6 ms·

Supernovae Evidence for Foundational Change to Cosmological Models

107 points by jandrewrogers 2y ago

api 2y ago
Good wikipedia article on these types of cosmologies including timescape cosmology: https://en.wikipedia.org/wiki/Inhomogeneous_cosmology https://en.wikipedia.org/wiki/Inhomogeneous_cosmology
- numpy-thagoras 2y 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 2y 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?useskin=vector#Timescape_cosmology https://en.wikipedia.org/wiki/Inhomogeneous_cosmology?useski...
- vlovich123 2y 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 2y 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).
    - vlovich123 2y ago
      Right so is the paper saying that lambda CM completely ignored clock differences due to heterogeneity in mass distribution in the universe where isolated galaxies would be experiencing less time slowing than galaxies near other galaxies which would experience more time dilation?
      - raattgift 2y ago
        In the standard cosmology the Integrated Sachs-Wolfe effect captures the redshift/blueshift of distant light sources (up to the Cosmic Microwave Background) as it traverses relatively dense regions and relative voids. https://en.wikipedia.org/wiki/Sachs%E2%80%93Wolfe_effect https://en.wikipedia.org/wiki/Sachs%E2%80%93Wolfe_effect Note that in the next paragraph I depart significantly from the vocabulary that the Timescapes programme proponents have been using for the past twenty years. ISW and comparable spectroscopy is easy enough to think about in terms of an accelerating cosmic expansion, i.e., relative voids are becoming spatially bigger with the expansion. It becomes much less intuitive how to fit the data if one keeps relative voids at roughly constant volume instead implying that there is a significant false vacuum above the ground state and in voids the false vacuum is slowly decaying to that state. (Outside the supervoids, near matter, this false vacuum decays much more slowly still). Because "vacuum" in the voids isn't really vacuum, one is stuck with a running function on the constant c (it gets faster with time from the formation of the CMB; this is because the false vacuum evolves towards a real vacuum) or adapting lightlike geodesics by imposing refraction (since the false vacuum is a medium). The usual terminology is reasonably capture in the first paragraph here at <https://en.wikipedia.org/wiki/Inhomogeneous_cosmology#Inhomogeneous_universe https://en.wikipedia.org/wiki/Inhomogeneous_cosmology#Inhomo...> ("Inhomogeneous universe"). The following short section ("Perturbative approach") is what is done in the standard cosmology when one wants to do detailed studies of filamentary distributions and other structures that are lumpy at some (larrrrrge) length scale of interest: the perturbed homogenous background is practically always the standard FLRW. The justification for perturbation theory on FLRW is that even though there are dense spots (notably most galaxies' central black holes), principles like the Birkhoff theorem capture the idea that as you get far enough away from a galaxy it behaves more and more like a small shell, and this happens at intragalactic scales for these SMBHs: gravitationally, even to its arms' structure, it makes practically no difference whether Andromeda's central bulge has a lot more stars/gas/dust or whether it has one, two, or six central SMBHs (at enough spatial separation that they're not mutually orbiting in a way that would generate gravitational radiation our observatories are sensitive to). The same idea applies to galaxies->galaxy clusters->filamentary structures: as you "zoom out" the density variations become less important: filaments are pretty sparse on average. The Timescapes programe wants a sharper difference in matter sparseness between voids and filaments, and proposes that gravitational backreaction by the matter is responsible for generating that: the presence of matter steepens the density of matter over time (without the visible matter clearly becoming denser). I don't personally see how that's much different from a false-vacuum decay in the voids, conceptually. (ETA: well, it depends somewhat on how the Timescape void fraction evolves, but the local universe VF doesn't run void clocks fast enough, unless we do violence to the Copernican principle.) (Also ETA, mostly a note-to-self: I also don't understand how they capture the angular diameter turnover point in their dressed geometry <https://journals.aps.org/prd/abstract/10.1103/PhysRevD.80.123512 https://journals.aps.org/prd/abstract/10.1103/PhysRevD.80.12...> PDF available from institution at <https://ir.canterbury.ac.nz/items/36fe829a-0e7a-45d6-8db6-c24ea4384e01 https://ir.canterbury.ac.nz/items/36fe829a-0e7a-45d6-8db6-c2...> (cf <https://astronomy.stackexchange.com/questions/21006/understanding-the-turnover-point-of-angular-diameter-distance https://astronomy.stackexchange.com/questions/21006/understa...>.)) Finally, I think the most important result of this latest Timescapes paper is a reminder to everyone that supernova data are a mess. A good X-mas present would be a couple readily visible Milky Way supernovae. -
- brotchie 2y 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.
  - deleted 2y ago
    [deleted]
  - cma 2y ago
    There's a Danny Hillis talk on this but I couldn't find it.
- T-A 2y 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.
  - SpaceManNabs 2y 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.
    - webdoodle 2y ago
      Can't censor it, so you gaslight it?
    - andrewflnr 2y ago
      I don't know, the evidence for dark energy has always seemed a lot sketchier than the evidence for dark matter. Dark matter has lots of interlocking lines of evidence. Isn't dark energy pretty much entirely based on various cosmic distance measures that all have huge stacks of assumptions embedded?
      - SpaceManNabs 2y ago
        I agree. Until i see better evidence for 1a, wmap, and cluster formation in another theory, i really want all the charlatans to be quiet. We dont know what dark energy is, but we have decent evidence to say it is there and also decent theory. I am not saying this paper is made by charlatan btw. This type of work attracts those people though.
ajross 2y 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 2y ago
  I’ll be happy to see all the dark matter, dark energy stuff explained away.
  - SpaceManNabs 2y 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?
    - uoaei 2y ago
      We have a century of curve-fitting for dark matter, not theory.
PaulHoule 2y 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) 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?
- glompers 2y 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-energy-doesnt-exist-so-cant-be-pushing-lumpy-universe-apart https://ras.ac.uk/news-and-press/research-highlights/dark-en...
  - raattgift 2y 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#Late-time_integrated_Sachs%E2%80%93Wolfe_effect https://en.wikipedia.org/wiki/Sachs%E2%80%93Wolfe_effect#Lat...
mutagen 2y 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 https://en.wikipedia.org/wiki/A_Fire_Upon_the_Deep#Setting
- shepardrtc 2y 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.
scrubs 2y 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 2y ago
  Huh? https://en.wikipedia.org/wiki/Cosmic_time https://en.wikipedia.org/wiki/Cosmic_time
- codethief 2y 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.)
  - scrubs 2y ago
    Point taken. Thanks.
eximius 2y ago
Is anyone familiar with the (ln B > x) notation being used? What is this value being referenced?
- the8472 2y ago
  See section 2 of the paper.
tigerlily 2y 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 2y ago
  Sounds fascinating. Anywhere I can read more about the build-up to this moment? Has David Wiltshire written about this?
  - tigerlily 2y 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&page=1&q=find%20a%20wiltshire%2Cd 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 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 2y ago
An implication is that you would expect ancient advanced civilizations to form in the voids.
- largbae 2y ago
  Wouldn't such a civilization slow down as it gathers?
haxiomic 2y 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 https://www.youtube.com/watch?v=YhlPDvAdSMw
- haxiomic 2y ago
  Typo: Dark Energy*, not Dark Matter
idw 2y 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-a-simple-century-old-idea-but-new-observations-demand-a-radical-rethink-204190 https://theconversation.com/cosmological-models-are-built-on...
astro-cosmo-q 2y 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 2y 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 2y ago
  Funny. This is exactly how I feel about most of the AI/ML papers posted here. Very strange selection of pretty sketchy papers.
  - codethief 2y ago
    https://en.m.wikipedia.org/wiki/Michael_Crichton#Gell-Mann_amnesia_effect https://en.m.wikipedia.org/wiki/Michael_Crichton#Gell-Mann_a...
- andrewflnr 2y 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.
throwaway290 2y ago
Why is it a "change"? We already have two cosmology models. This just gives one of them more support right?
raattgift 2y ago
Sean Carroll has a bluesky thread on this: https://bsky.app/profile/seanmcarroll.bsky.social/post/3lec7s6v6wc2k https://bsky.app/profile/seanmcarroll.bsky.social/post/3lec7...

107 points by jandrewrogers 2y ago

api 2y ago

Good wikipedia article on these types of cosmologies including timescape cosmology: https://en.wikipedia.org/wiki/Inhomogeneous_cosmology https://en.wikipedia.org/wiki/Inhomogeneous_cosmology

numpy-thagoras 2y 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 2y 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?useskin=vector#Timescape_cosmology https://en.wikipedia.org/wiki/Inhomogeneous_cosmology?useski...

vlovich123 2y 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 2y 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).
  - vlovich123 2y ago
    Right so is the paper saying that lambda CM completely ignored clock differences due to heterogeneity in mass distribution in the universe where isolated galaxies would be experiencing less time slowing than galaxies near other galaxies which would experience more time dilation?
    - raattgift 2y ago
      In the standard cosmology the Integrated Sachs-Wolfe effect captures the redshift/blueshift of distant light sources (up to the Cosmic Microwave Background) as it traverses relatively dense regions and relative voids. https://en.wikipedia.org/wiki/Sachs%E2%80%93Wolfe_effect https://en.wikipedia.org/wiki/Sachs%E2%80%93Wolfe_effect Note that in the next paragraph I depart significantly from the vocabulary that the Timescapes programme proponents have been using for the past twenty years. ISW and comparable spectroscopy is easy enough to think about in terms of an accelerating cosmic expansion, i.e., relative voids are becoming spatially bigger with the expansion. It becomes much less intuitive how to fit the data if one keeps relative voids at roughly constant volume instead implying that there is a significant false vacuum above the ground state and in voids the false vacuum is slowly decaying to that state. (Outside the supervoids, near matter, this false vacuum decays much more slowly still). Because "vacuum" in the voids isn't really vacuum, one is stuck with a running function on the constant c (it gets faster with time from the formation of the CMB; this is because the false vacuum evolves towards a real vacuum) or adapting lightlike geodesics by imposing refraction (since the false vacuum is a medium). The usual terminology is reasonably capture in the first paragraph here at <https://en.wikipedia.org/wiki/Inhomogeneous_cosmology#Inhomogeneous_universe https://en.wikipedia.org/wiki/Inhomogeneous_cosmology#Inhomo...> ("Inhomogeneous universe"). The following short section ("Perturbative approach") is what is done in the standard cosmology when one wants to do detailed studies of filamentary distributions and other structures that are lumpy at some (larrrrrge) length scale of interest: the perturbed homogenous background is practically always the standard FLRW. The justification for perturbation theory on FLRW is that even though there are dense spots (notably most galaxies' central black holes), principles like the Birkhoff theorem capture the idea that as you get far enough away from a galaxy it behaves more and more like a small shell, and this happens at intragalactic scales for these SMBHs: gravitationally, even to its arms' structure, it makes practically no difference whether Andromeda's central bulge has a lot more stars/gas/dust or whether it has one, two, or six central SMBHs (at enough spatial separation that they're not mutually orbiting in a way that would generate gravitational radiation our observatories are sensitive to). The same idea applies to galaxies->galaxy clusters->filamentary structures: as you "zoom out" the density variations become less important: filaments are pretty sparse on average. The Timescapes programe wants a sharper difference in matter sparseness between voids and filaments, and proposes that gravitational backreaction by the matter is responsible for generating that: the presence of matter steepens the density of matter over time (without the visible matter clearly becoming denser). I don't personally see how that's much different from a false-vacuum decay in the voids, conceptually. (ETA: well, it depends somewhat on how the Timescape void fraction evolves, but the local universe VF doesn't run void clocks fast enough, unless we do violence to the Copernican principle.) (Also ETA, mostly a note-to-self: I also don't understand how they capture the angular diameter turnover point in their dressed geometry <https://journals.aps.org/prd/abstract/10.1103/PhysRevD.80.123512 https://journals.aps.org/prd/abstract/10.1103/PhysRevD.80.12...> PDF available from institution at <https://ir.canterbury.ac.nz/items/36fe829a-0e7a-45d6-8db6-c24ea4384e01 https://ir.canterbury.ac.nz/items/36fe829a-0e7a-45d6-8db6-c2...> (cf <https://astronomy.stackexchange.com/questions/21006/understanding-the-turnover-point-of-angular-diameter-distance https://astronomy.stackexchange.com/questions/21006/understa...>.)) Finally, I think the most important result of this latest Timescapes paper is a reminder to everyone that supernova data are a mess. A good X-mas present would be a couple readily visible Milky Way supernovae. -
brotchie 2y 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.
- deleted 2y ago
  [deleted]
- cma 2y ago
  There's a Danny Hillis talk on this but I couldn't find it.
T-A 2y 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.
- SpaceManNabs 2y 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.
  - webdoodle 2y ago
    Can't censor it, so you gaslight it?
  - andrewflnr 2y ago
    I don't know, the evidence for dark energy has always seemed a lot sketchier than the evidence for dark matter. Dark matter has lots of interlocking lines of evidence. Isn't dark energy pretty much entirely based on various cosmic distance measures that all have huge stacks of assumptions embedded?
    - SpaceManNabs 2y ago
      I agree. Until i see better evidence for 1a, wmap, and cluster formation in another theory, i really want all the charlatans to be quiet. We dont know what dark energy is, but we have decent evidence to say it is there and also decent theory. I am not saying this paper is made by charlatan btw. This type of work attracts those people though.

ajross 2y 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 2y ago
I’ll be happy to see all the dark matter, dark energy stuff explained away.
- SpaceManNabs 2y 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?
  - uoaei 2y ago
    We have a century of curve-fitting for dark matter, not theory.

PaulHoule 2y 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) 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?

glompers 2y 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-energy-doesnt-exist-so-cant-be-pushing-lumpy-universe-apart https://ras.ac.uk/news-and-press/research-highlights/dark-en...
- raattgift 2y 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#Late-time_integrated_Sachs%E2%80%93Wolfe_effect https://en.wikipedia.org/wiki/Sachs%E2%80%93Wolfe_effect#Lat...

mutagen 2y 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 https://en.wikipedia.org/wiki/A_Fire_Upon_the_Deep#Setting

shepardrtc 2y 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.

scrubs 2y 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 2y ago
Huh? https://en.wikipedia.org/wiki/Cosmic_time https://en.wikipedia.org/wiki/Cosmic_time
codethief 2y 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.)
- scrubs 2y ago
  Point taken. Thanks.

eximius 2y ago

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

the8472 2y ago
See section 2 of the paper.

tigerlily 2y 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 2y ago
Sounds fascinating. Anywhere I can read more about the build-up to this moment? Has David Wiltshire written about this?
- tigerlily 2y 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&page=1&q=find%20a%20wiltshire%2Cd 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 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 2y ago

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

largbae 2y ago
Wouldn't such a civilization slow down as it gathers?

haxiomic 2y 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 https://www.youtube.com/watch?v=YhlPDvAdSMw

haxiomic 2y ago
Typo: Dark Energy*, not Dark Matter

idw 2y 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-a-simple-century-old-idea-but-new-observations-demand-a-radical-rethink-204190 https://theconversation.com/cosmological-models-are-built-on...

astro-cosmo-q 2y 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 2y 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 2y ago
Funny. This is exactly how I feel about most of the AI/ML papers posted here. Very strange selection of pretty sketchy papers.
- codethief 2y ago
  https://en.m.wikipedia.org/wiki/Michael_Crichton#Gell-Mann_amnesia_effect https://en.m.wikipedia.org/wiki/Michael_Crichton#Gell-Mann_a...
andrewflnr 2y 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.

throwaway290 2y ago

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

raattgift 2y ago

Sean Carroll has a bluesky thread on this: https://bsky.app/profile/seanmcarroll.bsky.social/post/3lec7s6v6wc2k https://bsky.app/profile/seanmcarroll.bsky.social/post/3lec7...