Two recent PF threads were interesting IMO. Why no time before the BB? and A Farewell to Falsifiability Here on PF I can read about collapse-rebound, quantum fluctuations, multiverses, and many more speculative theories about pre-BB eras or universes beyond the observable. But it is my understanding that we have no observational evidence to support or refute these theories, and also no prospects for obtaining such evidence. No disrespect intended, but total lack of evidence or prospects for evidence makes it impossible to separate these theories from "turtles all the way down." But Professor Susskind once said, "Physicists aren't interested in what is true. They want to know what is useful." In his lectures on string theory he also said that some of the math developed by string researchers has been useful in refining the standard model, even if string theory itself is not yet falsifiable. The point being that there can be serendipitous side benefits to research into unprovable theories. My questions for researchers in these fields are: What kinds of observational evidence do you prospectively hope to see? In what ways might research in these theories become useful even the theories can't be proved?