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Comment by andyjohnson0 | Hacker News Reader

I'm not sure why time travellers from the future would bother to leave prescient messages on the net. What's the motivation? Something like graffiti artists tagging difficult locations?

What I can see them (hypothetically) doing is manipulating present-day financial markets by exploiting their knowledge of future events (e.g. sudden commodity shortages or unexpected mineral discoveries) to increase their wealth. Even small manipulations would produce large downstream gains due to compound interest.

So perhaps market data is a place to look for abnormalities - particularly in existing systems that look for signs of insider trading, or investment accounts/trusts that are untouched over very long periods of time. Of course, such data is usually protected and inaccessible anyway.

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Yes, I would probably go back to 2009 and mine bitcoins (or fill captchas for 5 BTC a piece..) with a CPU..

Good point. All the early bitcoin miners are clearly suspect. And Satoshi Nakamoto's sudden appearance and then disappearance now makes total sense.

Combining time travel and computation has interesting results:

http://www.frc.ri.cmu.edu/~hpm/project.archive/general.artic...

Totally serious question: If I go back to 1990, can I distribute a current version of emacs? The toolchain to build the current source tree won't exist for a while.

Why not? Any computer program is just a very large number. Even thought the emacs build process that calculates the large number corresponding to the current version of emacs hadn't been performed in 1990, the number itself "existed" back then as the outcome of any number of other possible computations.

On the other hand, you might have problems with dll dependencies.

Or maybe Emacs can't run in a home machine of 1990

Remember? Eight Megs And Constantly Swapping

I assume @danielweber was asking whether it was possible in principle - as in, can information exist before it is created.

My remark about dlls was an attempt at humour, not a comment on practicalities.

Oh, youre running a binary that uses CPU extensions or dependent on a kernel that doesn't exist yet? Enjoy your segfaults.

GCC stage1 is deliberately written in K&R C so that you can do this kind of bootstrapping. You need a few unix tools (e.g. make - but again, a version from 1990 should work, find yourself a solaris machine or something); I don't remember exactly what emacs depends on, but it should be fine. Getting a modern environment on old unix boxes (or under windows SUA, whose unix stuff is old enough that it comes with X11R5) is fun and usually requires a bit of fiddling but nothing too serious.

If time travel was possible there would be a lot of ways to make money more efficiently than with bitcoins.

You are all assuming that money is still in use in the future.

I'd say the very fact that most Bitcoins weren't created in the first few hours is a good indicator that there are no time travellers. Or if travellers do exist, access to time travel has been restricted, or perhaps Bitcoins and possibly even currency is not of interest in the future.

In fact, time travel could render investments obsolete.

There, you just found proof that Bitcoin is going to collapse in the future!

I think the idea is that they would go back to stop the 9/11 attacks, and then on the day prior would look up "flight 11, flight 175, flight 77, flight 93" in google (maybe in separate searches) to see exactly when/where they took off. They wouldn't mean to leave the clue, but no one should have any reason to connect those 4 flights together until the next day.

I guess that would be one motivation. But wouldn't they just do the searches in their present (our future) before travelling back to 2001?

And if they did prevent 9/11 then nobody would connect the searches anyway, because there'd be nothing to associate them.

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