WIDE ANGLE: Is time travel possible?

 Time as a Flowing River

"Time flows like a river and it seems as if each of us is carried relentlessly along by time's current. But time is like a river in another way. It flows at different speeds in different places and that is the key to traveling into the future," Hawking writes.

                  

Albert Einstein first proposed this idea 100 years ago that there should be places where time slows down, and others where time speeds up, notes Hawking. "He was absolutely right."

The proof, says Hawking, lies in the Global Positioning System satellite network, which in addition to helping us navigate on Earth, reveals that time runs faster in space.

"Inside each spacecraft is a very precise clock. But despite being so accurate, they all gain around a third of a billionth of a second every day. The system has to correct for the drift, otherwise that tiny difference would upset the whole system, causing every GPS device on Earth to go out by about six miles a day," Hawking writes. The clocks aren't faulty -- it's the pull of Earth that's to blame.

"Einstein realized that matter drags on time and slows it down like the slow part of a river. The heavier the object, the more it drags on time," Hawking writes. "And this startling reality is what opens the door to the possibility of time travel to the future."

Black Holes and Flying at the Speed of Light

The keys to time travel are black holes, objects so dense that not even light can escape their gravitational grip. "A black hole has a dramatic effect on time, slowing it down far more than anything else in the galaxy. That makes it a natural time machine," Hawking writes.

Here's how it might work: Imagine a spaceship orbiting the super-massive black hole at the center of the Milky Way galaxy, 26,000 light years away. From Earth, it would look like the ship is making one orbit every 16 minutes, Hawking writes. "But for the brave people on board, close to this massive object, time would be slowed down," Hawking writes. "For every 16-minute orbit, they'd only experience eight minutes of time." Again, if they circled for five years, local time, 10 years would have passed back on Earth. This scenario doesn't produce the paradoxes inherent in wormhole travel, but it's still pretty impractical, Hawking acknowledge.

But there's one more possibility: traveling super fast. "This is due to another strange fact about the universe," writes Hawking -- the cosmic speed limit: 186,000 miles per second, or the speed of light. "Nothing can exceed that speed. It's one of the best established principles in science,” writes Hawking, but believe it or not, traveling at near the speed of light transports you to the future. Imagine a track that goes right around Earth, a track for a super-fast train. Onboard are passengers with a one-way ticket to the future. The train begins to accelerate, faster and faster. Soon it's circling the Earth over and over again. To approach the speed of light means circling the Earth seven times a second. But no matter how much power the train has, it can never quite reach the speed of light, since the laws of physics forbid it.

"Instead, let's say it gets close," writes Hawking. "Something extraordinary happens: Time starts flowing slowly on board relative to the rest of the world, just like near the black hole, only more so. Everything on the train is in slow motion." This slowed down the time inside the train when you get out of train after one year you would observe 10 years has been past outside the train. Here is how time travel is possible.

This is the burning question in front of the theoretical physicists. Mathematical calculation supports for wormhole theory but in real it has never seen yet. When this theory turns true in future we probably may find out the key of our creator & uncover the secrets of universe.

 (source): Discovery Network

Pradip Subedi

B.Sc 2^nd year (Physics)