Counterfactual outcomes at various measurement settings

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Counterfactual outcomes at various measurement settings

Postby Dirkman » Thu May 18, 2017 10:08 pm

"If there are counterfactual outcomes at various measurement settings, what are they? In other words: if there is objective realism a la EPR, one should be able to identify the hypothetical values that would have been obtained if a different measurement pair had been chosen."
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Re: Counterfactual outcomes at various measurement settings

Postby Mikko » Fri May 19, 2017 12:18 am

Dirkman wrote:"If there are counterfactual outcomes"

There are not. That's what the word "counterfactual" means.
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Re: Counterfactual outcomes at various measurement settings

Postby Joy Christian » Fri May 19, 2017 2:02 am

Dirkman wrote:"If there are counterfactual outcomes at various measurement settings, what are they? In other words: if there is objective realism a la EPR, one should be able to identify the hypothetical values that would have been obtained if a different measurement pair had been chosen."

Such values are completely specified by the measurement functions A(a, lambda) defined by Bell in his infamous paper of 1964. Given a measurement setting "a" and an initial state "lambda" of the physical system, the counterfactual outcome A(a, lambda) is unambiguously given to be either +1 or -1. There is no serious issue here.

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Re: Counterfactual outcomes at various measurement settings

Postby minkwe » Sat May 20, 2017 1:38 pm

Dirkman wrote:"If there are counterfactual outcomes at various measurement settings, what are they? In other words: if there is objective realism a la EPR, one should be able to identify the hypothetical values that would have been obtained if a different measurement pair had been chosen."


If you can identify the flaw in the following argument, you will be able to answer your own question:

A photon A is heading toward Alice's detector on a distant galaxy. It will interact with the detector tomorrow to produce an outcome of +1 or -1. But the 'laws' of the excluded middle (no third truth-value) and of non-contradiction (not both truth-values), mandate that one of the propositions "Alice's will get +1", "Alice's will get -1", is true (always has been and ever will be) and the other is false (always has been and ever will be).

Suppose 'Alice's will get +1' is true today. Then whatever Alice does (or fails to do) before the photon hits her detector will make no difference: the outcome is already settled. Similarly if 'Alice's will get +1' is false today, no matter what Alice does (or fails to do), it will make no difference: the outcome is already settled.

Therefore, the future will be what it will be, irrespective of Alice's planning, choices or, intentions.



Consider the following statements:

a) If I look at the moon, I will see it.
b) Had I looked at the moon yesterday, I would have seen it.

(a) is a True statement. In this case, it is implicit that the possibility of either looking at the moon or not looking at the moon still exists.
(b) is a counterfactual statement. Statement (b) will be valid even if it is impossible for me to look at the moon now (perhaps I was blinded overnight). Accepting (b) as a valid/true statement does not mean: (c) "Seeing the moon" exists prior to me looking at the moon.

Most confusion about the meaning of counterfactual outcomes originates from sloppy use of the concepts of "Truth", "Possibilities" "Existence", "Actualities". EPR/Bell discussions are often exhibitions of serious misunderstandings of those concepts.
Dirkman wrote:"If there are counterfactual outcomes at various measurement settings, what are they?"

The counterfactual outcomes are the outcomes she could have gotten had she chosen any other settings than the one she actually chose. The result which Alice will get when she tilts her detector to angle a, could not possibly exist before Alice actually makes a measurement!!! However, the statement "If Alice turns her detector to angle a she will obtain the result A." is a True statement, which will continue to be True even if Alice had her detector to angle b, instead.

Consider the EPRB example:
Let us denote observable "what Alice observes when she tilts her device to angle a" as A, and "what Alice observes when she tilts her device to angle b" as B and "what Alice observes when she tilts her device to angle c" as C. For a single photon, All three observables A, B, C are possible, however if Alice never measures anything, none of them exist as actual outcomes. Therefore although A,B,C are all "possible", only the one which Alice actually measures, will exist. The other two will be counterfactual. For the specific particle, once Alice measures at "a", it is now impossible to measure the other two, therefore, the counterfactual outcomes B and C can not possibly exist at the same time as A. Let's look at it another way by rephrasing the statements:

A: if Alice measures the photon at angle "a" she will obtain "A"
B: If Alice measures the photon at angle "b" she will obtain "B"
C: If Alice measures the photon at angle "c" she will obtain "C"

All three statements can be True simultaneously. However, outcomes A, B, C can't exist simultaneously because of a contradiction: If Alice measures the photon at angle "a", then certainly she did not measure the photon at angles "b" or "c". In other words, all three are possibilities are simultaneously true, but only one of them can and will exist. The others will be counterfactual.

Bell's problem was that he did mathematics by mixing and combining A,B and C in the same expression. At best, he can tell you about mathematical relationships between possibilities. Drawing any inference from such relationships about what exists, or actual results of experiments is utter stupidity.

Dirkman wrote:In other words: if there is objective realism a la EPR, one should be able to identify the hypothetical values that would have been obtained if a different measurement pair had been chosen.

Do you agree that if Alice had picked a setting different from the one she actually picked she would have obtained a result? That result, whatever it is, is the counterfactual result.
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Re: Counterfactual outcomes at various measurement settings

Postby minkwe » Mon May 22, 2017 9:29 am

I am not the one asserting there are counterfactual cases. Everything I see points to an observer dependent universe, one that lacks local realism. So when someone asks about a particular local realistic theory, one which is excluded by Bell but that the author claims is not, I always ask: Please describe those counterfactual cases.


Interesting that he did not answer the question.

Do you agree that if Alice had picked a setting different from the one she actually picked she would have obtained a result?

I wonder why. Let us break down the situation fully:

Monday:
If Alice picks setting "a" on Tuesday she will obtain result "A"
If Alice picks setting "b" on Tuesday she will obtain result "B"
If Alice picks setting "c" on Tuesday she will obtain result "C"

Tuesday:
Alice picks setting "a" and obtains result "A"

Wednesday:
Alice picked setting "a" on Tuesday and obtained result "A"
If Alice had picked setting "b" on Tuesday she would have obtained result "B"
If Alice had picked setting "c" on Tuesday she would have obtained result "C"

The original question then becomes clear: Do you agree that if Alice had picked a different setting on Tuesday than the one she picked, she would have obtained a result?

Note that I don't care what the value of the actual result is, just the fact that there is a result. Also note that A, B, C are not actual values, but just labels for whatever result it is that Alice obtains for the corresponding setting.
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Re: Counterfactual outcomes at various measurement settings

Postby Dirkman » Mon May 22, 2017 10:20 pm

minkwe wrote:Bell's problem was that he did mathematics by mixing and combining A,B and C in the same expression.



"It's not Bell's problem. Bell proved a theorem along the lines of: "All theories of type X have property Y. QM does not have property Y. Therefore, QM is not a theory of type X."

What are you disagreeing about? "
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Re: Counterfactual outcomes at various measurement settings

Postby Joy Christian » Mon May 22, 2017 10:37 pm

Dirkman wrote:
minkwe wrote:Bell's problem was that he did mathematics by mixing and combining A,B and C in the same expression.

"It's not Bell's problem. Bell proved a theorem along the lines of: "All theories of type X have property Y. QM does not have property Y. Therefore, QM is not a theory of type X."

What are you disagreeing about? "

This is pure BS. Bell proved no such thing.

Please don't keep reproducing BS from PhysicsForums on this forum. Here we are engaged in serious physics. Most of the guys over there are complete fruitcakes. Take, for example, "DrChinese." He is a software developer who wouldn't know how to write (let alone understand) a single physics equation correctly.

Besides, Bell's "theorem" is history. Read (or tell them to read) the following two papers line-by-line and try to understand what is presented in them. No silly excuses:

https://arxiv.org/abs/1704.02876

http://philsci-archive.pitt.edu/13019/

I repeat: Read (or make them read) these two papers, and try to understand them. No silly excuses.

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Re: Counterfactual outcomes at various measurement settings

Postby minkwe » Tue May 23, 2017 5:20 am

Dirkman wrote:"It's not Bell's problem. Bell proved a theorem along the lines of: "All theories of type X have property Y. QM does not have property Y. Therefore, QM is not a theory of type X."

What are you disagreeing about? "

Perhaps if you spell out exactly what X and Y mean mathematically, I we will show you what we are disagreeing about.

For example, please describe to me a physical situation for which the relationship P(AB|λ) = P(A|λ)P(B|λ) is true
But the relationship P(AB|λ) = P(A|λ)P(B|Aλ) is false.

In discussions of Bell's inequality, "counterfactual" is mentioned in the context of "counterfactual definiteness". CFD says that there is a definite answer to questions such as "What result would Alice have gotten if she had measured X instead of Y?"

And you think, QM disagrees with that?

Bell in 1964 Paper wrote:Measurements can be made, say by Stern-Gerlach magnets, on selected components of the spins and . If measurement of the component , where is some unit vector, yields the value +1 then, according to quantum mechanics, measurement of must yield the value -1 and vice versa.


Bell says according to QM, Alice would have gotten a definite answer if she had measured at the same angle as Bob. Is that CFD or not?

BTW, you didn't answer the first question. Would Alice have definitely obtained a result (any result at all) had she measured at a different setting?
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Re: Counterfactual outcomes at various measurement settings

Postby Mikko » Thu May 25, 2017 1:58 am

minkwe wrote:For example, please describe to me a physical situation for which the relationship P(AB|λ) = P(A|λ)P(B|λ) is true
But the relationship P(AB|λ) = P(A|λ)P(B|Aλ) is false.

Both P(AB|λ) = P(A|λ)P(B|λ) and P(AB|λ) = P(A|λ)P(B|Aλ) are true or both are false if P(B|λ) = P(B|Aλ).
Because P(B|λ) = P(A|λ)P(B|Aλ) + (1 - P(A|λ))P(B|Āλ) — where Ā means the logical negation of A — a situation is asked where
(1 - P(A|λ))P(B|Āλ) ≠ 0, i.e., P(A|λ) ≠ 1 and P(B|Āλ) ≠ 0.
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Re: Counterfactual outcomes at various measurement settings

Postby minkwe » Thu May 25, 2017 9:48 pm

Mikko wrote:
minkwe wrote:For example, please describe to me a physical situation for which the relationship P(AB|λ) = P(A|λ)P(B|λ) is true
But the relationship P(AB|λ) = P(A|λ)P(B|Aλ) is false.

Both P(AB|λ) = P(A|λ)P(B|λ) and P(AB|λ) = P(A|λ)P(B|Aλ) are true or both are false if P(B|λ) = P(B|Aλ).
Because P(B|λ) = P(A|λ)P(B|Aλ) + (1 - P(A|λ))P(B|Āλ) — where Ā means the logical negation of A — a situation is asked where
(1 - P(A|λ))P(B|Āλ) ≠ 0, i.e., P(A|λ) ≠ 1 and P(B|Āλ) ≠ 0.

Huh!?
P(AB|λ) = P(A|λ)P(B|λ) if and only if P(B|λ) = P(B|Aλ). Therefore, there will never be a situation, physical or otherwise, for which the relationship P(AB|λ) = P(A|λ)P(B|λ) is true while the relationship P(AB|λ) = P(A|λ)P(B|Aλ) is false.

In fact P(AB|λ) = P(A|λ)P(B|Aλ) is never false (chain rule).
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Re: Counterfactual outcomes at various measurement settings

Postby Joy Christian » Sat May 27, 2017 1:37 am

***
I think some of the readers here would agree with my claim that the industry of Bell's "theorem" is an ideologically manufactured and politically sustained nonsense.

Take, for example, the following statement, sometimes attributed to one of the ardent followers of Bell, namely Adrian Kent of the Cambridge University in the UK:

" ... the general consensus is that a local hidden variable mechanism which exploits either or both loopholes in a way which would not have shown up in experiments to date would require a theory so perversely conspiratorial as to be almost incredible."

Now, to begin with, in my opinion "loopholes" are totally irrelevant, because Bell's so-called "theorem" itself is hopelessly irrelevant (if not completely wrong).

But, to my mind, the following is an excellent response to the idea of a "consensus" in science:

Image

In fact, appearance of consensus is often manufactured in science by systematic suppression of dissent: https://www.uow.edu.au/~bmartin/pubs/93nw.html.

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Re: Counterfactual outcomes at various measurement settings

Postby thray » Sat May 27, 2017 4:22 am

Right on, Joy. I couldn't agree more.
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Re: Counterfactual outcomes at various measurement settings

Postby FrediFizzx » Sat May 27, 2017 11:29 am

Well, when a theory is not experimentally verifiable then perhaps consensus means something for science. There is also the tricky business of "interpretation" that has to be dealt with. I'm not so sure it is so clear cut as Crichton paints it to be. Lot's of grey areas. Especially now-a-days since experimental facts have fallen way behind theory. Even when you have experimental facts, sometimes they are still subject to interpretation.

That is the problem with all the Bell test experiments. They are using the wrong interpretation. Mainly because they don't see the mistake in Bell's reasoning.
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Re: Counterfactual outcomes at various measurement settings

Postby thray » Sun May 28, 2017 4:37 am

FrediFizzx wrote:Well, when a theory is not experimentally verifiable then perhaps consensus means something for science. There is also the tricky business of "interpretation" that has to be dealt with. I'm not so sure it is so clear cut as Crichton paints it to be. Lot's of grey areas. Especially now-a-days since experimental facts have fallen way behind theory. Even when you have experimental facts, sometimes they are still subject to interpretation.

That is the problem with all the Bell test experiments. They are using the wrong interpretation. Mainly because they don't see the mistake in Bell's reasoning.


Fred, even a thought experiment has to be do-able in principle. And if a theory can't support at least a thought experiment, it's not much of a theory.

A theory that is incomplete -- as quantum mechanics surely is -- can't be saved by the right interpretation. There is no way to validate it.
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Re: Counterfactual outcomes at various measurement settings

Postby minkwe » Sun May 28, 2017 9:01 am

thray wrote:
FrediFizzx wrote:Well, when a theory is not experimentally verifiable then perhaps consensus means something for science. There is also the tricky business of "interpretation" that has to be dealt with. I'm not so sure it is so clear cut as Crichton paints it to be. Lot's of grey areas. Especially now-a-days since experimental facts have fallen way behind theory. Even when you have experimental facts, sometimes they are still subject to interpretation.

That is the problem with all the Bell test experiments. They are using the wrong interpretation. Mainly because they don't see the mistake in Bell's reasoning.


Fred, even a thought experiment has to be do-able in principle. And if a theory can't support at least a thought experiment, it's not much of a theory.

A theory that is incomplete -- as quantum mechanics surely is -- can't be saved by the right interpretation. There is no way to validate it.

Tom, I believe a theory does not have to be complete to be useful.The problem with quantum mechanics is IMHO not quantum mechanics itself. It is a sociological problem, owing largely to how the theory came about. The mathematics did not come out of a core principle or idea that was then formulated into it's current form. Rather, we have a mish-mash of mathematical tricks patched together, that sort of worked by trial and error and nobody knows exactly why it works, so everybody proposes their own wild "interpretation" that fits the mathematics -- some of them are outlandish, mystical and unfortunately given weight by large swaths of the community. Add to that the current political situation in science (http://www.math.columbia.edu/~woit/wordpress/?p=9207), and that explains what we are observing.

If the current QM theory had been derived out of a clear first-principle idea. There would be more progress, even if the mathematical form were essentially the same, and the theory still just as incomplete. There would be less time wasted debating nonsensical "interpretations". Unfortunately, it has now become unfashionable, and career-ending to even suggest that Quantum Mechanics should make sense. The very mechanism that is supposed to get us out of this rot, is being actively stifled in the name of "consensus".

I believe the same problem would exist in any theory if it was arrived at in a similar manner, no matter how successful the theory. Actually, a similar issue existed (and probably still does to some extent) in the field of Probability Theory. There were lots of debates about the interpretation of Probability Theory. At least, there are now very clear derivations of all the rules of probability theory starting from basic first-principle desiderata. This is still lacking in Quantum Mechanics.
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Re: Counterfactual outcomes at various measurement settings

Postby FrediFizzx » Sun May 28, 2017 11:26 am

thray wrote:A theory that is incomplete -- as quantum mechanics surely is -- can't be saved by the right interpretation. There is no way to validate it.

Tom, QM has plenty of validation. That is part of the problem is that it does in fact give us the right answers. It doesn't need saving; it just works. Probably the correct interpretation is that it is a workaround probabilistic method that gets us around our incomplete knowledge of Nature. We are working on that.
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Re: Counterfactual outcomes at various measurement settings

Postby thray » Mon May 29, 2017 8:34 am

minkwe wrote:
thray wrote:
FrediFizzx wrote:Well, when a theory is not experimentally verifiable then perhaps consensus means something for science. There is also the tricky business of "interpretation" that has to be dealt with. I'm not so sure it is so clear cut as Crichton paints it to be. Lot's of grey areas. Especially now-a-days since experimental facts have fallen way behind theory. Even when you have experimental facts, sometimes they are still subject to interpretation.

That is the problem with all the Bell test experiments. They are using the wrong interpretation. Mainly because they don't see the mistake in Bell's reasoning.


Fred, even a thought experiment has to be do-able in principle. And if a theory can't support at least a thought experiment, it's not much of a theory.

A theory that is incomplete -- as quantum mechanics surely is -- can't be saved by the right interpretation. There is no way to validate it.

Tom, I believe a theory does not have to be complete to be useful.The problem with quantum mechanics is IMHO not quantum mechanics itself. It is a sociological problem, owing largely to how the theory came about. The mathematics did not come out of a core principle or idea that was then formulated into it's current form. Rather, we have a mish-mash of mathematical tricks patched together, that sort of worked by trial and error and nobody knows exactly why it works, so everybody proposes their own wild "interpretation" that fits the mathematics -- some of them are outlandish, mystical and unfortunately given weight by large swaths of the community. Add to that the current political situation in science (http://www.math.columbia.edu/~woit/wordpress/?p=9207), and that explains what we are observing.

If the current QM theory had been derived out of a clear first-principle idea. There would be more progress, even if the mathematical form were essentially the same, and the theory still just as incomplete. There would be less time wasted debating nonsensical "interpretations". Unfortunately, it has now become unfashionable, and career-ending to even suggest that Quantum Mechanics should make sense. The very mechanism that is supposed to get us out of this rot, is being actively stifled in the name of "consensus".

I believe the same problem would exist in any theory if it was arrived at in a similar manner, no matter how successful the theory. Actually, a similar issue existed (and probably still does to some extent) in the field of Probability Theory. There were lots of debates about the interpretation of Probability Theory. At least, there are now very clear derivations of all the rules of probability theory starting from basic first-principle desiderata. This is still lacking in Quantum Mechanics.


Well spoken, Michel -- though if utility is all we demand from a theory, we don't need theory. We can simply debate the merits, "for all practical purposes", of the various interpretations of an experimental result. Then there would be no separation of science from technology.

From the time I was introduced to Joy's framework (8 years ago?) I was impressed with its mathematical completeness. Completeness that renders it independent of phenomena. And being independent of phenomena, free of physical probability which is entirely dependent on phenomenology.

IMO the inability of quantum mechanics to be mathematically complete makes it a limiting case in quantum configuration space. Joy's framework is powerful enough to incorporate spacetime as a real phenomenon.
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Re: Counterfactual outcomes at various measurement settings

Postby thray » Mon May 29, 2017 8:41 am

FrediFizzx wrote:
thray wrote:A theory that is incomplete -- as quantum mechanics surely is -- can't be saved by the right interpretation. There is no way to validate it.

Tom, QM has plenty of validation. That is part of the problem is that it does in fact give us the right answers. It doesn't need saving; it just works. Probably the correct interpretation is that it is a workaround probabilistic method that gets us around our incomplete knowledge of Nature. We are working on that.



Fred, I think my reply to Michel applies here, too -- if right answers are all we need, right answers are all we'll get. We don't need theory for that. We need theory to tell us what assumptions are right -- then we might get the questions right, too.
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