1. Time Travel Branching Time Lines

2. Back to the Future External time is objective or real time. Personal time is time measured on your wristwatch. A time-traveler is someone whose personal time diverges from real time.

3. The Altered Past Paradox 1)If time travel were possible, it would be possible to change the past. 2)Its not possible to change the past. 3)[So] Time travel isnt possible.

4. Branching Time-Lines Objection #1: Marty doesnt really change the past. Objection #2: Marty doesnt really avoid contradictions.

5. The Block Universe The Analysis of North: An utterance of John is having dinner to the north at place P1 is true iff there is a place P2, such that John is having dinner at P2 and P2 is north of P1. The Analysis of Will: An utterance of John will have dinner tonight at time T1 is true iff there is a time T2, such John is having dinner at T2 and T2 is later than T1.

6. Branching Time-Lines Objection #1: Marty doesnt really change the past. Objection #2: Marty doesnt really avoid contradictions. Objection #3: Marty doesnt really travel in time.