IS TIME TRAVEL POSSIBLE?

IS TIME TRAVEL POSSIBLE?

If humans were to invent a time machine in the future, why have they never traveled back in time to visit us? As far as we know, there are no records... The most famous argument against time travel asks what would happen if you traveled back in time and killed your grandparents before your parents were born. Then you could not have been born. So, either way, it would not be possible for you to kill your grandparents—a relief to grandparents everywhere. Some scientists have come up with an ingenious solution to this paradox. They say that, if you did go back in time, it would be impossible to change anything that would affect things in the time you have come from. So, maybe the gun jams, or the shot misses. They call this idea “self-consistency.” Another answer to the grandparent paradox can be found in quantum physics (the study of subatomic particles). Simply put, it says that a new world opens up for every possible choice. So, if you did choose to kill your grandparents, then you would find yourself living in a parallel world to your own. But in a
next-door world, granny and grandad are alive and well. Phew! Physicist Albert Einstein was a great thinker about space and time. His famous “theory of relativity” shows that time is not fixed. For example, if you were to travel into space at a speed close to the speed of light, and then return to Earth, people on Earth would have aged more than you have. Einstein demonstated this with some very clever math, but his math also showed it was impossible to travel faster than the speed of light. Einstein believed that you needed to travel faster than light to travel through time. So, a no-go.

Even though Einstein thought time travel was impossible, other scientists have used his ideas to theorize how it might be done. Amazingly, they have discovered that there is nothing in the laws of physics to forbid it. Here are two of the time-travel options.

BLACK HOLES, WHITE HOLES, AND WORMHOLES:
Time travel could be achieved using black holes—areas in space where gravity is so powerful that they suck in everything, including light. Black holes could provide the entrance to wormholes—shortcuts through space and time. Wormholes can tunnel through space and time like a worm through an apple, and emerge at the other end through reverse black holes, called white holes. There are a lot of holes in this theory.
Davies surmises that, given our current understanding of the nature of time and physics, time travel into the past simply isn't possible. But the universe is full of mysteries, and one of them -- the hypothetical wormhole -- might just permit such a journey.

"This is a little bit like a tunnel or shortcut between two distant points," Davies says, "So for example, if I had a wormhole here in my hotel room and I jumped through it I wouldn't come out on Pennsylvania Avenue, I'd maybe come out near the other side of the galaxy."

Scientists have theorized that such a shortcut through time and space could be turned into a time machine.

"If a worm hole could exist and could be traversable, then it would provide a means of going back in time," Davies says. "So it all hinges on whether stable wormholes are a reality or if there's some aspect of physics -- not relativity, because there's nothing wrong from that point of view -- but some other aspect of physics might intercede and prevent the wormhole from forming. That's an open question."

World-famous theoretical physicist Stephen Hawking has proposed that wormholes occurring at a quantum level could theoretically provide a foothold for time travel, but University of California at Santa Barbara physicist Andrew Cleland urges caution on that front.

"I'm an experimentalist, and physics is ultimately an experimental science," Cleland says. "Any predictions that are made based on mathematics or on philosophical or intellectual speculation have to pass the test of experiment, and I am certainly not aware of any experiment that demonstrated the possibility of traveling backward in time."

ROLLING UP TIME:
US astronomer Frank Tipler believes it is possible to build a time machine with a piece of incredibly dense material—say 10 times as dense as the Sun. Simply roll it into a cylinder shape a few billion miles long, then set it spinning. Once it’s spinning fast enough, space and time will bend around it. A spaceship sent on a precisely plotted spiral course around it should emerge almost instantly in a different galaxy and time. So, make sure you are up to date with your travel vaccinations. Of course, there are no materials available today that could withstand the massive forces encountered on these “trips.” But scientists are working on that.