Information from the past

The television police series Crime Traveller uses the plot device of a time machine that enables a detective to travel back in time to solve crimes. There is nothing in the laws of physics that forbids the uncovering of information from the past: archaeologists do it all the time. The use of a time machine in this series just adds some interesting novelties to police procedures. Any attempt by the detective to change the past is always thwarted in some way: a murder cannot be prevented but the identity of the murderer can be discovered. In one episode, the hero detective goes back in time and places a winning bet in a lottery, knowing its outcome, but the attempt fails due to one oversight or another. This is the weakest element in these stories, because information is contextual: marks on a piece of paper may be a winning lottery number to a man but meaningless to a dog. That the universe would know the difference and conspire to erase information from the future depending on its context seems not credible to say the least.

Temporal consistency

In the fourth Star Trek film ‘Star Trek IV: The Voyage Home’ (the one with the whales), whilst back on the Earth of their past, Dr McCoy asks the Engineer Scotty if giving information from the future to the past about transparent aluminium might not cause a temporal paradox. Scotty replies that they don’t know for sure that such a temporal circle of information flow was not responsible for transparent aluminium existing in the future in the first place. That answer satisfies McCoy, as it is logically consistent. The moral here is that time travel need not cause inconsistencies, a point made by Novikov [Novikov, 1998].

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