Jim Baggott and Mike Duff debate the limits of physics
I agree with Duff. While observation and confirmation of theory will always be fundamental to the process of real science, the fact that we can not directly observe something in the present does not invalidate a theory that is developed through scientific analysis.
As Duff explains:
Similarly, string theorists did not assume supersymmetry, extra dimensions, the dualities of M-theory or the myriad possible universes; they discovered them to be consequences of a theory that subsumes empirically well-established features such as general relativity, gauge field theory and chiral quarks and leptons. Current research is devoted to finding out what else M-theory requires. Moreover, there is a feeling, hard to convey to the layman but shared by many experienced theorists, that these ideas all hang together. As Peter Higgs said recently, "I'm a big fan of supersymmetry because it seems the only way to get gravity into the game''.Finally, you offer no credible alternative. If you don't like string theory the answer is simple: come up with a better one. The battle for the correct theory will not be won on Amazon or on the blogosphere, however. It will be won in the pages of scholarly scientific journals. Sadly, many critics of string theory, having lost their case in the court of science, try to win it in the court of popular opinion. A science writer calling the theorists who are actually doing the research "confidence tricksters'' or Stephen Hawking "a fairytale physicist'' doesn't cut the mustard.