Relativity and Time

What does the fourth dimension have to do with time travel?
Answered by Discovery Channel
  • Discovery Channel

    Discovery Channel

  1. Space-time is a structural model of the universe that follows Einstein's theories of special and general relativity. Though modern physics tells us that there could be as many as 10 or 11 different dimensions, under normal circumstances, humans are able to observe four dimensions. We experience three dimensions (height, width and depth) actively, meaning we can navigate them, and one dimension (time) passively, meaning we can detect and observe it, but we can't control how we move through it.

    There are essentially two types of proposed time travel that one could imagine. The first is to reverse course so that the time traveler may re-experience time that has already happened. The second is to slow the time traveler's relative experience of time, essentially allowing him or her to travel into the future. According to what we know about special relativity, progressive time travel is a much more feasible possibility than the regressive time travel. Special relativity tells us that your experience of time slows down as your velocity approaches the speed of light. Given this knowledge, all that it would really take to carry an astronaut to the future is an extremely fast space vehicle.

    Regressive time travel is much trickier -- in fact, it's probably impossible for humans. However, those who believe it is possible often put their faith in the potential of fourth-dimensional tunneling. Going back in time most likely depends on the discovery of space phenomena such as black holes and wormholes, which could create tunnels through the fourth dimension and link different areas of space-time together.

    A black hole is formed when a large star that has burned up all its fuel collapses upon itself due to the pressure of its own mass. The gravitational field that is formed by the implosion is so strong that it sucks in everything that comes in contact with its "event horizon" (the edge of a black hole from which nothing can get back out). Although this kind of black hole crushes any matter that reaches its center, there are other types of black holes, such as rotating Kerr holes, which astronomers have proposed could serve as portals for time travel.

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