Time travel poses difficult challenges

Feb 7, 2009 08:28 GMT  ·  By

Over the years, theoretical physicists have identified a number of potential deterrents for time travel, including general obstacles, as well as various paradoxes of such a travel. The predestination issue is one of the most complex and with most implications, as it advocates that people going back or forth through space-time do so because they were destined to by a higher power. But perhaps one of the best-known problems associated with traveling through time is the Grandfather Paradox, which has thus far been considered to be unbreakable, simply because it addresses the very origin of the potential traveler.

 

A perfect example of this paradox is a man going back in time to kill his biological grandfather before he met his grandmother. If the traveler succeeds, then one of his parents, and by extension himself, wouldn't have been born. Then, it would have been impossible for him to travel back in the first place, and his grandfather wouldn't have been killed. Consequently, he could have gone back in time and killed the grandfather, but then the same issue would arise.

 

This is why this matter is considered to be a logical paradox. You can do something in the past, but if that action nullifies something in the present, then the very factors acting for the change are not there. If they are, then the past is unchanged. The same holds true if, for example, a traveler goes back in time and kills himself as a baby. Then, naturally, the child would not grow to be an adult and go back in time to kill himself.

 

There are a few theories that propose methods of bypassing this paradox, or argue that such actions would have no effect on the time line the traveler moves backwards from, on account of parallel universes. In other words, a new time line is created when the man kills his grandfather, one in which the man himself is not born. But that time line, with all the new possibilities that derive from it, develops alongside to the one in which the traveler grew to the appropriate age to move back and kill his predecessor.

 

The Novikov self-consistency principle holds that, if the man was standing in front of his grandfather ready to shoot him, then nature or other forces would intervene, so as to eliminate the threat to the normal flow of time. The gun would jam or misfire, the man would not hit the target, or the person killed could prove not to be the actual biological grandfather.

 

Other scientists say that the appearance of such a paradox would mean the destruction of the Universe, as nature would find itself incapable to deal with the changes in the fabric of time. Some say that only the portion of space-time affected by the changes would disappear. Science fiction holds that potential “ripples” could travel in time from the point of the change to the point from which the traveler embarked on his way back. These so-called ripples would re-arrange history in such a way that it's conclusive with the changes made in the past.