There is no way to prove it and there is no way to travel between them and there never will be. The ability to travel between them is impossible by fact, theory and reality. The only way is actualy the way they managed it in back to the future where traveling back in time could change your future and the lines you would travel down.

The multiverse theory is where two distinct realitys come out of it, they can never rejoin, they will never even be able to acknolidge the existance of the other. I surgest people look up (Hugh) Everett's Reviews of modern physics 1957 paper. (if anyone finds it PM me or Email me thanks )
To argue against the multiverse theory is to argue against the Copenhagen Interpretation which is main stream Quantum physics which was conceived by (Niels) Bohr and (Werner) Heisenberg in Copenhagen in about 1927.

Oh and before anyone says anything about two equal realitys being formed would cause some error in the conservation of anything, your wrong because it simply doesn't. Nothing is lost and nothing is gained because they become seperate universes which can never join again so there will never be a break in conservations.
Sorry just had to mention that because there is bound to be someone who will mention it, this just saves time