I would say since time by definition is simply movement, then we would have to assume that to travel in time to the past would simply mean to *undo all that has been done (revearse all movement) this would mean the past is relative to what is current, meaning if we are ever able to travel in time to the past we would be finding people from the future "popping up in the now."
So because time in essence is also unlimited, sooner or later regardless of how *long it takes 1m years 100m years, proves that we will never travel backwards in time, because our *past has already proved it.
this prolly makes no sence at all
