Although most people consign time travel to the realm of science fiction or fantasy, time travel into the future is established scientific fact, and Einstein and numerous physicists have presented the world with irrefutable evidence not only mathematically but in practical experiments like the one conducted by Hafele and Keating in 1971. Two atomic clocks were put aboard a plane which traveled around the world. When the plane landed, the clocks aboard it were "behind" by 59 nanoseconds in comparison to those that had remained on the ground. This is because as the speed increases, the clocks aboard a plane, train, spacecraft or other vehicle "slow down" in relation to clocks that remain behind.
Just as the mechanism of a clock in a vehicle moves more slowly compared to one which is relatively stationary, the metabolism of a human body will slow relatively as well. The heart, the digestive organs, respiration, brain activity, and similar functions will slow in relation to those of the human beings left behind and the faster the speed, the greater the difference. In the well known Twin Paradox, one identical twin leaves earth aboard a spacecraft traveling at a speed close to the speed of light. He travels a distance of five light years, turns around and returns to earth to find that, while he has been away, fifty years have gone by. While he has aged only ten years, his identical twin is now fifty years older. If our traveler had traveled at a greater speed and/or been away longer, the results would be even more dramatic, e.g., he could return to find that his twin had died centuries or even millennia before.
In A Briefer History of Time, Stephen Hawking says flatly, "It is possible to travel to the future. That is, relativity shows that it is possible to create a time machine that will jump you forward in time. You step into the time machine, wait, step out, and find that much more time has passed on the earth than has passed for you. We do not have the technology today to do this, but it is just a matter of engineering; we know it can be done."
Scientists at Fermilab have been able to get protons up to 99.999946 percent of the speed of light using their particle accelerator. In Time Travel in Einstein's Universe: The Physical Possibilities of travel Through Time, the renowned physicist J. Richard Gott says "if we can accelerate protons to greater than 99.995 percent of the speed of light, we could also send off an astronaut at the same speed. It's just a matter of cost." That cost would, he goes on to say, be huge because a human being weighs about 40 octillion times as much as a proton. Sadly, it doesn't appear to be in our immediate future.
Are there any other methods besides achieving speeds near the speed of light? Gott describes another method that would definitely work, but would be even more difficult. The first step is to "disassemble the planet Jupiter and use its material to construct around yourself an incredibly dense spherical shell needed for that mass to collapse to a black hole (for a Jupiter-mass shell, that is a bit bigger than 5.64 meters, roomy enough for you to sit inside)." Gott goes on to provide detailed instructions of the steps necessary to construct this machine. "The bits of mass in the shell would completely surround you, and the forces they exert on you would act in all different directions, canceling each other out exactly, leaving a net zero effect [so] no gravitational forces would affect you." Inside, time would go by four times more slowly than outside the sphere. After what would be 50 years, the occupant would emerge to find that 200 years had gone by. This would work, but no person or government on earth has the resources to construct such a device.
Are there any other methods of travelling to the future? None that we know will work. A number of scientists theorize that wormholes could be used, but this is only a hypothesis. At this point there is no evidence that wormholes even exist.
Nevertheless, time travel continues to fascinate us. It has always been a part of legends, folk tales and myths, always a part of literature and fantasy. Perhaps its day will come sooner than we imagine. Science always surprises us.