What's the current thinking on multiverse theory in physics?

[Mason_C]

Multiverse theory has been popping up everywhere lately, from physics discussions to pop culture. But what's the actual scientific basis for it? I know there are different types of multiverse theories - some from quantum mechanics, some from cosmology, some from string theory. Which ones have the most evidence? Is multiverse theory physics just speculation or is there real mathematical support? And if there are multiple universes, how could we ever test or detect them?