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Dark Matter: The Situation Has Changed
- chris1993 5y agoIn the comments why does everyone refer to the author as ‘Sabine’? It seems overly familiar and derisory. Men are granted the respectful use of their full name or their surnames.
- deleted 5y ago[deleted]
- adolfojp 5y agoBecause Sabine is easier to type and pronounce than Hossenfelder.
- spopejoy 5y agoThere is a fair amount of branding on the Youtube channel around "Sabine", so she might be deliberately encouraging the informality.
- DemocracyFTW 5y agoMy hunch is that she'd be alright with this. Somehwat relatedly, there's a Dr. Axel Rauschmeyer (also from Germany) who talks about JavaScript and is almost always referred to as "Dr. Axel". Then there's Dr. Tedros Adhanom Ghebreyesus, who is quite correctly addressed by his title and given name, "Dr. Tedros", omitting the patronymic components. And no, you usually do not quote a person's full name unless in court as you'd usually leave out the middle name(s). But in the end it's up to Dr. Hossenfelder I guess.
- azalemeth 5y agoQuite. Many colleagues I know want to be addressed by their first name and almost shy away from being called professor. I myself feel awful ramming my titles down others' throats, and basically never correct people unless it's relevant -- it's very easy to make yourself look like a jerk...
- DemocracyFTW 5y agoAlso in order to answer the question for yourself don't miss out [How to speak English like Einstein](https://www.youtube.com/watch?v=Hmy-N4AFNDM https://www.youtube.com/watch?v=Hmy-N4AFNDM) which may give you an idea of the personality we're talking about.
- Diti 6y agoIs it possible that what we call dark matter might be the positive equivalent of gravity?
- Svoka 6y agoDark Matter is something producing regular gravity (bending spacetime in a way regular matter would) except we don't see the source, hence the name.
- dvfjsdhgfv 5y agoI always thought the name is quite sinister for this kind of mostly neutral (or even positive in the large scheme of things) phenomenon that we don't understand the nature of. We could give it a more interesting name like Barbēlō.
- posix_me_less 5y agoThe name "dark matter" is bad, because matter that is dark absorbs a lot of light. Dark matter does not interact with light, light passes right through. It should have been called invisible matter, or non-electromagnetic matter.
- samatman 5y agoI like "subtle matter", personally. It isn't just light, as far as we know baryonic matter also passes through without interacting in any measurable way. It has certain... resonances with mystic traditions such as Theosophy, and I could see that being unwelcome in some circles. To my taste it's perfect.
- meowface 6y agoIf you mean something like an inverted form of gravity, that would be the hypothetical dark energy, I think. Dark energy is hypothesized to be a repulsive force, while gravity is an attractive force.
- Svoka 6y agoI don't get why people are so attracted to idea of "modified gravity". So far it is a body of knowledge without predictive power struggling to adjust itself to things predicted by GR.
- enkid 6y agoIs that a swipe against the article? I think she would argue Dark Matter is so over parametrized it no longer makes meaningful predictions. And the argument that any new particle requires a new quantum field makes total sense. So Dark Matter is Modified Gravity, there's not clear distinction because of the need for new fields anyways. Of course, IANAP, so I could be totally misreading it.
- akvadrako 5y agoThe difference between dark matter and modified gravity is how it varies throughout space. Modified gravity is a formula that applies exactly at every point based on other mass, like Newtonian gravity F=G(m₁m₂)/r^2. The density of dark matter varies throughout space and it isn't based on a simple formula, but all the complicated dynamics of the past.
- Svoka 5y agoHow exactly Dark Matter is overparameterized? So far there was just constraints on what it could be from actual physical representation, not from what effects it has in terms of spacetime curvature.
- enkid 5y agoI'm not a physicist, I'm just trying to represent what's in the article.
- joeberon 5y agoOne huge motivation is the disturbingly fierce incompatibility between the Standard Model and GR
- bcgraham 6y agoThis seems like the kind of thing that got decisively ruled out decades ago, but could the estimates of star mass be wrong?
- posix_me_less 5y agoYes. And dark matter hypothesis contains this possibility. Just add correct amount of dark matter to ever star and you can get almost any rotation curve.
- cheesejeez 5y agoCan dark matter be just deformed space ? I am not any good with GR but most of the introductions to it assumes that all frame references are considered uniform to each others, what if that's not the case.
- forgotpwd16 5y agoIn GR geometry is equivalent to matter and energy. So dark matter in GR *is* curved spacetime. Except if you're saying it's an intrinsic property of space but then you break that equivalence and do not speak for GR anymore. If you put it down, this ends up being more complicated.
- pydry 5y agoIsn't the equivalence already demonstrably broken by space expanding faster than the speed of light?
- forgotpwd16 5y agoThat's why you've dark energy added as the infamous cosmological constant in the equations.
- ravi-delia 5y agoNo, you can construct clean solutions to GR that involve all sorts of expansions. The faster than the speed of light thing governs acceleration, not velocity.
- eloff 5y agoTo me dark matter has always seemed inelegant, like a hack, which is exactly why and how it was introduced. Now nature doesn't care what's elegant or not, so maybe that's how things actually are. I always thought it'd be nicer if we found out our equations for gravity were off instead. Something that's a rounding error at small scales but that matters at large scales and could explain the faster orbits at the edges of galaxies and in galaxy clsuters. However, as Sabine points out, it seems that really, at the mathematical level it's the same thing. Add a field, add a particle, both ways you're just adding some terms to the equations . Fields and particles are two sides of the same coin. I guess MOND and dark matter aren't as different as I thought.
- nicklecompte 5y agoI am sympathetic to the recently-advocated view that the effects of dark matter are really “gravitational magnetism” associated with rotating large masses[1]. That said: dark matter is no more a “hack” than the discovery of Neptune or Alpha Centauri C: the existence of both were inferred from deviations from theoretically expected gravitational motion, and only later confirmed by direct observation. If Neptune did not exist it might have implied Newton’s equations of gravity were wrong - but it’s existence and correctly-predicted mass were instead a major validation of those laws. So I think the dark matter hypothesis and the subsequent research activity are fully justified areas of scientific inquiry. [1] https://link.springer.com/article/10.1140/epjc/s10052-021-08967-3 https://link.springer.com/article/10.1140/epjc/s10052-021-08...
- posix_me_less 5y agoNeptune hypothesis was successful, Vulcan wasn't [1] [1] https://en.wikipedia.org/wiki/Vulcan_(hypothetical_planet) https://en.wikipedia.org/wiki/Vulcan_(hypothetical_planet) In both cases, the assumption about another planet was a reasonable thing to investigate. Dark matter is much worse, because we are not introducing single planet to explain another planet behaviour, but we are introducing new "stuff" that can be distributed in space largely arbitrarily and we have great amount of freedom to fit the observations. Add a little dark matter here, remove little dark matter there, now we can fit a bear.
- snarfy 5y agoIn antenna theory there is the concept of the near field and far field. I had an idea that maybe black holes have an additional near field component that becomes exposed once the singularity is formed, like there is a limit/floor to infinite density. Energy in the far field falls of at 1/r^2 but near field is 1/r.
- 867-5309 5y agoinfinite density is not physically possible, that's why general relativity fails to account for the existence of singularities
- posix_me_less 5y agoHow would near field of black holes explain galaxies' rotation curves?
- snarfy 5y agoIt would mean black holes have different gravitational properties. Normal matter's field falls off at 1/r^2, but a black hole would be more like 1/r^2 + x(1/r). The 1/r term would make the outer edges spin faster than expected.
- hwillis 5y agoYour theory is that at far distances black holes act like normal gravity wells, and at near distances the gravity is lower (or higher?) than would be expected for the real mass. This is directly contradicted by evidence specifically for the case of galactic-scale supermassive black holes, and broadly by observations of black holes. We have directly observed accretion disks, which would look very different if the near field of a black hole was different from the far field. We have directly observed discrete objects falling into black holes with minimal accretion disks, ie with no other forces except for gravity, and have found that redshift evidence very strongly agrees with general relativity. There is just no way you are correct for most black holes. They behave the same close up as they do from far away. If supermassive black holes acted differently then we would have seen evidence of your theory with Sagittarius A*. It's our galaxy's central supermassive black hole. We have measured the orbits of objects light years (cluster GCIRS 13E) away and light hours (star S2) away from its center. Gravity changes as expected. A near-field linear effect is not sufficient to cause us to think that black holes are less massive than they actually are, which would be necessary for your theory to explain why stars in the near parts of galaxies don't orbit as quickly as we'd expect based on the outer stars. If gravity stopped increasing as quickly below a certain radius, we would have seen it.
- RobertoG 5y agoI'm not a physicist, so, please take my opinion like you would take the opinion of somebody chatting in the groceries shop queue, but I find the subject fascinating and I just want to share my crazy theory. At least, I think it would make for good science fiction. I "think" that dark matter observations are the effect of interference between different Everett branches. The smaller is a volume space, the less possible states it has, so gravity in the center of a galaxy would be less that in the borders. The borders of the galaxy are more entropic because more different states are possible, ergo the stars there experience interference with more Everett universes. Gravity being so weak, it would only show its effects in other branches at huge scales. In this "theory", it seems that dark matter effects would be less visible the further away in space (time) we look. No idea if that's the case. Again, I have no idea what I'm talking about, so this is just for fun.
- dooglius 5y agoAn article on HN a couple months ago https://news.ycombinator.com/item?id=26442021 https://news.ycombinator.com/item?id=26442021 claims that our theory of gravity is perfectly fine, we just haven't been taking into account the proper relativistic corrections at galactic scales. This seems much more plausible and elegant of an explanation to me.
- rich_sasha 5y agoI meant to comment there but never got round to it: we have now found galaxies apparently without dark matter. They behave exactly as you’d expect from direct measurements. So either somehow that explanation doesn’t apply there (but why?) or dark matter is real, and just somehow absent from some galaxies. Link: https://www.space.com/19-galaxies-missing-dark-matter.html https://www.space.com/19-galaxies-missing-dark-matter.html
- XorNot 5y agoAlso specifically artifacts like the bullet nebula, where observationally we can see gravitational lensing totally removed from the colliding gases in the X-ray spectrum - exactly what would be expected if dark matter had been separated from the object by it's inability to collide with itself via normal mechanisms.
- TrispusAttucks 5y agoFTA: Then there are collisions of galaxy clusters at high velocity, like the bullet cluster or the el gordo cluster. These are difficult to explain with particle dark matter, because dark matter creates friction and that makes such high relative velocities incredibly unlikely. Yes, you heard that correctly, the Bullet cluster is a PROBLEM for dark matter, not evidence for it. Yes, you heard that correctly, the Bullet cluster is a PROBLEM for dark matter, not evidence for it.
- pavel_lishin 5y agoDoes "friction" refer to something different here? I thought that Dark Matter didn't even interact with itself in any meaningful sense, and therefore had no friction.
- fpoling 5y agoThe third explanation for the problem is that we use wrong approximations of equations of the General Relativity. Even Wikipedia entry on the rotational curves site a paper that shows that properly accounting for General Relativity is enough to explain the rotational curves of our Galaxy. Then there is very interesting take on the equations in [1] that also explains the rotational curves and few more observed effects again without any extra particles or fields. [1] https://link.springer.com/article/10.1140/epjc/s10052-021-08967-3 https://link.springer.com/article/10.1140/epjc/s10052-021-08...
- forgotpwd16 5y agoThe galactic rotation curves isn't the only reason for requiring dark matter. And gravitomagnetism is a known effect. I don't think for decades being studied everyone was doing it wrong.
- fpoling 5y agoThe problem of rotational curves and few other effects attributed to the dark matter appears if one applies Newtonian mechanics on a galaxy or intergalactic scales. Yet to this day there is no proof that this is a sound approximation even for small galaxies. It is just assumed that is a valid approximation without justification. And the reason for that is that accounting for General Relativity is hard even if one consider just next order approximation after Newtonian gravity. So yes, it could be that almost everybody was doing it wrong.
- nicklecompte 5y agoHas there been any updates from the astrophysics community about this “gravitational magnetism” explanation[1]? GR/cosmology is not my area of expertise, but if astrophysicists were indeed neglecting the impact of rotating masses on gravitation that seems like a major oversight that needs to be investigated. [1] A static charge generates an electric field and a moving charge generates a magnetic field. There is a similar effect for gravity: the Einstein equations have a sort of symmetry to the Maxwell equations.
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- irjustin 5y agoAs an arm-chair/youtube scientist, I admit I don't like MOND, but apparently I shouldn't like Dark Matter either. I I hope in my life time this question is solved. Probably one of my favorite areas to follow - that and the quantization of gravity.
- nolroz 5y agoWhat's "MOND"? Is "Dark Matter" referring to the show or the substance?
- mmusson 5y agoDark Matter is an unfortunate term. The intent was simply to say that observations did not match predictions in a way that seemed to imply that a galaxy had more mass than it seemed from existing measurements. That wasn’t even so controversial at first because measuring the visible mass of distant galaxies is a hard problem.
- caspper69 5y agoI prefer the science fiction alternative: black holes are made by intelligent beings. The reason none of the numbers make sense with respect to dark matter and inflation is because life is actually actively altering the Universe. Supermassive black holes accomplished two things: (i) they captured vast quantities of resources for future use; and (ii) they acted as gargantuan propulsion systems, thus allowing any captured matter (what we would refer to as a "galaxy") to be directed far, far, far away from any/all other captured matter. And thus ended the great intergalactic war, which brought about the end of the homogeneous Universe, ensuring that no single civilization could ever start such a widespread conflict again. The distances would make it so. Life was the big bang. (I'll throw the /s and #notserious tags here; Poe's law and all that...)
- ballenf 5y agoSo what’s the R value in terms of insulation of a black hole? If I’m trying to capture energy in the form of really hot things a black seems like a great way to do it. Hawking radiation takes eons.
- rossdavidh 5y agoActually it's just that the alien TV shows are broadcast from there, and the only way you can receive it is via advanced dark matter/dark energy technology we don't have. It's basically just intellectual property law that is screwing up physics.
- AnimalMuppet 5y agoYou should write that book. Seriously.
- Fellshard 5y agoSo the obvious problem is that the unobservable, untestable, unrepeatable current hypothesis of origins is clung to, then, in flagrant disregard for the observable, testable, repeatable theories regarding gravity and basic mechanics. I wonder what would incentivize such irrational, anti-scientific behavior.
- gus_massa 5y ago> I wonder what would incentivize such irrational, anti-scientific behavior. A) We have a very good model of gravity, tested in a lot of systems (like the lab, planets orbits, ...) B) We have some other systems (like galaxies, ...) were the model fail. So the possibilities are: 1a) The model of gravity we have is wrong. [We know it's wrong in other cases and we need a Quantum Gravity theory, but this correction is necessary for other king of systems, like very small and with huge gravity fields, so it's probably not relevant.] 1b) The model is correct, but we are making bad approximations. [Other comments are about gravitomagnetism. I doubt that's the problem, but this is not my specialty.] 2) We have a bad understanding of galaxies and other systems where the current model of gravity appears to fail. Perhaps we are only considering the matter we can see. Perhaps there is more matter that is somewhat "invisible". We can guess where that "invisible" things are and see if we can fix the predictions of the gravity model. We only need a catchy name for this "invisible" thing because it may not be actually invisible [1]. What about "Dark Matter"? 3) As this article explain, perhaps both are correct and we need to fix gravity at a galactic scale and also find some part of the thing that are inside a galaxy. What is the correct rational scientific behavior? [1] They may be invisible from here using a telescope, but they many be visible if you are nearby. Nobody is sure. The names of the models are weird. https://en.wikipedia.org/wiki/Massive_compact_halo_object https://en.wikipedia.org/wiki/Massive_compact_halo_object https://en.wikipedia.org/wiki/Weakly_interacting_massive_particles https://en.wikipedia.org/wiki/Weakly_interacting_massive_par... https://en.wikipedia.org/wiki/Robust_associations_of_massive_baryonic_objects https://en.wikipedia.org/wiki/Robust_associations_of_massive...
- nxpnsv 5y agoDoes this really add any thing to the current status quo? This nor theory or hypothesis yields no new predictions, no ground breaking insights, and actually nothing has changed.
- optimalsolver 5y agoYou don't need to introduce anything new in order to point out flaws in the current status quo.
- nxpnsv 5y agoIf she pointed out a flaw other than a lack of discovery then that should be no surprise to anybody. It is the whole reason so many people are looking for so many different signals in so many experiments...
- mxcrossb 5y agoIt sounds to me like what the author is really saying is that a quantum theory of gravity would look like some of these modified gravity equations in the classical limit. Of course it would be nice to kill two birds with one stone and knock out quantum gravity and dark matter with one discovery. I am curious if some of the proposed theories could be made to look like that.
- TrispusAttucks 5y agoDark Matter Superfluid [1] [1] https://arxiv.org/abs/1507.03013 https://arxiv.org/abs/1507.03013
- Fooloo 5y agoHow many dyson spheres do we need to account get rid of the dark matter and modified gravity?
- forgotpwd16 5y agoOne Dyson sphere of radius 1 AU (Sun-Earth distance) having mass 600 kg/m^2 (8-20 cm thick) will require[1] 10^26 kg of material. The Milky Way's dark mater halo is considered[2] to have mass 10^12 M_Sun = 10^42 kg. So you will need a total of 10^16 (10 quadrillion) spheres. [1]: https://www.aleph.se/Nada/dysonFAQ.html#ENOUGH https://www.aleph.se/Nada/dysonFAQ.html#ENOUGH [2]: https://arxiv.org/abs/1306.4013 https://arxiv.org/abs/1306.4013
- Fooloo 5y agowouldn't you undercount the stars enclosed?
- forgotpwd16 5y agoTrue. I only considered the spheres (shells) themselves. If you include the star then the result is even simpler. M_Sun is 10^30 kg so for a back of the envelope calculation you don't even have to consider the shell. Therefore you can say 10^12.
- paul_f 5y agoWhat's truly amazing is that all 10 quadrillion spheres are dedicated to cryptocurrency mining.
- samatman 5y agoA common misconception, up to 18% are in fact running Doom.
- gilbetron 5y agoDyson spheres would not qualify as dark matter, as they would be made of Baryonic matter.
- TrispusAttucks 5y agoThe conclusion drawn in the article, but not mentioned by name, is a reference to Dark Matter Superfluid [1] [1] https://arxiv.org/abs/1507.03013 https://arxiv.org/abs/1507.03013
- sega_sai 5y agoIt's a bit of the same from Sabine. Dark matter hypothesis allowed us to simulate a vast range of processes in the Universe, from large scale cosmological simulations, predicting clustering of galaxies, cosmic microwave background to smaller scale simulations of galaxy formation and individual galaxies. The hypothesis have been extremely successful and predictive. It is also true, that some of the systems we've been discovering are a bit harder to explain within our Cold Dark matter framework, requiring changing some things about how galaxies form (i.e. making star formation less efficient in small galaxies, introducing feedback effects from accreting supermassive black hols and things like that). I (and many astrophysicists) do not see that as a problem or evidence that dark matter needs to be abandoned, but instead see that as a refinement to the theory. Regarding modified gravity theories, it's true that you can mimic some of the dark matter behaviour by the modification of gravity laws. Also if you can add some kind of global scalar field you can similarly mimic dark matter behaviour. The problem however is that the modified gravity theories (at this point) do not allow the same range of simulations that cold dark matter(CDM) simulations can do (for various reasons, such as many of those theories do not have a general relativity formulation). Because these theories can't make as many/as varied simulations as CDM ones, they are not as tested as regular CDM and much less predictive. Therefore based on that fact alone IMO these theories are less useful. It is also true that if we continue for many years searching for the dark matter particle and will still be unable to find it, maybe we will need to refocus our attention on alternative gravity theories, but the problem is that so far the part of parameter space where we looked for the dark matter particle is still pretty small and there is no strong reason to think that dark matter should have been there.
- posix_me_less 5y ago> The hypothesis have been extremely successful and predictive. Epicycles were successful and predictive. But they were later found to be the wrong way to understand the celestial motions. The problem is these calculations with dark matter are just fitting observations with zillion parameters. It is busywork, yes sometimes it is useful, but it is not discovering new laws, just chugging along without having to challenge our concept of how star/galaxy motions really work.
- ww520 5y agoCould gravity in higher dimensional space be a way to explain dark matter?
- idlewords 5y agoNot really. See Penrose for good rants about why higher dimensions introduce insuperable problems. Basically, if you start adding new dimensions, almost everything will leak into those higher dimensions and then you need to start adding on kluges for why we don't notice them except for the one desired effect. There's a good discussion of this in his book "Fashion, Faith, and Fantasy in the New Physics of the Universe".
- austincheney 5y agoThe elephant in the room is that you can’t find something if it isn’t there. Dark matter is, so far, a human invention to correct for gaps in particle theory. It works great until it doesn’t, which doesn’t imply it’s working or even existing. It does imply dark matter is a really convenient answer until accounting for it breaks something in the math that comes from actual observations. In other words dark matter must be there, according to the evidence, only because otherwise our math is wrong. It could just be that our math is wrong.
- 6gvONxR4sf7o 5y agoIsn’t that just a paraphrasing of dark matter? Our math is wrong and something is up/missing from the calculations. Call it dark matter or an incorrect gravitational field, or whatever you like. I always took dark matter to just refer to the observed phenomenon that doesn’t line up with the calculations, and that gap definitely exists.
- ravi-delia 5y agoI mean, dark matter specifically refers to mass of some kind that interacts gravitationaly but not electromagnetically. It posits a real, actual material floating around in space. MOND is another attempt to explain the gap, and it isn't dark matter at all.
- 6gvONxR4sf7o 5y agoI'm conflating them the way the article does: > But more importantly, if you look at the mathematics, modified gravity and particle dark matter are actually very similar. Dark matter adds new particles, and modified gravity adds new fields. But because of quantum mechanics, fields are particles and particles are fields, so it’s the same thing really. The difference is the behavior of these fields or particles. It’s the behavior that changes from the scales of galaxies to clusters to filaments and the early universe. So what we need is a kind of phase transition that explains why and under which circumstances the behavior of these additional fields, or particles, changes, so that we need two different sets of equations.
- Sniffnoy 5y agoNon-mobile link: http://backreaction.blogspot.com/2021/05/dark-matter-situation-has-changed.html http://backreaction.blogspot.com/2021/05/dark-matter-situati...
- slowmovintarget 5y agoEven on desktop, the mobile link is better (opinion). :) ...Unless you like a narrow column of text on your 1080p or wider display.
- Sniffnoy 5y agoMy main point is doing this is to have the canonical link, not the best-looking link.
- idatum 5y agoThere is something about this scientist's style of writing I like. She conveys complex ideas, gives details, and keeps the reader engaged. Bookmarked. EDIT: And looking at the non-mobile link I realize now it is a transcript. So that crispness in writing came out from essentially a lecture. Nice.
- weeboid 5y agoJust leaving this here https://news.ycombinator.com/item?id=23541043 https://news.ycombinator.com/item?id=23541043
- mleonhard 5y agoWhen you post links, please explain why they are relevant to the current discussion. Posts saying "just leaving this here <link>" are popular on Reddit, but not here on HN. We try to put more effort into our comments here. From the HN Guidelines [0]: > Comments should get more thoughtful and substantive, not less, as a topic gets more divisive. [0]: https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html
- weeboid 5y agoThank you. I've added a reply to clarify as edit window has passed.
- weeboid 5y agoAdded detail: Ever since I first encountered G, I always wondered, "is gravity really constant? Is it emergent from 'the universe', or from matter?" This eventually led to thinking about, "well maybe gravity has more or different properties than G". As evidenced by the link to a typical comment from me above, these thoughts are always dismissed out of hand. For good reason. But now that a "legit" particle physicist is raising these questions, I hope to see some movement.
- Kranar 5y agoI recently finished reading the first volume of The Feynman Lectures and he brings up the possibility that G may not be constant, that it may vary over time or space. The argument why G likely doesn't vary over time is that a different value of G in the past, either bigger or smaller, would be inconsistent with what we understand about the formation of the Earth. If it were bigger by even a small factor then the Earth would be closer to the Sun and hence too hot for oceans to form and vice-versa if it were smaller. Based on all current observations, G is constant.
- throwaway64643 5y agoRegarding the meta of physics posts on here. I'd just like to tell my feeling. Reading science related or physics related opinions of people on Reddit, I feel like most of them are lay people. They express their admiration of science, their surprise for new knowledge, etc. What they wrote indicates them being lay. Reading physics or science related opinions here on HN, I feel like I've fallen into a rabbit hole of personal crackpot ideas of pseudo-experts that are ubiquitous on the net. If this is cutting-edge science, why wouldn't we non-experts just be a bit more conservative with our words? (Alsolutely no offense to any real expert out there).
- j9461701 5y agoIn Starcraft, you get a curious phenomena with regards to how good people think they are based on the league they're in: Bronze league players (lowest) know they're bad and that they don't understand the game. Silver and Gold league players (2nd and 3rd lowest) think they're better and are really starting to get a grasp on how Starcraft operates Platinum league players think they basically know everything and just need to work on a few minor issues Diamond league players begins to realize there is so much more depth than they imagined, and those 'minor issues' are actually oceans of complexity and depth Master league players fully comprehend the depths of their own ignorance and lack of skill, as they are now finally able to look at the professionals and grasp the massive gulf between themselves and the pros. Reddit has bronze league understanding of physics, HN has platinum level understanding.
- phkahler 5y ago>> The velocity of a star which orbits around the center of a galaxy depends on the total mass within this orbit. And the distribution of it. Also on the matter outside their orbit. Galaxies are not spherical distributions of matter. Physicists have been misapplying the divergence theorem for years in this context. I hope shes over simplifying here, but somehow I doubt it.
- phkahler 5y agoA down vote for pointing out a critical error, with no refutation?
- ngcc_hk 5y agoI am more convinced by the argument that dark matter is not new matter but just primordial black hole https://scitechdaily.com/all-dark-matter-in-the-universe-could-be-primordial-black-holes-formed-from-the-collapse-of-baby-universes-soon-after-the-big-bang/ https://scitechdaily.com/all-dark-matter-in-the-universe-cou... And even our planet 9 is (unlikely but ...) https://phys.org/news/2020-08-planet-primordial-black-hole.html https://phys.org/news/2020-08-planet-primordial-black-hole.h...
- pontifier 5y agoI've been thinking a lot about dark matter lately, and came up with a new candidate particle set based on size magnitudes. A "large" particle would be extremely difficult to interact with. Think of something the size of a baseball. Normal matter would pass through it easily if it was so diffuse. They would have to have a mass outside the range of our current accelerators or we would see them by their absence in collision traces.
- amai 5y ago" So what we need is a kind of phase transition that explains why and under which circumstances the behavior of these additional fields, or particles, changes, so that we need two different sets of equations. And once you look at it this way, it’s obvious why we have not made progress on the question what dark matter is for such a long time. There’re just the wrong people working on it. It’s not a problem you can solve with particle physics and general relativity. It a problem for condensed matter physics. That’s the physics of gases, fluids, and solids and so on." See also Justin Khoury (2015) : A Dark Matter Superfluid, https://arxiv.org/abs/1507.03013 https://arxiv.org/abs/1507.03013 and Silvermann (2002): Dark Matter as a Cosmic Bose-Einstein Condensate and Possible Superfluid, https://link.springer.com/article/10.1023/A:1015934027224 https://link.springer.com/article/10.1023/A:1015934027224
- ColinHayhurst 5y agoPhysicists have argued for decades for A (Dark Matter) or B (Modified Gravity). B was a fringe theory with no support; you sacrified your career by advocating for it. The academic mainstream are A proponents and have tried to kill off B, but failed. Sabine has a played a part in it's poularisation. Just A doesn't work. Just B doesn't work. So Sabine suggests A and B. Who dares to question Lambda-CDM? As a prior for A and B isn't that where the answer lies? If you aim to screw up your chances of an academic career in physics go and pursue that. Let me know how you get on.