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to prevent time travel into the past.

However, physicists have come up with possible solutions to get around such paradoxes. One of which being the theory of parallel universes'. This concept means the existence of endless alternate versions of the universe. This conveniently does away with the paradoxes of time travel by allowing the time traveler to return to a parallel universe that is different to the universe which he started from. The time traveler simply creates an alternate universe by going back in time. Killing your grandmother before she could conceive your mother means that you would not have existed in this newly created universe. Nevertheless, you were still born in the universe from which you originated from. This is known as the many worlds" interpretation of quantum mechanics.

Novikov self-consistency conjecture has also been proposed as another solution to the time travel paradoxes. It states that if an event will lead to a paradox, then the possibility of an event occurring is zero. Using a mathematical model involving a billiard ball being launched into a wormhole, the paradox lies when the billiard ball exits the wormhole moments earlier in time to collide the incoming billiard ball, preventing it from ever entering the wormhole in the first place.

Novikov found that a given initial condition could result in many different paths for the billiard ball. He also found that the probability of the billiard ball doing something that is logically inconsistent (such as the above paradox) was zero. The ball cannot pass through the wormhole in such a way that it will prevent itself from passing through the wormhole, but that does not stop the ball from passing through the wormhole in the first place.

This means that a time traveler could presumably travel back to the past, but will be incapable of taking paradoxical actions. Such a conclusion might contradict the human concept of free will, but a human's free will, however great, does not allow the laws of physics to be broken.

Time travel appeals, irresistibly, to the romantic soul of anyone who is human. In spite of the problems posed by the time travel paradoxes presented earlier, it does not fundamentally rule out time travel in itself. Have we already been visited by time travelers from the future? Who knows?

Learn more about this author, Wenbin Nah.
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