[HN Gopher] Supernovae evidence for foundational change to cosmo...
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Supernovae evidence for foundational change to cosmological models
Author : JumpCrisscross
Score : 161 points
Date : 2025-01-01 15:53 UTC (5 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.
| Bengalilol wrote:
| <https://watermark.silverchair.com/slae112.pdf?token=AQECAHi2..
| .> I hope it helps
| 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.)
| skirmish wrote:
| > Vernor Vinge's SF idea of slower and faster areas of
| space
|
| His ideas were more ambitious: there are advanced
| technologies (e.g. FTL travel) that work in "fast" space
| but completely stop working in the "slow zone" (where the
| Solar system is located). On the other hand, even human-
| level intelligence would stop functioning close to the
| galactic center, the crew would not be able to operate the
| ship and would be stranded.
| lazide wrote:
| Also, if I remember correctly wasn't it implied that this
| was constructed/controllable a bit, and was due to some
| kind of 'nature preserve' from a super alien race? I
| might be misremembering.
| 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?
| pdonis wrote:
| _> the speed of light is constant_
|
| That's not a good way of describing the actual law in a
| curved spacetime, i.e., a spacetime that contains
| gravitating masses. In such a spacetime there is no
| single global definition of "speed"; you can't compare
| speeds at spatially separated points.
|
| A better way to state the law is that the light cone
| structure of the spacetime constrains the motion of all
| bodies: timelike bodies move within the light cones,
| lightlike bodies (like light itself) move exactly on the
| light cones. But once you state it that way, it becomes
| obvious that this law does not impose any constraints on
| "time/space fluctuations".
| User23 wrote:
| Einstein's wonderful book Relatvity clarified (sort of)
| this for me. It's not too hard to develop an intuition
| about special relativity, but GR is a whole other ball of
| wax.
| mgsouth wrote:
| As another layman, no, I don't think so.
|
| The "twin paradox" [1] is a prime example. The two twins
| depart from a common point in time and space, go about
| their separate travels, and meet again at a common point
| in space-time. Despite both twins always having the same
| constant speed of light, one of the twins takes a
| _shorter path through time_ to get to the meeting point--
| one twin aged less than the other. In the paradox case,
| the shorter /longer paths are due to differences in
| acceleration. But the same thing happens due to
| differences in gravitation along two paths. (In fact,
| IIUC, acceleration and gravitational differences are the
| same thing.)
|
| Just thinking about the math makes my head hurt, but it's
| apparent that two different photons can have taken very
| different journeys to reach us. For example, the universe
| was much denser in the dim past. Old, highly red-shifted
| photons have spent a lot of time slogging through higher
| gravitational fields. As a layman, that would suggest to
| me that, on average, time would have.. moved slower for
| them?... they would be even older than naive appearances
| suggest. I don't think the actual experts are naive, so
| that's been accounted for, or there's confounding
| factors. But I could also imagine that more chaotic
| differences, such as supernovas in denser galatic centers
| vs. the suburbs, or from galaxies embedded in huge
| filaments, could be hard to calculate.
|
| [1] https://en.wikipedia.org/wiki/Twin_paradox
| a_cardboard_box wrote:
| From our perspective, the light in the void moves faster
| than it does here. But so do clocks, so someone in the
| void would measure their light moving at the same speed
| as we measure our light moving here.
| s1artibartfast wrote:
| speed of light is constant, but distance and time are
| not.
| lukasb wrote:
| Does the idea of a single cosmological time even make
| sense? I thought one of the key parts of relativity is that
| which events happen simultaneously depends on your
| perspective.
| layer8 wrote:
| That's only if you are moving relative to another
| observer. There is, however, an approximate "universal"
| rest frame that corresponds to the CMB (cosmic microwave
| background), and you can define simultaneity relative to
| that rest frame.
| pdonis wrote:
| _> Does the idea of a single cosmological time even make
| sense?_
|
| Sure, it's just a convenient choice of coordinates. Even
| in a model that is not exactly homogeneous and isotropic,
| it can still be a convenient choice of coordinates to
| have cosmological time track some kind of average of the
| low mass and high mass regions. As I understand it,
| that's basically what the alternate models described in
| the article are doing.
|
| _> I thought one of the key parts of relativity is that
| which events happen simultaneously depends on your
| perspective._
|
| That's true, but it doesn't actually mean very much. In a
| particular spacetime geometry, you can still have
| particular things that are picked out physically by the
| properties of that specific spacetime, and one of them
| can be "cosmological time". In an exactly homogeneous and
| isotropic model, that time is picked out by the
| symmetries of homogeneity and isotropy. But even in a
| model where homogeneity and isotropy are only average
| properties, their average is still picked out physically
| --for example, by the CMB, which is much, much closer to
| being exactly homogeneous and isotropic than galaxies and
| galaxy clusters (it's homogeneous and isotropic to within
| about 1 part in 100,000). So picking "cosmological time"
| based on observers who see the CMB that way is a physical
| method of picking them out; it's not an arbitrary choice.
|
| Bear in mind that in special relativity, when you talk
| about relativity of simultaneity, you are talking about
| spacetime that is empty--there are no gravitating bodies
| anywhere. So all inertial frames are indeed equivalent in
| that spacetime, not just mathematically but physically.
| But as soon as you put gravitating bodies in, that
| symmetry is broken: the gravitating bodies have a
| definite state of motion, and that picks out certain
| choices of coordinates as being aligned with the
| gravitating bodies. So while it's true that you don't
| _have_ to use those coordinates, they are convenient and
| they do reflect an actual physical property of the
| spacetime, and so does the definition of time they give.
| hnuser123456 wrote:
| You can define the moment when the universe stopped being
| a singularity as t=0 and its "end state" at t=1, without
| knowing what that end state is, and still make general
| observations about the beginning, middle, and end of the
| universe. Of course, you can't derive any specifics about
| specific regions of spacetime when thinking this way.
| Keysh wrote:
| > there could be empty regions of space in which billions of
| years more have elapsed than in e.g. a galaxy.
|
| A problem with that idea would be that the ages of galaxies in
| low-density regions (including voids) tend to be _younger_ than
| galaxies in denser regions, suggesting that galaxy evolution
| proceeds _more slowly_ in voids.
|
| https://www.iaa.csic.es/en/news/galaxies-great-cosmic-voids-...
| 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
| User23 wrote:
| Calculation is harder in a world of functionally limitless
| compute is sort of interesting. Where do we go from here?
| bsder wrote:
| > dropping the fairly convincingly invalidated assumption of
| large scale uniformity in the mass distribution of the
| universe.
|
| The problem with that is then you need a _mechanism_ that
| creates non-uniformly distributed mass.
|
| Otherwise, you are simply invoking the anthropic principle:
| "The universe is the way it is because we are here."
| zmgsabst wrote:
| You don't need a mechanism to point out a fact contradicts
| an assumption, eg, our measurements show non-uniform mass
| at virtually all scales (including billions of light
| years). There simply is no observable scale with uniform
| mass.
|
| Obviously there's _some_ mechanism which causes that, but
| the mere existence of multi-billion light year structures
| invalidates the modeling assumption -- that assumption
| doesn't correspond to reality.
| throwawaymaths wrote:
| yeah the ~1b ly nonuniformity is pretty much there. the
| ~10b ly uniformity is still early days but looking more
| and more likely as more data roll in (unless there is a
| systematic problem)
| marcyb5st wrote:
| I think that can be mitigated in three ways: our
| understanding of inflation is flawed, there were more
| "nucleation" sites where our universe came to be, and there
| are the already theorized baryonic acoustic oscillations
| that could introduce heterogeneity in the universe.
|
| Maybe is a combination of these, maybe something else. If
| nothing else, the uniformity is less probable than a mass
| distribution with variance (unless there is a phenomenon
| like inflation that smoothen things out, but also that was
| introduced to explain the assumption of a homogeneous
| universe). I concede that explaining the little variance in
| the CMB with our current understanding is hard when
| dropping homogeneity assumption however.
| jcarreiro wrote:
| > The problem with that is then you need a mechanism that
| creates non-uniformly distributed mass.
|
| The mechanism is gravity; and we have good observational
| evidence that the mass distribution of the universe is not
| uniform, at least at the scales we can observe (we can see
| galaxy clusters and voids).
| throwawaymaths wrote:
| > The problem with that is then you need a mechanism that
| creates non-uniformly distributed mass.
|
| you need no such thing. thats like saying "i refuse to
| acknowledge the pacific ocean to be so damn large without a
| mechanism". you dont need that. it just is. this doesnt
| preclude the existence of such a mechanism. but for any
| (legit) science, mechanistic consideration should be
| strictly downstream of observation.
| austin-cheney wrote:
| That sounds like regression.
|
| If this problem of regression occurs as regularly as your quote
| implies then the fault is not in these proposed alternatives,
| or even in the likely faulty existing model, but in the gaping
| wide holes for testing these things quickly and objectively.
| That is why us dumb software guys have test automation.
| bubblyworld wrote:
| I think automated hypothesis testing against new data in
| science is itself an incredibly difficult problem. Every
| experiment has its own methodology and particular
| interpretation, often you need to custom build models for
| your experimental setup to test a given hypothesis, there are
| lots of data cleanup and aggregation steps that don't
| generalise, etc. My partner is in neuroscience, for instance,
| and merging another lab's data into their own workflows is a
| whole project unto itself.
|
| Test automation in the software context is comparatively
| trivial. Formal systems make much better guarantees than the
| universe.
|
| (not to say I think it's a bad idea - it would be incredible!
| - but perhaps the juice isn't worth the squeeze?)
| austin-cheney wrote:
| > Every experiment has its own methodology
|
| That is bias. Bias is always an implicit default in any
| initiative and requires a deliberate concerted effort to
| identify.
|
| None of what you said is unique to any form of science or
| engineering. Perhaps the only thing about this unique to
| this field of science, as well as microbiology, is the
| shear size and diversity of the data.
|
| From an objective perspective test automation is not more
| or less trivial to any given subject. The triviality of
| testing is directly determined by the tests written and
| their quality (speed and reproducibility).
|
| The juice is always worth the squeeze. Its a business
| problem that can be answered with math in consideration of
| risk, velocity, and confidence.
| abdullahkhalids wrote:
| You are oversimplifying science, especially theoretic
| physics. At the point where we are, there are neither any
| quick/cheap tests, and there is no objectivity. The space of
| possible correct theories is infinite, and humans are simply
| not smart enough to come up frameworks to objectively
| truncate the space. If we were, we would have made progress
| already.
|
| There is a lot of subjectivity and art to designing good
| experiments, not to mention a lot of philosophical insight. I
| know a lot of scientists deny the role of philosophy in
| science, but I see all the top physicists in my fields
| liberally use philosophy - not philosopher type philosophy
| but physicist type philosophy - to guide their scientific
| exploration.
| austin-cheney wrote:
| I am not. You are using bias as an excuse to qualify poor
| objectivity. I am fully aware that astrophysics contains a
| scale and diversity of data beyond my imagination, but that
| volume of data does not excuse an absence of common
| business practices.
|
| > The space of possible correct theories is infinite
|
| That is not unique to any form of science, engineering, or
| even software products.
|
| > and humans are simply not smart enough to...
|
| That is why test automation is a thing.
| naasking wrote:
| > and humans are simply not smart enough to come up
| frameworks to objectively truncate the space.
|
| We are, but some people stubbornly resist such things. For
| instance, MOND reproducing the Tully-Fisher relation and
| being unexpectedly successful at making many other
| predictions suggests that any theories purporting to
| explain dark matter/gravitational anomalies should probably
| have MOND-like qualities in some limit. That would
| effectively prune the space of possible theories.
|
| Instead, they've gone in the complete opposite direction,
| basically ignoring MOND and positing different matter
| distributions just to fit observations, while MOND, against
| all odds since it's not ultimately correct, continues to
| make successful predictions we're now seeing in JWST data.
| abdullahkhalids wrote:
| Note that when I say humans, I mean how the whole
| worldwide social institution/network of scientists, with
| all its inherent hierarchies and politics. Because that
| is the social network that ultimately comes to some
| consensus on what the best theories at any given moment
| are.
|
| Its indeed possible, in fact "necessary" that some
| individual scientists within this network by luck or
| brains come up with much better theories, but sometimes
| those theories are not accepted by others or they are.
| But ultimately all that matters is the consensus.
| austin-cheney wrote:
| Holy fuck guy. Take a step back and do some self-
| reflection. Any time people post about physics on here
| its all emotions about how hard life is. With so much
| longing for sympathy its amazing anything in the field
| ever gets published.
|
| Unless you are looking for research grants stop crying
| about consensus and instead return to evidence and
| proofs. There will always be a million sad tears in your
| big sad community. If that is your greatest concern its
| going to take you a million years to prove what you
| already know, because all the sad people you are showing
| it to are just as sad and self-loathing about social
| concerns as you are.
| 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.
| User23 wrote:
| GR says that you can pick any frame that you want. The
| Earth-centered, Earth-fixed coordinate system happens to be
| really convenient practically, for things like navigation
| satellites.
| justlikereddit wrote:
| Sure you can do that. But the context of what is going on
| in different frames will be mostly lost.
|
| Explain the history of earth seen from a probe hovering
| one inch above the event horizon of Sagittarius A*?
|
| From the perspective of the probe: "The solar system,
| home of mankind was a blink in the sky that lasted 1
| second according to probe time. As was most other stars,
| as seen from here. Surely nothing important could ever
| happen in such a short timeframe. Fin."
|
| There's important nuances to what perspective one have.
| Something that seems to not just be missed but actively
| fought against in modernity.
| uoaei wrote:
| In the context of GR, at cosmological scales, every frame
| is an inertial frame. That means fictitious forces will
| arise if you're not careful to account for that.
| 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.
| geysersam wrote:
| How would
|
| > that we literally can't calculate it (the age of the
| universe) anymore
|
| crash with our observation of the CMB?
|
| I don't see how us being unable to calculate a quantity from
| one set of observations could possibly clash with another set
| of observations (the cmb).
|
| What am I missing?
| hnuser123456 wrote:
| The CMB suggests we get a picture of the entire early
| universe.
|
| However, other things are suggesting we might not be seeing
| the whole universe just by looking as far away as possible.
| It could be we can see some regions on the CMB that have
| already expanded outside of our observable universe. These
| regions aren't just "even fainter and we need a better
| telescope", they're "the last photon from that region that
| will ever reach us came and left billions of years ago."
|
| Therefore, there might not be one singular hubble constant,
| there might be two. One that applies to our local
| observable universe, and one that applies to the entire
| universe.
|
| It could be that the universe is 26 billion years old: http
| s://academic.oup.com/mnras/article/524/3/3385/7221343?lo...
|
| And because at great enough distances(/times), expansion is
| faster than light, and we simply can't see a significantly
| different epoch of the universe just by looking deeper.
| User23 wrote:
| Even more fun, once you abandon isotropy you don't even need
| to posit matter inhomogenities. It could just be that
| spacetime itself has irregular topology.
|
| Which, incidentally, is probably a better theory than dark
| matter. For example it can produce the same results without
| the problem of undetectable matter.
| cryptonector wrote:
| Presumably we should be able to build a theory of spacetime
| that yields no need for dark matter, but we're not there
| yet.
|
| On the other hand, determining the local time dilation
| factor based on all mass beyond the local area is
| essentially not possible. We can talk about how the great
| voids have less time dilation than galaxy clusters, sure.
| But what about the universe as a whole? Our universe could
| be embedded in a larger one that contributes to time
| dilation in ours and we could never sense that. Time
| dilation at cosmological scales is _relative_ for this
| reason.
| 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?
| pezezin wrote:
| My very limited understanding of the topic is that for a
| gravitationally bound system like the Earth, the usual rules
| apply, but on cosmological scales the expansion of the universe
| means that time-translation is not invariant and thus
| conservation of energy is not well-defined.
|
| https://en.wikipedia.org/wiki/Conservation_of_energy#General...
| jmward01 wrote:
| Getting rid of the time side then, think of it as an orbit.
| If the universe was expanding then something could be
| orbiting slower than gravity would allow. Basically this
| question keeps bringing me back to the ties between mass and
| the expansion of the universe. No matter how you look at it
| mass must be special when it comes to expansion because it is
| either giving off 'free' energy in the form of slow orbits
| and acceleration between two objects or it -isn't- giving off
| that energy and something is canceling it out. Following this
| rabbit-hole is pretty interesting at a minimum.
| thomquaid wrote:
| if you throw less than escape velocity, about the energy you
| threw with less system losses. if you throw greater than escape
| velocity, about any energy is possible less system losses, if
| you allow enough time for it to come back after its trip around
| the solar system. if you throw it into the milky way, same
| thing, easier potentials. if you throw it at relativistic
| velocities, expansion of the universe could play a significant
| role.
| 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 (though WIMPs and axions are plausible) but
| adding equally mysterious and physically unmotivated dark energy
| made it seem just an exercise in curve fitting.
|
| There have been a longstanding problem 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
| colechristensen wrote:
| On the topic of early black hole growth I saw this released a
| couple of months ago, an early black hole apparently growing at
| 40x the Eddington limit 1.5 billion years after the big bang.
|
| https://chandra.si.edu/press/24_releases/press_110424.html
|
| > A super-Eddington-accreting black hole ~1.5 Gyr after the Big
| Bang observed with JWST
|
| https://www.nature.com/articles/s41550-024-02402-9
| dotancohen wrote:
| Correct me if I'm wrong, but the term Eddington limit is a
| bit misleading as it does not describe some physical rate
| that cannot be exceeded. Lots of super Eddington objects are
| known.
| PaulHoule wrote:
| It's the point where light pressure can blow off the outer
| layers of a star
|
| https://en.wikipedia.org/wiki/Eddington_luminosity
|
| Objects that pulse like
|
| https://en.wikipedia.org/wiki/Eta_Carinae
|
| can evade it and there are other ways too.
|
| When it comes to super-massive black holes there is the
| question of how quickly stuff can even get close enough to
| the black hole to get into the accretion disk.
|
| 500M years is a long time for the kind of large star that
| becomes a black hole (blows up in 10M years or so), but if
| one black hole is going to merge with another black hole
| and that is going to merge with another black hole and so
| on there is no Eddington limit (no EM radiation!) but
| rather the even slower process of shedding angular momentum
| via gravitational radiation. (One highlight of grad school
| was the colloquium talk where we got to hear the signal
| from two black holes colliding almost 20 years before it
| was detected for real)
|
| I hope JWST sees
|
| https://en.wikipedia.org/wiki/Stellar_population#Population
| _...
|
| Note those Pop 3 stars have a higher Eddington limit
| because they've got hardly any "metal" in them which means
| light interacts with them differently, although astronomers
| have the strange (to me) conventional that anything heavier
| than Helium is a metal which includes, say, oxygen. (As a
| cond-mat PhD I think a metal is something that has free
| electrons, which could be one of those elements towards the
| left side of the periodic table or could be a doped
| semiconductor or polymer like polyaniline)
| dotancohen wrote:
| Thank you. I did not know that the first cosmic
| generation of stars had a higher Eddington limit. Why
| does light interact differently with hydrogen and helium
| than it does with the other elements? Does it have
| anything to do with having only a single layer of
| electrons in the atom?
| somenameforme wrote:
| Slightly tangential but how does the ad hoc nature of things
| like cosmic inflation seemingly not bother more people? Quite
| the opposite, it's a rather lauded discovery. This is more
| cosmology than astronomy, but at least reasonably related. That
| topic alone destroyed my interest in an academic pursuit of
| astronomy.
|
| 'Here's an idea that makes no logical sense, has no physical
| argument whatsoever (let alone evidence) in support of its
| existence, and just generally seems completely absurd - but if
| we ignore all of that, it solves a lot of other pesky problems
| with reality, as observed, practically falsifying other lauded
| theories.'
|
| Just add more epicycles?
| stouset wrote:
| Nobody's happy with dark energy, it's just the only framework
| we have that fits the data. All the other ideas might be
| brilliant and inspired but are measurably worse at describing
| the real world.
|
| Even the name "dark energy" is a tacit acknowledgment that--
| along with dark matter--we have no clue what the underlying
| physics actually is.
| cryptonector wrote:
| How is timescapes measurably worse? It's not a new theory,
| so perhaps it's been tested, and if it's failed why is it
| back in the news? (Sometimes failures get back in the news.
| It's a fair question.)
| russdill wrote:
| It starts with the assumption that our observations of
| cosmic expansion are false and due to time dilation from
| a clumpy universe, then works out how clumpy the universe
| must be to account for our observations.
|
| For timescapes to "work" time must run 38% faster in
| cosmic voids. This works out to a density difference of
| about 100,000 times what we observe with many existing
| methods.
| cryptonector wrote:
| > It starts with the assumption that our observations of
| cosmic expansion are false
|
| It starts with the assumption that our measurements
| (observations!) of attenuation and red-shift of standard
| candles are correct. Your characterization is wildly
| wrong, unless you meant to use a different word than
| 'observations'.
|
| > and due to time dilation from a clumpy universe, then
| works out how clumpy the universe must be to account for
| our observations.
|
| Yes, it does work backwards. That's insufficient by
| itself to say that timescapes is incorrect. It's
| concerning though because they work out what densities
| must be in order to explain away _all_ of the attenuation
| /red-shift disparities. However the reasoning time
| dilation is not wrong -- in fact, it's blindingly
| obviously correct if GR is correct, it's just that it
| might also be wildly insufficient -- it might just be in
| the noise.
|
| > For timescapes to "work" time must run 38% faster in
| cosmic voids. This works out to a density difference of
| about 100,000 times what we observe with many existing
| methods.
|
| Thanks. This is responsive to my question, but it's not
| yet dispositive. We could find that: -
| some of our observations are incorrect - some of
| our interpretations of those observations are
| incorrect - timescapes explains some but not all
| of the apparent acceleration of the expansion of
| the universe
|
| Also, density differences need to take into account
| density differences at the time that a ray of starlight
| we observe today entered each void along the way to us,
| not current apparent density disparities. It has to be
| that 8 billion years ago the difference in density
| between clusters and voids was much starker, though the
| voids would have been smaller, and perhaps the difference
| was not enough orders of magnitude.
| russdill wrote:
| There's a ton of theoretical work out there that is about
| building a foundation for future work. This is one of
| those works. But people tend to overlook the part where
| the work is just a piece, and many other things most
| first fall into place and over hype it. This is course
| isn't the fault of the authors.
| lutorm wrote:
| Well, it's not like people pulled it out of thin air. Both
| inflation and the lambda-CDM models are solutions to the GR
| equations, so in that sense it's perfectly justifiable to see
| if general relativity can explain the data. I don't think
| it's fair to say that it "makes no logical sense".
| misja111 wrote:
| I assume that OP was talking about the cosmic inflation
| theory that claims there was a rapid expansion immediately
| after the big bang. I don't see how that's a solution to
| the GR equation, could you maybe explain/give a link?
| russdill wrote:
| There is an addition of a inflation field. Observations
| show that such an inflation happened, and there's several
| ideas of inflation fields that are compatible with the
| standard model and match observations. The equations that
| make the observed expansion happen in the presence of
| such a field the friedmann equations, which are GR
| solutions.
|
| The field isn't just something that magically expands
| things, it just effects energy density. The rapid
| expansion is then a consequence of GR.
| gosub100 wrote:
| What do you mean by "bother"? The universe appears to be
| expanding, so I assume you don't deny that evidence, correct?
| Keysh wrote:
| > There have been a longstanding problem 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.
|
| You're (mis)remembering a different (old) problem and confusing
| it with a new one. The problem in the 1970s and 1980s was: what
| is the local expansion rate of the universe? Where "local" mean
| "within a few hundred megaparsecs". There were two main groups
| working on the problem: one group tended to find values of
| around 50 km/s/Mpc and other values of around 100. Gradually
| they began to converge (in the early 1990s, the low-H0 group
| getting values of around 60, the high-H0 group values of around
| 80), until a consensus emerged that it was in the low 70s,
| which is where we are now.
|
| The "Hubble tension" is a disagreement between what we measure
| locally (i.e., a value in the low 70s) and what theory (e.g.,
| LCDM) says we _should_ measure locally, if you extrapolate the
| best-fitting cosmological models -- based on cosmological
| observations of the CMB, etc. -- down to now (a value in the
| upper 60s). This has only become a problem very recently,
| because the error bars on the local measurement and the
| cosmological predictions are now small enough to suggest (maybe
| /probably) meaningful disagreement.
|
| > 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
|
| That's not a "longstanding" problem, it's a problem from the
| last 25 years or so. In order for there to be a problem, you
| have to have what you think are reliable estimates for the age
| of the universe _and_ evidence for large supermassive black
| holes very early in the universe. This is something that has
| emerged only relatively recently.
|
| (Your link, by the way, is to a paper that has nothing to do
| with black holes.)
| Maro wrote:
| I was doing an astrophsyics Phd 15 years ago, and one of the
| many reasons I abandoned it is exactly this. To get published,
| I would have had to start all my papers introducing and
| assuming the LCDM model, even though it just didn't seem right
| to me (too many "dark" components, too many assumptions,
| inflation).
|
| To be fair, people a lot smarter than me think it's good, or
| good enough.
| nimish wrote:
| Finally. We should use numerical relativity and simulate using
| full-fat GR. Not the half-assed approximations.
| XorNot wrote:
| Yes I'm sure the problem was no physicist working in the field
| their entire career thought to just do this.
| nimish wrote:
| Well no one bothered to actually implement it so who cares
| whether they thought it first or not?
| russdill wrote:
| Spoiler alert, this paper does not reach these conclusions
| by doing the thing you are asking.
| nimish wrote:
| Hence the subjunctive :)
| SaintSeiya wrote:
| The LCDM model always felt "wrong" in my gut: dark matter? dark
| energy? is just the modern equivalent of the aether theory. The
| fact that is more complex to calculate is not an excuse to prefer
| the LCDM model. The God's theory is even simpler as it spares of
| any math and physics, yet we do not use it.
| cryptonector wrote:
| Most recently discussed in
| https://news.ycombinator.com/item?id=42587826 ?
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