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time travel

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time travel

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  1. time travel vranas on changing the past

  2. If time travel is possible, then one can change the past. • One cannot change the past. • [So] Time travel is not possible. the altered past paradox

  3. peter vranas

  4. Someone affects the past iff he does something that has a causal effect on the past. • Someone changes the past iff he does something that makes the past qualitatively different from what it is. definitions

  5. It is possible to transform the past iff there is a possible world W and time T such that: Someone does something at T which makes the past in W different from the past in W. • It is possible to replace the past iff there is a possible world W and time T such that: Someone does something at T which makes the past in W different from the past in the actual world. definitions

  6. If time travel is possible, then it is possible to affect the past. • If it is possible to affect the past, then it is possible to replace the past. • If it is possible to replace the past, then it is possible to change the past. • [So] If time travel is possible, then it is possible to change the past. vranas’s argument

  7. Qualitative change occurs when something has different properties (or “qualities”) at different times. • Substantial change occurs when different things (or “substances”) exist at different times. • Intrinsic change occurs when something has different intrinsic properties at different times. • Extrinsic change occurs when something has different extrinsic properties at different times. definitions

  8. It is possible to change the past in the qualitative senseiff there is a possible world W and times T1 and T2 such that: Someone does something in W that makes the past in W have different properties at different times. • It is possible for someone to change the past in the substantial senseiff there is a possible world W and times T1 and T2 such that: Someone does something in W that makes different pasts exist at different times. • It is possible to “change the past” in the vranas senseiff there is a possible world W and time T such that: Someone does something at T which makes the past in W different from the past in the actual world. definitions

  9. It is possible to “change the unchangable monument” in the vranas senseiff there is a possible world W and time T such that: Someone does something at T which makes the unchangeable monument in W different from the unchangeable monument in the actual world. • It is possible to “change the past” in the vranas senseiff there is a possible world W and time T such that: Someone does something at T which makes the past in W different from the past in the actual world definitions

  10. If time travel is possible, then it is possible to affect the past. • If it is possible to affect the past, then it is possible to replace the past. • If it is possible to replace the past, then it is possible to change the past. • [So] If time travel is possible, then it is possible to change the past. vranas’s argument