An Introduction to String Theory

Slide 36 of 37
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The bad news about string theory is that the strings are just too small: it is essentially certain that we will never be able to observe them directly. For that reason, the hope of most string theorists is that we will one day understand the theory so well that we will be able to make indirect predictions. But that day lies a long way in the future, and there are several very different opinions on just what sort of predictions we will be able to make.

In the meantime, string theorists hope that other upcoming observations of fundamentally new physics will give hints about what form the theory should take. Particle coliders like the "Large Hadron Collider" (soon to come online at CERN in Switzerland) will hunt for evidence of supersymmetry, and will look for signs of extra dimensions in case they are large enough for their effects to be visible. And at the other extreme, new observations of the Cosmic Microwave Background may contain information about what happened in the extraordinarily high energies of the Big Bang, which may have been the only "particle accelerator" strong enough to probe string theory directly. It is unlikely that any of this will provide final answers for string theory, but we're eager for any experimental input we can get.

Without that input, the ultimate test (and value) of string theory may simply be its ability to make sense of the complicated and at times conflicting web of existing physical theories. String theory's premise (fundamental objects being 1-dimensional instead of 0-dimensional) is so simple that there isn't much room for "hand tuning" of the theory to fit already-known facts. Thus, when string theory "postdicts" gravity (because it always contains a particle that must act like a graviton), that really may be a meaningful result. But by and large, string theorists understand that some sort of testable experimental predictions are necessary in the long run for the theory to be fully accepted as good science.