What if tomorrow, you woke up in the past? What if, when you went outside, the only vehicles you saw were horse-drawn carts? In fact, the only roads that are paved and only appear when you get closer to the town. The town itself has a main drag including, yes, a vintage barber shop. And a barber shop pole. You have woken up in the past.
What if, during your time in the past, you killed somebody? And that somebody turned out to be none other than your great-grandfather? This is of course one of the most simple and famous paradoxes of time travel. This one in particular is explored in the Back to the Future movies (highly recommended). Also in the science fiction short story called The Sound of Thunder. For those uncultured among us, I’ll summarise as quick as I can:
- Guys in the future invent a time machine.
- They go back in time to hunt a Tyrannosaurus Rex.
- One of the crew accidentally crush a butterfly.
- This single event has repercussions which drastically affect their present.
This is of course known as the butterfly effect. The effect of every action possibly having severe consequences in the future is known as the Grandfather Paradox. The impossibility lies in the fact that if one kills their own ancestor, they will never be born. If this is the case, then how could they even travel back in time in the first place? The simple and most obvious solution to this paradox is that the universe would prevent such impossibilities would occur. That is, time travel is not possible. The second possibility is that of parallel universes. This concept is pretty difficult to explain; it’s a bit of a mindblow. The basic idea is that if you alter anything in the past, a separate universe is instantly created in which the effects of changing the past can be seen. This in itself creates even more paradoxes (paradi?). When the time traveller returns to the present, which present will he be in? The affected one or the original universe?
This opens up some really cool possibilities. Do parallel universes already exist? If so, how many are there? Do we live in a parallel universe, or the ‘original’? How different are parallel universes?
My own personal opinion is that if you could manage to travel back in time, you wouldn’t be able to change anything. You would be much like a ghost, not a part of the physical reality of your environment. You can perceive the past, but you cannot edit it. Kind of like viewing a ‘read only’ version of the past universe. This opens up the possibility that time travellers are already among us. The popular theory that if time travel were possible, we would know about it because of contact from people from the future becomes irrelevant, because we wouldn’t know that they’re here.
Another huge paradox – is it possible for there to be two of yourself in the universe at the same time? What if you were to visit yourself? This paradox is far more philosophical. Physically it is possible for one set of billions of atoms to be identically arranged to another billion atoms, although the chances of that occurring are slim. The essence of a person is a little more complicated. This is the part of you that defines you as being you. And for you to be truly you, there can only be one of you. I’ll try to explain. When somebody describes your location, they say you are over there, and point to the spot. You cannot be over here while you are over there. This is called the principle of noncontradiction. Two contradictory facts cannot both be true at the same time. For the same reason, you cannot describe a person as being one thing and another. For this to be true, there can not be two identical versions of you on earth at the same time. I hope I explained that concept well enough to be understood. It’s scarily complicated.
Another point to consider is the location of the past. I mean, if you’re going to travel to the past, you need to have somewhere to travel to. Where is the past? Only the present moment in time exists, the future does not yet exist, and the past no longer exists. Or does it? Is the past stored in some way in the nature of the universe? One suggestion I would have is to reverse everything that has ever been done to travel into the past. If we as humans could somehow find that all subatomic particles have within them a record of where they have been relative to each other, and how they have reacted with each other, we may also find a way to trace back this path through history, to reverse all of time. The only problem with this is, it may not be selective. You may not be able to reverse just some of the universe, or everything excluding the time machine itself. The most likely case would be the reversal of the entire universe, including the invention of the time machine, and the memories of the person who invented it. Life up until that point would simply be relived by everybody on earth. For all we know, it may have already happened. We can’t tell. It’s a very difficult concept to explain well, and I think I did a pretty terrible job.
But I think we’re a long way ahead of ourselves. These are all paradoxes which all point towards one simple fact – time is a dimension which can only be measured at a constant rate, which is pre-defined. The closest humans have come to postulating time travel is wrapped up in Einstein’s theory of relativity. Even so, it would require something to be able travel faster than the speed of light. As far as we know, that’s also impossible.
So, time travel. It would be absolutely awesome if it were developed. But it might also wreck some sort of fundamental aspect of the universe. Then we would have nowhere to live.
If you want something extra on time travel, check this video out. VSauce is probably one of the best Youtube channels when it comes to explaining heavy science.
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