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Newton's law of gravity passes its biggest test
- GuB-42 6mo agoIf you follow Sabine Hossenfelder's channel, she has a MONDOmeter. With MOND (modified Newtonian gravity) on one side and dark matter on the other side. As new papers come out the needle goes back and forth, and I guess that she will make a new video if she hasn't already, with the needle moving one step towards dark matter. I find it interesting how it doesn't seem to settle. Dark matter is still the favorite, but there is a lot of back and forth between "MOND is dead" and "we found new stuff we couldn't explain with dark matter, but it matches MOND predictions".
- ReptileMan 6mo agoOnce I joked that a lot of things in the universe make sense if you view it as a "simulation with optimizations like lazy loading".
- nathan_compton 6mo agoEverything we don't understand we conceptualize using the most similar tools which we do have command over.
- sebzim4500 6mo agoYeah until you get to quantum computing and then it seems as if the universe is doing enormously more work than you would think necessary.
- cvoss 6mo agoThis comment and GP are two of the most concise and punchy descriptions I've ever heard of some of the deepest aspects of modern physics. On the one hand we have principles of locality and finite propagation speed, which limit the computational work to a small neighborhood, and on the other hand we have principles of non-locality and superposition, which cause the computation to explode as it swallows up potentially everything and every possible thing.
- davrosthedalek 6mo agoIt might just be a reflection of the architecture the universe simulation is running on...
- pixl97 6mo agoSee Timmy, this is what happens when you run your universe on a holographic medium at an infinite distance.
- ReptileMan 6mo agoBut only if someone observes it. The act of observation forces reality into existence.
- fooker 6mo agoNot necessarily. You'd be correct given hidden variables. But we know pretty convincingly that quantum anything does not have hidden variables. https://en.wikipedia.org/wiki/Bell%27s_theorem https://en.wikipedia.org/wiki/Bell%27s_theorem
- messe 6mo agoIt doesn't have local hidden variables. That's an important distinction. I'm not sure a non-local hidden variable explanation of QM is any distinct from superdeterminism though.
- jiggawatts 6mo agoThe analogy goes surprisingly far: - Locality is a consequence of the use of a scaled compute cluster with peer-to-peer networking only. - The speed of light is the speed of information exchange between compute nodes. - General Relativity is caused by network links with finite bandwidth taking longer to exchange information if there is more of it. (Effectively slowing down time) - Quantum Mechanics is caused by finite precision of the n-bit numbers at small scales. - MOND is caused by cumulative summation and rounding errors that show up only in the case of weak fields over large distances. Etc…
- PaulHoule 6mo agoMOND does amazingly well at galactic rotation curves, less well at anything else. If you think it started with Vera Rubin in 1966 MOND seems natural, but if you know that it started with Fritz Zwicky in 1933 than dark matter is easier to believe.
- adgjlsfhk1 6mo agoMOND only really does well on galactic rotation curves because it has free parameters that are tuned to "predict" the correct answer for galactic rotation curves.
- wetpaws 6mo ago[dead]
- dnautics 6mo agoI think you mean LCDM only does well on galactic rotation curves because it has free parameters per galaxy. MOND only has one free parameter, maybe two if you use the MOND+Relativity model that doesn't work.
- drdeca 6mo agoI don’t think these are free parameters in the same sense. Like, if one theory says that a hunk of metal actually is made of many microscopic grains of various sizes and orientations, where the sizes and orientations of these grains has an effect on the behavior of the metal, you don’t count the “the sizes and orientations of these grains” as free parameters, do you?
- adgjlsfhk1 6mo agoYou would if you didn't have any ability to observe those sizes and orientations.
- jahnu 6mo agoThere are galaxies that appear to be free of dark matter and rotate accordingly. How does MOND account for that? My understanding is that these observations are a fatal blow to any serious MOND models.
- cwmma 6mo agomy understanding is that there are a few MOND champions who are still holding on to the idea while everyone else has moved on.
- stronglikedan 6mo agoso MOND is the new String Theory...
- pfdietz 6mo agoIt never had the institutional imprimatur of string theory.
- layer8 6mo agoString theory is still the leading contender for quantum gravity.
- SiempreViernes 6mo agoI don't think "leading" is correct, more like "ill regarded but still standing". It has fallen far from its glory days, and is more an old reliable tool than a leading physical theory.
- layer8 6mo agoIt’s correct because there is no competing theory for quantum gravity that most physicists would consider being more likely to be on the right track. This is different from MOND, which is a distant second contender compared to dark matter.
- SiempreViernes 6mo agoOk, I'll present my evidence an you can present yours. In the latest Marcel Grossman meeting (2024) there was no string theory parallel session but there was an explicit Loop Quantum Gravity session: https://indico.icranet.org/event/8/program https://indico.icranet.org/event/8/program So string theory is now pretty officially an "also ran", definitely not a leading theory.
- elashri 6mo agoMOND is dead is a true statement if we say MOND is dead as a general theory of gravity. It does not mean is does not have its success with explaining galactic rotation curves but failing at mostly everything else.
- cowl 6mo agoIt's funny how for MOND we cant accept that it has some unknowns yet but we are more than willing to accept the FULL UNKNOWN Dark Matter. it's easy. put "Dark" in front of something and you don't have to explain it at all, no matter that something else explains at least 60-70% instead of 0.
- gus_massa 6mo agoWe make a similar guess for the stuff that is in the center of Earth. We measure local gravity and speed of sound velocity, and we guess here is liquid, here is solid, here is this rock, here is this another rock [1]. See for example https://www.livescience.com/64943-nobody-understands-the-giant-mantle-blobs.html https://www.livescience.com/64943-nobody-understands-the-gia... nobody has seen them, we guess they are there. Dark matter is another guess. We guess there is more matter in galaxies than what the telescopes show. We can compare the amount of mater guessed from galaxy rotation with other measurements. In this case they compare it with the gravity between a few galaxies. Nobody is happy that we don't know what dark mater is. There are a few theories, but none of them has enough experimental support. More lack of confirmed details in https://en.wikipedia.org/wiki/Dark_matter#Composition https://en.wikipedia.org/wiki/Dark_matter#Composition [1] I don't know enough about rocks https://xkcd.com/2501/ https://xkcd.com/2501/
- cowl 6mo agoDark matter is not another Guess. is no guess at all. its the same as saying the center of the earth is made of Dark Core. and when someone proposed liquid core, there would be papers how a liquid core doesnt explain 100 %, and neither does rock or solid so Dark Core it is because it's sIMpLer to have just one Dark Something than 3 different somethings to explain anything. The fact that there are tentatives to identify what it might be does not ammegliorate the fact that at it's core (pun intented) Dark matter is something to make equations fit without any other thought behind it or whether there might be several things behind it or god forbid that we juddge the equations themselves. I mean we got relativity because of a minor discord with newtonian Laws. (the orbit of Mercury). just a tiny percentage of obeservable behaviour at that time but it was a different time. a time where you could bring down the existing science of the day for a tiny percentage and now we accept 90% observation disaccordance (dark energy+dark matter) with what the equation require.
- fooker 6mo agoWe are likely going to find out that both are unfixably faulty. It'll take either the next Einstein or some groundbreaking experimental observation to get there in my opinion. If it was possible to incrementally fix these theories, the army of postdocs working on these would have already done so in the last decade or so.
- wongarsu 6mo agoBut at least the experimental results disproving these incremental fixes should be exactly the kind of thing the next Einstein should need for coming up with an entirely new way of looking at things
- fooker 6mo agoInterestingly, more often than not it happens the other way. Some once-in-a-generation scientist has an intuition that turns out to be true and mathematically elegant. It gets proven experimentally years or decades later. Relativity was exactly like this.
- messe 6mo agoIt was far from exactly like that. GR was in part prompted by the precession of the perihelion of mercury for which there was plenty of data.
- fooker 6mo agoLook at the timeline here https://en.wikipedia.org/wiki/Tests_of_general_relativity https://en.wikipedia.org/wiki/Tests_of_general_relativity
- SiempreViernes 6mo agoDude, if you genuinely want to know what happened, you should read some proper history of science. Here take this: https://arxiv.org/pdf/physics/0405066 https://arxiv.org/pdf/physics/0405066 It shows both how Einstein very much didn't make the theory alone, was inspired to take impotat technical steps by work of other thats that created a theory based on his principles before him, and that actually he first created (in intense collaboration) a failed theory that got Mercury's anomaly all sorts of wrong.
- raverbashing 6mo agoMOND is kinda like a dead horse now, that people like to keep flogging I think it's possible for an alternative gravitational law to work, but not MOND MOND is stronger at longer distances than Newtonian Gravity. To me that does not pass the sniff test. It could be a step in understanding a more exact law but to me it feels weird
- htx80nerd 6mo agoDark Matter : supposedly makes up a big amount of the mass of the universe, but cant be seen, does not emit, absorb, or reflect light. Also it can 'pass through' other normal matter, and other dark matter. It's basically magic aka not actually real, just something in vogue to pretend is real at the present moment.
- njarboe 6mo agoDark Unknown Matter would be a better name for lay people to understand what's going on. I'm no cosmologist but isn't it just a placeholder for something that gravity interacts with (and not much else) and we don't know what it currently is. When we discover what it is the name will change.
- _ZeD_ 6mo agoOr, you know, as aether. It's a scientific theory. It's the best that we have right now to model the real world and be able to do prediction on its behavior. Does it seems to be kept together by duct tape? Maybe. Is it yet useful? Yep. Will it be discarded if anything more fitting will came up? You can be sure of it.
- Joker_vD 6mo agoYeah, pretty much, which is why this adherence to dark matter seems even more puzzling: we already had a mysterious substance with nonsensical mechanical properties (perfectly solid, but has zero collision) that turned out to be completely superfluous; the actual answer was the different shape of the physical laws. Now we again have a mysterious substance with nonsensical properties (has gravitational pull, doesn't interact with normal matter in any other way) — could it be that it simply doesn't exist? And it's not like the concept of aether itself was really all that useful for anything. The physicists wanted the light to have some mechanical medium to propagate through instead of being a thing of itself, that actual itself shaped mechanical media, not the other way around (mechanical properties arise from the E-M interaction, not the other way around), simply because all other known waves phenomena existed in mechanical media.
- vonneumannstan 6mo agoUntil you definitively rule out all the dark matter candidates or get a direct detection the controversy will remain
- Sniffnoy 6mo agoI mean, there are modified gravity candidates other than MOND. I think people should perhaps give more consideration to those and not focus on MOND as their idea of modified gravity. I feel like the evidence is pretty well against MOND at this point. But other ideas of modified gravity, that aren't MOND-like, may still be worth considering. Framing it as "dark matter vs MOND" implicitly excludes these and I think that's a mistake.
- Lvl999Noob 6mo agoI thought newtonian gravity was already proven to be inaccurate with Einstein's Special Relativity (or General Relativity?) giving better results on cosmic scales (basically analogous to an approximation vs an exact formula)?
- GuB-42 6mo agoAt these scales (entire galaxies, very weak forces), it doesn't make a significant difference. There are ways of adapting MOND to match general relativity, should it turn to be correct at explaining what it is supposed to explain (like the movement of galaxies).
- NewEntryHN 6mo agoI think OP's question is more how could Newton's law "pass" a test any more than General Relativity would, considering that it's merely an edge case of GR?
- GuB-42 6mo agoOh yes, I think the title is a bit misleading. It is an argument against MOND, a theory that says that gravity has to be modified to account for some observations. But for these particular observations, general relatively and Newton's laws gives the same results in practice, the difference is negligible, so showing that these observations can be explained by Newton's laws implicitly mean that they can also be explained by general relativity. No need for modifications.
- magicalhippo 6mo agoGeneral Relativity reduces to Newtonian gravity as the curvature goes to zero, that is when you're very far away from objects relative to their masses, for slow non-relativistic objects like stars and galaxies. Galaxies are typically so far away from another they're almost like point sources to each other, hence Newtonian gravity explains their motion very well. However, inside galaxies things do not behave as expected, as stars in almost all the galaxies we've measured does not move like Newtonian (nor GR) behaves based on the matter in the galaxy we see. One alternative to the mainstream theories of dark matter is to modify Newtonian gravity, called MOND. This work tested if MOND fit the motion of galaxies in galaxy clusters. They found it did not. MOND already does not explain other phenomena that dark matter can so it's not terribly surprising. Here[1] is a nice accessible talk going through all the evidence for dark matter. But it is technically a possibility that there's two things are going on, something MOND-like as well as dark matter, so worth checking. [1]: https://pirsa.org/26030070 https://pirsa.org/26030070
- Michael666 6mo ago[flagged]
- deleted 6mo ago[deleted]
- DivingForGold 6mo agojust another nag screen ...
- rappatic 6mo agoWhen I see dark matter in the news I'm always reminded of the story of Vulcan. In the 1800s, detailed observations of the planet Mercury showed that its orbit was slightly different than Newtonian mechanics predicted-- a difference of about 43 arcseconds per century. The study was rigorous enough to rule out any observation errors. Le Verrier, the astronomer who made these observations, wondered how to explain the difference. A decade earlier, he had noticed a similar irregularity in the orbit of Uranus, which led to the discovery of Neptune, whose gravity caused these perturbations. So Le Verrier reasoned that something similar must be going on for Mercury, and he posited the existence of Vulcan, a tiny planet close to the Sun. Many attempts were made for decades to observe Vulcan. It was even included on some maps of the Solar System at the time (https://www.loc.gov/resource/g3180.ct003790 https://www.loc.gov/resource/g3180.ct003790). But it was never conclusively observed. When Einstein published his theory of relativity in 1915, the mystery of Mercury's orbit was finally explained-- Newtonian mechanics were simply incomplete, and the irregularity of Mercury's orbit was due to relativistic effects. Could it be that something similar is happening today? Observations of gravity on galactic scales doesn't quite align with what relativity would predict, so we use dark matter to fill the gaps. We've tried for decades to detect dark matter, with no dice. Is our theory of gravity simply incomplete? MOND may not be the solution, but I'm still skeptical about dark matter.
- gwynforthewyn 6mo agoOf course it can be that this is the case. There are predictions from the dark matter hypothesis, though, that have been testable. For example, there're some of the asymmetries in the cosmic microwave background that are explained presently by the dark matter hypothesis. Something that's worth bearing in mind is that "dark matter" doesn't actually mean "totally new never before seen thing" it means "we don't know what this matter is". So, for example, a candidate that wouldn't be super novel but could fit the bill is microscopic black holes. In that sense, the hypothesis is more mundane than it might seem.
- MattPalmer1086 6mo agoAs far as I know, dark matter hasn't made any testable predictions which were subsequently proved correct. It's an infinitely tunable hypothesis that can be retro fitted to new observations, since it has many tweakable parameters. Could you point me to a prediction made by dark matter theory which was subsequently confirmed by observation, rather than a dark matter theory which explains it post facto?
- sipsi 6mo ago[flagged]
- ricksunny 6mo agoIf it had failed, would we be hearing about it in Science before the researchers continued testing it until it passed? (i.e. is this a blindspot in our collective epistemology?)
- yongjik 6mo agoIf it had failed it would've been a top science news. Every scientist dreams about the day when they're mentioned as "(...)'s experiment puts Newton's law of gravity in jeopardy."
- ricksunny 6mo agoWould it? Or would it be treated as an errant experiment by either the journal or the experimentalists themselves, foregoing publishing until they had a result that was better aligned with established norms? Rightly or wrongly, I expect that stakeholders would tend to invoke Sagan’s ECREE over the course of the publication process.
- ykonstant 6mo agoYes. Yes, it would. This is so tiring.
- ricksunny 6mo agoIt is not my intention to induce fatigue in anyone, though I am impressed that a reply comment in a forum is capable of doing so.
- alirezaxdehghan 6mo agonow I'm tired too
- ricksunny 6mo agoI hope you manage to get some rest after the tiring tribulations people pose on forums.
- adrian_b 6mo agoFree variant of this research paper: https://arxiv.org/abs/2604.14327 https://arxiv.org/abs/2604.14327
- DoctorOetker 6mo agoIt's bizarre that Newton's law passes this test, when the linearization of general relativity predicts a gravitational equivalent of a magnetic analog for gravity. Gravity Probe B. There exists an even simpler derivation for a magnetic term, but its in my file drawer... (simpler in that it just relies on observations from special relativity)
- tech_hutch 6mo ago[flagged]
- ligoangela 6mo agoWoow
- ligoangela 6mo agoWe measure the matter distribution by its affect on light (strong/weak lensing). We also measure the matter distribution by the amount of light coming from it. The results are not the same. The simplest explanation is that there is matter which does not produce or reflect light via e/m, i.e. it is dark. Dark Matter. We know of particles which behave the same way. Neutrinos for example.
- notorandit 6mo ago> We know it holds incredibly well terrestrially and within individual galaxies I somehow thought that this was not really holding true and that Mr. Einstein had something to say. I thought that without Einstein's "corrections" stuff like GPS wouldn't be useful at all. Maybe I misunderstood last 100+ years in gravitational physics.