Einstein and "spooky actions"

[idav]

(1) A consequence of QM is that a measurement over here can have an instant effect on another measurement occurring very far away. This is, by definition, "nonlocality" and it has been demonstrated by experiments.

Has this particular type of non-locality shown to occur in particles that were not already entangled locally to begin with? I've heard non-locality has been shown to occur apart from entanglement, are there limitations?

 

[zaybu]

Since you are not capable of realizing and admitting instances when you are definitely shown to be wrong, you have disqualified yourself from this debate, as I explained here. Therefore, you are free to declare yourself whatever you like, and no one will care.

On top of ad hominem attack, you think you are God, deciding for everyone who is right and who is wrong. Sorry, no one appointed you referee. Your explanations were debunked in post #133.

(1) A consequence of QM is that a measurement over here can have an instant effect on another measurement occurring very far away. This is, by definition, "nonlocality" and it has been demonstrated by experiments.

False, non-locality was never ever demonstrated. What has taken place are researchers who upon having results that violate Bell theorem concluded that they have proven the existence of non-locality. And I have shown that such conclusions aren't justified.

(2) However, this "quantum nonlocality" is of a special kind. You can't control how your measurement turns out, and therefore you can't control how the other distant person's measurement turns out, either. In other words, this is a statistical effect, not a strictly deterministic or causal effect. Because of this, quantum nonlocality does not violate Special Relativity, which prohibits faster-than-light causal influences. It is worth distinguishing nonlocality as it occurs in QM from other kinds of nonlocality. For example, a faster-than-light force transmitting a casual influence, or a faster-than-light communication transmitting information, would violate Special Relativity. Sometimes people call all of these things "nonlocality" even though they are distinct, and this can cause confusion.

No one has talked about faster-than-light communication As far as I know. So stop blurring the discussion with tangent issues that are irrelevant.

(3) In order to escape the straightforward QM interpretation of (1), you have to do some work. You might claim that QM makes correct statistical predictions, but really underneath it all everything is a deterministic clockwork (classical). So, for example, you might suppose that by some mechanism unknown to physicists ("hidden variables"), each particle in an entangled pair actually has a well-defined spin (up or down) as soon as they are separated from each other, before anyone does any measuring. If this were true, then QM would still give correct statistical predictions. But the QM interpretation in (1) would be wrong: my measurement over here would NOT actually affect your measurement way over there, in any way. IOW, there wouldn't be ANY kind of nonlocality, not even the weak "quantum" kind described in (2).

Your babbling is flabergasting. I'll bet you don't even understand your own post.

(4) Bell showed, in a nutshell, that supposing QM is incomplete and we adopt the seemingly reasonable alternative in (3), we get predictions which are in conflict with experiments. In other words, the alternative in (3) is wrong. The only way to save it is to modify it by: (a) assuming instantaneous influences can occur between distant particles, i.e. nonlocality; or (b) assume that QM is at least partially correct, in that particles really do follow statistical rules not just in appearance but in actuality--IOW the entangled pair discussed in (3) really didn't have definite spins (up or down) before measurement. Or you could assume both (a) and (b). Finally, you could give up on this alternative altogether and just accept QM as described in (1).

Bell derived a theorem that one can derive with simple Venn's diagram, ignoring the very mathematical foundation of QM, a fact that you can't reconciled with your confused, misunderstanding of this issue.

(5) Most physicists feel that since alternatives to QM still require weird assumptions or consequences in order to be compatible with experiment, we may as well just accept QM and the straightforward interpretation of experiments as described in (1).

Oh I see, now you are speaking in the name of most physicists. Again, no one appointed you to that position. Is it because your position is untenable that you need to make this appeal to authority? Secondly, your (1) has been answered. Non-locality hasn't been proved, it needs no further interpretation.

For what it's worth: I'm a PhD candidate in physics with 2 grad courses and 1 undergrad course in QM, I've watched all the videos and read all the refs. posted by zaybu, I also checked my QM textbooks, and Legion and I consulted a number of peer-reviewed papers from Science, Nature, PNAS etc. I know from experience what my profs. and fellow students would say. This doesn't in and of itself make me right; again take it for what it's worth.

So, instead of providing new light into this problem, you much preferred that they stick with your version, which is so convulted and wrong in so many ways, that I can help but feel sorry for your students.

 

[PolyHedral]

In ordinary space, a vector is made of a line segment, with an arrow indicating direction. The line segment can be considered to be made of an infinite number of points and can be subdivided to any arbitrary size. If we look at position and momentum in classical physics, just looking at their magnitude, ignoring their direction for now, they can be represented by a point . Similarly for energy, which is a function of position and momentum, can take arbitrarily any value, and can be represented by points.

These two things aren't very connected at all.

This is not the case for QM. Take for example, the hydrogen atom. The energy is quantized , and we talk about energy levels labelled by n=1,2,3... An electron can jump between any two levels, but it can't jump from n=1 to n=2.5 or 3.7 as these levels don't exist. These energy levels are represented by vectors in a Hilbert space. But these vectors cannot be reduced to points, and they cannot take any arbitrary value. It is in that sense that vectors in quantum physics are different than vectors in classical physics.

The energy levels are not represented by vectors in Hilbert space (AFAIK) The state of the electron is, and one component of that state is the electron's binding energy. That energy is in turn quantized because of the exclusion principle allowing only an integral number of wavelengths to fit into the space around the atom.

You can see that there is no equivalence in classical physics. That's why QM is developped along an entirely different mathematical framework.

Setting h=0, AFAIK, produces classical physics, so it's not completely dissimilar logic.

In Bell's theorem, the derivation used is the ordinary framework of classical physics: ordinary vectors, points, etc. Its theoretical results will be satisfied by the experimental values of a classical system

Answer what I said earlier. How do you apply Bell's inequality to a classical system?

(1) A consequence of QM is that a measurement over here can have an instant effect on another measurement occurring very far away. This is, by definition, "nonlocality" and it has been demonstrated by experiments.

IMO, you're confusing measured and inferred values. A measurement over here has no effect on the measurement over there - it does, however, allow you to infer the result you'd get if you did the measurement over there. (After all, something else might've put the other particle into a different superposition by the time you get to it!)

For what it's worth: I'm a PhD candidate in physics with 2 grad courses and 1 undergrad course in QM, I've watched all the videos and read all the refs. posted by zaybu, I also checked my QM textbooks, and Legion and I consulted a number of peer-reviewed papers from Science, Nature, PNAS etc. I know from experience what my profs. and fellow students would say. This doesn't in and of itself make me right; again take it for what it's worth.

Maths or it didn't happen!

 

[zaybu]

The energy levels are not represented by vectors in Hilbert space (AFAIK)

Well now you know:

let

|j > be the state in which our system is in the jth quantized energy level.

From last page in: http://www.pa.msu.edu/~mmoore/Lect2_DiracNot.pdf

How do you apply Bell's inequality to a classical system?​

That's not the point I'm making. The point is that you can derive Bell`s theorem with Venn`s diagram, ignoring the whole mathematical framework of QM. As such if it applies to anything it would be to a classical system. How would you do such experiments, I have no idea.​

 

[Reptillian]

Susskind has derived Bell's theorem using only Venn's diagram, ignoring the whole mathematical apparatus of QM. Go figure.

This link may be of interest to you: Violation of Bell’s theorem | Lecture 5 - Quantum Entanglements - Susskind Lectures - Lecture Notes

It doesn't look like he's ignoring quantum math when performing the calculations to me.

 

[zaybu]

This link may be of interest to you: Violation of Bell’s theorem | Lecture 5 - Quantum Entanglements - Susskind Lectures - Lecture Notes

It doesn't look like he's ignoring quantum math when performing the calculations to me.

Read that again. In the first part he derives Bell's theorem using Venn's diagram. In the second part he shows on a theoretical level using the proper mathematical framework that a quantum system will violate Bell's theorem. And that's without doing any experiment. So even before setting an experiment, you know that Bell's theorem doesn't apply to a quantum system.

 

[zaybu]

http://www.cosmolearning.com/video-lectures/differences-between-classical-and-quantum-mechanics/

At 1:21:35

Susskind: "States in classical physics are points in a set."

A little later:

"In quantum mechanics, sets do not form sets... States form vectors in a vector space."

 

[Reptillian]

Read that again. In the first part he derives Bell's theorem using Venn's diagram. In the second part he shows on a theoretical level using the proper mathematical framework that a quantum system will violate Bell's theorem. And that's without doing any experiment. So even before setting an experiment, you know that Bell's theorem doesn't apply to a quantum system.

Ah, I think I see where the confusion comes from. That's kind of the whole point of Bell's Theorem...In the first part we start with, "Let's assume that quantum mechanics is incomplete and particles really do have well defined properties prior to measurement, what would we expect to observe?" In the second part, it's "Here's what good ol' supposedly incomplete quantum mechanics predicts we'll observe." They make incompatible predictions, which do we observe experimentally? The "incomplete" quantum prediction.

Bell's Theorem states that "local hidden variable theories are fundamentally incompatible with quantum mechanics"

You're right that on the one hand, it isn't a surprising statement since we knew before Bell that quantum mechanics seems to suggest non-realism, but prior to Bell's work, some physicists had held out hope for a more classical interpretation of the mathematics of the quantum theory. Bell proved that they shouldn't be holding their breath unless they're willing to give up locality.

 

[Mr Spinkles]

Ah, I think I see where the confusion comes from. That's kind of the whole point of Bell's Theorem...In the first part we start with, "Let's assume that quantum mechanics is incomplete and particles really do have well defined properties prior to measurement, what would we expect to observe?" In the second part, it's "Here's what good ol' supposedly incomplete quantum mechanics predicts we'll observe." They make incompatible predictions, which do we observe experimentally? The "incomplete" quantum prediction.

Bell's Theorem states that "local hidden variable theories are fundamentally incompatible with quantum mechanics"

You're right that on the one hand, it isn't a surprising statement since we knew before Bell that quantum mechanics seems to suggest non-realism, but prior to Bell's work, some physicists had held out hope for a more classical interpretation of the mathematics of the quantum theory. Bell proved that they shouldn't be holding their breath unless they're willing to give up locality.

You're right, but don't expect zaybu to get it. This has been explained to him before. His (incorrect) objection will be that there's nothing "nonlocal" to begin with about the good o'l supposedly incomplete quantum mechanics, that "nonlocality" only becomes something to consider when we are attempting to rescue a local hidden variable theory.

 

[idav]

The particle has mass which obeys classic interpretation. Example with the double slit experiment, consider what happens when there are no slits. They bounce back or go around the experiment area.

 

[Mr Spinkles]

On top of ad hominem attack, you think you are God, deciding for everyone who is right and who is wrong. Sorry, no one appointed you referee. Your explanations were debunked in post #133.

That's the post which most demonstrates my point. You won't even admit that you were wrong when you said I wrote down the singlet state "in the wrong format" for dealing with entanglement. That is kind of remarkable when your own source (your link to Susskind's lecture notes) uses the same format for dealing with entanglement as anyone can see. (Tangentially, I can see how you probably got confused based on the way Susskind treated the two-slit experiment in one of your videos (where he imagined a "spin" being used to measure which slit the particle travels through). Needless to say, that state is different from a singlet state of two spins, but past experience indicates you'll dismiss whatever I say rather than concede you might have been mistaken about something, so why should I bother?)

False, non-locality was never ever demonstrated.

Let's forget the word, "nonlocality" for a moment. Suppose I measure the spin of one of the particles in the singlet state. Does this affect the state of the other particle, or not? A simple yes-or-no answer will suffice.

No one has talked about faster-than-light communication As far as I know. So stop blurring the discussion with tangent issues that are irrelevant.

Oops! Someone didn't watch the Susskind YouTube video he posted, did he?

Student: I don't understand why you can't use this (Bell-type experiment) to signal.

Susskind: As far as I understand Aspect's experiment was done in such a way that a [speed of] light signal could not have been sent between the two measurements. .... If there was time for a light signal to go from one to the other, then it would not be a contradiction .... with causality or locality or whatever you want to call it. ... But the trick is to do the experiment in such a way that a light signal could not have gone from one electron to the other electron.
...
(paraphrasing) When people talk about hidden-variable theories, that is, a classical theory that can "mock up" the effects of quantum mechanics, what they mean by "nonlocality" is signals traveling faster than the speed of light.

So your own source clarified the same points about faster-than-light signals, and different usages of the word "nonlocality", that I clarified. BTW in the first paragraph quoted of Susskind, notice it is implied that since there was NOT "time for a light signal ..." in Aspect's experiments, there WAS therefore "a contradiction ... with causality or locality or whatever you want to call it". This shows that (1) you dismiss helpful clarifications with childish insults, instead of understanding and acknowledging them; (2) you expect others to watch a video you post in support of your arguments, yet you have either not watched, or not understood, the video yourself.

Again: such behavior disqualifies a person from reasoned debate, until he/she changes their approach.

Oh I see, now you are speaking in the name of most physicists. Again, no one appointed you to that position.

[yawn] ... It's not a position I've been appointed to, it's just a fact most physicists feel that way; I happen to be a physicist (as it happens, someone DID appoint me to that position) so I'm just passing along my firsthand experience ... Griffiths says the same thing ... [/yawn]

So, instead of providing new light into this problem, you much preferred that they stick with your version, which is so convulted and wrong in so many ways, that I can help but feel sorry for your students.

Students? I don't teach physics, I do physics. Not that it matters ...

 

[Mr Spinkles]

IMO, you're confusing measured and inferred values. A measurement over here has no effect on the measurement over there - it does, however, allow you to infer the result you'd get if you did the measurement over there. (After all, something else might've put the other particle into a different superposition by the time you get to it!)

Right. Sure. But assuming the experimenters have agreed beforehand they will do the measurements in a particular order (or set up machines to do the experiment automatically), then the first measurement affects the second. In general the first measurement affects the state of the other particle instantaneously, that is, in a nonlocal way.

Maths or it didn't happen!

I don't understand this expression. You'll have to excuse me ... I am after all just a simple, country physicist.

 

[zaybu]

Ah, I think I see where the confusion comes from. That's kind of the whole point of Bell's Theorem...In the first part we start with, "Let's assume that quantum mechanics is incomplete and particles really do have well defined properties prior to measurement, what would we expect to observe?" In the second part, it's "Here's what good ol' supposedly incomplete quantum mechanics predicts we'll observe." They make incompatible predictions, which do we observe experimentally? The "incomplete" quantum prediction.

Bell's Theorem states that "local hidden variable theories are fundamentally incompatible with quantum mechanics"

You're right that on the one hand, it isn't a surprising statement since we knew before Bell that quantum mechanics seems to suggest non-realism, but prior to Bell's work, some physicists had held out hope for a more classical interpretation of the mathematics of the quantum theory.

I agree up to this point.

Bell proved that they shouldn't be holding their breath unless they're willing to give up locality.

I would add:

(1) If you assume hidden parameters, which Bell's theorem does, you get the wrong results. This shows that QM is COMPLETE.

(2) If you want to assume non-locality, then you need to prove that in some other kinds of experiments. But experiments that show violations of Bell's theorem don't prove non-locality.

 

[zaybu]

That's the post which most demonstrates my point. You won't even admit that you were wrong when you said I wrote down the singlet state "in the wrong format" for dealing with entanglement. That is kind of remarkable when your own source (your link to Susskind's lecture notes) uses the same format for dealing with entanglement as anyone can see. (Tangentially, I can see how you probably got confused based on the way Susskind treated the two-slit experiment in one of your videos (where he imagined a "spin" being used to measure which slit the particle travels through). Needless to say, that state is different from a singlet state of two spins, but past experience indicates you'll dismiss whatever I say rather than concede you might have been mistaken about something, so why should I bother?)

This is pointless, as it has no bearing on the arguments I have presented. You haven't followed the discussion that has taken placed with other members, and now your grasping at straws.

FYI, there are many ways to write the state vectors, it all depends on the problem you are trying to solve, or if you are doing an experiment, what observables will be involved in your experiment. To try to make everyone on this thread believe that there is only ONE way to write quantum states speaks loudly of you being very narrow-minded, or shaky on your understanding of the subject.

Let's forget the word, "nonlocality" for a moment. Suppose I measure the spin of one of the particles in the singlet state. Does this affect the state of the other particle, or not? A simple yes-or-no answer will suffice.

If you are saying that measuring one influences the other, the answer is a categorical NO.

Oops! Someone didn't watch the Susskind YouTube video he posted, did he?
So your own source clarified the same points about faster-than-light signals, and different usages of the word "nonlocality", that I clarified. BTW in the first paragraph quoted of Susskind, notice it is implied that since there was NOT "time for a light signal ..." in Aspect's experiments, there WAS therefore "a contradiction ... with causality or locality or whatever you want to call it". This shows that (1) you dismiss helpful clarifications with childish insults, instead of understanding and acknowledging them; (2) you expect others to watch a video you post in support of your arguments, yet you have either not watched, or not understood, the video yourself.

I was referring to the arguments presented in this thread, and those portions of the videos related to these arguments. We are not talking about faster-than-light signals. So stop bringing that issue as no one disagrees on that. Can you get that much?

Secondly, the assumptions in Bell's theorem are (1) logic, (2) there are hidden parameters. Can you get that straight?

Again: such behavior disqualifies a person from reasoned debate, until he/she changes their approach.

Why don't you focus on the arguments instead of constantly coming up with ad hominem attacks.

[yawn] ... It's not a position I've been appointed to, it's just a fact most physicists feel that way; I happen to be a physicist (as it happens, someone DID appoint me to that position) so I'm just passing along my firsthand experience ... Griffiths says the same thing ... [/yawn]

Your condescending attitude has been noted. (yawn)

 

[Reptillian]

I agree up to this point.

Good, I was hoping we would.

I would add:

(1) If you assume hidden parameters, which Bell's theorem does, you get the wrong results. This shows that QM is COMPLETE.

Yep, that was the point. Some people thought quantum mechanics wasn't wrong, but was incomplete and that the wavefunction wasn't the whole story. They thought that some additional "hidden" information would somehow save us from the inherent probabilities and uncertainties of quantum mechanics. Bell made the assumption that the hidden variables were local, because one of Einstein's objections to quantum mechanics was that a measurement here could "affect" the probability of a measurement 10 light years away seemingly instantly.

(2) If you want to assume non-locality, then you need to prove that in some other kinds of experiments. But experiments that show violations of Bell's theorem don't prove non-locality.

I agree here, Bell's theorem doesn't show that nature is non-local. It does however show that if you want to insist that particles possess certain properties prior to measurement or if you want to insist that particles have things like exact positions and momenta regardless of whether we can measure them, then we have to abandon locality. Most physicists opt to abandon realism and keep locality...but there are a few stubborn holdouts who insist on realism. Alternatively we could abandon both realism and locality, but then no theoretical physicist would have his way.

There is always the third option that quantum mechanics is wrong, and I'm a fan of this avenue...especially since we don't have an experimentally backed quantum theory of gravity. We know we'll need a general relativistic quantum theory at some point, so we'll have to change quantum mechanics as we now know it in the future. There might be a way to salvage both realism and locality, but it'll require us to change quantum mechanics in a fundamental way, perhaps modern quantum will be seen as a kind of special case where speeds are low compared to the speed of light and gravitational curvature is minimal. Thanks to Bell though, we know that any change we make can't look like a local hidden variable theory and be compatible with the quantum mechanical math that we all know and love.

 

[Reptillian]

You're right, but don't expect zaybu to get it. This has been explained to him before. His (incorrect) objection will be that there's nothing "nonlocal" to begin with about the good o'l supposedly incomplete quantum mechanics, that "nonlocality" only becomes something to consider when we are attempting to rescue a local hidden variable theory.

I think most of the disagreement can be chalked up to basic misunderstanding. I think we can get him to come around if we're patient and explain in greater and greater depth, or try varied approaches at explanation. He can be taught.

 

[zaybu]

Good, I was hoping we would.

Yep, that was the point. Some people thought quantum mechanics wasn't wrong, but was incomplete and that the wavefunction wasn't the whole story. They thought that some additional "hidden" information would somehow save us from the inherent probabilities and uncertainties of quantum mechanics. Bell made the assumption that the hidden variables were local, because one of Einstein's objections to quantum mechanics was that a measurement here could "affect" the probability of a measurement 10 light years away seemingly instantly.

I agree here, Bell's theorem doesn't show that nature is non-local.

Good. That has been my position from the very beginning of this debate. Now, can I declare myself to be the winner of this debate?

It does however show that if you want to insist that particles possess certain properties prior to measurement or if you want to insist that particles have things like exact positions and momenta regardless of whether we can measure them, then we have to abandon locality.

It's a free world. People can have different opinions, but to state that a violation of Bell's theorem proves that non-locality exists is totally, totally unjustified. And personally, I believe these people are wrong and are wasting their time. My personal opinion, of course.

There is always the third option that quantum mechanics is wrong, and I'm a fan of this avenue...especially since we don't have an experimentally backed quantum theory of gravity. We know we'll need a general relativistic quantum theory at some point, so we'll have to change quantum mechanics as we now know it in the future. There might be a way to salvage both realism and locality, but it'll require us to change quantum mechanics in a fundamental way, perhaps modern quantum will be seen as a kind of special case where speeds are low compared to the speed of light and gravitational curvature is minimal.

There's always the possibility that gravity can't be quantized. Nature has a nifty way of defeating our inclination. We might think there is a need of quantizing gravity. But the universe might have a different story in store for us.

Thanks to Bell though, we know that any change we make can't look like a local hidden variable theory and be compatible with the quantum mechanical math that we all know and love.

I agree, and it's unfortunate that many headlines in the news perpetrate this fallacy about spooky action at a distance.

I think most of the disagreement can be chalked up to basic misunderstanding. I think we can get him to come around if we're patient and explain in greater and greater depth, or try varied approaches at explanation. He can be taught.

Without me bringing my objections to this forum, you people would have continued with this nonsense that violations of Bell's theorem are proof of non-locality. So who is the teacher here?

 

[idav]

There's always the possibility that gravity can't be quantized. Nature has a nifty way of defeating our inclination. We might think there is a need of quantizing gravity. But the universe might have a different story in store for us.

I think so. Gravity is a result of mass and energy doesn't necessarily qualify for that.

 

[zaybu]

I think so. Gravity is a result of mass and energy doesn't necessarily qualify for that.

In a way, you are correct. If we use the Einstein-Hilbert Lagrangian, the coupling constant G has units of mass ^(-2), making the theory non-renormalized. And hence, any attempt of quantizing GR with QFT is a deadend. Now can have a different theory to do the trick? Mother nature seems to say no. If you try to probe at Planck scale, the energy required would be the size of its Schwarschild radius, turning it into a black hole. Therefore, we can't even probe the scale at which we think that gravity is quantized.

 

[Mr Spinkles]

FYI, there are many ways to write the state vectors ...

Yes, and you said the way I wrote it was "in the wrong format" for dealing with entanglement. But your own source (Susskind lecture notes) used the same "format" for dealing with entanglement. Ergo, you contradict your own source. This should be your first clue.

If you are saying that measuring one influences the other, the answer is a categorical NO.

I repeat: Suppose I measure the spin of one of the particles in the singlet state. Does this affect the state of the other particle, or not? For example, suppose I measure the spin of one of the particles and get "up". What is the state of the other particle? Is its state the same, or different, from what it was before I did the measurement?