Introduction

It is the opinion of this author that many theories of Quantum Gravity have already been discovered, but that the one which applies to the real world still remains a mystery. The theories I am referring to all go under the rubric of M/string-theory, and most practitioners of this discipline would claim that they are all “vacuum states of a single theory”. The model for such a claim is a quantum field theory whose effective potential has many degenerate minima, but I believe this analogy is profoundly misleading.

Among these theories are some which live in asymptotically flat space-times of dimensions between 11 and 4. The gauge invariant observables of these theories are encoded in a scattering matrix. All of these theories are exactly supersymmetric, a fact that I consider to be an important clue to the physics of the real world. In addition, they all have continuous families of deformations. These families are very close to being analogs of the moduli spaces of vacuum states of supersymmetric quantum field theory. They all have the same high energy behavior, and one can create excitations at one value of the moduli which imitate the physics at another value, over an arbitrarily large region of space. Except for the maximally supersymmetric case, there is no argument that all of these models are connected by varying moduli in this way. One other feature of these models is noteworthy.