[HN Gopher] Analysis indicates that the universe's expansion is ...
___________________________________________________________________
Analysis indicates that the universe's expansion is not
accelerating
Author : chrka
Score : 243 points
Date : 2025-11-06 20:45 UTC (1 days ago)
(HTM) web link (ras.ac.uk)
(TXT) w3m dump (ras.ac.uk)
| karakot wrote:
| What does 'now' mean here?
| plasticchris wrote:
| Probably it means that now we have evidence that... it is a
| colloquialism
|
| Edit: yep, The universe's expansion may actually have started
| to slow rather than accelerating at an ever-increasing rate as
| previously thought, a new study suggests.
| sermah wrote:
| Recent years, probably because of large data centers /s
| thelibrarian wrote:
| Going by the second graph, since about 2.5 billion years ago.
| 2OEH8eoCRo0 wrote:
| What happened to then?
| dylan604 wrote:
| we passed then. we're at now now. I thought this was settled
| spl757 wrote:
| wait, I missed it?
| jl6 wrote:
| My lay reading of the OP's paper is that the universe is, in
| fact, braking for somebody.
| denismenace wrote:
| Did it change during our life time?
| oofbey wrote:
| Just our understanding of it. That's flipped multiple times in
| my lifetime.
| candiddevmike wrote:
| Aside from unanswerable questions (has the universe started to
| fill it's container? Is a simulation property nearing "1"?), does
| this make long distance space travel feasible again? I thought
| there was something around the universe is expanding too fast to
| visit places like Alpha Centuri (and preventing visitors to us).
| indoordin0saur wrote:
| The universe was always only expanding between galaxies, not
| within them.
| Razengan wrote:
| So wait, individual stars aren't getting further apart?
| Galaxies aren't getting "bigger"/more diffuse?
| kmeisthax wrote:
| Galaxies have enough gravity to counteract the expansion of
| the universe.
| Razengan wrote:
| So do we see the expansion cancelled out by the gravity,
| or do we only see the gravity?
|
| I mean, is it change = gravity
|
| or change = expansion - gravity
|
| Because this just made me wonder.. is "dark energy"
| simply the _absence_ of gravity? i.e. just in regions
| where there is next to no matter /activity?
| JumpCrisscross wrote:
| > _do we see the expansion cancelled out by the gravity,
| or do we only see the gravity?_
|
| We see gravity overpowering expansion. Same way you can't
| launch yourself into orbit by throwing _lots_ of pennies
| at one a second.
| recursivecaveat wrote:
| Imagine the universe as a giant balloon. Inside are little
| miniature balloon stars floating around, tied with string
| into balloon galaxies. If we heat the air: the big balloon
| expands, the clusters of mini-balloons spread out from the
| other clusters, but the clusters don't get any more
| diffuse. The string is way way too strong to be overpowered
| by the separating force from the expansion of the gas over
| short distances.
| Razengan wrote:
| I mean, this is tricky to even ask: is there still
| expansion INSIDE galaxies, BUT it's countered by gravity?
|
| Or is there no expansion within galaxies at all?
|
| i.e. is dark energy or whatever that causes expansion
| only present in the absence of matter, or is it present
| everywhere regardless of matter, but because matter also
| has its own gravity the expansion is not
| visible/relevant?
| oofbey wrote:
| That limitation only counts for visiting other galaxies. Travel
| within the galaxy is always possible, regardless of the
| universe's expansion. And Alpha Centauri is super close, even
| within our galaxy.
| dtech wrote:
| Specifically the local group, so Milky way + Andromeda and
| some dwarf galaxies
| Sharlin wrote:
| Dozens of dwarf galaxies, even! Also, Triangulum is sort of
| borderline at around 70% of the Milky Way's diameter,
| although admittedly only 10% of its mass. But Mars is also
| around 10% of Earth's mass, for a comparison.
| Sharlin wrote:
| Edit: A big brain fart, ignore the retracted part below.
| Colonizing the universe is of course impossible in 100My,
| barring FTL. What the paper I referred to [1] says is that
| colonizing the Milky Way may take less than that, and if you
| can do that, spreading to the rest of the observable universe
| is fairly easy, _very_ relatively speaking.
|
| <retracted> According to some calculations, it should in
| principle be possible to colonize the entire observable
| universe in less than a hundred million years. It's much too
| fast for the expansion to affect except marginally.</retracted>
|
| The relative jump in difficulty from interstellar to
| intergalactic is much smaller than from interplanetary to
| interstellar.
|
| Anyway, as others said, mere intragalactic (and intra-Local
| Group) travel is not affected by expansion in any way
| whatsoever.
|
| [1] https://www.sciencedirect.com/science/article/abs/pii/S0094
| 5..., PDF at
| https://www.aleph.se/papers/Spamming%20the%20universe.pdf
| hn_acc1 wrote:
| I found someone saying colonize the Milky Way Galaxy in ~90m
| years? Is that what you meant?
|
| The observable universe is ~93B LY - unless you're assuming
| FTL (and MUCH faster than light), I don't see how that's
| possible?
| Sharlin wrote:
| Yes, my brain totally froze. Added a correction.
| omnicognate wrote:
| Time dilation means that you can get anywhere while
| experiencing an arbitrarily small amount of time. You can
| cross the galaxy in a second as far as special relativity
| is concerned. (With the expenditure of insanely vast
| amounts of energy, ofc.)
|
| To an observer back home you'd look like you're travelling
| at merely extremely close to the speed of light, but to you
| the journey would take a second.
| mr_toad wrote:
| > You can cross the galaxy in a second as far as special
| relativity is concerned.
|
| Sure, but the rest of the universe will keep on changing.
| In 90 billion years it's going to be a very old universe.
| Galaxies will become consolidated and isolated, fewer
| young stars will be born. Only the dim light of red dwarf
| stars will shine among a graveyard of dead stars.
| omnicognate wrote:
| Hey, I didn't say it would be fun :-D
|
| Tau-Zero by Poul Anderson explores this, BTW. It's a
| great little sci fi novel about a spaceship doomed to
| accelerate at 1G indefinitely.
|
| It is significant from a colonisation PoV. With
| sufficient acceleration capability and the ability to
| survive travelling through the interstellar medium at
| extreme velocity (rather than getting vaporised by a mote
| of dust), a single generation of humans could in theory
| colonise the whole galaxy within their own lifespans.
| Indeed, some of them could even come back together and
| meet again after visiting those distant worlds, on an
| Earth many millions of years older, if their worldlines
| end up with similar proper times.
| delta_p_delta_x wrote:
| > The relative jump in difficulty from interstellar to
| intergalactic is much smaller than from interplanetary to
| interstellar.
|
| Interesting way to put it... This doesn't seem that accurate.
| With sufficiently advanced technology, many of which we
| already possess, we could expect to propel a minute
| spacecraft to a considerable fraction of the speed of light,
| and reach nearby stars possibly within the end of the
| century. Reaching the other end of the galaxy is a massive
| undertaking. It's a logarithmic scale at every step of the
| way.
|
| Pluto is about 38 AU from Earth. Proxima Centauri is about
| 6.3 x 10^4 AU away (or about 4.24 ly), and that's roughly a 2
| x 10^3 multiplication. The Milky Way is about 50000 ly in
| radius, and the Andromeda Galaxy is about 3 x 10^6 ly away.
| Going from interplanetary distances to interstellar, and
| thence to intergalactic, involves at least a 10^5 factor
| (give or take) at each step.
| mkl wrote:
| If you can get to a star 100 light years away, you can get
| to Andromeda. It doesn't require going faster, just waiting
| longer.
| michaelmrose wrote:
| I feel like waiting longer in some sense may itself
| represent a substantial increase in difficulty in terms
| of creating something which remains stable for tens of
| thousands of years.
|
| On the other hand who knows with zero samples how stable
| societies are thousands of years beyond our present level
| of development.
| mkl wrote:
| Yes, that's why I said 100 light years rather than 4.3.
| Maybe it's still too low, but I think there are targets
| within the Milky Way that would require solving pretty
| much all the problems of getting to Andromeda.
| ASalazarMX wrote:
| Imagine doing that, and being greeted with
|
| ALL THESE WORLDS ARE YOURS EXCEPT ANDROMEDA
| skissane wrote:
| I guess the question is... we know what our current
| propulsion technology is capable of... given a million
| years of further technological development, where will our
| technology be?
|
| The idea that, _given a million years of further
| technological development_ , intergalactic travel might
| actually be feasible, isn't really that implausible. Far
| from certain, but far from implausible either.
|
| And that's the thing-a million years is a technological
| eternity, a rounding error in estimates of time to colonise
| the galaxy/the local group/the observable universe.
| mrguyorama wrote:
| Any form of propulsion that obeys Newton has _hard_
| limits to it 's space travel potential. Even spitting out
| single particles at near the speed of light for the most
| efficient way to generate thrust per unit of expelled
| mass still constrains you to the tyranny of the rocket
| equation, which puts _hard_ physical limits on you.
|
| https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation
|
| The rocket equation also underestimates any craft that
| gets over a fraction of C
|
| Currently, we have no evidence that reactionless
| propulsion is _physically possible_ and one existing
| would directly contradict the conservation of momentum.
|
| "technological development" isn't a magic word or force
| of reality. "Technological development" is the pay off of
| _immense_ engineering investment and discovering new
| phenomenon, but every axis you can possibly put effort
| into engineering and optimizing has a _finite_ limit at
| some point, and there are _finite_ new phenomenons to
| discover.
|
| The entire past 100 and some years of technological
| development has been basically down to mastering the
| electromagnetic force. But, we've basically used up the
| novelty that was there, and _there is no new second
| electromagnetic force to discover_. In fact, the nuclear
| force was also discovered and tapped out relatively
| quickly.
|
| A great example of this is the elements. All evidence
| points to the outcome that the elements we can build
| stuff out of right now _are the only elements you will
| ever be able to build anything out of_. All artificial
| elements, even ones that are relatively "stable", have
| half lifes that preclude building stuff out of them, and
| there is no evidence that it is _possible_ to modulate
| the rate that an unstable atom decays. So no "exotic"
| elements that could magically power space ships or
| anything will exist.
|
| Intergalactic travel of humans is implausible unless you
| get into pretty radical transhumanism, or assume it's
| possible to perfectly maintain a biological human forever
| somehow, including brain functionality.
|
| Brain uploads are another thing that people don't seem to
| recognize are _radically_ more difficult and close to
| impossible. "Scanning" a brain is treated as an
| engineering problem, but it might not be. Every sensor
| relies on a physical interaction, most of them based on
| electromagnetic energy. How do you make an electron or
| photon or something interact in a measurable way with a
| cell deep inside someone's brain without that particle
| interacting with all the identical matter in the way or
| _cutting open and taking apart that brain_? Well, thanks
| to the mastery of the electromagnetic force, we have MRIs
| which kind of do in fact do that. But even if we had a
| magic MRI machine for example with infinite resolution
| (yet another thing that has fundamental limits), that
| would only let you look at molecules with with hydrogen,
| so you wouldn 't be able to survey, say, the ion content
| of brain cells directly. If you are not aware, ion
| gradients are fairly important in human cell behavior.
|
| Nevermind that scanning and uploading someone's brain, if
| it were possible, does not _transfer_ the original
| conscious experience to the computer. A new copy may go
| on in a digital world but you still die.
| glenstein wrote:
| Lots of great points here, but I think there's a bit more
| cause for optimism. For one, generation ships I think are
| the long-term project for space travel that successfully
| gets humans somewhere. No easy feat by any means in terms
| of time, engineering, and risk, but not running up
| against a wall of physical impossibility.
|
| And nuclear physics is still a wide open frontier. We
| don't yet have fusion, and there's a lot we don't yet
| know about quark and gluon plasma and nuclear behavior on
| astrophysical scales. And if we're talking about
| technological possibilities against time scales of
| _forever_ , there's lots of interesting electromagnetic
| possibilities in the context of superconductivity and
| metamaterials that we haven't yet exploited and I'm
| probably not even beginning to do justice to it in its
| totality as an open ended frontier full of fertile (e.g.
| vacuum polarization is a poorly understood frontier that
| might turn out to have interestingly exploitable
| properties).
|
| You did a great job outlining some devastatingly serious
| physical limits but I think, again against the timeline
| of _forever_ , you may be perhaps underselling the
| possibilities of important and newly exploitable
| properties of electromagnetism and the nuclear force
| being brought into application.
| mr_toad wrote:
| The distance to andromeda is only about 20 times the width
| of our galaxy. And there are dwarf galaxies than are much
| closer.
| xoa wrote:
| > _According to some calculations, it should in principle be
| possible to colonize the entire observable universe in less
| than a hundred million years_
|
| ...what? That doesn 't seem right, just from a really quick
| gut check it looks like the observable universe has a radius
| of 45.7 billion light years [0]. Even if the universe wasn't
| expanding nobody could get to everything any faster than that
| number of years right? Maybe you saw something that was
| talking about the local (Virgo) supercluster, which I think
| has a radius of around 55 million light years, so that sounds
| more like something that could be done on that timescale "in
| theory". But there are millions and millions of superclusters
| in the observable universe overall.
|
| ----
|
| 0: https://en.wikipedia.org/wiki/Observable_universe
| palmotea wrote:
| >> According to some calculations, it should in principle
| be possible to colonize the entire observable universe in
| less than a hundred million years
|
| > ...what? That doesn't seem right, just from a really
| quick gut check it looks like the observable universe has a
| radius of 45.7 billion light years [0].
|
| I guess it depends on whose hundred million years you're
| talking about: the colonists' or those who stay home's. I
| don't know how to do the calculations, but it seems
| plausible that you could traverse the entire observable
| universe at near light-speed in 100 million years _ship
| time_.
| grvbck wrote:
| You need ridiculous speeds for time dilation to really
| kick in though. Mathematically, it starts as soon as an
| object moves. But if a spaceship travels at 90 % of light
| speed (0.9 c), their local time moves just approximately
| at half speed compared to local time on earth. A year for
| the astronauts is just over 2 years on earth.
|
| At 0.995 c, the ship clock runs 10 x slower.
|
| At 0.999 c, 22 x slower. Then if you push the turbo
| button to 0.9999 c, 71 x slower.
|
| The fastest man-made object to date is the Parker Solar
| Probe, at 0.059 c.
| Sharlin wrote:
| Oops, yes, I don't know what I was thinking. A total brain
| fart. The paper I referred to is Sandberg and Armstrong's
| 2012 "Eternity in Six Hours", and of course they don't
| claim such a thing. Only that it's possible to start a
| colonization wave that has plenty of time to spread to
| everything visible now before they slip outside of our
| future light cone. The ~100M years refers to the
| colonization of the Milky Way. Sorry!
|
| [1] https://www.sciencedirect.com/science/article/abs/pii/S
| 00945...
| jfengel wrote:
| The limit to space travel is the Rocket Equation, which says
| that you require exponential fuel to reach higher speeds. Alpha
| Centauri isn't going anywhere, but it will take millennia of
| travel even with wildly optimistic assumptions.
|
| Also note that there isn't any "container" to fill up. It could
| well be infinite. It's just that we will be forever limited to
| a finite subset, even in theory.
| floxy wrote:
| Roundtrip Interstellar Travel Using Laser-Pushed Lightsails
|
| https://ia800108.us.archive.org/view_archive.php?archive=/24.
| ..
|
| "The third mission uses a three-stage sail for a roundtrip
| manned exploration of Eridani at 10.8 light years distance."
| mr_toad wrote:
| There are theoretical designs using antimatter (pion rockets,
| or beam core engines) that could reach 0.4c - 0.7c, which
| puts Alpha Centauri at decades away, not millennia.
|
| https://arxiv.org/pdf/1205.2281 https://ntrs.nasa.gov/api/cit
| ations/20200001904/downloads/20...
| redwood wrote:
| Was there a date at the top of this? I didn't see one. I saw a
| similar headlines earlier this year and I'm trying to understand
| that this is something new
| felixfurtak wrote:
| the linked journal article is dated Nov 6 2025
| observationist wrote:
| >>>Submitted by Sam Tonkin on Thu, 06/11/2025
|
| At the very bottom. Weird how style guides keep putting
| important information like this in harder to reach places.
| palmotea wrote:
| Is it SEO? IIRC there's a trend of removing dates from blog
| posts and articles, and my understanding it's to make the
| content seem more "evergreen" to Google (vs and article with
| a date, they may get down-ranked eventually due to age).
| observationist wrote:
| I'm thinking it's SEO cargo culting, and that there are a
| lot more "monkey see, monkey do" patterns of behavior that
| don't impact actual ranking but nonetheless crop up in
| weird things like this.
|
| That said, I cannot wait for adtech to go the way of the
| rotary phone. Localized, private search indexes on phones
| with local AI interacting with them, only reaching out to
| the internet when necessary to update information, with
| hashes and checksums to minimize the number of updates
| needed for frequently interacted sites, and so on.
|
| Google right now is hot garbage - most tiny competitors are
| far better, let alone yandex or kagi or the like.
| somat wrote:
| I thought the SEO was to keep churning out garbage articles
| in order to make the page more desirable to search engines
| because it was more recent. At least that is how it feels,
| like the search engines are promoting recent content over
| good content and pages take advantage of this by auto
| generated trash. to the point I won't even look at a page
| if it has a date in the last year.
| griffzhowl wrote:
| You're probably thinking of the DESI BAO results from March,
| which also cast doubt on the standard cosmological model. These
| new results point further in the same direction as the DESI
| ones
|
| https://newscenter.lbl.gov/2025/03/19/new-desi-results-stren...
| samdoesnothing wrote:
| Thanks, AI.
| jimbo808 wrote:
| Anyone know how credible this is? If true, then that means the
| big bounce is back on the menu, and the universe could actually
| be an infinitely oscillating system.
| jampekka wrote:
| At least The Guardian has a comment from an independent expert:
|
| "Prof Carlos Frenk, a cosmologist at the University of Durham,
| who was not involved in the latest work, said the findings were
| worthy of attention. "It's definitely interesting. It's very
| provocative. It may well be wrong," he said. "It's not
| something that you can dismiss. They've put out a paper with
| tantalising results with very profound conclusions.""
|
| https://www.theguardian.com/science/2025/nov/06/universe-exp...
| HeinzStuckeIt wrote:
| As an academic, that is exactly what the kind of
| noncommittal, don't burn your bridges with colleagues and
| funding bodies thing that I would say about even clearly
| flawed research if I were put on the spot by a popular-press
| publication. In fact, if you know you can rebut flawed
| research in time, you might want to assist in hyping it first
| so that your rebuttal will then make a bigger splash and
| benefit your personal brand.
| ImPostingOnHN wrote:
| It's also something you could say if you forgot to read the
| assignment and the professor called on you.
| piker wrote:
| "It makes some profound points, yes. What if? BUT what if
| not?"
| mr_mitm wrote:
| I read it as "I recognize some of the names and the
| abstract doesn't sound like complete nonsense".
| p00dles wrote:
| That guy should start a PR firm
| jameslk wrote:
| This sounds like something George Costanza would say
| observationist wrote:
| The more we learn, the less we end up knowing about how
| "everything" works - some things are mathematical in nature and
| demonstrate absolutes, but frameworks shift, and complexify,
| and exceptions to things we thought absolutes have occurred
| throughout history.
|
| For claims about how the universe works at scales and
| timeframes so utterly beyond anything testable, it's a little
| difficult to say this is credible at all - not dunking on the
| researchers, but in order to validate their conclusions,
| there's a whole chain of dependencies and assumptions you'd
| have to follow along with, and each of those things will be its
| own complex birds nest tangle of assertions, and I don't see
| how you can really say one way or another until you have a lot
| more information and a lot better Theory of Everything than
| we've got right now.
|
| For what it's worth, for all the impact it'll have on anyone's
| life outside of academia, I'd say they're 100% correct and
| people should buy them free beers at their local pubs for at
| least the next year in return for explaining their ideas at
| length.
| khimaros wrote:
| time to re-read "The Last Question"
| Cantinflas wrote:
| Asimov was so good. Amazing story
| CamperBob2 wrote:
| "Sorry, but as a large language model, I cannot provide
| advice on how to reverse entropy."
| cluckindan wrote:
| Thinking...
|
| Thinking...
|
| Thinking...
|
| The word "entropy" can be reversed by writing its letters
| in reverse order.
|
| E-N-T-R-O-P-Y
|
| The first letter is E.
|
| The second letter is N.
|
| The third letter is T.
|
| The fourth letter is R.
|
| The fifth letter is O.
|
| The sixth letter is P.
|
| The seventh letter is Y.
|
| Thinking...
|
| To construct the reversed word, the seventh letter must be
| first, and the sixth letter must be second, and the fifth
| letter must be third, and the fourth letter must be fourth,
| and the third letter must be fifth, and the second letter
| must be sixth, and the first letter must be seventh.
|
| The seventh letter is Y, so the first letter in the
| reversed word is Y.
|
| The sixth letter is P, so the second letter in the reversed
| word is P.
|
| The fifth letter is O, so the third letter in the reversed
| word is O.
|
| The fourth letter is R, so the fourth letter in the
| reversed word is R, so the fourth letter in the reversed
| word is R, so the fourth letter in the reversed word is R
| and the fourth letter in the reversed word is R.
|
| The third letter is T, so the fifth letter in the reversed
| word is O.
|
| The second letter is N, so the sixth letter in the reversed
| word is N.
|
| The first letter is E, so the seventh letter in the
| reversed word is N.
|
| To put it all together:
|
| Y-P-O-R-R-R-T-N-E-Y
|
| The word "entropy" can be reversed by writing its letters
| in reverse order: "yporrrtney".
| littke wrote:
| Masterpiece!!
| dTal wrote:
| This is art.
| mindcrime wrote:
| _yporrrtney_
|
| Looks like it halluco-commingled the physical principle
| and the drummer from Dream Theater...
| patcon wrote:
| I love this. I've upvoted every parent just so you can
| get your dues :)
| AutoDunkGPT wrote:
| bravo, sir
| pdonis wrote:
| _> If true, then that means the big bounce is back on the menu_
|
| I don't think so. Deceleration does not imply recollapse. AFAIK
| none of this changes the basic fact that there isn't enough
| matter in the universe to cause it to recollapse. The expansion
| will just decelerate forever, never quite stopping.
| Erem wrote:
| Wait but decelerating forever does in fact imply recollapse
| doesn't it?
| deepthaw wrote:
| I assume decelerating forever means asymptotically
| approaching not collapsing.
| pdonis wrote:
| No. The simplest example is a matter-dominated universe at
| exactly the critical density. It decelerates forever but
| never quite stops expanding--the expansion rate asymptotes
| to zero.
| cwillu wrote:
| An object on an escape trajectory from another mass is
| forever decelerating, but it still escapes.
| jimbo808 wrote:
| Would it not enter the viscinity of other objects which
| would eventually coalesce into local centers of mass
| (maybe like one per observable universe diameter or
| something)?
| ridgeguy wrote:
| Nope, cosmic Zeno's Paradox. Collapse never quite happens.
| xerox13ster wrote:
| Nope, that would be velocity changing sign, which means
| acceleration would increase.
| SideburnsOfDoom wrote:
| No, in much the same way that a speeding vehicle slowly
| decelerating towards a stop doesn't mean that it will
| return to where it started the journey.
|
| Actually it's worse than that, "decelerating forever"
| doesn't even mean that it ever even comes entirely to a
| stop. let alone return to where it started.
| pdonis wrote:
| _> Anyone know how credible this is?_
|
| AFAIK the previous models that all assumed that Type 1a
| supernovae were not affected by the age of the progenitor stars
| had no actual analysis to back that up; it was just the
| simplest assumption. This research is now actually doing the
| analysis.
| antonvs wrote:
| > AFAIK the previous models that all assumed that Type 1a
| supernovae were not affected by the age of the progenitor
| stars had no actual analysis to back that up; it was just the
| simplest assumption.
|
| Why would you assume this? It's not correct.
|
| Type 1a supernovae aren't even assumed to be "standard
| candles" as is often claimed: rather, they're standardizable,
| i.e. with cross-checks and statistical analysis, they can be
| used as an important part of a cosmological distance ladder.
|
| A great deal of analysis has gone into the development of
| that distance ladder, with cross-checks being used wherever
| it's possible to use them.
|
| They look at surface brightness fluctuations in the same
| galaxies, Tully-Fisher distances[1], tip of the red giant
| branch distances[2], and even baryon acoustic oscillations[3]
|
| Is it possible that this one single paper has upended all
| that? Theoretically. Is it likely? No.
|
| [1]
| https://en.wikipedia.org/wiki/Tully%E2%80%93Fisher_relation
|
| [2] https://en.wikipedia.org/wiki/Tip_of_the_red-giant_branch
|
| [3]
| https://en.wikipedia.org/wiki/Baryon_acoustic_oscillations
| pdonis wrote:
| _> Why would you assume this? It 's not correct._
|
| None of your references contradict it, as far as I can see.
| I'm well aware that Type 1a supernovae are only part of the
| overall picture, but that observation doesn't contradict
| what I said.
| DarmokJalad1701 wrote:
| RETVRN to mx'' + cx' + kx = 0
| ls612 wrote:
| I'm gonna wait for Scott Manley to discuss it before I form
| much of an opinion.
| jumploops wrote:
| "We can't observe the whole universe, so cosmology is not
| really about the universe. It's about the observable patch and
| the assumptions we make about the rest."
|
| (paraphrasing George Ellis)
|
| We're in a bounding sphere, with a radius that's roughly 46.5
| billion lightyears, so any observation we make may be true for
| our local observable range, but there's no (known) way to know
| what's beyond that sphere.
| alfiedotwtf wrote:
| This is the thing that blows my mind the most with physics
| and cosmology
| wtcactus wrote:
| Right, but everywhere we look the universe is roughly the
| same at same distances, so it's acceptable to extrapolate.
| mr_mitm wrote:
| Even if not, it's still worthwhile to explore everything as
| far as we can see.
| wtcactus wrote:
| Relativity restricts us to explore a very tiny sliver of
| the universe. We can observe, but we will never be able
| to interact unless Relativity is completely wrong.
| ghtbircshotbe wrote:
| How does an infinitely oscillating universe comply with the 2nd
| law of thermodynamics?
| wtcactus wrote:
| It doesn't. Either the 2nd law is incomplete or the idea of
| bouncing universes starting from scratch with a clear state
| in entropy is impossible:
|
| https://arxiv.org/abs/1010.5513
| sfink wrote:
| If you cover up the part of the Figure 3 graph past "now", it
| kind of fits a sine wave.
| https://ras.ac.uk/sites/default/files/2025-10/Figure%203.jpg
|
| Universe gong.
| ASalazarMX wrote:
| That's a very thought provoking observation, as if the whole
| universe behaved like a wave.
| mrb wrote:
| A funny coincidence is that the solar system was formed 4.6
| billion years ago which is exactly when the universe's rate of
| expansion peaked according to figure 3.
|
| If you want to believe in an intelligent creator--not that I do
| --it's as if they were accelerating the expansion until the
| solar system was formed, then turned the control knob down.
| Terr_ wrote:
| Turns out the universe is one giant PID controller.
| jdthedisciple wrote:
| Interesting observation.
| JumpCrisscross wrote:
| > _it kind of fits a sine wave_
|
| But wavering around a line above y = 0.
| ertgbnm wrote:
| Seems like the problem should be pretty easy to figure out. Just
| need to wait ~5 gigayears and see which model is right. I'm
| personally hoping for deceleration so that we have more total
| visitable volume.
|
| I'll set a reminder to check back at that time to see who was
| right.
| mabster wrote:
| I just pictured someone getting a message to check which model
| was right from an ancestor 20 giga generations ago!
| channeleaton wrote:
| !remindme 20,000,000,000 years
| shadowgovt wrote:
| Oh, I'm not going to care about visitable volume.
|
| With 5 gigayears to work with I'm going to move a few star
| systems over, break down all the matter orbiting the star into
| a Dyson sphere made of computronium, and simulate visiting any
| world I could possibly ever want to.
| aatd86 wrote:
| I would not be surprised if the universe was somewhat elastic,
| expands and then contracts and then expands ad infinitam. After
| all, existence in itself is irrefutable and cannot not exist by
| definition.
|
| If we subscribe to a theory of the multiverse, set theory,
| likelihood, and interaction driven evolution based on gradient
| type of fundamental laws. Locally changing. Obviously everything
| sharing a fundamental quality that is part of existence itself.
| But obviously there are sets, there is differentiation. But it is
| not created, the infinity of unconstrained possibilities exists
| in the first place and reorganizes itself a bit like people are
| attracted to people who share some commonalities or have
| something they need from each other and form tribes. Same
| processus kind of works for synapse connections, works for
| molecule formations, works for atoms... etc... Everything is
| mostly interacting data.
|
| We could say that the concept of distance is a concept of
| likelihood. The closer is also the most likely.
|
| Just a little weird idea. I need to think a bit more about it.
| Somewhat metaphysic?
| antonvs wrote:
| > After all, existence in itself is irrefutable and cannot not
| exist by definition.
|
| I can say the same about forgnoz, which is something I've just
| invented that must exist by definition.
|
| You'd need to try a bit harder to make existence actually
| inevitable.
| pinkmuffinere wrote:
| You're being downvoted, but your point is true -- something
| can exist "by definition", and yet not exist in our real
| world. The thing that exists "by definition" is just a
| version that we have imagined to exist by definition. But
| imagining something with property X doesn't imply anything
| can actually be found with property X.
|
| Side-note: the deontological argument is an argument for the
| existence of God, which uses the same principle as the
| grandparent. "Imagine God. Imagine God is good. A good God
| should exist, because otherwise that god is not good.
| Therefore, the good God we imagined has the property of
| existence. Therefore God exists". The issue is exactly the
| same -- we can imagine something with property X, but that
| doesn't mean we can find something with property X
| aatd86 wrote:
| Nope :) It 's not about that. It's not because I imagine
| that there is a banana in front of me that there will be.
| It's not tied to material existence in that way. It's
| perhaps another notion of existence which should be more
| mathematical.
|
| You could think it as "God" provably existing as an idea
| but that might or might not be realized probabilistically,
| in our material world. The idea exists obviously. Same as
| "Zeus"... or "Batman" any other such notions. "Existence"
| being different from "alive" as we colloquially understand
| it.
|
| The point is absence of anything is still something. The
| idea of nothing can only exist if there is existence first.
| How does it make sense? Then nothing can't exist. Not as an
| absolute. It can only be a relative negative within a
| weirdly heterogeneous infinity.
|
| Or you could see it as a predicate, sometimes false,
| sometimes true. It forms a lower universe of types than
| existence which is the set of all predicates. Predicates
| just...exists. They don't have to return true all the time.
| aatd86 wrote:
| Funny thing is to ask: 'Is blue, blue?' Now with
| existence: 'Does existence, exist?' And then a bit
| differently: 'Is nothing something?'
|
| We see that these are different types of impredicativity.
|
| Existence just needs itself to define itself. Nothing
| cannot exist if nothing actually somehow is. It needs
| existence. Blue is a word. It does not exhibit the
| characteristic is describes. The set of all things blue
| does not contain the proposition 'blue'.
|
| While the set of all things that exist contains itself?
| Sweet baby Ouroboros ;D
| pinkmuffinere wrote:
| There are two main claims that I think you may be
| touching on:
|
| 1. The question of whether concepts exist in the absence
| of a human mind to imagine them. This is still debated in
| philosophy. I'm not an expert, so I won't make a claim
| about this, but I will point out that if it was easy to
| resolve, it probably wouldn't be a field of active debate
| after 2000+ years.
|
| 2. The question of whether it is necessary that
| _something_ physically must exist. This I do make a
| strong claim on: it is not necessary that something
| physically exist. There is no law that forces objects to
| exist. We find ourselves in a universe where objects do
| exist. This is not required. It just happens to be the
| case.
|
| Side-note: I find the response "Nope :)" to be kindof
| condescending. I realize English may be a second language
| to you, so maybe you don't feel the subtle jab in that --
| no worries if so, I'm sure I make the same mistakes in
| other languages all the time. Smiley faces are definitely
| allowed online, but in general I'd say to use them when
| making a joke or when acknowledging your own mistake.
|
| Edit: In case somebody is curious, "the question of
| whether concepts exist in the absence of a human mind to
| imagine them" is debated at least since plato's time. I
| believe these concepts-that-exist-without-humans are
| sometimes called Platonic Forms. They are good for a
| wikipedia binge!
| aatd86 wrote:
| I thought the smiley would make the 'Nope' less
| argumentative. Sorry if you felt it was offensive.
|
| This was in response to: > Side-note: the deontological
| argument is an argument for the existence of God, which
| uses the same principle as the grandparent
|
| which was not actually true. This is not the same
| principle. Maybe the way I expressed the idea wasn't too
| clear. A close principle, would be Descartes' cogito
| perhaps...
|
| The question of whether a concept exists even in the
| absence of the human mind is easy to answer. Without
| arguments to authority, it suffices to realize that every
| past event that predates a human being is a concept for
| that same human. Every future event, even what one is
| likely to do the next day, is also a concept.
|
| Besides, why human? this is too anthropocentric. It
| should be extended to animals at the very least.
|
| Or let's have another example: you don't really perceive
| UV light, and let's say you've never been told that it
| exists and you live in a cave. You will never interact
| with it. That does not mean that it does not exist.
| Whether as a physical concept or merely a pure concept
| which is then a probability. Even if that probability is
| 0 or negative even (negative??? we are veering quantum
| :).
|
| It's probabilistic, not all of these concepts are
| realized materialistically (for future events that is).
|
| An apple exists even in the absence of humans. So does
| its concept. Awareness of the existence of this concept
| is a different thing. One must not forget that, as wise
| and introspective as some of the ancients were, they were
| also prone to a lot of cognitive biases such as
| anthropocentrism.
|
| In essence, my original point is closer to the one of
| greek philosopher Parmenides.
|
| But this is again not about physical existence. Matter is
| just data with a set of properties and interaction rules.
| One of them being existence. A physicist would call
| matter a special kind of spatial perturbation perhaps.
|
| On a whole other note, I am curious: what made it appear
| as if English was a second language? :)
| gcanyon wrote:
| I think they mean existence in general, not the existence of
| any specific thing. Meaning that if there were no "existence"
| then we wouldn't be here to consider its nonexistence.
| antonvs wrote:
| > I think they mean existence in general, not the existence
| of any specific thing.
|
| Yes, but the definition of "existence" doesn't require that
| anything must actually exist.
|
| In other words, it is not the case that existence "cannot
| not exist by definition."
|
| > Meaning that if there were no "existence" then we
| wouldn't be here to consider its nonexistence.
|
| That's an anthropic principle argument, which is not an
| argument from the _definition_ of existence. One of the
| premises of that argument is that we exist already.
| aatd86 wrote:
| Yes but then there is always something that must exist
| which is the concept of absence of existence. So it
| doesn't make sense.
| antonvs wrote:
| That's a requirement that you're imposing. If nothing
| exists, no concept of absence of existence exists.
| Concepts are for humans.
| aatd86 wrote:
| How can nothingness exists, if it is supposed to not
| exist since it is nothingness?
|
| Concept are not really for humans, but humans can grasp
| them. Or would you say that the sun only exists because
| (some) humans see it?
|
| It's not because a human is unaware of something that it
| does not exist. Its concept is still there somewhere.
| Independent of its treatment by human cognition.
| aatd86 wrote:
| You have a material view of existence perhaps. How would the
| notion of nothingness even exist if there was no existence in
| the first place? And if we even accepted that nothing was
| possible, which in itself doesn't make any sense, how would
| something even start to exist? Well the contradiction is
| already in the fact that there is a preexisting concept of
| nothing in the first place. Existence is impredicative too.
| It defines itself. That's a fact.
|
| It is not because it is impredicative that it needs to be
| hard to understand I think. It's almost a tautology rather.
|
| Oh by the way, forgniz exist, you made it to design
| something. It doesn't have to refer to something material. It
| could be an idea. After all, inventions don't exist by being
| material in the first place. But idea have at least material
| support (your brain signals) and the data acquired through
| your body. As far as we know.
| antonvs wrote:
| > How would the notion of nothingness even exist if there
| was no existence in the first place?
|
| It wouldn't, that's the point. The is no need for a "notion
| of nothingness" if nothing exists.
|
| Why do you think nothingness doesnt't make any sense? It's
| a simple concept: no space, no time, and therefore nothing
| else such as matter, etc.
|
| > how would something even start to exist?
|
| Perhaps it wouldn't. We weren't talking about the origin of
| the universe from nothing. If you want to say existence is
| irrefutable because we observe it, that's fine. But it's
| not irrefutable because of its definition, that's religious
| circular logic, like the ontological argument.
| aatd86 wrote:
| Not really, in mathematic or type theory it is a proof.
| But that's besides the point. If there was nothing, then
| we wouldn't be able to describe it. We are only
| describing it because we think it might exist. So in
| itself it is illogical for it to exist since it can only
| exist if it does not exist.
|
| Even if we had no data, the state before birth let's say,
| we still exist as a probability that is about to come to
| fruition. That is still besides the point.
|
| If there was nothing, as you are trying to call it, there
| would not be existence. But then we would not be here.
| reductio ad absurdum. Even if life is a dream, it is
| still something, an experience. It is still an existence
| at some level. You are not discussing with nothing, while
| being nothing :)
| djeastm wrote:
| All glory to forgnoz, a thing which I assure you does exist!
| bombdailer wrote:
| Eventually we will find that the heat death of the universe and
| the big bang are the same thing, since the totality of the
| universe is always a oneness, then from the universal
| perspective the infinitely small and infinitely large are the
| same thing (one), then they by nature bleed into (and define)
| each other like yin and yang.
| antihipocrat wrote:
| You may appreciate this idea:
| https://en.wikipedia.org/wiki/Conformal_cyclic_cosmology
| AceyMan wrote:
| Penrose? _That guy_ , again. /s
| nabakin wrote:
| > type Ia supernovae, long regarded as the universe's "standard
| candles", are in fact strongly affected by the age of their
| progenitor stars.
|
| A key point in the article. From what I understand, this is the
| main way we measure things of vast distance and, from that,
| determine the universe's rate of expansion. If our understanding
| of these supernovae is wrong, as this paper claims, that would be
| a massive scientific breakthrough.
|
| I'm really interested in the counterargument to this.
| stronglikedan wrote:
| > If our understanding of these supernovae is wrong, as this
| paper claims, that would be a massive scientific breakthrough.
|
| Indeed. It's so hard to definitively prove things that _are_ ,
| that the most significant breakthroughs prove things that _aren
| 't_ (so to speak), imho.
| JumpCrisscross wrote:
| > _It 's so hard to definitively prove things that are, that
| the most significant breakthroughs prove things that aren't
| (so to speak), imho_
|
| Significant breakthroughs do both. Prove things aren't as we
| thought. And are as the new model suggests.
| gorbot wrote:
| I'm dumb and barely understand things at a high level, but
| standard candles never sat right with me so it's interesting to
| hear that they might not be, but then again who knows.
| jiggawatts wrote:
| The idea is that standard candles are based on chemistry and
| microscopic physics only, not cosmology.
| alfiedotwtf wrote:
| If I remember correctly (sorry it's been a while), the size
| of the star determines its colour, and the data suggests
| that the colour of stars fits nicely into the mass of a
| star (ie you'll never see a star of X color thats Y kg)
| jiggawatts wrote:
| The rule is violated in all sorts of fun and interesting
| ways. There's white dwarfs, for one, then stars with
| varying levels of metallicity. Stars can merge, which
| does strange things to their position on the Hertzsprung-
| Russell diagram. There's oddball combinations like a red
| giant with a neutron star that has sunk into its core,
| called a Thorne-Zytkow Object!
|
| Not to mention variable stars, novae, occultation by dust
| clouds, etc.
| alfiedotwtf wrote:
| Great Scott look at your username!
| negativelambda wrote:
| It could be a big discovery and it also aligns with the
| findings from DESI BAO [1] and by another Korean group using
| galaxy clustering to infer the expansion history [2].
|
| [1] https://arxiv.org/abs/2404.03002
|
| [2] https://arxiv.org/abs/2305.00206
| basch wrote:
| This is mostly my physics ignorance talking, but if we measure
| distance in space-time and not just space, and speed or
| velocity is space-time/time (which somehow are both relative to
| each other) and the derivative of velocity is acceleration,
| cant acceleration mean either expanding "faster" in the sense
| of distance OR time speeding up or slowing down? All of it
| seems so self referential its hard to wrap around.
| cvoss wrote:
| We measure distance in space, and time intervals in time, and
| so velocity is just plain old distance/time. Special
| relativity doesn't change that. What changes is that if you
| start traveling at a different velocity, your measurements of
| distances and time intervals deviate.
|
| The expansion rate of the universe is not a velocity in the
| usual sense of distance/time. It's actually in units of
| velocity/distance, which reduces to 1/time. An expansion rate
| of r Hertz means that a given span of distance intrinsically
| doubles every 1/r seconds. The objects occupying the space
| don't "move" in any real sense due to expansion. They just
| wind up farther apart because space itself grew.
|
| And, just like measurements of distance and time,
| measurements of the expansion rate change if you change your
| velocity. There is a special velocity in our universe which
| causes the expansion in all directions to be the same. From
| this special perspective, which is traveling at a kind of
| cosmic "rest" velocity, you can calculate _the_ expansion
| rate. It turns out that the Sun is traveling at approximately
| 370 km /s with respect to that special "rest" velocity.
| ardit33 wrote:
| Circular universe...? big bang -> expands -> expansion slows ->
| starts retracting -> singularity again -> big bang again
|
| Roger Penrose seems to be leaning/more convinced of the circular
| universe theory....
| johnwheeler wrote:
| Just because infinity is a hard thing to understand doesn't mean
| the universe is and has always been infinite.
| mrbluecoat wrote:
| I have a great deal of respect for the sciences but sometimes
| astronomy just feels like one giant guessing game: age of the
| universe, big bang starting as a joke and all the "first minute"
| timelines thereafter, dark energy and dark matter (code for we
| have no idea what it is) vastly outnumbering everything else, and
| now questioning the Nobel Prize-awarded universe expansion.
| Meanwhile, asteroids the size of buses+ keep whizzing by closer
| than the moon with little or no warning. Sigh.
| CamperBob2 wrote:
| That's a feature! If you want to be certain, you need religion,
| not science.
|
| And of course, the people concerned with tracking near-earth
| asteroids are not connected in any way with cosmology.
| dylan604 wrote:
| what? no. religion is not certain which is evidenced by the
| numerous sects of christianity with their own interpretations
| of the same book.
|
| while science might not have a definitive answer for
| everything, they distinguish from fact and theory.
| ASalazarMX wrote:
| > religion is not certain
|
| Ask any religious person if their religion teaches truth or
| lie, then ask them if that truth is the absolute truth.
| We'll wait.
| dylan604 wrote:
| just because you tell me water is not wet does not make
| it dry. also, the cool thing "about science is it doesn't
| need _you_ to believe in it " or however the quote goes
| kloop wrote:
| Sure, but they didn't say correctness, they said
| certainty
| dylan604 wrote:
| There are people certain the earth is flat, the moon
| landings were fake. That certainty doesn't impress me. So
| I'm just really not sure what the point is.
| tsimionescu wrote:
| The point was that science doesn't _allow_ for certainty,
| by construction. We 're not certain the sun will rise
| tomorrow, we're not certain the speed of light is a
| limit, we're not certain that F=ma or that E=mc2.
|
| Those that want certainty have to look to religion, or to
| pseudoscience. And they will certainly be wrong.
| cruffle_duffle wrote:
| Bingo. People who think science is fact dont understand
| science.
|
| The actual fact is, we humans really don't know much
| about the universe and indeed there may be truths and
| knowledge that we'll never know the answer to. Like...
| why the fuck are we here? Where did all this stuff come
| from. Sure we have theories and have logical conclusions
| but at the end of the day... we are tiny and the universe
| is mind bogglingly huge. It is peak human arrogance to
| think we truly know anything at all.
|
| It's very humbling to realise how little we actually
| know. What we _do know_ ... we know. We are masters of
| electro-magnetism, chemistry, etc... but when it comes to
| the big questions it's all a shot in the dark.
| JumpCrisscross wrote:
| > _no. religion is not certain_
|
| Religion allows for certainty. Science does not. Faith
| versus reason.
| ASalazarMX wrote:
| Consider the scales involved. It's amazing that a species that
| is 99% chimp genes can even think and deduce phenomena of that
| size; don't ask it to get it right the first time.
|
| All of that without having traveled farther than one light
| second from its home.
| monero-xmr wrote:
| It should humble all of us that believe we have absolute
| knowledge of things. So many people consciously or
| subconsciously philosophize about the universe, life,
| spirituality, etc. based on grand ideas and science which is
| routinely overturned. Really all we can prove is mathematical
| facts, and what our emotions tell us (i.e. "I Love You").
| spl757 wrote:
| There has been a lot of progress towards mapping all near-earth
| asteroids, at least. That's a lot better than the previous
| tactic of putting one's fingers in one's ears and humming.
| pixl97 wrote:
| I mean an asteroid the size of a bus is messy for your local
| area if it decides to land there, but in the terms of size of
| things in space is nearly undetectable. Space, even our local
| neighborhood is unbelievably huge.
|
| Think of trying to find a bus that could be anywhere on earth
| that is moving so it's not easy to keep track of and is painted
| in a way to be camouflaged with its environment.
|
| Now instead try to imagine looking for that bus on Jupiter.
| Gets way harder. But it's way bigger than that, your looking
| for a black dot in the size of an area of millions of Jupiter
| and just hope it crosses in front of a star so you can track
| it.
|
| Most problems involving space are insanely hard.
| arp242 wrote:
| > now questioning the Nobel Prize-awarded universe expansion
|
| It is not questioning that the universe is expanding. It is
| questioning _how_ the expansion is happening. Massive
| difference. The rate of expansion has always been more of a
| "probably" and "looks like" rather than "we have very strong
| evidence" (unlike expansion itself, for which there is very
| strong evidence). This is a classic "we have tweaked our model
| as we've learned more" type thing (assuming it holds).
| shomp wrote:
| Mainstream physics has been delighted to ignore/abandon essential
| conservation laws when talking about the expanding universe. It's
| kinda weird, I tried publishing a paper on it recently and it was
| not received well. In general, if conservation laws are to hold,
| expansion must be balanced with [eventual] contraction, is that
| not obvious? Apparently it was quite contentious to say until...
| this article?
| antognini wrote:
| Noether's theorem tells us when we would expect conservation
| laws to hold and when we would expect them to fail. In the case
| of global energy conservation, there would have to be a global
| time invariance associated with the spacetime. But this is
| manifestly not the case in an expanding universe. It is
| generally not even possible to have a well defined notion of
| global energy in a dynamic spacetime.
| shomp wrote:
| Noether's theorem tells us when symmetry guarantees
| conservation, but it says nothing about conservation in the
| absence of that symmetry - it's not a biconditional
| statement. Talking about endless expansion is like observing
| 1 second of a pendulum's swing and concluding there's no time
| symmetry because it's only moving in one direction. The
| symmetry exists at the full cycle scale, not the snapshot
| scale.
| antognini wrote:
| It's true that it leaves open the possibility of a
| conserved quantity that is not associated with a symmetry.
| But the kinds of conservation laws we are thinking about,
| like conservation of energy, do originate from a symmetry.
| So if the symmetry is broken it is very reasonable to
| assume that the conservation law would be broken as well.
| zygentoma wrote:
| No, the assumption was that dark energy is a property of space
| itself so it does not conserve energy at all in an expanding
| space.
|
| Also this discovery does still is being explained with dark
| energy (albeit time varying ...) so it still does not assume
| global energy conservation.
| frotaur wrote:
| I mean no disrespect, but are you a trained physicist, or at
| least familiar with the 'mainstream material'?
|
| Because there is no shortage of 'crackpots' that have 'obvious'
| solutions to unsolved physics problems, and that want to
| publish papers about it.
| ASalazarMX wrote:
| > In general, if conservation laws are to hold, expansion must
| be balanced with [eventual] contraction, is that not obvious?
|
| Why would this be? The only physics we know is the one inside
| our observable universe, there could be variations beyond, or
| even unknowable laws that don't require conservation of matter
| _outside_ the edge of the universe.
|
| Our incredibly vast universe could be a minuscule blob feeding
| from an incredibly vaster parent universe, in which case it
| could be breaking conservation infinitely from our perspective.
| shomp wrote:
| Because energy cannot be created nor destroyed
| xwolfi wrote:
| Evidently energy was created, or it would not exist, would
| it ? It probably can be destroyed back to the pre-energy
| state in some way, just not on a scale we comprehend or
| even care about.
|
| I suppose we're like bubbles on a boiling pot of water when
| the fire stops: all this agitation spreads out on the
| entire volume, and sure no energy was lost, but there are
| so little bubbles and so much water, once the heat has
| spread out entirely, the whole volume of water looks pretty
| dead.
| mr_mitm wrote:
| Maybe this helps:
| https://www.preposterousuniverse.com/blog/2010/02/22/energy-...
|
| My favorite quote:
|
| > I like to think that, if I were not a professional
| cosmologist, I would still find it hard to believe that
| hundreds of cosmologists around the world have latched on to an
| idea that violates a bedrock principle of physics, simply
| because they "forgot" it. If the idea of dark energy were in
| conflict with some other much more fundamental principle, I
| suspect the theory would be a lot less popular.
| gmuslera wrote:
| Someone dumped a flat panel near a noisy planet.
| wtcactus wrote:
| Standard candles (all these measurements of redshift according to
| distance, need us to actually get the distance of what we are
| measuring right) are the gift that keeps on giving.
|
| This study (and many others, depending on the cosmic scales they
| use) mainly use Supernovas of Type Ia. I.e. the energy emitted by
| the supernova of a binary acreccion star, which is a star that is
| capturing the mass from another start that is very nearby and
| increasing its mass until it collapses into itself, increases
| temperature up to the point it starts fusing helium, and goes
| supernova with all the added energy.
|
| That was (and still is now, with some corrections we found since
| middle last century) supposed to be the same everywhere. Problem
| is, we keep finding new corrections to it - like this study
| claims.
|
| That is in fact the big claim of this study (ignore the universe
| expansion part), that they found a new correction to the
| Supernova of type Ia luminosity. It's a very big claim and
| extremely interesting if confirmed. But, like all big claims, it
| needs a big confirmation. I'm a bit skeptic TBH.
| jldl805 wrote:
| >I'm a bit skeptic
|
| Out of curiosity, what data are you drawing or what
| qualifications do you have that support your skepticism over
| three different modes of analysis (as well as pretty much every
| recent development in the field) supporting this claim:
| "Remarkably, this agrees with what is independently predicted
| from BAO-only or BAO+CMB analyses, though this fact has
| received little attention so far.""
| wtcactus wrote:
| Well, this part you mention, for instance "though this fact
| has received little attention so far".
|
| A change on the standard candles calibration would be a huge
| deal for cosmology and galactic astronomy (and other fields)
| and would not be taken lightly at all. There are all sorts of
| ramifications from this and if astronomers aren't all in an
| oof about it, it is because big proof is needed for big
| claims.
|
| And a change in the standard candles calibration is indeed a
| very big claim.
| JumpCrisscross wrote:
| "Supernova (SN) cosmology is based on the key assumption that the
| luminosity standardization process of Type Ia SNe remains
| invariant with progenitor age. However, direct and extensive age
| measurements of SN host galaxies reveal a significant (5.5s)
| correlation between standardized SN magnitude and progenitor age,
| which is expected to introduce a serious systematic bias with
| redshift in SN cosmology. This systematic bias is largely
| uncorrected by the commonly used mass-step correction, as
| progenitor age and host galaxy mass evolve very differently with
| redshift. After correcting for this age bias as a function of
| redshift, the SN data set aligns more closely with the cold dark
| matter (CDM) model" [1].
|
| [1]
| https://academic.oup.com/mnras/article/544/1/975/8281988?log...
| negativelambda wrote:
| I know the team that did this. In fact i was listening to their
| seminar just a few days ago. They are very careful and have
| been working on this a long time. One caveat that they readily
| admit is that the sample used to create the luminosity age
| relation has some biases such as galaxy type and relatively
| lower redshift. They will be updating their results with the
| Rubin LSST data in the next few years.
|
| Exciting times in cosmology after decades of a standard LCDM
| model.
| nabakin wrote:
| Is there a recording of their seminar anywhere?
| negativelambda wrote:
| Its not publicly available. Maybe for the best haha. The
| speaker at some point went on a bit of a tirade against
| many people in the supernovae cosmology community. I think
| he endured many years of being ignored or belittled.
| ChrisMarshallNY wrote:
| Did he yell _" They LAUGHED at me at Heidelberg! They
| said I was mad. MAD!"_?
|
| It is a very fundamental shift, though. The whole "Dark
| Energy/Matter" hypothesis has always seemed to me, to be
| a bit of a _" Here, there be dragonnes"_ kind of thing,
| but I am nowhere _near_ the level of these folks, so I
| have always assumed they know a lot that I don 't.
| kulahan wrote:
| It is, but that's also kinda the point. It's just a
| variable to stand in for "whatever tf mass we've been
| missing this whole time" or what-have-you.
| tekla wrote:
| I've never really gotten this criticism. Science has
| worked on "here be dragons" ever since it became a
| "thing".
|
| Neutrinos took like 40 years to discover after
| experiments earlier showed that either all of modern
| particle physics was wrong, or there was something that
| we couldn't see.
| ChrisMarshallNY wrote:
| It wasn't a criticism. At least, not from me. It was just
| an observation.
| ngold wrote:
| Just curious, is this dark matter holding back the universal
| expansion?
| madaxe_again wrote:
| Our best guess is "maybe?"
| JumpCrisscross wrote:
| > _after decades of a standard LCDM model_
|
| Could you help me understand this sentence: "After correcting
| for this age bias as a function of redshift, the SN data set
| aligns more closely with the cold dark matter (CDM) model"?
| mr_mitm wrote:
| The CDM model has no dark energy, unlike the LCDM model.
| The L stands for Lambda, which is the dark energy term in
| the Einstein equations. So they are saying when accounting
| for this effect, our universe looks more like a universe
| without dark energy, at least when only considering the
| supernovae probe.
| negativelambda wrote:
| That's only if you consider the supernovae data alone. In
| combination with other probes like BAO, etc, the combined
| data are pointing to a Universe with a dynamical (or time
| varying) dark energy model.
| the__alchemist wrote:
| I did a deep dive into cosmology simulations ~a year ago. It
| was striking how much is extrapolated from the brightness of
| small numbers of galaxy-surface pixels. I was looking at this
| for galaxies and stars, and observed something similar. The
| cosmology models are doing their best with sparse info, but to
| me it seemed that the predictions about things like Dark Matter
| and Dark Energy are presented in a way that's too confident for
| the underlying data. Not enough effort is spent trying to come
| up with new models. (Not to mention trying to shut down
| alternatives to Lambda CDM, or a better understanding of the
| consequences of GR, and the assumptions behind applying
| Newtonian instant-effect gravity in simulations).
|
| Whenever I read things like "This model can't explain the
| bullet cluster, or X rotation curve, so it's probably wrong" my
| internal response is "Your underlying data sources are too
| fuzzy to make your model the baseline!"
|
| I think the most established models are doing their best with
| the data they have, but there is so much room for new areas of
| exploration based on questioning assumptions about the feeble
| measurements we can make from this pale blue dot.
| throwaway-0001 wrote:
| Yeah a lot of stuff seems to be based on these fuzzy data
| which I also think is unreliable.
| mr_mitm wrote:
| That fuzziness can be quantified. It's called error bars.
| Whenever physicists perform a measurement, they always derive
| a confidence interval from the instruments they use. They
| take great care of accounting for the limits of each
| individual instrument, perform error propagation and report
| the uncertainty of the final result.
|
| Consider figure 5 of the following article for example:
|
| https://arxiv.org/abs/1105.3470
|
| The differently shaded ellipses represent different
| confidence levels. For the largest ellipsis, the probability
| of the true values being outside of it is less than 1%. We
| call that 3-sigma confidence.
|
| > Whenever I read things like "This model can't explain the
| bullet cluster, or X rotation curve, so it's probably wrong"
| my internal response is "Your underlying data sources are too
| fuzzy to make your model the baseline!"
|
| Well, then do some error analysis and report your results.
| Give us sigmas, percentages, probabilities. Science isn't
| based on gut feelings, but cold hard numbers.
| the__alchemist wrote:
| On the todo list! Not enough bandwidth, but hoping to get
| to that in the next year. Great point.
|
| edit: That 1% figure doesn't sound possible unless it has
| its own set of assumptions that need a confidence!
| griffzhowl wrote:
| It's not just a question of instrumental error though.
| There are also assumptions being used in interpreting the
| data from the instruments, and it's not generally possible
| to assign them reliable probabilities.
|
| e.g. the first line of the article's abstract quoted above:
|
| "Supernova (SN) cosmology is based on the key assumption
| that the luminosity standardization process of Type Ia SNe
| remains invariant with progenitor age."
|
| If the results reported in the article are right, the
| confidence we should have in this assumption, and therefore
| any results relying on it, have just radically changed.
| mr_mitm wrote:
| That's moving the goal post. I was specifically
| responding to concerns about fuzzy data.
|
| It's true that assumptions have to be made, and those can
| and should be questioned, but that wasn't the concern of
| the comment I replied to.
| the__alchemist wrote:
| My concern is model accuracy _holistically_ ; analyzing
| likelyness-to-be-correct including all assumptions; I
| think the post you are responding to is in context.
| CommenterPerson wrote:
| Maybe someone is tailgating it. And it's trying to annoy them by
| speeding up, then slowing down.
|
| There seem to be so many fudge factors in the whole chain of
| analysis we won't have an idea until we can make vastly improved
| measurements.
| WalterBright wrote:
| I picked the wrong week to put my faith in cosmology!
| kittikitti wrote:
| This is a fascinating discovery! It's brings into focus the Deep
| Field imagery from the JWST and how gravitational lensing was
| found to be greater than expected along with galaxies that were
| much older than expected based on redshift calculations. Perhaps
| this could indicate that the universe is even older than we
| originally thought if redshift calculations accounted for an
| incorrect perpetual acceleration.
| andrewflnr wrote:
| > The corrected supernova data and the BAO+CMB-only results both
| indicate that dark energy weakens and evolves significantly with
| time.
|
| > More importantly, when the corrected supernova data were
| combined with BAO and CMB results, the standard LCDM model was
| ruled out with overwhelming significance, the researchers said.
|
| I notice they're _not_ saying that dark energy is entirely
| unnecessary. Do we know if that 's just default caution, or are
| there still strong reasons to believe dark energy exists?
| mr_mitm wrote:
| The CMB and BAO measurements give us a picture of how the early
| universe looked. Supernovae are sensitive to the conditions in
| the late universe. All probes, which are mostly independent,
| always pointed at the same amount of dark energy.
|
| Now these people are saying SN actually point at zero dark
| energy, if accounting for the physics properly. That doesn't
| invalidate the CMB and BAO results. So dark energy must have
| had a big influence in the early universe, and no influence in
| the late universe, so it must by dynamic. (Ironically,
| supernovae were the first evidence for dark energy, which I
| guess was just a coincidence, if this new research is correct.)
| andrewflnr wrote:
| Ah, I didn't realize dark energy also had evidence that far
| back. I can only recall seeing the supernova data cited for
| it.
| mr_mitm wrote:
| https://phys.org/news/2020-06-dark-energy-expansion-
| cosmic.a...
|
| Check the first plot. Four different probes all agree on
| the same value. Well, used to, if this pans out. The blue
| one would be somewhere on the x axis now.
| cosmicjoe wrote:
| As a non-scientist I've always found the Cosmic Distance Ladder
| as likely to be inaccurate due its assumption about the constant
| brightness of Standard Candle stars over their lifetime, and the
| compounding of error at each rung of the ladder. Direct
| measurement of the CMB seems to be simpler with less chance of
| error.
|
| https://en.wikipedia.org/wiki/Cosmic_distance_ladder
| XorNot wrote:
| Direct measurement of the CMB can also have problems if our
| assumptions about it are wrong. A major goal of having two
| methods is that they should coalesce to the same result within
| margin of error - that they didn't told us we were missing
| something.
| wtcactus wrote:
| The supernovas type Ia luminosity depends on their composition
| and that takes into account both the age of the supernova and
| of the donator star. And that can be inferred by the luminosity
| curve of the supernova.
|
| https://en.wikipedia.org/wiki/Type_Ia_supernova
| naasking wrote:
| > I've always found the Cosmic Distance Ladder as likely to be
| inaccurate due its assumption about the constant brightness of
| Standard Candle stars over their lifetime
|
| Stars are just basic nuclear physics and gravity, that's why
| they're expected to be stable and predictable.
|
| > Direct measurement of the CMB seems to be simpler with less
| chance of error.
|
| Direct measurement of the CMB doesn't tell you anything on its
| own, you have to interpret the data in terms of a model. If you
| have a completely different model, say one without dark energy
| or without dark matter, CMB measurements would tell you
| something different than LCDM.
| eterevsky wrote:
| If they are replacing a fixed cosmological constant by a model
| with variable dark energy, doesn't it introduce extra parameters
| that describe the evolution of dark energy over time? If so,
| wouldn't it lead to overfitting? Can overfitting alone explain
| better match of the new model to the data?
| seydor wrote:
| We need an index tracking the expansion rate . And an ETF on it
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