Many people always dream of living in another time. Shooting off far into the future to see how the world is going to develop, or travelling back into the past and meeting heroes that are no longer with us. No such time machine is yet to have been invented but will one be made in the future? The argument with this is that if we a time machine was made in the future, we would never have to make one as it we could just pass it back through time to our past selves. However, this causes a problem as it would create a bootstrap paradox.
There are two parts to travelling through time: travelling forwards and travelling backwards. Let’s start off by looking at travelling forwards in time. If I told you that travelling forwards in time was possible, you would probably just think that I meant we are constantly passing through time as each second passes; but then what if I said you could travel forwards in time at a faster rate than everyone else? This is actually very possible and it is partly to do with Einstein’s theory of relativity.
This is a diagram of an immensely accurate clock, made accurate by the speed of light. It is universally known that the speed of light is 299,792,458 metres per second; so by bouncing a beam of light back and forth on a mirror, we can accurately keep time, as shown in the diagram on the left. Now this is where the theory of relativity comes into play. If you were to move this clock through space as well as time, it takes the light longer to bounce between the mirrors, since the speed of light is always the same and the distance it needs to travel is larger. So if we were to replace the clock with a person, time around them would be moving faster. You actually have this happening to you all the time, time passing differently relatively to how fast you are moving. Of course though, this has very little effect and does not change time around you at all by much. So could we travel thousands of years into the future? No. At least not yet. The speed you would have to travel at to make any sort of significant movement through time would be immense. If you travelled at 99.4% of the speed of light (297,993,703.252 metres per second) for 10 years, you would only have travelled 29.4 years into the future from when you first started, gaining 19.4 years. We are quite a long way off travelling that fast. The fastest record speed is 11082.569 metres per second, which is from Apollo 10 re-entering Earth’s atmosphere, after the moon landing in 1969. 11082.569 metres per second is only 0.0036967471% the speed of light, no where near fast enough to make any significant changes to time around you.
We’ve looked at travelling into the future, now let’s look at travelling into the past. This is a lot more complicated than travelling into the future. In theory, it is possible to travel to the past but in practicality it is very improbable. If you think of time and space as a graph with four quadrants, with the y axis being time and the x axis being space, in theory, you would need to bend this graph so that the y axis travelling forwards links up with a previous point on the graph, in the past, just as if you had rolled the graph into a cylinder. So by this theory you would be travelling into the past, by travelling forwards, while bending the whole timeline. This is very complicated, and seems impossible to say the least but there is one thing in our universe that can do this.
Black holes do have the ability to bend time as seen by the diagram above, drawn by Professor Brian Cox. The curved red line represents a person or an object travelling towards a black hole as time passes and the green line represents the observer. Each cross on the red line is a second that has passed and the green dotted line shows how these seconds are seen by the observer. For the object or person, time is carrying on as normal, a second is a second; but to the observer, the seconds are getting longer and longer, light taking longer to travel back, stretching out these seconds and making the person or object appear to be slowing down as they move. As you can see from the final green dotted line, it travels directly up, and will never reach the observer, meaning the person or object will just seem frozen in time to the observer just before that person or object is sucked into the black hole, time appearing to stop. If this effect were to continue, the next step would be time starting to reverse and therefore making time travel into the past possible. However, the point at which the person is frozen in time just before being sucked into a black hole, is also the time that they’re atoms get stretched out into a singularity, and therefore will result in death rather than time travel, even though to an observer they’ll be travelling much slower in time. This means to the best of our knowledge, at this point in time, travelling into the past is not possible.
Getting away from the heavy science, this image above shows a tablet that was carved around 800 years ago. It looks very much like an old Nokia phone, with the 12 keys for a number pad, menu selection keys and a display, although the weird symbols are a bit unexplainable. Many people see this as proof of time travel into the past, as how could a replica of a Nokia have been carved into a tablet 800 years ago? Of course this could just be a coincidence but many conspiracy theorists believe that someone travelled into the past with a Nokia and it was seen by people 800 years ago, or that aliens visited us at a more recent time, took a Nokia, then took it back into the past. Whether this is true is very unlikely but there are many similar examples of this with future technology cropping up in things of the past. One of the more famous examples is what seems to be a laptop in a greek carving, and another laptop cropping up in Egyptian drawings. So maybe it’s possible that we will discover a way to travel into the past at some point in the future; but right now there is no way to, or even any theoretical way to that is fully fledged out.
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