Wei_Dai comments on Where Experience Confuses Physicists - Less Wrong

17 Post author: Eliezer_Yudkowsky 26 April 2008 05:05AM

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Comment author: Wei_Dai 30 September 2009 11:08:15AM *  6 points [-]

Because then you could have a complete mathematical model of our world, to be looked over by the Flying Spaghetti Monster, and then afterward you would need to tell the Flying Spaghetti Monster an extra postulate: Things are real in proportion to the square of their fourth-dimensional thickness. You could change that postulate, and leave everything microphysically the same, but people would find... different proportions of themselves?... in different places.

What if, when you change that postulate, you (or the Flying Spaghetti Monster) can no longer find any sentient beings? Because when you do that, a completely different subset of 3D worlds come into prominence, and those worlds just don't have the right properties for sentient beings to evolve. The worlds where the Ebborians exist are still somewhere in the resulting distribution on worlds, but they are now just about impossible to find.

Now suppose there was a fifth dimension, where at coordinate c, things are real in proportion to thickness^c. Then the above implies that most of the sentient life in this universe is going to be concentrated at coordinate c=2.

If this was true, wouldn't it explain the mystery just as well as if Ha'ro's "when a world-side gets thin enough, it cracks to pieces and falls apart" was true?

Comment author: Wei_Dai 30 September 2009 09:07:53PM 3 points [-]

To expand upon this a bit more, consider:

  • In standard anthropic reasoning, you should expect to find yourself at coordinate 2 with high probability before you've observed anything other than "I'm sentient", and also anticipate observing experimental results consistent with being at coordinate 2.
  • Under SIA, you should expect to live in a world with measure proportional to thickness^2, even if the world has no fifth dimension.
  • Under UDT, you care equally about every coordinate c, but will act as if you care mostly about c=2, because that is where you can create the most value with your decisions. (And same for worlds without the fifth dimension.)

So this seems to be a perfectly good (possible) solution.

Comment author: steven0461 30 September 2009 10:53:22PM *  4 points [-]

sentient

I think it would be a good habit for people here to take explicit notice whenever decision-making concepts and consciousness/sentience concepts occur in association. Other than that decision-makers can have preferences about consciousness/sentience, decision-making and consciousness/sentience don't obviously have anything to do with each other. (Not that I object to parent comment, I just needed a place to say this.)

Comment author: Wei_Dai 30 September 2009 11:53:34PM *  2 points [-]

Yes, I agree. In fact, in UDT, decision making doesn't depend on consciousness/sentience, but in the standard formulation of anthropic reasoning, it does. So I would count that as an advantage for UDT (and actually it was the original motivation for me to consider it).

Comment author: steven0461 01 October 2009 12:18:05AM *  1 point [-]

Under UDT, you care equally about every coordinate c, but will act as if you care mostly about c=2, because that is where you can create the most value with your decisions. (And same for worlds without the fifth dimension.)

It seems to me that this is where proofs of the Born rule by philosophers lend strong further support. The proofs, if I understand correctly, depend on assumptions that don't quite seem mandatory, but without which any decision strategy is practically impossible to specify or carry out. For example, the defense of "branching indifference" in section 9 of this paper:

If we are prepared to be even slightly instrumentalist in our criteria for belief ascription, it may not even make sense to suppose that an agent genuinely wants to do something that is ridiculously beyond even their idealised capabilities. For instance, suppose I say that I desire (ceteris paribus) to date someone with a prime number of atoms in their body. It is not even remotely possible for me to take any action which even slightly moves me towards that goal. In practice my actual dating strategy will have to fall back on “secondary” principles which have no connection at all to my “primary” goal — and since those secondary principles are actually what underwrites my entire dating behaviour, arguably it makes more sense to say that they are my actual desires, and that my ‘primary’ desire is at best an impossible dream, at worst an empty utterance.

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