Is Time Travel Possible? – Part 1
In an earlier post, we talked about the concept of time where we briefly touched upon the idea of time travel. Now it’s time to delve deeper into that particular subject and offer an opinion on whether or not it’s actually possible. In his book ‘Brief Answers to the Big Questions’, Stephen Hawking said that if anyone applied for a grant to research time travel, that application would be instantly dismissed. Now, he may well have been right about that. But then he also said that time travel is a valid question that could be legitimately attacked with a scientific approach. So, let’s explore what we know about the science behind it so far. Hawking went on to say that time travel can’t be ruled out by our current level of understanding but where does that cautious optimism leave us? There may not be an instruction manual for a time machine in the present but what about in the future?
Let’s first look at what we can do right now. We can video call our family and friends, no matter where they might be, to ask them anything we want. But whether we can find out from that call what activity they are engaged in right at this instant is another thing entirely. The signals that carry their images and voices travel at an incomprehensive speed, but it takes a finite time for them to reach our location. Accessing the “right now” of another person from a great distance was central to Einstein’s theories on time and space.
Albert Einstein said that time and space are just parts of spacetime and that we need to be willing to consider distances in time because we are distances in space. As peculiar as this sounds, we seem to have no problem answering “around seven to eight hours” when asked the distance between London and New York. What we essentially mean is that the flight takes that length of time at a speed of around 500 miles per hour.
An equivalent of that statement would be to say that the distance between London and New York is around 3,500 miles. Physicists Jeff Forshaw and Brian Cox wrote in the book they co-authored ‘Why Does E=mc²?’ that time and space can be interchangeable using something with speed as its currency. Einstein supposed an exchange rate from a time to s distance in spacetime is universal and that that exchange rate is the speed of light.
The problem with causality
No signal can travel faster than the speed of light, which provides us with a finite number on how quickly we can learn what is happening at another location in the world. This offers us causality, which is a law that states effects come after causes. This is a problem for anyone attempting to prove that time travel is possible. For someone to go back in time and conduct actions that would prevent them from being born would be to place effect (the time traveller) before cause (birth).