"M-theory suffers from the same flaws that string theories did. First is the problem of empirical accessibility. Membranes, like strings, are supposedly very, very tiny—as small compared with a proton as a proton is compared with the solar system. This is the so-called Planck scale, 10^–33 centimeters. Gaining the kind of experimental confirmation of membranes or strings that we have for, say, quarks would require a particle accelerator 1,000 light-years around, scaling up from our current technology. Our entire solar system is only one light-day around, and the Large Hadron Collider, the world's most powerful accelerator, is 27 kilometers in circumference."
So, basically, they have posited (i.e. made up) a bunch of theoretical entities the existence of which it is completely impossible to determine. And this explains everything. But that's alright because it is logical:
Hawking recognized long ago that a final theory—because it would probably involve particles at the Planck scale—might never be experimentally confirmable. "It is not likely that we shall have accelerators powerful enough" to test a unified theory "within the foreseeable future—or indeed, ever," he said in his 1980 speech at Cambridge. He nonetheless hoped that in lieu of empirical evidence physicists would discover a theory so logically inevitable that it excluded all alternatives.
Maybe rational choice should be driving at more becoming more tautologous rather than less. Then it would be more like physics.