Transcripts


Slideshow – Can we travel through time? It’s morning. You wake up in your bed, open the curtains and look out onto the street. You do the same thing every day. But today, something is very different. The cars look strange and some of the buildings are different. And the people are wearing funny clothes! You go into the living room and everything looks odd here too. The furniture is very old-fashioned and the carpet is … interesting. You switch on this vintage TV and see the news. It says it’s 1964! It seems you have travelled back in time! Oh my goodness! Where will you go? What will you do? Who will you look for? What news will you give the people of the past? With all the questions it poses and the situations it presents, time travel makes the perfect device for science fiction films, TV programmes and books. You might think people have been fantasizing about time travel for centuries. Actually, the first account of time travel that really excited the public was in 1895 with The Time Machine by H. G. Wells. It’s no coincidence that this was around the time that Albert Einstein and others were starting to reach a greater understanding of time itself. First, let’s clarify what we mean by ‘time’. It’s funny isn’t it? We talk about time a lot … all the time in fact. But how often do you stop and think about what time is? It’s not as easy as you might think. In fact, two thousand years ago, Aristotle described time as ‘the most unknown of all unknown things’. But over time … there it is again … many people have attempted to define the concept. There are dictionary definitions, like ‘the dimension of the physical universe that orders the sequence of events at a given place.’ And there are also more light-hearted definitions. For example, one physicist described time as ‘nature’s way of stopping everything happening at once’. But for our current purposes, let’s just remind ourselves that time can be described as a dimension – the fourth dimension in fact. A good way to illustrate this is by imagining two planes in the sky and thinking about how they might crash. Now, in order for this to happen, they would need to have all the same three-dimensional coordinates. That is, left and right, up and down and forwards and backwards. If all three sets of coordinates were the same, the planes would be in exactly the same place, right? Well, not if one plane was there two minutes before the other one. In order to be certain that the two planes crash, we need to know they are both at that specific point in space at the same time. In that sense, time is the fourth dimension of something we call ‘spacetime’. So, what has all this got to do with time travel? Well, if we picture spacetime as a four-dimensional piece of fabric, then anything very heavy – the Earth, for example – will cause the spacetime to bend. This bending – or ‘curvature’ – of space around the earth is what we call ‘gravity’. But it also affects time. And this is one way in which we could – potentially – travel through time, because time effectively moves slower closer to earth and


194 English for the 21st Century • Transcripts


faster further away from earth. This is called ‘time dilation’. Imagine there were two twins and one lived at the top of a very high mountain and the other twin lived at the bottom. Because of time dilation, time would actually move very slightly faster for the first twin and therefore she would be older than her twin at the bottom of the mountain. Ok, we’re talking billionths of a second difference here. But imagine the first twin wasn’t at the top of a mountain, but instead she was in a spaceship millions of miles above the earth. In theory, after travelling in the spaceship for twenty years, when she came back to earth she would be noticeably older than her twin. And it’s not only proximity to earth that can affect time. Speed can also make time move faster. Did you know that time goes more slowly for someone on a speeding train than for another observer on the platform? Again, it’s not much slower. At train speeds, it only makes billionths of a second difference. However, if someone was on a train (or again, a spaceship) that travelled at almost the speed of light, in theory time travel might be possible. A year for the passenger of the superfast train would occur at the same time that 200 years passed at the platform. So when he returned, the earth would be a very different place! So are we saying time travel is possible? Professor Stephen Hawking recently said he used to feel like a crank talking about time travel, but these days it is being discussed as a serious topic in the scientific community. Most experts agree that travelling back to a time before now will be impossible. In fact, they maintain that people will only ever be able to travel back to a time when a time machine was invented. So, unfortunately you won’t be able to choose a point in history and go back to see it with your own eyes. But, because of the strange nature of time already discussed, many believe travelling forwards in time could be possible one day. However, as we have learned, it would probably involve spaceships flying much, much faster than anything we have invented so far. And at those sort of speeds, no human would survive. Clearly it will be extremely expensive and require engineering skills we simply don’t have currently. But since time travel might just be possible in the future, let’s look at it from another angle. So far, we have looked at time travel from a physicists’ point of view, but there are also many questions posed by philosophy. It’s time for another thought experiment. Imagine a young time traveller is very angry with his grandfather because of the way the old man has lived his life. So the time traveller decides to go back in time, to when his grandfather was young, and shoot him. He buys a gun and practises his aim every day until he is a top marksman. He then travels back in time, finds his grandfather, aims the gun at him and pulls the trigger. What happens? If he kills his grandfather, then his father will never be born and nor will he. And if he is never born, how is any of this happening. This is called the grandfather paradox. Some philosophers claim it would be impossible for the man to shoot his grandfather. The gun would jam, the bullets would miss or


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