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# faul_sname comments on Open Thread, November 16–30, 2012 - Less Wrong Discussion

3 18 November 2012 01:59PM

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Comment author: 19 November 2012 12:11:48AM 6 points [-]

A one page story from Ted Chiang I hadn't seen linked here before: http://www.concatenation.org/futures/whatsexpected.pdf

If you enjoyed it I strongly recommend reading more Ted Chiang.

Comment author: 19 November 2012 10:35:20PM *  7 points [-]

I think something is very, very wrong with me. Instead of feeling Lovecraftian horror upon reading that, I immediately began trying to think of ways to use Predictors to hack the universe. Here's what I came up with (you may want to try for yourself before reading further):

• I can respond to a light by pushing a button in less than a second.
• It's possible to set up a sensor that will send a signal when the light lights up.
• I can hook the light up to the sensor and hook that sensor up to a processor and its own light, allowing my decision to press the button to become entangled with the processor's state before my observation of the light. I can then cover the light of the Predictor so I only see and respond to a light when the processor decides to show it.
• Trivially, I could set up the processor to only show me a light when there has not been a light from the predictor in at least one second. Since the sum of the time it takes the processor to show the light and the time it takes me to respond to that light, this system is forbidden. This selects for a stable time loop in which, for whatever reason, I don't press the button when I see the light, the processor breaks, or something else happens to disrupt the system (probably not something good for me either).
• I can add a quantum random number generator of some variety into the mix, and have that generate numbers that correspond to possible solutions of a problem. If there was no light in the past second or if a solution is found, the device will light up. This will exclude universes in which no solutions are found.
• I can now implement Quantum Bogosort. More importantly and more practically, I can now solve all problems that have solutions that can be verified in 0.1 s or so, which breaks RSA (I think) and a lot of other cryptography.

That's just what I thought of in the first 5 minutes. I think the Predictors would be insanely dangerous, but primarily for reasons other than driving humans insane.

Comment author: [deleted] 20 November 2012 09:33:31PM 4 points [-]

Hi, Harry James Potter-Evans-Verres... Is that you?

Comment author: 19 November 2012 11:01:15PM 4 points [-]

It wouldn't really break RSA or other algorithms, it would just push the security parameters on everything way up until you can't verify the solutions in <1 second. In particular, encoding a single code word would always require at least 1 second of time, so cryptographic algorithms would become slow.

If I were a jerk, I could publish a prime number as my RSA public key. Then anyone who tries to use stable time loops to find my private key would find themselves or their computers disrupted by bizarre coincidences (and as you've mentioned, those coincidences probably aren't a good thing for the most part).

Comment author: 20 November 2012 12:43:14AM 1 point [-]

If I were a jerk, I could publish a prime number as my RSA public key.

Ooh, that's evil. I like that.

Comment author: 20 November 2012 02:06:41AM 0 points [-]

Well, this particular method can be defeated by running a primality tester first. Still, it's important that the problem you're solving in this method has a solution (or a short proof of lack of a solution) which I think restricts us to problems in the intersection of NP and co-NP.

Comment author: 27 November 2012 12:41:39AM *  0 points [-]

Footnote: "One curious property of predictors is that whenever anyone tries to do something clever with them they convert into antimatter annihilating the experimenter and surrounding area"

Comment author: 27 November 2012 01:13:53AM *  3 points [-]

I like the idea of allowing a sufficiently clever person with a webcam turn a predictor into a potent weapon.