Many young physicists feel that string theory, as the primary theory of quantum gravity, is the best (or only) avenue for making a significant contribution to our understanding of this topic. Over the last two decades, high-energy theoretical physics (especially in the United States) has become dominated by string theorists. In the high-stakes world of “publish or perish” academia, this is a major success.
Why do so many physicists turn toward this field when it offers no experimental evidence? Some of the brightest theoretical physicists of either the 20th or the 21st centuries — Edward Witten, John Henry Schwarz, Leonard Susskind, and others — continually return to the same common reasons in support of their interest:
If string theory were wrong, it wouldn’t provide the rich structure that it does, such as with the development of the heterotic string that allows for an approximation of the Standard Model of physics within string theory.
If string theory were wrong, it wouldn’t lead to better understandings of quantum field theory, quantum chromodynamics, or the quantum states of black holes, as have been presented by the work of Leonard Susskind, Andrew Strominger, Cumrun Vafa, and Juan Maldacena.
If string theory were wrong, it would have collapsed in upon itself well before now, instead of passing many mathematical consistency checks and providing more and more elaborate ways to be interpreted, such as the dualities and symmetries that allowed for the presentation of M-theory.
This is how theoretical physicists think, and it’s why so many of them continue to believe that string theory is the place to be. The mathematical beauty of the theory, the fact that it’s so adaptable, is seen as one of its virtues.
The theory continues to be refined, and it hasn’t been shown to be incompatible with our universe. There has been no brick wall where the theory failed to provide something new and (in some eyes, at least) meaningful, so those studying string theory have had no reason to give up and look somewhere else.
Whether this resilience of string theory will translate someday into proof that the theory is fundamentally correct remains to be seen, but for the majority of those working on the problems, confidence is high.
This popularity is also seen by some critics as a flaw. Physics thrives on the rigorous debate of conflicting ideas, and some physicists are concerned that the driving support of string theory, to the exclusion of all other ideas, isn’t healthy for the field.
For some of these critics, the mathematics of string theory has, indeed, already shown that the theory isn’t performing as expected (or, in their view, as needed to be a fundamental theory) and the string theorists are in denial.