subject:"Re\: The Nature of Contingency\: Quantum Physics as Modal Realism"

On 15-05-2022 09:30, Bruce Kellett wrote:

On Sun, May 15, 2022 at 5:11 PM smitra wrote:

On 15-05-2022 00:55, Bruce Kellett wrote:

On Sun, May 15, 2022 at 1:17 AM smitra wrote:

The big advantage is that decoherence is a well researched area

(mathematical) physics, results like the density matrix becoming
approximately diagonal, and relations between decoherence to

entropy

increase making it effectively irreversible are all rigorous

results

that are uncontroversial. People may still have objections

against the

MWI, but they'll still accept these results on decoherence.

Yes. And decoherence says that with time, the off-diagonal

elements of

the density matrix become arbitrarily small. If there is a

smallest

non-zero probability, then eventually these off-diagonal elements
become zero. This reduces the pure state to a mixture. Which is to

say

that there is a collapse; unitary evolution ceases, and we have
reached a classical world.

Non-zero minimum probability on its own, however, does not cause

system to evolve in a non-unitary way.

It does when decoherence is taken into account. See the above
explanation. Bruce has not omitted anything.

Bruce

I see, but these sorts of models can already be ruled out. There are

plenty of simple systems where one can make extremely accurate
measurements on which can be kept totally isolated and quantum
coherent
for long enough where such effects would have become visible.

The effects are due to decoherent entanglement with the environment.
So of course they are not seen in isolated systems. Duh.

If you don't trace over environmental degrees of freedom and include
everything in your description, then you just have a unitary evolution
operator U for a time step delta t. The evolution operator for n time
steps is U^n, which is unitary if U is unitary. The question is how we
end up with a non-unitary result this way. Your answer will then
probably be that we must modify this rule and remove entries in the
matrix U^n that are below some small cutoff value. If this is then the
general rule for the time evolution of quantum systems, then this can be
verified in the lab.

Saibal

Bruce

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

On 15-05-2022 05:11, Brent Meeker wrote:

On 5/14/2022 3:55 PM, Bruce Kellett wrote:

On Sun, May 15, 2022 at 1:17 AM smitra wrote:

On 13-05-2022 21:59, Brent Meeker wrote:

Right CI doesn't explain the collapse and MWI doesn't explain

the

collapse either but assumes it can be explained without new

physics.

I hypothesize (not assume) that CI+
probability> can

explain the collapse. I don't see any big advantage for MWI

here.

The big advantage is that decoherence is a well researched area of

(mathematical) physics, results like the density matrix becoming
approximately diagonal, and relations between decoherence to
entropy
increase making it effectively irreversible are all rigorous
results
that are uncontroversial.

But it is more than "effectively" irreversible because decohering
information spreads at the speed of light, and in an expanding
universe cannot be captured and reversed. This why I think there is
some relation between the holographic principle, expansion of the
universe, Hawking-Bekenstien entropy, and a non-zero minimum
probability.

It's still only effectively irreversible because nothing stops one from
reflecting all the escaping photons back. If we use mirrors that are
cooled to almost absolute zero, then the leakage of information from the
interior that results from having carried out a spin measurement there
can be made arbitrarily small, so the probability that the information
escapes from the confined region can be made arbitrarily small. There is
no connection between our ability to observe something and the processes
involved in making sure the photons don't escape, so whether or not
there are actually these supercool mirrors reflecting all the photons
back to recreate the initial state cannot be relevant.

Saibal

Brent

People may still have objections against the
MWI, but they'll still accept these results on decoherence.

Yes. And decoherence says that with time, the off-diagonal elements
of the density matrix become arbitrarily small. If there is a
smallest non-zero probability, then eventually these off-diagonal
elements become zero. This reduces the pure state to a mixture.
Which is to say that there is a collapse; unitary evolution ceases,
and we have reached a classical world.

Non-zero minimum probability on its own, however, does not cause a

system to evolve in a non-unitary way.

It does when decoherence is taken into account. See the above
explanation. Bruce has not omitted anything.

Bruce

Bruce is omitting something here,
perhaps some limits in which the time evolution operator becomes
degenerate or something like that. But a product of two unitary
transforms is a unitary transform, so the nth power of a unitary
transform is also a unitary transform. There is no ay you can get
anything non-unitary out of this, unless possibly in the limit of
n to
infinity.

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-05-15 Thread Bruce Kellett

On Sun, May 15, 2022 at 5:11 PM smitra  wrote:

> On 15-05-2022 00:55, Bruce Kellett wrote:
> > On Sun, May 15, 2022 at 1:17 AM smitra  wrote:
> >
> >> The big advantage is that decoherence is a well researched area of
> >> (mathematical) physics, results like the density matrix becoming
> >> approximately diagonal, and relations between decoherence to entropy
> >> increase making it effectively irreversible are all rigorous results
> >>
> >> that are uncontroversial. People may still have objections against the
> >> MWI, but they'll still accept these results on decoherence.
> >
> > Yes. And decoherence says that with time, the off-diagonal elements of
> > the density matrix become arbitrarily small. If there is a smallest
> > non-zero probability, then eventually these off-diagonal elements
> > become zero. This reduces the pure state to a mixture. Which is to say
> > that there is a collapse; unitary evolution ceases, and  we have
> > reached a classical world.
> >
> >> Non-zero minimum probability on its own, however, does not cause a
> >> system to evolve in a non-unitary way.
> >
> > It does when decoherence is taken into account. See the above
> > explanation. Bruce has not omitted anything.
> >
> > Bruce
>
> I see, but these sorts of models can already be ruled out. There are
> plenty of simple systems where one can make extremely accurate
> measurements on which can be kept totally isolated and quantum coherent
> for long enough where such effects would have become visible.
>

The effects are due to decoherent entanglement with the environment. So of
course they are not seen in isolated systems. Duh.

Bruce

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

On 15-05-2022 00:55, Bruce Kellett wrote:

On Sun, May 15, 2022 at 1:17 AM smitra wrote:

On 13-05-2022 21:59, Brent Meeker wrote:

Right CI doesn't explain the collapse and MWI doesn't explain the
collapse either but assumes it can be explained without new

physics.

I hypothesize (not assume) that CI+

can

explain the collapse. I don't see any big advantage for MWI here.

increase making it effectively irreversible are all rigorous results

that are uncontroversial. People may still have objections against
the
MWI, but they'll still accept these results on decoherence.

Non-zero minimum probability on its own, however, does not cause a
system to evolve in a non-unitary way.

It does when decoherence is taken into account. See the above
explanation. Bruce has not omitted anything.

Bruce

I see, but these sorts of models can already be ruled out. There are
plenty of simple systems where one can make extremely accurate
measurements on which can be kept totally isolated and quantum coherent
for long enough where such effects would have become visible.

Saibal

Re: The Nature of Contingency: Quantum Physics as Modal Realism

On 14-05-2022 21:11, Brent Meeker wrote:

On 5/14/2022 8:16 AM, smitra wrote:

On 13-05-2022 21:59, Brent Meeker wrote:

On 5/13/2022 12:32 PM, smitra wrote:

On 12-05-2022 22:27, Brent Meeker wrote:

On 5/12/2022 11:42 AM, smitra wrote:

All that the experiments demonstrate is that the wave function
evolves
unitarily between state preparation and measurement. This is most
easily accounted for by assuming that the wave function is a
purely
epistemic vehicle for the time evolution of probabilities. Since
it is
purely epistemic, collapse is not a problem since it is not a
physical
event. One does not have to go the whole way to QBism -- the wave
function can still be objective (inter-subjectively agreed).

That's possible but that means that QM is not a complete
fundamental

theory of reality. Anything that explains these probabilities is
then possible, including the existence of a multiverse.

Which is about as explanatory as "God did it." Explaining the
values
of the probabilities isn't the problem with MWI, it's explaining
that

there ARE probabilities even though nothing happens, and when and
where the probabilities arise.

I agree with what John Clark said in his reply.

Right CI doesn't explain the collapse and MWI doesn't explain the
collapse either but assumes it can be explained without new physics.
I hypothesize (not assume) that CI+
can

explain the collapse. I don't see any big advantage for MWI here.

The big advantage is that decoherence is a well researched area of
(mathematical) physics, results like the density matrix becoming
approximately diagonal, and relations between decoherence to entropy
increase making it effectively irreversible are all rigorous results
that are uncontroversial. People may still have objections against the
MWI, but they'll still accept these results on decoherence.

Non-zero minimum probability on its own, however, does not cause a
system to evolve in a non-unitary way. Bruce is omitting something
here, perhaps some limits in which the time evolution operator becomes
degenerate or something like that. But a product of two unitary
transforms is a unitary transform, so the nth power of a unitary
transform is also a unitary transform. There is no ay you can get
anything non-unitary out of this, unless possibly in the limit of n to
infinity.

My
attitude toward interpretations is that they are unimportant in
themselves, but they are useful in pointing to new, more
comprehensive

and accurate theories. That's one reason I'm not impressed by MWI
since it seems to ex hypothesi put any emprical testing out of reach.

But that's because MWI amounts to omitting something from a theory
that's not needed.

But something is needed. The appearance of the classical world we
experience (as well as quantum gravity, which maybe unrelated).

There is no evidence for any additional dynamic rule that induces
collapse. Evidence that it is actually needed can come from experiments
that demonstrates faster decoherence than what one would expect given
the theoretical modeling based on assuming only the usual unitary time
evolution.

Saibal

Brent

It's like what would have happened if Einstein had formulated his
theory of special relativity but he had kept the ether to serve as the
medium with strange properties such that you still have the
equivalence of inertial frames. If you then had formulated your
alternative version of special relativity by saying that the ether
doesn't exist, then people who would have stuck to the idea what an
ether must exist could have argued in the same way, i.e. that you are
not adding anything that can be tested experimentally.

Saibal

Brent

Those explanations may not be satisfactory as of yet, but that's
typical for most of science. There are phenomena that as of yet are
not well explained, but that does not (necessarily) lead us to
postulate new physics all the time. Doing so would make us like
creationists who tend to invoke a "God of the gaps".

Saibal

Brent

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-05-14 Thread Brent Meeker

On 5/14/2022 3:55 PM, Bruce Kellett wrote:

On Sun, May 15, 2022 at 1:17 AM smitra wrote:

On 13-05-2022 21:59, Brent Meeker wrote:

> Right CI doesn't explain the collapse and MWI doesn't explain the
> collapse either but assumes it can be explained without new
physics.
> I hypothesize (not assume) that CI+ can
> explain the collapse. I don't see any big advantage for MWI here.

But it is more than "effectively" irreversible because decohering
information spreads at the speed of light, and in an expanding universe
cannot be captured and reversed. This why I think there is some
relation between the holographic principle, expansion of the universe,
Hawking-Bekenstien entropy, and a non-zero minimum probability.

Brent

People may still have objections against the
MWI, but they'll still accept these results on decoherence.

Non-zero minimum probability on its own, however, does not cause a
system to evolve in a non-unitary way.

It does when decoherence is taken into account. See the above
explanation. Bruce has not omitted anything.

Bruce

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-05-14 Thread Bruce Kellett

On Sun, May 15, 2022 at 1:17 AM smitra  wrote:

> On 13-05-2022 21:59, Brent Meeker wrote:
>
> > Right CI doesn't explain the collapse and MWI doesn't explain the
> > collapse either but assumes it can be explained without new physics.
> > I hypothesize (not assume) that CI+  can
> > explain the collapse.  I don't see any big advantage for MWI here.
>
> The big advantage is that decoherence is a well researched area of
> (mathematical) physics, results like the density matrix becoming
> approximately diagonal, and relations between decoherence to entropy
> increase making it effectively irreversible are all rigorous results
> that are uncontroversial. People may still have objections against the
> MWI, but they'll still accept these results on decoherence.
>

Yes. And decoherence says that with time, the off-diagonal elements of the
density matrix become arbitrarily small. If there is a smallest non-zero
probability, then eventually these off-diagonal elements become zero. This
reduces the pure state to a mixture. Which is to say that there is a
collapse; unitary evolution ceases, and  we have reached a classical world.

Non-zero minimum probability on its own, however, does not cause a
> system to evolve in a non-unitary way.


It does when decoherence is taken into account. See the above explanation.
Bruce has not omitted anything.

Bruce

Bruce is omitting something here,
> perhaps some limits in which the time evolution operator becomes
> degenerate or something like that. But a product of two unitary
> transforms is a unitary transform, so the nth power of a unitary
> transform is also a unitary transform. There is no ay you can get
> anything non-unitary out of this, unless possibly in the limit of n to
> infinity.
>

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-05-14 Thread Bruce Kellett

On Sun, May 15, 2022 at 5:03 AM Brent Meeker  wrote:

> On 5/14/2022 4:35 AM, Bruce Kellett wrote:
>
>
> The trouble is that the duplicating machine makes only one copy, so there
> is one for Moscow and one for Helsinki. There are no multiple copies in the
> original scenario. Changing the nature of the question is not an answer.
>
> The reason I repeat this is that the Schrodinger equation gives one branch
> for each component of the superposition -- one branch for each dimension of
> the Hilbert space. So I ask again, how do you accommodate a situation in
> which there is a 90% chance of being on one branch and a 10% chance of
> being on the other branch, as per the Born rule? Changing the number of
> branches (or duplicates) is fine in a general theory, but not in QM. The SE
> gives only one branch for each outcome. What you are really saying is that
> the SE is inconsistent with the Born rule --  a point I have been making
> all along.
>
>
> Even Sean Carroll who is a proponent of MWI says that it's necessary to
> associate "weights" or "amplitudes" with branches.  I think it's possible
> to do it with branch counting if you assume some sufficiently large number
> are available to split...but that's not much different than assigning
> amplitudes.
>

As I have pointed out, no finite number can be "sufficiently large". You
need an infinite number of branches, and then you have moved well outside
the domain of the SE, since the SE only ever predicts a finite number of
branches. You cannot get the Born rule from the SE applied to a normal wave
function. The SE does not assign probabilities, those have to be imposed as
an additional assumption. Assign weights to branches all you like, but you
then have to show that these weights correspond to normal probabilities in
the prediction of experimental results.

Bruce

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

On Sat, May 14, 2022 at 3:03 PM Brent Meeker  wrote:

 > *I think it's possible to do it *[assign probabilities] *with branch
> counting if you assume some sufficiently large number are available to
> split...but that's not much different than assigning amplitudes.*


Agreed.

John K ClarkSee what's on my new list at  Extropolis

ecd

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-05-14 Thread Brent Meeker

On 5/14/2022 8:16 AM, smitra wrote:

On 13-05-2022 21:59, Brent Meeker wrote:

On 5/13/2022 12:32 PM, smitra wrote:

On 12-05-2022 22:27, Brent Meeker wrote:

On 5/12/2022 11:42 AM, smitra wrote:

That's possible but that means that QM is not a complete fundamental
theory of reality. Anything that explains these probabilities is
then possible, including the existence of a multiverse.

Which is about as explanatory as "God did it." Explaining the values
of the probabilities isn't the problem with MWI, it's explaining that
there ARE probabilities even though nothing happens, and when and
where the probabilities arise.

I agree with what John Clark said in his reply.

My
attitude toward interpretations is that they are unimportant in
themselves, but they are useful in pointing to new, more comprehensive
and accurate theories. That's one reason I'm not impressed by MWI
since it seems to ex hypothesi put any emprical testing out of reach.

But that's because MWI amounts to omitting something from a theory
that's not needed.

But something is needed. The appearance of the classical world we
experience (as well as quantum gravity, which maybe unrelated).

Brent

Saibal

Brent

Saibal

Brent

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-05-14 Thread Brent Meeker




On 5/14/2022 4:35 AM, Bruce Kellett wrote:

On Sat, May 14, 2022 at 9:19 PM John Clark  wrote:

On Fri, May 13, 2022 at 10:41 PM Bruce Kellett
 wrote:

>> After my body has been duplicated but before I have open
the door of the duplicating chamber to see where I was I
won't know if Iwill be the John Clark who has seen Moscow
or the John Clark who has seen Helsinki, and indeed the
distinction between the two would be meaningless because
the two would be identical until the door is opened and
they differentiate because then one has the memory of
seeing Moscow but the other has the memory of seeing
Helsinki.  So if both decided to place a bet on what they
would see after the door was opened (and if one decided to
place a bet then the other certainly would too because
they're identical) then, provided they were logical,and I
think I am at least most of the time, they would both put
the odds at 50-50.


/> So how do you accommodate a situation in which there is a
90% chance of seeing Moscow and a 10% chance of seeing Helsinki?/


*You've asked that exact same question several times before so
I'll answer it the exact same way I did before because you never
made an argument against what I said, you just keep asking the
same question again. If I know the duplicating machine has made 10
copies of me and that 9 of them are in Helsinki and 1 is in Moscow
then then 9 John Clark's will remember seeing Helsinki but only 1
will remember seeing Moscow; so if they place odds after the
duplication but before the door was opened and they observe where
they are they would all say there was a 90% chance they were in
Helsinki, and 90% of them would turn out to be correct and would
win their bet. *


The trouble is that the duplicating machine makes only one copy, so 
there is one for Moscow and one for Helsinki. There are no 
multiple copies in the original scenario. Changing the nature of the 
question is not an answer.


The reason I repeat this is that the Schrodinger equation gives one 
branch for each component of the superposition -- one branch for each 
dimension of the Hilbert space. So I ask again, how do you accommodate 
a situation in which there is a 90% chance of being on one branch and 
a 10% chance of being on the other branch, as per the Born rule? 
Changing the number of branches (or duplicates) is fine in a 
general theory, but not in QM. The SE gives only one branch for each 
outcome. What you are really saying is that the SE is inconsistent 
with the Born rule --  a point I have been making all along.


Even Sean Carroll who is a proponent of MWI says that it's necessary to 
associate "weights" or "amplitudes" with branches.  I think it's 
possible to do it with branch counting if you assume some sufficiently 
large number are available to split...but that's not much different than 
assigning amplitudes.


Brent

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-05-14 Thread smitra

On 14-05-2022 03:06, Bruce Kellett wrote:

On Sat, May 14, 2022 at 5:51 AM smitra wrote:

On 12-05-2022 22:18, Brent Meeker wrote:

I agree. And in fact SE fails all the time. It fails to predict

definite outcome...which is OK if you accept probabilistic

theories.

Physics doesn't work in this way. You always need to define a well
defined hypothesis first in order to interpret experimental results
and
be able to test various alternative hypotheses/theories. If you
don't do
this, you are not doing physics.

Tell that to the army of people who pounce on every anomaly that
appears in analyses of partial data from the LHC or Tevatron. Every
anomaly produces a slew of papers, all proposing "explanations" of the
anomaly. This is an industry, it is not physics. Generally the
anomalies go away with time and further data -- there are no "well
defined hypotheses" at work here.

These are well defined hypotheses. They then explain the anomaly, but
not much else. They are not going to be accepted as a promising
candidate for a new theory unless a lot more experimental data comes in
to confirm one of them.

But then its real failure is that it doesn't tell you exactly when

and

where and why it stops unitary evolution and produces a result.

That's a failure of particular interpretations of QM, e.g. the CI
that
postulate collapse.

The Born rule tells us the probability of a result...IF there is

one.

Decoherence tells there's an asymptotic approach to a result and
why...but not when and where it arrives.

Decoherence does does tell you how the different sectors split over
time.

Not if unitary evolution is exact and always. You have often argued
that the original superposition never really goes away. Strictly, that
means that the initial state is still intact, and nothing has in fact
happened.

Why would nothing have happened? The observer is internal to the system
and is in an entangled state with the measured system and the local
environment.

Decoherence has to work through to a conclusion if the
sectors are to split and a definite result is to emerge.

Definite results are not needed because the observers are internal to
the system, there is no outside observer external to the entire
universe.

This is where
unitary evolution breaks down. Taken literally it never leads to a
result. Just as in a quantum computer -- the internal unitary
evolution has to invoke decoherence and collapse in order for a result
to emerge.

Only from the point of view of an external observer. But there is
nothing external to the universe.

You need some marker of the point at which the different sectors
finally differentiate. The SE itself is clearly not the whole
story...you need something like a minimum non-zero probability! Or
an acceptance that FAPP is good enough, along with an understanding of
when FAPP is good enough.

Or just accept that we also consist of partielces and are not external
to the universe.

Saibal

Bruce

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-05-14 Thread smitra

On 13-05-2022 22:06, Brent Meeker wrote:

On 5/13/2022 11:47 AM, smitra wrote:

On 12-05-2022 22:18, Brent Meeker wrote:

On 5/12/2022 11:17 AM, smitra wrote:

On 11-05-2022 23:02, Brent Meeker wrote:

On 5/11/2022 11:51 AM, smitra wrote:

On 11-05-2022 07:25, Bruce Kellett wrote:

On Wed, May 11, 2022 at 3:11 PM smitra wrote:

On 11-05-2022 06:06, Bruce Kellett wrote:
On Wed, May 11, 2022 at 1:56 PM smitra
wrote:

On 09-05-2022 00:34, Bruce Kellett wrote:

That still treats the SE as indubitally true. No theory in

physics is

'indubitably true'.

The Everett program is to say that the SE is all that there
is

-- it
explains everything. That is clearly false (no Born rule in
the

SE),

so it might be wise to doubt the universal application of the

SE.

There is no good reason to doubt the SE without any
experimental

hints

that it breaks down, or any good theoretical reasons why it is
likely to break down in some regime.

Such faith would be touching if it weren't so naive. There are

good
theoretical and experimental reasons to believe that it cannot
be

the

whole story.

As John Clark has also mentioned, the opposite is true. There
are no

good arguments for collapse theories. There are no experimental
hints
for real collapse

That depends on how you read the data. We only see one outcome
for

each experiment, after all!

And the results of those experiments lead to a theory where time
evolution is given by a unitary transform. It's as John Clark also
mentioned in one of his replies, analogous to how time reversal
symmetry is not apparent in the macroscopic world. But we know
that the fundamental laws are time reversible. This apparent
discrepancy can be explained, it's not evidence for time
reversibility being violated in nature.

and if we argue based on theory, then we see that it
leads to many problems.

The SE also has many problems., as I have taken pains to point
out.

There are no problems with the SE. It's not inconsistent with the
Born rule. The only issue is that it looks a bit unnatural for a
fundamental law of physics to require both a dynamical ruke and
the Born rule. But a real collapse is inconsistent with the SE.

Not in QBism. It's just updating your prior. Seems a perfect fit
for
someone who wants to take an information theoretic approach and
model

consciousness as an algorithm.

A real collapse is nevertheless inconsistent with the SE, there
would exist physical processes where the SE would fail. If real
collapse is supposed to happen in experiments, then because
experiments are ultimately just many particle interactions then that
means that, in general, the SE cannot be exactly valid. We may then
try to observe small violations of the SE in the lab.

I agree. And in fact SE fails all the time. It fails to predict a
definite outcome...which is OK if you accept probabilistic theories.

Physics doesn't work in this way. You always need to define a well
defined hypothesis first in order to interpret experimental results
and be able to test various alternative hypotheses/theories. If you
don't do this, you are not doing physics.

Which is why assuming the SE is the whole truth even though it
predicts that everything possible happens, isn't doing physics.

Everything possible also happens in eternal inflation theories due to
the infinite universe that these theories predict. So, that feature of
the theory isn't the relevant physics content. The same is true for the
MWI, where the relevant physics content isn't that I have a copy
somewhere in the multiverse, but the prediction that isolated systems
always evolve according to a unitary time evolution. IF CI is true then
even a totally isolated system must have a probability of undergoing a
non-unitary collapse.

Saibal

Brent

Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-05-14 Thread smitra

On 13-05-2022 21:59, Brent Meeker wrote:

On 5/13/2022 12:32 PM, smitra wrote:

On 12-05-2022 22:27, Brent Meeker wrote:

On 5/12/2022 11:42 AM, smitra wrote:

That's possible but that means that QM is not a complete fundamental
theory of reality. Anything that explains these probabilities is
then possible, including the existence of a multiverse.

Which is about as explanatory as "God did it." Explaining the values
of the probabilities isn't the problem with MWI, it's explaining
that

there ARE probabilities even though nothing happens, and when and
where the probabilities arise.

I agree with what John Clark said in his reply.

Non-zero minimum probability on its own, however, does not cause a
system to evolve in a non-unitary way. Bruce is omitting something here,
perhaps some limits in which the time evolution operator becomes
degenerate or something like that. But a product of two unitary
transforms is a unitary transform, so the nth power of a unitary
transform is also a unitary transform. There is no ay you can get
anything non-unitary out of this, unless possibly in the limit of n to
infinity.

But that's because MWI amounts to omitting something from a theory
that's not needed. It's like what would have happened if Einstein had
formulated his theory of special relativity but he had kept the ether to
serve as the medium with strange properties such that you still have the
equivalence of inertial frames. If you then had formulated your
alternative version of special relativity by saying that the ether
doesn't exist, then people who would have stuck to the idea what an
ether must exist could have argued in the same way, i.e. that you are
not adding anything that can be tested experimentally.

Saibal

Brent

Saibal

Brent

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

On Sat, May 14, 2022 at 7:35 AM Bruce Kellett  wrote:

*>>> So how do you accommodate a situation in which there is a 90% chance
>>> of seeing Moscow and a 10% chance of seeing Helsinki?*
>>>
>>
>> >> You've asked that exact same question several times before so I'll
>> answer it the exact same way I did before because you never made an
>> argument against what I said, you just keep asking the same question again.
>> If I know the duplicating machine has made 10 copies of me and that 9 of
>> them are in Helsinki and 1 is in Moscow then then 9 John Clark's will
>> remember seeing Helsinki but only 1 will remember seeing Moscow; so if
>> they place odds after the duplication but before the door was opened and
>> they observe where they are they would all say there was a 90% chance
>> they were in Helsinki, and 90% of them would turn out to be correct
>> and would win their bet.
>>
>
> *> The trouble is that the duplicating machine makes only one copy, so
> there is one for Moscow and one for Helsinki. There are no multiple copies
> in the original scenario. Changing the nature of the question is not an
> answer.*
>

Huh?!  The question asked of me was how could I explain a 90% chance of
seeing Moscow and a 10% chance of seeing Helsinki and I have done so. If
only one copy has been made then there would *NOT* be a 90% chance of
seeing Moscow and a 10% chance of seeing Helsinki.

>  > *So I ask again, how do you accommodate a situation in which there is
> a 90% chance of being on one branch and a 10% chance of being on the other
> branch*

And I would answer that question exactly precisely the same way I have
already answered it so many times before and absolutely refused to do again
until somebody points to an objection I haven't already answered a dozen
times before.

*> Changing the number of branches (or duplicates) is fine in a
> general theory, but not in QM. The SE gives only one branch for each
> outcome.*
>

And moving one hydrogen atom in your big toe (or even the big toe of your
neighbor across the street) one nanometer to the left is a change that will
split a universe if MWI is correct, but that outcome will not make a
difference to your conscious experience, at least not immediately, perhaps
in time it will due to classical chaos but that's irrelevant for this
discussion.

> *> What you are really saying is that the SE is inconsistent with the Born
> rule --  a point I have been making all along.*
>

We already know mathematically that if you want to get probabilities out of
the wave equation and have all the probabilities add up to exactly 1 and
none of the probabilities have a negative value (and you need those things
for the very concept of probability to make any sense) then the Born rule
is the only way to do it; I think that's why Brent said "*Explaining the
values of the probabilities isn't the problem with MWI, it's explaining
that there **are** probabilities**". *I guess for some reason you disagree
with Brent.

John K ClarkSee what's on my new list at  *Extropolis*

zmv

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

On Sat, May 14, 2022 at 2:27 AM Quentin Anciaux  wrote:

*> It has taken almost 20 years, but finally you acknowledge first person
> indeterminacy...*


Well I have always acknowledged that if a conscious brain is exactly
duplicated then there is only 1 conscious experience not 2 because the 2
brains are identical and identical objects do identical things in identical
circumstances. And I have always acknowledged that if a single change is
then made, one remembers seeing Moscow but the other remembers seeing
Helsinki, then there are now 2 brains producing 2 different conscious
experiences. And I have always insisted, and still insist, that after the
duplication has been made but before an observation is allowed, it would be
meaningless to ask if you are The Moscow Man or The Helsinki Man because
neither The Moscow Man or the Helsinki Man will exist until Moscow and
Helsinki are observed and a memory is made to differentiate the 2.

And I certainly think it is absolutely ridiculous to claim a great
discovery and base a philosophy on nothing but a grammatical quirk in the
English language and in most if not all human languages; in particular in
the way they use personal pronouns such as "you"; that word works fine in
everyday life but certainly *NOT* when posing thought experiments designed
to probe the fundamental nature of personal identity.

John K ClarkSee what's on my new list at  Extropolis

nte

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-05-14 Thread Bruce Kellett

On Sat, May 14, 2022 at 9:19 PM John Clark  wrote:

> On Fri, May 13, 2022 at 10:41 PM Bruce Kellett 
> wrote:
>
> >> After my body has been duplicated but before I have open the door of
>>> the duplicating chamber to see where I was I won't know if I will be
>>> the John Clark who has seen Moscow or the John Clark who has seen Helsinki,
>>> and indeed the distinction between the two would be meaningless because the
>>> two would be identical until the door is opened and they differentiate
>>> because then one has the memory of seeing Moscow but the other has the
>>> memory of seeing Helsinki.  So if both decided to place a bet on what they
>>> would see after the door was opened (and if one decided to place a bet then
>>> the other certainly would too because they're identical) then, provided
>>> they were logical,and I think I am at least most of the time, they would
>>> both put the odds at 50-50.
>>>
>>
>> *> So how do you accommodate a situation in which there is a 90% chance
>> of seeing Moscow and a 10% chance of seeing Helsinki?*
>>
>
> *You've asked that exact same question several times before so I'll answer
> it the exact same way I did before because you never made an argument
> against what I said, you just keep asking the same question again. If I
> know the duplicating machine has made 10 copies of me and that 9 of them
> are in Helsinki and 1 is in Moscow then then 9 John Clark's will remember
> seeing Helsinki but only 1 will remember seeing Moscow; so if they place
> odds after the duplication but before the door was opened and they observe
> where they are they would all say there was a 90% chance they were in
> Helsinki, and 90% of them would turn out to be correct and would win their
> bet. *
>

The trouble is that the duplicating machine makes only one copy, so there
is one for Moscow and one for Helsinki. There are no multiple copies in the
original scenario. Changing the nature of the question is not an answer.

The reason I repeat this is that the Schrodinger equation gives one branch
for each component of the superposition -- one branch for each dimension of
the Hilbert space. So I ask again, how do you accommodate a situation in
which there is a 90% chance of being on one branch and a 10% chance of
being on the other branch, as per the Born rule? Changing the number of
branches (or duplicates) is fine in a general theory, but not in QM. The SE
gives only one branch for each outcome. What you are really saying is that
the SE is inconsistent with the Born rule --  a point I have been making
all along.

Bruce

>

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

On Fri, May 13, 2022 at 10:41 PM Bruce Kellett 
wrote:

>> After my body has been duplicated but before I have open the door of the
>> duplicating chamber to see where I was I won't know if I will be the
>> John Clark who has seen Moscow or the John Clark who has seen Helsinki, and
>> indeed the distinction between the two would be meaningless because the two
>> would be identical until the door is opened and they differentiate because 
>> then
>> one has the memory of seeing Moscow but the other has the memory of
>> seeing Helsinki.  So if both decided to place a bet on what they would see
>> after the door was opened (and if one decided to place a bet then the other
>> certainly would too because they're identical) then, provided they were
>> logical,and I think I am at least most of the time, they would both put the
>> odds at 50-50.
>>
>
> *> So how do you accommodate a situation in which there is a 90% chance of
> seeing Moscow and a 10% chance of seeing Helsinki?*
>

*You've asked that exact same question several times before so I'll answer
it the exact same way I did before because you never made an argument
against what I said, you just keep asking the same question again. If I
know the duplicating machine has made 10 copies of me and that 9 of them
are in Helsinki and 1 is in Moscow then then 9 John Clark's will remember
seeing Helsinki but only 1 will remember seeing Moscow; so if they place
odds after the duplication but before the door was opened and they observe
where they are they would all say there was a 90% chance they were in
Helsinki, and 90% of them would turn out to be correct and would win their
bet. *

*And even if the machine made an infinite number of copies, all slightly
different, there would still only be a FINITE number of them that have
brains similar enough to mine to produce a conscious experience virtually
identical to that of John Clark's.*

John K ClarkSee what's on my new list at  *Extropolis*

w61

lmt

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-05-14 Thread Stathis Papaioannou

On Sat, 14 May 2022 at 12:06, John Clark  wrote:

> On Fri, May 13, 2022 at 9:46 PM Stathis Papaioannou 
> wrote:
>
> *>>> Explaining the values of the probabilities isn't the problem with
 MWI,  it's explaining that there are probabilities*
>>>
>>>
>>> >> That's easy in MWI. Probabilities exist because until you actually
>>> look at it there is no way to know if you are the Brent Meeker who lives in
>>> a universe where the electron went left or you are the Brent Meeker who
>>> lives in a universe where the electron went right, due to the fact that the
>>> only difference between the two Brent Meekers is what the electron does.
>>>
>>
>> > But you don’t think this applies with non MWI duplication.
>>
>
> That is simply NOT true! After my body has been duplicated but before I
> have open the door of the duplicating chamber to see where I was I won't
> know if I will be the John Clark who has seen Moscow or the John Clark
> who has seen Helsinki, and indeed the distinction between the two would be
> meaningless because the two would be identical until the door is opened and
> they differentiate because then one has the memory of seeing Moscow but
> the other has the memory of seeing Helsinki.  So if both decided to place a
> bet on what they would see after the door was opened (and if one decided to
> place a bet then the other certainly would too because they're identical)
> then, provided they were logical,and I think I am at least most of the
> time, they would both put the odds at 50-50.
>

Well, I’m sorry, because I previously had the impression that you
vehemently disagreed with this.

> --
Stathis Papaioannou

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-05-14 Thread Quentin Anciaux

Le sam. 14 mai 2022, 04:06, John Clark  a écrit :

> On Fri, May 13, 2022 at 9:46 PM Stathis Papaioannou 
> wrote:
>
> *>>> Explaining the values of the probabilities isn't the problem with
 MWI,  it's explaining that there are probabilities*
>>>
>>>
>>> >> That's easy in MWI. Probabilities exist because until you actually
>>> look at it there is no way to know if you are the Brent Meeker who lives in
>>> a universe where the electron went left or you are the Brent Meeker who
>>> lives in a universe where the electron went right, due to the fact that the
>>> only difference between the two Brent Meekers is what the electron does.
>>>
>>
>> > But you don’t think this applies with non MWI duplication.
>>
>
> That is simply NOT true! After my body has been duplicated but before I
> have open the door of the duplicating chamber to see where I was I won't
> know if I will be the John Clark who has seen Moscow or the John Clark
> who has seen Helsinki, and indeed the distinction between the two would be
> meaningless because the two would be identical until the door is opened and
> they differentiate because then one has the memory of seeing Moscow but
> the other has the memory of seeing Helsinki.  So if both decided to place a
> bet on what they would see after the door was opened (and if one decided to
> place a bet then the other certainly would too because they're identical)
> then, provided they were logical,and I think I am at least most of the
> time, they would both put the odds at 50-50.
>

It has taken almost 20 years, but finally you acknowledge first person
indeterminacy...

藍

Quentin

>
>   John K ClarkSee what's on my new list at  Extropolis
> 
> lmt
>
>
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> 
> .
>

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-05-13 Thread Bruce Kellett

On Sat, May 14, 2022 at 12:06 PM John Clark  wrote:

> On Fri, May 13, 2022 at 9:46 PM Stathis Papaioannou 
> wrote:
>
> *>>> Explaining the values of the probabilities isn't the problem with
 MWI,  it's explaining that there are probabilities*
>>>
>>>
>>> >> That's easy in MWI. Probabilities exist because until you actually
>>> look at it there is no way to know if you are the Brent Meeker who lives in
>>> a universe where the electron went left or you are the Brent Meeker who
>>> lives in a universe where the electron went right, due to the fact that the
>>> only difference between the two Brent Meekers is what the electron does.
>>>
>>
>> > But you don’t think this applies with non MWI duplication.
>>
>
> That is simply NOT true! After my body has been duplicated but before I
> have open the door of the duplicating chamber to see where I was I won't
> know if I will be the John Clark who has seen Moscow or the John Clark
> who has seen Helsinki, and indeed the distinction between the two would be
> meaningless because the two would be identical until the door is opened and
> they differentiate because then one has the memory of seeing Moscow but
> the other has the memory of seeing Helsinki.  So if both decided to place a
> bet on what they would see after the door was opened (and if one decided to
> place a bet then the other certainly would too because they're identical)
> then, provided they were logical,and I think I am at least most of the
> time, they would both put the odds at 50-50.
>

So how do you accommodate a situation in which there is a 90% chance of
seeing Moscow and a 10% chance of seeing Helsinki?

Bruce

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-05-13 Thread John Clark

On Fri, May 13, 2022 at 9:46 PM Stathis Papaioannou 
wrote:

*>>> Explaining the values of the probabilities isn't the problem with
>>> MWI,  it's explaining that there are probabilities*
>>
>>
>> >> That's easy in MWI. Probabilities exist because until you actually
>> look at it there is no way to know if you are the Brent Meeker who lives in
>> a universe where the electron went left or you are the Brent Meeker who
>> lives in a universe where the electron went right, due to the fact that the
>> only difference between the two Brent Meekers is what the electron does.
>>
>
> > But you don’t think this applies with non MWI duplication.
>

That is simply NOT true! After my body has been duplicated but before I
have open the door of the duplicating chamber to see where I was I won't
know if I will be the John Clark who has seen Moscow or the John Clark who
has seen Helsinki, and indeed the distinction between the two would be
meaningless because the two would be identical until the door is opened and
they differentiate because then one has the memory of seeing Moscow but the
other has the memory of seeing Helsinki.  So if both decided to place a bet
on what they would see after the door was opened (and if one decided to
place a bet then the other certainly would too because they're identical)
then, provided they were logical,and I think I am at least most of the
time, they would both put the odds at 50-50.

  John K ClarkSee what's on my new list at  Extropolis

lmt

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-05-13 Thread Stathis Papaioannou

On Fri, 13 May 2022 at 22:09, John Clark  wrote:

>
> On Thu, May 12, 2022 at 4:27 PM Brent Meeker 
> wrote:
>
> *> Explaining the values of the probabilities isn't the problem with MWI,
>> it's explaining that there are probabilities*
>
>
> That's easy in MWI. Probabilities exist because until you actually look at
> it there is no way to know if you are the Brent Meeker who lives in a
> universe where the electron went left or you are the Brent Meeker who lives
> in a universe where the electron went right, due to the fact that the only
> difference between the two Brent Meekers is what the electron does.
>

But you don’t think this applies with non MWI duplication.

  John K ClarkSee what's on my new list at  Extropolis
> 
> mbe
>
>
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> .
>
-- 
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Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-05-13 Thread Bruce Kellett

On Sat, May 14, 2022 at 5:51 AM smitra  wrote:

> On 12-05-2022 22:18, Brent Meeker wrote:
> >
> > I agree.  And in fact SE fails all the time.  It fails to predict a
> > definite outcome...which is OK if you accept probabilistic theories.
>
> Physics doesn't work in this way. You always need to define a well
> defined hypothesis first in order to interpret experimental results and
> be able to test various alternative hypotheses/theories. If you don't do
> this, you are not doing physics.
>

Tell that to the army of people who pounce on every anomaly that appears in
analyses of partial data from the LHC or Tevatron. Every anomaly produces a
slew of papers, all proposing "explanations" of the anomaly. This is an
industry, it is not physics. Generally the anomalies go away with time and
further data -- there are no "well defined hypotheses" at work here.

> But then its real failure is that it doesn't tell you exactly when and
> > where and why it stops unitary evolution and produces a result.
>
> That's a failure of particular interpretations of QM, e.g. the CI that
> postulate collapse.
>
> > The Born rule tells us the probability of a result...IF there is one.
> > Decoherence tells there's an asymptotic approach to a result and
> > why...but not when and where it arrives.
>
> Decoherence does does tell you how the different sectors split over
> time.
>

Not if unitary evolution is exact and always. You have often argued that
the original superposition never really goes away. Strictly, that means
that the initial state is still intact, and nothing has in fact happened.
Decoherence has to work through to a conclusion if the sectors are to split
and a definite result is to emerge. This is where unitary evolution breaks
down. Taken literally it never leads to a result. Just as in a quantum
computer -- the internal unitary evolution has to invoke decoherence and
collapse in order for a result to emerge.

You need some marker of the point at which the different sectors finally
differentiate. The SE itself is clearly not the whole story...you need
something like a minimum non-zero probability! Or an acceptance that FAPP
is good enough, along with an understanding of when FAPP is good enough.

Bruce

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-05-13 Thread Brent Meeker

On 5/13/2022 11:47 AM, smitra wrote:

On 12-05-2022 22:18, Brent Meeker wrote:

On 5/12/2022 11:17 AM, smitra wrote:

On 11-05-2022 23:02, Brent Meeker wrote:

On 5/11/2022 11:51 AM, smitra wrote:

On 11-05-2022 07:25, Bruce Kellett wrote:

On Wed, May 11, 2022 at 3:11 PM smitra wrote:

On 11-05-2022 06:06, Bruce Kellett wrote:

On Wed, May 11, 2022 at 1:56 PM smitra wrote:

On 09-05-2022 00:34, Bruce Kellett wrote:

That still treats the SE as indubitally true. No theory in

physics is

'indubitably true'.

The Everett program is to say that the SE is all that there is

-- it

explains everything. That is clearly false (no Born rule in the

SE),

so it might be wise to doubt the universal application of the

SE.

There is no good reason to doubt the SE without any experimental

hints

that it breaks down, or any good theoretical reasons why it is
likely to break down in some regime.

Such faith would be touching if it weren't so naive. There are

good

theoretical and experimental reasons to believe that it cannot be

the

whole story.

As John Clark has also mentioned, the opposite is true. There
are no

good arguments for collapse theories. There are no experimental
hints
for real collapse

That depends on how you read the data. We only see one outcome for
each experiment, after all!

and if we argue based on theory, then we see that it
leads to many problems.

The SE also has many problems., as I have taken pains to point out.

Not in QBism. It's just updating your prior. Seems a perfect fit for
someone who wants to take an information theoretic approach and model
consciousness as an algorithm.

I agree. And in fact SE fails all the time. It fails to predict a
definite outcome...which is OK if you accept probabilistic theories.

Physics doesn't work in this way. You always need to define a well
defined hypothesis first in order to interpret experimental results
and be able to test various alternative hypotheses/theories. If you
don't do this, you are not doing physics.

Which is why assuming the SE is the whole truth even though it predicts
that everything possible happens, isn't doing physics.

Brent

Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-05-13 Thread Brent Meeker

On 5/13/2022 12:32 PM, smitra wrote:

On 12-05-2022 22:27, Brent Meeker wrote:

On 5/12/2022 11:42 AM, smitra wrote:

That's possible but that means that QM is not a complete fundamental
theory of reality. Anything that explains these probabilities is
then possible, including the existence of a multiverse.

I agree with what John Clark said in his reply.

Right CI doesn't explain the collapse and MWI doesn't explain the
collapse either but assumes it can be explained without new physics. I
hypothesize (not assume) that CI+ can
explain the collapse. I don't see any big advantage for MWI here. My
attitude toward interpretations is that they are unimportant in
themselves, but they are useful in pointing to new, more comprehensive
and accurate theories. That's one reason I'm not impressed by MWI since
it seems to ex hypothesi put any emprical testing out of reach.

Brent

Saibal

Brent

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

On 12-05-2022 22:18, Brent Meeker wrote:

On 5/12/2022 11:17 AM, smitra wrote:

On 11-05-2022 23:02, Brent Meeker wrote:

On 5/11/2022 11:51 AM, smitra wrote:

On 11-05-2022 07:25, Bruce Kellett wrote:

On Wed, May 11, 2022 at 3:11 PM smitra wrote:

On 11-05-2022 06:06, Bruce Kellett wrote:

On Wed, May 11, 2022 at 1:56 PM smitra wrote:

On 09-05-2022 00:34, Bruce Kellett wrote:

That still treats the SE as indubitally true. No theory in

physics is

'indubitably true'.

The Everett program is to say that the SE is all that there is

-- it

explains everything. That is clearly false (no Born rule in the

SE),

so it might be wise to doubt the universal application of the

SE.

There is no good reason to doubt the SE without any experimental

hints

that it breaks down, or any good theoretical reasons why it is
likely to break down in some regime.

Such faith would be touching if it weren't so naive. There are

good

theoretical and experimental reasons to believe that it cannot be

the

whole story.

As John Clark has also mentioned, the opposite is true. There are
no

good arguments for collapse theories. There are no experimental
hints
for real collapse

That depends on how you read the data. We only see one outcome for
each experiment, after all!

And the results of those experiments lead to a theory where time
evolution is given by a unitary transform. It's as John Clark also
mentioned in one of his replies, analogous to how time reversal
symmetry is not apparent in the macroscopic world. But we know that
the fundamental laws are time reversible. This apparent discrepancy
can be explained, it's not evidence for time reversibility being
violated in nature.

and if we argue based on theory, then we see that it
leads to many problems.

The SE also has many problems., as I have taken pains to point out.

There are no problems with the SE. It's not inconsistent with the
Born rule. The only issue is that it looks a bit unnatural for a
fundamental law of physics to require both a dynamical ruke and the
Born rule. But a real collapse is inconsistent with the SE.

Not in QBism. It's just updating your prior. Seems a perfect fit
for

someone who wants to take an information theoretic approach and model
consciousness as an algorithm.

A real collapse is nevertheless inconsistent with the SE, there would
exist physical processes where the SE would fail. If real collapse is
supposed to happen in experiments, then because experiments are
ultimately just many particle interactions then that means that, in
general, the SE cannot be exactly valid. We may then try to observe
small violations of the SE in the lab.

I agree. And in fact SE fails all the time. It fails to predict a
definite outcome...which is OK if you accept probabilistic theories.

Physics doesn't work in this way. You always need to define a well
defined hypothesis first in order to interpret experimental results and
be able to test various alternative hypotheses/theories. If you don't do
this, you are not doing physics.

But then its real failure is that it doesn't tell you exactly when and
where and why it stops unitary evolution and produces a result.

That's a failure of particular interpretations of QM, e.g. the CI that
postulate collapse.

The
Born rule tells us the probability of a result...IF there is one.
Decoherence tells there's an asymptotic approach to a result and
why...but not when and where it arrives.

Decoherence does does tell you how the different sectors split over
time.

Saibal

Brent

Re: The Nature of Contingency: Quantum Physics as Modal Realism


On 13-05-2022 14:08, John Clark wrote:

On Thu, May 12, 2022 at 4:27 PM Brent Meeker 
wrote:


_> Explaining the values of the probabilities isn't the problem with
MWI,  it's explaining that there ARE probabilities_


That's easy in MWI. Probabilities exist because until you actually
look at it there is no way to know if you are the Brent Meeker who
lives in a universe where the electron went left or you are the Brent
Meeker who lives in a universe where the electron went right, due to
the fact that the only difference between the two Brent Meekers is
what the electron does.



Indeed!

Saibal


  John K ClarkSee what's on my new list at  Extropolis [1]

mbe

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

On 13-05-2022 02:58, Bruce Kellett wrote:

On Fri, May 13, 2022 at 5:22 AM smitra wrote:

On 12-05-2022 00:44, Brent Meeker wrote:

On 5/11/2022 1:06 PM, smitra wrote:

There is effective collapse in experiments we do, but the
experiments nevertheless demonstrate that the fundamental

processes

proceed under unitary time evolution.

Except when you measure them and actually get a result.

No, there exist no experiment results that demonstrate that unitary
time
evolution is not exactly valid. What you are referring to is that in

experiments we do the wavefunction of the measured system
(effectively)
collapses. But, because we also know from all the experimental
results
that the wavefunction evolves in a unitary way, and experiments are
ultimately nothing more that many particle interactions, that either

unitary time evolution cannot be exactly valid or that the collapse
during measurement is an artifact of decoherence where the observer
(and
the local environment) gets into an entangled superposition with the

measured system. The former hypothesis lacks experimental support.

The multiverse hypothesis also lacks experimental support. We observe
collapse every day and in every experiment. We never observe a
multiverse.

Which is consistent with the multiverse hypothesis.

Saibal

Bruce

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

On 13-05-2022 02:50, Bruce Kellett wrote:

On Fri, May 13, 2022 at 5:57 AM smitra wrote:

On 12-05-2022 01:36, Bruce Kellett wrote:

On Thu, May 12, 2022 at 9:24 AM smitra wrote:

On 11-05-2022 07:30, Bruce Kellett wrote:

Who proved that the universe was finite?

If it's infinite, one can focus on only the visible part of it.

The visible part is only locally defined -- go to the edge and

there

is another, larger, region.

Yes, but in the end this doesn't really matter due to there only
being
local interactions. After a finite time any finite system can only
interact with a finite number of degrees of freedom in its
environment.

But that does not mean that variables are discrete rather than
continuous.

I agree, not by itself.

If there are only a finite number of states the entire universe

can

be in, then that's also true for observers.

That simply begs the question.

Finite or infinite universe, observers are always finite.

The universe itself is not defined by observers.

The state of the observer can then factor out of the branches the
universe is in.

That is just a meaningless contention. The state of the observer, or
what the observer is aware of, or can or cannot factor out, is
irrelevant to the universe. Reality is not defined by observers.

I fully agree. But this is precisely an argument in favor of the
multiverse when applied to the different sectors.

Saibal

Bruce

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

On 12-05-2022 22:39, Brent Meeker wrote:

On 5/12/2022 12:08 PM, smitra wrote:

On 12-05-2022 01:46, Bruce Kellett wrote:

On Thu, May 12, 2022 at 9:08 AM smitra wrote:

On 11-05-2022 08:14, Bruce Kellett wrote:

On Wed, May 11, 2022 at 3:39 PM Brent Meeker

wrote:

On 5/10/2022 9:43 PM, smitra wrote:

If there are only a finite number of states the entire universe

can be

in, then that's also true for observers.

So what does the SE for this discrete universe look like? The

one

every cites assumes a continuum. If the universe is finite then

there's

smallest non-zero probability, which as Bruce says, raises some
problems.

Not the least of these problems is the fact that a smallest

non-zero

probability makes the collapse real; destroys the ongoing
superposition; renders everything absolutely irreversible; and

screws

the hell out of unitary evolution.

Counterexample: The internal state of an ideal quantum computer will

always evolve under unitary time evolution.

If there is a smallest non-zero probability, this may no longer be
the

case.

A quantum computer implements exactly the sort of a discrete system
that is discussed, and yet it works just fine, evolving under the
unitary time evolutions as it should during the time it can be
maintained in a quantum coherent state.

But it doesn't give an answer by evolving unitarily.

True, but as long as we (can) keep it isolated, the evolution is
unitary, and that contradicts the point Brice was making about discrete
systems and unitary time evolution.

Actually, a smallest non-zero probability would certainly
resolve a lot of the problems with many worlds theory. Unitarity
would

no longer work to all levels; pure states would automatically become
mixtures under decoherence; reversibility would vanish; collapse
would

make sense, and the emergence of the classical world from the
underlying quantum substrate would be explained. All this follows if
there are no continuous quantities in physics, and continuous
variables are just approximations to underlying discrete
quantities..

Solves a lot of problems. I can see why Brent is attracted to this
idea.

This does not follow from the non-existence of continuous quantities,
because nothing on the current laws of physics implies that continuous
quantities objectively exist.

All the more reason to suspect that there is a smallest non-zero
probability.

Yes, but the point Brice makes about unitary time evolution is not true,
at least not in the general way he formulated it.

Saibal

Brent

Re: The Nature of Contingency: Quantum Physics as Modal Realism

On 12-05-2022 22:27, Brent Meeker wrote:

On 5/12/2022 11:42 AM, smitra wrote:

That's possible but that means that QM is not a complete fundamental
theory of reality. Anything that explains these probabilities is
then possible, including the existence of a multiverse.

I agree with what John Clark said in his reply.

To add to that, the "God did it" thing applies far more to the CI,
because there one postulates the collapse without explaining the
mechanism for it. In the MWI one assumes that the appearance of collapse
can be explained from the known dynamics. Those explanations may not be
satisfactory as of yet, but that's typical for most of science. There
are phenomena that as of yet are not well explained, but that does not
(necessarily) lead us to postulate new physics all the time. Doing so
would make us like creationists who tend to invoke a "God of the gaps".

Saibal

Brent

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

On 12-05-2022 22:23, Brent Meeker wrote:

On 5/12/2022 11:27 AM, smitra wrote:

On 12-05-2022 00:44, Brent Meeker wrote:

On 5/11/2022 1:06 PM, smitra wrote:

That's complete and audacious question begging. What you mean by
"real" is "modeled within the SE". There is NOTHING BUT collapse
experimentally; every result recorded in every notebook and every
tape
is evidence of a collapse.

There is effective collapse in experiments we do, but the
experiments nevertheless demonstrate that the fundamental processes
proceed under unitary time evolution.

Except when you measure them and actually get a result.

No, there exist no experiment results that demonstrate that unitary
time evolution is not exactly valid. What you are referring to is that
in experiments we do the wavefunction of the measured system
(effectively) collapses. But, because we also know from all the
experimental results that the wavefunction evolves in a unitary way,
and experiments are ultimately nothing more that many particle
interactions, that either unitary time evolution cannot be exactly
valid or that the collapse during measurement is an artifact of
decoherence where the observer (and the local environment) gets into
an entangled superposition with the measured system. The former
hypothesis lacks experimental support.

"we also know from all the experimental results that the wavefunction
evolves in a unitary way"...until we get a result and then it doesn't.

So does the latter. It's based purely on the absence of a theory of
collapse, beyond, perhaps, decoherence which provides a (sort of)
theory of pointer basis and approach to collapse.

As I wrote in the previous reply, physics does not work in the way you
are arguing here. You always have to formulate a well defined set of
hypotheses first which you can then test with experimental data. There
are plenty of examples where people tried to do test in a supposedly
model independent way and then got results that were not at all model
independent.

In this case, that the wavefunction collapses or at least appears to, is
something that's treated radically different between the CI-like
hypotheses and the MWI-like hypotheses. So, we can consider a class of
MWI-like theories where there is no collapse with CI-like theories where
there is collapse and then consider how they explain all of the
experimental data.

If you do that, then you see that CI-like theories postulate a new
physical mechanism for collapse that's left unspecified that cannot be
explained from the interaction Hamiltonian that one uses. Here I'm
staying within the context of the CI, I'm not introducing any baggage
from the MWI.

In MWI-like theories, there is nothing else than what is described by
the interaction Hamiltonian. The problem here is to get to a better
explanation of ho decoherence leads to the effective classical world.

The former problem is a real physics problem where one depends on a new
phenomena, just like e.g. dark matter in cosmology. It has to exist
according to the theory, but it hasn't yet been discovered yet. But
unlike in case of dark matter where there are multiple independent
observational results that point to its existence, in case of collapse,
you only have the mere fact that in experiments the wavefunction
collapses.

The problems with MWI-like theories is usual business that's seen in
most other theories. Take e.g. superconductivity and we have plenty of
experimental data that's not well explained yet by the theory. But this
does not lead physicists to postulate new physics.

Saibal

Brent

Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-05-13 Thread John Clark

On Thu, May 12, 2022 at 4:27 PM Brent Meeker  wrote:

*> Explaining the values of the probabilities isn't the problem with MWI,
> it's explaining that there are probabilities*


That's easy in MWI. Probabilities exist because until you actually look at
it there is no way to know if you are the Brent Meeker who lives in a
universe where the electron went left or you are the Brent Meeker who lives
in a universe where the electron went right, due to the fact that the only
difference between the two Brent Meekers is what the electron does.

  John K ClarkSee what's on my new list at  Extropolis

mbe

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-05-12 Thread Bruce Kellett

On Fri, May 13, 2022 at 5:22 AM smitra  wrote:

> On 12-05-2022 00:44, Brent Meeker wrote:
> > On 5/11/2022 1:06 PM, smitra wrote:
> >
> >> There is effective collapse in experiments we do, but the
> >> experiments nevertheless demonstrate that the fundamental processes
> >> proceed under unitary time evolution.
> >
> > Except when you measure them and actually get a result.
> >
>
> No, there exist no experiment results that demonstrate that unitary time
> evolution is not exactly valid. What you are referring to is that in
> experiments we do the wavefunction of the measured system (effectively)
> collapses. But, because we also know from all the experimental results
> that the wavefunction evolves in a unitary way, and experiments are
> ultimately nothing more that many particle interactions, that either
> unitary time evolution cannot be exactly valid or that the collapse
> during measurement is an artifact of decoherence where the observer (and
> the local environment) gets into an entangled superposition with the
> measured system. The former hypothesis lacks experimental support.
>

The multiverse hypothesis also lacks experimental support. We observe
collapse every day and in every experiment. We never observe a multiverse.

Bruce

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-05-12 Thread Bruce Kellett

On Fri, May 13, 2022 at 5:57 AM smitra  wrote:

> On 12-05-2022 01:36, Bruce Kellett wrote:
> > On Thu, May 12, 2022 at 9:24 AM smitra  wrote:
> >
> >> On 11-05-2022 07:30, Bruce Kellett wrote:
> >>> Who proved that the universe was finite?
> >>
> >> If it's infinite, one can focus on only the visible part of it.
> >
> > The visible part is only locally defined -- go to the edge and there
> > is another, larger, region.
> >
>
> Yes, but in the end this doesn't really matter due to there only being
> local interactions. After a finite time any finite system can only
> interact with a finite number of degrees of freedom in its environment.
>

But that does not mean that variables are discrete rather than continuous.

>  If there are only a finite number of states the entire universe can
>  be in, then that's also true for observers.
> >>>
> >>> That simply begs the question.
> >>>
> >>
> >> Finite or infinite universe, observers are always finite.
> >
> > The universe itself is not defined by observers.
>
>
> The state of the observer can then factor out of the branches the
> universe is in.
>

That is just a meaningless contention. The state of the observer, or what
the observer is aware of, or can or cannot factor out, is irrelevant to the
universe. Reality is not defined by observers.

Bruce

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

On 5/12/2022 12:08 PM, smitra wrote:

On 12-05-2022 01:46, Bruce Kellett wrote:

On Thu, May 12, 2022 at 9:08 AM smitra wrote:

On 11-05-2022 08:14, Bruce Kellett wrote:

On Wed, May 11, 2022 at 3:39 PM Brent Meeker

wrote:

On 5/10/2022 9:43 PM, smitra wrote:

If there are only a finite number of states the entire universe

can be

in, then that's also true for observers.

So what does the SE for this discrete universe look like? The

one

every cites assumes a continuum. If the universe is finite then

there's

smallest non-zero probability, which as Bruce says, raises some
problems.

Not the least of these problems is the fact that a smallest

non-zero

probability makes the collapse real; destroys the ongoing
superposition; renders everything absolutely irreversible; and

screws

the hell out of unitary evolution.

Counterexample: The internal state of an ideal quantum computer will

always evolve under unitary time evolution.

If there is a smallest non-zero probability, this may no longer be the
case.

But it doesn't give an answer by evolving unitarily.

Actually, a smallest non-zero probability would certainly
resolve a lot of the problems with many worlds theory. Unitarity would
no longer work to all levels; pure states would automatically become
mixtures under decoherence; reversibility would vanish; collapse would
make sense, and the emergence of the classical world from the
underlying quantum substrate would be explained. All this follows if
there are no continuous quantities in physics, and continuous
variables are just approximations to underlying discrete
quantities..

Solves a lot of problems. I can see why Brent is attracted to this
idea.

This does not follow from the non-existence of continuous quantities,
because nothing on the current laws of physics implies that continuous
quantities objectively exist.

All the more reason to suspect that there is a smallest non-zero
probability.

Brent

Re: The Nature of Contingency: Quantum Physics as Modal Realism




On 5/12/2022 11:42 AM, smitra wrote:

All that the experiments demonstrate is that the wave function evolves
unitarily between state preparation and measurement. This is most
easily accounted for by assuming that the wave function is a purely
epistemic vehicle for the time evolution of probabilities. Since it is
purely epistemic, collapse is not a problem since it is not a physical
event. One does not have to go the whole way to QBism -- the wave
function can still be objective (inter-subjectively agreed).



That's possible but that means that QM is not a complete fundamental 
theory of reality. Anything that explains these probabilities is then 
possible, including the existence of a multiverse. 


Which is about as explanatory as "God did it."  Explaining the values of 
the probabilities isn't the problem with MWI,  it's explaining that 
there *are* probabilities even though nothing happens, and when and 
where the probabilities arise.


Brent

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

On 5/12/2022 11:27 AM, smitra wrote:

On 12-05-2022 00:44, Brent Meeker wrote:

On 5/11/2022 1:06 PM, smitra wrote:

There is effective collapse in experiments we do, but the
experiments nevertheless demonstrate that the fundamental processes
proceed under unitary time evolution.

Except when you measure them and actually get a result.

"we also know from all the experimental results that the wavefunction
evolves in a unitary way"...until we get a result and then it doesn't.

So does the latter. It's based purely on the absence of a theory of
collapse, beyond, perhaps, decoherence which provides a (sort of) theory
of pointer basis and approach to collapse.

Brent

Re: The Nature of Contingency: Quantum Physics as Modal Realism