Well i want to share here my point of view. i am not astronomer but i have great intrest in astronomy . 1500 years back a prophet name Muhammad (Peace be upon him) travelled in time exactly in the way that J. Richard Gott is proving that it is possible. that is A PERSON CAN COME BACK BEFORE HIS DEPARTURE. Prophet Muhammad (PBUH) went on Meraj where he visited various things of future and came back in exactly the same way. CAME BACK BEFORE HIS DEPARTURE. his vehicle was named as "BURAAK" which travelled with extremely high speed. this was maricle of Prophet Muhammad (PBUH)