About dark matter... by MLR

I wanted to bitch a little bit, to an audience of people who aren't at all colleagues of mine, in the sense that they aren't people in any way involved in my field of study.

So, if you know anything at all about modern astronomy and/or astrophysics (to be clear, the former is the observational and experimental side, the latter theoretical), you've at least heard the terms 'dark matter' and 'dark energy'. They're two of the biggest cornerstones of cosmology right now, and craploads of money are spent annually in an attempt to determine better what they are. They're also often heralded as being two of the greatest discoveries in the field, like, ever.

There's just one problem: they haven't been discovered. Neither of them. And if they haven't been discovered, they can't be two of the greatest discoveries ever.

Let me back up a bit. I'm going to focus on dark matter here, since dark energy is even more of a mystery right now and hence hasn't created that many strong opinions about what it is.

So, 'dark matter', if you're unaware, is the term given to what is apparently missing mass in the universe; matter that doesn't shine and hence is not visible in our telescopes/other photon detectors. The idea came from a variety of different places: spiral galaxies rotate faster than we'd expect under the laws of gravity as they are currently known, galaxies in galaxy clusters move too fast and should be flying out of clusters all the time, and so on and so forth. So when things don't behave like they should under normal gravity, you have two options, really: either there's missing matter that's holding it all together despite the large speeds, or you have gravity wrong. The former is given the name 'dark matter', and the latter is given the name 'Modified Newtonian Dynamics' (MOND; sometimes called Milgromian Dynamics after the Israeli fellow who came up with the idea). Right now, for whatever reason, dark matter is the favored choice.

But here's the thing; it's not a perfect choice. It's actually just a placeholder, an idea injected into the body of knowledge to fix the known problems. Cold Dark Matter, the thing every physicist loves to use in their simulations, is this highly convenient, perfectly non-interacting, heavy kind of matter, so that all it does is have mass and therefore affect things gravitationally (this makes it very easy to simulate; much easier than normal matter--baryons--which constantly is interacting with itself, losing energy, gaining energy, turning into stars and planets and black holes, etc.), and it tends to produce pretty good facsimiles of what we know the distribution of galaxies is in the universe. It also does a good job reproducing things like galaxy clusters, and it fixes some problems, like why stars and galaxies apparently collapse into what they are so quickly after the Big Bang (when everything was just a haze of protons and electrons and photons).

Unfortunately, though, it does a rather crap job at reproducing individual galaxies and their satellite systems. Dark matter simulations right now, for example, WAY overpredict the number of satellites (companions that orbit it) any given galaxy is supposed to have, on every mass scale (too many little ones, too many intermediate ones, too many big ones). It also has a terribly hard time reproducing the motions of known satellites around the Milky Way (dark matter halos like to make things merge into other things super fast via something called dynamical friction; simulations of Milky Way satellites usually just turn off dynamical friction to bypass this issue). It also has nothing to say about one of the most precisely-known empirical relationships in galactic astronomy, the Tully-Fisher relation (which is so universal as to be essentially a physical law; we just don't know the physics underlying it). These are acknowledged problems, and generally the people doing the simulations try to fix them by invoking normal matter physics, things like energy feedback into the system by supernovae going off, active nuclei of galaxies shooting crap off into space, and so on and so forth. And you can certainly fix the problems by messing around with these things, but right now we don't have a solid grasp of the physics involved in such processes, in which case what the simulation folks are really doing is tweaking the nobs and pulling the levers necessary to fine-tune the result they want (which is the observed properties of galaxies; reality). But this process has no predictive power at all, and therefore sucks gleet from a dead hawk's intestines as a scientific theory.

There's also the fact that people have been doing extensive searches for the 'dark matter' particle for decades now, checking every variation of every theory they can possibly branch off of the Standard Model of particle physics to account for it, and every single experiment so far has ended in a null result (except for one, called DAMA/LIBRA, which claims to have found a signal, but it conflicts with another experiment that found no such thing so no one believes them).

To me, these things are problematic, and definitely call for more investigation into alternative theories. You know, because we're scientists, and we should be considering the evidence at hand.

But there's a super strong backlash to anyone who even brings up alternative theories (e.g. MOND). The MOND idea rarely gets funding, and apparently if you bring it up at conferences you get personally attacked, or laughed at, or generally ignored. Refereed journal article editors might ask you to adjust your paper to essentially state that your conclusions are invalid so as to avoid contradicting a more well-respected scientist (this happened to a colleague of mine). 'Dark matter', despite that it is still and has always been a placeholder idea for something nobody on Earth understands right now, has become an article of faith amongst scientists.

I'm pretty new to this whole 'science' thing, myself. I've only been seriously involved for about 4 years now. But I find the treatment of this issue incredibly irritating and incredibly disheartening. Now, I'm generalizing a bit; there are still loads of people who are fighting the good fight (otherwise, I wouldn't even know of these problems with the dark matter theory, as they would have been buried). But here's the thing: astronomy, to me, is not important enough to daily life to be placing powerful personal stakes in any given idea within it. We study astronomy because we're interested in it. That's all. It's not going to cure cancer, it's not going to solve world hunger, it's not going to create world peace. I study galaxies whose light takes 30 million years to reach us; my results are only going to affect the world from a purely philosophical standpoint (it's nice to know our place in the universe, I guess). And because of that, if someone finds out that I came to the wrong conclusion, and they can argue that point to me in a way that I find convincing, I'll change my stupid opinion and move on with my life knowing that I've learned something new. What I won't do is buckle down and start calling that person names.

And yet that's the kind of behavior we're seeing with regard to this whole 'dark matter' thing. If it's dark matter or if it's a modification of gravity at low accelerations due to quantum effects, what's the difference? These are scales that occur literally at the edges of galaxies and in the empty spaces in between them. Humanity won't be getting to either of those places for centuries, millenia, maybe never. So if you're curious about the universe, just try to find out which one it is! There are ways to test both theories, and right now one of them happens to be floundering a bit. That's because we're doing science. Sometimes you're wrong. It happens. Get over it.

So why am I telling this to you fine folks who probably don't care one way or the other? I guess just to let you in on a little secret regarding how science is actually done, and to remind you that it's a human enterprise in the end and is therefore subject to the same kind of bullshit as everything else. But let me end with this: some day, this debate will be resolved, and the best theory will come out on top, because it is science, after all. It's just going to take more time than necessary due to primate chest-puffing and posturing slowing it down, and that's what I find annoying. I wonder if humankind had descended more closely from, say, social dinosaurs, if we would have made much faster progress?

About dark matter...


16 July 2014 at 20:55:35 MDT

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    I found this a delightful thing to pop up in my inbox, actually. I'm no astronomer but I still love to learn about it all, so a couple years ago I took it upon myself to read all available knowledge on this subject.

    But what made this a treat is to see another side of it, as you are absolutely right in that it seems like no-one even wants to acknowledge any other ideas. Back then when I read about the subject, it seemed off to me that it was being posed one way so resolutely.

    Something about the information always seemed too convenient, if that makes sense. So it's quite interesting to hear your thoughts here. I've heard that scientists are just as bad as anyone else when it comes to chest-puffing, perhaps a little worse due to other reasons.

    It's kind of sad though, isn't it? Astronomy is supposed to be a humbling thing. Not something you use to feel like Master of the Universe.

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      We could really use an Edit button for comments. I'd like to revise what I said to "read most available knowledge I could get my hands on within the time I had to spend on it"

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      It is very convenient... by design. Unless you start looking deeply into it, at which point it starts to become intractable. And honestly, MOND is overly convenient right now too: the theory started in much the same way as dark matter, which was a guy just artificially injecting a term into the gravity equation that takes over at a certain scale. No reason why that should happen, but let's see if that works out. And what was really interesting was that it did work, exceptionally well. But I guess because all the money is in particle physics these days, we're just going to pretend like this is a particle physics problem and only attack it from that angle.
      And shit, particle physics is doing way the hell better than gravity right now, from a theoretical standpoint. It's not often you come up with a theory, run an experiment, and then determine that the results of the experiment fall perfectly in line with your original theory (this happened with the Higgs Boson). General Relativity, though, is still totally disconnected from quantum mechanics, meaning it needs at least one serious revision to fall in line with the rest of physics. So if it were me I'd be focusing my energy there from here on out. And either way, if you expand on the Standard Model or if you expand on Einstein, you're getting a Nobel Prize. There should be people swarming all over this from both angles.

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        You have a point there. For the record, the Higgs Boson coming out like it did blew me away. I'd imagine that given enough time, other means will gain popularity as well. There's probably plenty of people raring to tread new ground, that sort of thing is what really impresses people.

        Maybe you just need new colleagues? Haha

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          My immediate colleagues are fine. They're the ones turning me into a heretic and a trouble-maker. :-)

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            Oh! Oh alright haha, in that case then I think you have some excellent company. Anyone that encourages others to be more curious.

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    I had no idea science could get like that. Especially not astronomy. :c What really sucks is that people want you to essentially lie about your readings, like what happened to your colleague, which is a serious setback for science for silly reasons.

    Like you said though, science will march on! Just at a slightly held-back pace. :P

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      We need more Vulcans, clearly.

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    So the primate chest-puffing and posturing is in the scientific world as well? I figured the higher education would get rid of some of that but I guess it ain't no different from blue collar or politics or anything else. This does explain a lot about the dark matter thing and why it's championed so much but is still such an unknown. That always confused me.

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      You know... it does get rid of some of it, but it also replaces some of it with giant egos, so that the chest-puffing takes on a slightly different morphology. But like I said, this isn't the case for everyone, and if a person is fair-minded enough about a topic, it will be recognized and due respect will usually be given (even if it takes a while). But it just reminds you that wherever people are involved, there will be bullshit. Even the smartest of us are still human.

      I guess if you wanted to, you could think of it as endearing. Maybe that's the healthier route to take, since it's a problem that's not going away anytime soon. At least in scientific enterprises, it doesn't cause any (or at least, not frequent) fatalities (like it often does in, say, politics).

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    First off, I want to thank you for mentioning the MOND theory. I had not heard about any alternatives to dark matter theories.

    There are some scientist that have even worse egos than politicians. I have one friend, a professor at the local university, that has the mentality that he knows better than you cause he has the paper on his wall to prove it. While I agree with this when the subject is within his field, he even has this mentality when the topic at hand isn't and he clearly doesn't know more than me.

    Research is were some of the worst happens. Some lie and twist their data to support their hypothesis since it means that they'll keep receiving funding or that they can sensationalize their findings. The latter being the most irritating since it can cause public to lash out at something innocuous.

    We can also be stubborn and thus resistant to ideas that say that what we thought we knew was wrong. I find it interesting that a job that curiosity should be a desired trait has so many people that get so defensive about questioning.

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      Very few people have heard of MOND, even amongst astronomers. So yeah, I try to spread the word about it to people who are interested, since it's actually a remarkably successful theory in a lot of ways (just as many ways, if not more ways, as dark matter).

      The magician James Randi once said that he thought there was probably some kind of special power that piece of paper (the PhD diploma) has, where as soon as it first touches the owner's hand, they forever lose the ability to say the words 'I don't know'. I'm sure that's true of some people. I'm going to make it a point not to be true of me in a couple years when I get mine.

      (PS: I should also say, thanks for all the faves.)

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    Gravity, still the odd man out in both theory and current knowledge. I find it weird after all these centuries, that little has been done despite a few attempts at extending it from Einstein's relativistic approach.

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      Well... a lot has been done, but not much of it so far has been of consequence, from what I understand. Einstein's equations have a lot of playroom, actually; he and his colleagues basically found the simplest solution, which is the one that reduces down to Newton's laws at low velocity and low curvature; the equations contain various things like the Riemann Curvature Tensor, some of which have over 700 different terms in them when expanded out. So for obvious reasons, in the 1910s-1930s when these guys were working on this problem, they wanted a way to simplify that down, and they found out that if you make some approximations and evoke some physics (like, say, that spacetime is Euclidean on small scales) it gives you a whole bunch of symmetry that can whittle that 700 down to more like 20 or 30. And it turns out those 20 or 30 work remarkably well, but those other 670 or so still exist and can still be played with if you want to (and now that we have computers, we can make those calculations). So now we've got all these so-called f(R) theories floating around, all of which are valid solutions to Einstein's equations, but most of which probably have little bearing on reality.

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    I imagine that if we descended from social dinosaurs, our chest-puffing and posturing would be different but just as ubiquitous; however, an intricate dance off for dominance and intimidatingly ornate display of feathers, scales, and other structures is quite entertaining to think about in the context of academia.

    Dark Matter has a very romantic air to it. Assuming it's real, it's mysterious and enigmatic, which is what I enjoy so much about it. The moment we figure out how it works or at least know a good bit more about it other than "hypothetical, non-luminous matter with a gravitational presence", it won't be nearly as interesting (to me at least). Anti-matter was like that for me. It was a bizarre other-thing that was mystically rare and avoided all but the most studious observation by annihilating itself almost immediately upon entering existence like nothing else did. Then you learn about quantum numbers, quarks, so forth and the mystique shatters over your oft-doodled notebook and the drab faux-wood finish of the particle board desk in one of the physics hall auditoriums.

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      Maybe arguments would get solved more quickly with dancing and feather displays... Or we could do what common wisdom has it that bonobos do and just start making out.

      I do get where you're coming from, but I also think there's always mystery to be found. Physicists like to claim they understand the universe, but what they really understand is how it works. Or, rather, they've built a set of mathematical tools that can be applied to make predictions about the universe that now often come true. But it's all still very abstract; 'anti-matter' is just a name given to the negative solution of the Dirac Equation. As to what it actually is... well, we don't even know what 'matter' actually is. We know it's a thing and we know it behaves in a certain way, but there's no real deeper understanding than that.

      But to me, knowing what I know, I don't find 'dark matter' all that romantic, at least not yet. Because again, it's just a placeholder right now. The romantic thing is not 'what is dark matter', it's 'why don't galaxies behave like the things that compose them'. And I personally tend to find the journey to answer such questions a lot of fun, even if, yes, the end result is to remove a little more mystery from the world. But it's more exciting than sitting around feeling awed by how little you understand. While that occasionally has its merits, you can only do so much of it before it gets boring.

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        A sexual congress, hm? Ripe for a filibuster joke.

        Mystery is fun and all, but I do agree that I'd rather be finding answers and explanations. After all, there's never yet been a short of mysteries uncovered by (purportedly) solving one. A little mystery is good for the imagination, I feel. Too much mystery lends itself to people thinking that Tiger's Eye can help you align your chakras of courage and assertive ferocity. (I've likely misrepresented Crystal Magic, but I'm not going to bother to correct myself)

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          I couldn't tell you thing one about crystal magic, but I know what you mean. Without at least some constraints (knowledge), you can explain anything with anything. The only limit there is imagination, which, granted, can be pretty limited on its own.