Thursday Throughput: The Dark Matter Is Still Missing Edition

Michael Siegel

Michael Siegel is an astronomer living in Pennsylvania. He blogs at his own site, and has written a novel.

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27 Responses

  1. Oscar Gordon says:

    With Dark Matter (the stuff, not the commenter), I can’t help but wonder if one of the base assumptions is wrong.Report

    • The problem is that it’s no longer one assumption. It’s a bunch of them. The structure of the universe kind of demand dark matter be present.Report

      • Oscar Gordon in reply to Michael Siegel says:

        I know the math regarding Dark Matter is much more developed, but it still strikes me as a modern incarnation of aether. Which makes me wonder about base assumptions (especially regarding gravity) and if we have something wrong.Report

      • Pinky in reply to Michael Siegel says:

        Then is the whole problem that the answer is unsatisfying? Let’s say the answer is that there is a kind of matter (or something whose closest analogy is matter) that has mass but doesn’t interact in any other way. If that would satisfy the equations, it doesn’t have to satisfy the physicists. I guess I’m asking if there’s any problem with undetectability.Report

        • Oscar Gordon in reply to Pinky says:

          Yes, because if it’s undetectable, then the theory can’t be falsified except by the development of a competing theory with more evidence to support it.Report

          • Pinky in reply to Oscar Gordon says:

            What if the nature of dark matter is that it’s only detectable by its gravitational effect? Not “really hard to spot”, but by definition able to interact with normal matter only through gravity. If the math backs up the observed gravitational effect and the lack of any other effect, wouldn’t that meet the criteria of falsifiability?Report

            • Dark Matter in reply to Pinky says:

              That would put us in “invisible fairies” territory. Or external to the universe Lovecraftian aliens pushing on the fabric of the universe trying to get in.

              We need to figure out what Dark Matter is. Particle? How is it that we can’t reproduce it, study it, fine it, or describe it?

              Can it be eaten by a black hole? If yes, then shouldn’t we see it being ripped apart and/or interacting with the black hole? Adding mass to it if nothing else. If no, then wtf?

              We’re in this weird area where it both clearly exists and every test to measure it says it doesn’t exist.Report

              • Pinky in reply to Dark Matter says:

                Lovecraftian aliens can be measured, but only by consulting the unnatural writings of the Mad Arab which are contained in the monstrous tome known by those who dare whisper of such things as the Necronomicon.

                My question is, do tests to measure dark matter fail to confirm its existence, or do they confirm its undetectability outside of gravity? By all means we should try to understand it better, and if it’s one of those things that exists just about everywhere for an incredibly short amount of time or something that only interacts with gravity and neutrinos, then there’s value in learning that. But if it’s characterized by, say, mass but no volume, or for some reason only affects dimensions we can’t measure, then it could be explained as fully as we can.Report

              • Dark Matter in reply to Pinky says:

                do tests to measure dark matter fail to confirm its existence, or do they confirm its undetectability outside of gravity?

                I’m not current with this but last I checked we have some clues which round to nothing after the margin of error.

                So other than gravity we’ve got nothing for sure (although if wiki disagrees with me I’d believe wiki).

                if it’s characterized by, say, mass but no volume, or for some reason only affects dimensions we can’t measure, then it could be explained as fully as we can.

                Darn right. Rewriting the law of gravity is one of the few ways we might come up with a star drive.

                I don’t actually have much hope for this, if we’re mis-measuring mass or mis-approximating gravity then the old theory will stay put and we’ll just change the rest.Report

          • JS in reply to Oscar Gordon says:

            I don’t think it’s undetectable so much as “difficult to detect”.

            The Higgs Bosun was difficult to detect, for instance, but not exactly aether.

            Dark matter is a bit of a placeholder — lots and lots of different observations basically say “We’re missing a lot of matter and energy here, stuff that seems to refuse to interact in any real way with anything but gravity (but we can see it’s gravitational shadow in multiple, independent ways). WTF is it even? Let’s call it “dark” matter and “dark” energy because of it’s refusal to interact with the EM field”.

            I mean there are some possible solutions that side-step the need for it, but at the moment it fits Occam’s razor better to say “There’s a subatomic particle we’re missing from our models — because it hates to interact with the EM field” than “All our models are hugely wrong in some key facet, despite being incredibly predictive everywhere else”.

            Because our current model is highly explanatory, and there are a number of ways (WIMPS for instance) there could be a particle we struggle to detect except gravitationally, and adding a new particle is…not exactly as huge a deal as overturning the applecart.

            That said, Einstein and Newton, you know?Report

            • Oscar Gordon in reply to JS says:

              I guess the question is (and particle physics is not my forte), do we have a model of fundamental particles that has room for a particle that can handily ignore the EM force, but not gravity?

              Or, do we just not understand gravity at the macro level as well as we think we do? I mean, last I checked, we don’t even know how gravity works. Is it mass bending space time, or a messenger particle (gravitons, anyone?), a combination of, or a dual nature?

              This is what I mean by the underlying assumptions. We think gravity behaves so, because our observations and equations say so, but what if we are missing some terms in those equations? We got the Euler Equations, instead of the full Navier-Stokes?Report

    • Dark Matter in reply to Oscar Gordon says:

      Oh, the commenter has been wrong in his base assumptions on occasion as well. 😉

      Big picture, if the theory requires invisible undetected things to make it work and we can’t find those things, then the theory is probably wrong.

      Ergo The Theory of Gravity is probably Wrong.

      Nobel Prize for you if you can resolve the issue.Report

    • The thing that really convinced me of dark matter was the bullet cluster result. I might make a video or something about it. A really elegant experiment showing that gravity does not follow the light.Report

  2. Michael Cain says:

    ThTh6: I see that they’re asking for three new space-based telescopes. Related to that, I found it interesting that when I went through my usual news sources this morning, I didn’t see a word about SpaceX successfully launching another crew headed for the ISS last night. I believe this was the 24th Falcon 9 launch this year. How quickly things become routine.Report

  3. Chip Daniels says:

    THTh2:
    This fact is a good companion to Dennis’ essay, for anyone wondering how to reach the Trumpists. There is a shockingly high percentage of people who, when faced with a choice between a lifesaving vaccine and their political cult, choose the cult even to the point of death.

    The idea that they will change their minds when presented with a calm reasoned set of facts needs to be retired.Report