Time travel is a concept that has most likely existed ever since man has realized his own mistakes and wished he could change them. Philosophers, physicists and authors popularized it. There are several theories that suggest time travel is possible. There are also basic human activities that prove time travel is possible. However, time travel as it occurs in fiction and time travel that actually moves you backward in time is simply out of our reach, thus far.
There are a few ways that we know time travel is possible, though they are very basic and are only perceptive or based on our definition of time zones. For example, a person on an aircraft is traveling forward in time because of the speed of the craft. They may even move forward in time through time zones. A person who stands on the edge of a time zone, walks through and then walks back is technically going forward and backward in time, but that is not really what is meant by time travel, though it technically fits the definition.
The special theory of relativity is a theory published by Einstein in 1905. In the most simplistic of terms, as it relates to this topic, Einstein postulated that time is relative. In other words, the length and speed of time can change depending on the observer, gravity and speed. Essentially, Einstein was saying that time can change; whereas it was initially thought that time was a fixed thing. Everything spent its time at the same rate. Nothing could change it. It appears now that is incorrect.
Einstein paved way for the idea that speed and gravity can affect age and, basically, how fast a clock ticks. In this way, a person can age faster at high rates of speed. A clock will tick slower depending on position and gravity. In this way, time has changed. These are the very basics of the idea. Any advanced discussion on time travel would be quite complicated to the layman. However, even at is most complicated, Einstein said nothing about moving backward in time. All of his ideas dealt with the concept of moving forward in time, which it is now clear is possible. Of course, we are always moving forward in time, but we are always in the same “present” as well.
Moving backward in time would not only be cool, it would be essential if we wanted to build very fast spaceships and man them. If we cannot move backward in time, the people on any of these hypothetical super fast spaceships would only go forward in time. They would be unable to go backward in time, reversing the effects that fast spaceships would theoretically have on time. There are a few theories about how this could be done. However, none of them could be put into use, even if we knew they worked.
The Cylinder Theory is one theory regarding backwards travel through time that we know is impossible, barring technological advances that we can scarcely imagine. Even then, it is doubtful that this theory will ever be put to the test. The idea is that an infinitely long and dense cylinder could bend time around itself by spinning at half the speed of light. If a ship were to travel around that cylinder, the ship and its occupants would travel backward through time. Just the idea of building an infinitely long cylinder is absurd without imagining what mechanism would make it turn so fast.
Two theories that are based on things that are not known to exist are the Wormhole Theory and the Cosmic String Theory. The former suggests that a person could travel through time in a black hole. These theoretical black holes are known as wormholes because they open up in two different “times.” You enter in one time and come out in another. The Cosmic String Theory revolves around thin strings of energy in the universe that could hypothetically bend and send you through time, in a nutshell.
A group of scientists reportedly sent a laser beam back in time by forcing it to travel faster than the speed of light, which was previously thought to be the fastest speed possible. The beam reportedly left a compartment it was shot into before it even entered it. This seems a bit more like traveling forward and then perhaps backward in time.
It is a far stretch to think this even comes close to making time travel possible. A person cannot travel faster than the speed of light. It is highly likely that some phenomena would be the result of any such thing. We cannot make an infinite cylinder and such things as wormholes and cosmic strings probably do not exist. Even if they did, they would still be uncontrollable methods of time travel. How could you tell a cosmic string of energy when to take you?
West, Robert, The Possibilities of Time Travel, retrieved 5/31/11, myweb.msoe.edu/~westr/time.htm
Special Relativity, retrieved 5/31/11, www2.slac.stanford.edu/wc/theory/relativity.html