Mm, it isn't. We're from different universes-- really, the only difference between those worlds is us. Robert and Rosalind . . . just one chromosome of difference.

I told you I did terrible things to ensure he was at my side. Most of those things were on the orders of a man who gave me money to fund my research. Eventually, I had enough money to build a machine to tear a hole between worlds. I pulled Robert through, and though he suffered physical side-effects, he survived the process.