We often wish that we could go back in time and rectify our mistakes or go to the future and see what it turns out to be like. One thought is that time travel is certainly not possible, because if it would have been, then we would already have been visited by time travelers! However, let us not jump to conclusions and explore the question of whether time travel is possible, by going deeper into the subject. To answer the question of whether time travel is possible, one must explore the very nature of time. So, let us question first what time is and what are the things that make time travel only a matter of fiction. What is Time? We all talk about having no time, passing time, killing time and even sparing time, but at no point of time do we question about what does time really mean? Time is simply change in all its forms. Time makes the world dynamic. Without time, everything would be like a still photograph; frozen and static. So, time is something that is felt due to and with reference to changing things. Periodic changes are used to quantify time in the form of a clock. As you can see, the concept is very elusive and though we have an idea about what it means, putting it in words is not that simple. So, let us just say, time is what is characterized by changing of things. A feature about time is that it has an inherent directionality built into it. This directionality becomes clear due to the concept of causality. Causes precede effect and not the other way round. This directionality brings in the doubt of whether time can change backwards. Special relativity propounded by Einstein demolished the concept of absolute time and unified time with space, creating the concept of space time. Time was understood to be relative in nature. Time came to be known as the fourth dimension, although it was quite different from the space dimensions in nature. You can move back and forth in space, but time as a dimension is different and doesn't allow that. The concept of time dilation in special relativity tells us, that time slows down for an object as it speeds up. The faster you move, the slower time changes for you! It is a fact which has been verified through experiments. What is Time Travel? Time travel is, being able to go backwards or forward in time! A favorite subject of science fiction movies, the concept of time travel creates some weird contradictions and paradoxes. Like the famous one of, what would happen if you went back in the past and accidentally killed your grandfather? I could create a time machine and simply go back in time and give it to my old self! When was the time machine really invented then? Many such paradoxes abound when it comes to traveling backwards in time. Let us get down to brass tacks and try to answer the question of, 'Is time travel really possible?'. Is Time Travel Possible or Not? The question of whether time travel is possible can be broken in to two separate questions - 'Is time travel into the past possible?' and 'Is time travel into the future possible?'. Let us try to see what theoretical physics, which is the only subject which can give us a realistic answer, says about both these cases of time travel theory. Is Time Travel to the Future Possible? Time travel in the forward direction is indeed possible due to the concept of time dilation. When a particle travels fast, time slows down for it. So, for a particle traveling close to the speed of light, what was one second, could be ten minutes for us! This is because time is relative to speed of the particle. This phenomenon has been observed in case of a particle called a Muon, which lasts longer (than the time in which it should have decayed if stationary) when it is traveling close to the speed of light. So in a way, it has lived longer and traveled into the future! So, time travel into the future is theoretically possible! Is Time Travel Into the Past Possible? Same is not the case with traveling backward in time. A major roadblock is the second law of thermodynamics about entropy. The disorder in the universe, termed as entropy, always goes on increasing. A reversal in time would mean an effect preceding a cause and entropy decreasing! It would violate the concept of causality and the law of ever-increasing entropy! That is why time travel backwards is not possible theoretically. There are speculations about time travel backwards possible through a concept called a wormhole. It arises out of general theory of relativity, which tells us that gravity is not a force but a manifestation of curvature of space time! Matter bends space time around it! A very massive star which dies, warps the space around itself in such a fashion, that it creates a black hole. Theoretically, this black hole could be one mouth of a worm hole, which connects two regions of space time with a passage and it is a mathematical solution of Einstein's equations of general relativity. However, there is no way one can verify the truth of this statement, as mere mathematical validity doesn't mean that it could exist! Hope this article has clarified the scientific viewpoint about the possibility of time travel. Traveling back in time is simply unrealistic! So, if anybody asks you about whether time travel possible, you know what to say!