Einstein perceive time as just another dimension, meaning there could be many realities that exist at any point in time (the concept of parallel universe). That every action that a human can take will spawn into various realities in which different choices are made. So, there might not be only one of you, but billions more. The concept of multiple versions of self in different parallel universes is somewhat illustrated in the action movie “The One” starring Jet Li, in which one version of him travels to other universes to kill other versions of himself, as to gain unlimited power from the other versions of himself.
Arguably whether this can be accepted or not, it has become very popular in science fiction, and also provides a continuing debate about the nature of the universe(s) that inhabits the world. If we are to accept paralle universe, then every single action that can be taken is existentially explored in many universes. Every action you decide in this universe, many versions of yourself decide to do other options in other universes.
Proponents to this theory believe that there is no way to travel to the other universes, provided they even exist in the first place. Moreover, proponents also believe that communication with these other universes is not possible. There is simply, no way to prove this theory in this manner.
How about time travel? Should time travel is possible, it would simply be another outcome in a universe where a time travel occurred. In another universe, the time travel never takes place. In a way, this can solve lots of those confusing time travel paradoxes.
My personal opinion? No, I do not believe that parallel universe exists, not in the way that every single choice is made in many universes. Humans are given one life, one life to do the right thing.