronomy and Astrophysics, astronomers challenge this cornerstone theory of cosmology. The results suggest that while the universe is expanding, it is not expanding at the same rate in all directions.

The study relies on observations of some of the cosmos' largest structures, galaxy clusters , by three X-ray observatories: the European Space Agency’s XMM-Newton, NASA’s Chandra, and the German-led ROSAT.

The researchers looked at 800 galaxy clusters across the universe, measuring the temperature of each cluster's hot gas. They then compared the data with how bright the clusters appeared in the sky.

If the universe was in fact isotropic, then galaxy clusters of similar temperatures, located at similar distances, would have similar levels of luminosity. But that was not the case.

A map showing the rate of the expansion of the Universe in different directions across the sky.

Instead, the researchers noted significant differences.

“We saw that clusters with the same properties, with similar temperatures, appeared to be less bright than what we would expect in one direction of the sky, and brighter than expected in another direction,” Thomas Reiprich , professor at the University of Bonn, Germany and co-author of the new study, said in a statement .

“These differences are not random, but have a clear pattern depending on the direction in which we observed in the sky.”

Ultimately, the new study suggests that the universe is anisotropic , meaning that it has a different value when measured in different directions.

Dark forces — The scientists don't know what would cause the universe to expand at different rates in different places.

At first, they didn't entirely trust the results. They considered other explanations for the observations, including undetected gas, or dust blocking the view of the clusters. But the data did not support either of those scenarios.

Instead, they believe the weird observations may have something to do with dark energy .

Dark energy is a mysterious force that accounts for more than 60 percent of the universe, and accounts for the space in between cosmic bodies and holds matter in place through gravitational force.

Previous work suggests the universe is expanding at an accelerating rate. Scientists believe dark energy, which is essentially pulling galaxies apart, drives the acceleration.

Very little is known about dark energy, because it is impossible to observe. But scientists believe that it is not uniform. As a result, dark energy may be stronger in some parts of the universe, and weaker in other parts. If that is true, then it could cause the universe to expand at different rates in different places.

Universal consequences — The results, while odd, do not suggest the universe will run out of space in one direction faster than the other.

The universe does not need more ‘space’ to expand — its very expansion changes the metric of spacetime itself.

Different galaxy clusters reveal different properties across the universe.

The findings, however, may have a major impact on future astronomical observations.

“If the Universe is truly anisotropic, even if only in the past few billion years, that would mean a huge paradigm shift because the direction of every object would have to be taken into account when we analyze their properties,” Konstantinos Migkas , a graduate student at the University of Bonn and first author of the new study, said in the statement.

“Today, we estimate the distance of very distant objects in the Universe by applying a set of cosmological parameters and equations. We believe that these parameters are the same everywhere," he said.

"But if our conclusions are right then that would not be the case and we would have to revisit all our previous conclusions."

Abstract: The isotropy of the late Universe and consequently of the X-ray galaxy cluster scaling relations is an assumption greatly used in astronomy. However, within the last decade, many studies have reported deviations from isotropy when using various cosmological probes; a definitive conclusion has yet to be made. New, effective and independent methods to robustly test the cosmic isotropy are of crucial importance. In this work, we use such a method. Specifically, we investigate the directional behavior of the X-ray luminosity-temperature ( L X – T ) relation of galaxy clusters. A tight correlation is known to exist between the luminosity and temperature of the X-ray-emitting intracluster medium of galaxy clusters. While the measured luminosity depends on the underlying cosmology through the luminosity distance D L , the temperature can be determined without any cosmological assumptions. By exploiting this property and the homogeneous sky coverage of X-ray galaxy cluster samples, one can effectively test the isotropy of cosmological parameters over the full extragalactic sky, which is perfectly mirrored in the behavior of the normalization A of the L X – T relation. To do so, we used 313 homogeneously selected X-ray galaxy clusters from the Meta-Catalogue of X-ray detected Clusters of galaxies. We thoroughly performed additional cleaning in the measured parameters and obtain core-excised temperature measurements for all of the 313 clusters. The behavior of the L X – T relation heavily depends on the direction of the sky, which is consistent with previous studies. Strong anisotropies are detected at a ≳4 σ confidence level toward the Galactic coordinates ( l ,  b ) ∼ (280°, − 20°), which is roughly consistent with the results of other probes, such as Supernovae Ia. Several effects that could potentially explain these strong anisotropies were examined. Such effects are, for example, the X-ray absorption treatment, the effect of galaxy groups and low redshift clusters, core metallicities, and apparent correlations with other cluster properties, but none is able to explain the obtained results. Analyzing 10 5 bootstrap realizations confirms the large statistical significance of the anisotropic behavior of this sky region. Interestingly, the two cluster samples previously used in the literature for this test appear to have a similar behavior throughout the sky, while being fully independent of each other and of our sample. Combining all three samples results in 842 different galaxy clusters with luminosity and temperature measurements. Performing a joint analysis, the final anisotropy is further intensified (∼5 σ ), toward ( l ,  b ) ∼ (303°, − 27°), which is in very good agreement with other cosmological probes. The maximum variation of D L seems to be ∼16 ± 3% for different regions in the sky. This result demonstrates that X-ray studies that assume perfect isotropy in the properties of galaxy clusters and their scaling relations can produce strongly biased results whether the underlying reason is cosmological or related to X-rays. The identification of the exact nature of these anisotropies is therefore crucial for any statistical cluster physics or cosmology study.

Advertisement

The universe is expanding, but what exactly is it expanding into?

12 January 2022

Nasa's Goddard Space Flight Center Conceptual Image Lab/Science Photo Library

Andrew Taubman

Queens Park, New South Wales, Australia

By definition, the universe is everything, so there is nothing external to it for it to expand into. It is not expanding into anything as such – everything is expanding.

Richard Swifte

Darmstadt, Germany

It is all too easy to think of the big bang and the resulting expanding universe as being like an ordinary explosion, with everything expanding out from a central point.

A better analogy is to consider the surface of an inflating balloon where the surface is a two-dimensional equivalent of our three-dimensional universe. The balloon fabric is space; dots marked on this surface (equivalent to galaxies) will move apart as the balloon expands, but only because the fabric (space itself) is expanding, and without any central point for the expansion.

The balloon is expanding into the third dimension, but here the analogy is more problematic. Is our universe also expanding into a higher dimension?

If the universe is all there is, and isn’t part of a larger multiverse, then there is nothing outside it (not even a vacuum, which is still space), so it probably makes no sense to ask what it is expanding into.

Nick Canning

Coleraine, County Londonderry, UK

A two-dimensional being on the surface of an expanding balloon can observe all distances in its surface world getting larger. It can’t see the third dimension into which the balloon is expanding.

We three-dimensional creatures see all the distances between galaxies expanding, indicating an inflation of space, but we can’t perceive extra space dimensions beyond our three, into which the expansion is taking place.

Roger Leitch

There are two parts to the answer to this question.

First, when mathematicians and physicists want to describe space – any space – the mathematical tools and techniques they use don’t depend in any way on the space being part of a higher dimensional space. So they can, for example, do geometry on the surface of a sphere without considering that the sphere is embedded in our everyday three-dimensional space.

Four-dimensional space-time is more complicated than the surface of a sphere, but the idea is the same. It is possible to calculate the shortest distance between two points, for example.

Second, if space is expanding into some higher dimensional space, we can’t, with our current knowledge of physics, know anything about it. And it may even be beyond our comprehension.

Mike Follows

Sutton Coldfield, West Midlands, UK

This isn’t a question that physics can answer with our present knowledge or without some form of qualification.

The trite answer is that both space and time were created at the big bang about 14 billion years ago, so there is nothing beyond the universe. However, much of the universe exists beyond the observable universe, which is maybe about 90 billion light years across.

Because the universe is homogenous on this scale, we imagine that what is beyond our observation looks much the same as what we can see.

If the universe is infinite, there is nothing beyond it, by definition. A finite expanding universe conjures up the idea that it would have a boundary or edge, separating it from something beyond. Of course, the universe has at least four dimensions (three for space and one for time) which is nigh on impossible for us to visualise.

However, space could be represented as two dimensions, confined to the gossamer-thin surface of a sphere. You could travel in any direction on the surface without encountering an edge. If the radius were to increase, the “universe” would expand as ours does, but it wouldn’t be expanding into anything.

Finally, we could speculate that our universe is part of a multiverse with many other universes beyond our own, but it is unlikely that we are expanding into them.

To answer this question – or ask a new one – email [email protected] .

Questions should be scientific enquiries about everyday phenomena, and both questions and answers should be concise. We reserve the right to edit items for clarity and style. Please include a postal address, daytime telephone number and email address.

New Scientist Ltd retains total editorial control over the published content and reserves all rights to reuse question and answer material that has been submitted by readers in any medium or in any format.

Terms and conditions apply .

Sign up to our weekly newsletter

Receive a weekly dose of discovery in your inbox! We'll also keep you up to date with New Scientist events and special offers.

More from New Scientist

Explore the latest news, articles and features

Mystery of 'impossible' star resolved by three-body solution

Subscriber-only

Oldest known human viruses found hidden within Neanderthal bones

Chatgpt got an upgrade to make it seem more human, ultrasound therapy could treat lung condition linked to heart failure, popular articles.

Trending New Scientist articles

• Newsletters

Giant structure in space challenges understanding of the universe

Evrim Yazgin

Evrim Yazgin has a Bachelor of Science majoring in mathematical physics and a Master of Science in physics, both from the University of Melbourne.

About 9.2 billion light-years from Earth is a colossal structure which has confounded astronomers.

The discovery might upend current cosmological theories.

What they’ve found is a 1.3-billion-light-year-across, almost perfect ring of galaxies. No such structure has been seen before. And it doesn’t match any known formation mechanism. It has been dubbed the “Big Ring.”

The discovery was presented at the 243rd meeting of the American Astronomical Society and is detailed in a pre-print paper available on arXiv .

It is the second giant structure found by teams led by Alexia Lopez, an astronomer at the University of Central Lancashire in the UK. The first, a giant arc of galaxies, was unveiled in 2022. That structure is 3.3 billion light-years across and appears in the same region of sky at the same distance from Earth as the Big Ring.

“Neither of these two ultra-large structures is easy to explain in our current understanding of the universe,” Lopez says. “And their ultra-large sizes, distinctive shapes, and cosmological proximity must surely be telling us something important – but what exactly?”

Inhospitable Venus could hold clues to finding extraterrestrial life

A possible explanation for the Big Ring, according to Lopez, is “Baryonic Acoustic Oscillations” (BAOs).

“BAOs arise from oscillations in the early universe and today should appear, statistically at least, as spherical shells in the arrangement of galaxies. However, detailed analysis of the Big Ring revealed it is not really compatible with the BAO explanation: the Big Ring is too large and is not spherical.”

Another possibility is the structures are remnants of “defects” in the early universe called cosmic strings.

The structures challenge the so-called “Cosmological Principle.”

“The Cosmological Principle assumes that the part of the universe we can see is viewed as a ‘fair sample’ of what we expect the rest of the universe to be like,” Lopez explains. “We expect matter to be evenly distributed everywhere in space when we view the universe on a large scale, so there should be no noticeable irregularities above a certain size.”

“Cosmologists calculate the current theoretical size limit of structures to be 1.2 billion light-years, yet both of these structures are much larger,” Lopez adds.

“From current cosmological theories we didn’t think structures on this scale were possible. We could expect maybe one exceedingly large structure in all our observable universe. Yet, the Big Ring and the Giant Arc are two huge structures and are even cosmological neighbours, which is extraordinarily fascinating,” Lopez says.

Originally published by Cosmos as Giant structure in space challenges understanding of the universe

Please login to favourite this article.

• school Campus Bookshelves
• menu_book Bookshelves
• perm_media Learning Objects
• login Login
• how_to_reg Request Instructor Account
• hub Instructor Commons

Margin Size

• Download Page (PDF)
• Download Full Book (PDF)
• Periodic Table
• Physics Constants
• Scientific Calculator
• Reference & Cite
• Tools expand_more
• Readability

selected template will load here

This action is not available.

26.5: The Expanding Universe

• Last updated
• Save as PDF
• Page ID 3810

\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)

\( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)

\( \newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\)

( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\)

\( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)

\( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\)

\( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)

\( \newcommand{\Span}{\mathrm{span}}\)

\( \newcommand{\id}{\mathrm{id}}\)

\( \newcommand{\kernel}{\mathrm{null}\,}\)

\( \newcommand{\range}{\mathrm{range}\,}\)

\( \newcommand{\RealPart}{\mathrm{Re}}\)

\( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)

\( \newcommand{\Argument}{\mathrm{Arg}}\)

\( \newcommand{\norm}[1]{\| #1 \|}\)

\( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\AA}{\unicode[.8,0]{x212B}}\)

\( \newcommand{\vectorA}[1]{\vec{#1}}      % arrow\)

\( \newcommand{\vectorAt}[1]{\vec{\text{#1}}}      % arrow\)

\( \newcommand{\vectorB}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)

\( \newcommand{\vectorC}[1]{\textbf{#1}} \)

\( \newcommand{\vectorD}[1]{\overrightarrow{#1}} \)

\( \newcommand{\vectorDt}[1]{\overrightarrow{\text{#1}}} \)

\( \newcommand{\vectE}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{\mathbf {#1}}}} \)

Learning Objectives

By the end of this section, you will be able to:

• Describe the discovery that galaxies getting farther apart as the universe evolves
• Explain how to use Hubble’s law to determine distances to remote galaxies
• Describe models for the nature of an expanding universe
• Explain the variation in Hubble’s constant

We now come to one of the most important discoveries ever made in astronomy—the fact that the universe is expanding. Before we describe how the discovery was made, we should point out that the first steps in the study of galaxies came at a time when the techniques of spectroscopy were also making great strides. Astronomers using large telescopes could record the spectrum of a faint star or galaxy on photographic plates, guiding their telescopes so they remained pointed to the same object for many hours and collected more light. The resulting spectra of galaxies contained a wealth of information about the composition of the galaxy and the velocities of these great star systems.

Slipher’s Pioneering Observations

Curiously, the discovery of the expansion of the universe began with the search for Martians and other solar systems. In 1894, the controversial (and wealthy) astronomer Percival Lowell established an observatory in Flagstaff, Arizona, to study the planets and search for life in the universe. Lowell thought that the spiral nebulae might be solar systems in the process of formation. He therefore asked one of the observatory’s young astronomers, Vesto M. Slipher (Figure \(\PageIndex{1}\)), to photograph the spectra of some of the spiral nebulae to see if their spectral lines might show chemical compositions like those expected for newly forming planets.

The Lowell Observatory’s major instrument was a 24-inch refracting telescope, which was not at all well suited to observations of faint spiral nebulae. With the technology available in those days, photographic plates had to be exposed for 20 to 40 hours to produce a good spectrum (in which the positions of the lines could reveal a galaxy’s motion). This often meant continuing to expose the same photograph over several nights. Beginning in 1912, and making heroic efforts over a period of about 20 years, Slipher managed to photograph the spectra of more than 40 of the spiral nebulae (which would all turn out to be galaxies).

To his surprise, the spectral lines of most galaxies showed an astounding redshift . By “redshift” we mean that the lines in the spectra are displaced toward longer wavelengths (toward the red end of the visible spectrum). Recall from the chapter on Radiation and Spectra that a redshift is seen when the source of the waves is moving away from us. Slipher’s observations showed that most spirals are racing away at huge speeds; the highest velocity he measured was 1800 kilometers per second.

Only a few spirals—such as the Andromeda and Triangulum Galaxies and M81—all of which are now known to be our close neighbors, turned out to be approaching us. All the other galaxies were moving away. Slipher first announced this discovery in 1914, years before Hubble showed that these objects were other galaxies and before anyone knew how far away they were. No one at the time quite knew what to make of this discovery.

Hubble’s Law

The profound implications of Slipher’s work became apparent only during the 1920s. Georges Lemaître was a Belgian priest and a trained astronomer. In 1927, he published a paper in French in an obscure Belgian journal in which he suggested that we live in an expanding universe. The title of the paper (translated into English) is “A Homogenous Universe of Constant Mass and Growing Radius Accounting for the Radial Velocity of Extragalactic Nebulae.” Lemaître had discovered that Einstein’s equations of relativity were consistent with an expanding universe (as had the Russian scientist Alexander Friedmann independently in 1922). Lemaître then went on to use Slipher’s data to support the hypothesis that the universe actually is expanding and to estimate the rate of expansion. Initially, scientists paid little attention to this paper, perhaps because the Belgian journal was not widely available.

In the meantime, Hubble was making observations of galaxies with the 2.5-meter telescope on Mt. Wilson, which was then the world’s largest. Hubble carried out the key observations in collaboration with a remarkable man, Milton Humason, who dropped out of school in the eighth grade and began his astronomical career by driving a mule train up the trail on Mount Wilson to the observatory (Figure \(\PageIndex{2}\)). In those early days, supplies had to be brought up that way; even astronomers hiked up to the mountaintop for their turns at the telescope. Humason became interested in the work of the astronomers and, after marrying the daughter of the observatory’s electrician, took a job as janitor there. After a time, he became a night assistant, helping the astronomers run the telescope and record data. Eventually, he made such a mark that he became a full astronomer at the observatory.

By the late 1920s, Humason was collaborating with Hubble by photographing the spectra of faint galaxies with the 2.5-meter telescope. (By then, there was no question that the spiral nebulae were in fact galaxies.) Hubble had found ways to improve the accuracy of the estimates of distances to spiral galaxies, and he was able to measure much fainter and more distant galaxies than Slipher could observe with his much-smaller telescope. When Hubble laid his own distance estimates next to measurements of the recession velocities (the speed with which the galaxies were moving away), he found something stunning: there was a relationship between distance and velocity for galaxies. The more distant the galaxy, the faster it was receding from us .

In 1931, Hubble and Humason jointly published the seminal paper where they compared distances and velocities of remote galaxies moving away from us at speeds as high as 20,000 kilometers per second and were able to show that the recession velocities of galaxies are directly proportional to their distances from us (Figure \(\PageIndex{3}\)), just as Lemaître had suggested.

We now know that this relationship holds for every galaxy except a few of the nearest ones. Nearly all of the galaxies that are approaching us turn out to be part of the Milky Way’s own group of galaxies, which have their own individual motions, just as birds flying in a group may fly in slightly different directions at slightly different speeds even though the entire flock travels through space together.

Written as a formula, the relationship between velocity and distance is

\[v=H \times d \nonumber\]

where \(v\) is the recession speed, \(d\) is the distance, and \(H\) is a number called the Hubble constant . This equation is now known as Hubble’s law .

Constants of Proportionality

Mathematical relationships such as Hubble’s law are pretty common in life. To take a simple example, suppose your college or university hires you to call rich alumni and ask for donations. You are paid $2.50 for each call; the more calls you can squeeze in between studying astronomy and other courses, the more money you take home. We can set up a formula that connects \(p\), your pay, and \(n\), the number of calls

\[p=A \times n \nonumber\]

where \(A\) is the alumni constant, with a value of $2.50. If you make 20 calls, you will earn $2.50 times 20, or $50.

Suppose your boss forgets to tell you what you will get paid for each call. You can calculate the alumni constant that governs your pay by keeping track of how many calls you make and noting your gross pay each week. If you make 100 calls the first week and are paid $250, you can deduce that the constant is $2.50 (in units of dollars per call). Hubble, of course, had no “boss” to tell him what his constant would be—he had to calculate its value from the measurements of distance and velocity.

Astronomers express the value of Hubble’s constant in units that relate to how they measure speed and velocity for galaxies. In this book, we will use kilometers per second per million light-years as that unit. For many years, estimates of the value of the Hubble constant have been in the range of 15 to 30 kilometers per second per million light-years The most recent work appears to be converging on a value near 22 kilometers per second per million light-years If \(H\) is 22 kilometers per second per million light-years, a galaxy moves away from us at a speed of 22 kilometers per second for every million light-years of its distance. As an example, a galaxy 100 million light-years away is moving away from us at a speed of 2200 kilometers per second.

Hubble’s law tells us something fundamental about the universe. Since all but the nearest galaxies appear to be in motion away from us, with the most distant ones moving the fastest, we must be living in an expanding universe. We will explore the implications of this idea shortly, as well as in the final chapters of this text. For now, we will just say that Hubble’s observation underlies all our theories about the origin and evolution of the universe.

Hubble’s Law and Distances

The regularity expressed in Hubble’s law has a built-in bonus: it gives us a new way to determine the distances to remote galaxies. First, we must reliably establish Hubble’s constant by measuring both the distance and the velocity of many galaxies in many directions to be sure Hubble’s law is truly a universal property of galaxies. But once we have calculated the value of this constant and are satisfied that it applies everywhere, much more of the universe opens up for distance determination. Basically, if we can obtain a spectrum of a galaxy, we can immediately tell how far away it is.

The procedure works like this. We use the spectrum to measure the speed with which the galaxy is moving away from us. If we then put this speed and the Hubble constant into Hubble’s law equation, we can solve for the distance.

Example \(\PageIndex{1}\): hubble's law

Hubble’s law (\(v = H \times d\)) allows us to calculate the distance to any galaxy. Here is how we use it in practice.

We have measured Hubble’s constant to be 22 km/s per million light-years. This means that if a galaxy is 1 million light-years farther away, it will move away 22 km/s faster. So, if we find a galaxy that is moving away at 18,000 km/s, what does Hubble’s law tells us about the distance to the galaxy?

\[d = \frac{v}{H} = \frac{18,000 \text{ km/s}}{ \frac{22 \text{ km/s}}{1 \text{ million light-years}}} = \frac{18,000}{22} \times \frac{1 \text{ million light-years}{1} = 818 \text{ million light-years} \nonumber\]

Note how we handled the units here: the km/s in the numerator and denominator cancel, and the factor of million light-years in the denominator of the constant must be divided correctly before we get our distance of 818 million light-years.

Exercise \(\PageIndex{1}\)

Using 22 km/s/million light-years for Hubble’s constant, what recessional velocity do we expect to find if we observe a galaxy at 500 million light-years?

\[v=d \times H = 500 \text{ million light-years} \times \frac{22 \text{ km/s}}{1 \text{ million light-years}} = 11,000 \text{ km/s} \nonumber\]

Variation of Hubble’s Constant

The use of redshift is potentially a very important technique for determining distances because as we have seen, most of our methods for determining galaxy distances are limited to approximately the nearest few hundred million light-years (and they have large uncertainties at these distances). The use of Hubble’s law as a distance indicator requires only a spectrum of a galaxy and a measurement of the Doppler shift, and with large telescopes and modern spectrographs, spectra can be taken of extremely faint galaxies.

But, as is often the case in science, things are not so simple. This technique works if, and only if, the Hubble constant has been truly constant throughout the entire life of the universe. When we observe galaxies billions of light-years away, we are seeing them as they were billions of years ago. What if the Hubble “constant” was different billions of years ago? Before 1998, astronomers thought that, although the universe is expanding, the expansion should be slowing down, or decelerating, because the overall gravitational pull of all matter in the universe would have a dominant, measureable effect. If the expansion is decelerating, then the Hubble constant should be decreasing over time.

The discovery that type Ia supernovae are standard bulbs gave astronomers the tool they needed to observe extremely distant galaxies and measure the rate of expansion billions of years ago. The results were completely unexpected. It turns out that the expansion of the universe is accelerating over time! What makes this result so astounding is that there is no way that existing physical theories can account for this observation. While a decelerating universe could easily be explained by gravity, there was no force or property in the universe known to astronomers that could account for the acceleration. In The Big Bang chapter, we will look in more detail at the observations that led to this totally unexpected result and explore its implications for the ultimate fate of the universe.

In any case, if the Hubble constant is not really a constant when we look over large spans of space and time, then the calculation of galaxy distances using the Hubble constant won’t be accurate. As we shall see in the chapter on The Big Bang, the accurate calculation of distances requires a model for how the Hubble constant has changed over time. The farther away a galaxy is (and the longer ago we are seeing it), the more important it is to include the effects of the change in the Hubble constant. For galaxies within a few billion light-years, however, the assumption that the Hubble constant is indeed constant gives good estimates of distance.

Models for an Expanding Universe

At first, thinking about Hubble’s law and being a fan of the work of Copernicus and Harlow Shapley, you might be shocked. Are all the galaxies really moving away from us ? Is there, after all, something special about our position in the universe? Worry not; the fact that galaxies are receding from us and that more distant galaxies are moving away more rapidly than nearby ones shows only that the universe is expanding uniformly.

A uniformly expanding universe is one that is expanding at the same rate everywhere. In such a universe, we and all other observers, no matter where they are located, must observe a proportionality between the velocities and distances of equivalently remote galaxies. (Here, we are ignoring the fact that the Hubble constant is not constant over all time, but if at any given time in the evolution of the universe the Hubble constant has the same value everywhere, this argument still works.)

To see why, first imagine a ruler made of stretchable rubber, with the usual lines marked off at each centimeter. Now suppose someone with strong arms grabs each end of the ruler and slowly stretches it so that, say, it doubles in length in 1 minute (Figure \(\PageIndex{4}\)). Consider an intelligent ant sitting on the mark at 2 centimeters—a point that is not at either end nor in the middle of the ruler. He measures how fast other ants, sitting at the 4-, 7-, and 12-centimeter marks, move away from him as the ruler stretches.

The ant at 4 centimeters, originally 2 centimeters away from our ant, has doubled its distance in 1 minute; it therefore moved away at a speed of 2 centimeters per minute. The ant at the 7-centimeters mark, which was originally 5 centimeters away from our ant, is now 10 centimeters away; it thus had to move at 5 centimeters per minute. The one that started at the 12-centimeters mark, which was 10 centimeters away from the ant doing the counting, is now 20 centimeters away, meaning it must have raced away at a speed of 10 centimeters per minute. Ants at different distances move away at different speeds, and their speeds are proportional to their distances (just as Hubble’s law indicates for galaxies). Yet, notice in our example that all the ruler was doing was stretching uniformly. Also, notice that none of the ants were actually moving of their own accord, it was the stretching of the ruler that moved them apart.

Now let’s repeat the analysis, but put the intelligent ant on some other mark—say, on 7 or 12 centimeters. We discover that, as long as the ruler stretches uniformly, this ant also finds every other ant moving away at a speed proportional to its distance. In other words, the kind of relationship expressed by Hubble’s law can be explained by a uniform stretching of the “world” of the ants. And all the ants in our simple diagram will see the other ants moving away from them as the ruler stretches.

For a three-dimensional analogy, let’s look at the loaf of raisin bread in Figure \(\PageIndex{5}\). The chef has accidentally put too much yeast in the dough, and when she sets the bread out to rise, it doubles in size during the next hour, causing all the raisins to move farther apart. On the figure, we again pick a representative raisin (that is not at the edge or the center of the loaf) and show the distances from it to several others in the figure (before and after the loaf expands).

Measure the increases in distance and calculate the speeds for yourself on the raisin bread, just like we did for the ruler. You will see that, since each distance doubles during the hour, each raisin moves away from our selected raisin at a speed proportional to its distance. The same is true no matter which raisin you start with.

Our two analogies are useful for clarifying our thinking, but you must not take them literally. On both the ruler and the raisin bread, there are points that are at the end or edge. You can use these to pinpoint the middle of the ruler and the loaf. While our models of the universe have some resemblance to the properties of the ruler and the loaf, the universe has no boundaries, no edges, and no center (all mind-boggling ideas that we will discuss in a later chapter).

What is useful to notice about both the ants and the raisins is that they themselves did not “cause” their motion. It isn’t as if the raisins decided to take a trip away from each other and then hopped on a hoverboard to get away. No, in both our analogies, it was the stretching of the medium (the ruler or the bread) that moved the ants or the raisins farther apart. In the same way, we will see in The Big Bang chapter that the galaxies don’t have rocket motors propelling them away from each other. Instead, they are passive participants in the expansion of space . As space stretches, the galaxies are carried farther and farther apart much as the ants and the raisins were. (If this notion of the “stretching” of space surprises or bothers you, now would be a good time to review the information about spacetime in Black Holes and Curved Spacetime. We will discuss these ideas further as our discussion broadens from galaxies to the whole universe.)

The expansion of the universe, by the way, does not imply that the individual galaxies and clusters of galaxies themselves are expanding. Neither raisins nor the ants in our analogy grow in size as the loaf expands. Similarly, gravity holds galaxies and clusters of galaxies together, and they get farther away from each other—without themselves changing in size—as the universe expands.

The universe is expanding. Observations show that the spectral lines of distant galaxies are redshifted, and that their recession velocities are proportional to their distances from us, a relationship known as Hubble’s law. The rate of recession, called the Hubble constant, is approximately 22 kilometers per second per million light-years. We are not at the center of this expansion: an observer in any other galaxy would see the same pattern of expansion that we do. The expansion described by Hubble’s law is best understood as a stretching of space.

• iai Academy
• iai Podcast
• iai Festivals
• About the iai
• Join the Team
• Debates and Talks
• Support the iai
• iai Education
• iai Speakers

Welcome to the IAI.

As a new reader of IAI News, your first article is completely free!

To discover 3000+ more articles and videos, start a free trial today.

New theory of gravity solves accelerating universe

Massive gravity and the end of dark energy.

Claudia de Rham

The universe is expanding at an accelerating rate but Einstein’s theory of General Relativity and our knowledge of particle physics predict that this shouldn’t be happening. Most cosmologists pin their hopes on Dark Energy to solve the problem. But, as Claudia de Rham argues, Einstein’s theory of gravity is incorrect over cosmic scales, her new theory of Massive Gravity limits gravity’s force in this regime, explains why acceleration is happening, and eliminates the need for Dark Energy.

You can see Claudia de Rham live, debating in ‘Dark Energy and The Universe’ alongside Priya Natarajan and Chris Lintott and ‘Faster Than Light’ with Tim Maudlin and J oão Magueijo at the upcoming  HowTheLightGetsIn Festival on May 24th-27th in Hay-on-Wye.

This article is presented in association with  Closer To Truth , an esteemed partner for the 2024  HowTheLightGetsIn Festival .

The beauty of cosmology is that it often connects the infinitely small with the infinitely big – but within this beauty lies the biggest embarrassment in the history of physics.

According to Einstein’s theory of General Relativity and our knowledge of particle physics, the accumulated effect of all infinitely small quantum fluctuations in the cosmos should be so dramatic that the Universe itself should be smaller than the distance between the Earth and the Moon. But as we all know, our Universe spans over tens of billions of light years: it clearly stretches well beyond the moon.

This is the “Cosmological Constant Problem”. Far from being only a small technical annoyance, this problem is the biggest discrepancy in the whole history of physics. The theory of Massive Gravity, developed by my colleagues and I, seeks to address this problem.

For this, one must do two things. First, we need to explain what leads to this cosmic acceleration; second, we need to explain why it leads to the observed rate of acceleration – no more no less. Nowadays it is quite popular to address the first point by postulating a new kind of Dark Energy fluid to drive the cosmic acceleration of the Universe. As for the second point, a popular explanation is the anthropic principle: if the Universe was accelerating at a different rate, we wouldn’t be here to ask ourselves the questions.

To my mind, both these solutions are unsatisfactory. In Massive Gravity, we don’t address the first point by postulating a new form of as yet undiscovered Dark Energy but rather by relying on what we do know to exist: the quantum nature of all the fundamental particles we are made out of, and the consequent vacuum energy, which eliminates the need for dark energy. This is a natural resolution for the first point and would have been adopted by scientists a long time ago if it wasn’t for the second point: how can we ensure that the immense levels of vacuum energy that fill the Universe don’t lead to too fast an acceleration? We can address this by effectively changing the laws of gravity on cosmological scales and by constraining the effect of vacuum energy.

The Higgs Boson and the Nature of Nothingness

At first sight, our Universe seems to be filled with a multitude of stars within galaxies. These galaxies are gathered in clusters surrounded by puffy “clouds” of dark matter. But is that it? Is there anything in between these clusters of galaxies plugged in filaments of dark matter? Peeking directly through our instruments, most of our Universe appears to be completely empty, with empty cosmic voids stretching between clusters of galaxies. There are no galaxies, nor gas, nor dark matter nor anything else really tangible we can detect within these cosmic voids. But are they completely empty and denuded of energy? To get a better picture of what makes up “empty space,” it is useful to connect with the fundamental particles that we are made of.

The discovery of the Higgs boson and its mechanism reveals fundamental insights into our understanding of nothingness

I still vividly remember watching the announcement of the discovery of the Higgs boson in 2012. By now most people have heard of this renowned particle and how it plays an important role in our knowledge of particle physics, as well as how it is responsible for giving other particles mass. However, what’s even more remarkable is that the discovery of the Higgs boson and its mechanism reveals fundamental insights into our understanding of nothingness .

To put it another way, consider “empty space" as an area of space where everything has been wiped away down to the last particle. The discovery of the Higgs boson indicates that even such an ideal vacuum is never entirely empty: it is constantly bursting with quantum fluctuations of all known particles, notably that of the Higgs.

This collection of quantum fluctuations I'll refer to as the “Higgs bath.” The Higgs bath works as a medium, influencing other particles swimming in it. Light or massless particles, such as photons, don’t care very much about the bath and remain unaffected. Other particles, such as the W and Z bosons that mediate the Weak Force , interact intensely with the Higgs bath and inherit a significant mass. As a result of their mass the Weak Force they mediate is fittingly weakened.

Accelerating Expansion

When zooming out to the limits of our observable Universe we have evidence that the Universe is expanding at an accelerating speed, a discovery that led to the 2011 Nobel Prize in Physics . This is contrary to what we would have expected if most of the energy in the Universe was localized around the habitable regions of the Universe we are used to, like clusters of galaxies within the filaments of Dark Matter. In this scenario, we would expect the gravitational attraction pulling between these masses to lead to a decelerating expansion.

So what might explain our observations of acceleration? We seem to need something which fights back against gravity but isn’t strong enough to tear galaxies apart, which exists everywhere evenly and isn't diluted by the expansion of the cosmos. This “something” has been called Dark Energy.

A different option is vacuum energy . We’ve long known that the sea of quantum fluctuations has dramatic effects on other particles, as with the Higgs Bath, so it’s natural to ask about its effect on our Universe. In fact, scientists have been examining the effect of this vacuum energy for more than a century, and long ago realized that its effects on cosmological scales should lead to an accelerated expansion of the Universe, even before we had observations that indicated that acceleration was actually happening. Now that we know the Universe is in fact accelerating, it is natural to go back to this vacuum energy and estimate the expected rate of cosmic acceleration it leads to.

The bad news is that the rate of this acceleration would be way too fast. The estimated acceleration rate would be wrong by at least twenty-eight orders of magnitude! This is the “Cosmological Constant Problem” and is also referred to as the “Vacuum Catastrophe.”

Is our understanding of the fundamental particles incorrect? Or are we using Einstein’s theory of General Relativity in a situation where it does not apply?

General Relativity may not be the correct description of gravity at large cosmological scales where gravity remains untested

The Theory of Massive Gravity

Very few possibilities have been suggested. The one I would like to consider is that General Relativity may not be the correct description of gravity at large cosmological scales where gravity remains untested.

In Einstein’s theory of gravity, the graviton like the photon is massless and gravity has an infinite reach. This means objects separated by cosmological scales, all the way up to the size of the Universe, are still under the gravitational influence of each other and of the vacuum energy that fills the cosmos between them. Even though locally the effect of this vacuum energy is small, when you consider its effect accumulated over the whole history and volume of the Universe, its impact is gargantuan, bigger than everything else we can imagine, so that the cosmos would be dominated by its overall effect. Since there is a lot of vacuum energy to take into account, this leads to a very large acceleration, much larger than what we see, which again is the Cosmological Constant Problem. The solution my colleagues and I have suggested is that perhaps we don’t need to account for all this vacuum energy. If we only account for a small fraction of it, then it would still lead to a cosmic acceleration but with a much smaller rate, compatible with the Universe in which we live. Could it be that the gravitational connection that we share with the Earth, with the rest of the Galaxy and our local cluster only occurs because we are sufficiently close to one another? Could it be that we do not share that same gravitational connection with very distant objects, for instance with distant stars located on the other side of the Universe some 10 thousand million trillion km away? If that were the case, there would be far less vacuum energy to consider and this would lead to a smaller cosmic acceleration, resolving the problem.   

Just as Einstein himself tried to include a Cosmological Constant in his equations, what we need to do is add another term which acts as the mass of the graviton

In practice, what we need to do is understand how to weaken the range of gravity. But that’s easy: nature has already showed us how to do that. We know that the Weak Force is weak and has a finite range distance because the W and Z bosons that carry it are massive particles. So, in principle, all we have to do is simply to give a mass to the graviton. Just as Einstein himself tried to include a Cosmological Constant in his equations, what we need to do is add another term which acts as the mass of the graviton, dampening the dynamics of gravitational waves and limiting the range of gravity. By making the graviton massive we now have ourselves a theory of “massive gravity.” Easy! The possibility that gravity could have a finite range is not a question for science-fiction. In fact Newton, Laplace and many other incredible scientists after them contemplated the possibility. Even following our development of quantum mechanics and the Standard Model, many including Pauli and Salam considered the possibility of gravitons with mass. But that possibility was always entirely refuted! Not because it potentially contradicts observations – quite the opposite, it could solve the vacuum catastrophe and explain why our Universe’s expansion is accelerating – but rather because models of massive gravity appeared to be haunted by “ ghosts .” Ghosts are particles with negative energies that would cause everything we know, including you, me, the whole Universe, and possibly the structure of space and time to decay instantaneously. So if you want a theory of massive gravity you need to either find a way to get rid of these ghosts or to “ trap ” them.

For decades, preventing these supernatural occurrences seemed inconceivable. That’s until Gregory Gabadadze, Andrew Tolley and I found a way to engineer a special kind of “ghost trap” that allowed us to trick the ghost to live in a constrained space and do no harm. One can think of this like an infinite loop-Escherian impossible staircase in which the Ghosts may exist and move but ultimately end up nowhere.

Even in science, there are many cultures and mathematical languages or scientific arguments that individuals prefer.

Coming up with a new trick was one thing, but convincing the scientific community required even more ingenuity and mental flexibility. Even in science, there are many cultures and mathematical languages or scientific arguments that individuals prefer. So, throughout the years, whenever a new colleague had a different point of view, we were bound to learn their language, translate, and adjust our reasoning to their way of thinking. We had to repeat the process for years until no stone remained unturned. Overcoming that process was never the goal, though: it was only the start of the journey that would allow us to test our new theory of gravity.

If gravitons have a mass, this mass should be tiny, smaller than the mass of all the other massive particles, even lighter than the neutrino. Consequently, detecting it may not be straightforward. Nevertheless, different features will appear which may make it possible to measure it.

The most promising way to test for massive gravity involves observations of gravitational waves . If gravitons are massive, then we’d expect that low-frequency gravitational waves will travel ever so slightly slower than high-frequency ones. Unfortunately, this difference would be too slight to measure with current ground-based observatories. However, we should have better luck with future observatories. Missions like the Pulsar Timing Array , LISA and the Simons Observatory will detect gravitational waves with smaller and smaller frequencies, making possible the observations we need. Whether the massive gravity theory developed by my collaborators and I will survive future tests is of course presently unknown, but the possibility is now open. After all, even if the outcome isn’t certain, when it comes to challenging the biggest discrepancy of the whole history of science, addressing the Cosmological Constant Problem, eliminating the need for dark energy, and reconciling the effect of vacuum energy with the evolution of the Universe, some risks may be worth taking.

Claudia de Rham has recently published her first book The Beauty of Falling: A Life in Pursuit of Gravity with Princeton University Press.

This article is presented in partnership with  Closer To Truth , an esteemed partner for the 2024  HowTheLightGetsIn Hay Festival . Dive deeper into the profound questions of the universe with thousands of video interviews, essays, and full episodes of the long-running TV show at their website:  www.closertotruth.com .

Love the iai?

Sign up to get exclusive access.

Related Posts:

The most complex thing in the universe

Was the Big Bang a white hole?

The mistake at the heart of the physics of time

Einstein’s failed magic trick

Related videos:.

Roger Penrose | Interview

Fragments and reality

The trouble with string theory

The trouble with time

Continue reading.

Enjoy unlimited access to the world's leading thinkers.

Start by exploring our subscription options or joining our mailing list today.

Start Free Trial

Already a subscriber? Log in

Related Videos

Crack up capitalism

Danger, safety and the future

What ancient Greeks can teach modern economists

Join the conversation.

Sign in to post comments or join now (only takes a moment) . Don't have an account? Sign in with Facebook, Twitter or Google to get started: -->

All Human Existence May Have Begun in a Black Hole, Some Scientists Believe

There’s an intriguing possibility that the emergence of conscious life is not just a coincidence, but an inevitable outcome of cosmic evolution.

So let’s contemplate something simpler: why does the universe allow us to exist? Yet again, we run into the same problem: if the universe didn’t allow us to exist, we wouldn’t be here to think about it. This is called the “anthropic principle.” For some, it’s the only answer we need to explain, well , everything; but for others, it’s a philosophical thorn in the side. Everything we know about the universe so far—dating back to the 16th-century Polish astronomer Copernicus, who first proposed that Earth travels around the sun rather than the other way around—tells us that we have no special place in the cosmos. We are not at the center. This is the “Copernican principle.”

.css-2l0eat{font-family:UnitedSans,UnitedSans-roboto,UnitedSans-local,Helvetica,Arial,Sans-serif;font-size:1.625rem;line-height:1.2;margin:0rem;padding:0.9rem 1rem 1rem;}@media(max-width: 48rem){.css-2l0eat{font-size:1.75rem;line-height:1;}}@media(min-width: 48rem){.css-2l0eat{font-size:1.875rem;line-height:1;}}@media(min-width: 64rem){.css-2l0eat{font-size:2.25rem;line-height:1;}}.css-2l0eat b,.css-2l0eat strong{font-family:inherit;font-weight:bold;}.css-2l0eat em,.css-2l0eat i{font-style:italic;font-family:inherit;} Why do we exist as self-aware beings, tiny in size and minuscule in lifespan, relative to the lonely cosmic vastness mostly devoid of life?

The anthropic and Copernican principles are conflicting axioms about the universe’s existence and our place within it. The anthropic principle says the universe depends on our being here. Meanwhile, the Copernican principle says that we are not special, and no law of physics should depend on our existence. Yet, the vast and ancient universe we see in our telescopes appears to balance both principles, like a pin balanced on the edge of a glass.

So why is our universe the way it is, and why do we exist as self-aware beings , tiny in size and minuscule in lifespan, relative to the lonely cosmic vastness mostly devoid of life? If the universe were made just for us, surely it would be small, human sized, perhaps just one planet or solar system or galaxy, not billions. Why should a universe made for us have black holes, for example? They seem to contribute nothing to our welfare.

Some scientists believe the universe wasn’t finely tuned to create intelligent life like us at all. Instead, they say, the universe evolved its own insurance policy by creating as many black holes as possible, which is the universe’s method of reproduction. Following this line of thinking, the universe itself may very well be alive—and the fact that we humans exist at all is just a happy side effect.

A Finely-Tuned Universe

One of the biggest philosophical problems with the universe is that it has to be finely tuned for us to even exist. If the universe were random, things would quickly become messy. If modified only a tiny bit one way or another, physical parameters such as the speed of light ; the mass of the electron, proton, and neutron ; the gravitational constant ; and so on would eliminate all life—possibly all matter itself—and even the universe as a whole would not last long enough to evolve anything. For example, if their masses were slightly different, protons would decay into neutrons instead of the other way around, and as a result, there would be no atoms.

One possible solution to fine tuning is the multiverse . In this speculative theory, our universe is one of many in the same way that the planet Earth is one of many planets. Different universes have different laws of physics and, therefore, that ours supports life is simply a matter of luck. While some theories of the multiverse propose that these universes are essentially random and have no relationship to one another, one particular multiverse theory suggests that universes in fact reproduce like living beings and have ancestors and descendants. This theory is called cosmological natural selection (or CNS for short). First proposed by theoretical physicist Lee Smolin in 1992, the CNS theory is a strong contender for why our universe seems to balance both the Anthropic and Copernican principles.

When we look at the complexity of living things and the sheer number of non-living configurations there are, we’re left to assume that there’s no way species could appear randomly. Hence, some powerful being must have created all types of living creatures individually as a watchmaker builds a watch, the thinking often goes. However, Charles Darwin’s theory of evolution, which he first posited in his 1859 book, On the Origin of Species, provides a mechanism that explains why living things are non-random. Their parameters are not freely chosen; they are the product of natural selection , the process by which members of a species that are better fit to survive and/or reproduce more effectively are more likely to pass on their genes.

The theory of evolution is one of the greatest success stories in the history of science because it provided a mechanism by which a thing that is highly ordered, complex, and finely tuned for its survival could arise from natural processes. The theory was successful not only because it explained how species arise, but also because it generated new predictions that we could then test. For example, the theory of evolution explains why species appear related to one another.

The Beauty in Black Holes

The cosmological natural selection theory solves the pernicious problem of a universe finely tuned for life. That idea may make sense to us, living on a planet full of complex, multicellular organisms, but Earth is surrounded by mostly dead space and, as far as we know, dead planets, and moons and light years of interstellar dust and stray photons.

Earth is finely tuned for life; the universe is not. However, the cosmological natural selection theory says that the universe is finely tuned for something else: its method of reproduction, giving birth to new universes.

Under the CNS theory framework, every black hole becomes a baby universe . Our universe, likewise, started out as a black hole in its mother universe. The theory says that inside every black hole, the central singularity—which is matter highly compressed in space in the mother universe—becomes a highly compressed point in time in the new universe. This point expands, creating new matter and energy. You get a complete universe from even a tiny black hole .

This means that our universe is finely tuned not for life, but for black holes, which typically come from massive stars (although they can have other origins). It turns out that massive star formation depends on an element also important for life on Earth: carbon.

Carbon monoxide is the second-most common molecule in the universe after molecular hydrogen, even more common than water. In the molecular clouds of gas and dust that form from supernovae, massive stars coalesce amid gaseous carbon monoxide molecules, which act as a coolant. This cooling helps matter clump together and form the stars. Carbon is a critical component in all life that we know of. Therefore, life is, in fact, a byproduct of stellar formation, which is itself a byproduct of what the universe evolved to do: create as many black holes as possible.

The cosmological natural selection theory helps explain why our universe is so highly ordered, complex, and self-sustaining like Darwin’s theory explains the same for living things. That leads to the tantalizing, if speculative, conclusion that perhaps, by some definition, our universe itself is alive.

Dr. Tim Andersen is a principal research scientist at Georgia Tech Research Institute. He earned his doctorate in mathematics from Rensselaer Polytechnic Institute in Troy, New York, and his undergraduate degree from the University of Texas at Austin. He has published academic works in statistical mechanics, fluid dynamics (including a monograph on vortex filaments), quantum field theory, and general relativity. He is the author of The Infinite Universe on Medium and Stubstack and a book by the same name. He lives with his wife and two cats, and has a son and daughter at home as well as one grown son.

.css-cuqpxl:before{padding-right:0.3125rem;content:'//';display:inline;} Pop Mech Pro: Science .css-xtujxj:before{padding-left:0.3125rem;content:'//';display:inline;}

The CIA’s Secret Plan to Use Mind Control

The Universe Could Be Eternal, This Theory Says

Immortality Is Impossible Until We Beat Physics

How Vacuum Energy Could Help Us Reach Light Speed

Could the Chair You Sit on Have a Soul?

Here’s How We Could Live in Trees

The Engine Driving Our Oceans Could Die by 2100

Can AI Help Solve Math’s Thorniest Mysteries?

You Can Give Your Body Back to Nature When You Die

How Does UFO Footage Play Tricks on Your Mind?

Why Doesn’t the Living Human Body ‘Go Bad’?

Physicists Say They May Have Found a Powerful Glitch in the Universe

"once you reach a cosmic scale, terms and conditions apply.", einstein 2.0.

Researchers have discovered what they're calling a "cosmic glitch" in gravity, which could potentially help explain the universe's strange behavior on a cosmic scale.

As detailed in a new paper published in the  Journal of Cosmology and Astroparticle Physics , the team from the University of Waterloo and the University of British Columbia in Canada posit that Albert Einstein's theory of general relativity may not be sufficient to explain the accelerating expansion of the universe .

Einstein's "model of gravity has been essential for everything from theorizing the Big Bang to photographing black holes," said lead author and Waterloo mathematical physics graduate Robin Wen in a statement about the research . "But when we try to understand gravity on a cosmic scale, at the scale of galaxy clusters and beyond, we encounter apparent inconsistencies with the predictions of general relativity."

"It's almost as if gravity itself stops perfectly matching Einstein's theory," he added. "We are calling this inconsistency a 'cosmic glitch': gravity becomes around one percent weaker when dealing with distances in the billions of light years."

Glitchuationship

In response, the team came up with a new model of such a "glitch" that modifies Einstein's theory to resolve these inconsistencies.

"Think of it as being like a footnote to Einstein's theory," Wen said in the statement. "Once you reach a cosmic scale, terms and conditions apply."

It's one possible solution for a problem that astronomers and physicists have been racking their brains over for decades.

"Almost a century ago, astronomers discovered that our universe is expanding," explained coauthor and University of Waterloo astrophysics professor Niayesh Afshordi. "The farther away galaxies are, the faster they are moving, to the point that they seem to be moving at nearly the speed of light, the maximum allowed by Einstein's theory."

"Our finding suggests that, on those very scales, Einstein's theory may also be insufficient," he added.

According to Afshordi, their suggested patch for a "cosmic glitch" is only the beginning.

"This new model might just be the first clue in a cosmic puzzle we are starting to solve across space and time," he said.

More on the expansion of the universe: Physicists Suggest Universe Is Full of Material Moving Faster Than Light

Share This Article

Star explosion called “ONe novae” may be where life originated in the universe

W e all know that life is a complex symphony, but have you ever wondered about the origin of the key elements that make it possible? One such element, phosphorus, is essential for the creation of DNA, the blueprint of life itself.

Astronomers have long sought to understand how this crucial element came to be. Now, a new theory proposes that a type of stellar explosion , known as "ONe novae," could be the primary source of phosphorus in the universe.

Big bang theory

At the universe's inception, the Big Bang generated primarily hydrogen, the simplest and lightest element. Within the fiery cores of stars, intense pressure and heat fuse hydrogen atoms, forming heavier elements like helium. This process continues, progressively creating elements such as carbon and oxygen.

These stellar furnaces eventually exhaust their fuel, leading to cataclysmic explosions – novae and supernovae. These events disperse the newly forged elements into the cosmos, enriching the interstellar medium with the building blocks for planets, asteroids, and ultimately, life itself.

Our understanding of fundamental processes in astrophysics continues to grow. However, the exact mechanisms that create the diverse elements in the universe are still under investigation. This remains a key research area in astrophysics.

ONe novae: A recipe for phosphorus and life?

ONe novae are a specific category of stellar explosions that occur in white dwarf stars with a high composition of oxygen, neon, and magnesium.

These white dwarfs accrete matter from a companion star, and when the accumulated material reaches a critical mass, it triggers a runaway thermonuclear reaction.

This explosive event ejects a significant amount of stellar material, including newly synthesized elements, into the surrounding interstellar space.

Astronomers Kenji Bekki and Takuji Tsujimoto have put forth a hypothesis suggesting that these ONe novae could be the primary mechanism responsible for the production and distribution of phosphorus , a key element for life as we know it, throughout the universe.

"A ONe nova occurs when matter builds up on the surface of an oxygen-neon-magnesium rich white dwarf star and is heated to the point to ignite explosive run-away nuclear fusion," explains Tsujimoto.

Life, phosphorus production peaks, and ONe novae

Bekki and Tsujimoto's model suggests that the frequency of ONe novae reached its highest point approximately 8 billion years ago.

This peak in ONe novae activity would have led to a significant enrichment of phosphorus in the interstellar medium.

Given that our solar system formed about 4.6 billion years ago, this timeline implies that phosphorus, a crucial element for life , would have been abundant and accessible during the early stages of Earth's formation.

This availability of phosphorus may have played a pivotal role in the emergence and evolution of life on our planet.

Iron connection with a chlorine clue

The model introduces a novel aspect by suggesting a correlation between the frequency of ONe novae and the iron abundance within the progenitor stars .

Furthermore, the model predicts that ONe novae not only generate phosphorus but also lead to an increased production of chlorine.

Currently, available observational data regarding chlorine abundance in the context of ONe novae is limited. However, this prediction presents an opportunity for empirical verification of the model.

Future astronomical observations can specifically focus on measuring chlorine levels in regions where ONe novae are known to occur.

If the observed chlorine enhancement aligns with the model's predictions, it would provide strong evidence supporting the role of ONe novae as significant contributors to the production of both phosphorus and chlorine in the universe.

"The model predicts that ONe novae will produce a chlorine enhancement similar to the phosphorus enhancement," says Bekki. "There is not yet enough observational data for chlorine to confirm this and it provides a testable hypothesis to check the validity of the ONe novae model."

Looking to the stars for answers

Conducting astronomical observations of stars located in the outer regions of the Milky Way galaxy will be essential in verifying the validity of the proposed relationship between iron content and the frequency of ONe novae, as well as the predicted enhancement of chlorine.

These observations will provide valuable data to assess whether ONe novae are the principal mechanism responsible for generating phosphorus, a fundamental element for life.

The findings of these studies will have profound implications for our understanding of the origins of life's essential building blocks . If the observations align with the model's predictions, it would solidify the role of ONe novae as the primary source of phosphorus.

However, if the data deviates from the model, it would necessitate a reevaluation of our current understanding of the processes involved in the production and distribution of elements in the universe.

The spice of life

Phosphorus, often referred to as the "spice of life," is not only essential for DNA but also plays a vital role in energy transfer, cell signaling, and bone formation. Understanding its origin is crucial for unraveling the mysteries of life's emergence and evolution in the universe.

The new theory proposed by Bekki and Tsujimoto offers a tantalizing glimpse into the cosmic processes that have shaped our existence.

As we continue to explore the vastness of space, we may uncover even more secrets about the elements that make life possible, and perhaps even discover the existence of life beyond our own planet.

The study is published in The Astrophysical Journal Letters .

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap , a free app brought to you by Eric Ralls and Earth.com.