Theory Of Time Travel
Google was buzzing on October 28, 2010 with searchers looking for a glimpse of a possible time traveler after news broke that an Irish filmmaker spotted someone apparently talking on a cell phone in a 1928 Charlie Chaplin film.
Salon asks how the time traveler receives cellular service in 1928 (one might also wonder who she was talking to, decades before others had cell phones). Meanwhile, experts suggest an antiquated hearing aid as a plausible explanation.
The serendipitously named Time, on the other hand, went to physicist Michio Kaku to ask whether time travel was possible. He claims that time travel is possible, including the possibly paradoxical backwards time travel. He suggests that if someone were to attempt to change their past, they would simply make another possible world a reality and become someone else.
Various Philosophical Objections to Time Travel
Philosophers have discussed a number of objections to the possibility of time travel. One objection is that if backwards time travel were possible, then there would be evidence of time travelers around us.
Hearing-aid theory aside, perhaps the Charlie Chaplin film provides such evidence. Another line of reasoning argues that if time travel were possible, then it would be possible for the same person to have different properties at the same time. For example, you might have red hair in 1985, then you dye your hair black in 2010 and travel back to the time you had red hair. This would violate Leibniz's law of the Identity of Indiscernibles. Philosopher Paul Horwich argues for a simple solution by allowing that a 'proper time indexing' be a property of individuals.
The Grandfather Paradox
The most discussed philosophical objection to time travel, however, is the grandfather paradox. Although Michio Kaku's suggestion of creating an alternate universe would avoid this paradox, it would also raise a further puzzle: under common sense conceptions of causation, the person in this newly created reality would seem to exist without cause or history.
The grandfather paradox is often framed in terms of human agency: what if you tried to go back in time and kill your grandfather? If you were successful, you wouldn't be born, which means you wouldn't be able to go back in time and kill your grandfather. John Earman provides an alternate formulation which sidesteps human agency:
- Hotel Travel Yahoo
- Curling Irons Travel
- Costa Rica Travel Preparations
- Robots Travel Airfare
- Television Travel Channel
