hi there. I studied physics for years, even went as far as getting a PhD. but that was 13 years ago, since then rusty. Anyway something occurred to me and I wondered what you all would think about it. My question is, can anyone think of an experiment you could do to check if the "many worlds" interpretation (the one I like best) is the "correct" one? For example you might imagine this: let's say the universe splits into two, but somehow the two "paths" manage to come back together so that the two "worlds" can interfere with one another. Same idea as a single photon interfering with itself in a double-slit experiment, except instead of a photon interfering with itself, it's the entire universe. I was thinking maybe there's some experiment you could do in one universe that could detect something akin to the interference fringes of entire universes interfering with one another. Is this crazy? Perhaps this can't happen due to decoherence? it's hard to get much more macroscopic than the whole universe I suppose. Decoherence is always killing inteference patterns. OTOH decoherence comes from degrees of freedom that you aren't following right, ones that are connected to the environment. if the system is the entire universe then there is no "environment" to get mixed up with. One thing's for sure: Hilbert space is big! there aren't even words for how big it is!