[HN Gopher] Physicists who want to ditch dark energy
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Physicists who want to ditch dark energy
Author : dnetesn
Score : 75 points
Date : 2025-01-12 11:17 UTC (11 hours ago)
(HTM) web link (nautil.us)
(TXT) w3m dump (nautil.us)
| moffkalast wrote:
| > In this timescape model, what we observe in our vicinity, in
| our own patch, is governed by different laws than what happens on
| average at larger distances. It is much like how what you observe
| in your home city may be a poor description for what happens in
| the world on average.
|
| If a dark matter alternative ends up being an accepted theory,
| then RelMOND stans are gonna be beyond smug, and well rightfully
| so I suppose.
| MattPalmer1086 wrote:
| No, the laws are the same everywhere. The timescape model just
| takes into account gravitational time dilation in large voids
| (where time passes faster). They say this can explain the
| observation that the universe is expanding faster (in other
| words, it's not, it just looks like it).
|
| Also, this is about dark energy, not dark matter
| moffkalast wrote:
| Ah right yeah, had them mixed up for some reason.
| chuckadams wrote:
| Every science documentary I've watched tells me most physicists
| want to ditch "dark energy" because it's a placeholder term for
| something we still don't understand yet. Map-makers didn't
| actually believe there were dragons after all.
| the__alchemist wrote:
| I've heard the same about Dark Matter, and that was previously
| my amateur mental model. This was naive; in practice it
| confidently refers to CDM (cold dark matter), which is matter
| that interacts gravitationally, but not electromagnetically,
| with normal matter.
| XorNot wrote:
| That's literally what a placeholder is: it's a description of
| a suite of observed properties.
|
| Hot dark matter would be a black body emitter - we would see
| it.
|
| If it interacted electromagnetically then effects like the
| bullet cluster's gravitational lensing shouldn't happen.
|
| And if it didn't interact gravitationally then we should see
| normal galactic rotation curves.
| andrewflnr wrote:
| No, hot dark matter would not magically start interacting
| with the EM field to make black body radiation. I believe
| the hot/cold dark matter question is entirely about the
| velocities of the particles.
| uoaei wrote:
| > it's a description of a suite of observed properties
|
| "Looks like matter" is not a property, this interpretation
| already presupposes a theory that excludes many others that
| are heretofore still plausible. Physicists tend to ignore
| those other options, I believe, because of a combination of
| natural human linguistic biases and the desire for
| certainty in explanatory models that drives many of us into
| studying physics. Some get too confident too early and
| start making dogma their entire academic personality.
| the__alchemist wrote:
| I think we are on the same page. I was sloppy in my
| wording; my point is, "dark matter" is not a placeholder
| for _discrepancies in Newtonian simulations of cosmological
| features with observation_ , but a placemholder for a type
| of gravitational-interacting bodies.
| floxy wrote:
| >Hot dark matter would be a black body emitter - we would
| see it.
|
| Hot dark matter would be stuff like neutrinos and axions
| which don't interact electromagnetically.
|
| https://en.wikipedia.org/wiki/Dark_matter#Warm_dark_matter
| elashri wrote:
| The submission title is edited in a questionable way. Specially
| that the original one is not clickbait and does fit in the title
| letters limit.
|
| There is a world of difference between " These Physicists Want to
| Ditch Dark Energy " and " Physicists Want to Ditch Dark Energy".
| One is about new model from some physicists and the other
| implying a conciseness around ditching dark energy.
|
| edit: I didn't know that there is automatic re-write rules for
| HN. However the fact that the edited title is clickbait now
| regardless the reason. Just clarifying in case of this is
| considered an attack on the submitter.
| Tomte wrote:
| It' almost certainly Hacker News' automatic title rewriting,
| and not the submitter's fault. A missing word at the start is a
| sure sign.
| elashri wrote:
| That's interesting, I didn't know before that there are re-
| write rules applied. It seems that this at least a case of
| when this failed.
| jacknews wrote:
| I'm not a physicist but both dark energy and dark matter have a
| definite whiff of 'luminiferous aether' imho.
|
| Of course they're just placeholders for things we don't
| understand, but my guess is that they are not any form of energy
| or matter at all, but a misunderstanding of the geometry of space
| or something similar.
| devoutsalsa wrote:
| Totally! All these ideas are just a placeholder to make a note
| of something we can observe until we have a better theory.
|
| Luminiferous aether was invoked to explain the ability of the
| apparently wave-based light to propagate through empty space.
| [1] Eventually we found evidence that contradicted that idea.
|
| Dark matter is implied by gravitational effects which cannot be
| explained by general relativity unless more matter is present
| than can be observed. [2] We are searching for direct evidence,
| but haven't found any yet.
|
| [1] https://en.wikipedia.org/wiki/Luminiferous_aether
|
| [2] https://en.wikipedia.org/wiki/Dark_matter
| the__alchemist wrote:
| This applies here too: See my comment above; most
| cosmologists are confident (And/or focus most work on) Cold
| Dark Matter, e.g. in an ellipsoidal halo around galaxies. I
| am not making a qualitative judgement, but _dark matter_ is
| not used in cosmology papers as a placeholder.
| danparsonson wrote:
| It's a placeholder in the sense that we don't know
| specifically what it is though, right? No cosmologist uses
| "matter" when they mean "protons" for example.
| the__alchemist wrote:
| Yes; it's still reasonably broad. (MACHOs? WIMPs?) But
| this is still, in terms of all possible explanations for
| observations re rotation curves, and the Bullet Cluster
| etc, well defined. It includes a lot of possibilities,
| but also excludes.
| uoaei wrote:
| Unreasonably narrow, rather! We have not convinced
| _anyone_ , much less done the proper science, to stick to
| our guns so long that it is truly matter we are hunting
| to explain this phenomenon.
| elashri wrote:
| > No cosmologist uses "matter" when they mean "protons"
| for example.
|
| They will call that "baryonic matter".
| danparsonson wrote:
| No, they'd call them protons; baryons are a class of
| particles, of which protons are a member.
| elashri wrote:
| This is what a particle physicist use the term for. But
| for cosmologist on the question of matter composition
| they will use the term in different way. I was replying
| to exactly the quote from your reply.
| uoaei wrote:
| The point is, it's already a theory to even suggest it's
| "matter" and not any other explanation.
| devoutsalsa wrote:
| It certainly doesn't matter yet.
|
| I'll see myself out.
| floxy wrote:
| >No cosmologist uses "matter" when they mean "protons"
| for example.
|
| Don't astronomers call elements like neon metals? Maybe
| cosmologists don't?
|
| https://en.wikipedia.org/wiki/Metallicity
| ggambetta wrote:
| I've been saying this for at least 6 years [0]. Got downvoted
| to oblivion back then, glad to see opinions are changing.
|
| [0] https://news.ycombinator.com/item?id=21279144
| lutorm wrote:
| "Dark matter" is just a description that refers to matter which
| interacts gravitationally but not, or at least very weakly, in
| other ways. It doesn't imply anything about the nature of such
| matter. We _know_ that there are several types of dark matter,
| specifically neutrinos and brown dwarfs, although it is now
| established that they don 't make up anything near the density
| required by the cosmological models. Primordial black holes,
| which may exist, would be a dark matter. Some particle physics
| models, like supersymmetry, also naturally predict that there
| will be a massive particle that would behave like dark matter.
| So I don't think the analogy with the aether is very good,
| because that really was pulled out of thin air (pun intended).
| Given how successful general relativity is, it's perfectly
| rational to interpret the observations as probing mass
| distributions while assuming GR will continue to hold. There
| are of course people also assuming that GR is wrong and
| attempting to explain the observations without dark matter, but
| my impression is that they struggle to come up with self-
| consistent theories that fit all the data, although I'm not
| very familiar with that work.
|
| What other people have been doing over the past 40 years is
| attempting to devise tests for these various dark matter
| candidates. We know, for example, through lensing observations,
| that MACHOs/brown dwarfs don't exist in the required numbers
| and that the neutrino mass seems too low. The problem, of
| course, is that there are only so many ways to try to observe
| matter that is truly dark.
|
| I agree, though, that, in the end, it may be that dark matter
| will be an untestable hypothesis, just like quantum gravity or
| whatever.
| Chance-Device wrote:
| One of the better nautilus articles I've read, usually they're
| unreadable and boring, despite an interesting title. Unsurprising
| that it was written by Sabine Hossenfelder. Good science
| communication is a real skill.
| quantadev wrote:
| When you run the Schwarzschild radius calculation for the
| universe (relating mass of a black hole to event horizon radius)
| you get a prediction that's close enough to the size of the
| universe and it's mass, so to me that's pretty good evidence our
| universe is an event horizon.
|
| This means all 3D points in our space are on the horizon itself,
| and the time dimension is the normal vector to that "surface" (3D
| manifold). It explains why space is expanding, because Event
| Horizons always only expand (excluding considering Hawking
| evaporation of course, which happens too slowly to affect things)
| thrance wrote:
| Is there any experimental evidence for this model, does it
| actually lead to any verifiable predictions?
| quantadev wrote:
| There's more evidence for this Black Hole theory than there
| is for the Big Bang, but not it's not like there's any
| laboratory experiment that can be done afaik. It's all about
| measuring things in astronomy. Big Bang theory at this point
| is hilariously wrong, and doesn't fit much evidence nowadays.
| Big Bang is disproven.
| rosseitsa wrote:
| Really curious, how do you quantify "close" in such numeric
| ranges?
|
| Quick calculations say that ratio is 1.71:1
| (https://rentry.co/k85wy696). I guess given the scale of the
| numbers having such a low ratio is interesting.
|
| But my intuition says that in physics constants are scattered
| in a sort of logarithmic way, i.e. the orders of magnitude are
| uniformly scattered in some range. So small ratios between such
| constants not impossibly rare.
|
| I may be full of shit though!
| quantadev wrote:
| I admit I haven't run the calculation myself, nor even asked
| OpenAI (or other AI, which are almost certainly capable of
| doing it), but I heard a presentation say the number is off
| by a factor of 3. To me '3' is best described as "no where
| near an order of magnitude". Since there's no way we're
| measuring the radius of the universe nor the mass in it
| accurately, I think being off by only a factor of 3 is
| astoundingly "accurate". When you're dealing with many many
| orders of magnitude like these astronomically large numbers,
| and you end up being only off by 3x that's actually pretty
| close. Too close to be an accident. If the theory was "wrong"
| it would be off by many orders of magnitude.
| antonvs wrote:
| Sean Carroll discusses this in "The Universe is not a Black
| Hole":
| https://www.preposterousuniverse.com/blog/2010/04/28/the-uni...
|
| Relevant quote:
|
| > "Still, some folks will stubbornly insist, there has to be
| something deep and interesting about the fact that the radius
| of the observable universe is comparable to the Schwarzschild
| radius of an equally-sized black hole. And there is! It means
| the universe is spatially flat."
| quantadev wrote:
| Sean Carroll is not really an unbiased party. He has his
| entire reputation staked on him being right about his own
| theory, so he's going to simply disagree with anything else,
| and he's going to disagree with anything that's not a
| "standard" theory.
|
| He likely believes in the Big Bang too which is an absurd,
| and disproven theory. There are far too many mature galaxies
| that are far too old for the Big Bang theory to be correct.
| the__alchemist wrote:
| > This theory has it that all types of energy--including matter,
| radiation, and pressure--curve space, and the curvature in return
| influences how the energy-types move. The authors of the new
| paper, led by Antonia Seifert, don't question this. They question
| instead how we use Einstein's math.
|
| This is so fascinating. I think the principle applies to so much
| of the natural sciences. GR describes a set of rules
| (differential equations using tensors) that describe how matter
| moves in spacetime, and how it curves it. But outside of certain
| specific conditions (Schwarzschild etc), we can't (yet) use it to
| build useful models! We can use it to an extent to validate parts
| of models, but it leaves so much to the _imagination_. We are
| still using Newtonian models in cosmology, then applying _GR
| effects_ like GEM piecemeal, and the time dilation effects in the
| article, where complexity and understanding allow.
|
| We have these rules, but don't know how to use them to model! See
| also: Quantum mechanics and ab-initio chemistry. It's as if the
| universe is written in differential equations, but we are novices
| at how to use them.
| pclmulqdq wrote:
| Dark energy and dark matter aren't really theories. They are sort
| of the default solution to a set of problems that exist in
| cosmology. In a sense, every physicist wants to ditch dark matter
| or dark energy (or at least our current understandings of them),
| but they just don't know what to replace them with.
| Filligree wrote:
| Dark matter in particular strikes me as... "yes, obviously".
|
| There's about a dozen quantum fields corresponding to
| particles. These form a graph, which is by no means fully
| connected; the fields each interact with a subset of each
| other, and neutrinos in particular only interact with gravity
| and the weak force.
|
| If the connections are in some sense random, then it should
| come as no surprise whatsoever that the graph has disconnected
| subsets. In fact dark matter theory is effectively stating that
| the subset we're a part of is one of many, which also agrees
| with the copernican principle.
| antonvs wrote:
| That's all essentially true, but it doesn't necessarily mean
| that there's a quantum field that matches the properties
| needed to explain the phenomena dark matter is supposed to
| explain.
|
| It just means that it's plausible, and wouldn't be
| surprising, if there were such a field.
| MichaelZuo wrote:
| How are they so beyond direct detection if they similarly
| permeate the entire universe?
| antonvs wrote:
| Every quantum field only interacts ("couples with") a
| subset of other quantum fields. Undetectable quantum
| fields would be one that don't couple with any fields we
| interact with.
|
| We already see something like this with the neutrino:
| they only interact via the weak force and gravity, so we
| need massive detectors measured in kilometres and buried
| underground to detect them.
|
| It's estimated that about 100 trillion neutrinos pass
| through your body every second, traveling close to the
| speed of light.
|
| Now imagine a particle that doesn't even interact via the
| weak force. The only way we would be able to detect it is
| via gravity, but gravity is an extremely weak force at
| the individual particle level. That's a possible
| candidate for dark matter. (Even particles that interact
| only via the weak force and gravity are candidates, but
| it's generally believed they'd have to be more massive
| than neutrinos.)
|
| There's also the possibility that, if it turns out that
| gravity is an emergent property arising from quantum
| interactions or something along those lines, that there
| could be fields that don't participate in the
| gravitational interaction. But that's highly speculative
| territory.
| the__alchemist wrote:
| I've been doing a deep-dive in the past few weeks of papers and
| data sets regarding to rotation curves, mass densities etc.
| (SPARC, papers describing the rotation curves of various dwarf
| galaxies etc). The impression I get is that most of the authors
| are not critical of a CDM dark matter halo explaining rotation
| curve data. The papers I'm reading span from ~1990 to present.
| uoaei wrote:
| Have you seen any work from Stacy McGaugh?
| https://tritonstation.com/new-blog-page/
| the__alchemist wrote:
| No; checking it out. Ty!
| Retric wrote:
| That seems really time consuming.
|
| One question I've had for a while but didn't seem worth the
| look is if there any consideration for local gravitational
| interaction between stars exchanging momentum between them
| and thus flattening the rotation curve.
|
| I'm assuming that's one of the first things looked at but
| couldn't find a paper on the subject. Remember any references
| on the topic?
| Keysh wrote:
| The problem isn't so much the _flatness_ of the rotation
| curve, but it 's continued high value: as you go farther
| and farther out in distance, it should drop rapidly because
| most of the visible matter is concentrated toward the
| center of the galaxy, but it doesn't. This implies that
| there is more matter, _less_ centrally concentrated than
| the visible matter.
|
| Note that most "rotation curves" are actually measured from
| gas, not stars, and also that strong gravitational
| interactions between individual stars are _extremely_ rare
| except in very dense star clusters and galactic nuclei, due
| to the increasingly large distances between stars as you go
| out from galactic centers. The time required for individual
| stellar interactions in the main or outer parts of galaxies
| to significantly affect their motions is much larger than
| the age of the universe (see, e.g.,
| https://en.wikipedia.org/wiki/Stellar_dynamics).
|
| Finally, this wouldn't address other evidence for dark
| matter, like the halos of hot (millions or tens of millions
| of K) intergalactic gas in galaxy clusters. The pressure of
| the gas should have driven the gas to expand way billions
| of years ago, _if* you assume that only the gravity of the
| individual galaxies and the gas itself is restraining it._
| DoctorOetker wrote:
| What annoys many was the pretense of a theory. At some point in
| the history of physics we stopped calling open problems,
| puzzles and (yet) unresolved paradoxes as what different but
| similarly unexplained phenomena were called in the past and
| pretended we resolved them.
|
| It's simply unnecessary to pretend its a theory, it is possible
| to name things without pretending they are theories.
| uoaei wrote:
| Dark matter is and always has been curve-fitting to residuals
| between theory and data. There is no there there, every map you
| see is nothing more than subtracting theory from data and
| having residuals left over. Dark energy is similar except much
| more coarse, in that the "model" is just a single parameter
| with a very simplistic interpretation.
|
| Neither are theories, but good luck coming away unscathed when
| mentioning this in the presence of LCDM dogmatists.
| begueradj wrote:
| Maybe that's the evidence that dark energy and dark matter are
| the reality which our dark side refuses to admit.
| willmadden wrote:
| They shouldn't have named them then. What they really are is an
| approximation of what they think they do not know.
| plasticchris wrote:
| Yeah, the best analogy for people that know a little physics is
| aether - it's obviously ridiculous now, but there was a time
| when it filled in some unknowns and people took it seriously.
| It would be nice if it weren't presented as fact in tv and
| planetarium shows, but what can you do?
| jiggawatts wrote:
| > just don't know what to replace them with.
|
| Which is fine, but every physicist seems to just _assume_ that
| it must be a "force", a "particle", or a "field".
|
| It can be _other things_ , including errors in the math, errors
| in the models, errors in the observations, invalid assumptions,
| etc, etc...
|
| It's rather irritating to see the n-th experiment "searching"
| for some previously unseen particle while literally only one
| team thought of revisiting the maths to see if something was
| missed.
| readthenotes1 wrote:
| Alas, the top hits for "timescape" refer to a sci-fi book.
|
| But timescape wiltshire leads to a nice presentation:
|
| https://www.nottingham.ac.uk/physics/documents/talesoflambda...
|
| And without math,
| https://en.m.wikipedia.org/wiki/Inhomogeneous_cosmology
| pk-protect-ai wrote:
| Why don't they want to ditch dark matter? It is more plausible
| candidate to ditch :)
| jinushaun wrote:
| Ah yes, the "cosmological principle" that everything averages out
| to be basically the same everywhere over large distances. It
| makes sense that this principle would need to be violated in
| order to eliminate dark energy.
|
| One of my favorite sci fi concepts is a universe where the
| cosmological principle was false.
| nimish wrote:
| Good news, the cosmological principle is almost certainly false
| since it leads to absurd results like dark matter and dark
| energy!
|
| Or if it was true once (CMB-era) it sure as shit ain't true
| now.
| amelius wrote:
| Note that this can also be distances in time, rather than just
| space.
| andrewflnr wrote:
| The truncation of the title to remove "These" does severe
| violence to its meaning.
| propter_hoc wrote:
| The anti-clickbait truncation HN applies to headlines works
| well in the singular: "This politician wants to ban bicycles"
| --> "Politician wants to ban bicycles."
|
| In the plural it should probably convert "These" to "Some"
| rather than implying that " _all_ physicists want to ditch dark
| energy. "
| guybedo wrote:
| Although i'm not a physicist and i have an average understanding
| of these things, dark energy and dark matter always felt to me
| like physicists had created mystical entities with magical
| properties because they couldn't explain some experimental
| results.
|
| And my average brain always thought and still thinks that instead
| of chasing these unicorn entities that still can't be found,
| maybe we should reconsider some things, as it seems to be the
| case presented here in this article.
| Ekaros wrote:
| Also not physicist, but they always felt like smudge factors.
| Put in this stuff we don't know what it is and only interacts
| in certain ways to right places and finally math works out.
| Well it is obvious that they can work if you can mostly freely
| tune parameters until they do. But then you need two different
| things...
|
| Somewhat reminds me of aether...
| exmadscientist wrote:
| Former physicist here! I used to work on this stuff. I don't
| think anyone has ever been a "true believer" in dark matter
| or dark energy.
|
| There was a pattern in late-19th- through late-20th-century
| physics wherein someone noticed something weird, said "hey,
| if _X_ were true, it 'd be kind of weird, but it would
| explain it all", then people went out and looked for evidence
| of _X_. In many, many cases, people did indeed find _X_ ,
| some closely related _X '_, or at least got strong evidence
| in favor of something else _Y_ , which might have disproved
| _X_ but at least settled the matter.
|
| This has not happened with dark matter or dark energy. The
| questions still remain open, with no good evidence for _any_
| explanations.
|
| So... what I'm saying is, don't think less of people for
| trying to explain things, just because they tried and it
| didn't work out yet. You're seeing the scientific method play
| out right now: there is a whole lot of _wrong_. There was a
| lot of wrong in the old days, too, but we weren 't around to
| see it; only the successes got passed down.
| baq wrote:
| That's... kinda how it always worked. They invented something
| that fit existing observations. Remember when ether was a
| thing?
|
| The other problem is that nothing else really fit... until now.
| Science works, turns out.
| p2detar wrote:
| It feels somewhat like the Aether theory [0], which fell out of
| place after special relativity got introduced. It was
| interesting to me that the Aether was proposed by Isaac Newton.
|
| 0 - https://en.wikipedia.org/wiki/Aether_theories
| gdavisson wrote:
| Except that sometimes chasing these unicorn entitles leads
| to... finding the unicorn entities.
|
| That's basically what happened with the neutrino. Neutrinos
| were originally proposed in 1930 by Wolfgang Pauli to solve
| apparent violations of energy and momentum conservation in beta
| decay. He suggested that the missing energy and momentum were
| being carried off by some additional -- undetected and mostly
| undetectable -- particle. For a while, it looked like these
| proposed ghost particles might never be detectable, but Fred
| Reines finally managed it... in 1956, 26 years later.
|
| So don't write off unicorn particles. Sometimes they're real,
| even if you have trouble detecting them.
| tim333 wrote:
| Sabine's video version of the same stuff https://youtu.be/frJy-
| sSriHM
| fromMars wrote:
| Why are these anti-dark matter articles upvoted on hacker news.
|
| As I understand it, most cosmologists still thing dark matter is
| the most likely candidate as it explains multiple different daya
| points unlike Mond.
| constantlm wrote:
| It's really just a stopgap.
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