A better yodeling contest

I really pity
Schroedinger's kitty

Paul McEvoy

One of my current side projects is an over-the-top article on a kind of anthropic computing problem on sending information back in time. In a nutshell, anthropic computing involves computing a random piece of data - if this meets our specifications, then good! Otherwise we destroy the universe (or perhaps just ourselves). Therefore an experimenter never observes any world-state in which the "wrong" random choice was chosen. In most formulations of this concept (see the Jargon File for example) the device is assumed to be "perfect" and so an infinite amount of information can be sent back in time. However this doesn't seem physically feasible since it seems it assumes the device has zero probability of error, whereas common failure modes (such as accidental deactivation or nuclear war) have probabilities relatively high compared to many computational problems, and therefore despite the canonical paper's opinion on the subject, it doesn't look like this kind of computing provides a loophole to compute NP-complete problems in polynomial time.

This is just a roundabout way of explaining why I happened to run across the cool webcomic/puzzle Meanwhile, which is an exploration of sorts into time travel, mindreading, and destroying the universe. Definitely worth a look (even if you didn't get that last paragraph).

Oh, and FYI the amount of information that can be sent back to the present is
\[\frac{1}{\log2}\left(\frac{\log\alpha}{\alpha-1}-1-\log\left(\frac{\log\alpha}{\alpha-1}\right)\right)\]
bits, where $\alpha$ is the ratio between the probability that the universe survives when our "gun" is fired, vs. the probability the universe survives if the gun is not fired.

Information given survival ratio $\alpha$

This entry was posted on Thursday, September 7th, 2006 at 9.17 pm and is filed under Games, Mathematics. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.