# RE: PhD-thesis on Observational Selection Effects

From: Jacques Mallah <jackmallah.domain.name.hidden>
Date: Sat, 12 Aug 2000 20:24:41 EDT

Recently I have been busy. I will be a Physics Instructor at Ferris
State University this coming school year. This will be my first real job,
and I have to relocate.

>From: "Bostrom,N" <N.Bostrom.domain.name.hidden>
>Jacques wrote:
> So I take it you don't believe in "quantum immortality" or the "RSSA".
>
>Given MWI, you know what happens if you commit suicide. You may affect an
>increase in your average well-being at the cost of a decrease of your total
>measure.

Right.

>If qm suicide became common, creatures would evolve to care about their
>total measure. Such creatures would get a greater measure.

Right. Of course, natural selection implies objective measure.

>Suppose, without the MWI, he would know that on a usual day a deer is 1%
>likely to turn up. But since this is not a usual day, but the day that
>will determine whether he gives rise to a race, he would think a deer
>probably will turn up which then means he won't reproduce. (And not
>reproducing would give his own case more effective probability, which is
>why he thinks it's likely.)
>
>So far I'm with you...
>
>If he believes the MWI however, then he knows there is a branch where a
>deer turns up and one where it doesn't. He knows that for a usual day the
>effective probability of a deer turning up is about 1%.
>Since he has no reason to believe the laws of nature are specially
>configured to correlate the amplitude of the wavefunction's branches with
>his actions (especially since such correlation would be hard to reconcile
>with QM), he will still believe the effective probability of a deer turning
>up is just 1%.
>
>You may be confusing subjective and objective probability.

Nope. Why would you think I might do so?
In both cases I have so far discussed, his Bayesian probaility
distribution for the objective probability is sharply peaked about a
(stochastic xor effective) probability of 1%.
A common way this might occur is if he has observed, over the course of
10 years (3652 days) that about 37 times a deer has turned up. If he
assumes that there is a fixed probability p, and initially has a uniform
Bayesian distribution for p on (0,1), then his final distribution will be
sharply peaked about 1%.
The point, here, is that in such a case he *can't* suddenly assume
"today is different, so while on a usual day p=.01, I'll just have a uniform
Bayesian prior for p_today.", and then apply the "Adam paradox". So, in
both the non-MWI and the MWI case, p~=.01 is his prior probability before he
considers his own situation regarding reproduction, but the effect of the
latter is different. So far I think you agree with that.

>he may think that there is a 99% probability that the objective probability
>of deer is 0.000001% ("no deer in the neighbourhood) and a 1% probability
>of the objective probability being, say, 99.9%

This is the second thing about the MWI I discussed, for the case where
he hasn't nailed down that objective probability to be sharply peaked about
.01. Here the preexisting branches must come into play.

>In addition, in QM there will be many branches even before that day. So
>it's also true that branches will exist, with about equal amplitude to his
>own where e.g. maybe the weather was different and he chose a different day
>to go "deer hunting", where the Earth has two moons, or indeed where the
>first man's name was Jack, etc.
>These sort or branches do act exactly like regular old alien worlds for
>this purpose. Thus even if someone hands him a spin 1/2 particle, state
>unknown, he should not consider it just to have some wavefunction which he
>could apply the "Adam paradox" to like a classical coin; he
>must also consider the already parallel branches where the equivalent
>particle has some other wavefunction, and there are other versions of him
>there to see it.
>
>If there are all these other fat branches in the world, then yes, I agree
>with that. However, Adam and Eve were there from the beginning, before
>there deer paths had begun to spread out much as a probability cloud over
>the terrain. Or at least we can suppose they were - that's the nice thing
>about thought experiments!

But it would be foolish of Adam to believe that. Take his name, for
example. (Other examples are easily found.) There are millions of other
names he could have had. The laws of physics (or initial conditions) would
have to be set up in a very contrived way in order for the effective
probability of just the one name for the first man, Adam, to be of order
one. Of course, in the biblical story things are very contrived because
some guy (god) contrived it, and because this original guy was himself
unique to start with. It's not a coincidence that such a situation is
implausible, and even if it was true, only a fool would believe it. (Just
as only a fool believes he won the lottery before he even checks the
numbers.)

>And I do find the premise that he can be certain that no
>type of MWI can be true hard to swallow.
>
>He wouldn't have to be certain about that.

Well, he would certainly have to assign a ludicrously high probability
(e.g. 50%) to the idea that the MWI might be false.

>>Of course, everything I say in the thesis is compatible
>with accepting R=Ru (i.e. setting the reference class equal to the class of
>all observers) provided one is also willing to accept the Adam&Eve paradox.
>
>You still haven't presented any way to determine the
>proper "reference class". I suggest you use the logical approach: include
>all observers.
>
>I don't see what's so particularly "logical" about that. In either case, we
>have to deal with borderline cases and such, and make some seemingly rather
>arbitrary postulations.

Much less so if all observers are included. And it's certainly simpler
than any alternative.
As I see it, it is a priori possible that I could have been any
observer. Thus all observers must be included, by definition. This is just
basic Bayesian reasoning (applied to indexical information) and there is
absolutely no question of an alternative. This prior is then updated by
considering the various characteristics I have, such as the particular
observations that I have made, and comparing those with the various
observers as usual.

- - - - - - -
Jacques Mallah (jackmallah.domain.name.hidden)
Physicist / Many Worlder / Devil's Advocate
"I know what no one else knows" - 'Runaway Train', Soul Asylum
My URL: http://hammer.prohosting.com/~mathmind/

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Received on Sat Aug 12 2000 - 17:27:57 PDT

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