That is, nothing testible. String theory replaces the point particle with vibtrating 1D loops or lines, which however are too small for us to be able to verify. Since the various vibrations of the string is what gives us the zoo of elementary particles, there should be countless particle types that exist - but have not yet been discovered. String theory also predicts the existence of additional dimensions, but they are also too small to be detected. How convenient for string theorists.
M theory allows for the existence of larger extra dimensions that should be testible, but so far nothing has come of it.
Keep in mind that there are other ways than experimentally to differentiate between viable and pathological theories. In particular, we can ask whether a theory can be reconciled with what we already know and whether it's internally consistent. In the case of string theory the answer to both questions is yes. On the other hand, as far as we know, the answer with respect to LQG continues to be no. We can also ask about the plausability of a theory's basic assumptions. For example, the pattern of discovery with particle accelerators is that going to higher energies produces previously unseen phenonmena requiring reevaluation of current theory. Then given that we've only probed at energies which are a tiny fraction of the planck energy, how plausible is the idea that no new phenomena will emerge invalidating GR as a basis for quantization before we hit planck energies? Not very.
For example, SMT (String/M-theory) correctly produces the black hole entropy relation, LQG doesn't. Despite that fact that LQG was constructed to be a background independent QGT, the only thing it appears to be is a background independent theory of something we know not what, but it's a virtual certainty that "what" has nothing to do with our universe. On the other hand, any consistent string theory must contain the graviton and GR and in this sense not only is it our only genuine QGT, it aclually predicts (or more accurately retrodicts) spacetime itself!
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