We are all time travelers of course–we travel through time every millisecond of our lives.  It’s just we only move in one direction, into the future.

Conceptually, time travel into the future and into the past are two distinct concepts.  Traveling into the future could happen merely by slowing down your own time, rather than popping in and out of the future like in Primeval.

“If you want to advance through the years a little faster than the next person, you’ll need to exploit space-time. Global positioning satellites pull this off every day, accruing an extra third-of-a-billionth of a second daily. Time passes faster in orbit, because satellites are farther away from the mass of the Earth. Down here on the surface, the planet’s mass drags on time and slows it down in small measures.

We call this effect gravitational time dilation. According to Einstein’s theory of general relativity, gravity is a curve in space-time and astronomers regularly observe this phenomenon when they study light moving near a sufficiently massive object. Particularly large suns, for instance, can cause an otherwise straight beam of light to curve in what we call the gravitational lensing effect.

What does this have to do with time? Remember: Any event that occurs in the universe has to involve both space and time. Gravity doesn’t just pull on space; it also pulls on time.

You wouldn’t be able to notice minute changes in the flow of time, but a sufficiently massive object would make a huge difference — say, like the supermassive black hole Sagittarius A at the center of our galaxy. Here, the mass of 4 million suns exists as a single, infinitely dense point, known as a singularity [source:NASA]. Circle this black hole for a while (without falling in) and you’d experience time at half the Earth rate. In other words, you’d round out a five-year journey to discover an entire decade had passed on Earth [source: Davies].”  http://science.howstuffworks.com/science-vs-myth/everyday-myths/time-travel1.htm

Travel to the past is another thing entirely.  As David comments in Footsteps in Time, if it were possible, why aren’t people from the future stopping by to see us?  The esteemed Stephen Hawking says pretty much this in a long discussion on time travel to the past (holding open the idea of time travel to the future, as described above):  ”Any kind of time travel to the past through wormholes or any other method is probably impossible, otherwise paradoxes would occur. So sadly, it looks like time travel to the past is never going to happen. A disappointment for dinosaur hunters and a relief for historians.”

Read more: http://www.dailymail.co.uk/home/moslive/article-1269288/STEPHEN-HAWKING-How-build-time-machine.html#ixzz1pOekDSod

However, the idea of a multiverse, or a multiple parallel universes is one that holds more credence than you might think:  ”the idea that any given person can exist at the same time in more than one place. If, as humans, we were able to tap into the power of traveling to these other universes, we would be able to ‘meet’ our other selves. While this is a truly powerful thing to think about, one can imagine the possibilities it holds. If your own individual beings could meet and each one had different experiences, think of the intelligence and knowledge you could pass from one to another. Each one would have different experiences and different outcomes. In one world you could be a doctor, in another world a politician, in another world a drug addict. The options would be virtually limitless.”  http://www.quantumjumping.com/articles/parallel-universe/parallel-universes-theory/

“The existence of such a parallel universe “does not even assume speculative modern physics, merely that space is infinite and rather uniformly filled with matter as indicated by recent astronomical observations,” Max Tegmark, a cosmologist at MIT in Boston, Massachusetts concluded in a study of parallel universes published by Cambridge University.

Mathematician Hugh Everett published landmark paper in 1957 while still a graduate student at Princeton University. In this paper he showed how quantum theory predicts that a single classical reality will gradually split into separate, but simultaneously existing realms.

“This is simply a way of trusting strictly the fundamental equations of quantum mechanics,” says Barrau. “The worlds are not spatially separated, but exist as kinds of ‘parallel’ universes.”

The work has another strange implication. The idea of parallel universes would apparently side-step one of the key complaints with time travel. Every since it was given serious credibility in 1949 by the great logician Kurt Godel, many eminent physicists have argued against time travel because it undermines ideas of cause and effect. An example would be the famous “grandfather paradox” where a time traveler goes back to kill his grandfather so that he is never born in the first place.

But if parallel worlds do exist, there is a way around these troublesome paradoxes. Deutsch argues that time travel shifts happen between different branches of reality. The mathematical breakthrough bolsters his claim that quantum theory does not forbid time travel. “It does sidestep it. You go into another universe,” he said. But he admits that there will be a lot of work to do before we can manipulate space-time in a way that makes “hops” possible. While it may sound fanciful, Deutsch says that scientific research is continually making the theory more believable.”

http://www.dailygalaxy.com/my_weblog/2009/05/parallel-univer.html

So it could happen, right?  Maybe not time travel to the past, per se, but traveling to an alternate universe … What do you think?