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HalFinney comments on Timeless Identity - Less Wrong

23 Post author: Eliezer_Yudkowsky 03 June 2008 08:16AM

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Comment author: HalFinney 03 June 2008 06:16:46PM 1 point [-]

I wrote a comment this morning on the monthly open thread which addresses some of the questions that have been raised above, but I will copy it here since that is a stale thread.

A couple of people asked about the relationship between quantum randomness and the macroscopic world.

Eliezer wrote a long essay here, http://www.sl4.org/wiki/KnowabilityOfFAI, about (among other things) the difference between unpredictability of intelligent decisions, and randomness. Decisions we or someone else make may be unpredictable beforehand, but that doesn't mean they are random. It may well be that even for a close and difficult decision where it felt like we could have gone either way, that in the vast majority of the MWI branches, we would have decided the same way.

At the same time, it is clear that there would be at least some branches where we would have decided differently. The brain ultimately depends on chemical processes like diffusion that have a random component, and this randomness will be influenced by quantum effects as molecules interact. So there would be some quantum fluctuations that could cause neurons to behave differently, and ultimately lead to different brain activities. This means that at the philosophical level, we do face the fact that every decision we make goes "both ways" in different branches. Our decision making is then a matter of what fraction of the branches go which way, and our mental efforts can be thought of as maximizing the fraction of good outcomes.

It would be interesting to try to figure out the degree to which quantum effects influence other macroscopic sources of randomness. Clearly, due to the butterfly effect, storms will be highly influenced by quantum randomness. If we reset the world to 5 years ago and put every molecule on the same track, New Orleans would not have been destroyed in almost all cases. How about a coin flip? If it comes up heads, what fraction of the branches would have seen tails? My guess is that the major variable will be the strength with which the coin is thrown by the thumb and arm. At the molecular level this will have two influences: the actin and myosin fibers in the muscles, activated by neurotransmitter packets; and the friction between the thumbnail and the forefinger which determines the exact point at which the coin is released. The muscle activity will have considerable quantum variation in individual fiber steps, but there would be a huge number of fibers involved, so I'd guess that will average out and be pretty stable. The friction on the other hand would probably be nonlinear and chaotic, an avalanche effect where a small change in stickiness leads to a big change in overall motion. I can't come up with a firm answer on this basis, but my guess would be that there is a substantial but not overwhelming quantum effect, so that we would see close to a 50-50 split among the branches. I wonder if anyone has attempted a more quantitative analysis.

One thing I will add, I imagine that ping-pong ball based lottery machines would be substantially affected by quantum randomness. The many bounces will lead to chaotic behavior, sensitive dependence on initial conditions, and even very small randomness due to quantum effects during collisions will almost certainly IMO be amplified to produce macroscopically different circumstances after several seconds.