  The current debate about a possible change of paradigm from a single universe
to a multiverse scenario could have deep implications on our view of cosmology
and of science in general. These implications therefore deserve to be analyzed
from a fundamental conceptual level. We briefly review the different multiverse
ideas, both historically and within contemporary physics. We then discuss
several positions within philosophy of science with regard to scientific
progress, and apply these to the multiverse debate. Finally, we construct some
key concepts for a physical multiverse scenario and discuss the challenges this
scenario has to deal with in order to provide a solid, testable theory.
