As explained by a failed future-physicist
By Shaer Reaz
Ever since H. G. Wells wrote his fictions on time travel, man has had an obsession with what might as well be the most debatable branch of theoretical science. Even the fact that the most celebrated physicists from the 20th and 21st century still talk about the concept lends some credibility to it.
The whole story begins an apple falling on Issac Newton's head. Newton goes on to define gravity as the force that holds objects down to the earth and also explains how and why the earth and the other planets in the solar system “gravitate” towards the Sun, thus moving in an orbit around it. This gives us some other slightly important stuff, like powered flight, bungee jumping, and countless apple-falling-on-head jokes. Most importantly, though, it gets a certain patent-office clerk in Germany thinking, almost 200 years later.
While Newton may have defined how gravity affects objects on any scale, no one really bothered to ask WHY gravity acts the way it does. Until a little old fella called Albert Einstein started thinking about it. Einstein was a man who liked everything organised, and “Everything” happened to include the entire known universe. He spent more than half his life lusting after “Unification”: the linking of any number of scientific theories that would further the explanation of how the universe works.
Einstein published the Special Law of Relativity in 1905, that postulates that there is a difference between time as observed by people at two different places, and that the difference between the time depends on one of those persons' relative speed. A very common example of this is the theory that if one brother of a twin pair, somehow managed to fly off into space at speeds close to that of light (3X108 m/s) and then returned to earth, he would find that his twin brother is much older than him. One of the most important points that Einstein stressed on was that nothing can travel faster than, or at, the speed of light on earth (or anywhere else theoretically, except for in space).
Around the 1920's, a new generation of scientists led by Niels Bohr established the field of Quantum Mechanics. It explained the behaviour of matter (any object, made up of atoms) through mathematical equations, properties of waves, and probability. This pretty much up-ended Einstein's theory of relativity in ways whose explanations are beyond the scope of this article. Why are all these details important? Well, to travel in time, you have to travel at the speed of light. This isn't permitted by Albert Einstein's Theory of Relativity, but when Quantum Mechanics is brought in, some of the loopholes that existed before can now be closed and you can travel through time. There exists a paradox here, however, one exploited by science fiction movies for eternity. When you go back in time, you make your existence there go against the very laws of existence. If you happen to run over your grandfather while you're in the past, you remove your dad from existence forever and that leaves no concrete explanation for you to exist, whether in the past or the present.
So going to the future is the only option you have.
Of course, you'd have to accelerate your body to the speed of light first. Or find a suitable wormhole. Or Black hole.
On Thursday, 22nd September 2011, researchers at the CERN facility in Italy, a particle accelerator lab (which does exactly what it says on the label - it attempts to speed up particles to the speed of light), managed to accelerate a particle to almost the speed of light. The “almost” here refers to the tiny margin of error that allows you to say that, “Yes, this particle is indeed travelling at the speed of light.” This almost proves Einstein was wrong with his Theory of Relativity (ALMOST is the key word here - his theory has not been disproved yet) and that solid mass might just have the potential to reach the speed of light, making wild theories like time travel a bit more viable.
So. To recap, time travel can theoretically be only to the future: get on a spaceship, travel faster than light; come back to earth, and voila! You're in the future, sort of. Travelling back in time is highly unlikely because there is no physical way of turning back time and even if you could, you can't make sure that you'll exist in the present when you return. Einstein said that time travel isn't possible because nothing can travel at the speed of light (but that might be disproved by recent experiments).
Pretty simple, isn't it?