Ph103: Discussion Questions 1

Short Answer Questions

1. What is the Lewis definition of time travel? Explain all any terminology you must introduce to give the definition.
2. Formulate the grandfather paradox as a valid argument in premise-conclusion form, in which the conclusion is the contradictory statement, "you exist and you do not exist."
3. Explain two ways that one can escape the contradiction of the grandfather paradox.

For Further Discussion

• Understanding the spacetime diagrams. Draw the world line of an observer that... (a) Is at rest and never moves. (b) Moves with constant velocity to the left. (c) Accelerates from rest. (d) Deccelerates to a stop.
• List everything you can that is problematic about the following worldlines.
  
  
• Is there any possibility for time travel outside of these examples? Be creative; play around with the diagrams. There is at least one way that requires no advanced physics at all.