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It's time to take alternatives to dark matter seriously
- wpasc 6y agoDoesn't the bullet cluster provide strong evidence for the existence of dark matter? Shouldn't all alternatives need to explain the phenomenon seen there?
- deepnotderp 6y agoIirc it provides evidence against most modified gravity theories, but other alternatives could theoretically still be viable.
- Fnords 6y agoIt provides strong evidence of matter that we cannot detect. Milgrom's reply is worth a read: https://web.archive.org/web/20160721044735/http://www.astro.umd.edu/~ssm/mond/moti_bullet.html https://web.archive.org/web/20160721044735/http://www.astro....
- haolez 6y agoThus... dark matter?
- artsyca 6y agoIsn't dark matter something like a shadow DOM.. It's there but also not there? Edit! Wow really feeling the love on this comment What I mean is dark matter is different from matter we just can't detect, it's matter that should be there but we can't seem to find it
- BurningFrog 6y agoIt's pretty simple: Dark Matter can't be seen or felt. It probably just travels through regular matter without "colliding", muchlike neutrinos. It only interacts with other matter through gravity. Now, we can detect gravity, but only for fairly big and stationary objects. If DM is tiny particles travelling fast, we can only detect aggregate effects on galaxy level.
- artsyca 6y agoYes just like we can't detect the shadow DOM from the DOM but it's really there you know? I feel like my thinking is too orthogonal any more. There's a difference between matter that's there which we can't detect as opposed to matter which isn't there which we can oh geez
- BurningFrog 6y agoIf you're making sense, I can't detect it :)
- artsyca 6y agoEver feel like you're too salty for your shirt? Can you appreciate the juktaposition of shadow DOM and dark matter or nah? I just post these comments so I can whittle my score back to zero and give you something to think about while you churn out features.
- Rumudiez 6y agoMaybe it is similar in that the shadow DOM predicts the state of the actual DOM. In this interpretation dark matter predicts the shape of our universe. It might just be how one should go about simulating a universe..!
- raverbashing 6y agoNo. Because dark matter is understood mostly to be less interacting matter. Don't think it's a ball of dark stuff, think something you couldn't even see Whereas he's proposing regular (dark as in color) matter
- balfirevic 6y ago> Whereas he's proposing regular (dark as in color) matter Wouldn't that kind of matter be easily detectable because it would block EM radiation, including visible light?
- corty 6y agoYes. "Dark" is misleading, it should be "sparsely-interacting" or something. Well, MACHOs would have been dark in the traditional sense as well. Generally, "we would have seen it" excludes a lot of dark matter candidates, thats what actually makes it "dark"
- haolez 6y agoThat's my understanding as well.
- nwallin 6y agoYes, the bullet cluster effectively disproves most theories like MOND and similar. This article doesn't mention the bullet cluster. The article is dead on arrival as far as I'm concerned. Additionally, some galaxies have dramatically more or less dark matter than other galaxies. There's not a very good path forward for MOND-like theories with regards to explaining these galaxies. https://en.wikipedia.org/wiki/Ultra_diffuse_galaxy https://en.wikipedia.org/wiki/Ultra_diffuse_galaxy
- zamalek 6y agoMOND was a healthy idea to pursue, not because it was the correct alternative (I really have my doubts that it was) but because it was AN alternative. Maybe some postgrad might have had less of the mainstream science groupthink indoctrination because of it. That being said, dark matter is a real phenomenon: it is a measurable quantity of how wrong we are. Dark matter isn't the problem, WIMP is.
- Beldin 6y agoWe have a theory and observations. Observations don't match theory. So, at least one of them is incomplete. Dark matter puts the emphasis on observations(that is: assume the overall theory is roughly correct): there are things out there that, if we would have observed them, would make the theory fit. Alternatives for gravity focus on the theory (accepting observations as roughly complete): if we change the theory, it should fit the observations. TL;DR we ought to have A=B, but there's a mismatch. The problem could be due to either A or B. Or both. Both should be worked on - at least until one can be fully ruled out.
- phkahler 6y agoCan anyone Please point to the model used for the "expected" galactic rotation curve? This whole dark matter thing started with observation not matching prediction. I'd like to scrutinize the prediction.
- ellis-bell 6y agonewton's theory of gravitation was the model used for predicting expected galactic rotation curves
- corty 6y agoPlus mass distribution of bright matter inferred from brightness curves. It is a simple enough integral to do, grab any beginner's astronomy book.
- jfdi 6y agoMaybe dark matter is just a symptom of the universe’s connection to the multiverse. Externalities in action.
- amanaplanacanal 6y agoGravitational effect from nearby parallel universes maybe.
- kurthr 6y agoI just find this odd... we've seen Dark Matter fill in the gaps of standard astronomy (general rel) models of galactic evolution, but it's been predicted and seen in multiple places over the last 50 years and the measurements keep getting stronger (cosmic background spatial distribution, galactic rotation, bullet cluster). Each measurement rules out some model explanation, and we search for different particles (WIMPs, MACHOs, neutrinos) that fit the models that work. We still have interesting testable explanations... but let's give up now, it's boring? MOND again? Sorry, axions are interesting and may explain other things (antimatter ratio etc) and if that fails I think others will pop up, that don't require reexplaining astronomy. https://phys.org/news/2020-06-case-axion-dark-gains-traction.html https://phys.org/news/2020-06-case-axion-dark-gains-traction...
- sanxiyn 6y agoI think an argument can be made that we should have given up (figure of speech: rather, distributed most of resource to other experiments) on WIMP much sooner. These days we agree "WIMP didn't work out", but in retrospect, was it actually the most promising prospect for dark matter, even in 2010? Why was XENON a better experiment than, say, ADMX? I mean, if it were up to me I would fund both, but I think there was certain inertia and undeserved bias for WIMP.
- AmericanChopper 6y agoThe very nature of the study of physics has created a long history of untestable theories to fill in the gaps. Because candidate theories that can be tested either solve the problem or remove themselves from contention, so until the problem is solved, the untestable ones are the only ones that last any significant amount of time. The theory of luminiferous ether had a large amount of circumstantial experimental evidence for quite a long time, but all it really was, was a placeholder waiting for an actual explanation. Theories like that will always exist on the frontiers of science. It’s not really unique to physics either. Miasma theory played a similar role in the history of biology for instance.
- leoxvi 6y agoMaybe physics needs a more holistic light theory based on stillness and the two-way motion of each phenomena in the cosmos: https://wikischool.org/divided_light https://wikischool.org/divided_light
- augustt 6y agoHaha what on earth is this. Every article starts with a bunch of quotes from some crank with no scientific training. Reminds me of https://vixra.org/ https://vixra.org/.
- Nevermark 6y ago> But now it’s time to consider... Almost invariably when an article title says "it is now time to..." there has been no actual threshold that has been crossed making "now" special at all. The growing types of evidence for a "dark matter" effect on large scales, vs. the absence of any small scale evidence for it, has consistently begged for new particle, gravitational, and other types of theory to be explored. It is a strange situation to have something appear so consistent with one of our pillars (general relativity), while completely absent from the other (quantum mechanics). I am crossing my fingers that any successful understanding of dark matter on the small scale might shed light on how those two pillars could be combined into a single theory. But any explanation will be most interesting!
- deleted 6y ago[deleted]
- QuesnayJr 6y agoIt's pretty easy to get a dark matter candidate out of quantum mechanical theories of elementary particles. The current leading candidate, axions, was proposed all the way back in 1977 for reasons completely unrelated to dark matter.
- nautilus12 6y agoYes! I've been saying for years that dark matter is just a mathematical convenience and that we don't have any real evidence for its existence. Our model w repsect to it needs rethinking
- mrmonkeyman 6y agoGive this man his well-deserved Nobel. He has seen the light and is now willing to share this diamond-like insights with the world. He has been saying, for years, that the whole DM situation is unsatisfactory while we, idiots that we are, went about our lives thinking it was all fine. Shame on science. They ignored the siren call of nautilus12 and it came at a price.. Luckily nautilus12 is willing to forgive us. Without him, where would science be? It does need rethinking. Especially our model with respect to it.
- knzhou 6y agoThese articles always miss the mark because they get the history backwards. Modified gravity theories were taken much more seriously in the 1970s and earlier, where the evidence for dark matter was shakier. Cosmological and astrophysical observations from the 1980s to 2000s have vastly strengthened the case for dark matter, which is why it's the leading hypothesis now. Popular articles won't tell you this, because without exception they laser focus on galaxy rotation curves, a piece of evidence that's nearly a century old and by far the weakest one. But by neglecting to mention the actual evidence we base our conclusions on, they (purposely or not) make us look like fools. Furthermore, dark matter hasn't been ruled out. One particular candidate of what it could be (a WIMP) has been studied and mostly ruled out over the past 20 years, but by the nature of the business there are many possible candidates. And of course we've shifted attention towards those other options, which is exactly how science is supposed to work!
- sincerely 6y agoYou’ve also neglected to mention the evidence that the articles are leaving out ;0
- Filligree 6y agoFor example, galaxy collisions. Dark matter by its nature doesn't collide, so it behaves differently than the galaxies it's in when there are physical collisions, and that's visible. Basically, the galaxies stop; the dark matter keeps going. We can't directly see it, but we can see the gravitational lensing it causes. Dark matter isn't as invisible as believed. Then there are cases of galaxies which don't contain any dark matter, and therefore act the way we were expecting them to from simple gravitational mechanics on visible matter. That rules out any solution involving changes to the laws of gravity, since such a change would be universal. The fact that galaxies can exist which contain none means it must be a substance of some kind which can exist more in one spot than another.
- lostmsu 6y agoWhy does the dark matter stop? Don't colliding galaxies stop due to gravity, which dark matter is equally affected by?
- mysterypie 6y ago> [Milgrom's alternative theory:] But far in the outlying areas of the Milky Way, stars would feel a smaller gravitational force than previously thought Isn't it the opposite? Dark matter is extra matter which implies extra gravitational force to hold the galaxies together. If you want an alternative to dark matter, shouldn't the alternative theory predict a bigger gravitational force than previously thought?
- quotha 6y agoSo without dark matter explaining the planets not flying out of the system, there is actually less gravitational force, yet they are obviously still not flying out. Why? Simply due to the shape of space.
- saberdancer 6y agoAs far as I can understand, you are correct. The problem is that predicted gravitational force at the edge of the galaxies is smaller than observed, so any theory should find a solution for that problem. MOND in my opinion always looked like trying to fit a solution to the observations which will lead to overfit.
- exmadscientist 6y agoI used to work on dark matter experiments. (This was a few years ago now, and wasn't for very long -- I was helping out colleagues -- but I don't think the situation has changed much.) I don't think anyone worth listening to considers dark matter to be a Universal Truth or anything. It's a crappy theory that needs better experimental evidence on the micro scale. It's just that all attempts to find that evidence have turned up nothing. (Except DAMA/LIBRA, the bane of the previously mentioned colleague's days and motivating factor for the experiment in question... but nobody actually believes them, so let's value their reports at "nothing".) The biggest problem is that all alternatives to date are worse. They all have problems, problems of equal or greater severity than dark matter. That, more than any other reason, is the reason dark matter is still the leading theory. I do strongly believe we should work on the advancement of non-dark matter theories. That's how you lap the current leader, after all. And neglecting alternative theories was what got us into a couple decades of string theory stagnation, a mistake we'd be wise not to repeat. If a new theory or new evidence for an existing theory emerges, dark matter will lose mindshare amazingly quickly. There is, of course, a "nightmare scenario". The WIMP carries a weak charge, by definition. It was dreamed up that way to make it detectable and have a presence in the universe. (And there may have been a theoretical preference; I wouldn't know, I've always been an experimentalist.) But there's no reason it must carry a charge, weak, strong, or electromagnetic. That would make it really quite invisible to experiments. This may be the universe we live in.
- sgt101 6y agoBut doesn't it have to have some charge to interact with matter in some way so as to achieve the observed effects that show that gravity from normal matter is inadequate to explain how things move on a macro scale?
- corty 6y agoIt only has to have mass for gravitational interaction, and other charged (color, weak, em) are (mostly) excluded by observations. If there were much beyond gravity going on, we would have seen it. So our hope of detection is the remaining "not much"...
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- causality0 6y agoI would enjoy an explanation as to why the distribution of normal and dark matter in galaxies is roughly the same. My ignorant intuition tells me that since normal matter is subject to many more and different forces than dark matter, one of them should be much more densely-orbiting the galactic core than the other. But they aren't.
- choeger 6y agoWhat, exactly, is the prediction of dark matter, compared to MOND (or related theories)? As a layman it seems like: 1. Dark matter is not universal (i.e. it is a "random" property of space) 2. Dark matter interacts with itself (and other matter) via gravity. Is that all there is? I mean in such a case it seems to be no wonder that it fits the observations better, as DM theory is by far less constrained then MOND.
- oldcopernicus 6y agoIs it possible that the effects of dark energy are in reality a previous universe (like an outer sphere) that is pulling our universe matter?
- fhars 6y agoYou are reading too much Ian M. Banks. (Note: that’s fiction, not science.)
- oldcopernicus 6y agoNever read Ian M. Banks. This is just a question. If not possible why?
- JoeOfTexas 6y agoWhat if dark matter is really just regular matter that is not visible through our instruments? Like large swaths of ice or dust in the voids, similar to our kuiper belt that is difficult to analyze.
- goodcanadian 6y agoThere are some clever ways of detecting such things. The density of gas and dust can be determined by measuring the effect on starlight passing through it. Statistically, larger objects should occasionally pass in front of background stars making them "blink off" briefly or in the case of black holes, lens the light from the background star, making it briefly brighter. Surveys have been done looking for such things. We can put upper limits on the amount of "traditional" matter, and there simply isn't enough of it out there to explain our observations.
- Steko 6y agohttps://en.wikipedia.org/wiki/Baryonic_dark_matter https://en.wikipedia.org/wiki/Baryonic_dark_matter
- bronlund 6y agoIt's the ether, stupid. It's top secret :)
- tappio 6y agoI'm wondering always about the name "dark matter". It makes a good topic for all kinds of pseudo-science and scifi. The name implies something mystical and invites everyone to discuss a topic that no-one understands. If the name was something else like "Rubin's matter" or "Unknown matter", maybe it wouldn't invite so much unscientific discussion and speculation. I don't feel that everyone has an opinion about higgs boson, but you can start a discussion about dark matter with anyone. I'm not any kind of expert about the topic either, but could certainly start speculating about it with other laymen.
- mr_toad 6y agoIt’s literally dark.
- gorgoiler 6y agoIf you enjoy science fiction, one of the better recent SCPs was about dark matter: http://www.scp-wiki.net/scp-4170 http://www.scp-wiki.net/scp-4170 SCP is a world-building collaborative creating-writing project, focused on sci-fi cosmic horror. Each entry is standalone, though there is also some canon which contributors are encouraged to follow. SCP-4170 was generally received as a positive entry, though I read it as being far more sinister. Miriam: [Request to still be taken seriously]
- Baeocystin 6y agoThat really was a good one. Thanks for linking it!
- ubittibu 6y ago> But far in the outlying areas of the Milky Way, stars would feel a smaller gravitational force than previously thought from the bulk of matter in the galaxy; Shouldn’t it be: "a stronger gravitational force than previously thought"?
- LoveMortuus 6y agoHope this isn't a stupid question, but does dark matter have different states like solid, liquid, gas and plasma?
- Koshkin 6y ago“Dark matter” is the name of an observable effect. We do not know if it’s matter, even.
- Koshkin 6y agoMOND is appealing from a purely philosophical point of view: we have a separate (“modified”) theory for when thing are very small, another one for when things move very fast, so, the need for another modification for when things are very large should not be seen as entirely unexpected, should it?
- Misdicorl 6y agoWe have none of these things. We have theories which say interesting things about small and fast things. But the theories don't change when things are small or fast. MOND is excluded experimentally (violates observation of galaxies with and without dark matter). It is unsound theoretically.
- lytefm 6y agoWhile the stationary background universe model proposed by Peter Ostermann doesn't rule out „dark matter”, it at least doesn't require „dark energy“ in order to match with observational data. http://peter-ostermann.org/assets/sum_os14.pdf http://peter-ostermann.org/assets/sum_os14.pdf
- 8bitsrule 6y agoA simple back-of-the-envelope estimate shows that it takes an -extremely- small amount of very low-density 'invisible' matter - assuming that it's spread out over the huge 3D 'spherical' volume of a galaxy - to make up the missing mass. On the order of a few -atoms- per cc. Given all of the unknowns about interstellar/ intergalactic matter, including the density of EMF, it's not too hard to understand why the account sheet won't balance. It's a hard and wonderful problem.
- pontifier 6y agoI've often wondered if there is an equivalent of the magnetic field for gravity. The magnetic field seems to be a consequence of resolving charge interactions for relativistic observers, and the same could be true for gravity.
- tylerjwilk00 6y agoDoes anyone know if there are any effects from inflation [1] at galactic boundaries? [1] https://en.m.wikipedia.org/wiki/Expansion_of_the_universe https://en.m.wikipedia.org/wiki/Expansion_of_the_universe