"...The best evidence we have that time travel is not possible, and never will be, is that we have not been invaded by hordes of tourists from the future."
Dr. Stephen Hawkins author of "A brief History of Time" and " The Universe in a Nutshell" once made the above statement. Now even though Dr. Hawkins is by far one of the greatest minds in the 20th century I have to disagree with him. For me time travel is indeed a possibility. To the past I'm not quite convinced just yet, then again simply because no one has figured out how to do it just yet, doesn't mean it's not possible. However, to the distant future at least in theory I believe is a definite possibility.
Thinking about time travel confuses people and usually leads to unavoidable paradoxes regarding time. You've heard some of them before.... they are limitless it seems. "The grandfather paradox" comes to mind, in which you go into the past to kill your grandfather prior to your parents getting together. Yet if you were to do this, you would cease to exist. Now if you didn't exist, how could you kill your grandfather. Then there is the argument that a universe which allows for time travel and closed time-like loops is one in which intelligence could not evolve because it would be impossible for a being to sort events into a past and future or to make predictions or comprehend the world around them. In other words it would disrupt or distort the evolutionary process.
When the average person thinks of time he thinks of it in terms of seconds, minutes, hours or years. These are accurate measurements of time, however when dealing with physics one has to shift his thinking slightly. Time is also defined as the fourth dimension of space as it relates to the right angles of the other three observable spatial dimensions. Height, length, width are all spatial dimensions. Height cannot exist without length, or width. The same goes for time. Time cannot exist without space, and vise versa. Einstein's special theory of relativity proposed that as an object reaches the speed of light it's relative mass increases as well. The speed of light being at approximately 186,000,000 m/ps. Once the object reaches this speed it becomes infinite. There are various ways in which a person could "travel into the future" in a limited sense: the person could set things up so that in a small amount of their own subjective time, a large amount of subjective time has passed for other people on Earth. For example, an observer might take a trip away from the Earth and back at relativistic velocities, with the trip only lasting a few years according to the observer's own clocks, and return to find that thousands of years had passed on Earth. The theories are almost as endless it seems as the paradoxes.
Technically time travel to the future is already possible. You travel to the future every time you get on a plane to go into a time zone several hours ahead of the time zone you were originally in. Now time travel to the distant future this will be the kicker. I believe time travel to the distant future could one day be possible, given what little we know of Einstein Rosen Bridges or worm holes, and not to mention black holes. Worm holes at least in theory, would be able to take one from point a to point b in a relative small amount of time. Supposedly nothing exists on the other end of a black hole, yet we don't know that for sure because we have never been to the other side of one. Whose to say that more study of either one of these anomalies couldn't lead to a break through in time travel. The possibilities are endless.