7 ms·

Honestly, I'm a little tired of the whole dark matter thing. There's no evidence for it, and physicists keep coming up with more and more complex models to fit

• T-A 6y ago
  https://en.wikipedia.org/wiki/Dark_matter#Observational_evidence https://en.wikipedia.org/wiki/Dark_matter#Observational_evid...
  • nynx 6y ago
    Those are evidence for our physics not actually matching reality, not evidence for dark matter specifically.
    • T-A 6y ago
      If by "evidence" you mean "direct detection", presumably in an Earth-based experiment, then fine, there is none. However, that leads to your follow-up question why MOND and other modified models of gravity are not more popular. It's not for lack of trying: https://en.wikipedia.org/wiki/Alternatives_to_general_relativity#Results_of_testing_theories https://en.wikipedia.org/wiki/Alternatives_to_general_relati...
      • leeoniya 6y ago
        to add to this, the Higgs boson was predicted in 1964 and not detected till 2012: https://en.m.wikipedia.org/wiki/Higgs_boson https://en.m.wikipedia.org/wiki/Higgs_boson
        • dnautics 6y ago
          Huge difference: when Higgs was predicted there was a clear path to how to find it. We do not currently have a theory that describes a way to find LCDM that is not begging the question of its existence (not circular reasoning), although we do have several shots-in-the-dark that are ongoing (and a handful that have concluded with no observation). Also IIRC, Rubin's seminal observations on dark matter were in the 60s too, and dark matter was postulated in 1930.
          • leeoniya 6y ago
            > Huge difference: when Higgs was predicted there was a clear path to how to find it. is that really a huge difference? plenty of eventually-proven math conjectures were initially posed with no knowledge of how a proof will be found. perhaps with the higgs it was easier because it was conceivable that we could produce the necessary collision energies here on earth, while other problems remain at unattainable scales for a clear path to exist today.
            • dnautics 6y ago
              > plenty of eventually-proven math conjectures As a theoretical math major and a practicing scientist, I'm just going to have to say that these are not comparable, neither in process, nor ontologically. > conceivable that's a very weak way of saying the scaling factor of collision energies was known, and the technology to build the required machine right around the corner (we could have found the higgs with technology proposed for the hole in texas, only 20-or-so years after the prediction of the higgs; at the time higgs was postulated superconductors were already known for 10 years and the first superconducting NMR was 10 years away). Anyways, my point is that there is a categorical difference. At the time of its postulation, building an experiment that could say yay or nay about the existence of the higgs was largely an engineering problem.
        • Iwan-Zotow 6y ago
          True. But f.e. search for Higgs on Tevatron pretty much started after top quark discovery, ca 1995. And Tevatron was covering one energy range after another in search for Higgs, and would have found it if not being closed, around today date. We knew what to look for. With DMwe're shooting in the dark, so to speak, in hope something will turn up
    • heavenlyblue 6y ago
      You are arguing semantics
    • dogma1138 6y ago
      I'm not sure why this is being downvoted, it's technically correct (tho I'm not sure if it was in good faith) the observations don't explicitly require Dark Matter, it's just currently the most likely answer given the theoretical frameworks and observational evidence we have. There are essentially 3 (or 2.5) explanations, that we have (a lot of) missing mass, that we don't understand gravity or that we don't understand spacetime. Most theories revolve around the missing mass part this includes all possible theoretical candidates for Dark Matter from both within and beyond the standard model, overall a single candidate or a combination of a few likely ones seems to fit our observations the most. Modified Gravity; these theories actually have gotten plenty of attention in the 80's and 90's but the problem is that most of them don't fit observations especially modern ones like the bullet cluster and gravitational waves, most of them aren't relativistic (or don't have a relativistic formulation) and they overall suck at predicting everything else including the formation of galaxies and stars in the first place. "Modified Spacetime"; mostly relegated to the dark corners of the web and to pseudo scientific forums technically possible but I haven't seen anything that comes close to being an actual theory as in having an actual mathematical basis. They basically revolve around various possible ways of affecting spacetime curvature, basically if you could curve spacetime without out mass to the same extent as say the earth's mass does you'll technically will end up with the same gravity well. The more "serious" of these tend to revolve around various attempts at gauge gravity. I usually consider the "Modified Spacetime" as being an offshoot of Modified Gravity theories.
• lisper 6y ago
  "The most serious problem facing [MOND] is that it cannot completely eliminate the need for dark matter in all astrophysical systems: galaxy clusters show a residual mass discrepancy even when analysed using MOND. The fact that some form of unseen mass must exist in these systems detracts from the elegance of MOND as a solution to the missing mass problem..." https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics
  • DennisP 6y ago
    I don't really have an opinion but in fairness, the article is about a discrepancy between the data and current dark matter models.
    • lisper 6y ago
      Sure. But the question was: why doesn't MOND get more love? And the answer is: because it doesn't actually solve the problem. Nothing solves the problem at the moment. That's what makes this such a juicy mystery.
      • dogma1138 6y ago
        If we are being completely frank here MOND doesn't gets as much love because it goes against GR, besides the fact that General Relativity is one of the most observationally validated theories we have there is quite a bit of dogma revolving around it as well. MOND isn't a career ender as much as say cold fusion is, but it's pretty close. And in all honesty if we look at Modified Gravity theories as a whole they shouldn't be anymore more offensive to one's career than say string theory and despite string theory being essentially a dead end for decades now it doesn't get anywhere near that level of stigma that MOND does and that's more for a cultural / dogmatic reason than purely scientific ones.
  • dogma1138 6y ago
    MOND brings it down to levels that could potentially be explained with missing baryonic matter and other Dark Matter candidates that fall within the standard model. There are however other issues with MOND including that gravity is still instantaneous (in most variations) which we know with gravitational waves it isn't, as well as that most of them don't lend to the formation of stars and galaxies. If we take vanilla MOND then the universe as we know it shouldn't have been formed matter wouldn't clump up to form the formations we can see around us and the one we live on.
• jjoonathan 6y ago
  If MOND and Dark Matter both fit the data and MOND did it with few parameters while DM did it with a field of parameters, everyone would prefer MOND and it wouldn't be the slightest bit controversial. The problem is that MOND doesn't fit the data. Some galaxies behave one way, some behave the other way, and it isn't very inspiring when a MOND model fails to fit observations and its advocates try to hand-wave the problem away. DM: we see complexity, let's treat it as fundamental. MOND: we see complexity, let's ignore the inconvenient parts.
  • dnautics 6y ago
    Disclaimer, I'm not an astronomer. I think that is a mischaracterization; IIRC, MOND fits the overwhelming balance of galaxies with a single parameter, and there are only a handful of exceptions (probably around in the hundreds or so?) out of all of the galaxies. also: MOND doesn't explain intergalactic movement, or the clumpiness of the universe. But there's ALSO no good reason to believe that that "LCDM dark matter" does either, because by the "curve-fitting nature" of LCDM it could literally explain anything. If all of the oxygen in my room went to the northeast corner of my room and suffocated me, you could come up with a dark matter field that explained that phenomenon. As a scientist, that worries me. Also doesn't mean that LCDM is wrong.
• gbrown 6y ago
  > There's no evidence for it [citation needed]
• tiborsaas 6y ago
  If it's tireing for you imagine the scientists who dedicated significant amount of their lives to figure out what explains this baffling observation. Another problem with MOND is that no matter how you tune it, it can't explain the Bullet cluster for example.
  • dnautics 6y ago
    Sure, but a counterexample of one or two could be literally anything. After all, conventional dark matter theories don't do a good job of explaining why there just so happens to be galaxies with highly-deviant clumps of dark matter. If the bullet cluster is a great counter example for MOND, then conventional dark matter is highly opportunistic curve fitting (which doesn't mean it's not correct).
• joshocar 6y ago
  There is a LOT of evidence for the existence of dark matter. https://en.m.wikipedia.org/wiki/Dark_matter#Observational_evidence https://en.m.wikipedia.org/wiki/Dark_matter#Observational_ev...
  • nynx 6y ago
    What you've linked to is evidence that our understanding of gravity is wrong OR there is dark matter.
    • magicalhippo 6y ago
      And that's why there's groups working on both dark matter and modified/new theories of gravity. It seems quite difficult to modify GR or make a new theory of gravity which explains the new observations while matching GR in the old ones, where GR has been verified. But if someone manages, then you'll see scientists flock to it.
    • kmm 6y ago
      But the hypothesis of dark matter fits all of the evidence, while no alternative theory of gravity comes close. That's what makes dark matter so attractive to physicists. I'm not shunning the idea, I've worked on alternative explanations myself (with no concrete result), but for the moment we remain convinced that dark matter is the better theory.
      • ashildr 6y ago
        > That's what makes dark matter so attractive to physicists. I _really_ like what you did here :-)
  • dnautics 6y ago
    MOND does not reject the observational evidence for Dark Matter theory, it just postulates that it primary cause is not a "non-baryonic particle that interacts only via the gravitational field".
• ajkjk 6y ago
  Are you a physicist? What possibly makes you think you have enough background to disregard the (tremendous) evidence for it?
  • mellosouls 6y ago
    To be fair, there is a lot of evidence for the phenomena described as "dark matter", but as yet zero detection of actual matter that fits it's properties. Perhaps that is the complaint here - and asking for academic background is an argument from authority...
    • freeone3000 6y ago
      So the name of dark matter might be misleading, but there is some mass/pressure/something that's causing gravitational lensing but itself doesn't interact with light.
    • morelisp 6y ago
      > as yet zero detection of actual matter that fits it's properties. Except for all the ways we have to detect actual matter (i.e. gravitation) that fits its properties.
      • dbsmith83 6y ago
        You are assuming this thing exists because it has properties to fit your observations, and then using that as evidence that said thing exists. I'm not saying DM doesn't exist..it probably does, but your logic is flawed
    • yes_man 6y ago
      I am just another armchair physicist but saying there is no detection of dark matter sounds a bit like circular reasoning. You detect matter like your phone in your hand through electromagnetic interaction. We have detected that there is something in space that completely disregards electromagnetic force, but exerts gravitational force. Hence the idea that we have not detected it is simultaneously false in 2 ways: - it cannot be detected the way you detect your phone in your hand or see light so your definition of detection seems to escape the basic premise of dark matter: its ability to avoid electromagnetic force, and also, - we have detected it through gravitational anomalies
• morelisp 6y ago
  OK honestly this shit is equivalent to global warming denialism and should be tolerated just as much i.e. much less than HN let alone mainstream media allows.
• yongjik 6y ago
  Honestly I'm not sure why some people oppose "dark matter" so much. We know there's something out of ordinary, it behaves like matter, and it doesn't interact with light (hence "dark"). Given that, "dark matter" is as inoffensive a name as possible. People are acting like we named it "quasiflavored eleven-dimensional supersymmetry carriers."
  • daxfohl 6y ago
    I think it's a natural reaction after Einstein. The whole physics world was certain about this Aether thing, and it turned out to be wrong and much more beautifully solved by plain geometry. "Dark matter", taken at surface level, sounds like going down the exact same rabbit hole. There's a fundamental difference though. With dark matter, the evidence of the stuff is much more direct and precise. We can determine the shape and concentration of it. Aether on the other hand was a hand-wavy metaphysical concept from the beginning. There was never any experimental evidence that aether was a real thing; it was just a concept invented to patch up the inherent inconsistencies in electromagnetic theory near the speed of light.
    • duutfhhh 6y ago
      Or spacetime is that aether. This is like some dusty books have been claiming that there's an invisible fluid substance around us that supports life, then when science discovers oxygen, it says "See? There is no invisible ether or anything like that around us, only atoms."
  • ifdefdebug 6y ago
    > Honestly I'm not sure why some people oppose "dark matter" so much But I think you might be after something: > Given that, "dark matter" is as inoffensive a name as possible. Precisely. Dark matter is boring. People want Klingons.
  • StanislavPetrov 6y ago
    Its not the name "dark matter" have an objection too, its misleading and/or confused attitudes like the one you yourself exhibit in your comment! > We know there's something out of ordinary, it behaves like matter, and it doesn't interact with light That's wrong, and presupposes the existence of dark matter, rather than treating it as a possibility. What we know is that our formulas don't match up with our observations. We don't know why that is. One suggestion is that there is some sort of invisible stuff out there that we cannot detect, but would make our formulas add up, so it could exist. Its perfectly legitimate to speculate about the existence of dark matter, and to set up different experiments to try to detect it, but its not fine to pretend that its "settled science" that dark matter is out there and its only a matter of finding it. Unless and until someone detects "dark matter" or figures out another reason why our calculations don't add up its existence will remain an open question.
• daxfohl 6y ago
  It accumulates in blobs, around some galaxies, trailing others, and not in some galaxies at all. So the appearance and behavior of it matches the model that there's "stuff" there, not that there's some parameter missing from our gravitational model. With the latter you'd presumably get some less arbitrary accumulations of it.
  • dnautics 6y ago
    I think the point of MOND is that it explains a higher proportion of galaxies with a single parameter than something where you have to pick a parameter for each galaxy strictly from observation. Key to note that this doesn't mean it's right. But one wonders why there isn't more skepticism about conventional dark matter theories. Like what if I said "there isn't global warming, there's just a mysterious unobservable dark thermal input adjustment that we have to apply to every month's reading to make our models work out". You'd say that I was crazy.
    • matthewdgreen 6y ago
      I’m not a physicist but this seems like an arbitrary metric. One theory claims that there are fundamental rules that the physical forces obey, but they don’t seem to obey them in certain places we can observe. The other theory also says there are certain physical rules that govern matter, and those rules hold everywhere, but merely posits that the matter is distributed unequally. Since the latter condition is obviously true of normal baryonic matter, this doesn’t seem like a parameter explosion.
      • dnautics 6y ago
        Yes but we have independent observation of that baryonic matter. Suppose we hadn't discovered the theory of relativity. The rules for gravity hold everywhere except for the orbit of Mercury. For several decades it is reasonable to guess there is "mystery meat" planet somewhere that we can't see. Possibly even a hamburger sized black hole orbiting the sun. But to think that the field equations for gravity are wrong is nonsense. Fast forward a few decades and Eventually we can't find this mystery planet and it's decided that an interpretation that the gravity field equations are wrong is more sensible.
• mehrdadn 6y ago
  There's a lot of evidence for it, just not direct detection on it. It's like if you came into your room and saw writing on the wall, your carpets removed, your computer taken apart, etc. and then claimed there's no evidence anyone has been in your room just because you didn't physically find anyone in your room. There are things to be frustrated about with the dark matter hypothesis (and I am too), but lack of evidence isn't one. Dark energy seems to be another beast though...
• ChrisClark 6y ago
  > I am not a physicist, I am simply a concerned citizen. I don't think you can even be a 'concerned citizen' on this topic without some introductory knowledge of dark matter.