Doctor Who careers around the universe in his TARDIS from adventure to adventure meddling with the space / time continuum. He interferes, changes destinies and saves planets, yet how come he never falls foul of any of the paradoxes of time travel?
Firstly and most obviously it is creative license. If the Doctor was subject to all the laws of physics then the show would quickly become very boring.
“Doctor, we need to rescue those people from that burning building” his assistant shouted.
“Rose, we can’t rescue them, we’d be interfering in the space/time continuum and possibly create a paradox which could result in the instantaneous destruction of the universe.” The Doctor replies.
It wouldn’t make good prime time viewing!
There are many different temporal paradoxes, the best known of which is called the Grandfather Paradox. In this, you travel back in time and kill your grandfather. However, if you killed your grandfather, who would have married your grandmother and given rise to your parents, and then you?
The parallel universe theory may give us a way out of this. Every time a decision is made, an alternative universe branches out and every possible outcome for every interaction is played out. You wake up in the morning and think about your breakfast … in one universe you have muesli, in another toast, in another cereal, in another you skip breakfast and in another …
You get the picture.
Quantum theory provides us with a method for time travel without hitting the wall of paradoxes. When you observe something in quantum theory it causes the possible states to collapse into a single measured state. Therefore, the past, observed from the present is already determined. However, observing the present from the past, it has many possible states. Any actions taken can be seen to have been inevitable!
To end the discussion of paradoxes, it can be suggested that time travel will never exist, even if it is theoretically possible. The reasoning behind this is that as long as time travel exists, history will keep on changing. It will only stop changing when a timeline is reached in which there is no time travel and so no more changes can be made.
If we assume there is only one dimension of time, the timeline we see must be the one that exists when all the changes due to time travel have completed. So therefore, we will never actually become aware of the invention of time travel as it will have been removed from the time line by the time we would have reached it.
Putting the laws of physics to one side we can continue to enjoy shows as Doctor Who, because fantasy doesn’t have to obey our universe’s laws of physics.
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