Paper detail

String/M-theories About Our World Are Testable in the traditional Physics Way

Some physicists hope to use string/M-theory to construct a comprehensive underlying theory of our physical world a "final theory". Can such a theory be tested? A quantum theory of gravity must be formulated in 10 dimensions, so obviously testing it experimentally requires projecting it onto our 4D world (called "compactification"). Most string theorists study theories, including aspects such as AdS/CFT, not phenomena, and are not much interested in testing theories beyond the Standard Model about our world. Compactified theories generically have many realistic features whose necessary presence provides some tests, such as gravity, Yang-Mills forces like the Standard Model ones, chiral fermions that lead to parity violation, softly broken supersymmetry, Higgs physics, families, hierarchical fermion masses and more. All tests of theories in physics have always depended on assumptions and approximate calculations, and tests of compactified string/M-theories do too. String phenomenologists have also formulated some explicit tests for compactified theories. In particular, I give examples of tests from compactified M-theory (involving Higgs physics, predictions for superpartners at LHC, electric dipole moments, and more). It is clear that compactified theories exist that can describe worlds like ours, and it is clear that even if a multiverse were real it does not prevent us from finding comprehensive compactified theories like one that might describe our world. I also discuss what we might mean by a final theory, what we might want it to explain, and comment briefly on multiverse issues from the point of view of finding a theory that describes our world.