How can mankind or another very intelligent and developed race create their own universe/dimension/realm which is completely different from our universe (different physics equations, physics generally, dimensionality, topology, geometry and for example magic and other unbelievable things). Have we a theories that could answer this question as scientifically as possible? I hope that I set tags for this question properly because I had problem with it.
/create their own universe/dimension/realm /
If one considers such a realm to be an environment where different entities and objects interact according to preset rules, then various virtual worlds meet the criteria. Even Zork. These have rules for interaction which correspond to physical laws in the real world. Virtual objects can exist. People in things in the real world can exist as their avatars or projections into the virtual world. You can purchase such a world for your game system and interact with it for days on end. Is it as detailed as the real world? Of course not. Does the OP mandate that it must be? No.
Would it be possible to have a real live person so immersed in the virtual world that interactions seem to that person much like what they are used to in the real world? Of course this is a SF trope since Matrix and before. I recently tried on one of those Oculus Rift headsets and the idea does not seem so zany to me anymore.