What happens if you go back in time and kill your grandfather?
Answered by Science Channel
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    Science Channel

  1. The concept of time travel has intrigued man for years. Even before late 19th century authors such as H.G. Wells began to write about time travel, cultural and religious legends told of people entering trances or bouts of sleep that lasted hundreds of years. Today, physicists such as Stephen Hawking study the concept and theories of time travel.

    Some people would consider the scenario of a person going back into the past and killing one of his ancestors as a paradox. If you go back in time and kill your grandfather before he gave birth to your father, how could you have been born? And if you didn't exist, how could you go back in time to kill anyone? One way of sidestepping this problem is to assume the existence of parallel universes, where in one universe you've killed your grandfather and you no longer exist in that universe, having never been born, but in many other parallel universes, you're still alive. Some might even say that any action actually creates a new parallel universe, which is identical to the old one until you change past history, after which successive events are different from those in the old universe. Hawking once proposed using wormholes that would connect parallel universes to our universe [source: PBS].

    Yet another hypothesis regarding natural phenomena in the universe is proposed by physicist J. Richard Gott from Princeton University. He suggests that thinner-than-an-atom cosmic strings that are under millions of tons of pressure could be lining the universe. With all the pressure they're under, they also could exert a strong gravitational pull on whatever spaceship passes by them. If this is really the case, the cosmic strings could accelerate an object attached to them, distorting space-time with their gravitational force and hurling the object through time.

    In March 2011, Vanderbilt physics professor Tom Weiler admitted that his and Chui Man Ho's theory was a long shot, but that their Large Hadron Collider might be the first machine that could cause matter to travel back in time. The atom smasher was built to produce the Higgs boson, eventually leading to a singlet that could potentially jump into a fifth dimension [source: Science Daily].

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