The laws of physics allow for time travel. So why haven't humans become chrono-hoppers?
In movies, time travelers enter a machine and-poof.-they disappear. Then, they find themselves among cowboys, knights, or dinosaurs. Such movies basically show the time teleportation.
Scientists don't think this concept is possible in the real world, but they also don't relegate time travel to the realm of crackpots. Of course, the laws of physics allow chronological leaps, but the devil is in the details.
Time travel into the near future is easy: You're doing it at a rate of one second per second right now, and physicists say that rate could change. According to Einstein's special theory of relativity, the flow of time depends on how fast you're moving. The faster you're moving, the slower the seconds go. According to Einstein's general theory of relativity, gravity also affects clocks: the stronger the gravity nearby, the slower time goes.
Time passes significantly slower near huge bodies, near neutron stars, or even near the surface of the Earth, if even a very slight effect, says Dave Goldberg, a cosmologist at Drexel University.
Imagine if somebody is hanging on the edge of a supermassive black hole-where gravity is so strong-and that it took 1,000 years for a person on Earth, Goldberg said. If he finally moved back to this world, he effectively traveled into the future. "It's real," he said. "It's not completely controversial.
Going back in time is trickier, though-much trickier-than being torn apart inside a black hole. Scientists have devised a number of ways to do it, and they've known about the time travel paradoxes of general relativity for decades. Fabio Costa, physicist at the Nordic Institute for Theoretical Physics says the original solution to time travel was based on a vision written in the 1920s. This would involve a gigantic, long cylinder, rotating extremely fast, almost as one would twist a straw by twisting between one's palms. Decades later after scientists found an interesting phenomenon now known as "closed time warps", they also found out it can serve as a time machine through which the human being travels in time into the past and meets the present themselves- back in the 1970s.
"A closed time warp describes the trajectory of a hypothetical observer, always moving forward in time from their own perspective, and at some point creating a loop in time and space at the same point they started from," Costa says. "This is possible in a region of space-time that is distorted by gravity and loops back on itself."
"Einstein read about it and was very excited by the idea," he adds. The phenomenon though led to further research.
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