As a science fiction fan, I was always a big fan of time travel. I used to (still do!) read up or listen to each and every lecture on time travel. There has been no dearth of such movies coming in as well. I recently saw Looper, which was based on the concept of time travel. A well made movie, I must say, regardless of all the loopholes and paradoxes involved. Anyway, coming back to the eternal questions- Is time travel possible? If so, how? Can we travel to our past or into the future? In this post, with ample assistance from Messrs. Einstein and Hawking, I will attempt to tackle a few of those queries.
Believe it or not, the concept of time travel was first introduced by Einstein back in 1905. In his superhit 'General Theory of Relativity', he introduced the concept of the fourth dimension. We all know any point can be measured in three dimensions (x, y, z). Einstein proposed that there is yet another dimension, which along with the other three, will determine the exact position of the point. Yes folks, that quantity is 'time'. He said that since time itself is a variable (not constant as we all thought), there exists four dimensions - space (x, y, z) and time (t). Together, he called it space-time (t, x, y, z). He also proposed that space-time is a curved, or warped fabric. To understand this, consider a thin rubber sheet suspended in mid-air. Let us suppose this sheet is the space-time fabric. Now, when we place a ball on top of this sheet, the sheet will bend downwards (curve) under the mass of the ball. The ball here is equivalent to a star, or any other heavenly body. Hence, a star causes the space-time fabric to curve. Higher the mass of the star, higher the curve in space-time. This was later proved by numerous experiments. So, according to Einstein, if we can curve space-time sufficiently, we can travel through time.
Okay, hold on now! How is that even possible? Enter Prof. Stephen Hawking. In one of his hugely popular lectures, he touched on the topic of 'wormholes'. A wormhole is a point in the space-time fabric, which theoretically is a gateway to another dimension, a parallel universe. It is basically a gap in space-time, which can transport us through time. Hawking proposed that wormholes are all around us (there may be one right next to where you are sitting!). However, they are too tiny to have any significant impact. Any thing, if looked under the microscope, will have small holes or gaps, or a crack. Same is true of space-time. It has tiny cracks all over, which are all potential wormholes. Hawking said that if we can somehow enlarge those wormholes sufficiently, we can use them to travel to the past!
So let us dwell a bit on the topic of traveling to the past. As mentioned earlier, if we can enlarge those gaps in space-time, we can travel to the past. However, according to Hawking, there would be so much radiation and electromagnetic waves going in and out of the wormhole, that the wormhole will collapse within a few milliseconds of its formation. Bad luck folks! It seems like wormholes are highly unstable, and cannot be used for time travel. Well, at least not today. Okay, so let us suppose in the future, we do build a device that can stabilize a wormhole. This would make time travel to the past possible. However, if that is true, why don't we have visitors from the future coming in, and sharing that knowledge? It is human nature to show off, so surely travelers from the future would have come here to boast!
Also, there are many paradoxes involved in traveling to the past. Let us take a simple one. Suppose a scientist successfully creates a wormhole that takes him one minute into the past. He comes out and notices his old self standing. He then shoots down his old self. How, then, can he justify himself being there?
Let us take another interesting one. Let us say a scientist wants to build a time machine which will take him into the future. He tries a lot, but remains unsuccessful. Suddenly, there appears an old visitor from the future. He teaches the young scientist how to build the machine. Thrilled, the scientist travels to the future, and spends several years there, enjoying himself. He then realizes that he should share this knowledge with the people in the past. So, he uses his machine to travel to the past. On reaching there, he finds his younger self, sitting and wondering how to build the machine! This would mean that he has taught himself how to build the machine. If that is so, where did the original idea of building the machine come from?
According to Hawking, this is against the laws of nature. The 'effect' can never precede the 'cause'. That is not how nature works. Considering all these points, time travel to the past seems impossible, or at most, highly unlikely.
What about the future then? We can at least go there, right? Yes, we can! All we need to do, is go fast. Really, really fast. Einstein proved that mass is directly related to time. Time tends to move faster when we are closer to a massive object. This means that if a few of us decided to live in space, we would age slower than those living on earth (since we would be further away from the earth's mass). If we come back from space after a few years, we would notice that all others have aged more than us. In fact, the clocks on the satellites orbiting earth need to be corrected everyday to account for the time lag on earth. However, the difference is actually negligible.
Now, let us get to the moving fast part (who doesn't like speed!). Hawking says that all we need to do to travel into the future, is to move close to the speed of light (easier said than done, professor!). In his lecture, he gave the following hypothetical scenario - Let us say we build a train line, for a superfast train. This line goes all around the earth in a circle. A few brave souls decide to board this train. The train starts its journey around the earth, and slowly starts gathering speed. After some time, it almost reaches the speed of light. This would mean that it is making seven revolutions around the earth per second! At this scary speed, time would slow down considerably inside the train. Let us suppose the train keeps going around the earth for 100 years (who will bear the ever-rising fuel expenses?). For the people inside the train, only one week would have passed! That is the extent to which time would have slowed down! When they finally come out from the train, they would be effectively transported 100 years into the future. Awesome, right? Yes, surely, but the practicality is questionable at this point, or is it?
We already have a similar structure in place underground, which is accelerating particles at the speed of light! The Large Hadron Collider (LHC) at CERN is emulating time travel as we speak! And what's more, the particles inside the LHC which are traveling at the speed of light, are decaying slower then they would have normally done! Importantly, it shows us that Einstein was correct all along. Time is not constant for everyone as we previously thought. It is a variable which depends on a number of factors, including mass and speed. This makes time travel possible (Yay!).
The brilliant mind of Stephen Hawking deduced another interesting theory. Our universe is filled with dark beasts, creatures that swallow up everything in their path. They are called black holes. Black holes are super-massive points in space with infinite gravity. Such is the strength of its pull, that even light cannot escape from it. More importantly, due to the fact that it is super massive (normally a million times the mass of our sun), it curves space-time so much that standard laws of physics fail there. As Einstein, had pointed out, since it curves the space-time fabric considerably, this makes a black hole a natural time machine.
If we think along similar lines and someday are able to create a sustainable mini black hole on earth, we would effectively create a portal to travel through time. Of course, to create such a mini black hole is no easy task, not to mention putting our entire existence at risk! Moreover, it would be a one-way ticket into the future, with no way back to the present. Nevertheless, it provides yet another possibility of time travel.
I am sure you have noticed that I have always questioned the practicality of each scenario. You may think that all the above scenarios are impossible to create. However, science is constantly evolving. We have passed through the phase when the earth was thought to be flat, when the universe was thought be to stationery, when the earth was thought to be the center of the universe, so on and so forth. Hence, it is safe to think that at some point down the line, we may be able to put these theories into practice.
The bottom-line, though, is that time travel is theoretically possible. We are now poised at the threshold of the unknown, with infinite possibilities ahead of us. Hopefully one day, we would be able to book our tickets to the future. For now, let us keep using the only method of time travel available - sleep! Close your eyes, and when you open them after a nap, whoosh, you are transported a few hours into the future!
The following limerick does justice to everything we discussed in this post:
There was a young lady of Wight,
Who traveled much faster than light,
She departed one day,
In a relative way,
And arrived on the previous night.