Numerous atomic clock experiments have confirmed Einstein's calculation that the closer you are to the Earth's center of gravity, which is the Earth's core, the slower you will age. In one of these experiments, an atomic clock was taken from the National Bureau of Standards in Washington, D.C., near sea level, and moved to mile-high Denver. The results demonstrated that people in Denver age more rapidly by a tiny amount than people in Washington.
If you would like gravity's space-time warp to extend your life, get a home at the beach and a job as a deep-sea dever. Avoid living in the mountains or working in a skyscraper. That advice, like the advice about flying around the world, will enable you to slow your aging by only a few billionths of a second. Nevertheless, those tiny fractions of a second add up to more proof that time-stretching is a reality.
According to scientific skeptics, time reversal ―travel to the past ―for humans would mean an unthinkable reversal of cause and effect.
This reversal would permit you to do something in the past that changes the present. The skeptics worry that you even might commit an act that prevents your own birth.
Some scientists believe we should keep an open mind about time reversal. Open-minders speculate that time-travelers who change the past would be opening doors to alternative histories, rather than interfering with history as we know it. For example, if you prevented the assassination of Abraham Lincoln, then a new line of historical development would be create. The alternative history ― the one without Lincoln's assassination ― would have a completely separate, ongoing existence. Thus, no change would be made in anybody's existing history. Another possibility is that nature might have an unbreakable law preventing time travelers from changing the past.
If we did discover a source of energy that would enable us to travel beyond lightspeed, we might have access not only to the past, but also to the future. Suppose you went on a super-lightspeed trek to the Spiral Nebula in the Andromeda Galaxy. that location is separated from Earth by 1,500,000 lightyears, the distance light travels in 1,500,000 years. Suppose you make the round trip in just a few moments. If all goes well, you'll return to the Earth 3,000,000 years into its future, because that's how much Earth time will have elapsed.
Time is an abstraction. In other words, it cannot be seen, touched, smelled, or tasted. It seems to have no existence apart from the events it measures, but something tells us that time is out there, somewhere. "When we pursue the meaning of time," according the time-obsessed English novelist-playwright J.B.Priently, "We are like a knight on a quest, condemned to wander through innumerable forests, bewildered and baffled, because the magic beast he is looking for is the horse he is riding."
What about our quest for particles that travel faster than light? If we find them, will we be able to control their energy to tour the past? If we find them, will we be able to control their out mistakes and suffer the same consequences? Or will we be able to use our experience to make everything turn out better the second time around?
Will we ever be able to take instant trips to the distant future, the way people do in the movies, with a twist of a dial and a "Zap!, Zap!" of sound effects?
One cannot resist the temptation to respond that only time will tell.