[HN Gopher] Supernovae Evidence for Foundational Change to Cosmo...
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Supernovae Evidence for Foundational Change to Cosmological Models
Author : jandrewrogers
Score : 57 points
Date : 2024-12-23 16:44 UTC (6 hours ago)
(HTM) web link (arxiv.org)
(TXT) w3m dump (arxiv.org)
| api wrote:
| Good wikipedia article on these types of cosmologies including
| timescape cosmology:
|
| https://en.wikipedia.org/wiki/Inhomogeneous_cosmology
| numpy-thagoras wrote:
| 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 wrote:
| 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...
| vlovich123 wrote:
| 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 wrote:
| 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 wrote:
| 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?
| brotchie wrote:
| 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 wrote:
| There's a Danny Hillis talk on this but I couldn't find it.
| ajross wrote:
| 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 wrote:
| I'll be happy to see all the dark matter, dark energy stuff
| explained away.
| PaulHoule wrote:
| 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?
| api wrote:
| 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.
| PaulHoule wrote:
| 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.
| numpy-thagoras wrote:
| Black holes can survive a Big Crunch scenario? That can go
| a long way to explaining many things. Can you please
| provide a paper with more references to this, and
| potentially one with an example mechanism?
| mutagen wrote:
| 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
| scrubs wrote:
| 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 wrote:
| Huh?
|
| https://en.wikipedia.org/wiki/Cosmic_time
| codethief wrote:
| > 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 (Lemaitre-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.)
| eximius wrote:
| Is anyone familiar with the (ln B > x) notation being used? What
| is this value being referenced?
| the8472 wrote:
| See section 2 of the paper.
| tigerlily wrote:
| 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 wrote:
| Sounds fascinating. Anywhere I can read more about the build-up
| to this moment? Has David Wiltshire written about this?
| jandrewrogers wrote:
| An implication is that you would expect ancient advanced
| civilizations to form in the voids.
| largbae wrote:
| Wouldn't such a civilization slow down as it gathers?
| haxiomic wrote:
| 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
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(page generated 2024-12-23 23:00 UTC)