Can Physicists Prove String Theory?
Even if a precise version of string theory (or M-theory) is formulated, the question then moves from the theoretical to the experimental realm. Right now, the energy levels that scientists can reach in experiments are probably way too small to realistically test string theory, although aspects of the theory can be tested today.
Theory moves forward with directions from experiment, but the last input that string theory had from experiment was the realization that it failed as a theory describing the scattering of particles within particle accelerators.
The realm string theory claims to explain involves distances so tiny that it’s questionable whether scientists will ever achieve a technology able to probe at that length, so it’s possible that string theory is an inherently untestable theory of nature. (Some versions of string theory do make predictions in testable ranges, however, and string theorists hope that these versions of string theory may apply to our universe.)
There are some ways to possibly test string theory, although these are only speculative because right now science doesn’t even have a theory that makes any unique predictions. The best physicists can hope for are some hints, such as the discovery of extra dimensions of certain types, new cosmological predictions about the formation of our universe, or the missing supersymmetric particles, that would give some direction to the theoretical search.