Something is awry in our expanding cosmos.
Nearly a century ago, the astronomer Edwin Hubble discovered the balloon-like inflation of the universe and the accelerating rush of all galaxies away from each other. Following that expansion backward in time led to our current best understanding of how everything began — the Big Bang.
But over the past decade, an alarming hole has been growing in this picture: Depending on where astronomers look, the rate of the universe's expansion (a value called the Hubble constant) varies significantly.
Now, on the second anniversary of its launch, the James Webb Space Telescope (JWST) has cemented the discrepancy with stunningly precise new observations that threaten to upend the standard model of cosmology.
The new physics needed to modify or even replace the 40-year-old theory is now a topic of debate.
"It's a disagreement that has to make us wonder if we really do understand the composition of the universe and the physics of the universe," Adam Riess, a professor of astronomy at Johns Hopkins University who led the team that made the new JWST measurements, told Live Science. Reiss, Saul Perlmutter and Brian P. Schmidt won the 2011 Nobel Prize in physics for their 1998 discovery of dark energy, the mysterious force behind the universe's accelerating expansion.
Starting with a bang
On this much cosmologists can agree: It started with a bang.
Then in an instant, the young cosmos was formed: an expanding, roiling plasma broth of matter and antimatter particles that popped into existence, only to annihilate each other upon contact.
Left to their own devices, the matter and antimatter inside this plasma mire should have consumed each other entirely. But scientists believe that some unknown imbalance enabled more matter than antimatter to be produced, saving the universe from immediate self-destruction.
Gravity compressed the plasma pockets, squeezing and heating the matter so that sound waves traveling just over half the speed of light, called baryon acoustic oscillations, rippled across their surface.
Meanwhile, the high energy density of the early universe's crowded contents stretched space-time, pulling a small fraction of this matter safely from the fray.
As the universe inflated like a balloon, the standard story goes, ordinary matter (which interacts with light) congealed around clumps of invisible dark matter to create the first galaxies, connected together by a vast cosmic web.
Initially as the universe's contents spread out, its energy density and therefore its expansion rate decreased. But then, roughly 5 billion years ago, galaxies began to recede once more at an ever-faster rate.
The cause, according to this picture, was another invisible and mysterious entity known as dark energy.
The simplest and most popular explanation for dark energy is that it is a cosmological constant — an inflationary energy that is the same everywhere and at every moment; woven into the stretching fabric of space-time. Einstein named it lambda in his theory of general relativity.
As our cosmos grew, its overall matter density dropped while the dark energy density remained the same, gradually making the latter the biggest contributor to its overall expansion.
Added together the energy densities of ordinary matter, dark matter, dark energy and energy from light set the upper speed limit of the universe's expansion. They are also key ingredients in the Lambda cold dark matter (Lambda-CDM) model of cosmology, which maps the growth of the cosmos and predicts its end — with matter eventually spread so thin it experiences a heat death called the Big Freeze.
Many of the model's predictions have been proven to be highly accurate, but here's where the problems begin: despite much searching, astronomers have no clue what dark matter or dark energy are.
"Most people agree that the universe's present composition is 5% ordinary, atomic matter; 25% cold, dark matter; and 70% dark energy," Ofer Lahav, a professor of astronomy at University College London who is involved in galaxy surveys of dark energy, told Live Science. "The embarrassing fact is, we don't understand the last two of them."
But an even greater threat to Lambda-CDM has materialized: Depending on what method astrophysicists use, the universe appears to be growing at different rates — a disparity known as the Hubble tension. And methods that peer into the early universe show it expanding significantly faster than Lambda-CDM predicts. Those methods have been vetted and verified by countless observations.
"So the only reason that I can understand, at this point, for them to disagree is that the model that we have between them is perhaps missing something," Riess said.
Climbing the cosmic ladder
Measuring the universe's expansion takes a little bit more than a radar gun.
The first method to measure this growth looks at the so-called cosmic microwave background (CMB), a relic of the universe's first light produced just 380,000 years after the Big Bang. The imprint can be seen across the entire sky, and it was mapped to find a Hubble constant with less than 1% uncertainty by the European Space Agency's (ESA) Planck satellite between 2009 and 2013.
In this cosmic "baby picture," the universe is almost entirely uniform, but hotter and colder patches where matter is more or less dense reveal where baryon acoustic oscillations made it clump. As the universe exploded outward, this soap-bubble structure ballooned into the cosmic web — a network of crisscrossing strands along whose intersections galaxies would be born.
By studying these ripples with the Planck satellite, cosmologists inferred the amounts of regular matter and dark matter and a value for the cosmological constant, or dark energy. Plugging these into the Lambda-CDM model spat out a Hubble constant of roughly 46,200 mph per million light-years, or roughly 67 kilometers per second per megaparsec. (A megaparsec is 3.26 million light-years.)
Let's pause on this number for a moment: if a galaxy is at a distance of one megaparsec away from us, that means it will retreat from us (and us from it) at 67 kilometers per second. At twenty megaparsecs this recession grows to 1,340 kilometers per second, and continues to grow exponentially there onward. If a galaxy is any further than 4,475 megaparsecs away, it will recede from us faster than the speed of light.
A second method to find this expansion rate uses pulsating stars called Cepheid variables — dying stars with helium-gas outer layers that grow and shrink as they absorb and release the star's radiation, making them periodically flicker like distant signal lamps.
In 1912, astronomer Henrietta Swan Leavitt found that the brighter a Cepheid was, the slower it would flicker, enabling astronomers to measure a star's absolute brightness, and therefore gauge its distance.
It was a landmark discovery that transformed Cepheids into abundant "standard candles" to measure the universe's immense scale. By stringing observations of pulsating Cepheids together, astronomers can construct cosmic distance ladders, with each rung taking them a step back into the past.
"It's one of the most accurate means that astronomers have today for measuring distances," Wendy Freedman, an astrophysicist at the University of Chicago, told Live Science.
To build a distance ladder, astronomers construct the first rung by choosing nearby Cepheids and cross-checking their distance based on pulsating light to that found by geometry. The next rungs are added using Cepheid readings alone.
Then, astronomers look at the distances of the stars and supernovas on each rung and compare how much their light has been redshifted (stretched out to longer, redder wavelengths) as the universe expands.
This gives a precise measurement of the Hubble constant. In 2019, the method was used by Riess and his collaborators, who trained the Hubble Space Telescope on one of the Milky Way's closest neighbors, the Large Magellanic Cloud.
Their result was explosive: an impossibly high expansion rate of 74 km/s/Mpc when compared to the Planck measurement.
Yet Hubble lacked the necessary precision for the crowded regions of space the team was studying, causing some distant Cepheids to blur into neighboring stars. Dissenting cosmologists had some room left to argue that the result, however shocking, could have come from a measurement error.
So when JWST launched in December 2021, it was poised to either resolve the discrepancy or cement it. At 21.3 feet (6.5 m) wide, JWST's mirror is almost three times the size of Hubble's, which is just 7.9 feet (2.4 m) wide. Not only can JWST detect objects 100 times fainter than Hubble can, but it is also far more sensitive in the infrared spectrum, enabling it to see in a broader range of wavelengths.
By comparing Cepheids measured by JWST in the galaxy NGC 4258 with bright Type Ia supernovas (another standard candle because they all burst at the same absolute luminosity) in remote galaxies, Riess and his colleagues arrived at a nearly identical result: 73 km/s/Mpc.
Other measurements — including one made by Freedman with the Hubble Space telescope on the rapid brightening of the most luminous "tip of the branch" red giant stars, and another with light bent by the gravity of massive galaxies — came back with respective results of 69.6 and 66.6 km/s/Mpc. A separate result using the bending of light also gave a value of 73 km/s/Mpc. Cosmologists were left reeling.
"The CMB temperature is measured at the level of 1% precision, and the Cepheid distance ladder measurement is getting close to 1%," Ryan Keeley, a cosmologist at the University of California, Merced who has been working to explain the Hubble tension, told Live Science. "So a difference of 7 kilometers per second, even though it's not very much, is very, very unlikely to be a random chance. There is something definite to explain."
Cosmology in crisis
The new result leaves the answer wide open, splitting cosmologists into factions chasing staggeringly different solutions. Following the Hubble Space telescope result, an official attempt to resolve the issue at a 2019 conference at the Kavli Institute for Theoretical Physics (KITP) in California only caused more frustration.
"We wouldn't call it a tension or problem, but rather a crisis," David Gross, former director of the KITP and a Nobel laureate, said at the conference.
How things can be fixed is unclear. Riess is pursuing a tweak to the Lambda-CDM model that assumes dark energy (the lambda) isn't constant but instead evolves across the life of the cosmos according to unknown physics.
However Keeley's research, published Sept. 15 in the journal Physical Review Letters, contradicts this. He and his colleagues found that the expansion rates matched the predictions of Lambda-CDM all the way back to the CMB. So, if the model needs fixing anywhere, it's most likely in the very early universe, Keeley said.
It could be possible to add some extra dark energy before the emergence of the cosmic microwave background, Keeley said, giving some additional oomph to the universe’s expansion that needn't make it break from the standard model.
Another group of astronomers is convinced that the tension, alongside the observation that the Milky Way resides inside an underdense supervoid, means that Lambda-CDM and dark matter must be thrown out altogether.
What should replace it, according to Pavel Kroupa, a professor of astrophysics at the University of Bonn, is a theory called Modified Newtonian Dynamics (MOND).
The theory proposes that for gravitational pulls ten trillion times smaller than those felt on Earth's surface (such as the tugs felt between distant galaxies) Newton's laws break down and must be replaced by other equations.
Other astronomers say that their own calculations nix the MOND claims, yet Kroupa insists that cosmologists looking to tweak the standard cosmological model are "basically adding additional complications to an already very messy and complicated theory."
"What I am experiencing and witnessing is an essential breakdown of science," Kroupa said.
Lahav is agnostic. It's possible Lambda-CDM just needs a tweak, he said, or maybe dark matter and dark energy are the modern-day equivalent of epicycles, the small circles ancient Greek astronomers used to model planets orbiting Earth. "The orbits of planets were described very accurately by epicycles," Lahav said. "It was a good model! It fitted the data."
But once astronomers placed the sun in the center of the solar system in newer models, epicycles eventually became irrelevant, he added.
"If we want to go philosophical, maybe that's what's going on," Lahav said. "But maybe also there is dark matter and dark energy and it's just not been discovered yet."
Cosmologists are looking for answers in a number of places. Upcoming CMB experiments, such as the CMB-S4 project at the South Pole and the Simons Observatory in Chile, are searching for clues in ultraprecise measurements of the early universe's radiation. Others will look to the dark matter maps produced by ESA's Euclid space telescope or to the future dark energy survey conducted by the Dark Energy Spectroscopic Instrument.
Although it now may seem less likely, it's also still possible the Hubble tension could be resolved by figuring out some unseen systematic flaw hiding inside current measurements.
For Freedman, such a solution, or possibly further riddles, will come from the JWST. Her team is using the telescope’s powerful eye to make ultradetailed measurements of Cepheid variables; tip-of-the-red-giant-branch stars; and a type of carbon star called JAGB stars all at once distance.
"We'll see how well they agree and that will give us a sense of an overall systematic answer," Freedman said.
Freedman has looked only at stars in one galaxy so far but is already seeing a difference from the Hubble space telescope measurements.
"I'm really excited because I think we're going to have something really interesting to say," Freedman said. "I'm just completely open. I don't know where this is going to fall."
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Ben Turner is a U.K. based staff writer at Live Science. He covers physics and astronomy, among other topics like tech and climate change. He graduated from University College London with a degree in particle physics before training as a journalist. When he's not writing, Ben enjoys reading literature, playing the guitar and embarrassing himself with chess.
After having been aware of this topic for many years, I now think that the "scientists" don't know what they're talking about!!!!!!Reply
James Webb has broadened our understanding of the universe. It hasn't broken anything.Reply
The only thing that is broken is the goofy sensationalism that surrounds every discovery.
According to sites like this one, physics doesn't even exist anymore BUT you spend more time seriously pushing a religion based on the matrix. That religion is called Simulationism.
Adam Reiss discussed this subject during a recent panel hosted by World Science festival. Jo Dunkley, who studies the origins and evolution of the universe, was also on the panel. Together they talked about the different methods they used to measure the Hubble constant and the differences in their results. Neither of them resorted to the kind of misleading and sensationalist language used in the title and body of this article.Reply
Reiss explained that their measurements come “from opposite ends of the universe” (Dunkley’s measurements examine the early universe, whereas Weiss’s measurements are taken from stars in nearby galaxies.) Reiss also stated “what’s so profound about this is we may both be right, and it may be that the story of the universe that allows us to connect the beginning to the end that is a little bit different in some way.”
Anyone interested in the panel discussion can find it at World Science Festival website or on their YouTube page. Title is “Searching for Cosmic Origins”. Variances in the Hubble constant is touched on several times, but the main part of that discussions starts at 1:03:27.
Cosmology isn't broken or breaking. Conflicting ideas and fierce debate are a normal part of science. They don’t mean anything is broken, but are signs that things are working as they should.
To add to what KMcB said, I agree that JWST hasn't "broken" cosmology but that the ongoing work confirm that science and scientists work as they should. Even if today's supernova results were a fact the DES survey results showed that the universe would follow standard LCDM (being flat, i.e. having the same equation of state).Reply
A recent paper confirm that. They include supernova results by using modern extrapolation methods of systematic errors and find that there isn't any tension in near universe observation. The result prefer the far universe Hubble value, suggesting that indeed there may be systematic measurement problems with the cosmic ladder that it underestimates.
And Planck results tell us that if there is a problem with the ladder, it lies above the pivot scale z ~ 0.005 which is beyond the Cepheid scale. JWST can probe supernova distances that far, it just hasn't yet. Until then these articles are "misleading and sensationalist".
Meanwhile results have come in on suggestions that the early universe dark energy can alleviate the supernova result's problems. Turns out it cannot but BAO results assure us that LCDM is valid for high z of 5 < z < 1 and as a result they get H_0 = 67.9 +/- 0.4 km/s/Mpc.
We also have a suggestive update from the in principle fully independent near universe gravitational wave method. From eight localized GW events and using one single telescope distance for one of them, they get H_0 = 67.0+6.3−3.8 km/s/Mpc.
The article itself is problematic when it inserts the ever vanishing MOND from the long standing LCDM critic Kroupa. His latest work rests on the assumption that there is an extremely large supervoid. But the KBC void that the paper analyse is a proposed void associated with our own Laniakea Supercluster. It is not known yet if it is inconsistent with standard cosmology: “It is debated whether the existence of the KBC void is consistent with the ?CDM model. While Haslbauer et al. say that voids as large as the KBC void are inconsistent with ?CDM, Sahlén et al. argue that the existence of supervoids such as the KBC void is consistent with LCDM.”
The accompanying article on Freedman's upcoming JWST work is interesting though. "'It could be profound': How astronomer Wendy Freedman is trying to fix the universe", Ben Turner, LiveScience.
I hate the name. So does my firstborn who is reminded of the hatred this man had. Stop honoring men by naming equipment after them. This guy doesn’t deserve it. Give them letters and numbers so my child can participate. You know women contribute too, right, NASA?Reply
In 2019 Zbigniew Osiak published a paper saying that Einstein's formulas for energy in special relativity are wrong. The (rest) mass-energy equivalency law, E_0 = m c^2 (where c is the speed of light) according to Einstein should be E_0 = m c^2 /2 , Osiak found. Also, the general energy formula (per Einstein E = g m c^2, where g=sqrt(1/(1 - (v/c)^2)) with v the particle velocity, is the "Lorentz factor", that makes it impossible to accelerate an object to c, the speed of light) should be E = g^2 m c^2 /2. So, in addition to a factor of a half, like the rest mass energy, the general energy formula has an extra Lorentz factor, that approaches infinity as a, say, elementary particle's velocity approaches the speed of light. So if Osiak is correct, the very early universe , which consists of a lot of relativistic elementary particles (for a short time as a quark-gluon plasma) has a total energy that is greater than expected according to Einstein relativity by a truly huge factor. So it seems reasonable that such a huge amount of extra energy density might lead to star and galaxy formation more rapidly than the Einstein-relativity based cosmological models predict.Reply
So is Osiak relativity correct? How could such mistakes in special relativity have gone overlooked for over a hundred years? The answer is, the errors weren't overlooked. They were made deliberately because the correct formulas can be easily shown to violate energy conservation. A physical law that violated energy conservation was unacceptable to Einstein (and many co-workers such as Tolman and (later) Rindler and Penrose). However, the energy nonconservation is actually nearly impossible to measure because it occurs only under very extreme conditions such as in the early universe. Also, the quantity P_0 = g m c^2 is a conserved quantity (the temporal component of four-momentum) that is also important in Osiak relativity. The Osiak kinetic energy is actually equal to the classical formula E = p^2 / 2m, where p = g m v is the (relativistic) momentum. The Einstein form of kinetic energy only reduces to the classical form in the classical (low velocity) limit.
Until fairly recently, the idea of energy non-conservation was unthinkable to most or all physicists. After dark energy was proposed, however, some quantum gravity guys proposed energy non-conservation as an explanation for dark energy. All this was prior to the Webb launch but the paper I read was after Osiak published, still they do not seem to be aware of it.
In basic inflationary cosmology, gravitational potential energy from an unknown source (Guth thought originally the Higgs field but it didn't pan out) causes cosmic inflation. It's easy to suppose that energy nonconservation in special relativity can manifest in general relativity as gravitational potential energy. This would be a difficult thing to prove observationally, but if a modified cosmological standard model incorporating Osiak relativity can be constructed, it can be compared with the Webb results, and the matter of whether Osiak relativity is correct can be settled.
I think there is an easier way, though, to prove Osiak is correct. Not trivial, but not cosmological. It involves an old idea of Stuckelberg, that Richard Feynman was fond of, that antimatter particles move backward in time. Osiak relativity also predicts this in a much more straightforward way than in Einstein relativity. I think it could be observable directly.
Thanks. There is a lot there. It represents a lot of work by me actually. What Osiak found is amazing, but I don't think he understood the history. After I saw Osiak's paper and realized it solved the problem I was stuck on, I reproduced all his equations. Then I studied it historically. Einstein said about the energy formulas as he published, "It's best to keep things simple". It seems obvious he understood the natural form of relativity (based on the Minkowski equations of motion) is a lot more complicated than what he settled on. But it's far richer. If you google "Osiak relativity" you can find his paper for free and I think my "comment" paper will appear perhaps even first. It's only on researchgate but it's free. Still a draft but almost done. Doesn't have a chance in heck of getting published in Foundations of Physics, probably, but they're getting it soon. Osiak is there too.Reply
"....it all started with a bang."admin said:For decades, measurements of the universe's expansion have suggested a disparity known as the Hubble tension, which threatens to break cosmology as we know it. Now, on the eve of its second anniversary, a new finding by the James Webb Space Telescope has only entrenched the mystery.
After 2 years in space, the James Webb telescope has broken cosmology. Can it be fixed? : Read more
Big assumption of course, since no one can actually confirm it. Plus the "..unknown imbalance.." in matter versus anti-matter makes the whole idea into some kind of supernatural event - completely devoid of what is allowed in so-called "science"!
What if all the matter was created and formed into a ball of water 1 light year in diameter and then expanded - with the expansion being accompanied by the creation of stars and galaxies as we k now them?
How would one be able to tell a difference between this and the big bang? I propose that no one would be able to tell the difference. YMMV.
Cosmology, astrophysics has for some time wondered off the path of science by inventing hypothetical undetectable virtual stuffs everytime there is a failure to predict. Hubble Telescope revealed well formed galaxies too close the alleged big bang, so they invent dark energy. So far they have failed their burden off proof in proving its existence. And this has not been the first failure to predict for BB.Reply
Vera Rubin observed not enough mass in galaxies to explain their rotation. Again instead of questioning the physics, they invent a hypothetical undetectable stuff called dark matter. Again they have failed their burden of proof as every researcher looking for this dark stuff has come up empty handed.
To the unenumbered mind these failures to predict are refutations. They invalidate these models, yet, to the minds encumbered via emotiomally investing in them, they cannot see it. Their faith in these models is profound and innapropriate.
If gravity is not the dom force in space as Vera Rubins observations suggest, then it also puts Einstein's GTR in the scrap heap as it is considered by many to be the mechanism for gravity.
The universe is not expanding, the BB did not happen, gravity is not the dom force in space and Einstein's GTR is no longer relevant.
Be warned, any disrespectful insulting comments only prove your confirmation bias and emtional attachments.