Time Travel: Is It Possible?
Most people have lived their life without stopping and thinking about what time really is. But most people have heard of time travel from watching sci-fi movies. And now the question is: Are those time machines really possible? Yes, time travel is possible.
One approach of doing this is to warp space-time. The logic behind this is that a shortcut in space is created. Imagine a piece of paper as a timeline with two points, A and B, with A being on the farthest left (2012), and B being the farthest right (2020). The only way to get from A to B is to go straight along the paper. But if this paper is folded up into half, a shortcut is created. So instead of taking a long way from 2012 to 2020, there is now a shortcut- the vertical distance between A and B that allows one to jump from 2012 to 2020. The shortcut that is created is known as a wormhole.
However, there is a problem with the wormhole. It would not last long enough for a spaceship to get through. The wormhole would shrink to a point called a singularity in a short time. According to professor Stephen Hawking, there is a solution to this problem, but it requires something called a negative curvature. In order to understand negative density curvature, one must first understand the Casmir effect. Based on the uncertainty principle, even vacuum in space is filled with virtual particles. These are very high energy particles and exist for only a very short period of time. If you put two metal plates in a vacuum with a little space between them, only a certain wavelength of particles can live here. Beyond these two metal plates, however, there is every possible wavelength of particles. There are more particles living outside these plates than the inside. Therefore one can conclude that there is a negative energy inside the plates; and this is a negative density curvature.
Now, you may have heard of the grandfather paradox. It poses a question relating to backward time travel. What happens if one was to go back in time and shoot one's grandfather? Nature prevents you to do so. One explanation for this is the consistent history theory. It says that many of the mathematical analysis of the probabilities of different outcomes cancel out, leaving only a few probabilities. One of those probabilities came to be the world that we witness today. Therefore, this restricts one from going back in time and killing one’s grandfather because history has already been set. Stephen Hawking asked: If time travel is possible, then why is no one coming from the future to reveal to us its secrets? In his book A Brief History of Time, Hawking explained that our past is already observed and set so it might not have the right warping to allow one to travel from the future back to the past. But we have not yet observed the future, so it might provide the right warping to allow forward time travel.
But if traveling into the future is indeed possible, does that mean the traveler can come back and say that he or she can predict the future? Can we then prevent certain things from happening and send the traveler to the future again and see if our future has changed as a consequence of our preventive actions?