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Complete armchair novice here, but I always found "dark matter" as I have seen it to be pretty implausible. It just kind of feels like there's a scale with wei

• fknorangesite 5y ago
  > Complete armchair novice here I basically came into the comments here just to see all the complete armchair novices come out of the woodwork to explain how they think they're smarter than the actual physicists.
  • rootusrootus 5y ago
    Welcome to HN, and every other forum on the Internet. It's a conversation forum, not a debate forum. Speaking of which, shall we start a discussion on climate science? ;-)
    • fknorangesite 5y ago
      > Speaking of which, shall we start a discussion on climate science? ;-) Here's a Monty Hall explainer. Will a plane on a treadmill take off? When you shower, do you explicitly wash your legs? Did you know that 0.999...=1?
  • kortex 5y ago
    I think dark matter (and dark energy, for the same reason) invite lots of armchair discussion by curious non-experts precisely because they are basically fudge factors. There's no ontological baggage and the theories are fairly "decoupled" from other aspects of physics. It's basically data, a fitted curve, and some X factor (or Lambda for dark energy) added on to make the data fit the curve. That X does not interact with any other models outside of cosmology in any currently observable way, and not for lack of searching. That makes it really tempting to think "well maybe it's the model/equation that's wrong", which has been exactly the case throughout scientific history: planet Vulkan vs Relativity, phlogiston vs oxygen, luminiferous ether vs QED.
• russdill 5y ago
  It'd be a much different problem if everything it was like this. This is more of a "most things we measure" give a heavier reading, but not by any consistent amount. But not all. And very often the scale shows a number when there's absolutely nothing to see.
• mohaine 5y ago
  Except the scale is right locally, but not on the galaxy scale.
  • dboreham 5y ago
    The sim may be running a different version of code out there.
• Aachen 5y ago
  Yeah this comment is posted whenever dark matter comes up. I'm a similar novice and I feel the same way. However, I also know that the experts out there don't say this for no reason and that, even if "dark matter" just a construct/illusion that turns out to be something else (not a new kind of matter), it can still be a useful placeholder to work with (like how we still model gravity as a force). Dismissing it as an incorrect measurement ignores the depth people have long gone into to verify this discrepancy between predictions and reality is not a sensor problem.
  • jrm4 5y ago
    Yep, there's probably a big difference in how real scientists talk about it vs. what we end up seeing in casual magazines, etc.
  • bostonsre 5y ago
    I kind of had the same intuition as the op, but you are most likely correct. A lot of ridiculously smart people all seem to think it's out there somewhere. Are there any popular theories that posit that gravity behaves differently at these large scales? Or are all the smart people in the same camp of the being dark matter somewhere?
    • hnuser123456 5y ago
      Yes, https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics
  • nodja 5y ago
    Another novice here, but every time the matter of dark matter comes up I remember this story. Almost 2 centuries ago astronomers found that the orbit of Mercury didn't make sense according to Newton's laws, laws which were at the time considered infallible. The astronomers only explanation was that there was a planet closer to the sun that we couldn't see, they believed this so much that they even named the planet Vulcan and spent many years searching for it. Turns out that there was no Vulcan and general relativity explains the discrepancy in the orbit of Mercury. https://en.wikipedia.org/wiki/Vulcan_(hypothetical_planet) https://en.wikipedia.org/wiki/Vulcan_(hypothetical_planet)
• yk 5y ago
  The thing is, your proposed change to the scale has to work exactly like "invisible stuff on the scale." So, we can observe dark matter in the early universe with the CMB, we can observe it in the large scale structure, and we can observe it in rotation curves. And the results of these observations is, that dark matter has to behave like matter, just dark. So your proposed new theory would need to deviate from standard theory in precisely the way an additional matter component would.
  • veilrap 5y ago
    You're describing a https://en.wikipedia.org/wiki/Tautology_(logic) https://en.wikipedia.org/wiki/Tautology_(logic) Dark matter works well because it's designed to fill in the gaps in our current understanding of astrophysics data. Given it's origin it of course can perfectly explain the data, because that's what it was designed to do. However, that doesn't necessarily make dark matter particularly useful for understanding how nature actually works.
    • MadcapJake 5y ago
      This is not a tautology because it's not being used as a final explanation. It's called "matter" because the observational gaps appear to fit what would be some mass that we're missing and we think of matter as "stuff with mass". It's called "dark" because we can only observe it's gravitational impact and by all other observables, it doesn't show up. > Dark matter works well because it's designed to fill in the gaps in our current understanding of astrophysics data. "Works well" seems like you are looking at it the wrong way. Nobody is touting "dark matter" as a solution. It's the problem itself.
• specialp 5y ago
  This could be true, but it could also be true that there is something else at play that we are unaware of. In science there have been cases of things that did not fit the model, but the model was not wrong. One example is the precession of Mercury[1]. Newtonian models were right that this anomaly does not agree with our understanding and calculations of gravity. But later on it was shown by Einstein that this anomaly was caused by relativistic effects. It wasn't that there was a large miscalculation, or our understanding of gravity was completely wrong, it was that the model did not count on a previously undiscovered phenomenon. https://aether.lbl.gov/www/classes/p10/gr/PrecessionperihelionMercury.htm https://aether.lbl.gov/www/classes/p10/gr/Precessionperiheli...
• hannob 5y ago
  I am a novice as well, but as far as I understand, "Dark Matter" ultimately is really just a term for "there's a phenomena we don't understand yet, and we call it Dark Matter".
  • FrenchAmerican 5y ago
    I heard a podcast with top scientists about this (in French, still available online) about this: it's indeed a nickname for the phenomenon - but the scientists using it know that, of course. However, this nickname is not absurd, in the sense that the gravity equations for the movement of stars in galaxies don't match the observation. In order for the stars to move inside their galaxies at their observed speed, these galaxies should have much larger mass. Hence the "dark matter". Scientists do not all agree that there is an "invisible" matter to be found. Many think that Einstein's relativity has a more limited domain of validity than we thought. But then the issue is as dark (in the sense of mysterious), since many of Einstein's predictions - based on his equations - have been observed in experimentations. The gravitational waves (LIGO experiment and other replications) appear to prove that the relativity equations are right. The precision of this instruments are extraordinary. It's a terrible situation for Physics as a discipline: the equations are confirmed in all know situations, except this case (well, as far as I understood). There are plenty of theories for explaining the phenomenon, but they lack an feasible experiment to see if their predictions match the observation. Today, all the theories with feasible experiments have proven to be false. Physicists are stuck. Many think that we need a new Einstein or a new Newton, meaning a genius among the geniuses, capable of think a whole new paradigm for gravity. Gravity is a "law" and not a "force". It's as well the nickname for a phenomenon ; that phenomenon is sensible in the domain of validity of Newton, e.g. in our daily life. The planets in the solar system move all accordingly with Newton's equations, except Mercury. Einstein had to totally put upside down the way we represent the world we live in, from a 3D world with a totally independent time to a 4D world, where everything and everyone live in its own spacetime. Let's imagine two atomic clock set next to each other and synchronized. If we elevate one by 1 cm, then the clocks have a super slight desynchronizarion. And the tiny tiny difference match Einstein's equations. Newton and Einstein are a few centuries apart. When will such genius reveal itself? Some physicists point that both were outsiders in their times. Nowadays, the knowledge is so vast that it takes ten years to master a fraction of it: by that time, a brain is so entrenched in the current representations that it's difficult to break the paradigm. Others think likely that one of the theories already published is right but we'll need to wait a very long time, if ever, before being able to make the experiment that will prove it. Maybe we will have to accept not being able to explain our universe. After all, since Gödel, mathematicians have kept going despite his proof that the mathematics are based on a quite fragile foundation. I never quite understood that Gödel thing. Anyone to try and explain us that "dark" theorem?
• deleted 5y ago
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• nickpinkston 5y ago
  Yea, I'm with you and have been really interested the MOND (Modified Newtonian Dynamics) research, as their charts seem to fit the data better. For those who haven't heard of this, the idea is that the gravitational constant actually changes at very high rotational speeds / centripetal accelerations (such as those at the galactic scale), and this is why our Earth-based gravity experiments don't detect this because we're in roughly the same reference frame and don't see the effect. https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics (Also, I am really not a physicists, so I'll let them chime in)
  • Scarblac 5y ago
    But there are also galaxies that do agree with what our gravity laws say, and therefore don't seem to have much dark matter. That's a big problem for theories that want to change the laws of physics, I believe?
  • pdonis 5y ago
    > the idea is that the gravitational constant actually changes at very high rotational speeds / centripetal accelerations First, the MOND regime is not very high (large) accelerations, but very low (small) accelerations. Second, the MOND hypothesis is not quite that the gravitational constant changes; it's that the form of the gravitational force changes--it's no longer the Newtonian inverse square force. The key issue with this is that Newtonian gravity isn't our best current theory of gravity: General Relativity is. MOND as it was originally proposed is not a relativistic theory; there have been attempts to formulate a relativistic version, but none of them have resolved all of the open issues. > this is why our Earth-based gravity experiments don't detect this because we're in roughly the same reference frame and don't see the effect. No, that's not why MOND proponents say we don't detect the effect in Earth-based experiments. It's simply that we can't reproduce the required conditions on Earth (the net gravitational acceleration from all sources being small enough to get into the MOND regime).
    • nickpinkston 5y ago
      Thanks for chiming in to clarify! I'm unsure the differences between "same reference frame" vs. "can't reproduce the required conditions" - ie Isn't it that in order to reproduce the very low accelerations we can't be in our current location with its high accelerations? I'm guessing there's some nuance between location / ref frame here that I'm missing.
• dcolkitt 5y ago
  The difference is the existence and proportion of dark matter has been confirmed across multiple different scales and context, from galaxy rotation curves to the cosmic microwave background to gravitational lensing. We've also found galaxies where dark matter doesn't exist in any measurable quantities. So it'd be more like a couch that's supposed to weight 200 lbs reads 300 lbs on a scale. But we've tested it on a half dozen different scales from different makers and keep getting 300 lbs. In addition we've tested this other couch that's suppose to read 100 lbs on some of these scales, and it correctly reads 100 lbs.
• thereddaikon 5y ago
  Part of the problem is bad PR. Its induced by 1: a terrible name, dark matter implies a lot. and 2: Pop science doing an utterly awful job of explaining the topic. Many people walk away with the assumption that dark matter is literally massive lumps of stuff out there that is just really hard to see. Kind of analogous to stealth aircraft or something. This sounds absurd and it is. And its why a common reaction is to consider it absurd and that we probably just have gravity wrong. The reality is that dark matter is just the name given to a set of observations. It wasn't intended to be descriptive. We are talking about scientists here, not public relations. So they are liable to fumble in the PR bit. Its not what they are good at. I consider the Neil DeGrasse Tysons and Michio Kakus of the world more to blame than the community at large. They have chosen to become the popular face of science and with that have a responsibility to properly communicate it. Their failure contributes to why people distrust academia to some degree.