After reading this article, many people are going to ask me how this article belongs to a science blog and not a space blog. Well, the answer is, the possibilities I am going to describe here have been postulated by well-known theories of Science! Okay then, read on to find out what I mean.
Introduction
In some sense, we are all time travelers. As you sit at your desk, doing nothing more than clicking your mouse, time is traveling around you. The future is constantly being transformed into the past with the present only lasting for a fleeting moment. Everything that you are doing right now is quickly moving into the past, which means we continue to move through time.
Well, the idea for time travel has existed from the time of Mahabharata, but it gained some popularity around the time Einstein was around. So, its his contribution to relativity and Hawking's deep imagination that govern modern day concepts of time travel.
Understanding Time
Ask any person around you to define 'Time' and he'll start staring at a watch or a clock. But, in understanding time travel, we need to know that time is actually a fourth-dimension intermingled with space, giving rise to something known as the Space-time Continuum. AND according to Einstein's Theory of Special Relativity, time slows as an object nears the speed of light. This leads many scientists to believe that traveling faster than the speed of light could open up the possibility of time travel to the past as well as to the future. But, the problem is no object with a mass can travel at the speed of light, a fundamental law of physics. As an object nears the speed of light, its relativistic mass increases until, at the speed of light, it becomes infinite. Accelerating an infinite mass any faster than that is impossible, or at least it seems to be right now.
Theoretically possible Ways of Time Travel
I am going to outline here the possible ways with current technology by which time travel is possible,
The men pictured here have made great contributions to the concepts of time travel, and one of them continues to do so.
Time is a forth-dimension as stated by these men. This concept is not as head-banging as it seems at first. Hawking uses the example of driving in your car: You go forward. That's one direction. You turn left or right, that's a second. You journey up a mountain road, that's a third. The fourth dimension is time. This dimension is a length in time. While a human may survive for 80 years, the stones at Stonehenge, for instance, have stood around for thousands of years. And the solar system will last for billions of years. Everything has a length in time as well as space. Travelling in time means travelling through this fourth dimension.The laws of physics actually accommodate the notion of time travel, through portals known as wormholes.
"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.
Introduction
In some sense, we are all time travelers. As you sit at your desk, doing nothing more than clicking your mouse, time is traveling around you. The future is constantly being transformed into the past with the present only lasting for a fleeting moment. Everything that you are doing right now is quickly moving into the past, which means we continue to move through time.
Well, the idea for time travel has existed from the time of Mahabharata, but it gained some popularity around the time Einstein was around. So, its his contribution to relativity and Hawking's deep imagination that govern modern day concepts of time travel.
Understanding Time
Ask any person around you to define 'Time' and he'll start staring at a watch or a clock. But, in understanding time travel, we need to know that time is actually a fourth-dimension intermingled with space, giving rise to something known as the Space-time Continuum. AND according to Einstein's Theory of Special Relativity, time slows as an object nears the speed of light. This leads many scientists to believe that traveling faster than the speed of light could open up the possibility of time travel to the past as well as to the future. But, the problem is no object with a mass can travel at the speed of light, a fundamental law of physics. As an object nears the speed of light, its relativistic mass increases until, at the speed of light, it becomes infinite. Accelerating an infinite mass any faster than that is impossible, or at least it seems to be right now.
Theoretically possible Ways of Time Travel
I am going to outline here the possible ways with current technology by which time travel is possible,
The men pictured here have made great contributions to the concepts of time travel, and one of them continues to do so.
Time is a forth-dimension as stated by these men. This concept is not as head-banging as it seems at first. Hawking uses the example of driving in your car: You go forward. That's one direction. You turn left or right, that's a second. You journey up a mountain road, that's a third. The fourth dimension is time. This dimension is a length in time. While a human may survive for 80 years, the stones at Stonehenge, for instance, have stood around for thousands of years. And the solar system will last for billions of years. Everything has a length in time as well as space. Travelling in time means travelling through this fourth dimension.The laws of physics actually accommodate the notion of time travel, through portals known as wormholes.
"The truth is wormholes are all around us, only they're too small to see. They occur in nooks and crannies in space and time," Hawking writes. "Nothing is flat or solid. If you look closely enough at anything you'll find holes and wrinkles in it. It's a basic physical principle, and it even applies to time. Even something as smooth as a pool ball has tiny crevices, wrinkles and voids."
Quantum Foam and Nano-Warmholes
"Down at the smallest of scales, smaller even than molecules, smaller than atoms, we get to a place called the quantum foam. This is where wormholes exist. Tiny tunnels or shortcuts through space and time constantly form, disappear, and reform within this quantum world. And they actually link two separate places and two different times."
The tunnels, unfortunately, are far too small for people to pass through -- just a billion-trillion-trillionths of a centimeter -- but physicists believe it may be possible to catch a wormhole and make it big enough for people, or spaceships, to enter, Hawking writes.
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| Artist's Impression of a Wormhole |
"Theoretically, a time tunnel or wormhole could do even more than take us to other planets. If both ends were in the same place, and separated by time instead of distance, a ship could fly in and come out still near Earth, but in the distant past. Maybe dinosaurs would witness the ship coming in for a landing," Hawking writes.
Ultimately, scientists may find that only travel into the future is possible, as the laws of nature may make travel to the past impossible so the relationship between cause and effect is maintained. For example, if you could travel in the past and do something that prevents yourself from being born, how could you exist in the future to travel back in time?
The Flowing River of Time
Hawking suspects radiation feedback would collapse any wormholes scientists managed to expand to useable sizes, rendering them useless for actual travel. But there's another way -- navigating the variable rivers of time.
"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, is above our heads, 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." This effect is caused in accordance to the equivalence principle of relativity.
Einstein realised 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. And this startling reality is what opens the door to the possibility of time travel to the future.
| Artist's impression of a Supermassive Black Hole |
Right in the centre of the Milky Way, 26,000 light years from us, lies the heaviest object in the galaxy. It is a supermassive black hole containing the mass of four million suns crushed down into a single point by its own gravity. The closer you get to the black hole, the stronger the gravity. Get really close and not even light can escape. A black hole like this one has a dramatic e ffect on time, slowing it down far more than anything else in the galaxy. That makes it a natural time machine.
I like to imagine how a spaceship might be able to take advantage of this phenomenon, by orbiting it. If a space agency were controlling the mission from Earth they'd observe that each full orbit took 16 minutes. But for the brave people on board, close to this massive object, time would be slowed down. And here the e ffect would be far more extreme than the gravitational pull of Earth. The crew's time would be slowed down by half. For every 16-minute orbit, they'd only experience eight minutes of time. Thus when they return to earth after spending 5 years orbiting the black hole, ten years would have passed for the people back on earth. This implies that the people on the spaceship have time-traveled 5 years into the future of Earth.
Superfast Travel
This scenario doesn't produce the paradoxes inherent in wormhole travel, but it's still pretty impractical, Hawking acknowledges.
"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.
But there's one more possibility: traveling super fast.
"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 happens to protect the cosmic speed limit, Hawking said. Here's why:
Say there's a child running forward up the train. "Her forward speed is added to the speed of the train, so couldn't she break the speed limit simply by accident? The answer is no," writes Hawking. "The laws of nature prevent the possibility by slowing down time onboard. Now she can't run fast enough to break the limit. Time will always slow down just enough to protect the speed limit."
This is the essence of why time travel into the future is possible.
"Imagine that the train left the station on January 1, 2050. It circles Earth over and over again for 100 years before finally coming to a halt on New Year's Day, 2150. The passengers will have only lived one week because time is slowed down that much inside the train. When they got out they'd find a very different world from the one they'd left. In one week they'd have travelled 100 years into the future," Hawking writes.
Right now, the fastest motion on Earth is taking place in the circular tunnels of the world's largest particle accelerator at CERN, in Geneva.
"When the power is turned on (particles) accelerate from zero to 60,000 mph in a fraction of a second. Increase the power and the particles go faster and faster, until they're whizzing around the tunnel 11,000 times a second, which is almost the speed of light. But just like the train, they never quite reach that ultimate speed. They can only get to 99.99 per cent of the limit. When that happens, they too start to travel in time. We know this because of some extremely short-lived particles, called pimesons. Ordinarily, they disintegrate after just 25 billionths of a second. But when they are accelerated to near-light speed they last 30 times longer."
To accelerate humans to that speed, we'll need to be in space, concludes Hawking, noting that so far, the fastest that people have traveled is 25,000 mph aboard Apollo 10.
"To travel in time we'll have to go more than 2,000 times faster (than Apollo 10). And to do that we'd need a much bigger ship, a truly enormous machinebig enough to carry a huge amount of fuel, enough to accelerate it to nearly the speed of light. Getting to just beneath the cosmic speed limit would require six whole years at full power.
"We could, in theory, travel extraordinary distances within one lifetime," Hawking writes. "A trip to the edge of the galaxy would take just 80 years."
Yes, I feel Hawking is true and one day we'll be able to travel in time.
A Special Thanks to Mr. Stephen Hawking for his contribution to this article.
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