Strings, branes, extra dimensions, and superstring-m theory.
Who edited this? I can’t believe a particle physicist looked at it, or looked at more than just a slice or two of it. Lewis writes like a reporter: reasonably clearly, and with a charming breathless disregard for the facts.
The preface announces that this may soon be the most important theory of science…ever. Even back in June 2003 it was no secret that superstring theory was running into serious problems—such as not being able to predict anything. But set that aside and plow on. He brings in the “space particle” interpretation of strings to support a “continuous creation of space” and then brings in “an interpretation of a feature of SS-M theory;” namely the holographic principle “which seems to imply and allow a concept generally considered to be outside the realm of science. It is the concept of a human afterlife.”
That’s just the preface.
Next he addresses the origin of our universe in a breathless set of pagelets describing the time intervals starting with the initial nugget (which encoded our “universe to be”, never mind the Darwinian selection mentioned on the next page). Only 3 of the 10 space dimensions succeed in uncoiling.
Along the way he interjects descriptions of what he means by force and motion, space-time, matter-energy, and symmetry. I’d like to applaud him for trying to explain symmetry to the layman, except that he gets a bit hung up on jargon and forgets to include translational symmetry. (Translational symmetry is like driving in the Great Plains. Drive a hundred miles and the landscape looks exactly the same as it did before—nothing seems to change.) Then he proceeds to screw up what he did talk about when he addresses symmetry breaking. Water, inspected at the molecular level as he wants us to, isn’t really very symmetric at all. To understand what he’s talking about you have to think of yourself sunk in the middle of the ocean—water all around you. Move, turn—it always looks the same (just so you stay far away from the boundaries—pretend they aren’t there). But when the water starts to freeze a solid object appears; and now you can move nearer or farther from it, and look at it from different angles, and the view isn’t always the same. Some symmetry is now lost, or “broken.” “Building symmetries” is also possible, along similar lines.
The reason this sort of thing is important is that the equations that describe behavior of matter change in subtle and important ways when there is no longer one or another symmetry.
During the section on the inflation of the universe, he mentions quark formation, saying that up and down quarks appear and create protons and neutrons. Except, of course, that you have to generate anti-quarks as well, which generate antimatter, which annihilate with ordinary matter, and only an asymmetry in the weak interaction leaves us with any leftover matter at all. No mention of anti-quarks appears here (or anti-electrons in the next section)—a stunning omission.
In Chapter 11 when he yammers about “a new energy source?” he asks ”is it possible that (electron’s) mass could be converted directly into energy?” The answer is no, and if he understood the symmetries he wrote of earlier he’d know that. (He uses a picture that shows why, but I guess he didn’t understand it.) Then he calculates the energy equivalent of the electron—and gets .54 kilowatt hours! Of course this is wrong by a factor of more than 20 billion billion. I guess he was asleep during the lectures on measurement and units. I find it rather creepy that he professes to be able to explain arcana of M-theory and yet doesn’t know that cm/sec isn’t the same as m/sec. It comes as no great surprise that he completely omits any mention of the unification of electromagnetism and the weak force in his section on the standard model.
He starts out reasonably clearly describing the history of quantum mechanics, and then bollixes the section about Einstein’s contribution. On the whole that section is worthwhile, though: clear expositions of this are rare.
When he talks about omega, the expansion of the universe, and the microwave background he leaves the reader about as wise as before—maybe a little worse if the reader actually thinks that light can “cool.” If you’re going to talk about “curvature” of space, you need to open with a few examples; explaining what motion looks like in 2-d curved spaces like a sphere’s surface and handwaving your way to 3-d.
The missing dark energy and dark matter problems come up. It’s been long known that galaxies act like there’s more gravitating matter in them than meets the eye. Recent work untangling the “Einstein lensing” (light bends in gravity, so you can get extra images of remote objects) of distant galaxies shows that the intervening galaxies that cause the lensing have a distribution of gravitating matter that doesn’t quite match the visible part. Theoretical calculations of the universe’s overall curvature parameter (omega) suggest that the visible matter is only 4% of what’s needed to get omega=1. Even with estimates for “dark matter” this still only comes to less than a third. (They call the missing part the “dark energy.”) You’d think this was time to give the theory the old hairy eyeball, and that’s part of the appeal of string theory.
I’ll admit that I’m not an expert on string theory. The learning curve is pretty fierce, and the math is pretty hairy. The model is appealingly simple, and work that’s been done hints at interesting links tying together various physics and astrophysics mysteries in addition to putting gravity and quantum mechanics together in a natural way. You just have to ignore the fact that nobody’s been able to use it to predict anything yet because there are an infinite number of resulting models of the universes and some fundamental problems with getting the parameters right.
The fundamental model of string theory is fairly simple. All particles are vibrations in a space of 11 (or 10, or 23) dimensions. Eh? You only know of 3? (Don’t forget time!) Well, you wouldn’t see a dimension if it were coiled up on itself in a minute loop—unless there was something echoing around in that tiny loop like the sound in an organ pipe. You still wouldn’t see it directly (too tiny) but you could tell when an energetic one went by from the kicks it gave other things in the vicinity—which is how you spot the elementary particles. With a few simple rules about interpretation (faster vibration means more energetic means more massive) and about the interaction of these strings you can come up with a theory of particle physics and incorporate gravity naturally. The loops of tiny dimensions and vibrating strings in them put natural limits to the unpleasant infinities that show up when you try to describe gravity in quantum mechanics equations.
Some glitches arise: there should be a whole zoo of very heavy elementary particles, unless they all decayed away long ago. The theory demands some dramatic cancellations between positive and negative energies to give the small masses of the known particles: unbelievably large numbers differing only by minute amounts. (Truth to tell, quantum electrodynamics in the standard model has its own issues with things like that; but they’ve found some ways to justify and systematize them with “renormalization groups.” Don’t ask. Physicists do things that make mathematicians wince. They work, though.)
”Supersymmetry” (an elementary particle symmetry between particles with two different classes of spin) arises naturally out of string theory. This is regarded as a virtue, for some reason. Supersymmetry theories predict that every particle known so far (electron, up quark, Z-boson, etc) has an analogous particle of the opposite spin class. This makes a lot of calculations simple and the models beautiful, but we’ve never found one of these supersymmetric particles. As far as this experimentalist can tell the theorists can always tweak their model this way or that to predict that the lowest mass “super particle” was just outside the reach of the last experiment. Of course there’s all that dark matter that we don’t understand; maybe that’s stable supersymmetric particles. Or maybe not; I can’t seem to lay my hands on any to test it.
Chapter 8, on “Curled-up Shapes and Extra Dimensions,” is not terribly clear. It may seem so to a layman, but I found a lot of the theory described to be unmotivated and arbitrary. Which I suppose is natural when you don’t know the theory very well. But I’m not going to take Lewis’ descriptions as accurate given his track record, and neither should you. The chapter on “Building Credibility” doesn’t. In “The Search for Proof:’ finding the predicted supersymmetric particles would bolster all supersymmetry theories, not just string theory; neutrino interactions are rare but still happen often enough that we build detectors and find them; etc. If we had some ham we could have some ham-and-eggs if we had some eggs.
I will pass over the section on the holographic principle and life after death in silence.
It was kind of fun to see some old familiar names like the Icarus neutrino detector. I worked a little on that long ago—it is a liquid argon detector under the Gran Sasso mountain; one of Carlo Rubbia’s ideas.
In summary: the author doesn’t know what he’s writing about. Parts of the book are clear and accurate, and parts of it are clear and wrong. And for some parts I can’t tell one way or the other.
One interesting site critiquing string theory is Not Even Wrong
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