Time travelling 1

One time travel, no paradox please

Published on April 4, 2022

This is the first article of a series on time travel.

Time travelling is a recurring theme in movies and games. The problem of time travel is that it creates paradoxes… Scenarists for movies always struggle with time travel paradox. They always arise, in any time traveller movie: Terminator, Back to the Future… There are different ways to solve those paradoxes in films: different timelines, “it has always been like that”… See this video. Actually, the mere option of time travelling is already a paradox. In our world, you could not time travel without creating a paradox.

Time traveling without paradox?

Say that something bad happened in the past. For example, your fiancee died in an accident… So, you build a time machine, go back in the past and save her. However in this case, your fiancee is still alive, so you don’t need to time travel anymore! The motivation for time travelling itself is compromised.

Actually, the simple act of time travelling introduces paradoxes, even if you refrain yourself from doing anything in the past. You can stay well hidden in a bush, not interact with anything, especially not with yourself… But there will be paradoxes. Miriads of them.

By simply being there, existing, breathing, that will have rippling consequences that will break causality at some point. For instance, simply breathing during your stay in the past will kill some micro-organisms contained in the air. That mean that they will not be able to father the same micro-organisms that you brought on you skin.

Heck, even the photons emitted by your body will interact with the environment. After a long chain of atomic-level interactions, this initial radiation will modify very subtly the status of particles from your future self, at the moment of entering the time machine. This might prevent some of the photons to be emitted in the first place. Even your impact on the local gravity field will be changed, by your mere presence!

Time traveling without paradox!

The only way to time travel without paradoxes is to teleport outside of your cone of light, preventing any possible interactions. You’ll be teleporting effectively in a completely different world.

Time travel paradoxes arise in our world because there are too many parameters and too many causality chains. It arises inevitably. Time travel could be possible in a very simplified reality, with very few parameters. That’s why time travel may be possible at particles level. Particle are very simple objects, with only a few number of properties. In that case, time travel may be possible.