I agree with you; on a personal note, I'm not quite convinced either, be it Brian Greene or Kaku.
"It's pure speculation."
Frankly, that goes for most everything we 'know': they're all currently operative 'proven' hypotheses...until the next post-dead physicist comes up with another universal operative paradigm, then the cycle starts over and over.
so what else is new? lol.
Predictions in due Time...
"Let it not be said that no one cared, that no one objected once it's realized that our liberties and wealth are in jeopardy." - Dr. Ronald Ernest Paul