How do you know that?
You said: How do you know that?
Thank you, thank you, thank you. This is the last argument of all those who propose something is true on the basis of ???? (imagination, hallucination, superstition), but without any evidence whatsoever. How do you know there is not a Phoenix? Can you prove Santa Claus does not exist somewhere? etc. etc. etc.
There is no end of things people can imagine and then invent arguments for the existence of. First, let me see some evidence, some reason for supposing there is the imagined other world, or reality, or "parallel" existence, then we can consider the question. In the mean time, there is as much reason to believe in the Phoenix or a leprechaun as in other "realities."