In the Dark

In the 18th century, physicists were trying to understand what happened when things burned. It was theorized that combustible substances such as wood and coal contained something called phlogiston, which was released during burning. This theory seemed to explain some of the results of experiments, but of course it was completely wrong.

In what may turn out to be a similar flight of fancy, physicists today are enamored of the theory of dark matter. Like phlogiston, dark matter itself has never been observed; it’s proposed as a way to explain certain things that have been observed.

The problem that the dark matter theory attempts to address is quite real. The problem is that the outer parts of galaxies are spinning too rapidly. It’s possible to measure the spin of some galaxies — those that are tilted so that we observe them somewhat edge-on. This is possible because the light on one edge of the galaxy (the edge that’s spinning toward us) will be blue-shifted, while the opposite edge is red-shifted because it’s receding from us. This is basic physics. I couldn’t do the math, but I understand the concept.

We can also estimate the mass of a galaxy. This is done by estimating the number of stars in it (based on its brightness) and multiplying that estimate by the average mass of a star. Mass causes gravitational attraction, and gravity causes stuff to orbit the center of mass, in exactly the way that the Earth orbits the sun. The speed of the orbiting body depends on both the diameter of the orbit and the amount of mass around which the object is orbiting. Again, I couldn’t do the math, but this is basic stuff.

When the rate of spin of the outer parts of nearby spiral galaxies is calculated, it quickly becomes apparent that there’s not nearly enough mass to explain the speed of rotation. This means one of two things: Either there’s a bunch of mass that we don’t see, or we don’t understand how gravity works at galactic distances. The idea that the law of gravity needs to be revised is not popular, though some theorists are working on it. The general consensus is that these galaxies are embedded in a halo of dark matter — stuff we can’t see, but that adds significantly to the mass of the galaxy.

One idea, which seems not to be panning out, is that galaxies are studded with “brown dwarfs.” A brown dwarf is a a lot bigger than Jupiter, but a lot smaller than the sun. It’s small enough that nuclear fusion has failed to ignite; thus it doesn’t put out much in the way of visible light. It’s brown, and it’s a dwarf star. But while there are certainly brown dwarfs floating around, a survey of our own galactic neighborhood suggests that there aren’t nearly enough of them to account for the rapid spin of spiral galaxies like our own.

A more popular notion is that the dark matter is a cloud of non-baryonic particles. Protons, neutrons, and electronics are baryonic; they’re the stuff we’re made of. We can’t see this non-baryonic matter, so the theory goes, because it neither absorbs nor emits light. However, it has mass, so it generates a gravitational field. (Don’t ask me whether “generates a gravitational field” is how physicists would talk about it. I don’t know.)

I have no problem with the idea that the universe is filled with particles that we know nothing about. But I have yet to read an explanation of how this massive dark matter is supposed to be behaving.

I also have a problem with how confident some authorities are that such a mysterious thing exists. In poking around on the Web, I quickly found a site (detailing the findings of the Wilkinson Microwave Anisotropy Probe) that asserts, baldly, this: “The WMAP science team has … completed a census of the universe and finds that dark matter (matter not made up of atoms) is 24.0%.” Well, imagine that. They can’t see it; they don’t know what its properties might be; but they’ve done a census. Shee-it.

The idea that they’re treating as gospel is this: The clouds of dark matter are supposed to produce gravitational fields within which the baryonic matter (clouds of hydrogen, to start with) congregates, condenses into stars, and so forth. But if this cloud is imagined as consisting of zillions of tiny particles (perhaps not much larger than a proton), it doesn’t seem, to my muddled way of thinking, to be behaving in a sensible way. Some of these particles will be moving rather rapidly; some will be moving more slowly. That seems indisputable. Those that are moving too rapidly will have enough velocity to escape from the cloud. They’ll be gone. So there’s a maximum velocity that the dark matter particles (they’re called WIMPS — weakly interacting massive particles) can have, and some will be dawdling along more slowly than that.

Baryonic matter forms clumps under the influence of gravity. We call these clumps stars. So why hasn’t the dark matter formed clumps? Any variation in density of a dark matter cloud, no matter how slight, will gradually attract more and more of the slower-moving WIMPS. After a few billion years you won’t have a diffuse cloud anymore; you’ll have clots of the stuff. These clots will be drifting around within our galaxy. They will be invisible, but they will cause gravitational perturbations, because some of them will be rather massive.

No such perturbations are observed.

Not only that, but a massive object like a star will naturally acquire its own halo of dark matter. Slower-moving WIMPS that drift in close to our own sun won’t have enough velocity to escape. And we know for certain that this hasn’t happened. If there was any such halo around the sun, Newton’s law of gravitation would never have been discovered, because the planets in our own solar system would be orbiting more quickly than they are.

Thus the theory requires that dark matter (a) remain in a stable galaxy-sized cloud rather than drifting off into the cosmos but also (b) not form clumps. We haven’t the least idea what the characteristics of WIMPS might be, so we can’t actually rule that out, but it does seem rather implausible, doesn’t it?

When rain falls on a large flat paved area, you’ll soon see shallow pools of water. The pavement is never perfectly flat. I find myself wondering why physicists think the universe itself (spacetime) is perfectly flat except where there’s mass. One way of looking at gravitation (this is Einstein stuff) is that a massive object distorts spacetime. The sun, for instance, creates the three-dimensional equivalent of a large and very deep dimple in the fabric of spacetime. That’s what gravity is.

But why should we assume that mass is the only thing that can warp spacetime in this way? The supposed galactic halo might not be a cloud of massive particles at all; it might simply be a slightly lower place in spacetime, a sort of shallow 3D puddle of slightly enhanced gravity. The cloud of primordial hydrogen would naturally coagulate in such places, and that would create galaxies. It’s known that there are slight anisotropies (uneven places) in the hot, dense plasma that erupted in the Big Bang. Why shouldn’t some gravitational anisotropies still be hanging around?

Of course there’s no physics theory that would explain such a gravitational puddle — but there’s no theory that explains what dark matter is, either. We can be fairly sure it’s not phlogiston, but beyond that, who knows?


The Fact of Coherence

Einstein once said (I think it was Einstein, anyway), “The most incomprehensible thing about the universe is that it is comprehensible.” The universe we live in is really a very strange place, and the deeper physicists dig, the more strange it appears. And yet, everywhere we look within the strangeness, we find surprising patterns of regularity. That’s what Einstein was talking about.

I have a sort of half-formed idea about this. I present it not as a statement of fact, merely as a mild observation. Make of it what you will.

I got to thinking about this last month while trying to work through a personal dilemma (the details aren’t important) by consulting the Tarot and the I Ching. Now, any scientist who knows that the sun comes up in the East will assure you that the results you get by shuffling a deck of cards and then laying out ten or twelve of them are entirely random. Likewise casting the I Ching — toss three coins six times, and the results will be entirely random.

And yet, these oracle devices seem to work pretty well for me. As a rock-ribbed atheist, I don’t attribute the apparently meaningful outcomes to the guidance of invisible spirit entities. That would be very silly. But when you ask the I Ching whether to concentrate on music or fiction writing and you get a text that refers specifically to music … what is an atheist to think about this?

As we all know, the Second Law of Thermodynamics assures us that over time, in any closed system, entropy (that is, randomness) increases. Order decreases. And yet, everywhere we look in the universe, we see order.

A cosmology book I was reading a couple of months ago pointed out that at the time of the Big Bang, the distribution of particles in the universe was in a state of very high entropy. The distribution of particles was pretty much the same everywhere. It was smooth. We know this, because when we look at the cosmic background radiation we see that it’s pretty much the same in every direction. However, at the time of the Big Bang the force of gravity was in a state of extremely low entropy. That is, there was a huge amount of potential energy in the form of gravity, which began to turn into actual energy as bits of the early universe started clumping together. If gravity had already been in a state of high entropy, stars and galaxies would never have formed.

As an aside, this book explained that life on Earth doesn’t exist by virtue of the energy the sun shines down upon us, in spite of what you’re taught in biology class. In fact, the amount of energy on the surface of the Earth is pretty much constant. At night, just as much energy is radiated away into space as was absorbed during the day. What the sun actually sheds in our direction is low entropy.

The low entropy of gravitation was not, of course, the only way in which the early universe exhibited an extremely regular structure. All of the electrons in the universe (and there are quite a lot of them) are identical, as far as we’re able to determine experimentally. Why are they all the same? There’s no explanation for that; they just are, that’s all. Likewise, the speed of light is a constant. (In fact, there are more than 20 numerical constants — pure numbers — that physicists need in order to describe how the universe works. Physicists have no explanation at all for how those numbers came to have the values that they have.)

The charge of an electron exactly balances the opposite charge of a proton; it isn’t 5/8 of the value of a proton’s charge, or 1.374906 times the value of a proton’s charge. The precise balance of charges between the proton and the electron is about as anti-entropic a phenomenon as you could hope to find. Also the way electrons form shells around atomic nuclei, which is what allows molecules to form and remain stable. Nothing random going on among the electron shells, in spite of the incessant froth of quantum indeterminacy.

Everywhere we look in the universe, we see structure. Galaxies, stars, and planets. The organization of subatomic particles into atoms and molecules. And as we look around at the normal state of affairs on our lovely planet, we see trees, rocks, clouds, hair follicles — structure everywhere!

It may be objected that the existences of trees and hair follicles is accounted for by evolution. And that’s certainly true. Evolution is pretty much a logical necessity, once you have any type of cellular life that is kept organized by large molecules and can reproduce itself. But that fact doesn’t falsify what I’m suggesting; it’s just another example of it. Everywhere that structure can appear, structure appears. Look at a geode sometime. No evolution is involved in the production of geodes — the forces that produce geodes are of an entirely different character from the forces of evolution. Likewise the force of gravity. Gravity has nothing whatever to do with the ability of atoms to gather into large molecules endowed with unique properties. The causes of the structure are different in each case, but in each case, structure arises.

So when I cast the I Ching and get a meaningful answer, the reason it happens isn’t gravity, or evolution, or quantum mechanics. All I can say for certain is that the result of my action has a structure. It appears not to be governed by the Second Law of Thermodynamics, which would dictate that the fall of the coins be entirely random; instead, something different seems to be happening. It’s a pretty darn weak structure, frankly, but it appears to me that the universe is, here as in so many other ways, organizing itself into a regular structure.

Anyway, the Second Law is highly suspect. What it actually says is that entropy increases in a closed system. But we don’t actually know that the universe is a closed system. We don’t know whether the universe is finite (which would make it a closed system) or infinite. What we are fairly sure of is that the structure of subatomic physics — that is, the way electrons and quarks move and interact — has not increased in entropy during the past 3 billion years.

This is not an argument for the existence of “God.” We have no evidence at all that the universe was created. It just is. Nor is it an argument in favor of progress, morality, or anything else, though I’m sure some woolly-minded people would like to think of it that way. I’m just ruminating.