How does Bell's inequality rule out realism?

[rubi]

Spacetime isn't communicating. What is going wrong is the following:

Intuitively, we would think that objects carry around with them some numbers ##\lambda_1,\lambda_2,\ldots## that characterize all their properties. For example, their spin in ##z## direction may be calculated from these numbers by a function ##S_z(\lambda_1,\lambda_2,\ldots)##. You can prove that this naive idea is incompatible with quantum mechanics. However, our intuition for statistics derives from this idea. Only objects, whose spin can be calculated in such a way are forced to obey the statistics that we would find intuitive.

As I said, the previous naive idea is incompatible with QM. However, there are ways to fix it:
1. Give up the idea that objects have spin. The notion of spin changes depending on the situation. There are many observables ##S_z^{(1)}(\lambda_1,\lambda_2,\ldots), S_z^{(2)}(\lambda_1,\lambda_2,\ldots), \ldots## and you need to use a different one depending on the context. This is what hidden variable theories do.
2. Give up the idea that there is a (potentially transfinite) list of numbers ##\lambda_1, \lambda_2, \ldots## that characterizes the situation of the physics. Particles still have spin, but the naive way to describe it mathematically fails. This may produce statistics that is incompatible with our intuition, since the statistics that we would find intuitive is derived from the idea that there are numbers ##\lambda_1,\lambda_2,\ldots## that describe the situation completely.

The first way gives up locality. The second way gives up classicality. Some people call it "realism", but I don't think this is a good name. The universe is still real, but its mathematical description is less naive.

The reason for why we find quantum statistics non-intuitive is that in our daily life, we are used to statistics that can be derived from some underlying list of numbers. However, it is only a problem with our intuition and not with physics itself.

 

[atyy]

Spacetime isn't communicating. What is going wrong is the following:

Intuitively, we would think that objects carry around with them some sombers ##\lambda_1,\lambda_2,\ldots## that characterize all their properties. For example, their spin in ##z## direction may be calculated from these numbers by a function ##S_z(\lambda_1,\lambda_2,\ldots)##. You can prove that this naive idea is incompatible with quantum mechanics. However, our intuition for statistics derives from this idea. Only objects, whose spin can be calculated in such a way are forced to obey the statistics that we would find intuitive.

As I said, the previous naive idea is incompatible with QM. However, there are ways to fix it:
1. Give up the idea that objects have spin. The notion of spin changes depending on the situation. There are many observables ##S_z^{(1)}(\lambda_1,\lambda_2,\ldots), S_z^{(2)}(\lambda_1,\lambda_2,\ldots), \ldots## and you need to use a different one depending on the context. This is what hidden variable theories do.
2. Give up the idea that the the idea that there is a (potentially transfinite) list of numbers ##\lambda_1, \lambda_2, \ldots## that characterizes the situation of the physics. Particles still have spin, but the naive way to describe it mathematically fails. This may produce statistics that is incompatible with our intuition, since the statistics that we would find intuitive is derived from the idea that there are numbers ##\lambda_1,\lambda_2,\ldots## that describe the situation completely.

The first way gives up locality. The second way gives up classicality. Some people call it "realism", but I don't think this is a good name. The universe is still real, but its mathematical description is less naive.

The reason for why we find quantum statistics non-intuitive is that in our daily life, we are used to statistics that can be derived from some underlying list of numbers. However, it is only a problem with our intuition and not with physics itself.

Just to be clear, are you working within consistent histories?

 

[rubi]

Just to be clear, are you working within consistent histories?

No, this is essentially independent of the interpretation. The boundary is between hidden variable theories that describe the situation completely by a list of numbers ##\lambda_1,\lambda_2,\ldots## and theories that describe the situation using different mathematics.

 

[gva]

Spacetime isn't communicating. What is going wrong is the following:

Intuitively, we would think that objects carry around with them some numbers ##\lambda_1,\lambda_2,\ldots## that characterize all their properties. For example, their spin in ##z## direction may be calculated from these numbers by a function ##S_z(\lambda_1,\lambda_2,\ldots)##. You can prove that this naive idea is incompatible with quantum mechanics. However, our intuition for statistics derives from this idea. Only objects, whose spin can be calculated in such a way are forced to obey the statistics that we would find intuitive.

As I said, the previous naive idea is incompatible with QM. However, there are ways to fix it:
1. Give up the idea that objects have spin. The notion of spin changes depending on the situation. There are many observables ##S_z^{(1)}(\lambda_1,\lambda_2,\ldots), S_z^{(2)}(\lambda_1,\lambda_2,\ldots), \ldots## and you need to use a different one depending on the context. This is what hidden variable theories do.
2. Give up the idea that there is a (potentially transfinite) list of numbers ##\lambda_1, \lambda_2, \ldots## that characterizes the situation of the physics. Particles still have spin, but the naive way to describe it mathematically fails. This may produce statistics that is incompatible with our intuition, since the statistics that we would find intuitive is derived from the idea that there are numbers ##\lambda_1,\lambda_2,\ldots## that describe the situation completely.

The first way gives up locality. The second way gives up classicality. Some people call it "realism", but I don't think this is a good name. The universe is still real, but its mathematical description is less naive.

The reason for why we find quantum statistics non-intuitive is that in our daily life, we are used to statistics that can be derived from some underlying list of numbers. However, it is only a problem with our intuition and not with physics itself.

We are told that spacetime and quantum is only relevant below the Planck scale, and above it we have effective field theory and QFT (or quantum mechanics) is enough. But is our failure to understand what goes on in entanglement is because we still need to understand what goes on above the Planck scale, like how exactly is matter connected to geometry? Perhaps this would give us insight into entanglement? or totally no connection and how come?

 

[Nugatory]

But is our failure to understand what goes on in entanglement is because we still need to understand ...

It's unlikely. But without a candidate theory we'd just be speculating idly (something not allowed under the PF rules).

 

[stevendaryl]

The reason for why we find quantum statistics non-intuitive is that in our daily life, we are used to statistics that can be derived from some underlying list of numbers. However, it is only a problem with our intuition and not with physics itself.

I disagree with that diagnosis. To me, what makes quantum probability seem so weird is that the probabilities are contingent on performing a particular measurement. That would make sense in terms of a local interaction. If I have a glass bottle and I'm wondering how many pieces it would split into if I smashed with a hammer, I can only find out by actually smashing it. But in an quantum entangled system, it seems that my local measurement here affects the way I describe the situation at a far distant place. In an spin-1/2 anti-correlated twin pair EPR-type experiment, Alice's description of Bob's probabilities goes from: "For any orientation, the probability of his measuring spin-up is 1/2" to "His probability of measuring spin-up is [itex]sin^2(\frac{\theta}{2})[/itex] where [itex]\theta[/itex] is the angle between Bob's orientation and Alice's measured spin."

The mystery is how Alice's measurement can affect her description of Bob's probabilities, unless either (1) there is a nonlocal effect of Alice's measurement on Bob, or (2) Bob's particle's was already in the "collapsed" state, and Alice's measurement just informed her of this. Neither possibility is plausibly true, but they seem to be the only two possibilities.

 

[DrChinese]

Yes, non-reality is quite absurd.

In this case, it's all in the eye of the beholder as to what is reasonable and what is absurd...

I think in many cases, it is more useful for "non-reality" to be replaced by "contextual reality" or "subjective reality" or "acausal reality". Those are probably less of a turn-off.

 

[atyy]

No, this is essentially independent of the interpretation. The boundary is between hidden variable theories that describe the situation completely by a list of numbers ##\lambda_1,\lambda_2,\ldots## and theories that describe the situation using different mathematics.

But this definition of reality doesn't seem to have much to say about whether the moon is there when one is not looking at it.

 

[rubi]

We are told that spacetime and quantum is only relevant below the Planck scale, and above it we have effective field theory and QFT (or quantum mechanics) is enough. But is our failure to understand what goes on in entanglement is because we still need to understand what goes on above the Planck scale, like how exactly is matter connected to geometry? Perhaps this would give us insight into entanglement? or totally no connection and how come?

I don't think there is a connection. Quantum gravity is rather going to make the situation even more complicated, since the causal structure of spacetime is a consequence of gravitational physics and quantum gravity is a more complicated theory than classical gravity.

The mystery is how Alice's measurement can affect her description of Bob's probabilities, unless either (1) there is a nonlocal effect of Alice's measurement on Bob, or (2) Bob's particle's was already in the "collapsed" state, and Alice's measurement just informed her of this. Neither possibility is plausibly true, but they seem to be the only two possibilities.

I don't think these are the only possibilities. They are the only possibilities if we insist on an underlying description of the universe by a list ##\lambda_1, \ldots## of numbers, but if we give that up, I can't think of an argument that would enforce these to be the only possibilities. I believe that Bob would have gotten the same result if Alice hadn't performed her measurement. But that doesn't mean that there must be numbers ##\lambda_1,\ldots## such that Bob's measurement can be computed from them by a function ##S(\lambda_1,\ldots)##. At least I don't see how this logically follows. And if this doesn't follow logically, I don't expect the statistics to be consistent with the statistics that is implied by such an assumption.

But this definition of reality doesn't seem to have much to say about whether the moon is there when one is not looking at it.

Well, quantum theory just doesn't have an opinion on whether the moon is there when nobody is looking or not. That doesn't mean that the moon isn't there. The theory is just silent on this issue. I think physical theories in general can't answer such kind of questions.

My definition of reality is "that which I experience". And quantum theory adequately describes that which I experience. Hence, it adequately describes reality. I can't think of any other useful definition of "reality".

 

[gva]

Well let's think of the classic example of a pair of spin-1/2 particles that are maximally entangled. So up to a normalization constant we've got a state that is the form |0>|1> + |1>|0>.

Now let's imagine the following scenario. Bob is going to prepare 2 different ensembles - so basically 2 boxes.
box 1 : contains N spin-1/2 particles each taken from a maximally correlated pair as above
box 2 : contains N spin-1/2 particles where for each particle a coin toss has determined whether it's a spin up or spin down (let's say in the z-basis)

Bob is going to randomly choose which of the 2 boxes to give to Alice. Alice is then allowed to perform ANY experiment whatsoever on the particles in this box she's been given. Her job is to figure out whether she's been given box 1 or box 2 with a probability that's better than guessing.

There's no experiment she can perform, on the particles in the box alone, that will enable her to distinguish which box she's been given any better than guessing.

So if from her particles alone she cannot tell whether she has one of a pair of entangled spins, or simply a randomly chosen up or down particle - how then can we say that in this example the results of (local)* experiments depend on the settings of remote devices in QM?

*by 'local' here I mean in Alice's lab - that is, 'local' in the same kind of sense that I would say "my local supermarket", for example.

What other situation in life that a sentence can mean many things and people understood it differently depending on one's experience. That following sentence is one such:

"Results of measurements in (standard) QM DEPEND of the settings of remote devices"

It can be answered Yes or No. No. Because Alice doesn't know the settings of remote devices.. Yes.. because there are correlations later on. Simon was using the context of the former.. but it also be answered in the affirmative.. correct Science Advisors?

 

[atyy]

Well, quantum theory just doesn't have an opinion on whether the moon is there when nobody is looking or not. That doesn't mean that the moon isn't there. The theory is just silent on this issue. I think physical theories in general can't answer such kind of questions.

My definition of reality is "that which I experience". And quantum theory adequately describes that which I experience. Hence, it adequately describes reality. I can't think of any other useful definition of "reality".

Sure, but then I don't think you should make out that Ilja or the rest of us realists are not understanding something profound. As he and most of us say - quantum theory in the minimal interpretation is not a theory about fundamental reality. We all understand the minimal interpretation well. In fact, we may understand it better than those who claim to use it. If it is only important that quantum theory makes accurate predictions, then what is so important about a technical point that in some obscure sense one is still able to say that quantum theory is able to "explain" the correlations and preserve "locality"?

It's pretty much the same as vanhees71's confusion over collapse. If he is truly using the minimal interpretation, then why should he care about collapse, since it isn't necessarily real?

Realists do not deny the minimal interpretation - we in fact support it. But we also say that the measurement problem points to new physics (or new conceptions of reality, eg. MWI)

 

[rubi]

Sure, but then I don't think you should make out that Ilja or the rest of us realists are not understanding something profound.

I don't remember saying this. However, it is certainly true for Ilja.

As he and most of us say - quantum theory in the minimal interpretation is not a theory about fundamental reality.

I disagree. It's a theory about fundamental reality as much as classical physics is. Classical physics also doesn't tell us whether the moon is there when nobody is looking at it. Such questions are just completely inaccessible to physics or even pure reason. It's like asking about the existence of god.

There is a difference between reality and the mathematical description of reality. Physical theories can only ever describe reality. The belief in the existence of reality is independent of physics. I am a theorist and I am only interested in the mathematical desciption. I'm interested in whether the mathematical reasoning that leads to certain conclusions about the theory is watertight. All I'm telling you is that the claims of some people (such as Ilja) that quantum theory must be non-local are false. That's just a hard mathematical fact. Nobody can prove that quantum theory is non-local. One can only get this idea by being sloppy about the mathematical arguments and this is unacceptable in science.

If it is only important that quantum theory makes accurate predictions, then what is so important about a technical point that in some obscure sense one is still able to say that quantum theory is able to "explain" the correlations and preserve "locality"?

I don't find the explanation obscure at all. If you find it obscure, it means that you cannot let go the idea that reality can be described by a list ##\lambda_1,\lambda_2,\ldots## of numbers and the consequences that follow from it. Someone who doesn't adhere to this idea should have no problem with explanations of correlations and locality. And if there is no problem, then there is also no necessity to give them up.

It's pretty much the same as vanhees71's confusion over collapse. If he is truly using the minimal interpretation, then why should he care about collapse, since it isn't necessarily real?

It's an interesting mathematical question whether the collapse postulate can be deduced from the other postulates (at least in some limit) by including more details about the evolution of the environment. This already justifies investigations. If the collapse is emergent from the other axioms, then the mathematical structure of quantum theory simplifies, which is beneficial to other parts of physics.

Realists do not deny the minimal interpretation - we in fact support it. But we also say that the measurement problem points to new physics (or new conceptions of reality, eg. MWI)

I also say that it points to new conceptions of reality. If we are interested in a local theory, we have to give up the idea that reality can be described by a set of numbers ##\lambda_1,\ldots##. We are not sure how to understand this, since evolution has only equipped us with intuition for situations that can be described by such a list, but that doesn't mean we cannot understand it. I don't think the goal should be to recover a description that uses such a list ##\lambda_1,\ldots##, since it seems like an unjustified ad-hoc assumption.

 

[morrobay]

If in an experiment locality is given.* And realism is rejected in accounting for Bell violations,
then how is it that this non realism is so consistent and derivable
As in this simple inequality where both entangled particles are detected at A & B
0⁰ and 45⁰
45⁰ and 90⁰.
0⁰ and 90⁰
Then the inequality for both particles detected based on 1/2 (sin θ/2)<sup>2
n(0+45+) + n(45+90+) ≥ n (0+90+)
Results in .1464 ≥ .25.
And in this example where A and B = ± 1.
(AB) + (AB') + (A'B) - (A'B') ≤ 2, in experiment approaches 2√2
* Locality
t₀ photons from source sent to detectors at A and B
t₁ photons reach detectors and measurement process starts, photons are sent from A to B and B to A
t₂ measurements completed.
t₃ photons reach detectors A and B</sup>

 

[Ilja]

So there is always communications whether there is realism or not..

If one uses "there is" that means one makes a claim about existence, thus, one has to presuppose some form of realism. Without realism, "there is" is meaningless. There would be no difference between "there is a stone" and "there is a ghost", because what makes the second invalid - the non-existence of ghosts - is a claim about reality.

 

[DrChinese]

If one uses "there is" that means one makes a claim about existence, thus, one has to presuppose some form of realism. Without realism, "there is" is meaningless. There would be no difference between "there is a stone" and "there is a ghost", because what makes the second invalid - the non-existence of ghosts - is a claim about reality.

Again, it is more useful for "non-realism" to be replaced by "contextual reality" or "subjective reality" or "acausal reality". In these scenarios, there is not an element of reality independent of the observer's choice of measurement basis.

As to whether there is communication between Alice and Bob in the realistic scenarios: who is "communicating" with whom? (This goes back to gva's statement that "there is always communications whether there is realism or not".)

 

[Ilja]

Again, it is more useful for "non-realism" to be replaced by "contextual reality" or "subjective reality" or "acausal reality".

I have to disagree. "Contextual reality" would be simply classical realism: dBB theory is as realistic as imaginable, but is a contextual theory.

"Acausal reality" is ok by underscoring that one has to give up causality (or distort it in such a way that Reichenbach's common cause is rejected). But it suggests too strongly that something remains from realism. But what remains, if one rejects the EPR principle of reality?

Only "subjective reality" seems quite accurate - if one interprets it in such a way that my remarks remain valid. There may be, of course, ghosts in some subjective reality.

 

[DrChinese]

"Contextual reality" would be simply classical realism: ...

Only "subjective reality" seems quite accurate - if one interprets it in such a way that my remarks remain valid. There may be, of course, ghosts in some subjective reality.

Classical physics is not contextual.

And there are no "ghosts" in subjective realism - that is not physics. Not sure why you keep ascribing a metaphysical component to accepted interpretations. If you don't like an interpretation, fine, but don't dog it with inaccurate assertions.

 

[Ilja]

Classical physics may be not contextual, but dBB theory is, and it is nonetheless completely realistic, even deterministic.

"Subjective realism" is, of course, nothing precisely defined. But I think it is clear that it assumes that there may be different realities for different subjects, and, therefore, no unique objective reality, which would allow to name one "subjective reality" true and another one "false".

I do not ascribe metaphysical components to accepted interpretations. Its new for me that "subjective realism" would be an accepted interpretation. The minimal interpretation explicitly rejects any metaphysics, the Copenhagen interpretation contains some classical common sense, combined with some elements of positivism which I reject, but this is not something I consider to be important. What matters IMHO much more are the common sense elements it preserves.
MWI is not something worth to be discussed, but if I nonetheless discuss it, I do not ascribe metaphysical components to it, but invectives. Inconsistent histories I do not discuss too. What else do you have in mind?

I do ascribe metaphysical components only to an explicit rejection of realism and causality. Given that realism as well as causality are quite well-known metaphysical concepts, and that we are not talking about some general, uncertain philosophical realism resp. abstract philosophical causality, but about very specific versions of realism and causality which have to be rejected - the EPR criterion of reality, as well as Reichenbach's principle of common cause - I'm completely justified to attribute to those who reject these principles some definite metaphysical elements.

All I do is that I try to explain what it would mean if one would reject these principles seriously and consistently. Of course, nobody does it. Everybody will apply EPR realism and causality with Reichenbach's common cause as usual everywhere, except in Bell theorem discussions. So, my polemics are directed against some purely hypothetic people who are really consistent in their philosophy.

 

[DrChinese]

"Subjective realism" is, of course, nothing precisely defined. But I think it is clear that it assumes that there may be different realities for different subjects, and, therefore, no unique objective reality, which would allow to name one "subjective reality" true and another one "false".

I do not ascribe metaphysical components to accepted interpretations. Its new for me that "subjective realism" would be an accepted interpretation. ... Everybody will apply EPR realism and causality with Reichenbach's common cause as usual everywhere, except in Bell theorem discussions. So, my polemics are directed against some purely hypothetic people who are really consistent in their philosophy.

Sorry, there are plenty of ways to describe subjective realism. If you accept that position and momentum are not simultaneously well defined - a standard viewpoint - you accept subjective reality in QM. There is nothing metaphysical about it.

As to "common cause": it should be obvious that there may be a lack of strict causality in the universe we inhibit. Were that the case, it would make no sense to attempt a local deterministic interpretation of QM.

Of course, we don't know the answer to this question. In the meantime, dBB is a good interpretation too. And I don't consider it objectively real either because it is fully contextual. Even though it is deterministic.

 

[Ilja]

Sorry, there are plenty of ways to describe subjective realism. If you accept that position and momentum are not simultaneously well defined - a standard viewpoint - you accept subjective reality in QM.

No. Now it is you who is ascribing a metaphysical component to accepted interpretations.

There is nothing metaphysical about it.

I claim, in agreement with dBB theory, that only the position is a well-defined property of the particle. Instead, momentum is not. It is the result of an interaction with something else, traditionally but misleadingly named "measurement device".

In this interpretation, position and momentum are not simultaneously defined properties of the particle. But, sorry, there is nothing "subjectively realistic" in this interpretation.

In the meantime, dBB is a good interpretation too. And I don't consider it objectively real either because it is fully contextual. Even though it is deterministic.

Sorry, I don't understand this. All what really exists is explicitly specified (the wave function and the configuration) and described by explicit evolution equations, which depend on nothing else but what actually exists.

Contextuality is a normal property of realism. There is nothing unrealistic with contextuality. It is the question if something is the result of an interaction, which depends on the state of all interacting parts, or if it is a "measurement", so that the result depends only on the state of one part.

As to "common cause": it should be obvious that there may be a lack of strict causality in the universe we inhibit. Were that the case, it would make no sense to attempt a local deterministic interpretation of QM.

Hm. Similarly, it should be obvious that there may be a God as described in various Holy Scriptures. Were that the case, it would make no sense doing science. Why should I care about this possibility? Why should I care about your possibility?

 

[stevendaryl]

Classical physics is not contextual.

From a check in Wikipedia and the first hundred or so hits from a Google search, I failed to find a definitive explanation of what "contextuality" means. The definition in Wikipedia is:

Quantum Contextuality means that in any theory that attempts to explain quantum mechanics deterministically, the measurement result of a quantum observable depends on the specific experimental setup being used to measure that observable, in particular the commuting observables being measured with it.

In the case of classical mechanics, the fundamental state is completely determined by variables such as positions, momenta, types of particles and values of the electromagnetic field. So those variables are non-contextual. But there can be other variables that don't exist independently of how you attempt to measure them, such as a chemical's color under a fluoroscope, or the shapes that an object shatters into when you smash it. I'm not 100% sure if those are examples of contextual properties, but they seem to fit the intuitive definition that I've seen.

So is there a clear definition of "contextuality" under which it is clear that classical mechanics is not contextual?

 

[Jilang]

And relativity?

 

[DrChinese]

... Why should I care about this possibility? Why should I care about your possibility?

The issue is not what you personally care about. The issue is your statements. Specifically, you deny the viability of non-realistic interpretations of QM. There is no scientific support for that position beyond "I don't like it". That's not good enough here. You have stated your personal opinion, and there is no point in repeating it as if it is generally accepted. It is not.

 

[DrChinese]

So is there a clear definition of "contextuality" under which it is clear that classical mechanics is not contextual?

Not that I am aware of. I consider that the EPR paper represents the "classical" viewpoint. Consequently, I equate contextuality with their definition of a subjective reality (which they reject out of hand as unreasonable). But there have been many hairs split over the words. Little to be gained there, IMHO.

 

[Ilja]

The issue is your statements. Specifically, you deny the viability of non-realistic interpretations of QM. There is no scientific support for that position beyond "I don't like it".

I have to repeat it once you heavily distort it. I do not at all deny the viability of the minimal or the Copenhagen interpretation, even if they remain silent about the issue realism and can be characterized as positivistic. And the issue has never been viability. Belief in ghosts can be viable too.

 

[Demystifier]

Classical physics also doesn't tell us whether the moon is there when nobody is looking at it.

Classical experimental physics does not tell us that. But classical theoretical physics does. Classical theory makes precise claims about the position of the Moon as a function of time, irrespective of whether someone is looking at it.

At least this is so in the standard formulation of classical mechanics. But it may be different in a non-standard one:
http://arxiv.org/abs/quant-ph/0505143

 

[rubi]

Classical experimental physics does not tell us that. But classical theoretical physics does. Classical theory makes precise claims about the position of the Moon as a function of time, irrespective of whether someone is looking at it.

That's your interpretation of the position variable. However, just like in QM, it might as well be that the position variable is only a container of information about what will happen when we observe the system. The theory itself is silent on such metaphysical questions. Just as in QM, we need to supply an interpretation of the mathematical equations. Physics can never answer such metaphysical questions. Of course, the standard interpretation is that the position position variable has relevance at all times, independent of observation, but this is not an implication of the theory.

 

[atyy]

That's your interpretation of the position variable. However, just like in QM, it might as well be that the position variable is only a container of information about what will happen when we observe the system. The theory itself is silent on such metaphysical questions. Just as in QM, we need to supply an interpretation of the mathematical equations. Physics can never answer such metaphysical questions. Of course, the standard interpretation is that the position position variable has relevance at all times, independent of observation, but this is not an implication of the theory.

So physics does or does not answer questions like: does the universe exist after physicsts die?

 

[rubi]

So physics does or does not answer questions like: does the universe exist after physicsts die?

No, of course not. That's a religious question. The answer is inaccessible to physics.
(I could now tell you that my religious belief is that the univsere still exists after physicists die, but that would be off topic on a physics forum.)

 

[atyy]

No, of course not. That's a religious question. The answer is inaccessible to physics.
(I could now tell you that my religious belief is that the univsere still exists after physicists die, but that would be off topic on a physics forum.)

But physics does have a standard religion, eg. the claim that quantum mechanics predicts the violation of the Bell inequality at spacelike separation.

 

[DrChinese]

But physics does have a standard religion, eg. the claim that quantum mechanics predicts the violation of the Bell inequality at spacelike separation.

That's the theory, and it is science - not religion. Backed by experimental evidence, not faith.

 

[zonde]

So physics does or does not answer questions like: does the universe exist after physicsts die?

Of course not. Physics assumes that the universe exist after physicsts die. That's philosophical basis for science in general. It's called realism.

 

[rubi]

But physics does have a standard religion, eg. the claim that quantum mechanics predicts the violation of the Bell inequality at spacelike separation.

As DrChinese said, this is a consequence of the theory and not religion. However, statements about the existence of the universe after the death of physicists are not consequences of the theory, so they belong to the realm of religion. Same for the existence of the moon when nobody is looking.

Of course not. Physics assumes that the universe exist after physicsts die. That's philosophical basis for science in general. It's called realism.

In fact, physics doesn't assume this. In physics, we judge theories depending on how well they fit experimental data and experimental data is compatible with different religious belief systems.

 

[stevendaryl]

As DrChinese said, this is a consequence of the theory and not religion. However, statements about the existence of the universe after the death of physicists are not consequences of the theory, so they belong to the realm of religion. Same for the existence of the moon when nobody is looking.

I think this is completely goofy. Physics is full of reasoning of the form: "If a cloud of hydrogen with a mass of 100 solar masses is allowed to contract under gravity, blah blah blah would happen." Typically, people don't counter with: "Well, if there are no physicists around, then physics doesn't make any predictions about what would happen."

Your attitude toward what are "consequences of the theory" and what are "religious beliefs" is completely unorthodox. I won't say it's wrong, because it's a matter of semantics, and you're free to define the boundary science and faith anywhere you want. But it certainly is not mainstream, and it seems very weird for you to claim that it is.

 

[rubi]

Typically, people don't counter with: "Well, if there are no physicists around, then physics doesn't make any predictions about what would happen."

I never said that I would argue this way. I just countered atyy's claim that answers to such questions would be implied by physical theories, which is wrong. My position is that these questions are completely irrelevant as long as we have no method to answer them and this is also the reason for why nobody cares about them.

Your attitude toward what are "consequences of the theory" and what are "religious beliefs" is completely unorthodox. I won't say it's wrong, because it's a matter of semantics, and you're free to define the boundary science and faith anywhere you want. But it certainly is not mainstream, and it seems very weird for you to claim that it is.

I think it is completely mainstream. It is just rigorous argumentation. Interpretations don't follow from mathematical equations. We need to specify how they are supposed to relate to observable facts. We always emphasize this in introductory courses in theoretical physics, so I consider it completely mainstream. I don't define any arbitrary boundary. The boundary between science and faith is precisely at the point, where questions become inaccessible in principle to the methods of science. Questions that can't be answered by science are not science. This is essentially just the difference between physics and metaphysics. I don't know any physicist who would count metaphysics to be a part of physics.