[HN Gopher] Supernovae evidence for foundational change to cosmo...
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Supernovae evidence for foundational change to cosmological models
Author : JumpCrisscross
Score : 102 points
Date : 2025-01-01 15:53 UTC (4 days ago)
(HTM) web link (academic.oup.com)
(TXT) w3m dump (academic.oup.com)
| sylware wrote:
| javascript-walled.
| thechao wrote:
| If the main barrier to your enjoyment of this article is some
| JavaScript, you're quite a bit heavier weight in the maths
| department than I'll ever be.
| JumpCrisscross wrote:
| Reading this as a layman, it looks like releasing LCDM's
| cosmological principle [1] reveals the nontrivial temporal
| effects mass clusters have via general relativity. As a result,
| there could be empty regions of space in which billions of years
| more have elapsed than in _e.g._ a galaxy. This not only changes
| how we interpret supernova data (the acceleration isn 't
| generally happening, but an artefact of looking through space
| which is older than our own), but may also negate the need for
| dark matter (EDIT: dark energy) and the meaning of a single age
| of our univese.
|
| (I'm also vaguely remembering a multi-universe model in which
| empty space inflates quicker than massed space.)
|
| [1] https://en.wikipedia.org/wiki/Cosmological_principle
| aeve890 wrote:
| >Reading this as a layman, it looks like releasing LCDM's
| cosmological principle
|
| You mean relaxing. Also... "as a layman"? Lol what kind of
| layman are you. Respect.
| JumpCrisscross wrote:
| > _You mean relaxing_
|
| Fair enough, at high redshift the cosmological principle
| could still hold under timescape. (It doesn't require, it
| however.)
|
| All that said, I'm generally sceptical about findings based
| on supernova data. They require so much statistical work to
| interpret correctly that the error rate on first publications
| is remarkably high.
| sesm wrote:
| Overturning Lambda-CDM model removes only one observation that
| is explainable by Dark Matter (peaks in spectrum of CMB). It's
| not the only observation.
| throwawaymaths wrote:
| well the edges of a galaxy are in less of a deep gravity well
| than the center, so time and thus rotation should go faster.
| is that enough to account for flat rotation curves? i dont
| know enough to do a back of the envelope calculation
| throwawaymaths wrote:
| > here could be empty regions of space in which billions of
| years more have elapsed than in e.g. a galaxy.
|
| important to note that the motivation for releasing the
| cosmological principle, is that we know that there are "small"
| voids and that there is strong evidence of much larger voids
| and structure on the scale of tens of billions of light years
| that is incompatible with the cosmological principle, so it's
| not just a thing to do on a whim, it's supported by
| observation.
| JumpCrisscross wrote:
| > _we know that there are "small" voids and that there is
| strong evidence of much larger voids and structure on the
| scale of tens of billions of light years that is incompatible
| with the cosmological principle_
|
| Two cosmologists debate which of their town's bars is better,
| the small one or the large one. The town has one bar.
| throwawaymaths wrote:
| fair, I should have also put voids in quotes. is the black
| sea part of the med and is the med part of the atlantic?
| escape_goat wrote:
| Back here on the lay benches, I think the best starting point
| in the Wikipedia is probably the the article on inhomogenous
| cosmology, of which the Timescape Comsology proposed by David
| Wiltshire (listed as an author on this paper) in 2007 is a
| notable example; it is discussed in the article.
|
| <https://en.wikipedia.org/wiki/Inhomogeneous_cosmology>
| Gooblebrai wrote:
| This is a mind-blowing theory!
| astrobe_ wrote:
| > As a result, there could be empty regions of space in which
| billions of years more have elapsed
|
| If they are empty, those billion years didn't happen. But
| nothing is really empty, right?
| ben_w wrote:
| Assuming I correctly understood the argument in the link:
|
| Even if the space was truly empty, the expansion of that
| space would have gone on for longer, and thus things on
| opposite sides would eventually notice they were more
| distant.
|
| But also yes the space isn't really totally empty.
| nine_k wrote:
| The higher the density, the more curved is the spacetime at
| that area, and the slower is the passage of time. You don't
| have to go to extremes like black holes vs absolute vacuum. A
| sufficient difference should be visible between regions
| closer to centers of galaxies, or just clusters of nearby
| galaxies, and really large "voids" between them, which
| contain some matter, and even some stars, but are vastly more
| empty. This is what the article explores.
|
| (This connects in a funny way to Vernor Vinge's SF idea of
| slower and faster areas of space. The "high" / "fast" space
| is mostly empty, so the time passes there faster than in the
| "unthinking depths" around galactic cores, and hugely more
| progress is done by civilizations in the "fast" space, as
| observed from the "slow" space.)
| pdonis wrote:
| _> If they are empty, those billion years didn 't happen._
|
| No, that's not correct. Here's a better way to look at it:
|
| In our cosmological models, we "slice up" the spacetime of
| the universe into slices of "space at a constant time"--each
| slice is like a "snapshot" of the space of the entire
| universe at a single instant of "cosmological time". The
| models, which assume homogeneity and isotropy, assume that
| the actual elapsed _proper_ time at every point in space in
| each "snapshot" is the same--in other words, that
| "cosmologcal time" is also proper time for comoving observers
| everywhere in space at that instant of cosmological time--the
| time actually elapsed since the Big Bang on a clock moving
| with each observer.
|
| What these supernova papers are examining is the possibility
| that "cosmological time" and proper time (clock time) for
| comoving observers do _not_ always match: roughly speaking,
| in areas with higher mass concentration (galaxy clusters),
| proper time lags behind cosmological time (the time we use in
| the math to label each "snapshot" slice of the space of the
| universe), and in areas with lower mass concentration
| (voids), proper time runs ahead of cosmological time. The
| idea is that this mismatch between proper time and
| cosmological time can be significant enough to affect the
| inferences we should be drawing from the supernova
| observations about the expansion history of the universe.
|
| As far as I know the jury is still out on all this; claims by
| proponents that what is presented in these papers is already
| sufficient to require "foundational change" are, I think,
| premature. But it is certainly a line of research that is
| worth pursuing.
| le-mark wrote:
| As a layman, what I don't get is; the speed of light is
| constant, so wouldn't that nullify any time/space
| fluctuations due to lack of mass gravity?
| chuckwfinley wrote:
| It is sure seeming like LCDM needs some work. It's not really
| clear if a timescape approach solves the outstanding issues
| though
| incognito124 wrote:
| Interesting that the following wiki has been updated with this
| paper:
|
| https://en.wikipedia.org/wiki/Inhomogeneous_cosmology
| dgroshev wrote:
| Previously (includes informed critique of the paper):
| https://news.ycombinator.com/item?id=42495703
| ckcheng wrote:
| Also just 1 day ago:
| https://news.ycombinator.com/item?id=42587826
| Maro wrote:
| Python source:
|
| https://github.com/antosft/SNe-PantheonPlus-Analysis
|
| Input data:
|
| https://zenodo.org/records/12729746
| gammarator wrote:
| Here's an extended comment by another astrophysicst:
| https://telescoper.blog/2025/01/02/timescape-versus-dark-ene...
|
| The most important bit:
|
| > The new papers under discussion focus entirely on supernovae
| measurements. It must be recognized that these provide just one
| of the pillars supporting the standard cosmology. Over the years,
| many alternative models have been suggested that claim to "fix"
| some alleged problem with cosmology only to find that it makes
| other issues worse. That's not a reason to ignore departures from
| the standard framework, but it is an indication that we have a
| huge amount of data and we're not allowed to cherry-pick what we
| want.
| throwawaymaths wrote:
| the thing is, this is not _really_ an alternative model. it 's
| rather _actually bothering to do the hard math_ based on
| existing principles (GR) and existing observations, dropping
| the fairly convincingly invalidated assumption of large scale
| uniformity in the mass distribution of the universe.
|
| if anything the standard model of cosmology should at this
| point be considered alternative as it introduces extra
| parameters that might be unnecessary.
|
| so yeah it's one calculation. but give it time. the math is
| harder.
| sandgiant wrote:
| This has the same number of free parameters as LambdaCDM.
| Also this result only looks supernovae, i.e. low redshift
| sources. LambdaCDM is tested on cosmological scales.
|
| Very interesting, but "more work is needed".
| throwawaymaths wrote:
| thats not the case, if, as is increasingly speculated, the
| lambda is not constant over time. you figure two parameters
| for linear and three for a quadratic experience
| uoaei wrote:
| The "shut up and calculate" attitude has done a lot of harm to
| physics research over the past decades. It is quite remarkable
| and more than a bit surprising that the primary tenet of general
| relativity -- that spacetime behaves differently where there is
| curvature vs where there is not -- was not sufficiently accounted
| for seemingly by any researchers this entire time.
|
| I am interested to see some retrospective metaanalysis on how
| many cosmological models have _not_ suffered from this glaring
| omission. I suspect it 's very few but I also think that it would
| be difficult to do this kind of modeling before we were able to
| do analysis _in silico_ so there would be an obvious bias in the
| set of theories.
| JumpCrisscross wrote:
| > _The "shut up and calculate" attitude has done a lot of harm
| to physics research over the past decades_
|
| This is a shut up and calculate paper. There is zero
| theoretical ground being broken. The meat is in the statistical
| analysis (which I concede is beyond me).
| uoaei wrote:
| This paper is distinct in that it's cogent about the
| underlying cosmological principles. "Shut up and calculate"
| poisoned academic physics by eliding the necessity of
| thinking of systems as systems, and not merely as sets of
| equations to be manipulated.
| ANewFormation wrote:
| This is also the biggest surprise for me, but I'd frame it as
| people largely just handwaving in the assumption of a (at
| scale) isotropic universe, even though that's highly
| questionable.
|
| I think the practical issue is that that assumption let a _lot_
| more work get done than would have been possible otherwise. Of
| course if it turns out the universe is not isotropic then most
| all of that work is worth less than nothing. So publish or
| perish strikes again?
| programjames wrote:
| It is somewhat surprising, because one of the most famous
| papers in chaos theory, "The Applicability of the Third
| Integral of Motion" (Henon & Heiles), basically starts by
| saying a similar assumption isn't true, that stars aren't
| ergodically distributed in the axial/radial directions.
|
| If you have five equations of motion in a six-dimensional
| universe (3 space + 3 velocity coordinates), you can compute
| the future trajectory of each point. Two equations come from
| constant energy & angular momentum, and these constrain where
| in phase-space the trajectories can go. Another two equations
| are do not make any such constraints, which implies stars are
| at least ergodically distributed in a 2D phase-space. Since
| none of these equations constrain the axial/radial velocity,
| you would expect the dispersions to be equal for both
| directions. However, this turns out to not be the case. This
| means there must be a third isolating equation of motion out
| there, and the surprising thing Henon & Heiles find is it's
| _chaotic_! Sometimes it constrains points to 2D regions of
| phase-space (i.e. concentric circles of orbits), and other
| times it lets them move in a 3D region (i.e. chaotic
| trajectories filling the space).
| sampo wrote:
| Also Pioneer Anomaly was solved, after dropping simple models
| treating the space probe as a simple or spherical particle, and
| accounting for the 3-dimensional shape of the probe.
|
| Because of the shape of the space probe, part of the thermal
| radiation emitted from its surfaces were hitting some other
| surfaces, and thus the probe did not emit radiation evenly into
| every direction.
|
| https://en.wikipedia.org/wiki/Pioneer_anomaly
| caconym_ wrote:
| > It is quite remarkable and more than a bit surprising that
| the primary tenet of general relativity -- that spacetime
| behaves differently where there is curvature vs where there is
| not -- was not sufficiently accounted for seemingly by any
| researchers this entire time.
|
| This was also my first thought when I heard about this paper.
| It seems almost impossible that nobody in the entire
| contentious field of physical cosmology had considered whether
| our current consensus models account for the relativistic
| effects of the (known!) large scale structure of space.
|
| Following from that, my second thought was that maybe there is
| something more subtle about this analysis---maybe the question
| the researchers asked is less obvious than the headline makes
| it seem ("we forgot about relativity"). Obviously the subject
| matter is beyond me to answer that question myself, and I
| haven't found any good answers elsewhere.
| justlikereddit wrote:
| The way I see it people got stuck in a mindset of universal
| background time that is pretty much what earth clocks run at.
| With any serious relativity effects only being locally
| compartmentalized next to extreme cosmic phenomena.
|
| Adding dark matter to this mindset makes it even worse
| because it homogenizes everything even further towards a
| Universal Standard Timeframe when 80% of all mass is finely
| dispersed as a background fog.
|
| Put the Real back in Relativity.
|
| It's by far a more satisfying solution than magic mystery
| matter.
|
| My pet theory is that black holes are also vastly
| misunderstood because they're always seen from the Universal
| Standard Timeframe, if we probe a black hole and their local
| space from strongly relativistic timeframe they'll start to
| make more sense, but I'll leave that to the daydreams of the
| reader.
| exe34 wrote:
| GR calculations are very hard, and it's easy to think the
| effects aren't relevant outside of extreme conditions. this
| reminds me of the (sadly not very well supported) paper about
| gravitomagnetism explaining the rotation curves without dark
| matter.
| sampo wrote:
| > It seems almost impossible that nobody in the entire
| contentious field of physical cosmology had considered
| whether our current consensus models account for the
| relativistic effects of the (known!) large scale structure of
| space.
|
| One of the authors of the present study (prof. Wiltshire) has
| published this idea first time already 18 years ago: https://
| en.wikipedia.org/wiki/Inhomogeneous_cosmology#Timesc...
| asplake wrote:
| It's early days on this, so let me ask again what I have asked
| previously: What does timescape do to estimates of the age of the
| universe?
| sigmoid10 wrote:
| It would mean that we literally can't calculate it anymore,
| because expansion and everything else we see might just be
| artefacts of inhomogeneities beyond the scale of the observable
| universe. But that would crash hard with our observation of the
| CMB and since this study only looks at supernovae, I would not
| bet on it holding up for long.
| block_dagger wrote:
| Maybe Vernor Vinge was right.
| Vecr wrote:
| He wasn't. He stated from the start that all of his stories
| were gimicked to remove the singularity.
|
| This theory does not do that.
| revskill wrote:
| Not much related but could we somehow calculate the Gravitational
| constant with only math ?
| jmward01 wrote:
| The expansion of the universe has always come down to one
| question for me. In an expanding universe when you throw a ball
| up what speed does it come down?
| PaulHoule wrote:
| When I worked at arXiv one of my coworkers was a fresh
| astrophysics PhD who was cynical about the state of the field. He
| thought that we didn't know what the hell was going on with
| accretion disks but that a few powerful people in the field
| created the impression that we did and that there was no dissent
| because it was so difficult to get established in the field.
|
| When I first saw the LCDM model my first impression was that I'd
| didn't believe it, it seemed bad enough to have dark matter that
| we didn't understand but adding equally mysterious and physically
| unmotivated dark energy made it seem just an exercise in curve
| fitting.
|
| There have been longstanding problems that the history of the
| universe and cosmological distance scale haven't made sense.
|
| https://medium.com/starts-with-a-bang/the-hubble-tension-sti...
|
| When I was getting my PhD in condensed matter physics I was going
| to the department colloquium all the time and seeing astrophysics
| talks about how some people thought the hubble constant was 40
| km/s/Mpc and others thought it was 80 km/s/Mpc. With timescape
| cosmology maybe they were both right.
|
| Another longstanding problem in astronomy is that since the 1970s
| it's been clear we have no idea of how supermassive black holes
| could have formed in the time we think the universe has existed.
| With the JWST there are a flood of results that show the first
| 500 million years of the universe probably lasted a lot more than
| 500 million years
|
| https://iopscience.iop.org/article/10.3847/2041-8213/ac9b22
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