Supernovae Evidence for Foundational Change to Cosmological Models

https://arxiv.org/abs/2412.15143

by jandrewrogers • 2 years ago

107 74 2 years ago

arxiv.org

api3• 2 years ago

Good wikipedia article on these types of cosmologies including timescape cosmology:

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

numpy-thagoras2• 2 years ago

Many advancements in science have happened because we stopped for a second, and then looked to generalize our assumptions. Consider,

e.g.

Euclidean geometry -> non-euclidean geometry; Classical analysis -> nonstandard analysis; Linearity -> non-linearity; Homogeneity -> inhomogeneity; Flat spacetime -> curved spacetime; Singular probabilities -> superposition.

All of these were loosening of certain criteria that opened up many possibilities. It is certainly erroneous to assume we must, by necessity, have a homogeneous cosmology.

molticrystal• 2 years ago

This paper argues that the Timescape model [0] provides a better fit than the cold dark matter model when examining Type Ia Supernovae. According to the Timescape model, clocks run faster in voids where the gravitational field is less, and significant differences exist between a galaxy floating in a void and one like the Milky Way Galaxy. The Timescape model suggests that other models, which fail to account for these differences, lead to less accurate calculations and less plausible solutions.

[0] https://en.wikipedia.org/wiki/Inhomogeneous_cosmology?useski...

vlovich1232• 2 years ago

If clocks run slower in the presence of gravity, wouldn’t it stand to reason it runs more quickly in a void where there’s less gravity? Or is the model saying that clocks run even faster in a void than Einstein’s theory predicts?

vecter• 2 years ago

Clocks run at "normal" speed (i.e. "1x" speed) in the absence of a gravitational field. The stronger the gravity, the slower they run (i.e. less than "1x" speed).

brotchie• 2 years ago

Pet theory is that our universe is run on some external computational substrate. A lot of the strangeness we see in quantum physics are side effects of how that computation is executed efficiently.

The inability to reconcile quantum field theory and general relativity is the that gravity is a fundamentally different thing to matter: matter is an information system that's run to execute the laws of physics, gravity is a side effect of the underlying architecture being parallelized across many compute nodes.

The speed of light limitation is the side-effect of it taking a finite time for information to propagate in the underlying computational substrate.

The top-level calculation the universe is running is constantly trying to balance computation efficiently among the compute nodes in the substrate: e.g. the universe is trying to maintain a constant complexity density across all compute nodes.

Black holes act as complexity sinks, effectively "garbage collection." The matter than falls below the event horizon is effectively removed from the computation needs of the substrate. The cosmological constant can be explained by more compute power being available as more and more matter is consumed by black holes.

This can be introduced into GR by adding a new scalar field whose distribution encodes "complexity density." e.g. some metric of complexity like counting micro-states, etc. This scalar field attempts to remain spatially uniform in order to best "smooth" computation across the computational substrate. If you apply this to a galaxy with a large central supermassive black hole, you end up with almost a point sink of complexity at the center, then a large area of high complexity in the accretion disk, and then a gradient of complexity away towards the edges of the galaxy. That is, the scalar field has strong gradients along the radius of the galaxy, and this gives rise to varying gravitational effects over the radius (very MOND-like).

Some back of the napkin calculations show that adding this complexity density scalar field to GR does replicate observed rotation curves of galaxies. Would love to formalize this and run some numerical simulations.

Would hope that fitting the free parameters of GR with this complexity density scalar field would yield some testable predictions that differ from current naive assumptions around dark matter and dark energy.

cma• 2 years ago

There's a Danny Hillis talk on this but I couldn't find it.

fsloth• 2 years ago

”External computation susbtrate” is a useful idea if it leads to falsifiable theories. As a ”theory of everything” it sucks because it’s clearly not motivated by any specific maths or observations, but by the human need to map nature into some comprehensible analogue. Ie. taking some simpler subset of nature and trying to pretend the rest of it is like that as well. Usually nature so far has become more incomprehensible the deeper we’ve looked at it.

Newtonian mechanics & mechanical clocks being hottest precision technique led scientists at the time to viewing nature as a clockwork. Now we have computers, we think ”nature is like computers” because it’s an appealing analogue.

But it’s a false analogue imo. Just like clocks are a thing enabled by nature (a subset, in every meaning of the word) similarly computers are a subset of nature. So yes, nature can think (with human brains) and nature can run computations (with cpu:s impregnated with programs) but that also is just a subset of nature.

Now: games of the mind and helpfull analogues rock. And asking ”how is nature analogous to a turing machine” is interesting for sure. But just because a game is fun or analogue appealing, should not one let forget in the philosophical sense that one is playing only with a limited subset of a thing.

T-A• 2 years ago

a better fit than the cold dark matter model

than the Lambda Cold Dark Matter model.

Lambda, i.e. the cosmological constant, a.k.a. dark energy, is what they do away with, not dark matter.

SpaceManNabs4• 2 years ago

Thanks for saving me time in dismissing this paper lol. Any time somebody wants to get rid of dark energy, i run into some garbage. Reminds me of the mond nuts

Just reading the rest of the comment section is enough to help me verify that.

For some reason, hackernews always gets kooky when it comes to this stuff.

ajross• 2 years ago

Webb is turning out to be one of the most impactful pieces of scientific apparatus of the last century or so. Not that it took all the relevant data, but that it was the final thing that broke open all the doors being held shut. We're watching a Kuhnian paradigm shift in astronomy unfold in real time.

epicureanideal• 2 years ago

I’ll be happy to see all the dark matter, dark energy stuff explained away.

SpaceManNabs4• 2 years ago

We have a century's worth of evidence for dark matter and about 20 years worth of evidence for dark energy.

Once an alternative theory stands up to scrutiny, maybe we shouldnt a priori dismiss things we dont understand?

PaulHoule2• 2 years ago

There's been a general problem in astronomy for a long time that it seems like there just hasn't been enough time for objects to develop

The oldest version of this I know of can be seen in a diagram of ways that large black holes could possibly form in this book

https://en.wikipedia.org/wiki/Gravitation_(book)

which shows as early in 1973 people knew they had no idea how supermassive black holes could possibly form. Lately these problems have intensified because Webb seems to see that all sorts of developments seemed to happen a lot more quickly than they should of which leaves one wondering if the first billion years were really the first ten billion years. Could Timescape explain that?

api3• 2 years ago

AFAIK one possible explanation for the black hole issues could be primordial black holes, which are also a candidate for at least a component of dark matter.

PaulHoule2• 2 years ago

Yep. There is the idea that you could get little primordial black holes (that maybe weigh as much as a mountain and could be evaporating now) and the idea that you could get huge primordial black holes. Also the occasional strange idea that the universe might be cyclic (not too fashionable but can fill the hole left by inflation) and that black holes can survive the crunch.

glompers2• 2 years ago

The Royal Astronomical Society's piece [1] on this study mentioned,

"The model suggests that a clock in the Milky Way would be about 35 per cent slower than the same one at an average position in large cosmic voids, meaning billions more years would have passed in voids."

If the gases pulled in toward a black hole were experiencing only tens-of-millions-of-years of time during a full billion years (as compared with the billion that elapsed on a clock experiencing a lower-gravity "universal average" condition of gravitation and of time), then does that mean...

that those magnetic fields and gases must emit to us any greater or smaller intensity of radiation vs. the amount that they would emit if they had been rubbing together within our own rate of time?

[1] https://ras.ac.uk/news-and-press/research-highlights/dark-en...

raattgift6• 2 years ago

It's just substituting gravitational redshift for cosmological redshift; one can also substitute kinematic redshift for cosmological redshift. The redder bits are running slower, which one sees from spectral lines that are reliably generated by quantum processes. There are reasons for preferring cosmological redshift, and in particular it's because whatever is going on with the distribution and motion of galaxies, it's doing an excellent excellent imitation of a big (~70%) stable energy-density smoothly at every point.

The reverse of your question is interesting: a quasar host galaxy or a Seyfert galaxy isolated deep within a supervoid should be much less redshifted than similar cluster and filament galaxies (one would have to "weigh" the galaxies, and so would lean on angle-diameter-distance and other geometrical relations, relative redshift of hydrogen-alpha (and millimeter CO and 21cm neutral hydrogen spin-flip etc.) at the galactic limbs and in globular clusters). The side-effect of Timescapes running clocks much slower in filaments is that they run much faster in supervoids. Many known voids have small numbers of galaxies in them (the emptiest of voids have something like a tenth of the radio-generating matter compared to large galaxy clusters, so they're nothing like "empty", which in turn drives the focus to the evolution of Timescape's "void fraction") so looking for faster-running galaxies in voids is not an impossible observational test.

Going forward again, the late-time Integrated Sachs-Wolfe structure would be anisotropic, with strong nonlinear differences between ISW radiation through filaments (because of the significant gravitational backreaction central to Timescapes) and ISW radiation through voids. Coarsely, that's not what we see (nonlinear effects are subdominant) and is an obvious target of study of the Timescapes proponents.

https://en.wikipedia.org/wiki/Sachs%E2%80%93Wolfe_effect#Lat...

mutagen• 2 years ago

So Vernor Vinge was on to something[0] with his 'Zones of Thought'...

[0] https://en.wikipedia.org/wiki/A_Fire_Upon_the_Deep#Setting

shepardrtc2• 2 years ago

Well his idea was that the laws of physics actually change depending on the distance from the galactic center. Far enough out, information can be transferred faster than the speed of light. Too close and life stops working. Which honestly seems much more fun than gravity slowing things down a bit.

scrubs2• 2 years ago

I'm surprised cosmology hasn't accounted for differences in clocks given how central GR is to astronomy. Granted I am no expert, but adding this dynamic was, until today, a bridge too far, or thought to average out somehow and not be pertinent

itishappy• 2 years ago

Huh?

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

codethief4• 2 years ago

cosmology hasn't accounted for differences in clocks given how central GR is to astronomy

Of course it has. Yes, LCDM's FLRW metric, by its defining assumption of spatial homogeneity, doesn't allow the metric (let alone the speed of clocks) to vary spatially. However, it is very common to do perturbation theory on top of the FLRW metric to account for density fluctuations. Besides, there are also models like LTB (Lemaître-Tolman-Bondi) which give up on homogeneity at the non-perturbative level (while still preserving isotropy, though).

All in all, the idea that local voids could explain away the Lambda in LCDM is anything but new. It's just that the OP's timescape approach is the first one that seems to produce promising results. (Disclaimer: I merely skimmed the paper.)

scrubs2• 2 years ago

Point taken. Thanks.

eximius• 2 years ago

Is anyone familiar with the (ln B > x) notation being used? What is this value being referenced?

the8472• 2 years ago

See section 2 of the paper.

tigerlily2• 2 years ago

This is the opening salvo in cosmology's Battle of Trafalgar. Dave Wiltshire has lined up a set piece 20 years in the making that is going to obliterate both lambda CDM and MOND and all the rest.

dcsommer• 2 years ago

Sounds fascinating. Anywhere I can read more about the build-up to this moment? Has David Wiltshire written about this?

tigerlily2• 2 years ago

He's been quietly publishing over the years, and waiting for instruments like Webb and Euclid to return data. Here's an up to date list:

https://inspirehep.net/literature?sort=mostrecent&size=25&pa....

Another list on his homepage, but not up to date:

http://www2.phys.canterbury.ac.nz/~dlw24/dlw-pub.html

I think the most exciting thing is probably the team he's got together now, and some of the computational stuff his associates have going at the moment.

jandrewrogers• 2 years ago

An implication is that you would expect ancient advanced civilizations to form in the voids.

largbae• 2 years ago

Wouldn't such a civilization slow down as it gathers?

haxiomic2• 2 years ago

A very compelling argument that the need for dark matter may be an artifact of a in incorrect assumption about the universe; the extent to which it is homogeneous and large scale structures can be ignored in calculations

Dr Ridden, an author of this paper, has a great explainer video: https://www.youtube.com/watch?v=YhlPDvAdSMw

haxiomic2• 2 years ago

Typo: Dark Energy*, not Dark Matter

idw• 2 years ago

"Cosmological models are built on a simple, century-old idea – but new observations demand a radical rethink" (2023) < by David Wiltshire, one of the authors of this paper, aimed at non-physicists

https://theconversation.com/cosmological-models-are-built-on...

astro-cosmo-q3• 2 years ago

As someone who works decently close to, but not in, this area, I am surprised to see this on the front page of HN. The paper authors do not use correct statistical practices (e.g. H_0 cannot be fixed “as a nuisance parameter” to remove a degeneracy with another parameter - nuisance parameters must be marginalized over!) and the authors fail to account for several effects in their model (e.g. stretch/color factors for each supernova must be varied) which are known to be necessary for robust inference of cosmological parameters from supernovae data.

This is an honest question since I have seen this phenomenon occur a few times now with cosmology/astrophysics papers on HN: How did the original poster find this? And why has it gotten such interest/points? I sincerely hope it is simply a well-intentioned interest in our universe (which it greatly heartens me to see!) combined with naïveté (not meant pejoratively, just to refer to lacking context) wrt the technical nature of this work, but I am interested to hear your thoughts.

throwaway81523• 2 years ago

It has been circulating on the intertubes. I saw it on a more general interest site earlier today, before seeing it on HN just now.

light_hue_1• 2 years ago

Funny. This is exactly how I feel about most of the AI/ML papers posted here. Very strange selection of pretty sketchy papers.

codethief4• 2 years ago

https://en.m.wikipedia.org/wiki/Michael_Crichton#Gell-Mann_a...

andrewflnr2• 2 years ago

well-intentioned interest in our universe

I mean, probably. Though HN does have a taste for fringe theories, which might color your interpretation of "well-intentioned". And most of us aren't really qualified to assess the statistical rigor of astrophysics papers, myself certainly included.

necubi• 2 years ago

I saw it floating around Twitter with some expansive commentary "This could be an incredible revolution in Cosmology. The Dark Energy model of the universe, which won a Nobel Prize in 2011, may be completely wrong.", etc.

For whatever reason, engineers really hate dark energy and will glom onto any fringe theory that appears to disprove it. Not to psychoanalyze too much, but it seems to be a topic where non-experts get to feel like they're smarter than those PhD cosmologists because they watched a Sabine Hossenfelder video.

See literally any thread about dark energy (or dark matter, which elicits similar reactions) on HN.

marcosdumay• 2 years ago

That is probably the same phenomenon that makes the most sketchy papers on nutrition science to appear on popular news.

Sketchy things have the most interesting results. People that want entertaining news select for interesting results, and the sketchy ones get over-represented.

mmooss2• 2 years ago

why has it gotten such interest/points?

For context: The top comment on most HN stories, especially research, tries to completely discredit the OP, often by finding flaws, and especially in statistical methods.

Everything has flaws. I think people are interested in what is valuable and possible. Shakespeare's work has many flaws, but that's not what people focus on.

Also, while you aren't responsible for all those other top comments, why should I believe yours? Usually I just ignore these comments (but I appreciate your curiosity).

JoeAltmaier• 2 years ago

Failures in statistical methods are not covered by 'everything has flaws'. Those are fatal, existential flaws. Something that is not likely true (though it is erroneously presented as likely of being true) are likely false.

SpaceManNabs4• 2 years ago

I have mentioned this in two comments but HN gets really kooky when it comes to cosmology. A few years ago i saw a barrage of highly upvoted papers on MOND and de Broglie stuff.

It really made me wonder what else gets posted here that is patently absurd but i dont have the prerequisite knowledge to filter it.

codethief4• 2 years ago

I can't speak to the technical nature of the work, as I don't work in the field, but the last-named author, likely the advisor, seems to be a respectable researcher.

I have served on the committee of the International Society on General Relativity and Gravitation 2017-2022, and am a past President of the Australasian Society for General Relativity and Gravitation and a past President of the New Zealand Institute of Physics. I served 8 years on the editorial board of Classical and Quantum Gravity, 2012-2019.

http://www2.phys.canterbury.ac.nz/~dlw24/

So while your criticism may well be justified, you make it sound like this is a fringe paper, which I don't think is the case. So instead of opening a meta discussion about what physics papers get posted & upvoted on HN and why (which is hardly novel), I'd be much more interested in how big the issues you're mentioning are and whether the results of the paper could be salvageable. I at least do think that Wiltshire's research is interesting and he has made good points[0] about the challenges of coarse-graining spacetime structures and where & why the underlying assumptions of LCDM might fail to hold.

[0]: See e.g. the lecture notes on https://arxiv.org/abs/1311.3787

astro-cosmo-q3• 2 years ago

I am certainly not suggesting anything negative about the character or reputation of the authors of the work. I think that work on alternatives to the accepted concordance cosmology model (LCDM) should definitely be explored, and David Wiltshire et al. should pursue this if they deem it promising.

As an aside: You may not find this compelling, which is understandable, but I will note that the vast majority of cosmologists (very conservatively 95%) do not question the FLRW aspect of the cosmological concordance model (which is what the paper here does away with in the alternative timescape cosmology), even if they question other parts of it (i.e. by considering dynamical dark energy, neutrino interactions, etc.). I agree that timescape is an interesting idea, but it seems like only a few people have been working on it for over a decade now - unless you have a very (and I think unfairly) dim view of professional cosmologists, if there was a strong case to be made for the timescape model based in data, the greater community would have adopted it by now.

Finally, and independent of the sociological points above, an answer to your question about specifics aside from the types of statistical/modeling issues of the type I mentioned above. Again this is not exactly my area and I have not done the analysis myself, so I will refrain from strong opinions. However, my immediate reaction to this is that it is easy to fit one particular dataset (in this case part of the Pantheon+ supernovae sample) with a more complicated model than LCDM, but often these types of models fail when other cosmological datasets are included. Considering such joint constraints with multiple datasets is not an “extra ask” of alternatives to LCDM - to be taken seriously any alternative model should hold up in a joint analysis of precision cosmological datasets (see, for example, the tests of a more seriously considered alternative model in the community, early dark energy [0]). These days, this is often the combination of Cosmic Microwave Background (CMB) Anisotropies, galaxy Baryon Acoustic Oscillations (BAO), and one of several supernovae samples - see e.g. [1] for a somewhat pedagogical overview. The failure to fit several datasets is a common issue e.g. with many MOND papers. In this case, the authors do not try to fit data to anything but a single (modified) supernovae dataset. I would expect that if they included a fit to CMB/BAO data, there would be trouble with the timescape model, as this is exactly what was found in an analysis of the timescape model in another state-of-the-art supernova dataset [2] - there the timescape model could not accommodate the supernova data when combined with CMB/BAO data [2].

[0] https://arxiv.org/abs/2302.09032 [1] https://arxiv.org/pdf/2007.08991 [2] https://arxiv.org/pdf/2406.05048

shepardrtc2• 2 years ago

If this is the case then the paper is easily dismissed, correct? How is it being published if the flaws are immediate, obvious, and completely destructive to the idea being presented? I'm legitimately asking - I've published papers and reviewed them, and if I thought something was so thoroughly wrong, I certainly wouldn't give it the ok.

astro-cosmo-q3• 2 years ago

A parenthetical remark just to clarify since I was reading quickly. Wrt the second point in parentheses about stretch factors - upon a second look it is not clear to me exactly what is happening since they say the factors are both fixed for each supernova but then also list the (global?) stretch and color factors in Table 1 (implying that they are varied).

mnau• 2 years ago

And why has it gotten such interest/points?

* I have seen incredible incompetency in my field. I have no illusions that it is better in other fields (plus personal stories from others about their fields).

* Replication crisis. Generally speaking, it threw a massive shade on a lot of fields.

* Generally speaking, the "trust the science" message during COVID did a massive damage.

* Science news influencers. Dark energy is one of common themes of Sabine Hossenfelder and generally rather negative.

* Dark energy is supposed make up ~70% of everything in universe. Yet basically nothing is know about it. That's a hard sell.

And yes, every point has a massive asterisk/that's a massive simplification/incorrect. That doesn't help overall perception. Perception is everything on social media.

Basically, if there was a theme, it would be "WTF are they doing?" Or if you want a more poetic version "Modern science has been a voyage into the unknown, with a lesson in humility waiting at every stop."

There is something seductive about an idea that instead of using existing stuff, scientists just made something new and shiny and were wrong. Happens in our field every day.

Your comment only reinforces this. This is a peer-reviewed paper in a reputable journal (Monthly Notices of the Royal Astronomical Society). Yet you are asserting a significant failures to use correct statistical practices. If you are correct, that is just another notch to the "WTF are they doing?" category.

SiempreViernes• 2 years ago

Maybe it's some deep cultural hangup the CS people got at university, there's certainly too much "I could have done physics" in the top personas of tech for it to be pure coincidence.

https://www.youtube.com/watch?v=GmJI6qIqURA&t=1

throwaway290• 2 years ago

Why is it a "change"? We already have two cosmology models. This just gives one of them more support right?

raattgift6• 2 years ago

Sean Carroll has a bluesky thread on this: https://bsky.app/profile/seanmcarroll.bsky.social/post/3lec7...

Supernovae Evidence for Foundational Change to Cosmological Models

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