1. time travel the bootstrapping paradox

2. causal loops A causal loop is a series of events c 1, c 2, c 3, … c n such that c 1 is a cause of c 2 which is a cause of c 3 which… is a cause of c n, which is cause of c 1. Transitivity: For any events x, y, and z: if x is a cause of y and y is cause of z, then x is a cause of z.

3. the bootstrapping paradox 1. If time travel is possible, then causal loops are possible. 2. If causal loops are possible, then self- caused events are possible. 3. Self-caused events are not possible. 4. [So] Time travel is not possible.

4. the restoration paradox 1. If time travel is possible, then object loops are possible. 2. Object loops are not possible (at least not physically possible). 3. [So] Time travel is not possible (at least not physically possible).

5. the ex nihilo paradox 1. If time travel is possible, then causal loops are possible. 2. If causal loops are possible, then uncaused things are possible. 3. Uncaused things are not possible. 4. [So] Time travel is not possible.