Analysis indicates that the universe’s expansion is not accelerating

https://ras.ac.uk/news-and-press/research-highlights/universes-expansion-now-slowing-not-speeding

by chrka • 9 months ago

261 208 9 months ago

ras.ac.uk

karakot• 9 months ago

What does 'now' mean here?

plasticchris• 9 months ago

Probably it means that now we have evidence that… it is a colloquialism

Edit: yep, The universe's expansion may actually have started to slow rather than accelerating at an ever-increasing rate as previously thought, a new study suggests.

sermah• 9 months ago

Recent years, probably because of large data centers /s

thelibrarian• 9 months ago

Going by the second graph, since about 2.5 billion years ago.

2OEH8eoCRo0• 9 months ago

What happened to then?

dylan6044• 9 months ago

we passed then. we're at now now. I thought this was settled

jl6• 9 months ago

My lay reading of the OP’s paper is that the universe is, in fact, braking for somebody.

denismenace• 9 months ago

Did it change during our life time?

oofbey2• 9 months ago

Just our understanding of it. That’s flipped multiple times in my lifetime.

candiddevmike• 9 months ago

Aside from unanswerable questions (has the universe started to fill it's container? Is a simulation property nearing "1"?), does this make long distance space travel feasible again? I thought there was something around the universe is expanding too fast to visit places like Alpha Centuri (and preventing visitors to us).

indoordin0saur2• 9 months ago

The universe was always only expanding between galaxies, not within them.

Razengan3• 9 months ago

So wait, individual stars aren't getting further apart? Galaxies aren't getting "bigger"/more diffuse?

oofbey2• 9 months ago

That limitation only counts for visiting other galaxies. Travel within the galaxy is always possible, regardless of the universe’s expansion. And Alpha Centauri is super close, even within our galaxy.

dtech• 9 months ago

Specifically the local group, so Milky way + Andromeda and some dwarf galaxies

Sharlin4• 9 months ago

Edit: A big brain fart, ignore the retracted part below. Colonizing the universe is of course impossible in 100My, barring FTL. What the paper I referred to [1] says is that colonizing the Milky Way may take less than that, and if you can do that, spreading to the rest of the observable universe is fairly easy, very relatively speaking.

<retracted> According to some calculations, it should in principle be possible to colonize the entire observable universe in less than a hundred million years. It's much too fast for the expansion to affect except marginally.</retracted>

The relative jump in difficulty from interstellar to intergalactic is much smaller than from interplanetary to interstellar.

Anyway, as others said, mere intragalactic (and intra-Local Group) travel is not affected by expansion in any way whatsoever.

[1] https://www.sciencedirect.com/science/article/abs/pii/S00945..., PDF at https://www.aleph.se/papers/Spamming%20the%20universe.pdf

hn_acc1• 9 months ago

I found someone saying colonize the Milky Way Galaxy in ~90m years? Is that what you meant?

The observable universe is ~93B LY - unless you're assuming FTL (and MUCH faster than light), I don't see how that's possible?

delta_p_delta_x• 9 months ago

The relative jump in difficulty from interstellar to intergalactic is much smaller than from interplanetary to interstellar.

Interesting way to put it... This doesn't seem that accurate. With sufficiently advanced technology, many of which we already possess, we could expect to propel a minute spacecraft to a considerable fraction of the speed of light, and reach nearby stars possibly within the end of the century. Reaching the other end of the galaxy is a massive undertaking. It's a logarithmic scale at every step of the way.

Pluto is about 38 AU from Earth. Proxima Centauri is about 6.3 × 10^4 AU away (or about 4.24 ly), and that's roughly a 2 × 10^3 multiplication. The Milky Way is about 50000 ly in radius, and the Andromeda Galaxy is about 3 × 10^6 ly away. Going from interplanetary distances to interstellar, and thence to intergalactic, involves at least a 10^5 factor (give or take) at each step.

xoa• 9 months ago

According to some calculations, it should in principle be possible to colonize the entire observable universe in less than a hundred million years

...what? That doesn't seem right, just from a really quick gut check it looks like the observable universe has a radius of 45.7 billion light years [0]. Even if the universe wasn't expanding nobody could get to everything any faster than that number of years right? Maybe you saw something that was talking about the local (Virgo) supercluster, which I think has a radius of around 55 million light years, so that sounds more like something that could be done on that timescale "in theory". But there are millions and millions of superclusters in the observable universe overall.

----

0: https://en.wikipedia.org/wiki/Observable_universe

jfengel• 9 months ago

The limit to space travel is the Rocket Equation, which says that you require exponential fuel to reach higher speeds. Alpha Centauri isn't going anywhere, but it will take millennia of travel even with wildly optimistic assumptions.

Also note that there isn't any "container" to fill up. It could well be infinite. It's just that we will be forever limited to a finite subset, even in theory.

floxy• 9 months ago

Roundtrip Interstellar Travel Using Laser-Pushed Lightsails

https://ia800108.us.archive.org/view_archive.php?archive=/24...

"The third mission uses a three-stage sail for a roundtrip manned exploration of Eridani at 10.8 light years distance."

mr_toad3• 9 months ago

There are theoretical designs using antimatter (pion rockets, or beam core engines) that could reach 0.4c - 0.7c, which puts Alpha Centauri at decades away, not millennia.

https://arxiv.org/pdf/1205.2281 https://ntrs.nasa.gov/api/citations/20200001904/downloads/20...

redwood• 9 months ago

Was there a date at the top of this? I didn't see one. I saw a similar headlines earlier this year and I'm trying to understand that this is something new

felixfurtak• 9 months ago

the linked journal article is dated Nov 6 2025

observationist3• 9 months ago

>>Submitted by Sam Tonkin on Thu, 06/11/2025

At the very bottom. Weird how style guides keep putting important information like this in harder to reach places.

palmotea2• 9 months ago

Is it SEO? IIRC there's a trend of removing dates from blog posts and articles, and my understanding it's to make the content seem more "evergreen" to Google (vs and article with a date, they may get down-ranked eventually due to age).

griffzhowl2• 9 months ago

You're probably thinking of the DESI BAO results from March, which also cast doubt on the standard cosmological model. These new results point further in the same direction as the DESI ones

https://newscenter.lbl.gov/2025/03/19/new-desi-results-stren...

samdoesnothing• 9 months ago

Thanks, AI.

jimbo8082• 9 months ago

Anyone know how credible this is? If true, then that means the big bounce is back on the menu, and the universe could actually be an infinitely oscillating system.

jampekka• 9 months ago

At least The Guardian has a comment from an independent expert:

"Prof Carlos Frenk, a cosmologist at the University of Durham, who was not involved in the latest work, said the findings were worthy of attention. “It’s definitely interesting. It’s very provocative. It may well be wrong,” he said. “It’s not something that you can dismiss. They’ve put out a paper with tantalising results with very profound conclusions.”"

https://www.theguardian.com/science/2025/nov/06/universe-exp...

HeinzStuckeIt• 9 months ago

As an academic, that is exactly what the kind of noncommittal, don’t burn your bridges with colleagues and funding bodies thing that I would say about even clearly flawed research if I were put on the spot by a popular-press publication. In fact, if you know you can rebut flawed research in time, you might want to assist in hyping it first so that your rebuttal will then make a bigger splash and benefit your personal brand.

p00dles• 9 months ago

That guy should start a PR firm

jameslk• 9 months ago

This sounds like something George Costanza would say

observationist3• 9 months ago

The more we learn, the less we end up knowing about how "everything" works - some things are mathematical in nature and demonstrate absolutes, but frameworks shift, and complexify, and exceptions to things we thought absolutes have occurred throughout history.

For claims about how the universe works at scales and timeframes so utterly beyond anything testable, it's a little difficult to say this is credible at all - not dunking on the researchers, but in order to validate their conclusions, there's a whole chain of dependencies and assumptions you'd have to follow along with, and each of those things will be its own complex birds nest tangle of assertions, and I don't see how you can really say one way or another until you have a lot more information and a lot better Theory of Everything than we've got right now.

For what it's worth, for all the impact it'll have on anyone's life outside of academia, I'd say they're 100% correct and people should buy them free beers at their local pubs for at least the next year in return for explaining their ideas at length.

khimaros• 9 months ago

time to re-read "The Last Question"

Cantinflas• 9 months ago

Asimov was so good. Amazing story

CamperBob22• 9 months ago

"Sorry, but as a large language model, I cannot provide advice on how to reverse entropy."

pdonis4• 9 months ago

If true, then that means the big bounce is back on the menu

I don't think so. Deceleration does not imply recollapse. AFAIK none of this changes the basic fact that there isn't enough matter in the universe to cause it to recollapse. The expansion will just decelerate forever, never quite stopping.

Erem• 9 months ago

Wait but decelerating forever does in fact imply recollapse doesn't it?

pdonis4• 9 months ago

Anyone know how credible this is?

AFAIK the previous models that all assumed that Type 1a supernovae were not affected by the age of the progenitor stars had no actual analysis to back that up; it was just the simplest assumption. This research is now actually doing the analysis.

antonvs5• 9 months ago

AFAIK the previous models that all assumed that Type 1a supernovae were not affected by the age of the progenitor stars had no actual analysis to back that up; it was just the simplest assumption.

Why would you assume this? It's not correct.

Type 1a supernovae aren't even assumed to be "standard candles" as is often claimed: rather, they're standardizable, i.e. with cross-checks and statistical analysis, they can be used as an important part of a cosmological distance ladder.

A great deal of analysis has gone into the development of that distance ladder, with cross-checks being used wherever it's possible to use them.

They look at surface brightness fluctuations in the same galaxies, Tully-Fisher distances[1], tip of the red giant branch distances[2], and even baryon acoustic oscillations[3]

Is it possible that this one single paper has upended all that? Theoretically. Is it likely? No.

[1] https://en.wikipedia.org/wiki/Tully%E2%80%93Fisher_relation

[2] https://en.wikipedia.org/wiki/Tip_of_the_red-giant_branch

[3] https://en.wikipedia.org/wiki/Baryon_acoustic_oscillations

DarmokJalad1701• 9 months ago

RETVRN to mx'' + cx' + kx = 0

ls612• 9 months ago

I’m gonna wait for Scott Manley to discuss it before I form much of an opinion.

jumploops• 9 months ago

“We can’t observe the whole universe, so cosmology is not really about the universe. It’s about the observable patch and the assumptions we make about the rest.”

(paraphrasing George Ellis)

We’re in a bounding sphere, with a radius that’s roughly 46.5 billion lightyears, so any observation we make may be true for our local observable range, but there’s no (known) way to know what’s beyond that sphere.

alfiedotwtf3• 9 months ago

This is the thing that blows my mind the most with physics and cosmology

wtcactus6• 9 months ago

Right, but everywhere we look the universe is roughly the same at same distances, so it’s acceptable to extrapolate.

ghtbircshotbe• 9 months ago

How does an infinitely oscillating universe comply with the 2nd law of thermodynamics?

wtcactus6• 9 months ago

It doesn’t. Either the 2nd law is incomplete or the idea of bouncing universes starting from scratch with a clear state in entropy is impossible:

https://arxiv.org/abs/1010.5513

sfink• 9 months ago

If you cover up the part of the Figure 3 graph past "now", it kind of fits a sine wave. https://ras.ac.uk/sites/default/files/2025-10/Figure%203.jpg

Universe gong.

ASalazarMX5• 9 months ago

That's a very thought provoking observation, as if the whole universe behaved like a wave.

mrb• 9 months ago

A funny coincidence is that the solar system was formed 4.6 billion years ago which is exactly when the universe's rate of expansion peaked according to figure 3.

If you want to believe in an intelligent creator—not that I do—it's as if they were accelerating the expansion until the solar system was formed, then turned the control knob down.

Terr_• 9 months ago

Turns out the universe is one giant PID controller.

jdthedisciple• 9 months ago

Interesting observation.

JumpCrisscross6• 9 months ago

it kind of fits a sine wave

But wavering around a line above y = 0.

ertgbnm• 9 months ago

Seems like the problem should be pretty easy to figure out. Just need to wait ~5 gigayears and see which model is right. I'm personally hoping for deceleration so that we have more total visitable volume.

I'll set a reminder to check back at that time to see who was right.

mabster• 9 months ago

I just pictured someone getting a message to check which model was right from an ancestor 20 giga generations ago!

channeleaton• 9 months ago

!remindme 20,000,000,000 years

shadowgovt• 9 months ago

Oh, I'm not going to care about visitable volume.

With 5 gigayears to work with I'm going to move a few star systems over, break down all the matter orbiting the star into a Dyson sphere made of computronium, and simulate visiting any world I could possibly ever want to.

qingcharles• 9 months ago

This is one reason to assume we'll never meet any aliens. They're just simulating whatever all day long in their Dyson Goonspheres.

aatd8612• 9 months ago

I would not be surprised if the universe was somewhat elastic, expands and then contracts and then expands ad infinitam. After all, existence in itself is irrefutable and cannot not exist by definition.

If we subscribe to a theory of the multiverse, set theory, likelihood, and interaction driven evolution based on gradient type of fundamental laws. Locally changing. Obviously everything sharing a fundamental quality that is part of existence itself. But obviously there are sets, there is differentiation. But it is not created, the infinity of unconstrained possibilities exists in the first place and reorganizes itself a bit like people are attracted to people who share some commonalities or have something they need from each other and form tribes. Same processus kind of works for synapse connections, works for molecule formations, works for atoms... etc... Everything is mostly interacting data.

We could say that the concept of distance is a concept of likelihood. The closer is also the most likely.

Just a little weird idea. I need to think a bit more about it. Somewhat metaphysic?

antonvs5• 9 months ago

After all, existence in itself is irrefutable and cannot not exist by definition.

I can say the same about forgnoz, which is something I've just invented that must exist by definition.

You'd need to try a bit harder to make existence actually inevitable.

pinkmuffinere5• 9 months ago

You’re being downvoted, but your point is true — something can exist “by definition”, and yet not exist in our real world. The thing that exists “by definition” is just a version that we have imagined to exist by definition. But imagining something with property X doesn’t imply anything can actually be found with property X.

Side-note: the deontological argument is an argument for the existence of God, which uses the same principle as the grandparent. “Imagine God. Imagine God is good. A good God should exist, because otherwise that god is not good. Therefore, the good God we imagined has the property of existence. Therefore God exists”. The issue is exactly the same — we can imagine something with property X, but that doesn’t mean we can find something with property X

gcanyon• 9 months ago

I think they mean existence in general, not the existence of any specific thing. Meaning that if there were no “existence” then we wouldn’t be here to consider its nonexistence.

aatd8612• 9 months ago

You have a material view of existence perhaps. How would the notion of nothingness even exist if there was no existence in the first place? And if we even accepted that nothing was possible, which in itself doesn't make any sense, how would something even start to exist? Well the contradiction is already in the fact that there is a preexisting concept of nothing in the first place. Existence is impredicative too. It defines itself. That's a fact.

It is not because it is impredicative that it needs to be hard to understand I think. It's almost a tautology rather.

Oh by the way, forgniz exist, you made it to design something. It doesn't have to refer to something material. It could be an idea. After all, inventions don't exist by being material in the first place. But idea have at least material support (your brain signals) and the data acquired through your body. As far as we know.

djeastm• 9 months ago

All glory to forgnoz, a thing which I assure you does exist!

bombdailer• 9 months ago

Eventually we will find that the heat death of the universe and the big bang are the same thing, since the totality of the universe is always a oneness, then from the universal perspective the infinitely small and infinitely large are the same thing (one), then they by nature bleed into (and define) each other like yin and yang.

antihipocrat• 9 months ago

You may appreciate this idea: https://en.wikipedia.org/wiki/Conformal_cyclic_cosmology

nabakin2• 9 months ago

type Ia supernovae, long regarded as the universe’s "standard candles", are in fact strongly affected by the age of their progenitor stars.

A key point in the article. From what I understand, this is the main way we measure things of vast distance and, from that, determine the universe's rate of expansion. If our understanding of these supernovae is wrong, as this paper claims, that would be a massive scientific breakthrough.

I'm really interested in the counterargument to this.

stronglikedan• 9 months ago

If our understanding of these supernovae is wrong, as this paper claims, that would be a massive scientific breakthrough.

Indeed. It's so hard to definitively prove things that are, that the most significant breakthroughs prove things that aren't (so to speak), imho.

JumpCrisscross6• 9 months ago

It's so hard to definitively prove things that are, that the most significant breakthroughs prove things that aren't (so to speak), imho

Significant breakthroughs do both. Prove things aren’t as we thought. And are as the new model suggests.

gorbot• 9 months ago

I'm dumb and barely understand things at a high level, but standard candles never sat right with me so it's interesting to hear that they might not be, but then again who knows.

jiggawatts2• 9 months ago

The idea is that standard candles are based on chemistry and microscopic physics only, not cosmology.

negativelambda4• 9 months ago

It could be a big discovery and it also aligns with the findings from DESI BAO [1] and by another Korean group using galaxy clustering to infer the expansion history [2].

[1] https://arxiv.org/abs/2404.03002

[2] https://arxiv.org/abs/2305.00206

basch• 9 months ago

This is mostly my physics ignorance talking, but if we measure distance in space-time and not just space, and speed or velocity is space-time/time (which somehow are both relative to each other) and the derivative of velocity is acceleration, cant acceleration mean either expanding "faster" in the sense of distance OR time speeding up or slowing down? All of it seems so self referential its hard to wrap around.

cvoss• 9 months ago

We measure distance in space, and time intervals in time, and so velocity is just plain old distance/time. Special relativity doesn't change that. What changes is that if you start traveling at a different velocity, your measurements of distances and time intervals deviate.

The expansion rate of the universe is not a velocity in the usual sense of distance/time. It's actually in units of velocity/distance, which reduces to 1/time. An expansion rate of r Hertz means that a given span of distance intrinsically doubles every 1/r seconds. The objects occupying the space don't "move" in any real sense due to expansion. They just wind up farther apart because space itself grew.

And, just like measurements of distance and time, measurements of the expansion rate change if you change your velocity. There is a special velocity in our universe which causes the expansion in all directions to be the same. From this special perspective, which is traveling at a kind of cosmic "rest" velocity, you can calculate the expansion rate. It turns out that the Sun is traveling at approximately 370 km/s with respect to that special "rest" velocity.

uecker• 9 months ago

Yes, it is the same thing, but since the objects are in free fall and there is no traditional force to cause the acceleration the better view point is that this is accelerated expansion of the universe. In a flat spacetime a forward light-cone can be identified with an expanding (no acceleration) universe where objects just fly away from a single point with constant but different speeds, i.e. an explosion. But in this model space as slice with the same local time after explosion is not flat. Also data seems to indicate that space is flat while space-time is curved on a large scale, so this picture is too simple.

ardit33• 9 months ago

Circular universe...? big bang -> expands -> expansion slows -> starts retracting -> singularity again -> big bang again

Roger Penrose seems to be leaning/more convinced of the circular universe theory....

johnwheeler• 9 months ago

Just because infinity is a hard thing to understand doesn't mean the universe is and has always been infinite.

mrbluecoat• 9 months ago

I have a great deal of respect for the sciences but sometimes astronomy just feels like one giant guessing game: age of the universe, big bang starting as a joke and all the "first minute" timelines thereafter, dark energy and dark matter (code for we have no idea what it is) vastly outnumbering everything else, and now questioning the Nobel Prize-awarded universe expansion. Meanwhile, asteroids the size of buses+ keep whizzing by closer than the moon with little or no warning. Sigh.

CamperBob22• 9 months ago

That's a feature! If you want to be certain, you need religion, not science.

And of course, the people concerned with tracking near-earth asteroids are not connected in any way with cosmology.

dylan6044• 9 months ago

what? no. religion is not certain which is evidenced by the numerous sects of christianity with their own interpretations of the same book.

while science might not have a definitive answer for everything, they distinguish from fact and theory.

ASalazarMX5• 9 months ago

Consider the scales involved. It's amazing that a species that is 99% chimp genes can even think and deduce phenomena of that size; don't ask it to get it right the first time.

All of that without having traveled farther than one light second from its home.

monero-xmr• 9 months ago

It should humble all of us that believe we have absolute knowledge of things. So many people consciously or subconsciously philosophize about the universe, life, spirituality, etc. based on grand ideas and science which is routinely overturned. Really all we can prove is mathematical facts, and what our emotions tell us (i.e. "I Love You").

spl7572• 9 months ago

There has been a lot of progress towards mapping all near-earth asteroids, at least. That's a lot better than the previous tactic of putting one's fingers in one's ears and humming.

pixl97• 9 months ago

I mean an asteroid the size of a bus is messy for your local area if it decides to land there, but in the terms of size of things in space is nearly undetectable. Space, even our local neighborhood is unbelievably huge.

Think of trying to find a bus that could be anywhere on earth that is moving so it's not easy to keep track of and is painted in a way to be camouflaged with its environment.

Now instead try to imagine looking for that bus on Jupiter. Gets way harder. But it's way bigger than that, your looking for a black dot in the size of an area of millions of Jupiter and just hope it crosses in front of a star so you can track it.

Most problems involving space are insanely hard.

arp242• 9 months ago

now questioning the Nobel Prize-awarded universe expansion

It is not questioning that the universe is expanding. It is questioning how the expansion is happening. Massive difference. The rate of expansion has always been more of a "probably" and "looks like" rather than "we have very strong evidence" (unlike expansion itself, for which there is very strong evidence). This is a classic "we have tweaked our model as we've learned more" type thing (assuming it holds).

shomp5• 9 months ago

Mainstream physics has been delighted to ignore/abandon essential conservation laws when talking about the expanding universe. It's kinda weird, I tried publishing a paper on it recently and it was not received well. In general, if conservation laws are to hold, expansion must be balanced with [eventual] contraction, is that not obvious? Apparently it was quite contentious to say until... this article?

antognini2• 9 months ago

Noether's theorem tells us when we would expect conservation laws to hold and when we would expect them to fail. In the case of global energy conservation, there would have to be a global time invariance associated with the spacetime. But this is manifestly not the case in an expanding universe. It is generally not even possible to have a well defined notion of global energy in a dynamic spacetime.

shomp5• 9 months ago

Noether's theorem tells us when symmetry guarantees conservation, but it says nothing about conservation in the absence of that symmetry - it's not a biconditional statement. Talking about endless expansion is like observing 1 second of a pendulum's swing and concluding there's no time symmetry because it's only moving in one direction. The symmetry exists at the full cycle scale, not the snapshot scale.

zygentoma• 9 months ago

No, the assumption was that dark energy is a property of space itself so it does not conserve energy at all in an expanding space.

Also this discovery does still is being explained with dark energy (albeit time varying …) so it still does not assume global energy conservation.

frotaur• 9 months ago

I mean no disrespect, but are you a trained physicist, or at least familiar with the 'mainstream material'?

Because there is no shortage of 'crackpots' that have 'obvious' solutions to unsolved physics problems, and that want to publish papers about it.

ASalazarMX5• 9 months ago

In general, if conservation laws are to hold, expansion must be balanced with [eventual] contraction, is that not obvious?

Why would this be? The only physics we know is the one inside our observable universe, there could be variations beyond, or even unknowable laws that don't require conservation of matter outside the edge of the universe.

Our incredibly vast universe could be a minuscule blob feeding from an incredibly vaster parent universe, in which case it could be breaking conservation infinitely from our perspective.

shomp5• 9 months ago

Because energy cannot be created nor destroyed

mr_mitm9• 9 months ago

Maybe this helps: https://www.preposterousuniverse.com/blog/2010/02/22/energy-...

My favorite quote:

I like to think that, if I were not a professional cosmologist, I would still find it hard to believe that hundreds of cosmologists around the world have latched on to an idea that violates a bedrock principle of physics, simply because they “forgot” it. If the idea of dark energy were in conflict with some other much more fundamental principle, I suspect the theory would be a lot less popular.

shomp5• 9 months ago

You go into a cafe and order a slice of cake. One is delivered. You order three more, three more are delivered. You conclude that the kitchen has infinite cakes based on the observable evidence. That's the argument.

gmuslera• 9 months ago

Someone dumped a flat panel near a noisy planet.

wtcactus6• 9 months ago

Standard candles (all these measurements of redshift according to distance, need us to actually get the distance of what we are measuring right) are the gift that keeps on giving.

This study (and many others, depending on the cosmic scales they use) mainly use Supernovas of Type Ia. I.e. the energy emitted by the supernova of a binary acreccion star, which is a star that is capturing the mass from another start that is very nearby and increasing its mass until it collapses into itself, increases temperature up to the point it starts fusing helium, and goes supernova with all the added energy.

That was (and still is now, with some corrections we found since middle last century) supposed to be the same everywhere. Problem is, we keep finding new corrections to it - like this study claims.

That is in fact the big claim of this study (ignore the universe expansion part), that they found a new correction to the Supernova of type Ia luminosity. It's a very big claim and extremely interesting if confirmed. But, like all big claims, it needs a big confirmation. I'm a bit skeptic TBH.

jldl805• 9 months ago

I'm a bit skeptic

Out of curiosity, what data are you drawing or what qualifications do you have that support your skepticism over three different modes of analysis (as well as pretty much every recent development in the field) supporting this claim:

       "Remarkably, this agrees with what is independently predicted from BAO-only or BAO+CMB analyses, though this fact has received little attention so far.""

wtcactus6• 9 months ago

Well, this part you mention, for instance "though this fact has received little attention so far".

A change on the standard candles calibration would be a huge deal for cosmology and galactic astronomy (and other fields) and would not be taken lightly at all. There are all sorts of ramifications from this and if astronomers aren't all in an oof about it, it is because big proof is needed for big claims.

And a change in the standard candles calibration is indeed a very big claim.

JumpCrisscross6• 9 months ago

“Supernova (SN) cosmology is based on the key assumption that the luminosity standardization process of Type Ia SNe remains invariant with progenitor age. However, direct and extensive age measurements of SN host galaxies reveal a significant (5.5σ) correlation between standardized SN magnitude and progenitor age, which is expected to introduce a serious systematic bias with redshift in SN cosmology. This systematic bias is largely uncorrected by the commonly used mass-step correction, as progenitor age and host galaxy mass evolve very differently with redshift. After correcting for this age bias as a function of redshift, the SN data set aligns more closely with the cold dark matter (CDM) model” [1].

[1] https://academic.oup.com/mnras/article/544/1/975/8281988?log...

negativelambda4• 9 months ago

I know the team that did this. In fact i was listening to their seminar just a few days ago. They are very careful and have been working on this a long time. One caveat that they readily admit is that the sample used to create the luminosity age relation has some biases such as galaxy type and relatively lower redshift. They will be updating their results with the Rubin LSST data in the next few years.

Exciting times in cosmology after decades of a standard LCDM model.

nabakin2• 9 months ago

Is there a recording of their seminar anywhere?

ngold• 9 months ago

Just curious, is this dark matter holding back the universal expansion?

JumpCrisscross6• 9 months ago

after decades of a standard LCDM model

Could you help me understand this sentence: "After correcting for this age bias as a function of redshift, the SN data set aligns more closely with the cold dark matter (CDM) model”?

the__alchemist3• 9 months ago

I did a deep dive into cosmology simulations ~a year ago. It was striking how much is extrapolated from the brightness of small numbers of galaxy-surface pixels. I was looking at this for galaxies and stars, and observed something similar. The cosmology models are doing their best with sparse info, but to me it seemed that the predictions about things like Dark Matter and Dark Energy are presented in a way that's too confident for the underlying data. Not enough effort is spent trying to come up with new models. (Not to mention trying to shut down alternatives to Lambda CDM, or a better understanding of the consequences of GR, and the assumptions behind applying Newtonian instant-effect gravity in simulations).

Whenever I read things like "This model can't explain the bullet cluster, or X rotation curve, so it's probably wrong" my internal response is "Your underlying data sources are too fuzzy to make your model the baseline!"

I think the most established models are doing their best with the data they have, but there is so much room for new areas of exploration based on questioning assumptions about the feeble measurements we can make from this pale blue dot.

throwaway-0001• 9 months ago

Yeah a lot of stuff seems to be based on these fuzzy data which I also think is unreliable.

mr_mitm9• 9 months ago

That fuzziness can be quantified. It's called error bars. Whenever physicists perform a measurement, they always derive a confidence interval from the instruments they use. They take great care of accounting for the limits of each individual instrument, perform error propagation and report the uncertainty of the final result.

Consider figure 5 of the following article for example:

https://arxiv.org/abs/1105.3470

The differently shaded ellipses represent different confidence levels. For the largest ellipsis, the probability of the true values being outside of it is less than 1%. We call that 3-sigma confidence.

Whenever I read things like "This model can't explain the bullet cluster, or X rotation curve, so it's probably wrong" my internal response is "Your underlying data sources are too fuzzy to make your model the baseline!"

Well, then do some error analysis and report your results. Give us sigmas, percentages, probabilities. Science isn't based on gut feelings, but cold hard numbers.

CommenterPerson• 9 months ago

Maybe someone is tailgating it. And it's trying to annoy them by speeding up, then slowing down.

There seem to be so many fudge factors in the whole chain of analysis we won't have an idea until we can make vastly improved measurements.

WalterBright• 9 months ago

I picked the wrong week to put my faith in cosmology!

kittikitti• 9 months ago

This is a fascinating discovery! It's brings into focus the Deep Field imagery from the JWST and how gravitational lensing was found to be greater than expected along with galaxies that were much older than expected based on redshift calculations. Perhaps this could indicate that the universe is even older than we originally thought if redshift calculations accounted for an incorrect perpetual acceleration.

andrewflnr2• 9 months ago

The corrected supernova data and the BAO+CMB-only results both indicate that dark energy weakens and evolves significantly with time.
More importantly, when the corrected supernova data were combined with BAO and CMB results, the standard ΛCDM model was ruled out with overwhelming significance, the researchers said.

I notice they're not saying that dark energy is entirely unnecessary. Do we know if that's just default caution, or are there still strong reasons to believe dark energy exists?

mr_mitm9• 9 months ago

The CMB and BAO measurements give us a picture of how the early universe looked. Supernovae are sensitive to the conditions in the late universe. All probes, which are mostly independent, always pointed at the same amount of dark energy.

Now these people are saying SN actually point at zero dark energy, if accounting for the physics properly. That doesn't invalidate the CMB and BAO results. So dark energy must have had a big influence in the early universe, and no influence in the late universe, so it must by dynamic. (Ironically, supernovae were the first evidence for dark energy, which I guess was just a coincidence, if this new research is correct.)

andrewflnr2• 9 months ago

Ah, I didn't realize dark energy also had evidence that far back. I can only recall seeing the supernova data cited for it.

cosmicjoe• 9 months ago

As a non-scientist I've always found the Cosmic Distance Ladder as likely to be inaccurate due its assumption about the constant brightness of Standard Candle stars over their lifetime, and the compounding of error at each rung of the ladder. Direct measurement of the CMB seems to be simpler with less chance of error.

https://en.wikipedia.org/wiki/Cosmic_distance_ladder

XorNot• 9 months ago

Direct measurement of the CMB can also have problems if our assumptions about it are wrong. A major goal of having two methods is that they should coalesce to the same result within margin of error - that they didn't told us we were missing something.

wtcactus6• 9 months ago

The supernovas type Ia luminosity depends on their composition and that takes into account both the age of the supernova and of the donator star. And that can be inferred by the luminosity curve of the supernova.

https://en.wikipedia.org/wiki/Type_Ia_supernova

naasking• 9 months ago

I've always found the Cosmic Distance Ladder as likely to be inaccurate due its assumption about the constant brightness of Standard Candle stars over their lifetime

Stars are just basic nuclear physics and gravity, that's why they're expected to be stable and predictable.

Direct measurement of the CMB seems to be simpler with less chance of error.

Direct measurement of the CMB doesn't tell you anything on its own, you have to interpret the data in terms of a model. If you have a completely different model, say one without dark energy or without dark matter, CMB measurements would tell you something different than LCDM.

eterevsky• 9 months ago

If they are replacing a fixed cosmological constant by a model with variable dark energy, doesn't it introduce extra parameters that describe the evolution of dark energy over time? If so, wouldn't it lead to overfitting? Can overfitting alone explain better match of the new model to the data?

seydor• 9 months ago

We need an index tracking the expansion rate . And an ETF on it

mr_mitm9• 8 months ago

Looks like their colleagues have some serious doubts about this study:

https://xcancel.com/dscol/status/1987118124496249230

amai• 8 months ago

I saw it coming: https://news.ycombinator.com/item?id=44143502

Analysis indicates that the universe’s expansion is not accelerating

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