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Physicists who want to ditch dark energy
- moffkalast 2y ago> 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 2y agoNo, 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 2y agoAh right yeah, had them mixed up for some reason.
- chuckadams 2y agoEvery 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 2y agoI'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 2y agoThat'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 2y agoNo, 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 2y ago> 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.
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- the__alchemist 2y agoI 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 2y ago>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 https://en.wikipedia.org/wiki/Dark_matter#Warm_dark_matter
- elashri 2y agoThe 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 2y agoIt‘ almost certainly Hacker News‘ automatic title rewriting, and not the submitter‘s fault. A missing word at the start is a sure sign.
- elashri 2y agoThat'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.
- deleted 2y ago[deleted]
- jacknews 2y agoI'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 2y agoTotally! 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 https://en.wikipedia.org/wiki/Luminiferous_aether [2] https://en.wikipedia.org/wiki/Dark_matter https://en.wikipedia.org/wiki/Dark_matter
- the__alchemist 2y agoThis 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 2y agoIt'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 2y agoYes; 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.
- Chance-Device 2y agoOne 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 2y agoWhen 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 2y agoIs there any experimental evidence for this model, does it actually lead to any verifiable predictions?
- quantadev 2y agoThere'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.
- thrance 2y agoOk, by that comment you told me everything I wanted to know: you're pulling this out of thin air. Please provide sources whenever you make insane claims like "Big Bang is disproven". Because it's not [1]. Also you told me there's "more evidence for this Black Hole theory than there is for the Big Bang", so please link to it, that I might examine it and maybe change my mind. [1] https://en.m.wikipedia.org/wiki/Big_Bang#Observational_evidence https://en.m.wikipedia.org/wiki/Big_Bang#Observational_evide...
- quantadev 2y agoThe Big Bang is disproven because we see fully formed galaxies when we look out at the edge of the universe using James Webb Telescope. That's conclusive proof it's wrong.
- the__alchemist 2y ago> 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 2y agoDark 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 2y agoDark 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 2y agoThat'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 2y agoHow are they so beyond direct detection if they similarly permeate the entire universe?
- antonvs 2y agoEvery quantum field only interacts ("couples with") a subset of other quantum fields. Undetectable quantum fields would be ones 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.[1,2] 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. [1] Ice Cube neutrino detector: https://icecube.wisc.edu/science/icecube/ https://icecube.wisc.edu/science/icecube/ [2] Super Kamiokande neutrino detector: https://www-sk.icrr.u-tokyo.ac.jp/en/sk/ https://www-sk.icrr.u-tokyo.ac.jp/en/sk/
- readthenotes1 2y agoAlas, 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/wiltshire.pdf https://www.nottingham.ac.uk/physics/documents/talesoflambda... And without math, https://en.m.wikipedia.org/wiki/Inhomogeneous_cosmology https://en.m.wikipedia.org/wiki/Inhomogeneous_cosmology
- pk-protect-ai 2y agoWhy don't they want to ditch dark matter? It is more plausible candidate to ditch :)
- jinushaun 2y agoAh 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 2y agoGood 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 2y agoNote that this can also be distances in time, rather than just space.
- throwawaymaths 2y ago> One of my favorite sci fi concepts is a universe where the cosmological principle was false. As it stands now, the cosmological principle seems false at every scale we look (with confidence decreasing in falshood slightly decreasing as scale gets larger). So that doesn't seem to be a "sci fi" concept, just a "sci" concept.
- andrewflnr 2y agoThe truncation of the title to remove "These" does severe violence to its meaning.
- propter_hoc 2y agoThe 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."
- cryptonector 2y ago@dang this title needs fixing.
- andrewflnr 2y agoWhy does it need to change at all? In a lot of cases it makes sense to tone them down, but "these physicists..." is already pretty mild IMO.
- throwaway314155 2y agoBecause paulg encoded a bunch of subjective rules on how to decrease community toxicity in lisp of all things, and no one knows how to program in lisp. Kidding, mostly. I do think it's an indicator of institutional issues with the site, its moderation staff and the motivations for keeping it alive. It wouldn't be surprising to me to find that many decisions were made by or for eccentric wealthy and/or smart people having a mild ego trip. "We're reducing the internet's toxicity via automated symbolic manipulation of media titles thus making the world a better place."
- guybedo 2y agoAlthough 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 2y agoAlso 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 2y agoFormer 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 2y agoThat’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.
- tim333 2y agoSabine's video version of the same stuff https://youtu.be/frJy-sSriHM https://youtu.be/frJy-sSriHM
- fromMars 2y agoWhy 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 2y agoIt's really just a stopgap.
- fromMars 2y agoNot sure what that even means. It's our best theory at the moment and helps explain multiple different cosmological phenomena. There are also hypothesized particles that fit within the Standard Model that researchers are searching for experimentally. Honestly, these articles are upvoted by people who know very little physics and think that dark matter is somehow a very mysterious idea.
- cryptonector 2y agoThis one is about dark energy.
- fromMars 2y agoThanks for the clarification. From the comments I gathered it was about both. I agree that the cosmological constant is the more puzzling of the two.
- throwawaymaths 2y ago> He called it the “timescape.” This is because, in Einstein’s theory, time runs at different speeds depending on the amount of matter that a region contains. I wonder if he called it "timescape" as a reference to the star trek the next generation episode where small bubbles of space experience time moving at different speeds.
- arcastroe 2y agoFrom the article, > discovering that the expansion of the universe was accelerating. They came to this conclusion by observing faraway exploding stars. These distant supernovae showed that the cosmos was getting bigger faster because the farther away the supernovae, the faster it appeared to be moving away from us. This explanation always bothers me. After a long time, things that move faster WILL be farther away than things that move slower. Thats just the definition of speed. It does not, by itself, demonstrate acceleration.
- mr_mitm 2y agoOh please. Do you really think the people who won the nobel prize for this discovery have a grade school level understanding of speed? You seem to be talking about peculiar velocities, which are absolutely negligible on cosmological scales and only the velocity caused by the expansion of spacetime is relevant. What they really did was measure the distances and redshifts of dozens of supernovae and looked which energy contents of the universe could explain the observed relationship assuming that the Friedman-Lemaitre-Robertson-Walker metric accurately describes the universe. Turns out you need 70% of something whose density does not change with the expansion. This is the original paper if Hossenfelder's summary of the explanation compressed in one sentence does not convince you: https://arxiv.org/abs/astro-ph/9812133 https://arxiv.org/abs/astro-ph/9812133 For a derivation of the relationship between redshift and distance see any introdctory text on cosmology, e.g. chapter 8 of https://arxiv.org/abs/gr-qc/9712019 https://arxiv.org/abs/gr-qc/9712019 (he arrives at the equation on the last page). Edit: This goes into more detail of matter species in sec. 1.5 and touches on the SN observations in sec. 1.7: https://www.thphys.uni-heidelberg.de/~amendola/teaching/adv-cosm.pdf https://www.thphys.uni-heidelberg.de/~amendola/teaching/adv-... (on an unrelated note: he was my PhD advisor)
- arcastroe 2y ago> Oh please. Do you really think the people who won the nobel prize for this discovery have a grade school level understanding of speed? Of course not. My comment is a quibble on the one sentence explanation. You seem to agree with me it's insufficient. Thank you for the additional resource.
- westurner 2y agoFrom https://news.ycombinator.com/item?id=36222625#36265001 https://news.ycombinator.com/item?id=36222625#36265001 : > Further notes regarding Superfluid Quantum Gravity (instead of dark energy)