Can one really travel Back to the Future?

Newtonian Universe - No, time is like an arrow in flight. It is impossible for an arrow to change its course and go in the opposite direction. Time moves in a linear path from beginning to end, there is no way to reverse this (Pickover).

Multi-Verse - No, there is no way to travel with time. One can travel to a different universe that is less evolved due to a divergence in the paths of the universes, but one cannot travel through time (Preston).

Einstein's Universe - Yes

There are two possible methods for traveling back in time. The first method is related to Einstein's theory of relativity. This theory believes that if one surpasses the speed of light then time will reverse and the traveler will go back in time. This theory is susceptible to the same problems as the idea of traveling at the speed of light to travel into the future; human technology is not evolved enough ("Brian's Views...").

The second method of traveling back in time involves wormholes. Imagine a rollercoaster loop and the time traveler is traveling along the tracks through the loop. At the end of the loop, the passenger rides past the beginning of the loop. If somehow, the cart was able to jump off of its current track and land on the track at the point where the loop began then the loop would be repeated. In this way, the passenger would be traveling back in time to re-ride the loop. The theory of wormholes proposed that if a hole was torn in the time-space continuum (the railroad track) a traveler would be able to travel back into time (Hawking 110). The problem with this method is that one needs a tremendously large amount of power to rip a hole in time-space to create a wormhole. Also, there would need to be too separate machines to create this hole, one at the start and one at the opposite end of the wormhole. This would make travel to a time before the creation of the time machine impossible. For this reason, traveling back in time using wormholes is also very impractical.

Other improbabilities that might prevent travel to the past are known as time travel paradoxes. There are two main paradoxes that seem to contradict this form of time travel. The first is known as the "chronology principle." This paradox comes from the idea that ideas can be continuously recycled with no original thought. For example, say Thomas Edison was able to travel back in time just before the end of his life. With him, he brought all of his inventions and ideas. The elderly Thomas Edison then met his younger self before the induction of any of his inventions. The elder Edison would then pass all of his knowledge on to his younger self so that the younger self would never originally have to invent the light bulb. As his days approached their end, the younger Edison would then repeat this process with his younger self. As a result, nothing new would have been created by Edison. This raises the question, where did the original idea for the light bulb come from ("Brian's Views...")?

The other paradox is known as "the grandfather paradox." This states that if a traveler were to go back in time and kill his grandfather, the traveler would never have been born. Thus, the traveler would have never traveled back into time to kill his grandfather. These two paradoxes also cast doubt on the idea of traveling into the past ("Brian's Views...").