It never fails to grate on my nerves when films fail to employ time travel correctly. Often I can get past my grievance and enjoy the story, however sometimes it is done so poorly that it spoils the film for me.

There are three possible theories on how time travel could successfully work, and I’ll explain them here:

1. The Impossibility of Change Time Travel.

For me to be able to travel into the past, I wouldn’t be able to change anything that has led up to the present situation – the situation where I am equipped to travel through time. This means that when in the past none of my actions would be able to affect anything, as to change even the smallest thing would be to change the progression of temporal events. I would be an observer; I could watch but not touch, nor interact in any other manner. Furthermore, I would be invisible as to be seen would be to affect the past, in that it would change the actions or thoughts of the people/animals that saw me.

People may think this form of time travel, even if possible, would be pointless or boring, yet not all value is found in interaction. To simply witness events such as the extinction of dinosaurs or the building of the pyramids would be amazing, not in the least diminished by my inability to change what was occurring.

2. Mass Genocide Time Travel

Let’s say that I want to go back in time to change the world; I might, for example, want to kill Hitler before the Holocaust or invest early in Google. Well there’s a valid philosophical theory of time that allows this, though the cost might be seen as quite high.

For me to change the past, everything after the moment I travel to must be destroyed. This means if I wish to travel back to 1900 I will effectively kill all the people born after that time (other than myself as I am removing myself from time whilst I travel), and destroy all the technological advances humans have made since that date. When I arrive at the date I travel to I will be able to use knowledge of that time to change new-future events. As the events I have knowledge of would have originally occurred without my presence, however, my every interaction would increase the possibility of events not occurring in the way I know, and so make any knowledge I have less and less useful.

This method of time travel means that there can only ever be one time traveller, or one group of people time travelling together. This is because the time traveller who travels furthest into the past will destroy all time that comes after the date he/she travels to – including any later times that other potential time travellers have attempted to reach.

3. Time Line Time Travel

The third valid method of time travel relies on the idea of multiple worlds. If, as is possible, there is a practically infinite number of time lines, due to new time lines being created every time a choice is made or chance event occurs, then it is possible, in theory, that a person could travel between time lines. This would mean that I could travel from 2014 to 1900 without destroying everything after that date. Instead I would begin a different timeline, starting in 1900, leaving the original timeline in tact. Again, because I would be starting a different timeline, my knowledge of history would become less and less useful as, due to my own appearance, the new timeline would differ from the one I had travelled from. This method of time travel might, by time travel purists, be thought of as closer to travelling dimensions than it is to travelling time, as the traveller wouldn’t ever be present in the same timeline as the one they travelled from.

Right, so now you know. If time travel was ever to work, paradox free, it would be through one of these methods. You can now distinguish the great time travel films from the merely good.

Featured Artwork by Sara Ambrosini (saretta). Http://artofsaretta.weebly.com/fractal-worlds-1.html