Time travel is one of those outlandish concepts that has mesmerised and troubled numerous curious minds, whether from a scientific perspective or just innocent speculation.
As non-scientists, we may perceive the wonders of science in action as ‘miracles’ or ‘magic’. However, it is only through understanding well-substantiated theories and mathematical proof that we come to realise that science is more of a rigorous, tiresome but incredibly rewarding method of investigation, rather than an instant solution to our problems.
No matter how fascinating the concept of time travel sounds, it is important to first define what ‘time’ is.
From a biological standpoint, time is a made-up concept in our minds that allows us to categorise information in a logical fashion. To make sense of the world. Our brain unconsciously organises the different segments of data it receives so that when put together they appear coherent and sensible.
To explain this further, Clap your hands.
The speed of light (300,000 metres per second) is several orders of magnitude faster than that of sound (340 metres per second); when you clap your hands, the information you receive from your eyes (light entering your retina, being processed and recording the image of two hands clapping) is far faster than the information you receive from your ears.
To account for this, your brain waits until it receives the information from your ears and processes it so that both the image of the hands clapping and the sound generated is experienced at the same time.
Imagine how weird it would be to first acknowledge the image and then hear the sound!
Philosophically speaking, it can be argued that our whole lives are a process of time travel.
We are constantly travelling into the future as our bodies grow older – in this sense, we are travelling in time but only in one direction and in a very passive (some might even call it boring) way. So, now what?
Enter Einstein.
Perhaps the greatest mind to have ever graced this earth, Einstein was fascinated with everything pertaining to the field of physics. In 1905 alone, Einstein published five groundbreaking scientific papers. The first paper earned him his doctorate, and the concepts presented in the next four papers helped change our understanding of the universe: Brownian Motion, The Quantum Theory of Light, The Link between and The Special Theory of Relativity.
The second postulate of The Special theory of relativity states:
As measured in any inertial frame of reference, light is always propagated in empty space with a definite velocity c that is independent of the state of motion of the emitting body. Or: the speed of light in free space has the same value c in all inertial frames of reference.
http://hermes.ffn.ub.es/luisnavarro/nuevo_maletin/Einstein_GRelativity_1916.pdf
i.e. the speed of light in a vacuum is constant.
But how does this tie in with time? Suppose you are standing on a train platform and it is very rainy. Ahead, you see a train passing by towards your right. Meanwhile, one of the passengers on the train is sitting by a window. At this exact moment, lightning strikes the ground twice, each site only a few metres apart.
Of course, if the two are striking this exact moment, surely then they must be striking the ground at the same time, albeit in different places – they do and they don’t. From the platform, you observe the strikes occurring at the same time, however, the passenger, as the train’s path is towards your right, observes first the rightmost strike, only for moments later for the leftmost to strike.
But the bolts of lightning hit the ground at the same time – what happened?
The speed of light is constant – it doesn’t change unless it passes through a medium – but even then the effect is way too subtle for us to observe. From your reference point, the lightning bolts strike at the same time as both sources of light travel the same distance to enter your eyes. However, from the passenger’s perspective, this differs as they are moving closer to one source and further away from the other. As a result, they perceive the right lightning strike to have occurred first and the left to have occurred second.
Are either of you wrong? No, because time isn’t absolute; time is relative to your reference point and so we may experience the same event differently. But what does this mean? Perhaps it means that we cannot build a time machine, but rather we can experiment in the present to allow the same event to be perceived differently.
If anything, this demonstrates the beauty of science and its method. Through Einstein’s thought experiment we can come to think that we do not need fancy, magical time machines to do the work for us, but rather through our own intellect and mathematical prowess, we can manage to travel in time – just not in the sense that a child might imagine it.
“The important thing is to not stop questioning. Curiosity has its own reason for existing.”
Albert Einstein
References:
- National Geographic’s “Genius” https://youtu.be/-jJ5PPcLUw8
- David Eagleman’s, “The Brain”
Attributions:
- https://commons.wikimedia.org/wiki/User:Evan-Amos, edits: transparency
- Ha, Sangwoo. (2018). Analysis of Special Relativity Theory in High School Physics Textbooks Under the 2009 and the 2015 Revised Curricula. New Physics: Sae Mulli. 68. 1069-1080. 10.3938/NPSM.68.1069.
Written by Konstantinos Lioulios