It's About Time!
Is it possible to travel in time? Would you believe that it would be easier to travel into a future that hasn't happened lyet than it would be to travel into a past that has? Odd as that may sound, of the two options, travel into the future would be the more feasible. If we can't travel backwards through time, we can at least see back in time.
When you see the moon in the sky, you see it as it was one and one-quarter seconds ago, or the sun, eight and one-half minutes ago. This is because it takes light 1 /1/4 seconds to travel from the moon to the Earth; 8 1/2 minutes to travel from the sun; 4.2 years from the nearest star, Proxima Centauri; 2 million years from the nearest galaxy, the Andromeda galaxy, and 65 million years from spiral galaxy M-66, the galaxy in which I co-discovered a supernova on February 11, 1989 (SN1989b).
Lets say we were to magically travel to M-66 and brought along a very powerful telescope. If we turned the scope back in the direction of the Earth, we would be able to watch (assuming the scope were sufficiently powerful) Tyrannosaurus Rex and his friends romping about the landscape--for the light that would just be entering our eyes originally left the Earth 65 million years ago. We are able to judge the age of the universe in this way by the distances of the furthest objects we can see (the so-called 'quasars', or 'quasi-stellar' objects at 14.5 billion light-years distant.)
In an essay I wrote about a year ago, called "The Twin Paradox", I described a space traveler who was traveling in his ship at nearly the speed of light and who had left a twin brother back on Earth. One of the consequences of general relativity is that time passes more slowly for someone traveling at nearly the speed of light than it does for someone (in this case the traveler's Earthbound twin brother, Marvin) who remains at rest.
When the traveler (Harvey) returns to Earth after a few years, he finds that Marvin has long since passed away of old age, and in fact, that centuries have passed on Earth while only a few years have passed for him. In this way, Harvey has 'traveled' centuries into the future while on his three year journey in his spaceship (since it was Harvey who did the moving it was also he who did the traveling 'forward' in time and not Marvin 'backward' in time.) This interesting and hopelessly un-intuitive phenomenon is called time-dilation and is described in Albert Einstein's second or, 'general' theory of relativity.
I should mention here that all this traveling and not traveling assumes that events in 'time' are not static events - in other words, they have no 'fixed' place in relation to other events. I am assuming that all events are of the "here and now"; in other words, all events are laid out before us and are available to access on demand. There are no "past" or 'future" events--only events--regardless of how it might appear otherwise, and they can be accessed from more than one vantage point. Depending on one's approach, one event may or may not come before or after another event and, in fact, may be approached in such a way that all events appear to be simultaneous, and in reality, they are simultaneous. Because of this 'fluid' nature of events, time can be manipulated (bear in mind that this is just the opinion of this writer, but it seems to me that Harvey has irrefutably proved this to be the case.) Harvey's travels not only demonstrate time dilation but seem to demonstrate "event dilation" by compressing or expanding one's physical position in space and time, as measured by an outside observer, of course. Harvey experiences the same events as Marvin, but in one order or at one interval, while Marvin experiences them occurring in quite another order or at another interval.
As far as any traveling 'backward' in time, it doesn't seem to be a possibility, if only in that it would introduce one or more paradoxes, e.g., killing one's mother before one is born, etc.