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From: Bostrom,N <N.Bostrom.domain.name.hidden>

Date: Mon, 7 Aug 2000 20:02:34 +0100

Nick Bostrom

Dept. Philosophy, Logic, and Scientific method

London School of Economics

Homepage: [I tried sending parts of this message before, but don't think it

worked, so I re-send. Nick.] <http://www.hedweb.com/nickb>

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. (By "you" I here mean the totality of observer-moments that are

subjectively similar in certain ways to your present observer-moment). It is

then depends on your preferences whether suicide is rational. I believe most

people actually do care about their total measure. If qm suicide became

common, creatures would evolve to care about their total measure. Such

creatures would get a greater 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. Let's say that

the subjective probability is 1%. This is compatible with the objective

probability being, for instance, 99.9%. Adam may be ignorant as to whether

the objective probability is 99.9% or 0.0001%, but his degrees of beliefs in

these two possibilities may be such that his subjective probability for deer

turning up is 1%. (Subjective probability can be set equal to the weighted

sum over the potential objective probabilities that the system may have (for

all you know) of producing a given outcome; the weights being given by your

subjective probability of each such objective chance being the actual

chance.)

Applying this to the present case: 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% (a deer is about to appear). After forming his reproductive

intention, the objective probability would remain unchanged, but Adam's

subjective probability that the objective chance is high (99.9%) would

increase dramatically (perhaps to 80%, just to pick a number), provided the

no outsider requirement is satisfied. This would lead to his subjective

probability of deer appearing also increasing.

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!

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.

* >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.

Nick Bostrom

Dept. Philosophy, Logic, and Scientific method

London School of Economics

Homepage: http://www.hedweb.com/nickb <http://www.hedweb.com/nickb>

Received on Mon Aug 07 2000 - 12:09:49 PDT

Date: Mon, 7 Aug 2000 20:02:34 +0100

Nick Bostrom

Dept. Philosophy, Logic, and Scientific method

London School of Economics

Homepage: [I tried sending parts of this message before, but don't think it

worked, so I re-send. Nick.] <http://www.hedweb.com/nickb>

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. (By "you" I here mean the totality of observer-moments that are

subjectively similar in certain ways to your present observer-moment). It is

then depends on your preferences whether suicide is rational. I believe most

people actually do care about their total measure. If qm suicide became

common, creatures would evolve to care about their total measure. Such

creatures would get a greater 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. Let's say that

the subjective probability is 1%. This is compatible with the objective

probability being, for instance, 99.9%. Adam may be ignorant as to whether

the objective probability is 99.9% or 0.0001%, but his degrees of beliefs in

these two possibilities may be such that his subjective probability for deer

turning up is 1%. (Subjective probability can be set equal to the weighted

sum over the potential objective probabilities that the system may have (for

all you know) of producing a given outcome; the weights being given by your

subjective probability of each such objective chance being the actual

chance.)

Applying this to the present case: 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% (a deer is about to appear). After forming his reproductive

intention, the objective probability would remain unchanged, but Adam's

subjective probability that the objective chance is high (99.9%) would

increase dramatically (perhaps to 80%, just to pick a number), provided the

no outsider requirement is satisfied. This would lead to his subjective

probability of deer appearing also increasing.

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!

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.

with accepting R=Ru

observers)

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.

Nick Bostrom

Dept. Philosophy, Logic, and Scientific method

London School of Economics

Homepage: http://www.hedweb.com/nickb <http://www.hedweb.com/nickb>

Received on Mon Aug 07 2000 - 12:09:49 PDT

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