Re: language, cloning and thought experiments

[George Levy]

Jack,

You say "Q_i (which is _your_ utility per unit measure for the observer i)."
 This is an oxymoron. How can observer i know or care what YOUR Q (Quality) is? How can this observer feel what it feels being you?. The only observer that matters in evaluating your Q is you as a self-observer. The sum is no sum at all:

U = M_o Q_o  where o = you as observer.

George

Wei Dai wrote:

Jack Mallah wrote:
  

They might not, but I'm sure most would; maybe not exactly that U, but a 
lot closer to it.
    

Can you explain why you believe that?

  

No.  In U = Sum_i M_i Q_i, you sum over all the i's, not just the ones 
that are similar to you.  Of course your Q_i (which is _your_ utility per 
unit measure for the observer i) might be highly peaked around those that 
are similar to you, but there's no need for a precise cutoff in 
similarity.  And it's even very likely that it will have even higher peaks 
around people that are not very much like you at all (these are the people 
that you would sacrifice yourself for).

By contrast, in your proposal for U, you do need a precise cutoff, for 
which there is no justification.
    

Ok, I see what you're saying, and it is a good point. But most people 
already have a personal identity that is sufficiently well-defined in the 
current environment where mind copying is not possible, so in practice 
deciding which i's to sum over isn't a serious problem (yet).
 




  

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[Stathis Papaioannou-2]

2009/3/11 Wei Dai <weidai@...>:

>
> Jack Mallah wrote:
>> They might not, but I'm sure most would; maybe not exactly that U, but a
>> lot closer to it.
>
> Can you explain why you believe that?
>
>> No.  In U = Sum_i M_i Q_i, you sum over all the i's, not just the ones
>> that are similar to you.  Of course your Q_i (which is _your_ utility per
>> unit measure for the observer i) might be highly peaked around those that
>> are similar to you, but there's no need for a precise cutoff in
>> similarity.  And it's even very likely that it will have even higher peaks
>> around people that are not very much like you at all (these are the people
>> that you would sacrifice yourself for).
>>
>> By contrast, in your proposal for U, you do need a precise cutoff, for
>> which there is no justification.
>
> Ok, I see what you're saying, and it is a good point. But most people
> already have a personal identity that is sufficiently well-defined in the
> current environment where mind copying is not possible, so in practice
> deciding which i's to sum over isn't a serious problem (yet).

The same problem would apply to calculating probabilities. If one copy
of me will see heads and a million copies of me who have a one
millionth degree of similarity to me will see tails, what is my
expectation of heads? I suggest introducing a factor R, a number
between 0 and 1 representing the degree of similarity to the original:

Pr(H) = M1R1 / (M1R1 + M2R2) = (1*1) / (1*1 + 10^6*10^-6) = 1/2

The analogous equation for utility, where Q is the absolute utility
experienced by an individual copy, is then:

U = (M1R1Q1 + M2R2Q2) / (M1R1 + M2R2)


--
Stathis Papaioannou

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[Bruno Marchal]

Nice! I did refer often to the Saibal Mitra backtracking procedure (in  
immortality discussions). I will take a further look on your paper.
If valid, it should work in the comp frame. Amnesia could lead you to  
the "original singularity", which could be a kind of blind spot of  
"universal consciousness", except that with comp such a singularity  
should looks like a "little Mandelbrot" set, at first sight, I mean  
something like a compact view of a universal dovetailing.

Bruno

On 10 Mar 2009, at 19:55, Saibal Mitra wrote:

>
> http://arxiv.org/abs/0902.3825
>
> I've written up a small article about the idea that you could end up  
> in a
> different sector of the multiverse by selective memory erasure. I had
> written about that possibility a long time ago on this list, but now  
> I've
> made the argument more rigorous.
>
>
> >

http://iridia.ulb.ac.be/~marchal/




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[Jack Mallah]

--- On Tue, 3/10/09, Saibal Mitra <smitra@...> wrote:
> http://arxiv.org/abs/0902.3825
>
> I've written up a small article about the idea that you could end up in a different sector of the multiverse by selective memory erasure. I had written about that possibility a long time ago on this list, but now I've made the argument more rigorous.

Saibal, I have to say that I disagree.  As you acknowledge, erasing memory doesn't recohere the branches.  There is no meaningful sense in which you could end up in a different branch due to memory erasure.

You admit the 'effect' has no observable consequences.  But it has no unobservable meaning either.

In fact, other than what I call 'causal differentiation', which clearly will track the already-decohered branches (so you don't get to reshuffle the deck), there is no meaningful sense in which "you" will end up in one particular future branch at all.  Other than causal differentiation tracking, either 'you' are all of your future branches, or 'you' are just here for the moment and are none of them.




     


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[Saibal Mitra]

Thanks!  This is like undoing historical events. If you forget about the
fact that dinosaurs ever lived on Earth and there is an alternative history
that led to your existence in the multiverse, and you do the memory erasure
also in sectors were dinosaurs never lived, you have some nonzero
probability of finding yourself on an Earth were the dinosaurs never lived.

----- Original Message -----
From: "Bruno Marchal" <marchal@...>
To: <everything-list@...>
Sent: Wednesday, March 11, 2009 06:54 PM
Subject: Re: Changing the past by forgetting

>
> Nice! I did refer often to the Saibal Mitra backtracking procedure (in
> immortality discussions). I will take a further look on your paper.
> If valid, it should work in the comp frame. Amnesia could lead you to
> the "original singularity", which could be a kind of blind spot of
> "universal consciousness", except that with comp such a singularity
> should looks like a "little Mandelbrot" set, at first sight, I mean
> something like a compact view of a universal dovetailing.
>
> Bruno
>
> On 10 Mar 2009, at 19:55, Saibal Mitra wrote:
>
> >
> > http://arxiv.org/abs/0902.3825
> >
> > I've written up a small article about the idea that you could end up
> > in a
> > different sector of the multiverse by selective memory erasure. I had
> > written about that possibility a long time ago on this list, but now
> > I've
> > made the argument more rigorous.
> >
> >
> > >
>
> http://iridia.ulb.ac.be/~marchal/
>
>
>
>
> >

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[Saibal Mitra]

If we consider measuring the spin of a particle, you could also say that the
two possible outcomes just exist and thatthere are two possible future
versions of me. There is no meaningful way to associate myself with either
of the two outcomes.

But then, precisely this implies that after a measurement and forgetting
about the result will yield a version of me who is in a similar position as
that earlier version of me who had yet to make the measurement. If one could
perform measurements in a reversible way, this would be possible to
experimentally confirm, as David Deutsch pointed out. You can start with a
spin polarized in the x direction. Then you measure the z-component. There
then exists a unitary transformation which leads to the observer forgetting
about the outcome of the measurement and to the spin to be restored in the
original state. The observer does remember having measured the z-component
of the spin.

Then, measuring the x-component again will yield "spin-up" with 100%
probability, confirming that both branches in which the observer measured
spin up and spin down have coherently recombined. This then proves that had
the observer measured the z-component, the outcome would not be a priori
determined, despite the observer having measured it earlier. So, both
branches are real. But then this is true in general, also if the quantum
state is of the form:

|You>[|spin up>|rest of the world knows the spin is up> + |spin down>|rest
of the world knows spin is down>]

although you cannot directly verify it here. But that means that you cannot
rule out an alternative theory in which only one of the branches is real
when performing a measurement in this case. But if the reality of both
branches is accepted, then each time you make a measurement and you don't
know the outcome, the outcome is not fixed (proovided, of course, there is
indeed more than one branch).


----- Original Message -----
From: "Jack Mallah" <jackmallah@...>
To: <everything-list@...>
Sent: Thursday, March 12, 2009 03:47 AM
Subject: Re: Changing the past by forgetting




--- On Tue, 3/10/09, Saibal Mitra <smitra@...> wrote:
> http://arxiv.org/abs/0902.3825
>
> I've written up a small article about the idea that you could end up in a
different sector of the multiverse by selective memory erasure. I had
written about that possibility a long time ago on this list, but now I've
made the argument more rigorous.

Saibal, I have to say that I disagree.  As you acknowledge, erasing memory
doesn't recohere the branches.  There is no meaningful sense in which you
could end up in a different branch due to memory erasure.

You admit the 'effect' has no observable consequences.  But it has no
unobservable meaning either.

In fact, other than what I call 'causal differentiation', which clearly will
track the already-decohered branches (so you don't get to reshuffle the
deck), there is no meaningful sense in which "you" will end up in one
particular future branch at all.  Other than causal differentiation
tracking, either 'you' are all of your future branches, or 'you' are just
here for the moment and are none of them.









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[Brent Meeker-2]

Saibal Mitra wrote:

> If we consider measuring the spin of a particle, you could also say that the
> two possible outcomes just exist and thatthere are two possible future
> versions of me. There is no meaningful way to associate myself with either
> of the two outcomes.
>
> But then, precisely this implies that after a measurement and forgetting
> about the result will yield a version of me who is in a similar position as
> that earlier version of me who had yet to make the measurement. If one could
> perform measurements in a reversible way, this would be possible to
> experimentally confirm, as David Deutsch pointed out. You can start with a
> spin polarized in the x direction. Then you measure the z-component. There
> then exists a unitary transformation which leads to the observer forgetting
> about the outcome of the measurement and to the spin to be restored in the
> original state. The observer does remember having measured the z-component
> of the spin.
>
> Then, measuring the x-component again will yield "spin-up" with 100%
> probability, confirming that both branches in which the observer measured
> spin up and spin down have coherently recombined. This then proves that had
> the observer measured the z-component, the outcome would not be a priori
> determined, despite the observer having measured it earlier. So, both
> branches are real. But then this is true in general, also if the quantum
> state is of the form:
>
> |You>[|spin up>|rest of the world knows the spin is up> + |spin down>|rest
> of the world knows spin is down>]

You're contemplating reversing three different things:

1) Your knowledge, by forgetting a measurement result.  Something that's easy to do.

2) The spin state of a particle.

3) The state of what the rest of the world knows.

Because of the entanglement, I don't think you can, in general, reverse the spin
state of the  particle without reversing what is known about it by "the rest of
the world".
If it was a known state (to someone) the particle can easily be put back in that
state.  But to do so for a general, unknown state, after a measurement would
require invoking time-reversal invariance of the state of whole universe (or at
least all of it entangled with the particle spin via the measuring apparatus).

Brent Meeker

>
> although you cannot directly verify it here. But that means that you cannot
> rule out an alternative theory in which only one of the branches is real
> when performing a measurement in this case. But if the reality of both
> branches is accepted, then each time you make a measurement and you don't
> know the outcome, the outcome is not fixed (proovided, of course, there is
> indeed more than one branch).
>
>
> ----- Original Message -----
> From: "Jack Mallah" <jackmallah@...>
> To: <everything-list@...>
> Sent: Thursday, March 12, 2009 03:47 AM
> Subject: Re: Changing the past by forgetting
>
>
>
>
> --- On Tue, 3/10/09, Saibal Mitra <smitra@...> wrote:
>> http://arxiv.org/abs/0902.3825
>>
>> I've written up a small article about the idea that you could end up in a
> different sector of the multiverse by selective memory erasure. I had
> written about that possibility a long time ago on this list, but now I've
> made the argument more rigorous.
>
> Saibal, I have to say that I disagree.  As you acknowledge, erasing memory
> doesn't recohere the branches.  There is no meaningful sense in which you
> could end up in a different branch due to memory erasure.
>
> You admit the 'effect' has no observable consequences.  But it has no
> unobservable meaning either.
>
> In fact, other than what I call 'causal differentiation', which clearly will
> track the already-decohered branches (so you don't get to reshuffle the
> deck), there is no meaningful sense in which "you" will end up in one
> particular future branch at all.  Other than causal differentiation
> tracking, either 'you' are all of your future branches, or 'you' are just
> here for the moment and are none of them.

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[A. Wolf]

> Thanks!  This is like undoing historical events. If you forget about the
> fact that dinosaurs ever lived on Earth and there is an alternative
> history
> that led to your existence in the multiverse, and you do the memory
> erasure
> also in sectors were dinosaurs never lived, you have some nonzero
> probability of finding yourself on an Earth were the dinosaurs never
> lived.

The problem I'm having with this line of reasoning is that "memory" isn't a
fixed physical object.  Memory is reconstructive, and depends upon emotional
triggers both at the time when the memory was encoded and at the time when
it re-examined in the conscious mind.  No memories are particularly
accurate.

Most of the time, I'm not aware that dinosaurs existed because I'm not
thinking about it, or any other part of Earth's history, for that
matter...but I don't seem to have the experience that my environment is
impoverished of history altogether just because I hadn't been thinking hard
enough about it.  As another example, people who have false recovered
memories through psychotherapy invariably end up unable to confirm them when
they look for facts to back up their new memories, and that happens in my
universe even though I personally don't have any information to confirm or
deny their memories.

In other words, I don't see why forgetting something is any more likely to
change events than simply being wrong about having the memory in the first
place, the latter of which happens constantly.  If you want to argue about
what nonzero probability implies, you'd have a hard time showing that
anything non-contradictory at all has a nonzero probability of being true.
:)

> Because of the entanglement, I don't think you can, in general, reverse
> the spin
> state of the  particle without reversing what is known about it by "the
> rest of
> the world".

The rest of the world?  What's that?

Anna


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[A. Wolf]

> what nonzero probability implies, you'd have a hard time showing that
> anything non-contradictory at all has a nonzero probability of being true.

Er, I typed too quickly.  I mean you'd have a hard time of showing that
anything non-contradictory has zero probability.  Anything that isn't
mathematically contradictory has a nonzero probability, as far as I'm
concerned.

Anna


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[George Levy]

I agree with Anna. In addition, it all depends on where you define the boundary of the self. Just the brain? Brain + body? Brain + body + immediate surrounding (prescription glasses being worn, automobile being driven, binoculars or computer being used) ? Brain + body + Whole causally connected universe (CCU)?

There are good arguable reasons for including the CCU as part of the self. Forgetting would then mean resetting the  CCU  to  the last "remembered" state. In this case we have an identity relationship between the self and the universe it inhabits. Resetting the self is the same as resetting the universe. No more problem or paradox associated with forgetting!

George


A. Wolf wrote:

Thanks!  This is like undoing historical events. If you forget about the
fact that dinosaurs ever lived on Earth and there is an alternative 
history
that led to your existence in the multiverse, and you do the memory 
erasure
also in sectors were dinosaurs never lived, you have some nonzero
probability of finding yourself on an Earth were the dinosaurs never 
lived.
    

The problem I'm having with this line of reasoning is that "memory" isn't a 
fixed physical object.  Memory is reconstructive, and depends upon emotional 
triggers both at the time when the memory was encoded and at the time when 
it re-examined in the conscious mind.  No memories are particularly 
accurate.

Most of the time, I'm not aware that dinosaurs existed because I'm not 
thinking about it, or any other part of Earth's history, for that 
matter...but I don't seem to have the experience that my environment is 
impoverished of history altogether just because I hadn't been thinking hard 
enough about it.  As another example, people who have false recovered 
memories through psychotherapy invariably end up unable to confirm them when 
they look for facts to back up their new memories, and that happens in my 
universe even though I personally don't have any information to confirm or 
deny their memories.

In other words, I don't see why forgetting something is any more likely to 
change events than simply being wrong about having the memory in the first 
place, the latter of which happens constantly.  If you want to argue about 
what nonzero probability implies, you'd have a hard time showing that 
anything non-contradictory at all has a nonzero probability of being true. 
:)

  

Because of the entanglement, I don't think you can, in general, reverse 
the spin
state of the  particle without reversing what is known about it by "the 
rest of
the world".
    

The rest of the world?  What's that?

Anna




  

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[George Levy]

I agree with Anna. In addition, it all depends on where you define the boundary of the self. Just the brain? Brain + body? Brain + body + immediate surrounding (prescription glasses being worn, automobile being driven, binoculars or computer being used) ? Brain + body + Whole causally connected universe (CCU)?

There are good arguable reasons for including the CCU as part of the self. Forgetting would then mean resetting the  CCU  to  the last "remembered" state. In this case we have an identity relationship between the self and the universe it inhabits. Resetting the self is the same as resetting the universe. No more problem or paradox associated with forgetting!

George


A. Wolf wrote:

Thanks!  This is like undoing historical events. If you forget about the
fact that dinosaurs ever lived on Earth and there is an alternative 
history
that led to your existence in the multiverse, and you do the memory 
erasure
also in sectors were dinosaurs never lived, you have some nonzero
probability of finding yourself on an Earth were the dinosaurs never 
lived.
    

The problem I'm having with this line of reasoning is that "memory" isn't a 
fixed physical object.  Memory is reconstructive, and depends upon emotional 
triggers both at the time when the memory was encoded and at the time when 
it re-examined in the conscious mind.  No memories are particularly 
accurate.

Most of the time, I'm not aware that dinosaurs existed because I'm not 
thinking about it, or any other part of Earth's history, for that 
matter...but I don't seem to have the experience that my environment is 
impoverished of history altogether just because I hadn't been thinking hard 
enough about it.  As another example, people who have false recovered 
memories through psychotherapy invariably end up unable to confirm them when 
they look for facts to back up their new memories, and that happens in my 
universe even though I personally don't have any information to confirm or 
deny their memories.

In other words, I don't see why forgetting something is any more likely to 
change events than simply being wrong about having the memory in the first 
place, the latter of which happens constantly.  If you want to argue about 
what nonzero probability implies, you'd have a hard time showing that 
anything non-contradictory at all has a nonzero probability of being true. 
:)

  

Because of the entanglement, I don't think you can, in general, reverse 
the spin
state of the  particle without reversing what is known about it by "the 
rest of
the world".
    

The rest of the world?  What's that?

Anna




  

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[rmiller-2]

At 06:20 PM 3/15/2009, George Levy wrote:

I agree with Anna. In addition, it all depends on where you define the boundary of the self. Just the brain? Brain + body? Brain + body + immediate surrounding (prescription glasses being worn, automobile being driven, binoculars or computer being used) ? Brain + body + Whole causally connected universe (CCU)?

There are good arguable reasons for including the CCU as part of the self. Forgetting would then mean resetting the  CCU  to  the last "remembered" state. In this case we have an identity relationship between the self and the universe it inhabits. Resetting the self is the same as resetting the universe. No more problem or paradox associated with forgetting!

George

Helmut Schmidt's "retrocausation" (actually a sophisticated delayed choice) experiments suggested that causation might be associated with many-worlds---that is, it might be possible to choose a past that will lead to a present state of a Causally Connected Universe.   If different pasts can be associated with equivalent behavioral sets in the present then it would be impossible to differentiate the specific world lines that led to the present behavioral set.  If one's present behavioral state is a sum of histories over time, then one could focus on a particular history (say, one without dinosaurs) to subtly alter the present CCU, but if the difference can't be consciously detected, then (a la Copenhagen theory) then it would be irrelevent.

As for memory being reconstructive, the fact is we really don't know much about it at all.  If time doesn't exist except as a bundle of world lines, memory might involve "sampling" a section of the preceding bundle.  In that view we create our own particular CCU.  Wrong about past events?  Maybe you sampled the wrong world line.

R. Miller

A. Wolf wrote:

Thanks!  This is like undoing historical events. If you forget
about the
fact that dinosaurs ever lived on Earth and there is an alternative 
history
that led to your existence in the multiverse, and you do the memory 
erasure
also in sectors were dinosaurs never lived, you have some nonzero
probability of finding yourself on an Earth were the dinosaurs never 
lived.
   

The problem I'm having with this line of reasoning is that
"memory" isn't a 
fixed physical object.  Memory is reconstructive, and depends upon
emotional 
triggers both at the time when the memory was encoded and at the time
when 
it re-examined in the conscious mind.  No memories are particularly 
accurate.

Most of the time, I'm not aware that dinosaurs existed because I'm not 
thinking about it, or any other part of Earth's history, for that 
matter...but I don't seem to have the experience that my environment is 
impoverished of history altogether just because I hadn't been thinking
hard 
enough about it.  As another example, people who have false
recovered 
memories through psychotherapy invariably end up unable to confirm them
when 
they look for facts to back up their new memories, and that happens in my 
universe even though I personally don't have any information to confirm
or 
deny their memories.

In other words, I don't see why forgetting something is any more likely
to 
change events than simply being wrong about having the memory in the
first 
place, the latter of which happens constantly.  If you want to argue
about 
what nonzero probability implies, you'd have a hard time showing that 
anything non-contradictory at all has a nonzero probability of being
true. 
:)

 

Because of the entanglement, I don't think you can, in general,
reverse 
the spin
state of the  particle without reversing what is known about it by
"the 
rest of
the world".
   

The rest of the world?  What's that?

Anna




 

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[russell standish-2]

On Sun, Mar 15, 2009 at 11:06:42AM -0700, Brent Meeker wrote:

>
> Saibal Mitra wrote:
> > If we consider measuring the spin of a particle, you could also say that the
> > two possible outcomes just exist and thatthere are two possible future
> > versions of me. There is no meaningful way to associate myself with either
> > of the two outcomes.
> >
> > But then, precisely this implies that after a measurement and forgetting
> > about the result will yield a version of me who is in a similar position as
> > that earlier version of me who had yet to make the measurement. If one could
> > perform measurements in a reversible way, this would be possible to
> > experimentally confirm, as David Deutsch pointed out. You can start with a
> > spin polarized in the x direction. Then you measure the z-component. There
> > then exists a unitary transformation which leads to the observer forgetting
> > about the outcome of the measurement and to the spin to be restored in the
> > original state. The observer does remember having measured the z-component
> > of the spin.
> >
> > Then, measuring the x-component again will yield "spin-up" with 100%
> > probability, confirming that both branches in which the observer measured
> > spin up and spin down have coherently recombined. This then proves that had
> > the observer measured the z-component, the outcome would not be a priori
> > determined, despite the observer having measured it earlier. So, both
> > branches are real. But then this is true in general, also if the quantum
> > state is of the form:
> >
> > |You>[|spin up>|rest of the world knows the spin is up> + |spin down>|rest
> > of the world knows spin is down>]
>
> You're contemplating reversing three different things:
>
> 1) Your knowledge, by forgetting a measurement result.  Something that's easy to do.
>
> 2) The spin state of a particle.
>
> 3) The state of what the rest of the world knows.
>
> Because of the entanglement, I don't think you can, in general, reverse the spin
> state of the  particle without reversing what is known about it by "the rest of
> the world".
> If it was a known state (to someone) the particle can easily be put back in that
> state.  But to do so for a general, unknown state, after a measurement would
> require invoking time-reversal invariance of the state of whole universe (or at
> least all of it entangled with the particle spin via the measuring apparatus).
>
> Brent Meeker
>

By contrast, I think this line of reasoning can be used to create an
experiment that tests a couple of different versions of MWI.

Consider a Stern-Gerlach experiment where a particle is prepared in
the x+ state. Then measure the state of the particle's spin along the
z-axis, but _do not_ record the result. Finally measure the spin along
the x-axis.

According to Saibal's interpretation (which accords with my own
intuition), the result should be spin up (x+) always. According to the
interpretation you're suggesting Brent (the decoherence of the
environment to contain a memory of whether the spin was z+ or z- -
which I think accords with David Deutch's intuition), the final result
should be x+ or x- with 50% probability. It may be important to send
the result of the intervening measurement to a memory store somewhere
else that the experimenter does not look at.

This should be a doable experiment, and in fact may already have been
done. It is similar in some respects to a version of the two-slit
experiment performed a couple of years ago that generated a spark of
interest.


--

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[Brent Meeker-2]

russell standish wrote:

> On Sun, Mar 15, 2009 at 11:06:42AM -0700, Brent Meeker wrote:
>> Saibal Mitra wrote:
>>> If we consider measuring the spin of a particle, you could also say that the
>>> two possible outcomes just exist and thatthere are two possible future
>>> versions of me. There is no meaningful way to associate myself with either
>>> of the two outcomes.
>>>
>>> But then, precisely this implies that after a measurement and forgetting
>>> about the result will yield a version of me who is in a similar position as
>>> that earlier version of me who had yet to make the measurement. If one could
>>> perform measurements in a reversible way, this would be possible to
>>> experimentally confirm, as David Deutsch pointed out. You can start with a
>>> spin polarized in the x direction. Then you measure the z-component. There
>>> then exists a unitary transformation which leads to the observer forgetting
>>> about the outcome of the measurement and to the spin to be restored in the
>>> original state. The observer does remember having measured the z-component
>>> of the spin.
>>>
>>> Then, measuring the x-component again will yield "spin-up" with 100%
>>> probability, confirming that both branches in which the observer measured
>>> spin up and spin down have coherently recombined. This then proves that had
>>> the observer measured the z-component, the outcome would not be a priori
>>> determined, despite the observer having measured it earlier. So, both
>>> branches are real. But then this is true in general, also if the quantum
>>> state is of the form:
>>>
>>> |You>[|spin up>|rest of the world knows the spin is up> + |spin down>|rest
>>> of the world knows spin is down>]
>> You're contemplating reversing three different things:
>>
>> 1) Your knowledge, by forgetting a measurement result.  Something that's easy to do.
>>
>> 2) The spin state of a particle.
>>
>> 3) The state of what the rest of the world knows.
>>
>> Because of the entanglement, I don't think you can, in general, reverse the spin
>> state of the  particle without reversing what is known about it by "the rest of
>> the world".
>> If it was a known state (to someone) the particle can easily be put back in that
>> state.  But to do so for a general, unknown state, after a measurement would
>> require invoking time-reversal invariance of the state of whole universe (or at
>> least all of it entangled with the particle spin via the measuring apparatus).
>>
>> Brent Meeker
>>
>
> By contrast, I think this line of reasoning can be used to create an
> experiment that tests a couple of different versions of MWI.
>
> Consider a Stern-Gerlach experiment where a particle is prepared in
> the x+ state. Then measure the state of the particle's spin along the
> z-axis, but _do not_ record the result. Finally measure the spin along
> the x-axis.
>
> According to Saibal's interpretation (which accords with my own
> intuition), the result should be spin up (x+) always. According to the
> interpretation you're suggesting Brent (the decoherence of the
> environment to contain a memory of whether the spin was z+ or z- -
> which I think accords with David Deutch's intuition), the final result
> should be x+ or x- with 50% probability. It may be important to send
> the result of the intervening measurement to a memory store somewhere
> else that the experimenter does not look at.
>
> This should be a doable experiment, and in fact may already have been
> done. It is similar in some respects to a version of the two-slit
> experiment performed a couple of years ago that generated a spark of
> interest.
>
>

No need to do it.  Even more telling experiments have already been done in which
the "measurement" was just the unrecorded IR radiation from buckyballs.
Buckyballs which were sufficiently cold showed the 2-slit interference pattern
in a Young's slit type experiment.  But when they were warm enough to emit IR
radiation that, if detected, could have localized them, the interference
disappeared.  So it is not only a matter of the experimenter not looking at the
result, the rest of the universe has to not look too.

Brent

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[Stephen Paul King-2]

Hi Brent,

    But does not MWI imply that if we could somehow erase all (retrivable!)
records of a measurement,  that we would - in effect - be culling that
branch from the Tree?


----- Original Message -----
From: "Brent Meeker" <meekerdb@...>
To: <everything-list@...>
Sent: Sunday, March 15, 2009 10:06 PM
Subject: Re: Changing the past by forgetting


snip

>... Even more telling experiments have already been done in which
> the "measurement" was just the unrecorded IR radiation from buckyballs.
> Buckyballs which were sufficiently cold showed the 2-slit interference
> pattern
> in a Young's slit type experiment.  But when they were warm enough to emit
> IR
> radiation that, if detected, could have localized them, the interference
> disappeared.  So it is not only a matter of the experimenter not looking
> at the
> result, the rest of the universe has to not look too.
>
> Brent

    It is sad that Einstein was not made aware of this implication of QM. If
he was, his thought about the "moon not being there when I'm not looking at
it" would not have formed. I wish we had a better sense of exactly how
decoherence worked such that we could quantify how there might be "parts" of
a system's wave function that are entagled with its environment and other
parts that are not...

Onward!

Stephen


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[russell standish-2]

On Sun, Mar 15, 2009 at 07:06:06PM -0700, Brent Meeker wrote:

>
> No need to do it.  Even more telling experiments have already been done in which
> the "measurement" was just the unrecorded IR radiation from buckyballs.
> Buckyballs which were sufficiently cold showed the 2-slit interference pattern
> in a Young's slit type experiment.  But when they were warm enough to emit IR
> radiation that, if detected, could have localized them, the interference
> disappeared.  So it is not only a matter of the experimenter not looking at the
> result, the rest of the universe has to not look too.
>
> Brent
>

Interesting! Do you have some citations for this, or even let me know
who did the experiment?

Cheers

--

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Mathematics                        
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[Brent Meeker-2]

In "quantum eraser" experiments the erasure is done by making the measured value
ambiguous, e.g. by making a different measurement which does not commute with
the one to be erased.  In terms of MWI this has the effect or recohering (or
more accurately, not decohering) the branches rather than cutting one off.
After the erasure there is no fact of the matter as to what the value was.

Of course in these experiments care must be taken to avoid interaction with the
environment so that coherence is not lost before the second measurement.

Brent



Stephen Paul King wrote:

> Hi Brent,
>
>     But does not MWI imply that if we could somehow erase all (retrivable!)
> records of a measurement,  that we would - in effect - be culling that
> branch from the Tree?
>
>
> ----- Original Message -----
> From: "Brent Meeker" <meekerdb@...>
> To: <everything-list@...>
> Sent: Sunday, March 15, 2009 10:06 PM
> Subject: Re: Changing the past by forgetting
>
>
> snip
>
>> ... Even more telling experiments have already been done in which
>> the "measurement" was just the unrecorded IR radiation from buckyballs.
>> Buckyballs which were sufficiently cold showed the 2-slit interference
>> pattern
>> in a Young's slit type experiment.  But when they were warm enough to emit
>> IR
>> radiation that, if detected, could have localized them, the interference
>> disappeared.  So it is not only a matter of the experimenter not looking
>> at the
>> result, the rest of the universe has to not look too.
>>
>> Brent
>
>     It is sad that Einstein was not made aware of this implication of QM. If
> he was, his thought about the "moon not being there when I'm not looking at
> it" would not have formed. I wish we had a better sense of exactly how
> decoherence worked such that we could quantify how there might be "parts" of
> a system's wave function that are entagled with its environment and other
> parts that are not...
>
> Onward!
>
> Stephen
>
>
> >
>

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[Brent Meeker-2]

Here it is, quant-ph/0402146v1

Brent

russell standish wrote:

> On Sun, Mar 15, 2009 at 07:06:06PM -0700, Brent Meeker wrote:
>> No need to do it.  Even more telling experiments have already been done in which
>> the "measurement" was just the unrecorded IR radiation from buckyballs.
>> Buckyballs which were sufficiently cold showed the 2-slit interference pattern
>> in a Young's slit type experiment.  But when they were warm enough to emit IR
>> radiation that, if detected, could have localized them, the interference
>> disappeared.  So it is not only a matter of the experimenter not looking at the
>> result, the rest of the universe has to not look too.
>>
>> Brent
>>
>
> Interesting! Do you have some citations for this, or even let me know
> who did the experiment?
>
> Cheers
>

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[John Mikes]

Saibal and Stathis:

 

does this mean (in reverse) that some "new" idea (creative alteration or new combination) would CHANGE the (future) world as well?

What I mean: if erasing from the inventory (of our memory-mass) DOES change the PAST world(?), does some addition to it change it as well?

(Should I 'think' creatively and profusely about millions of dollars to get rich? I will).

 

Respectfully

 

John Mikes

On Sun, Mar 15, 2009 at 12:16 PM, Saibal Mitra <smitra@...> wrote:

Thanks!  This is like undoing historical events. If you forget about the
fact that dinosaurs ever lived on Earth and there is an alternative history
that led to your existence in the multiverse, and you do the memory erasure
also in sectors were dinosaurs never lived, you have some nonzero
probability of finding yourself on an Earth were the dinosaurs never lived.

----- Original Message -----
From: "Bruno Marchal" <marchal@...>
To: <everything-list@...>
Sent: Wednesday, March 11, 2009 06:54 PM
Subject: Re: Changing the past by forgetting


>
> Nice! I did refer often to the Saibal Mitra backtracking procedure (in
> immortality discussions). I will take a further look on your paper.
> If valid, it should work in the comp frame. Amnesia could lead you to
> the "original singularity", which could be a kind of blind spot of
> "universal consciousness", except that with comp such a singularity
> should looks like a "little Mandelbrot" set, at first sight, I mean
> something like a compact view of a universal dovetailing.
>
> Bruno
>
> On 10 Mar 2009, at 19:55, Saibal Mitra wrote:
>
> >
> > http://arxiv.org/abs/0902.3825
> >
> > I've written up a small article about the idea that you could end up
> > in a
> > different sector of the multiverse by selective memory erasure. I had
> > written about that possibility a long time ago on this list, but now
> > I've
> > made the argument more rigorous.
> >
> >
> > >
>
> http://iridia.ulb.ac.be/~marchal/
>
>
>
>
> >

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[Saibal Mitra]

Yes, I agree, and that's then why we cannot do this in practice. The
verification of the MWI would have to wait untilk we have artificially
intelligent observers implemented by quantum computers.

However, ass uming that the MWI is indeed correct, it doesn't matter if you
undo the measurement. If you just dump your memory in the nvironment in an
irreversible way, you end up in a superposition like:

|you>[ |universe_1| + |universe_2> ]

As far as |you> are concerned, it doesn't matter if |universe_1> and
|universe_2> differ by one electron state or the state of 10^23 particles:
the result of a new measurement is not pre-determined in either case.


----- Original Message -----
From: "Brent Meeker" <meekerdb@...>
To: <everything-list@...>
Sent: Sunday, March 15, 2009 08:06 PM
Subject: Re: Changing the past by forgetting


>
> Saibal Mitra wrote:
> > If we consider measuring the spin of a particle, you could also say that
the
> > two possible outcomes just exist and thatthere are two possible future
> > versions of me. There is no meaningful way to associate myself with
either
> > of the two outcomes.
> >
> > But then, precisely this implies that after a measurement and forgetting
> > about the result will yield a version of me who is in a similar position
as
> > that earlier version of me who had yet to make the measurement. If one
could
> > perform measurements in a reversible way, this would be possible to
> > experimentally confirm, as David Deutsch pointed out. You can start with
a
> > spin polarized in the x direction. Then you measure the z-component.
There
> > then exists a unitary transformation which leads to the observer
forgetting
> > about the outcome of the measurement and to the spin to be restored in
the
> > original state. The observer does remember having measured the
z-component
> > of the spin.
> >
> > Then, measuring the x-component again will yield "spin-up" with 100%
> > probability, confirming that both branches in which the observer
measured
> > spin up and spin down have coherently recombined. This then proves that
had
> > the observer measured the z-component, the outcome would not be a priori
> > determined, despite the observer having measured it earlier. So, both
> > branches are real. But then this is true in general, also if the quantum
> > state is of the form:
> >
> > |You>[|spin up>|rest of the world knows the spin is up> + |spin
down>|rest
> > of the world knows spin is down>]
>
> You're contemplating reversing three different things:
>
> 1) Your knowledge, by forgetting a measurement result.  Something that's
easy to do.
>
> 2) The spin state of a particle.
>
> 3) The state of what the rest of the world knows.
>
> Because of the entanglement, I don't think you can, in general, reverse
the spin
> state of the  particle without reversing what is known about it by "the
rest of
> the world".
> If it was a known state (to someone) the particle can easily be put back
in that
> state.  But to do so for a general, unknown state, after a measurement
would
> require invoking time-reversal invariance of the state of whole universe
(or at
> least all of it entangled with the particle spin via the measuring
apparatus).
>
> Brent Meeker
>
> >
> > although you cannot directly verify it here. But that means that you
cannot
> > rule out an alternative theory in which only one of the branches is real
> > when performing a measurement in this case. But if the reality of both
> > branches is accepted, then each time you make a measurement and you
don't
> > know the outcome, the outcome is not fixed (proovided, of course, there
is

> > indeed more than one branch).
> >
> >
> > ----- Original Message -----
> > From: "Jack Mallah" <jackmallah@...>
> > To: <everything-list@...>
> > Sent: Thursday, March 12, 2009 03:47 AM
> > Subject: Re: Changing the past by forgetting
> >
> >
> >
> >
> > --- On Tue, 3/10/09, Saibal Mitra <smitra@...> wrote:
> >> http://arxiv.org/abs/0902.3825
> >>
> >> I've written up a small article about the idea that you could end up in

a
> > different sector of the multiverse by selective memory erasure. I had
> > written about that possibility a long time ago on this list, but now
I've
> > made the argument more rigorous.
> >
> > Saibal, I have to say that I disagree.  As you acknowledge, erasing
memory
> > doesn't recohere the branches.  There is no meaningful sense in which
you
> > could end up in a different branch due to memory erasure.
> >
> > You admit the 'effect' has no observable consequences.  But it has no
> > unobservable meaning either.
> >
> > In fact, other than what I call 'causal differentiation', which clearly
will
> > track the already-decohered branches (so you don't get to reshuffle the
> > deck), there is no meaningful sense in which "you" will end up in one
> > particular future branch at all.  Other than causal differentiation
> > tracking, either 'you' are all of your future branches, or 'you' are
just
> > here for the moment and are none of them.
>
> >


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