At least one great advantage of string theory can be deduced intuitively from the spacetime diagrams alone, so this is a chance for you to think like a string theorist yourself.
Recall from our discussion of particle physics that interactions happen at special points in space and time (where an electron emits a photon, for instance). Now, special points like those are danger signs for a mathematical theory. We always design our theories so that the equations are guaranteed to work for "typical" points (if they could break down just anywhere, we'd pick a different theory), but interaction points are places where two sets of "typical" points have to be "patched together".
If that patching fails, the theory doesn't work. We saw that when we tried to combine quantum field theory with gravity: the interaction points had to be associated with the energy of the particles, and since the energy there can be infinite, patching them together consistently (and without fatal infinities) turned out to be impossible.
So now consider an interaction in string theory. Things already look promising, because no point on this spacetime diagram looks particularly different than any other. But there might be one special point in a string interaction: the moment where one string pinches off into two (or vice versa), so at first that seems like a problem.
But a careful look at the diagram shows that different observers won't agree on which point that is! We see this string pinch off right in the middle of the picture (the grey slice), but a fast-moving observer (our alien friend, for example) would see the pinch somewhere totally different. So we can assure him that his "danger point" is fine, and he can do the same for us.
(This is a lot like a "coordinate singularity" caused by using the wrong variables. Consider the north pole: it's a normal point on earth, but the usual latitude-longitude coordinates are degenerate there.)
The most exciting part about this result is that we found it without any explicit mathematics! Lots of progress in physics happens this way: the math is critical for confirmation and for working out the details, but simple intuitive arguments can tell us not just what to look for in our equations, but what those equations mean.
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Copyright © 2004 by Steuard Jensen.