At this session, we found out if science fiction, which involved time travel was just fiction, or if it had even an ounce of reality to it. We had Jim Al-Khalili, leading physicist and professor at the University of Surrey and most importantly one of the best storytellers in science, speaking at the session.
“Science is really becoming a part of popular culture,” he mused at the scientific nature of this session becoming a part of a literature festival. He also seemed quite pleased with the over-crowded audience in attendance. “One of the fascinating, exciting things about science is that we can tell stories about the most fantastic world, about the most improbable and ridiculous ideas that are actually part of our own universe,” he says, wiping clean the stereotypes that prevail against science as being boring and dry.
“Is it possible to travel through time?”, Jim Al-Khalili poses the rhetorical question to an audience that eagerly waits for him to answer. “Can we jump to the future? Can we travel to the past?”
Albert Einstein is the answer to our questions, he tells us. His theories of Relativity are what hold the key to unlocking the answers to these mysterious questions. Khalili tells us that there are two theories of Relativity. One is the ‘Special theory’ which was published in 1905, and the second is the ‘General Theory’ which was published ten years later.
“Einstein gave us a new picture of space and time,” Jim Al-Khalili says. Einstein proved the inaccuracy of Newton’s picture of gravity. Einstein said that there is something deeper about gravity. It’s to do with changing the nature of space and time; gravity curves space. We live in three dimensions and Einstein says space is curved. We can imagine it in terms of geometry, Jim says.
Next to him is a huge white screen, accessed by him to show us slides from the PowerPoint presentation he has designed especially for us. He shows us a picture of a triangle and states the simplest of mathematical ‘facts’ everyone is aware of: all the angles in a triangle add up to 180 degrees. But apparently, we have been lied to all our lives, for Jim claims that this is incorrect. It’s not always true. “That is only true if you draw your triangle on a flat piece of paper,” he says. “If you draw it on a curved surface, it’s not the same.”
The example given by him to illustrate his point, is of the Earth. On a picture of the Earth he draws a triangle. Geometry is different when you curve surfaces, he tells us.
Even the mathematics of General Relativity was very difficult. Einstein himself had to learn a new form of mathematics to explain his theory. Theory of Relativity among other things explains the structure of the whole universe. It says the world was born in a big bang and then evolved and expanded into the structure we see. It also tells us about what happens when objects are squeezed very tightly.
“What happens when a stars dies?” he pauses before answering, “Now our sun, when it runs out of hydrogen, it will just collapse in on itself, nothing very dramatic will happen. But if a large star dies, it would explode as a supernova, a massive violent explosion in space possibly leaving behind at the center, an object called the black hole. Now black hole is where a lot of the material of the star has been squeezed so tightly that gravity becomes so powerful that space and time themselves gets curved…” Jim Al-Khalili says. He speaks of the existence of huge massive black holes present at the center of the universe, which eat stars for breakfast. We’re not in danger, Jim assures the fretting audience members, but we can study them to learn more about them.
Einstein’s theory of relativity tells us about the nature of space and time. Einstein proves how time is not separate from space. “Time doesn’t flow at the same rate for everyone. You can change time. You can slow it down, you can speed it up,” Jim Al-Khalili makes it clear that he is not talking about the psychological perception of time.
If you were to travel at the speed of light, then your time would be seen to run slower than if you were not moving. He goes on to speak of the Twins Paradox. This paradox speaks of two twins, Alice and Bob who build a rocket which can travel close to the speed of light. Alice travels, for what she believes, a year. She has aged a year. But when she returns, she finds ten years have gone by. Her twin brother is ten years older. Travelling close to the speed of light gets you to the future.
Gravity slows time down, Jim Al-Khalili says. If you live in a place with a strong gravitational field, you would find you have traveled in the future. We can safely conclude from this, that yes, we can travel forward into the future. But the question of travelling back into the past has to be separately dealt with.
“Time travel into the past is not ruled out by Einstein’s theory of Relativity,” Jim Al-Khalili says. If time travel were possible it would lead to paradoxes, he adds.
Jim Al-Khalili speaks of the Grandfather Paradox, where if one person travels back in time to kill their grandfather, then the person himself will be obliterated. But because he exists at all means his grandfather was not killed, in the first place. And if your grandfather was killed by him, then he cannot exist. This paradox is often used by scientists to show how time travel into the past is not possible. But fret not, for even for this, Jim Al-Khalili says, are solutions and theories.
Some scientists believe we do not live in a universe but in a multiverse, that there are many parallel universes. And if it is true, then it would solve the paradox of travelling to the past, because now, we would have an infinite numbers of future and past realities available. So, if you’re travelling to the past, you travel to a parallel reality, and you can overcome the paradox and kill your grandfather in that universe.
We go back to the subject of black hole. The inside of it is a mystery but we can still speculate. One possibility is that one gets squashed to a point of the zero size. “But another option is that the black hole is a bridge, it’s a tunnel to somewhere else, either within our universe or, if parallel universe exist, into a parallel universe,” he says. We move on to the idea of wormhole, “It allows us to have a shortcut through space,” he begins. He illustrates the workings of a wormhole with an example. He speaks of two points A and B and if one wants to travel from A to B, the shortest way to travel, one would assume, is in a straight line.
“Well, not if you use Einstein’s General Theory of Relativity because Einstein’s relativity tells us that we can bend space through gravity,” he says. So, if we bend space in a way to ensure A falls on top of B, we can travel directly through the tunnel, the wormhole, to reach B. It is called the ‘Einstein-Rosen Bridge’. This is our time machine. If we bend space, it will also affect time.
We can safely conclude that time travel in the future is very much possible. All one needs to do is travel at the speed of light. Time travel to the past may be possible, if parallel universes exist. “Science is all about magic and mystery,” Jim Al-Khalili says, contradictory to people’s opinion that scientists are obsessed with packaging everything neatly.
This brilliant lecture leaves everyone astounded, satisfied yet aspiring to learn more about time travel. The most brilliant aspect of this lecture was that Jim Al-Khalili’s excellent rhetoric allowed even a layman to understand exactly what was happening and be interested. The whole excitement surrounding the idea of time travel received further impetus after this lecture, it proved that time-travel is not just a thing for fiction, it is entirely possible!