I don’t believe in dark matter.
Now, generally I take a dim view of refusal to accept well-established scientific propositions: heliocentrism, or evolution. But I’m a dark matter nonbeliever.
For many decades we’ve had the “standard model” of physics, standing up quite well to the crucial test of falsification through experiment and observation. This standard model encompasses Einsteinian relativity (modifying Newtonian physics), quantum mechanics, the Big Bang, four fundamental forces, and a zoo of subatomic particles. Physicists have so far been unable to unify it all into a “theory of everything,” reconciling gravity with the other three forces; but hey, Rome wasn’t built in a day.
Nevertheless I, in my naïve way, have long felt something’s wrong at the heart of this standard model.
Isaac Asimov said important moments in science don’t come with someone shouting “Eureka!” but saying, “That’s funny.”
That’s what Jan Oort must have said in 1932, upon noticing that other galaxies, based on calculating gravitational effects, ought to be flying apart, but they’re not. Galaxies are held together by gravity, and gravity’s force is a function of mass. Galaxies didn’t seem to have enough mass – i.e., matter – to account for what we observe.
So, apparently there had to be more matter than we were seeing. This non-visible stuff was named “dark matter,” until we could identify it, which was expected to be soon. Since then, there have been many hypotheses, but none very persuasive.
This is not a small issue. Our calculations indicate that around 84% of the matter in the Universe is dark matter. That’s a lot of stuff to be clueless about.
Meantime there’s another problem: dark energy.
Back in 1929, Edwin Hubble discovered that those little smudges in the night sky were actually other galaxies. The Universe suddenly got a lot bigger. Furthermore, most of those galaxies were flying away from us, and the farther away, the faster. Thus the Universe was not just huge but getting huger. And of course the final shocker was that if you run the film backwards, you end with . . . a Big Bang.
Now, we can readily picture a Big Bang exploding outward, with continued expansion as an after-effect. Though common sense tells us it should be slowing down over time. And so does physics: the gravitational force of all the Universe’s matter should counteract the outward oomph. The question seemed to be whether there’s enough matter to eventually stop the expansion and reverse it, pulling everything back, to end in a “Big Crunch.”
Then came another “That’s funny” moment. This time it was data showing the expansion is not slowing. It’s speeding up.
This made no sense at all, scientists hated it, and tried very hard to make it go away. However, though humanly imperfect, scientists always ultimately accept what evidence shows. So, after much tooth gnashing, it’s now a fact: the Universe’s expansion is accelerating.
What’s causing that? Dark energy. As in the case of dark matter, the “dark” translates to “we don’t know what the f— it is.” And putting dark matter and dark energy together, it’s now about 96% of the Universe we can’t account for.
All this is why I’ve long felt queasy about the standard model. No self-respecting standard model should be flummoxed in such big ways.
But let’s return to dark matter. Again, physics, and the law of gravity, say galaxies should be flying apart unless they have way more matter than we can detect.
But what is this law of gravity, actually? Newton figured it out: objects’ attraction is proportional to their masses and inversely proportional to the square of the distance between them. Simple and clear. But why is it the square of the distance? Aha – we have no clue.
For a long time we had no clue how gravity even worked. How does one object move another without touching? Einstein provided an answer. We’ve all seen those illustrations of the bowling ball in the bed, creating a dip. An object distorts the space around it, affecting how other objects move in that space. The Sun is like a bowling ball distorting the “bed” of our solar system, and that gravitation, balanced by the Earth’s own motion, keeps it in orbit.
I’ve frankly always found this a little glib; more a metaphor than an explanation. However, even if you accept it, why must the effect vary with the square of the distance? Of course, we’ve measured it, and it does. But not because it must; there isn’t (as far as we know) some deeper law of nature that requires that exact relationship, in lieu of some different proportionality.
Now, you can’t argue with nature’s laws, but their operation can vary with circumstances. A glaring example: quantum mechanics. Newtonian physics applicable to the everyday world does not apply when it comes to the extremely small, the subatomic world; entirely different laws apply. So – what if Newtonian gravitation does not apply to the extremely large: the galactic world?
This is not my own cockamamie idea. Some very serious scientists are working on this, as it relates to dark matter. Again, the problem is galaxies not behaving as conventional gravity theory says. But it turns out that you only have to tweak Newton’s law just a little – i.e., gravity just a bit stronger at extreme distances – in order to explain what we see – with no need for added matter. The hypothesis is called Modified Newtonian Dynamics, or MOND.*
Realize that we are talking about exceedingly minute effects. When gravity diminishes with the square of the distance, it becomes evanescently tiny when the distance is light years. Even with the proposed tweak, it’s still tiny. The difference between the two is not great enough to seem weird or implausible. Yet that difference is enough to resolve the dark matter mystery.
This also comports with Occam’s razor. It seems far more parsimonious and reasonable to postulate that square-of-the-distance doesn’t precisely hold at extreme distances than to swallow any of the other dark matter hypotheses generally requiring gigantic agglomerations of exotic particles none of which have ever even been detected. In contrast, MOND requires only a very minor adjustment to the standard model. The difference at extremely large scale is much more modest than the perversities that quantum mechanics gives at extremely small scale.
This is why I now believe there is no dark matter. (As to dark energy – let’s stay tuned.)
A final word. This essay may give superficial comfort to the “science knows nothing” mind-set – 96% of the Universe unknown! Well, forget it. That we have these kinds of problems actually shows how very far we’ve come in understanding the cosmos. Earlier generations couldn’t even have conceived questions like these. Science has progressed fantastically, and will continue to do so, improving our understanding (totally unlike certain other constructs by which humans have tried to understand Creation, which conspicuously lack any methodology for adding knowledge).
* I learned about this in Michael Brooks’s book, 13 Things That Don’t Make Sense.