In movies, the time traveler usually steps into the machine and vanishes. Then instantly reappear between cowboys, knights, or dinosaurs. What these movies show is basically time teleportation.
Scientists don’t believe the concept exists in the real world, but neither does it relegate time travel to crackpot territory. The devil is in the details.
Time travel to the near future is easy. Right now, we’re doing it at a rate of one second per second, but physicists say the rate could change. According to Einstein’s special theory of relativity, the flow of time depends on the speed of movement. The faster you move, the slower the seconds pass.and according to Einstein Universal According to the theory of relativity, gravity also affects watches. The stronger the nearby gravity, the slower the time.
Drexel University cosmologist Dave Goldberg said:
If a person hangs out near the edge of a black hole whose gravity is staggering, it could take only a few hours to pass while 1,000 years have passed for someone on Earth, says Goldberg. If anyone who was near the black hole returned to this planet, they would have effectively traveled into the future. “It’s totally incontrovertible.”
But going backwards in time is nasty (worse than being torn to shreds in a black hole). Scientists have come up with a few ways it might be possible, and have recognized the paradox of time travel in general relativity for decades.Fabio, physicist at the Nordic Institute for Theoretical Physics Costa says that early time travel solutions began with scenarios written in the 1920s. The idea involved a giant long cylinder spinning at high speed like a straw rolled between the palms, with an accompanying twisted space-time. The understanding that this object could act as a time machine allowing travel to the past came in the 1970s, decades after scientists discovered a phenomenon called the “closed temporal curve.” only happened.
“A closed temporal curve represents the trajectory of a hypothetical observer, who at some point finds himself in the same place and time as he started, constantly moving forward in time from his point of view. Realize and create a loop, ”says Costa. “This is possible in a region of spacetime that is distorted by gravity and loops on itself.”
“Einstein read [about closed timelike curves] And I was very disturbed by this thought,” he adds.
Science started taking time travel seriously in the 1980s. For example, in 1990, Russian physicist Igor Novikov and American physicist Kip He Thorne jointly published a research paper on closed time-like curves. “They started researching not just how to build a time machine, but how it works,” says Costa.
But just as importantly, they explored the issue of time travel. For example, what if you throw a billiard ball into the time machine, and the ball travels to the past, colliding with your past self and preventing your present self from entering the time machine? “It looks like a paradox,” says Costa.
Since the 1990s, there has been occasional interest in this topic, but little progress has been made. This field is not very active today. One of the reasons is that there is a problem with all models of the proposed Time his machine. Gaurav Khanna of the University of Rhode Island said:
For example, most time travel models require negative mass and therefore negative energy. Because Albert he revealed when Einstein discovered his E=mc.2, mass and energy are the same thing. At least in theory, just as charge can be positive or negative, so can mass, but no example of negative mass has yet been found. Why would time travel rely on such exotic matter? Often wormholes (space-time tunnels predicted by general relativity that connect one point in the universe to another) should be left open.
Without the negative mass, gravity would cause this tunnel to collapse. “You can think of it as counteracting any positive mass or energy that tries to pass through the wormhole,” he says Goldberg.
Although Khanna and Goldberg agree that matter with negative mass is unlikely to exist, Khanna notes that some quantum phenomena, for example, the possibility of negative energy on very small scales. It is pointed out that But that’s “far from the scale needed” for a realistic time machine, he says.
These challenges explain why Khanna initially discouraged Caroline Mallary, then a graduate student at the University of Massachusetts-Dartmouth, from doing a time travel project. Malally and Khanna go ahead anyway and come up with a theoretical time machine that doesn’t require negative mass.In simplified form, Malally’s idea involves her two bodies, each made of normal matter. Includes 2 parallel cars. With one parked and the other zoomed in with extreme acceleration, a closed time-like curve forms between them.
It’s easy? But while Malalee’s model removes the need for negative matter, it adds another hurdle.In order to affect space-time in a way that is useful for time travel, we need an infinite density inside the car.Black holes An infinite density is found inside the . Gravity is so strong in a black hole that it squashes matter into a dauntingly small space called a singularity. In the model, each car should contain such a singularity. “One of the reasons this kind of research hasn’t been done actively, he says, is because of these limitations,” he says.
Other researchers have created models of time travel involving wormholes, or space-time tunnels from one point in the universe to another. “It’s like a shortcut through space,” says Goldberg. Imagine accelerating one end of a wormhole to near the speed of light and sending it back to where it came from. “These he two sides are no longer in sync,” he says. One is in the past. One is the future. ” If you walk between them, you are time traveling.
Something similar can be achieved by moving one end of the wormhole near a large gravitational field, such as a black hole, and keeping the other end near a smaller gravitational field. That way, time slows down on the side of greater gravity, essentially allowing particles or other clumps of mass to exist in the past relative to the other side of the wormhole.
However, creating wormholes requires nasty negative mass and energy. Wormholes created from normal mass collapse due to gravity. “Most designs tend to have similar problems,” Goldberg says. It’s theoretically possible, but there’s currently no way to make something like delicious, zero-calorie pizza.
Perhaps the problem is that not only do we not know how to build a time travel machine, we can only build it on a microscopic scale. This is what the late physicist Stephen Hawking believed. He proposed a chronological protection conjecture. The universe does not allow time travel, as it does not allow changes to the past. In a 1992 paper, Dr. Hawking wrote, “There appears to be a chronological protection agency that prevents the emergence of closed temporal curves and makes the universe safe for historians.” Physical Review D.
Some of his reasoning included paradoxes created by time travel, such as the aforementioned billiard ball and its counterpart, the grandfather paradox. I couldn’t time travel because I was born, and I couldn’t kill my grandfather. Yet you are there.
But it’s these complexities that interest Massachusetts Institute of Technology philosopher Agustín Lajo. They also cast doubt on free will. If physics says you can go back in time, why Can’t you kill grandpa? “What’s stopping you?” he says. aren’t you free?
However, Rayo believes that time travel is consistent with free will. “The past is the past,” he says. “In fact, even if my grandfather survived long enough to have children, going back in time would not change that. All I know is that I somehow fail.
This means that if you go to kill your grandfather, you may slip a banana on the way or miss the bus. “It’s not like finding a special power to force you not to,” says Costa. “You wouldn’t do it for completely mundane reasons.”
In 2020, Costa worked with Jermaine Tovar, then an undergraduate at the University of Queensland, Australia, on the mathematics underlying similar ideas. Time travel is free from paradoxes and is possible if you have the freedom of choice.
Goldberg kind of agrees with them. “I am definitely [thinking that] If you have time travel, it will be constructed in a way that creates a coherent view of history,” he says. “Because that seems to be how all the rest of our laws of physics are constructed.”
No one knows what the future holds for time travel to the past. And so far, travelers have never told us about it.
