[HN Gopher] New Evidence Against the Standard Model of Cosmology
___________________________________________________________________
New Evidence Against the Standard Model of Cosmology
Author : nsoonhui
Score : 169 points
Date : 2021-09-05 04:29 UTC (18 hours ago)
(HTM) web link (backreaction.blogspot.com)
(TXT) w3m dump (backreaction.blogspot.com)
| [deleted]
| bryan0 wrote:
| > They also point out that if we live in a local hole then this
| means that the local value of the Hubble rate must be corrected
| down. This would be good news because currently measurements for
| the local value of the Hubble rate are in conflict with the value
| from the early universe. And that discrepancy has been one of the
| biggest headaches in cosmology in the past years.
|
| Wow so a local hole might solve the Hubble measurement problem? I
| never heard that proposed at a potential solution before...
| rich_sasha wrote:
| Not knowing much about the subject: cosmological principle
| appears to say that laws of physics are uniform in space. Then,
| with known matter and forces, this leads to some structure, with
| fluctuations, and hence some scale over which matter is uniformly
| distributed.
|
| If we calculate such a scale and find matter is still not uniform
| at that scale, wouldn't the first conclusion be that there are
| missing terms in either matter or interactions (or both)? Rather
| than saying that laws of physics are not space-homogeneous.
|
| The article itself states that the length scale where the c10l
| principle kicks in is derived from a particular model for matter
| and interactions (lambda CDM).
|
| I think there is plenty of discrepancies between standard model
| and observations (most of them small). We don't know what dark
| matter is, either. So to me the interesting point wouldn't be, is
| the model wrong, but _how_ is it wrong?
| evgen wrote:
| > the c10l principle
|
| Don't do this. It is bad enough that every major devops/infra
| component needs to create some
| <letter><number_of_missing_letters><letter> tag, but dropping
| it in to random places is worse than the regular backronyms and
| cute project names science and tech people use to try to hide
| complexity. It just adds confusion for no rhyme or reason other
| than trying to sound like you are a part of some club of
| insiders.
| rich_sasha wrote:
| Dude I'm typing on my phone and autocorrect doesn't know
| "cosmological". There, I spelled it out.
| lurquer wrote:
| > Don't do this.
|
| Do not do that.
| beeboop wrote:
| You see it everywhere really. Military and politicians and
| government orgs all do it to embarrassing lengths too
| EGreg wrote:
| They also call things polintelcom and codenames like
| eschelon and prism, doesnt mean it's great practice for us
|
| Btw ESCHELON and Five Eyes coordination existed for so long
| and people only woke up when Snowden revealed prism
| nextaccountic wrote:
| the name is echelon
| ianai wrote:
| Per Sabine H on YouTube ( https://youtu.be/JETGS64kTys ), the
| cosmological constant might be smaller than called for in
| current cosmology. That would agree with some other
| observations.
| [deleted]
| teilo wrote:
| > Rather than saying that laws of physics are not space-
| homogeneous.
|
| No one is saying that, and if the cosmological principle falls,
| it does not imply that in the least. It just means we need to
| revisit our assumptions about things like hyperinflation, dark
| matter, etc. Even more exciting, it may mean we need to look
| for the remnants of a force active during the initial inflation
| of the universe, that can account for the non-uniformity of
| matter's distribution.
| rich_sasha wrote:
| Hmm, but if the principle comes with a model-dependent length
| scale, that experimentally looks wrong, why should I discard
| the principle when it might as well be an incomplete model?
|
| Or frankly inaccurate estimation, my understanding is that it
| is extremely hard to actually sully simulate the lambda-CDM
| model from Big Bang.
| drran wrote:
| n 2004, New Scientist, published an open letter from Eric Lerner
| and about 30 other scientists,[1] criticizing the Big Bang
| theory, and noting that Big Bang theory requires Dark Matter to
| exists.
|
| <<Without some kind of dark matter, unlike any that we have
| observed on Earth despite 20 years of experiments, big-bang
| theory makes contradictory predictions for the density of matter
| in the universe. Inflation requires a density 20 times larger
| than that implied by big bang nucleosynthesis, the theory's
| explanation of the origin of the light elements. And without dark
| energy, the theory predicts that the universe is only about 8
| billion years old, which is billions of years younger than the
| age of many stars in our galaxy.>>
|
| Can we finally abandon Big Shrink (BS) theory? It's obvious now
| that Oort cloud of Shapley attractor just collided with Dipole
| Repeller cloud [2].
|
| [1]: https://www.plasma-universe.com/an-open-letter-to-the-
| scient...
|
| [2]: https://vimeo.com/189355968
| sahil50 wrote:
| (1/H * c) = (1/a * ke^2 / (electron mass * c^2)) * (h / (proton
| mass * c * pi/2)) / (2G * proton mass / c^2)
| mkl wrote:
| What does that mean in this context? How does it relate to the
| cosmological principle in the article?
| sahil50 wrote:
| Hubble's constant is related to all the other fundamental
| constants. And is not a measure of "expansion", which is one
| of the core ideas of the Standard Model.
|
| Relation to the cosmological principle: self-similarity not
| just in terms of density and homogeneity, but also macro and
| micro scales. H, a measure of cosmic stuff, is literally
| derivable from atomic stuff.
| sharpener wrote:
| I'm not a cosmologist but...
|
| Is it possible to have both photon tiring and expansion and
| still measure the same numbers in experiment?
|
| Also wouldn't the arc separation of deep field stars
| increase detectably with expansion?
| sahil50 wrote:
| Maybe. But my reasoning is to assume as little as
| possible and start reasoning up from the point in history
| where the need for an explanation arose.
|
| And the need for an explanation arose when Hubble saw the
| redshift. He and Zwicky preferred tired light over
| galactic recession, but the halfwit academic
| establishment went with galactic recession.
| sharpener wrote:
| A fair approach.
|
| Incidentally, I just drew some diagrams and with the
| assumptions that the Earth is not at the centre of
| expansion, Earth orbit has extremes (for parallax), and
| all light only takes straight routes, my second question
| has a negative answer.
|
| But if one puts a gravitational lens on the view of one
| of the two stars then (based on a fast doodle though) it
| looks like maybe expansion could be detected.
| shmageggy wrote:
| Any time dissenting physics/astronomy opinions show up on here,
| it's always Sabine Hossenfelder. Is she a lone wolf or the face
| of a larger community?
| phkahler wrote:
| I have another error I'd like to discuss with her, but she
| charges to speak with one of her people. Sorry, I'm not paying
| for that :-)
| lytefm wrote:
| I wonder if she heard about the Stationary Universe Model of
| Peter Ostermann [1]. He argues along similar lines reagarding
| the inference of dark energy from the supernovae data.
|
| [1] http://www.peter-osterman.org/index.html
| vuldin wrote:
| She's discussing findings that come from papers written by
| other scientists, so she is obviously not a lone wolf.
| StephenAmar wrote:
| I also watch PBS spacetime series.
|
| I think https://youtu.be/dsCjRjA4O7Y is relevant here.
| tlogan wrote:
| She might be right but, as of now, the evidence shows that she
| is probably not right.
|
| But as with everything, contrarian point of view is always
| popular on the internet. And we all want be in the know (have
| some secret knowledge) thus posts like this are popular.
|
| So if she is really right we will feel like winners - if not,
| who cares: it is internet.
| JohnJamesRambo wrote:
| I love her so much. Everything she explains is so crystal
| clear.
| varjag wrote:
| She's a new kind of popular science presenter, with refreshing
| depth and command of the subject that's been lacking in this
| field for ages. She's popular and popular content is getting HN
| front page often. Add here the dynamics of social media
| engagement, meaning that more disputed/controversial topics get
| promoted and shared more.
|
| As a physicist she does have certain opinions (would be strange
| if she didn't), they make for good material so naturally she
| brings it up. The disputed subjects however are a fraction of
| her content, which includes covering the well established
| basics.
| dgellow wrote:
| Her music videos are also awesome :)
| Semaphor wrote:
| Thanks for the tip.
|
| Her current music video channel [0] and a playlist [1] of
| her older music videos on her science channel. Some of them
| are her own songs, others are covers. I'm currently
| enjoying "Cassandra (Prophet of the Dark)" [2]
|
| [0]:
| https://www.youtube.com/channel/UCPtRwW9i43BXbCRQa7BJaiA
|
| [1]: https://www.youtube.com/playlist?list=PLwgQsqtH9H5ckD-
| v9Ux3T...
|
| [2]: https://www.youtube.com/watch?v=PX0k0WfMSi0
| k__ wrote:
| I like her much more than Harald Lesch or MaiLab.
|
| She makes a smart, but also down to earth impression.
|
| The other science presenters are always so full of themselves
| that I can't watch them.
| swhalen wrote:
| I think it's probably fair to say most cosmologists would
| consider her views marginal, but she is certainly not a crank.
| My (limited) understanding is that LCDM fits cosmological
| observations extremely well; however, neither dark matter nor
| dark energy has actually been shown unambiguously to exist.
| 'Mainstream' cosmology invariably also includes inflation,
| which remains essentially a speculative idea unsupported by any
| hard observational evidence. Sabine Hossenfelder has become a
| popular commentator by drawing attention to discussions of
| these and other issues.
| plutonorm wrote:
| She comes into the field from a mathematical background. In
| that sense she is an outsider.
| tsimionescu wrote:
| I think she is a really credible voice, given her background in
| theoretical physics and her matter-of-fact demeanor, plus her
| tendency to express all the necessary caveats. As such, when
| you see a dissenting belief from her, you are more likely to
| have people actually believe there is something there and not
| just BS. I think this is a major factor - basically, dissenting
| opinions discussed by Sabine Hossenfelder carry more weight
| than others.
| hannob wrote:
| There are a bunch of people with similar thoughts. Just
| recently a blogpost by Peter Woidt showed up here [1]. While
| I'm only following this as a lay person I think you can say
| Woidt and Hossenfelder come from the same corner of "critics of
| contemporary physics" or however you want to call them.
|
| [1] https://news.ycombinator.com/item?id=28325753
| mdoms wrote:
| Careful there, you're standing on a Hacker News landmine. For
| whatever reason, whenever Woit's name is invoked here the
| downvote brigade is not far away.
| hannob wrote:
| Huh, is that so? Why?
|
| Anyway, I haven't even said whether I agree with him or not
| (which tbh wouldn't be very relevant, as I know where my
| limits are, and judging debates in physics is definitely
| outside my area of expertise).
| gtsop wrote:
| I am so excited to see new observations and theories challenging
| the current model
|
| (Link to earlier comment of mine summarizing what I think is
| wrong with the established mentality)
|
| https://news.ycombinator.com/item?id=27399696
| oolonthegreat wrote:
| > It increasingly looks like we live in a region in the universe
| that happens to have a significantly lower density than the
| average in the visible universe. This area of underdensity which
| we live in has been called the "local hole"
|
| that sounds really weird, if the cosmological principle is
| invalidated, does that mean that we have to reject the Copernican
| principle as well? the text seems to imply that there is
| something "special" about our location in the universe.
| raattgift wrote:
| 1/2
|
| For space reasons I'll cut my reply into two parts. The first
| discusses the Copernican principle in question, the second
| answers your question about this specific blog post.
|
| The modern understanding (and name) of the Copernican principle
| is really owed to mid-20th-century Hermann Bondi's work in
| general relativity, and it is a generalization of the initial
| Copernican model of heliocentricity, with the sun at the centre
| of the universe, and the Earth, other planets, and distant
| stars tracing out exactly circular concentric orbits around it.
|
| At its most general while still retaining its strength, the
| Copernican principle says that in a system with certain
| symmetries, there is no distinguished position on a circular
| orbit. This is not just orbits within a 4-dimensional
| spacetime; it applies in certain many-dimensional phase spaces
| too.
|
| (One can generalize further by giving up some strength and say
| that most spaces with certain symmetries admit a notion of
| _typicality_ which applies to any choice of initial momentum
| almost everywhere in the space. We can then discuss how such a
| measure breaks in more complicated systems. Consider
| translational symmetry on the Earth on an overcast moonless
| night. If you choose a random spot on Earth and then swim or
| walk a kilometre or ten in any direction, your view of the
| surface features out to the horizon is unlikely to change. If
| you found yourself somewhere in a salty body of water nowhere
| near land you would struggle to tell with any precision where
| on Earth you were or which compass direction you had moved. If
| you found yourself somewhere in a sandy desert or flat
| scrubland far from human settlement and no "celestial guides"
| like the position of the sun, again you would struggle to tell
| with any precision where on Earth you were or the direction you
| are facing. There are however atypical features of the surface
| of the Earth which break translation symmetry: coasts, edges of
| forests, peaks of mountains, human settlements, Manhattan, you
| name it. Moving from water to land or vice-versa clearly breaks
| some _global_ notions of typicality. However there is a lot of
| coast on the Earth. You 'd probably only find complete _a_
| typicality when close enough to major landmarks like the Great
| Pyramids of Giza or Niagara Falls. We can also add in a notion
| of _temporal_ typicality -- sufficiently close to sunrise or
| sunset, or on starry nights, it is easier to orient oneself
| towards compass points.)
|
| Our solar system's mass distribution is only approximately
| spherically symmetric, and planetary orbits are non-circular
| ellipses, so Copernican heliocentricity holds only
| approximately. And of course we now know that other stars do
| not orbit our own (even nearby ones do not move in a circular
| or even elliptical orbit around it). The Copernican
| approximation is still _locally_ useful as a basis for
| comparison with observations, and those led quickly to Kepler
| discovering the features of stable elliptical orbits, Galileo
| discovering the large moons of Jupiter and their orbits around
| it, he and others the phases of various planetary bodies, and
| ultimately Newtonian gravitation.
|
| Copernican heliocentrism is thus correct in some effective
| limit: it works as long as we do not look too closely at small
| details of the sun's wobbles or perturbation of various orbits
| by Jupiter, and as long as we are only considering things at a
| solar system scale. (It applies in many other solar systems
| too: a central mass tends to entrain smaller masses into
| nearly-circular orbits. And it is useful for comparison studies
| of star systems where orbits are far from circular (many many
| comets, strange exoplanets) or where there are two or more
| stellar masses surrounded by smaller bodies.). And that it is
| not exactly correct made (and still makes) it even more useful
| in exploration of the real solar system.
|
| There is a notion of Copernican typicality in galaxies too.
| There is nothing clearly special about our solar system's place
| on its orbit through the Milky Way, thanks to the galaxy's
| approximate axisymmetry. Likewise, except close to the galactic
| centre, the galactic edge, or well outside the plane of the
| disc, virtually all star system orbits through the Milky way
| are highly typical. As in Copernican heliocentrism where the
| position of Earth at any time isn't particularly special,
| "Copernican Sgr A* centrism" means the position of the sun
| isn't particularly special either. Of course we are adapted to
| "goldilocks" atypicality at the solar system scale: we thrive
| in a family of approximately 1 a.u. orbits, and would struggle
| to survive in most others. We are less sensitive to the path
| our solar system takes through the galaxy.
|
| Next, there is the Copernican principle in cosmology. This
| Cosmological Principle starts with the greatest symmetry: a
| universe which looks the same in every direction from every
| possible vantage point. Cosmology is in many ways a study of
| how the Cosmological Principle breaks down. It does in various
| ways:
|
| * Locally, we're on a planet. On a starry night, down looks
| very different from up. There are our solar system's planets in
| various directions but not in most directions.
|
| * We're also in a galaxy in a local cluster: from the southern
| hemisphere we see the galactic bulge. Dust and gas
| distributions are denser in some directions than others. We can
| also see satellite galaxies like the large Magellanic cloud. We
| can also see M31 taking up a surprisingly large solid angle of
| the sky (more than the moon; it's just that the Andromeda
| galaxy is dim), and a handful of others.
|
| * There is a Cosmic Web structure to bright clusters of
| galaxies, and (misleadingly named but definitely sparser)
| "supervoids" between the filaments of the web. There are also
| smaller overdensities and underdensities in these large
| regions.
|
| However, we have not done much damage to the _typicality_ of
| our vantage point. There are lots of similar star systems in
| lots of similar galaxies in lots of similar clusters in some
| area of similar Cosmic Web density.
|
| It is clear, though, that the entire cosmos is not uniform,
| that there are various boundaries against which one can take an
| orientation.
|
| Cosmology is also about understanding temporal typicality too.
| Even in the very early 20th century, there were questions being
| studied: has the universe always looked like this, with lots of
| galaxies containing many stars like our own? Trying to answer
| this question with the _hard requirement_ that any answer be in
| concordance with available evidence led us to a definite no. In
| the reddest, dimmest, smallest-solid-angle galaxies we have
| observed, our sun would be extremely atypical based on its
| spectral lines indicating elements other than hydrogen and
| helium, but in less-red, less-dim, less-small-solid-angle
| galaxies (right up to M31) we see that our sun would be less
| and less unusual.
|
| We can then think of temporal boundaries: what happens in the
| very earliest times? What's at the highest redshift (answer:
| the cosmic microwave background and no bright galaxies)? What
| does that imply about the deeper past? Does it imply anything
| about the future?
|
| The concordance cosmology -- the standard cosmology, with
| \Lambda-CDM serving as its mathematical expression -- works
| exactly with all these various "distractions" smoothed out.
| Rather than considering star-filled galaxies forming clusters
| of various sizes, we consider a _dust_ uniformly scattered
| through an expanding space, with non-gravitational interactions
| (radiation pressure) becoming more important in the past and
| less important in the future. This picture is then deliberately
| _perturbed_ with features found by astronomers, and those
| perturbations are studied for their impact. Most remain local,
| a scale far far from cosmological.
|
| Informally, this means "We don't care what happens inside
| individual galaxies, each of which is just one mote of the
| cosmological dust, and we track the components generating the
| energy-density of a _typical_ point in space as the dust -- or
| its various components -- dilute with the expansion, or grow
| denser as we look into the deep past ".
|
| 1/2
| raattgift wrote:
| 2/2
|
| Some years ago there was no reason to think that the dust was
| diluting away with any driver other than some single impulse
| in the distant past. An initial acceleration, followed by an
| eternity of inertial motion. More recently evidence has
| tended to disfavour purely inertial motion, driving the study
| of possible mechanisms for (and expressions of) ongoing
| acceleration.
|
| A strong enough violation of the cosmological principle --
| that there is something unexpected and _atypical_ about the
| local neighbourhood our galaxy cluster is in -- might drive
| us back to a purely inertial expansion, if that atypicality
| is causing us to mistake a _local_ gravitational acceleration
| for a cosmological one. This is the topic of the Hossenfelder
| blog entry.
|
| However, one possible result is that there is something
| unexpected about the gravitation in the local neighbourhood,
| but that it applies in _other_ local neighbourhoods too,
| including those containing extremely bright sources like
| quasars, returning us to the problem of accelerated
| expansion. Real proposals that are under investigation
| include the dynamical outflow of gas and stars from galaxy
| clusters, driven by the internals of these clusters and the
| gravitational influence of neighbouring overdensities (our
| "local hole" is adjacent to several including the Shapley
| Supercluster, about 231 Mpc distant). Such processes over
| cosmological timescales may serve to drive galaxy clusters
| _towards_ typicality.
|
| There are also many open questions about the intermediate
| regime between the cosmological scale and the galactic scale
| each of which can be studied with a much more easy to work
| with approximation of the full theory of General Relativity.
| z ~ 0.04-0.55 - ~ 100-250 Mpc is right in that intermediate
| regime. The growth of our theoretical toolbox may resolve
| some blurry problem at the length scales that are at the root
| of the arguments in several of the papers Hossenfelder's blog
| post refers to. The result might be that the allegedly
| unexpected local phenomenon ("the local hole") should have
| been expected after all. See
| https://astrobites.org/2021/09/01/gravity-on-all-scales/ for
| some details.
| throwaway81523 wrote:
| No I don't think it's like that. We know that matter and vacuum
| clump together at a series of increasing scales: the solar
| system, our galaxy, the local cluster, some surrounding
| supercluster, maybe there is a superdupercluster level after
| that, but the theory being disputed is that the hierarchical
| clustering stops after those N levels, and after that, the
| superduperclusters (or whatever) are distributed randomly
| instead of grouping into even more enormous structures. The
| idea is that the universe started as a random fluctuation and
| that the clusters etc. came from a diffusion process, like
| stripes on a zebra. The stripes are locally correlated, but
| less so over longer distances.
|
| Sabine H is saying that the clustering goes further than the
| theory can account for, and that the "local hole" is a feature
| of this bigger structure, not that it's something special.
|
| Anyway, even if our part of the universe is special, there can
| be an anthropic explanation, like saying we live on the special
| part of the Earth that has a habitable climate and is not
| covered with water.
| Ericson2314 wrote:
| The local hole doesn't seem so contrarian, as the 600 Mly is
| smaller than the multiple Gly of the funny quasars.
| throwaway81523 wrote:
| The multiple-Gly funny quasar clusters are also in tension
| with the existing theory.
| ben_w wrote:
| > the text seems to imply that there is something "special"
| about our location in the universe.
|
| The counterpoint to the Copernican principle is the anthropic
| principle: we can only find ourselves in places which support
| the existence of beings like us.
|
| I have no idea if the density variation even _might_ be
| important for chances of industrial intelligence, but people
| have suggested galactic (not just stellar) Goldilocks zones as
| one requirement (and separately "having a very large moon"), so
| I also wouldn't automatically dismiss anyone who said it was
| important.
| Semiapies wrote:
| In honor of weekend HN: https://xkcd.com/1758/
| sesm wrote:
| If you are interested in cosmology, there is a series of papers
| by Gorkavyi building a cyclic universe cosmological model that's
| entirely based on Einstein's general relativity and doesn't
| require any quantum gravity theory. It's based on black holes
| mergers with mass loss and convertion of mass into gravitational
| waves, that later get captured by black holes again.
|
| https://pos.sissa.it/335/039/
|
| https://academic.oup.com/mnras/article/476/1/1384/4848298
|
| https://academic.oup.com/mnras/article/461/3/2929/2608669
|
| https://www.sao.ru/Doc-k8/Science/Public/Bulletin/Vol76/N3/A...
| (this one is available only in Russian for now)
| JetSetWilly wrote:
| > Two years ago, I told you about a paper by Subir Sarkar and his
| colleagues, that showed if one analyses the supernovae data
| correctly, without assuming that the cosmological principle holds
| on too short distances, then the evidence for dark energy
| disappears. That paper has been almost entirely ignored by other
| scientists.
|
| Is this a case of science advancing one funeral at a time? We
| have to wait for the dark energy "establishment" do die off?
| rich_sasha wrote:
| There is more evidence for dark energy. Discrepancies in
| redshift vs distance are just one, and there are interestingly
| also other explanations for it.
|
| IIRC in lambda-CDM, if you don't have dark energy, the whole
| universe just looks very different, eg the structures of
| galaxies, groups and supergroups etc are not the same.
|
| It might still be wrong, but more nails are needed for this
| coffin.
| raattgift wrote:
| The value for \Lambda, the cosmological constant, is tiny and
| positive. It's so tiny that as we take it to zero, the
| universe is still filled with clusters spiral and elliptical
| galaxies with a strong solid-angle-on-the-
| sky/brightness/redshift relation, and those galaxies filled
| with the same sorts of stars we see in the sky.
|
| Indeed the evidence available prior to 1998 or so favoured a
| \Lambda of zero, and the early evidence favouring a tiny
| positive value was very much a surprise. The Hubble Space
| telescope had already been running and taking deep views for
| several years. COBE (https://science.nasa.gov/missions/cobe)
| and the Saskatoon experiment had already finished. None
| presaged the results of the Supernova Cosmology Project and
| High-Z Supernova Search Team. Follow-ons by Hubble (and
| others) and successors to COBE support the accelerated
| expansion.
|
| The physical interpretation of the zero versus the tiny
| positive value is that in the former there was a last early
| acceleration which ended essentially all at once, with galaxy
| clusters then moving purely inertially; or alternatively
| there was an early acceleration which decayed, possibly in
| several steps, into a tiny persisting constant acceleration
| well before the formation of the surface of last scattering
| (the observed cosmic microwave background). Or alternatively
| there were mutiple sources of acceleration, one very large
| and which ceased early, and one which has been always-a-small
| constant.
|
| There are different lines of evidence for how this residual
| acceleration has evolved. Practically all of it favours it
| settling down into one constant tiny value in the very early
| universe, and that the value can be determined with ever
| greater precision mostly by studying the fine detail in the
| cosmic microwave background and the various observables of
| highly red, dim, low-angular-diameter galaxies backlit by
| quasars and internally lit both by quasars and supernovae.
| The exact value is a matter of active research, as some of
| the data is conflicting.
|
| None of the data disfavours _some_ ongoing acceleration, and
| the conflict is generally within 10%. As an example of the
| physical consequences of the discrepency, the lower value
| means we can see more galaxies (and more galaxies will be
| able to see the light from the Crab supernova and other
| historical galactic supernovae), while the higher value fewer
| galaxies we can see and a _lot_ fewer galaxies who could see
| a recent supernova within the Milky Way.
|
| There are also various ideas that the tiny value of \Lambda
| is not constant but continues to evolve. Most of these
| unfailingly generate observables consistent with a new non-
| vanishing long-range force to accompany electromagnetism and
| gravitation, and such an extra ("fifth") force is almost
| wholly ruled out by evidence. Some store up this fifth
| force's energy until local matter-energy density is very low
| (trillions of trillions of years in our future) and unhide it
| then at various powers (often very high, in an essentially
| global phase change).
|
| Attempts to remove ongoing acceleration altogether by setting
| \Lambda to zero seem somewhat contrived. A typical approach
| is to assume that the universe is much less homogeneous than
| it appears, and that we are being mislead by being in a
| highly unusual place exceptionally close to the centre of a
| large matter underdensity. This was of interest to several
| teams of theoreticians (Clifton, February) around 2008-2009,
| as they developed specific models -- _within_ general
| relativity as the theory of gravitation -- in order to try to
| distinguish whole families of such models from the standard
| cosmology rather than outright advocating for those models in
| preference to the standard cosmology. More broadly, this is
| related to cosmologies that are wildly inhomogeneous at large
| scales compared to the standard cosmology, such that in some
| greater-than-galaxy-sized regions of spacetime the matter is
| much older than in others (in Wiltshire 's voids, and in
| dense areas close to their boundaries, clocks run a lot more
| quickly so observers will see outside-the-void matter as
| gravitationally (collapse) rather than cosmologically
| (accelerated expansion) redshifted). Some of these models are
| designed to explore how one can generate an averaging
| procedure for general curved spacetimes, or at least for
| "lumpy" 3+1-dimensional ones, rather than to really challenge
| the most general form of the Copernican principle (i.e., they
| don't really want to put Earth pretty much at the centre of
| the universe).
|
| Motivations do vary though; there are some productive
| everyday cosmologists whose single-author papers occasionally
| develop alternatives to the standard cosmology that fit
| closer to some scripture or other. There are also some
| modified gravity proponents (some of whom work every day with
| the standard cosmology) whose theories of gravitation "need
| help" from a favourable distribution of matter that picks out
| the region around us as atypical.
| michelpp wrote:
| Sarkar addresses this other evidence in this interview:
|
| https://youtu.be/JJzU9hDjiRk?t=819
|
| In summary, there is a strong selection bias in cosmology
| toward the standard model which induces "predictions" that
| confirm themselves. One bit of evidence he presents, dozens
| of studies were found to be within one sigma of the wmap
| measurement and not naturally distributed as one would
| expect.
| The_rationalist wrote:
| MOND lead to less paradoxes/mispredictions than dark
| matter/energy
| whatshisface wrote:
| One thing that can happen when you are doing computer
| modeling to find the input parameters that explain your
| observations is getting stuck in a local maximum. I am
| absolutely ready to believe that eliminating dark energy from
| current models makes their results look less like the real
| universe, but the number of re-runs that would be required to
| sample the entire parameter space and demonstrate that there
| were no other parameterizations that looked like our universe
| would be enormous, and if you include the possibility of new
| theories, infinite.
|
| There would either have to be some kind of theoretical reason
| to think that the best known parameterization of a simulated
| lambda-CDM universe is not merely a local maximum, or the
| parameters would have to be well-constrained, by
| observations, so that the free parameter space was small
| enough to exhaustively explore. I am not aware of either
| condition being true so I will express some skepticism about
| the conclusions from the models. Nonetheless, my lack of
| knowledge about those conditions is not very strong evidence
| for their absence, and I know there could be someone reading
| this and feeling very annoyed that I don't know about the
| Backhausen-Thule principle, or whatever piece completes this
| puzzle. (Your contribution to the discussion, oh annoyed
| reader, would be greatly appreciated.)
| neuronic wrote:
| Of course. Science is just a chase for grant money. Lots of
| entertainment money to be earned and documentaries can be made
| about "dark energy".
|
| Knowledge discovery is secondary or tertiary to modern science.
| The field is full of greedy egomaniacs, leaving the honest
| scientists at a competitive disadvantage. It's about reputation
| and $$$.
| analog31 wrote:
| I think this is an aside to what you're asking, but "science
| advances one funeral at a time" was a clever slogan and not an
| empirically tested hypothesis.
| avereveard wrote:
| > without assuming that the cosmological principle holds on too
| short distances
|
| There's still the problem of colliding galaxies showing a
| weakly interacting centroid that's shifted compared to the
| masses but interacts with the visible masses. If truly are
| variation in the local constants, then one has to explain why
| these variations shows inertia, at such point it starts looking
| more and more like matter
| mdturnerphys wrote:
| That is evidence for dark matter, not dark energy.
| Ericson2314 wrote:
| That's about dark matter, this was about dark energy.
| The_rationalist wrote:
| Is this related to MOND?
| Svoka wrote:
| That would be true if young scientists wouldn't continuously
| make successful predictions based on cosmological principle
| among other observable effects of the general relativity and
| standard model. Make observable prediction, coherent thesis,
| then we'll talk. Of course our models are not perfect, but it
| is best we have. Physics so far never dealt in "fundamental
| truths", just good enough models. So far, this is best we got.
| zeven7 wrote:
| I'd argue that Einstein in particular cared a lot about
| "fundamental truths".
|
| Not everyone can be Einstein, but I'm glad some people care
| about asking deeper questions.
| simonh wrote:
| He cared about fundamental truths, but he didn't think we
| had them.
|
| " all our science, measured against reality, is primitive
| and childlike -- and yet it is the most precious thing we
| have."
|
| The best we can ever say about science is that it is
| useful, that's what truth means in science, that it
| produces accurate predictions. Truth in any deeper sense is
| a matter for philosophers.
| kkylin wrote:
| I don't disagree with your point, but do want to add that
| not publishing on "fundamental truths" isn't the same as
| not asking those questions. Not everyone's going to have
| something novel, plausible, and fundamental to say on a
| regular basis, hence most publications (even if everyone's
| asking these questions, which granted they're probably not)
| are going to be much more incremental.
| rich_sasha wrote:
| Ironically, it was Einstein who introduced the
| "cosmological constant" (and thus indirectly dark energy).
| I think later in life he called it a glorified fudge factor
| and his biggest regret.
| raattgift wrote:
| Wikipedia covers this sufficiently at https://en.wikipedi
| a.org/wiki/Cosmological_constant#Sequence...
|
| The five-line tl;dr: non-expanding cosmologies with no
| big bang but lots of galaxies tend to collapse in finite
| time. One can avoid collapse with a positive cosmological
| constant. That approach predated the work of Hubble
| (expansion) and Lemaitre (big bang). Expanding
| cosmologies with a sufficiently large initial big bang do
| not need a cosmological constant to keep expanding
| forever. Einstein, not being stupid, recognized that and
| carried on.
|
| Since 1998: an accelerating expanding universe is
| inconsistent with just a single big bang as impulse, but
| is consistent with a small positive cosmological
| constant.
|
| Einstein and Schrodinger certainly discussed whether to
| treat the cosmological constant as an energy entering
| into the right hand side of the Einstein Field Equations
| instead of a multiplier on the metric in the left hand
| side: [Harvey 2012] https://arxiv.org/abs/1211.6338 Their
| conclusion is that choice of side is principally a matter
| of aesthetics, and that remains true today.
|
| Harvey2012 SS5 is a good reminder not to put too much
| weight into the early days of general relativity. Exact
| solutions were few and simple but still extraordinarily
| hard to work with by hand. Numerical approaches didn't
| exist, nor did formalisms that provide post-Newtonian
| approximations that are more tractable. Realistic
| distributions of matter were largely as-yet undiscovered
| (compare 1917 introduction of cosmological constant and
| low estimates of the number of spiral galaxies in the
| sky, their mass, and the light-travel distance to them:
| https://en.wikipedia.org/wiki/Great_Debate_(astronomy)
| which came _later_ ).
|
| Einstein's adaptation to the flood of astronomical
| discoveries during his productive lifetime is part of
| what made him _Einstein_ rather than any less celebrated
| figure.
| didibus wrote:
| > Physicists believe they understand quite well how the universe
| works on large scales
|
| Why would a physicist write an article and talk about physicists
| like they were some mystical "other" single minded group of
| people. I just hate that characterization, so unhelpful and
| damaging in my opinion, and kind of manipulative to open up an
| article with that.
|
| I don't actually believe most physicist believe they understand
| how the universe works, I think most of them feel like there's
| still so much they don't understand, that it's probably why they
| wanted to become a physicist in the first place. But I might also
| be wrong, and in any case, you just shouldn't start your article
| with a big fallacious generalization that has no data or
| rationale to back itself up and also somehow position yourself as
| some sort of "knows better".
| JoBrad wrote:
| Side tangent: Why are most of her numbers, except dates, spelled
| out? Is this some convention specific to her country of origin or
| something?
| platz wrote:
| This is a transcript of the video embedded below. Some of the
| explanations may not make sense without the animations in the
| video.
| tsimionescu wrote:
| Which numbers are you referring to? "3 billion" instead of
| "3,000,000,000"? That could just be efficiency of typing (not
| to mention, German uses , and . inversely from English: Pi is
| 3,1415... in German writing, while a thousand is 1.000).
| JoBrad wrote:
| I was thinking of this paragraph. However, after I re-read
| the article, it seems that there are other numbers that
| aren't spelled out. Maybe it was an auto-transcription?
|
| > Already in nineteen-ninety-one they found the Clowes-
| Campusano-Quasar group, which is a collection of thirty-four
| Quasars, about nine point five Billion light years away from
| us and it extends over two Billion Light-years, clearly too
| large to be compatible with the prediction from the
| concordance model.
| CurtHagenlocher wrote:
| Yes, but a German billion isn't the same as an American
| billion either... .
| codethief wrote:
| > Two years ago, I told you about a paper by Subir Sarkar and his
| colleagues, that showed if one analyses the supernovae data
| correctly, without assuming that the cosmological principle holds
| on too short distances, then the evidence for dark energy
| disappears. That paper has been almost entirely ignored by other
| scientists.
|
| I suppose she's referring to the things discussed in her
| interview with Sarkar here ->
| https://www.youtube.com/watch?v=B1mwYxkhMe8 .
|
| I can't claim I understand the details of what Sarkar is talking
| about since I dabbled in cosmology only very briefly but I at
| least made sure to forward the interview to my former advisor
| (whose name is on several hundreds of papers on cosmology and
| astrophysics, including those of the PLANCK collaboration and
| several others) and his response was along the lines of:
|
| > I appreciate Subir Sarkar very much but I'm afraid I don't
| agree with barely any of his statements. He never looks at the
| full picture but only individual pieces and then he ends up
| modifying those until look prettier individually but no longer
| fit the rest of the cosmological model.
| DudeInBasement wrote:
| I need more grant money to keep looking for dark garbage. I
| can't be bothered to question my grants
| DinosaurShampoo wrote:
| If even the Cosmological constant is debunked,there's truly no
| rules to what's possible.
| sahil50 wrote:
| Another problem with the standard model is attributing the
| cosmological redshift to the Doppler effect.
| FridayoLeary wrote:
| could you pls elaborate on that?
| JPLeRouzic wrote:
| sahil50 posted this 2 months ago:
|
| https://colab.research.google.com/drive/1K1qoUFvqZp1fWbpcKJW.
| ..
| andyjohnson0 wrote:
| I'm not the parent commenter, and I'm not a physicist, but
| this might be a reference to the non-mainstream theories that
| are often grouped under the heading of "plasma cosmology".
|
| https://en.m.wikipedia.org/wiki/Plasma_cosmology
| sahil50 wrote:
| What Hubble objectively measured wasn't galaxies receding. He
| measured redshift. Or photon energy loss.
|
| And there's another way to explain this, that is simpler,
| self-consistent, and doesn't require the concept of
| "inflation" where apparently space expanded faster than the
| speed of light.
|
| The explanation: photon hubbling, tired light. That galaxies
| are frankly right where they are. They're not receding. The
| photon loses energy. It costs energy to forge a path through
| spacetime.
| naasking wrote:
| "Tired light" has failed other tests, so it's probably not
| the answer.
| sahil50 wrote:
| How so?
|
| Considering all the data on redshift we have, tired light
| fits. Not galactic recession.
|
| Rough calculations https://docs.google.com/spreadsheets/d
| /1HI61-pDIzzSItw48K0ga...
|
| Data from https://ned.ipac.caltech.edu/Library/Distances/
| phaemon wrote:
| Galaxies are either approaching or receding from our
| perspective. How could they possibly be stuck in some
| "place"? Your theory makes no sense.
| sahil50 wrote:
| How do you know?
| phaemon wrote:
| How do I know that two objects are either receding or
| approaching? Because it's obvious. Think about it
| yourself.
|
| Edit: ah, wait, your theory says that approaching objects
| look the same as receding ones. I think you need to
| justify that.
| sahil50 wrote:
| You misread.
|
| The cosmological redshift is not attributable to galaxies
| receding.
|
| The cosmological redshift is photons losing energy as
| they forge a path through the gravitationally connected
| universe. It's the cost of traveling.
|
| Total redshift = Cosmological redshift (photon forging a
| path through spacetime) + Doppler redshift (for example,
| Andromeda drifting toward us) + Gravitational redshift
| (like how Sun-to-Earth photons are redshifted because the
| Sun is more massive)
| teilo wrote:
| As opposed to what?
| sahil50 wrote:
| Photon hubbling, tired light. The photon is doing work as it
| moves through spacetime. Modeled as E_t / E_0 = e^(-Ht),
| where H is Hubble's constant, and t is time of travel.
| drran wrote:
| As opposed to one of "tired light" models.
|
| Light is not immortal, so it loses some energy with time.
| E.g. gravitational noise can affect photon energy, or photon
| can lose some energy to medium due to friction, or photon can
| lose some energy because of truncation of ideal sinusoidal
| wave at Planck scale, or speed of light is a bit slower than
| c (because light arrived 16 seconds later than gravitational
| waves, when gravitational waves were discovered), thus photon
| is not frozen in time and expands at very slow rate.
| zozbot234 wrote:
| The standard argument against 'tired light' is that it
| should lead to scattering of light from more distant
| objects, but this has not been observed in the data.
| drran wrote:
| The intensity of scattering is proportional to loss of
| energy. It is impossible to detect such low scattering
| level in our visible Universe because it is full of
| gasses and dust, which created many many orders of
| magnitude stronger scattering, which is still hard to
| notice except for very bright objects near to dense
| clouds of dust. It's not possible to confirm or
| disapprove this argument yet.
|
| Moreover, if we are talking about friction and medium
| (the Ether), then it was predicted long time ago[1], that
| discussion will be resolved in favor of Ether when Higgs
| field will be discovered, because Higgs field must be
| present everywhere, like Ether, and because medium is
| required for transverse waves to propagate. Discovery of
| Higgs boson and Higgs field was announced in 2012, so
| discussion is resolved, but we still call the medium as
| (physical, quantum) vacuum, like we still call atom as
| atom (<<unbreakable>>) after breaking it, or we use <<->>
| for presence of electrons instead of absence of
| electrons.
|
| (non-native speaker)
|
| [1]:
| https://physicstoday.scitation.org/doi/10.1063/1.882562
| sahil50 wrote:
| The standard argument is a straw man argument. Tired
| light is not photons getting scattered, and is not
| photons bumping into stray electrons.
|
| Tired light is because there is a cost to traveling
| through spacetime. The photon is warping the shape of all
| the universe mass around it. The photon is doing work.
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