Introduction
Physicists and philosophers take seriously questions of the physical, technological, and metaphysical possibility of time travel. The physical possibility of time travel depends on the consistency of time travel with the laws of nature. In this regard, relativity theory has provided physicists with a framework of laws that permit time travel. The further question of technological possibility asks: if time travel is physically possible, will we ever have the technology to take a trip? Will our computational and engineering capabilities allow us to test our theories? Metaphysical possibility is our focus. We concentrate on matters that are even more basic than the issues of physical possibilty and technological possibility. There are arguments that seem to show that time travel doesn't even make sense, that it is illogical, that it is contradictory.
When apparently sound reasoning leads to a contradictory conclusion, a paradox is the result. Many paradoxes arise in the consideration of time travel. Below are some of the paradoxical topics we explore:
- Grandfather Paradox: Can a person who has traveled to the past kill his or her own Grandfather?
- Self-Visitation Paradox: Can a person visit himself or herself? Can there be two of one person at the same time?
- Nowhere Argument: If only the present moment exists, how could we travel to the past or the future?
- Double-Occupancy Problem: Can a person time travel backwards in time without colliding with his or her self?
If you are ready to dive into these questions, please select a paradox to explore. If you need more convincing that physicists really do take the possibility of time travel seriously, please see our page on the physics of forward time travel. For something a little bit different, consider the philosophical repercussions of dropping the assumption that time is one-dimensional by reading our page on multidimensional time.