Scientists who adhere to a strictly “naturalistic” interpretation of science claim that only approaches which can be tested empirically (verified and/or falsified) are valid. The nobel laureate in physics Richard Feynman, for example, argued that string theory was not testable and therefore not scientific. A number of physicists and philosophers of science recently met in Munich to discuss the problems which have arisen in physics because theories, such as string theory, become increasingly more difficult to test. Some theoreticians at the meeting provided arguments to show that philosophical approaches, which in the foreseeable future (if at all) cannot be tested empirically, might well be valid.
For a full discussion see here:
“String theory, the multiverse and other ideas of modern physics are potentially untestable. At a historic meeting in Munich, scientists and philosophers asked: should we trust them anyway?”