Time travel 101

By Maarten van Sluijs - 4 October 2023

Travelling back in time

Journeying through time is a dangerous endeavor, so be careful dear Intermaatjes. Should you desire to rewind the clocks and go back to the past with a blast it is important to keep in mind the different methods and modes of time travel. We don’t want to mess up now and erase our own existence now do we? It is important to consider the following question:

“If you travel back in time to the past, was a version of you there already when ‘the past’ happened the first time around?”

I hear the cogs in your head turning, time travel theorizing can be totally tiring. Fret not, for I have foreseen this (or traveled back in time) and prepared a picture for explanation. Behold! My Paint skills1:

1The astute students of you may recognize this from a minutephysics video on time travel. I’ve adapted some of their ideas to write this article.

The image shows a timeline. You’re initially just going along the orange path through time. At some point however, you invent a time machine and decide to go back. Back to where the red line starts. From then onwards, you travel along the red path through time. The idea here is, that even when you were walking the orange path, a version of you from the future was at some point in your timeline, existing simultaneously. “But Maarten, why do I care about this shit picture you’ve drawn”, and “why does it matter how time travel works”, I hear your cries. You see, this is important to note, because it means that you cannot go into the past and change events. The past that you know already includes the actions done by anyone from the future, and so the act of going back and messing with things has already happened and is always meant to happen for your past to be your past. From this follows only one logical conclusion: 

Time travel is purely deterministic, and we are all mere slaves to the ebb and flow of time, completely incapable of having any sort of free will or lasting impactful change on our environment.

Okay, maybe I’m just being a drama queen now. However, it does raise an interesting, wonderfully paradoxical, question:

“If in the future a time machine is invented, and going back in time was always meant to happen, is the only way to actually change the past to not go there at all?”

I’ll leave your lovely little meat computers to ponder that proposition for a bit while we go on to the second type of backwards time travel.

Now this is where shit gets interesting. The second type of time travel is what we’re all dreaming of, where we can go back in time and change the future. This is where we kill baby Hitler. To illustrate this version of time travel, let me delight you once more with Paint. 

In this lovely image, we see the same orange line, nothing new there. However, once we discover the time machine and travel back, we are actually set on a new and different path than the timeline that used to be our past. This means that some or all events that happen in the orange timeline after the branching point don’t exist anymore. In the case of killing baby Hitler it means that World War 2 likely never happened, or for the glass half empty intermaatjes, happened in a different way.

Now, this doesn’t sound all that bad does it? Millions of lives saved, and the name Adolf can be fashionable again. Maybe that is true, but there is a not insignificant probability that it isn’t. Without being creepy like Ian Malcolm, I’d like to bring up a little piece of information from chaos theory known colloquially as the “Butterfly effect”. You’re all smart people, so I’m guessing you’re familiar with it. But if not, let me give you the quick Wikipedia rundown:

“The butterfly effect is the idea that small things can have non-linear impacts on a complex system. The concept is imagined with a butterfly flapping its wings and causing a typhoon.”  - Wikipedia

They say don’t use Wikipedia as a source, but I think this went pretty well. Anyway, I bring this up because even though we might all agree that killing baby Hitler was a solid 10/10 move, it can have disastrous unforeseen consequences. What if events in World War 2 caused your grandparents to meet, and therefore your birth? What if Hitler wasn’t so bad after all and WW2 with Hitler 2.0 is way worse than what we know now. You just can’t know the full consequences of your actions. So, let me impart to you a little bit of wisdom: when you go back to make sure you actually pass that test, or pass up on that extra beer and prevent the hangover, please don’t change too much, I’m quite comfortable with the way things are right now. And if you do, be prepared to rule as the omnipotent deity you are and fix every small issue. You can never be too sure what little nuisance grows to be a genocide.

 Gosh, that sounds tiring now doesn’t it?

Let’s move on to a lighter topic, the actual possibilities of time travel. I assume that like our brief foray into chaos theory, you have all taken the pre-requisite courses and are intimately familiar with the relativistic and quantum mechanical theories. I will therefore not bore you by going over trivialities such as the many-worlds interpretation and wormholes. Instead, I’d like to talk to you about when Stephen Hawking threw a party and no one in the world attended.

You see, Stephen Hawking threw a big party, and invited only time travelers by sending the invitation after the party had concluded. The logic being that if someone from the future had gotten their hands on one of the invitations they would surely cease the opportunity to sip champagne with Mr. Hawking himself. Now unfortunately, this doesn’t actually give any conclusive proof on whether or not time travel is possible. There are two possible reasons Stephen Hawking partied alone that night, the first being:

1.      Time travel is impossible and therefore no one could have been able to rid Hawking of his loneliness

I try not to believe in this reason since I think it would be cool if time travel was possible. The second, and much more hopeful reason is this:

2.      Time travel is possible, however people travelling back in time cannot reveal themselves to people from the past or cannot reveal the existence of time travel or something like that.

Travelling forwards in time

I’m sure you’ve all noticed I’ve blown right past the 45-minute mark, and you’re supposed to have a break now, however let me quickly tell you about the case where time travel is certainly possible, and in fact inevitable. Travelling to the future! We are all expert time travelers in that regard. Furthermore, it is actually possible to change the rate at which we travel to the future, though it can only be sped up unfortunately. People who have seen the movie Interstellar know what I mean. Einstein’s theories of relativity give way to something called “time dilation”. Again, I’ll let Wikipedia do the talking:

“Time dilation is the difference in elapsed time as measured by two clocks, either due to a relative velocity between them (special relativity) or due to a difference in gravitational potential between their locations (general relativity). When unspecified, "time dilation" usually refers to the effect due to velocity.” – Wikipedia

Thanks Wikipedia, for saving me some time! Oh, spoiler alert btw: In the movie Interstellar, time dilation shows up when McConaughey travels much faster than those back on earth. In the movie, when he returns to mankind, he is actually younger than his daughter. Anyway, this would be a case of time dilation because of special relativity. Time dilation from general relativity is actually quite common and is measured a lot. Even more interesting is that it affects the way our GPS systems work. You see, because of time dilation, the clocks in GPS satellites run faster than those on the surface of the earth. The satellites are travelling faster to the future, which needs to be accounted for. So, time travel is not only possible, but also always happening, and actually annoying if you deal with GPS.

Now. I’d like to leave you with some closing remarks, before you go off to your next lecture and forget everything I’ve said. Wanting to go back in time and change things is a very human desire. We strive for perfection and excellence, and when we don’t achieve that it can be tormenting. However, it is important for a healthy mind to be able to let go of the past and play the rest of the game with the cards you’re dealt. Live and let live! Furthermore, don’t worry so much about the future. Do what feels right, even if you’re scared of the consequences.  


Carpe Diem! And see you in the future! 


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