Re: another anthropic reasoning

From: Jacques Mallah <>
Date: Tue, 20 Mar 2001 18:14:58 -0500

>From: Wei Dai <>
>I'm sorry for this greatly delayed response. I shouldn't have sent off the
>original message right before I hoped onto a plane and moved to Boston. If
>anyone can't remember what this thread was about, please see


>On Thu, Mar 01, 2001 at 03:14:03AM -0500, Jacques Mallah wrote:
> > True, they could be more "selfish". Effectively they are playing a
>prisoner's dilemma type of game where first Bob is given a move, then Alice

>This experiment is not a "game", since the action of each participant only
>affects his or her own payoff, and not the payoff of the other

    Effectively it is, since Bob has a Bayesian probability of affecting
Alice and so on.

>Actually you can do this with just one participant, and maybe that will
>make the paradoxical nature of anthropic reasoning clearer.

    It should make the _non_paradoxical nature clearer.

>Suppose the new experiment has two rounds. In each round the participant
>will be given temporary amnesia so he can't tell which round he is in. In
>round one he will have low measure (1/100 of normal). In round two he will
>have normal measure. He is also told:
>If you push button 1, you will lose $9.
>If you push button 2 and you are in round 1, you will win $10.
>If you push button 2 and you are in round 2, you will lose $10.
>According to anthropic reasoning, the participant when faced with the
>choices should think that he is much more likely to be in round 2, and
>therefore push button 1 in both rounds, but obviously he would have been
>better off pushing button 2 in both rounds.

    You are correct as far as him thinking he is more likely to be in round
2. However, you are wrong to think he will push button 1. It is much the
same as with the Bob and Alice example:
    He thinks he is only 1/101 likely to be in round 1. However, he also
knows that if he _is_ in round 1, the effect of his actions will be
magnified 100-fold. Thus he will push button 2.
    You might see this better by thinking of measure as the # of copies of
him in operation.
    If he is in round 1, there is 1 copy operating. The decision that copy
makes will affect the fate of all 100 copies of him.
    If he is in round 2, all 100 copies are running. Thus any one copy of
him will effectively only decide its own fate and not that of its 99

                         - - - - - - -
               Jacques Mallah (
         Physicist / Many Worlder / Devil's Advocate
"I know what no one else knows" - 'Runaway Train', Soul Asylum
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Received on Tue Mar 20 2001 - 15:48:55 PST

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