If you like sci-fi and time travel movies, you may have dabbled with the idea of what you would do if it was possible in real life. And if you are in the soldiering business, you may have wondered how you might have changed the course of history — preventing a terrorist attack, stopping this or that war.

I always found stories and movies dealing with time travel fascinating. The idea that armed with the 20/20 vision of hindsight and modern scientific knowledge, you could make a huge impact on world history is both amazing and terrifying at the same time, and the paradoxes created by such actions are really mind-boggling.

Yes, you stopped Hitler and Germany was not turned Nazi thus averting WW2 and the deaths of millions. But what are the second and third order effects? Maybe the USSR becomes the next threat, like in the hit game for us older folks Red Alert, and by stopping WW2 and averting seventy million deaths you create a war that cost humanity two hundred million dead. Not to mention the immediate dangers you create for your own self with that change.

WW2 made people from all over the world to change their daily life for one reason or the other, and the conditions during the war and immediately after affected billions. It is the 50s and your grandpa is stationed in Germany where he is to meet your grandma. If WW2 doesn’t happen, your grandpa will never be in Germany at that time, and just like that you have erased yourself from existence.

BUT! if you were never born then you never get to change the past and your grandparents meet and your parents are born and tada! there you are again … going in the time machine.

That is a variation of the so-called grandfather paradox.

All that without mentioning that even if you don’t erase yourself out of existence either permanently or temporarily, you wipe out the reason for you to go back in the first place.

“Adolf Hitler? Who is that dude?” But if no one remembers Hitler then no one has reason to go back in time and kill him, and if no one goes back in time to kill him then Hitler lives and WW2 plays out as we know it and … and … and …

This concept is so pervasive that it even has its own name: the “Hitler Murder Paradox.”

I recently saw a very interesting video on YouTube, on a channel I suggest you to follow if you like swords and history, called Skallagrim. In the video, Skallagrim Nilsson was examining how much of a positive experience it would be if you could visit the middle ages. SPOILER ALERT! It’s not all that positive.

Now you may ask, if when we kill Hitler we may erase ourselves out of existence, what would be the implications of going further back and, let’s say, killing a man? Who that man’s ancestors might be one day?

Nobody. He will have no ancestors: you killed him. “But I traveled back in time and killed him, I changed history” you might say, but according to the Novikov self-consistency principle, you were allowed to do that by the very laws of nature.

The principle states that if an event exists that would cause a change or a paradox in the past whatsoever, then the chances of that event happening are ZERO. The Novikov principle, though it has some requirements, assumes that either there is only one timeline or that the other timelines (that the many-world theory of Quantum mechanics predicts) are not reachable. So you might feel it is an excuse to cop-out in theorizing about time travel.

Also another interesting theory is that you can’t really change anything because you are part of history too. Yes, you did go back and yes you changed things in your visit but whatever changes you did were already made because you did go back in time to begin with. That means you did have a usable time machine and you didn’t use it kill Hitler … Shame!


Featured image courtesy of Wikimedia Commons.