You know the expression “He couldn’t see the forest for the trees,” of course. I suffered from this recently. I’d submitted three chapters of a novel to my agent, and he came back with three paragraphs that said, essentially, “This is shit.” He was right. Upon reflection, I realized that I’d been focusing so much upon what I wanted the characters to do that I’d failed to notice that they were acting like self-absorbed assholes. My agent’s letter was the slap on the head I needed to see the obvious.
I think string theorists need a good slap on the head, too.
Now and then I like to read (Okay—force myself to read) a popular science book at the “forefront of knowledge”—one of those books written by a “leading physicist” and aimed at the educated and interested layman. I used to gobble such books down the same way I devour Harry Potter novels. I now find them much harder going because on almost every page I notice oversimplifications or misstatements of fact or faulty reasoning. If I review such a book, my own idiosyncratic complaints tend to obscure to my readers just how valuable the book might be for them to read. That is, though my bitch is with 2 percent of what’s on the page, the other 98 percent is probably worthy material.
Recently I finished reading The Fabric of the Cosmos by string theorist Brian Greene. (Alfred A. Knopf, 2004. ISBN 0-375-41288-3) I’m not particularly interested in string theory, but it is out there as one of the best ideas yet to lead to a Theory of Everything. I figured I’d see what was in the book so that, at minimum, I’d be in a better position to justify why I ignore this stuff. To assist me with this column, I enlisted the help of an old friend to balance out my above-mentioned idiosyncrasies.
His name is Jeff Ballast and I’ve known him since kindergarten. Always a good student, he became senior class president, won the lead in the school play two years running, and became a professional musician. He played the trombone, but in his early thirties his “lip blew out,” and his music career was over. Undaunted, he returned to school and is now a physician’s assistant. Jeff is exactly that sort of educated layman that people like Greene hope to reach with their books—the intelligent nonscientist interested in science. Jeff has also read Greene, and last January we attended Greene’s lecture on Fabric together at our alma mater.
This column is not a review of Greene’s book but more of a screed about how string theorists fail to note the obvious. Still, a few words about the book are in order.
As expected, Fabric began to annoy right away. Right there on page x of the preface it says: “But during the last hundred years, discoveries in physics have suggested revisions to our everyday sense of reality that are as dramatic, as mind-bending, as paradigm-shaking as the most imaginative science fiction.” No, they aren’t. On page 486, it says: “That we’ve gotten as far as we have—that we’ve revealed numerous features of space and time vastly beyond common experience—attests to progress unfathomable a century ago.” Nonsense. Much of what is cutting edge today was being “fathomed” a hundred years ago, which Greene would have known if he’d bothered to look.
I deliberately picked two quotes from widely separated parts of the book because the excessive length of this tome is another annoyance. With the index, it runs to 569 pages. Jeff and I agree it should be cut to maybe 300 or so. Perhaps Greene needs an editor to tell him to resist the constant urge to run to the hyperbole jar (see quotes above).
As most Analog readers know by now, quantum mechanics and general relativity (the theory of the very small and the theory of the very large, respectively) are incompatible with each other. All attempts to unify them have fallen short of the goal. Greene is convinced that string theory (or superstring theory) will eventually carry the day and lead to the unification that physicists seek.
How does it do this? Modern physics treats subatomic particles as mathematical points. Electrons, for instance, are indivisible and have no size and no internal structure. But “according to superstring theory, every particle is composed of a tiny filament of energy . . .” (p. 17) You can picture the superstring as a tiny, little rubber band, and its vibrational modes determine what kind of particle it is.
How does this help? With particles of zero size, this leads to mathematical problems equivalent to trying to divide a number by zero—that is, it leads to infinities. Superstrings, which have extent in one dimension, solve that problem. (You might think that simply insisting that elementary particles are small spheres of some size rather than of no size would do the same thing, but that also leads to problems.)
Greene explains how the mathematics of string theory is compatible with what we know empirically about the behavior of elementary particles, quantum mechanics, and gravity. The only hitch is that we have to assume that the universe has ten (or eleven) dimensions; otherwise the theory isn’t mathematically consistent. Given that, we’re essentially home free. On page 352 Greene says, “With the description I’ve given so far, it might seem baffling that any physicist would resist the allure of string theory.”
I quoted Greene earlier saying strings are “filaments of energy.” He also says: “The mass of a particle in string theory is nothing but the energy of its vibrating string. For instance, the explanation string theory offers for why one particle is heavier than another is that the string constituting the heavier particle is vibrating faster and more furiously than the string constituting the lighter particle. Faster and more furious vibration means higher energy, and higher energy translates, via Einstein’s equation, into greater mass. Conversely, the lighter a particle is, the slower and less frenetic is the corresponding string vibration; a massless particle like a photon or a graviton corresponds to a string executing the most placid and gentle vibrational pattern that it possibly can.” (Pg. 354. All italics in the original.)
Whew. How can I resist the allure?
But isn’t a gamma ray photon both high energy and also massless like any other photon? That seems contradictory with the above, and Greene doesn’t clear up this question. I also find it odd that a string is both made up of energy and yet also has vibrational energy that is, presumably, not quite string-like. To me this makes “energy” look even more fundamental than the strings, so shouldn’t he be figuring out precisely what energy is?
If the point of string theory is just to unify QM with GR, maybe the theory can help us do this above the level of what the cosmological fabric really is. But the point of the book is supposed to be that the fabric of the cosmos is made of strings, yet Greene sometimes writes as if the fabric of the cosmos is actually “energy,” and that’s a tricky word to wrap an image around.
All the hand waving in the world won’t help.
Cutting to the chase, my big problem with string theory is that I don’t see the point in starting with an obviously non-physical object and building a theory around it. Subatomic particles, treated as points (and few working physicists think they really are points) and thus not having any extent, can’t be things. But a string isn’t any better. It has length, but no width. So when it’s vibrating, what, pray tell, is this width-free stuff that’s moving?
Why not simply start with an extended three-dimensional object in the first place? For all the reasons put forth by Greene, we obviously do need an extended object. And the idea that the properties of said object derive from the vibrational (or more generally, motional) modes is a good one—particles must be dynamic entities. Since to even obtain mathematical consistency, string theory requires ten (or eleven) dimensions, why not accept this as evidence that string theory is wrong, and go about building our theory around 3-d objects that might fill the bill in our 3-d universe?
The only objection I can see is that once you start talking about 3-d objects in a real universe, you can’t avoid asking what they’re made of. And you’re not going to be able to get away with a flip answer like “energy.”
This leads us inexorably back to the aether, an idea that I’ve discussed previously in both my March 2000 and my February 2001 columns.
Greene deals with the aether a bit himself, mostly in the usual modern-day dismissive way (although he thinks the theorized Higgs field might be akin to it). He believes wrongly, as most physicists do, that the Michelson-Morley experiment failed to find the aether, and that Einstein proved there wasn’t one. But Greene accepts those extra dimensions only because they’re needed to make string theory consistent with itself. He says, “. . . physicists showed that these extra dimensions have the capacity to bridge the gap between string theory’s vibrational patterns and the elementary particles experimenters have discovered.” (pp. 359-360) (My friend Jeff doesn’t have a problem with adding in extra dimensions to a mathematical theory. It did, after all, work for geocentrism whenever an additional epicycle was needed to get the model to match observation.)
I say, instead of invoking extra dimensions, why not accept the obvious truth that there is something rather than nothing, and invoke a three-dimensional mathematically perfect fluid, which is by definition self-consistent? Since string-like forms are useful, we can ask ourselves if such string-like things exist in perfect fluids. The answer is yes—line vortices. Can these line vortices do all the things that strings do, like vibrate? Yes, they can. Can they form solitonic (particle-like) structures? Think smoke rings.
We already know that one vortex will attract another depending on their respective rotational directions—reverse the spin on one, and they’ll repel each other. So we can directly associate vortical properties with particle properties—in this case, charge. We know that fluid dynamics are compatible with electrodynamics since the latter came out of the former. The same holds true for General Relativity.
Even Greene acknowledges (on pages 345, 474, 488, and 490) that strings may indeed be made of “finer stuff” (his claim that they’re made out of energy notwithstanding).
Indeed, how can any physicist resist the allure of aether theory?
A clue can be found on page 486, at least for physicists like Greene. There he says, “. . . serious thought regarding (spacetime’s) microscopic makeup required the twentieth-century discoveries of general relativity and quantum mechanics. . . . That we’ve gotten as far as we have—that we’ve revealed numerous features of space and time vastly beyond common experience—attests to progress unfathomable a century ago.” To them, the aether is an old idea, long discredited, as relevant today as gaslights and horse drawn carriages. It seems never to have crossed his mind that most of the physicists responsible for both QM and GR never dismissed the aether as easily as he and his fellows do.
They knew better.
Maybe it’s just a matter of personal taste, but it seems to me that if the path to the future of physics requires six or seven extra dimensions to get there, maybe we’d better first make sure we didn’t take a wrong turn somewhere.
Even an ordinary educated layman like my friend Jeff understands that.
