"If time travel is
possible what happens if I go back
in time and kill my own mother before I was born?"
By James Sharman.
The problem of paradox in time travel has always been interesting, some people have attempted to 'prove' that time travel is not possible by citing possible paradox cases and others have speculated vastly complex systems to explain why paradox can't occur. The information presented here is based partially on my own thinking and partially on numerous papers I read at university while I was supposed to be researching something less interesting.
A paradox is essentially a contradiction. In the above quoted case if I shoot my mother before she gives birth to me then I am no longer alive and could not perform the brutal act. This the most commonly quoted example of a time paradox, there are however lots of examples you may or may not have come across involving all sorts of bizarre situations involving anything from being your own father to total non existence of anything.
I am not intending to set out to prove or disprove the possibility of practical time travel, I do how ever intend to give a good idea of what the logical mind can deduce would happen if time travel were possible and did occur.
This document starts off with simplified cases before letting the complexities creep in, so if you think I have missed something then please read on before sending the death squads round. If you do however get to the end and think I have missed something then I would love to hear from you.
Before We Start
Time as any 'bloke down pub' will tell you is just another dimension somewhat similar to the three dimensions we can consciously move around. The difference seems to be that we move through time in one specific direction at a pretty much continuous speed (it is possible to change the speed we traverse time by invoking Einstein's special theory of relativity *). We are not then looking at time travel since we do this all the time, we are looking at time travel that goes against the grain of normal behaviour. For example if we were to look at a flashing light from outside of time we would see a dashed line of light and non light.
* In this context Einstein's special theory of relativity essentially states that speed and acceleration have an effect on the speed of our passage of time, the commonly quoted case being that if a traveller were to leave Earth in a space ship and travel at near light speeds before returning he would have experienced much less time than those who had remained on earth. This essentially constitutes a form of what we would call forward time travel.
To start things of we can take a look at the previously mentioned case of shooting your own mother. Now presuming that I have a mechanism for going back in time and there is no mystical force stopping me from carrying out my brutal intentions then the deed will be carried out. The universe now has a very basic problem: If I do exist then I don't exist, if I don't exist then I do exist. You can surmise that since there is no way out of this problem the universe will continuously switch between two the states, one state where I exist and go back in time and the other where my mother was killed and I don't exist. In effect the universe has split into two parallel universes to solve the problem. The time line has split at the point of paradox giving two futures with one common past, since I created the split then I am now in the universe in which my mother is killed so if I return to my time of origin then I return to the future of the alternative reality, a world that knows nothing of my existence, the other universe that I originated from however caries on never to see me again. To clarify this new situation we can look at it from the two perspectives of myself and an observer who remained in the present. In my mind I have travelled back in time, killed my mother and then returned to my time of origin to find that there is no record of my existence since someone brutally killed my mother before I was born, I however am still alive and well in this new future wondering why my bank cards get spat out of all the machines. The observer who watched me go back in time but remained in the present remains a product of the original time line, absolutely nothing changes since the change that produced the split does not affect him. The observer continues life as normal in a universe that I simply never returned to.
A very interesting question to ask now concerns the past before the split occurs. What would happen if a new time traveller (along with his parallel persona from the other universe) were to travel back to just before the event and observe what happened. The logical answer would be that each would return to the past that gave rise to their version of the future. We can however conclude from this that the split has resulted not in a single past with two futures but a total split with duplicate pasts.
When a split occurs it would be impossible to ever get back to the universe you originated in, it may however be possible to create a similar universe. For example in our little case study when I find myself in a future void of any knowledge of me I might decide to go back in time and kill myself when I appear in the time machine (before my other self gets a chance to kill my mother). Then presuming that I haven't changed things too much the duplicate of me in this universe will be born, grow up and travel back in time with the same purpose (disappearing out of this new universe) and I will be ready to travel forwards in time again to take his place. It will look to our observer friend of this (yet another) new universe as if I had simply disappeared and then reappeared a few moments later (and with any luck my bank cards work again!).
Add A Little Chaos And Stir Gently
When you take chaos theory into account things can get a little more complex but we can start to forget about having to kill people. In regards to time travel chaos theory means that however small a change made in the past, the change made will have greater and greater effect as you look further down the time line. You could for example slightly move a blade of grass that has an effect on your decision to travel to the past (even if it only causes a delay of a few seconds this is still a paradox). In fact any change at all creates a different future (however slight) and therefore a paradox is irrelevant to its effect or lack of effect on the traveller's future. So now any communication at all with the past will create a split, at this time it really becomes useful to start forgetting where splits occur and only pay attention to what any given observer will actually experience.
Travellers From The Future?
A commonly asked question concerning time travel is "If time travel is possible and it gets invented in the future, why haven't we ever met someone travelling from the future?". If you look at the theory closely you will see that if someone were to travel back to visit us from the future they would create a paradox (and a split) that would cause us to not meet them, parallel versions of ourselves in the new universe would of course meet them but that doesn't help us (That puts pay to the theory that aliens are travellers from Earth's future!).
The Pre-Destination Paradox
The pre-destination paradox (a term used predominantly in science fiction) refers to a paradox situation whereby there is a self reliant circle of events. The most common example of the man with a time machine who is his own father (e.g. Lister in Red-Dwarf) although there are more plausible examples (Genetic degradation would cause the father-son problem to fall apart after only a few cycles). If you think carefully about any of the examples of pre-destination paradox you should be able to see that something had to create them (see the debunking of The Terminator Films for a good example). If you apply the theory to pre-destination paradox it is also apparent that the effect is not cyclic as it would appear but there is an apparently endless loop causing split after split.
Forward Time Travel
Forward time travel on its own will never create a paradox situation, we can by applying Einstein's special theory of relativity suggest that this is in fact possible to an extent with today's technology. A paradox is caused by a modification of the natural order of events as defined by the basic laws of physics, forward time travel does not do this. Of Course if you were to return back to your time of origin then this is a direct form of future events affecting past events and so a paradox is inevitable.
Interesting Points Raised By This Theory
Following are number of obscure by-products and questions raised by this theory that make interesting reading. These are purely out of personal interest but may help you understand some of the after effects of Time travel as presented here.\
Some people seem to think that meeting a past or future self would be interesting, however it would be possible by careful creation of paradox situations to meet alternative equivalents to yourself. By building a time machine and then travelling back and forward again after disabling the device you would be able to come face to face with a near identical match to yourself.
If Time Travel is actually possible it may be possible to use this effect to build a matter replication device that would appear to produce perfect copies of anything placed into it. This like other forms of using time travel presented here does not go against the suggested law that no matter can exist in two different places at the same time, in all cases here the matter in question comes from a duplicate universe.
If there is some kind of supernatural method of predicting the future then this need not cause paradox, we must assume that whatever causes such predictions (if it exists) is part of the normal running of the universe and whatever change it would seem to bring about is inevitable.
Films Concerning Time Travel
Time travel has always been an favourite subject for science fiction writers. Although most films use this with a distinct amount of artistic licence. The following sections are brief examinations of some popular films I have enjoyed with relatively good use of time travel, these are not supposed to be critical but are intended to raise some interesting points to think about.
This is a very interesting film when you apply these theories to it. For those who don't know the basic plot revolves around a future where a master computer computer called SKY-NET that is attempting to destroy the human race sends a cyborg back into the past to kill the mother of the rebel leader before he is born. The rebels send their own man back (who we later discover is the leader's father) to sort matters out. In the second film both the rebels and SKY-NET send cyborgs back to kill the now teenage leader and to discover that the main chip from from the first cyborg was being studied to design the computer technology that the SKY-NET computer is based on, classic fictional pre-destination paradox. We know from only a brief look that the SKY-NET computer that sends the first computer back is never going to get anything out of the deal since the time line it exists in will remain unchanged. The real characters in our present would not have met the travellers from the future, the events of the film would be occurring in the universe created from a split. The real key is of course that despite the computer chip existing as a result of a pre-destination paradox in the original time line the equivalent of the new computer technology would have been built in the distant future in order for the paradox to occur in the first place. In stopping the cycle all the characters in the film have achieved is to revert the universe they are in back to something resembling the original state in which the creation of SKY-NET and subsequent near distruction of the human race happens at a later time.
StarTrek First Contact
Another Great Film with thankfully not even a hint of pre-destination paradox. The crew of the enterprise destroy a Borg ship that has come to assimilate Earth. Just before distruction the ship lets out an escape pod that creates a temporal field to travel back in time to do the deed before mankind has developed the technology to defend itself. The Enterprise is caught in the wake of the temporal field and sees the terrible results of the Borg's work before bravely following them back in time to set things straight. The actual technology used for time travel here is very interesting. If time travel is possible and it uses a field similar to the one the film speculates then it is entirely possible that the Enterprise would be shifted into the split universe created by the paradox. Applying the theory reveals that their position is a little bad, if they had stayed out of the field the Borg ship would have disappeared never to be seen again, instead the crew find themselves in a situation where they head back in time to fight for right to return to a future similar to the one they left behind.
Time travel is yet to be proven even as a possibility so any theory as to exactly what it's effects will be just speculation, one day me might just find out. If you subscribe to this theory then their is no danger in other people time travelling whatever their purpose, this unfortunately makes quite a bit of science fiction irrelevant so until someone builds a time machine we may as well lay back and enjoy the films. I do of course welcome any feed back from the contents of this document.
Stuff To Read.
Here are some random links concerning time travel I found whilst wandering the net.
I cannot be held responsible for the accuracy of the information contained here, if you build a time machine and go back into to kill your mother don't come running to me if you find yourself caught in a state between existence and non-existence.