The basic premise of string theory is remarkably simple: rather than QFT, where there are many different types of particles and interactions, string theory describes just one type of string, and its only interaction is the ability for a loop to pinch into two loops (or the reverse). Amazingly, that simple premise (and the steps needed to make it self-consistent in the context of quantum mechanics and special relativity) automatically gives a quantum mechanical description of gravity, and has the potential to describe all of the other forces and all of the particles in nature as well.
The pictures here are once again snapshots in time at the left and the corresponding spacetime diagram at the right (with slices showing where each "snapshot" was taken). It is easy to see that if the "tube diameter" gets very small, this would look just like the Feynman diagrams for particles that we saw earlier.
In fact, that illustrates an important aspect of string theory: the size of the string loops is small enough that we have never been able to tell the difference between strings and particles in our experiments so far. (This is only vaguely related to the "tightrope picture" of small extra dimensions that we discussed early in the talk. We will soon discuss how those extra dimensions actually appear here.)
Even a qualitative picture like this can lead to important conclusions...
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Copyright © 2004 by Steuard Jensen.