Einstein and "spooky actions"

[zaybu]

Emphasis added. This contradicts what I said in the post which you shrieked agreement to, namely that Bob's particle is "NO LONGER in the singlet state" after Alice's measurement. Do you stand by your shouted agreement with that, or not? Please make this clear.

Get lost, you are clueless.

 

[zaybu]

To everyone

Suppose Alice is measuring the spin of particles coming at her with a detector. Suppose they are coming at her one by one. So she records their spin, which might look like:

UP, DOWN, UP, DOWN, DOWN, UP, UP, DOWN, DOWN UP, ....

She notices that 50% are UP, and 50% are down. According to QM, this is what she should get.

Bob does the same at his end. He gets:

DOWN, UP,DOWN, UP,UP, DOWN,DOWN, UP,UP, DOWN, ...

He also notices that 50% are UP, and 50% are down. And according to QM, this is what he should get.

Then one day, Alice and Bob get together and compare their data. Not only their data agrees with QM, but there's a correlation between them; every time Alice measured an UP spin, Bob measured a corresponding DOWN spin, and vice versa. So they wonder why.

So sometime later, a clever physicist points out to them that the particles they were measuring came from a common source which was at rest and was decaying, giving off particles going in opposite direction with opposite spin.

They now know the reason behind this correlation - conservation of angular momentum.

IMPORTANT NOTE: Alice doesn't know anything about the existence of Bob during her experiment. She doesn't know what Bob will measure at any time. Spinkles arguments are from a God's POV, so it's no wonder he concludes there is a spooky action at a distance.

 

[PolyHedral]

So, what can we say about all this? Well, everyone in all frames agree on the objectively established outcomes. Naturally, the sentences in bold in each paragraph bother you.

The part that bothers me is not the sentences individually, but that all of them are true, which is not supposed to happen within QM: all objects are described by one and only one state vector. Whereas, in the experiment with the three moving observers, it is simultaneously true that Bob's particle is in the entangled and non-entangled state, depending on who is doing the looking.

This would be fine if it were like Relativity, but it isn't: there is no "underlying reality" (ala spacetime) that the observers are each getting different slices of. That would be acceptable. Instead, there's simply disagreement with no resolution.

 

[PolyHedral]

IMPORTANT NOTE: Alice doesn't know anything about the existence of Bob during her experiment. She doesn't know what Bob will measure at any time. Spinkles arguments are from a God's POV, so it's no wonder he concludes there is a spooky action at a distance.

You're changing the experiment. In the original problem, Alice is perfectly aware of Bob and his particles, and could stick state-vector labels on them as easily as she could with particles which are "local."

 

[idav]

Emphasis added. This contradicts what I said in the post which you shrieked agreement to, namely that Bob's particle is "NO LONGER in the singlet state" after Alice's measurement. Do you stand by your shouted agreement with that, or not? Please make this clear.

I think what this points out about QM is that the particle is never in two states to begin with. There was only one state which is unknown until observed. Once one state is known then the other is known since there is non longer a 50/50 shot. Whether or not Bobs particle collapsed or not is pure conjecture.

 

[Mr Spinkles]

Get lost, you are clueless.

This is not an argument, it's just flailing.

 

[idav]

I think what this points out about QM is that the particle is never in two states to begin with. There was only one state which is unknown until observed. Once one state is known then the other is known since there is non longer a 50/50 shot. Whether or not Bobs particle collapsed or not is pure conjecture.

A more simple example of this is the particle going through two slits at the same time. It isn't doing this literally, only visually and even in affect, but at the end the particle either went through point A or point B.

 

[Mr Spinkles]

So sometime later, a clever physicist points out to them that the particles they were measuring came from a common source which was at rest and was decaying, giving off particles going in opposite direction with opposite spin.

They now know the reason behind this correlation - conservation of angular momentum.

... which requires that once one particle goes into the spin-up state, the other particle must immediately be in the spin-down eigenstate. As I showed in post #257, which you wisely ignored, if you are correct and one of the particles remained "singlet" somehow but the other did not, it would violate conservation of angular momentum:

According to what you have said:

Before Alice measures: Total spin = (total spin of singlet state) = 0
After Alice measures: Total spin = (total spin of Alice's particle) + (total spin of Bob's particle) = (spin-up) + (total spin of singlet state) = spin-up + 0 = spin-up

... which violates conservation of (spin) angular momentum. As I said above, a single particle "singlet" state makes no sense to begin with, but if we are generous we could also try to interpret your argument this way:

After Alice measures: Total spin = (total spin of Alice's particle) + (total spin of Bob's particle) = (spin-up) + (spin of one particle in a singlet state) = spin-up + (50% chance of spin-up) = 2 x spin-up

... which again violates conservation of angular momentum 50% of the time.

That's just 1 of 3 good reasons explained in that post why Bob's particle cannot remain all alone in the "singlet" state after Alice's particle is no longer in the singlet state.

 

[PolyHedral]

A more simple example of this is the particle going through two slits at the same time. It isn't doing this literally, only visually and even in affect, but at the end the particle either went through point A or point B.

Nope, sorry. It actually does go through both at once.

 

[idav]

Nope, sorry. It actually does go through both at once.

it appears as if the wave function of each individual photon travels both paths and engages in interference at the last beam splitter

We know there is interference but it isn't literally in two places or else when you collapsed it you'd find two particles. The affects are there and you may even be able to see the two states at the same time but it is either up or down not both. Experiments show it's both but its an illusion .

 

[Mr Spinkles]

The part that bothers me is not the sentences individually, but that all of them are true, which is not supposed to happen within QM: all objects are described by one and only one state vector.

I commend you for your passion for quantum mechanics. But you are misinformed on this particular point. If you don't believe me, crack open Griffiths or Shankar. QM says there is generally limited freedom to choose any one of a number of different state vectors. For example the Schrodinger equation in general does not have just one solution but many solutions. You can typically change a phase in the wavefunction, or choose real/imaginary solutions or only "separable" solutions to the Schrodinger equation, etc. at your convenience. As long the different state vectors or wavefunctions all agree on the probabilities of observables (spin, position, energy, momentum) they are all acceptable, according to QM. This is sort of analogous to the fundamental beginnings of QM, is it a particle or a wave? There are multiple acceptable descriptions. Personally, I don't view this as throwing "objective reality" out the window because, even though there may be a number of acceptable states, there are still many more unacceptable states. So personally I don't view this freedom to choose different states in QM as a philosophical "game-changer" any more than the freedom to choose different reference frames in classical mechanics.

In classical mechanics, what is the state of a system of particles? Their velocities and positions. Do different observers have to exactly agree on this? No. There is limited room for disagreement. Even the same observer could add a constant to the position and velocity of all his particles, and the resulting physics would be fundamentally the same. Does this mean the particles don't have a "real" state? I don't think so. They have a real state, and there are many accurate ways to describe it. It's "real", to me, in the sense that there are many more inaccurate ways to describe the state.

 

[PolyHedral]

I commend you for your passion for quantum mechanics. But you are misinformed on this particular point. If you don't believe me, crack open Griffiths or Shankar. QM says there is generally limited freedom to choose any one of a number of different state vectors. For example the Schrodinger equation in general does not have just one solution but many solutions. You can typically change a phase in the wavefunction, or choose real/imaginary solutions or only "separable" solutions to the Schrodinger equation, etc.

I know about the phase equivalence relationship, etc, but you implicitly admit the problem in the very next sentence:

As long the different state vectors or wavefunctions all agree on the probabilities of observables (spin, position, energy, momentum) they are all acceptable, according to QM.

Alice's and Bob's results do not predict the same probability distributions on the observables!

 

[PolyHedral]

We know there is interference but it isn't literally in two places or else when you collapsed it you'd find two particles. The affects are there and you may even be able to see the two states at the same time but it is either up or down not both. Experiments show it's both but its an illusion .

So how do you explain the "illusion" of particles being aware of a path they haven't gone down?

 

[Mr Spinkles]

I think what this points out about QM is that the particle is never in two states to begin with. There was only one state which is unknown until observed. Once one state is known then the other is known since there is non longer a 50/50 shot. Whether or not Bobs particle collapsed or not is pure conjecture.

That's not what QM says. QM says both particles in the singlet state truly do not have definite, assignable spin directions (up or down). It's not simply a matter of us lacking knowledge.

To the uninitiated, that seems preposterous. I sympathize. But I can assure you that is what QM says--like it, hate it, believe it, or doubt it.

I have been inside a physics building, doing physics, every working day for many years now. That doesn't mean I am infallible--far, far from it. But at least be assured, I'm not simply talking out of my rear end (unlike certain parties in this thread).

 

[Mr Spinkles]

Alice's and Bob's results do not predict the same probability distributions on the observables!

Hmm well it seems to me that they do predict the same probability distributions ... and on this particular point, zaybu and I agree (God help us all) ... did you read my post #279?

 

[idav]

So how do you explain the "illusion" of particles being aware of a path they haven't gone down?

Poly, particles being aware? It doesn't know except for it's superposition having done the work. The effects are there, this jives with the experiment. The particle is only in one place though it doesn't split into a twin. It is both a wave and a particle after all.

 

[idav]

That's not what QM says. QM says both particles in the singlet state truly do not have definite, assignable spin directions (up or down). It's not simply a matter of us lacking knowledge.

To the uninitiated, that seems preposterous. I sympathize. But I can assure you that is what QM says--like it, hate it, believe it, or doubt it.

I have been inside a physics building, doing physics, every working day for many years now. That doesn't mean I am infallible--far, far from it. But at least be assured, I'm not simply talking out of my rear end (unlike certain parties in this thread).

Forgive me, I've been reading these types of experiments over and over and still can't see the particles doing what the experimenters claim. I'm likely missing something cause you guys keep telling me I'm wrong, lol. I don't know why the experimenters start saying things like the particles know which box to pick and stuff like that. Goes back to my questions to you about QM being mystical.

 

[PolyHedral]

Hmm well it seems to me that they do predict the same probability distributions ... and on this particular point, zaybu and I agree (God help us all) ... did you read my post #279?

In the moment(s) when Alice has measured her particle and Bob hasn't (or vice versa)

Alice has a collapsed particle with her, which she's measured and found in an eigenstate. She also knows that Bob has a particle with him, which she is able to predict with 100% certainty (given conservation of momentum) will produce a result opposite to hers if measured. She therefore assigns the opposite eigenstate to this particle not yet measured.

Bob, however, has not measured his particle yet, and has not seen Alice measure hers either. He does not know which of the two spins his particle will yield when measured, and so says that it is in a superpositioned state.

They disagree over expected observables. That's not supposed to happen.

 

[zaybu]

You're changing the experiment. In the original problem, Alice is perfectly aware of Bob and his particles, and could stick state-vector labels on them as easily as she could with particles which are "local."

I did change the problem slightly, and that points out to a "dilemma":

If she knows, somehow it influences the result, but if she doesn't know, there is no influence?

What's your answer?

 

[Mr Spinkles]

Forgive me, I've been reading these types of experiments over and over and still can't see the particles doing what the experimenters claim. I'm likely missing something cause you guys keep telling me I'm wrong, lol. I don't know why the experimenters start saying things like the particles know which box to pick and stuff like that. Goes back to my questions to you about QM being mystical.

LOL it's okay. It's a notoriously difficult subject. Please keep in mind that it's just as difficult to explain as to understand. I apologize if I've done a poor job explaining things. My restricted goal has really just been to clear up what QM says, not to try to prove that what QM says is correct.

I recommend reading Griffiths' wonderful introduction to quantum mechanics. (If you aren't familiar with the mathematics of calculus, you will have to skip the equations and just accept "on faith" the conclusions that Griffiths states in English.)

For the most illuminating sections in the context of this discussion, I suggest reading pages 1-4 of Ch. 1 for a very brief introduction to the principles (you can still get a gist of it without looking at the equations). Then read pages 374-381 of the Afterward (you can neglect the derivation in 377-378).

You can read all of this for free, here (PDF): http://www.physics.umd.edu/courses/Phys270/Jenkins/Griffiths_EPR_BellInequality_Excerpt.pdf

I posted that earlier in this thread. This is such a difficult topic that any attempt by me to explain it better than Griffiths is almost certain to fail, and would require way too much work. So rather than risk confusing you and wasting my energies, I direct you to Griffiths.