i always think time and space as not being linear. no beginning, no end. sort of like a sphere. different points coexisting all at the same time. separate yet with the ability to share certain properties. i think this explains the idea of time travel. although we exist in one universe its possible to experience parallel universes by varying our perception of different frequencies which which take place in the same time-space fabric. Stephen Hawking doesnt believe in time travel because he believes time is linear. guess you can tell i think about this stuff a lot.