Time travel has been a trope of Science Fiction since its inception as a genre. Perhaps the most famous is H. G. Wells “The Time Machine,” which gives us brief glimpses of the future at several points. The idea is certainly seductive. Who wouldn’t want to be able to whiz off to the future to view the progress humanity has made, or travel to the past and witness historic events?

But whether or not time travel is possible is still an open debate among physicists. In this post I want to discuss some of the paradoxes that would seem to result if time travel is possible, as well as an interesting algorithm for solving NP problems using a time machine.

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XKCD posted a logic program titled Blue Eyes: The Hardest Logic Puzzle in the World. The problem got posted to reddit, and of course a large argument erupted in the comments thread about how the question doesn’t make sense, the solution doesn’t make sense / doesn’t work / is flawed / etc. etc. etc.

Rather than futilely attempt to make myself heard above the din, I’m writing this post which explains what the solution is, how you get to the conclusion, why it is in fact correct, and why the guru’s statement is necessary.

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At a philosophical discussion last night, we read “Jipi and the Paranoid Chip” by Neal Stephenson (Which, I just noticed, was posted to reddit 9 days ago, and got 1 up vote and 1 down vote. WTF?). If you’ve never read anything by him, I suggest you stop right this moment, go out and buy Cryptonomicon, Snowcrash and the Baroque Cycle, and do nothing until you’ve read them all.

The story is about a piece of software that was evolved to be indistinguishable from a paranoid schizophrenic. In the course of discussing the plot, someone asked if the paranoid schizophrenic chip would pass the Turing Test, with their inclination being no, it couldn’t.

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