Einstein and "spooky actions"

[zaybu]

... 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:

In the scenario I presented in in post # 282, There's no violation of angular momentum. http://www.religiousforums.com/forum/3329998-post282.html

Here it is again:

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.

Show me where there are violations?


Your post 257 is totally ridiculous: you are calculating the total spin BEFORE they are measured. Of course in that situation, you would get violations of conservation of angular momentum. Didn't they tell you back in school, you need to make measurement first and then do your calculations to verify if angular momentum is conserved?

 

[PolyHedral]

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?

My answer is that normal quantum mechanics is inconsistent with Relativity.

 

[zaybu]

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

If you look at experiments in which one electron at a time are sent through a double-slit experiment, they arrives on the screen one by one, forming over a long period of time the bright and dark fringe that we know from a classical inteference pattern.

Here's a link for the explanation:

Interference - Young's experiment with single photons: Physclips - Light

Here's a live demonstration on youtube:

[youtube]MbLzh1Y9POQ[/youtube]
Interference pattern built up photon by photon - YouTube

You can't explain that by claiming the electrons went through both slit at the same time.

 

[zaybu]

My answer is that normal quantum mechanics is inconsistent with Relativity.

Ok, we know there are inconsistencies between GR and QM when we look at Planck scale, for instance. But here, we have an experiment involving just measuring the spin of particles by two observers. Relativity doesn't play a part here. So I would ask, does it make sense that in the first scenario, in which Alice knows that Bob will make a measurement, it will influence the result, but in the second case, same experiment, but Alice doesn't know about Bob, there is no influence?

 

[Mr Spinkles]

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.

Emphasis added. That conclusion does not rigorously follow from what you said above it. Notice BTW that you aren't referring to any relativistic reference frames anymore. Everything you said above applies to just two observers, Alice and Bob, doing measurements in the same (rest) frame. So I'll stick to that for now.

The expected observables are as follows.

Alice predicts with 100% confidence what Bob will measure for each individual trial. Alice then goes and compares her predictions to Bob's measurements, and Alice finds her predictions were correct. Bob predicts he will measure spin-down 50% of the time. He has to do many measurements to test this prediction, and when he looks at his many measurements, they agree with his prediction.

Now, because Bob is a competent scientist with a working understanding of quantum mechanics (unlike zaybu), Bob is aware that if Alice measured her particle, he would be none the wiser. In other words, even if Bob was receiving his particles in a spin eigenstate instead of a singlet state (as he originally thought), he knows that he would still measure spin-down 50% of the time over many measurements. And Bob knows that if that were true, Alice could tell Bob with 100% confidence what Bob will measure in each individual trial. Bob acknowledges this possibility and, if he wanted to check, he could walk over to Alice and compare notes to find out whether she measured, and if so, what the state of his particle really is (singlet, or spin eigenstate). Bob could then predict with 100% certainty each individual measurement he makes. This would not contradict Bob's previous prediction, that 50% of many measurements are spin-down.

The point is that at no point do we run into an irreconcilable disagreement. The only ambiguity arises from Bob's lack of knowledge about what Alice did to her (and therefore his) particle. But that's the ordinary kind of ambiguity that can arise whenever someone messes with your experiment without telling you, whether you are doing classical mechanics, relativity, or QM.

By the way, if we followed zaybu's logic then there really would be an irreconcilable disagreement. According to zaybu's (incorrect) argument, Bob's particle remains in the singlet state even after Alice measures hers. Therefore, if Bob walked over to Alice and compared notes, they would still disagree on the state of Bob's particle. Even worse, Bob would deny that Alice can predict with 100% confidence what Bob will measure each time. Bob, like zaybu, would be wrong.

 

[zaybu]

Now, because Bob is a competent scientist with a working understanding of quantum mechanics (unlike zaybu), Bob is aware that if Alice measured her particle, he would be none the wiser. .

But I changed the scenario in post #301. Pay attention to what was said so far. Alice doesn't know that Bob is taking measurement, Neither does Bob about Alice. Your answers no longer make any sense. As usual you are clueless.

See: http://www.religiousforums.com/forum/3330179-post301.html

 

[Mr Spinkles]

Show me where there are violations?

Instead of screaming, try listening. The violation occurs if we assume Alice measures first AND we accept your (wrong) assertion that Bob's particle remains "singlet", somehow.

Your post 257 is totally ridiculous: you are calculating the total spin BEFORE they are measured.

Not in the second interpretation of your (wrong) argument--I offered two possible interpretations of your (wrong) notion of a single-particle being in a "singlet" state because I knew you would try to wriggle out of it.

Besides, if we are given a singlet state then it's a given that its total spin is zero. If we didn't know this from the beginning, before Alice and Bob measure, then how could we know whether Alice and/or Bob's measurements violate conservation of spin? The effect of measurement is only to put each particle separately into a definite spin eigenstate (up or down); but we already knew, before that measurement, that we had a definite total spin, and we already knew what it was (zero). Because once you tell me it's a singlet state, I already know the total spin is zero.

I notice you still have not explained how one particle, by itself, can even be in a "singlet" state. Again it's just math. The singlet state is a sum of two-particle spin eigenstates, |up,down> + |down,up> (neglecting a factor for normalization). The possible results of Alice's measurement are the eigenkets of the appropriate operator applied to that state. Those eigenkets are, of course, |up,down>, and |down,up>, which we can simply read off from the state since we chose to write the singlet state as a sum of terms in the spin basis. Each of these eigenkets is just the (tensor) product of the single-particle spin eigenstates. For example, |up,down> = |up>|down>. That state means that particle 1 is in the |up> state AND particle 2 is in the |down> state. It means they are not entangled. It means neither particle is in the singlet state. |up>|down> is the state you write down if someone gives you particle 1 in state |up>, AND particle 2 is in state |down>, without any mention that they may have previously been in an entangled singlet state together.

So when Alice measures a singlet, the state that results from her measurement cannot be a single-particle spin eigenstate |up>, or |down>, according to the rules of QM. Those are NOT possibilities, since they are NOT eigenkets of the appropriate operator applied to the singlet. Instead, the only possibilities are the eigenkets |up>|down> or |down>|up>. In other words, BOTH particles must go to a spin-eigenstate, and NEITHER particle can remain in the singlet state after Alice's measurement. According to the rules of QM. It's just math.

Of course in that situation, you would get violations of conservation of angular momentum. Didn't they tell you back in school, you need to make measurement first and then do your calculations to verify if angular momentum is conserved?

Try again.

 

[Mr Spinkles]

But I changed the scenario in post #301.

In order for your argument to be right, it has to avoid being wrong in all scenarios, not just one (convenient) treatment you picked in post #301. Why won't your argument work in the much simpler case of just one measurement by Alice? See my post #257 and maybe read my post #307 too, for good measure. Read them carefully, before shouting, please.

 

[zaybu]

Why won't your argument work in the much simpler case of just one measurement by Alice?

So since you don't want to consider the second scenario, I will answer for you.

In scenario 1, Alice knows that Bob will measure. So Spinkles says, her measurement affects Bob's measurement.

In scenario 2, same experiment, except Alice and Bob don't know what the other is doing. So Spinkle says: don't bother me with your silly questions.

Yep, Spinkles the great physicist only knows the answer to one and only one scenario. Present him with a different scenario, and he is lost.

 

[PolyHedral]

Emphasis added. That conclusion does not rigorously follow from what you said above it. Notice BTW that you aren't referring to any relativistic reference frames anymore. Everything you said above applies to just two observers, Alice and Bob, doing measurements in the same (rest) frame. So I'll stick to that for now.

You've lost the contradictory aspect of the scenario - that Alice has simultaneously measured and not measured, depending on where you are standing.

The only ambiguity arises from Bob's lack of knowledge about what Alice did to her (and therefore his) particle. But that's the ordinary kind of ambiguity that can arise whenever someone messes with your experiment without telling you, whether you are doing classical mechanics, relativity, or QM.

Alice has done no messing of the experiment within Bob's past light cone, i.e. his observable "universe." It'd be equivalent to a dragon in the garage to allow things outside the observable universe to affect Bob's experiment - if we allow that, we might as well throw up our hands and say, "God did it!"

 

[zaybu]

It'd be equivalent to a dragon in the garage to allow things outside the observable universe to affect Bob's experiment - if we allow that, we might as well throw up our hands and say, "God did it!"

:yes:

 

[Reptillian]

If you look at experiments in which one electron at a time are sent through a double-slit experiment, they arrives on the screen one by one, forming over a long period of time the bright and dark fringe that we know from a classical inteference pattern.

That video definitely works well with the ensemble interpretation.

My answer is that normal quantum mechanics is inconsistent with Relativity.

Having followed the discussion on my phone and having given it a little thought at my boring job today, I think that the uncertainty principle may offer a way out of our problem of conflicting states in different frames.

I'd like to elaborate and respond to a bunch of other posts, but I've got to head to bed soon. TOMORROW!!!

 

[Mr Spinkles]

So since you don't want to consider the second scenario, I will answer for you.

In scenario 1, Alice knows that Bob will measure. So Spinkles says, her measurement affects Bob's measurement.

In scenario 2, same experiment, except Alice and Bob don't know what the other is doing. So Spinkle says: don't bother me with your silly questions.

Yep, Spinkles the great physicist only knows the answer to one and only one scenario. Present him with a different scenario, and he is lost.

I'm honored and touched that you would think of me as a great physicist, especially given how little elementary physics one has to understand in order to engage in this discussion with you.

Our dispute is about what happens to Bob's particle after Alice's measurement. In your scenario 2, not enough information has been given to resolve this dispute one way or the other. To wit, did Alice and Bob measure simultaneously or did Alice measure before Bob? If as you say "Alice and Bob get together and compare their data", and they find that one of Alice's measurements occurred before Bob's (or vice versa), only then can the data potentially resolve our dispute. If that was the case, then given the data you reported, Alice and Bob would have to conclude that Bob actually measured (unbeknownst to him at the time) a particle which was "NO LONGER in the singlet state" after Alice's measurement. Those, by the way, are the precise words in my post which to which you howled agreement. (Do you stand firmly behind your bellowing, or do you take it back? You still haven't made it clear.)

That takes care of your scenario 2. I note, for the record, you have not answered substantive arguments or direct questions in my posts #280, #257, and #307. Not an impressive record.

 

[Mr Spinkles]

You've lost the contradictory aspect of the scenario - that Alice has simultaneously measured and not measured, depending on where you are standing.

You mean, depending on the relative speed of your reference frame, right? Everyone in Alice and Bob's inertial frame agrees (or can be made to agree) on what happened, no matter where they are standing.

Alice has done no messing of the experiment within Bob's past light cone, i.e. his observable "universe."

I think you've recognized an important subtlety and it does take some effort to grasp. To be precise, Bob's observable universe is not confined to his past light cone. He can observe the emission of a photon traveling at light speed, for example, even if the emission occurred outside his past light cone, but not at the present moment--in Bob's future, he can observe it. Additionally, superluminal propagation (a shadow, for example, or the propagation of the max height of a wave) can be observed by Bob at the present moment, even if it started outside his past light cone, as long as the propagation does not carry information, energy, etc. from one place to another faster than light. Relativity simply says that causal events cannot occur outside Bob's past light cone. That is because if an event outside Bob's past light cone caused something to happen to Bob (not in the future, but at the present moment) this would lead to inescapable logical contradictions.

However, the effect of Alice's measurement on Bob's particle is statistical, not causal. Alice's measurement can indeed change Bob's particle from the singlet to a spin eigenstate, but Alice cannot make her measurement turn out spin-up or down. Because of this, the aforementioned logical contradictions do not arise and this kind of superluminal influence is acceptable. Furthermore, since BOTH particles go from the singlet state to a spin eigenstate at the exact moment Alice measures, no spin angular momentum is carried from Alice to Bob faster-than-light. See this excerpt from Griffiths, a standard undergraduate introductory QM textbook (PDF): http://www.physics.umd.edu/courses/Phys270/Jenkins/Griffiths_EPR_BellInequality_Excerpt.pdf

BTW, I know you aren't trying to suggest this, but for the record this doesn't rescue zaybu's confused argument. He is still struggling with the much simpler case where Alice sends an ordinary light signal to Bob fully informing him of her measurement. In that case, the reasoning is much more straightforward: Bob certainly can observe Alice's signal as it would indeed be within Bob's past light cone, and there is no question then that Alice changed the state of Bob's particle. That is because Bob could use the info. from Alice to predict with 100% accuracy the future outcome of his spin measurements, which would be impossible unless his particles were already in spin-eigenstates before he measured them, NOT singlet states. Therefore, Alice's measurement MUST have changed the state of Bob's particle. Zaybu is still stuck there. But we can move on. The remaining question would be, did the effect of Alice's measurement on Bob's particle propagate faster-than-light, or not? According to QM the effect was instantaneous and this, too, can be tested. This would be done by having Bob always measure very soon after Alice, so soon as to be almost (but not quite) simultaneous. Once Alice's signal arrived after Bob measured, he would still conclude as before that his particles had been influenced by Alice, though this time he would conclude it in hindsight. In addition, Bob would conclude the influence of Alice's measurement on his particle was instantaneous, to the precision with which this can be measured. Taking all of this together, this is, by definition, what we mean by quantum "nonlocality". Why zaybu hates that word with such irrational passion, is beyond me.

It'd be equivalent to a dragon in the garage to allow things outside the observable universe to affect Bob's experiment - if we allow that, we might as well throw up our hands and say, "God did it!"

Your premise is mistaken: the observable universe is not strictly confined to the past light cone.

 

[zaybu]

I'm honored and touched that you would think of me as a great physicist, especially given how little elementary physics one has to understand in order to engage in this discussion with you.

Obviously sarcasm is something way above your head.

To wit, did Alice and Bob measure simultaneously or did Alice measure before Bob?

Some of those measurements were taken before, others after, and some at the same time. The two observers are unaware of each other. The time of collecting the data obviously makes no difference in explaining the data.

If as you say "Alice and Bob get together and compare their data", and they find that one of Alice's measurements occurred before Bob's (or vice versa), only then can the data potentially resolve our dispute. If that was the case, then given the data you reported, Alice and Bob would have to conclude that Bob actually measured (unbeknownst to him at the time) a particle which was "NO LONGER in the singlet state" after Alice's measurement.

But the time at which the data was collected makes no difference. And say if they have recorded the time, and it is shown that sometimes Bob measured after Alice, but there are other data collected before, or even some at the same time. Your explanation would be: when Bob knew, spooky action put Alice's particle out of singlet; when Alice knew, spooky action put Bob's particle out of singlet. Either there is a spooky action at a distance or there isn't, regardless of what time the data was collected. You obviously believe there is such a spooky action.

Now, there are two explanations of the data: mine, which does not include spooky action at a distance; and yours, which includes the spooky action at a distance.

Occam's razor says, choose the simplest one.

Those, by the way, are the precise words in my post which to which you howled agreement. (Do you stand firmly behind your bellowing, or do you take it back? You still haven't made it clear.)

I have already explained that, but it went way over your head, what would be the point in repeating something you can't understand.

I note, for the record, you have not answered substantive arguments or direct questions in my posts #280, #257, and #307. Not an impressive record.

I have answered them, but you're not paying attention.

 

[Mr Spinkles]

But the time at which the data was collected makes no difference. And say if they have recorded the time, and it is shown that sometimes Bob measured after Alice, but there are other data collected before, or even some at the same time. Your explanation would be: when Bob knew, spooky action put Alice's particle out of singlet; when Alice knew, spooky action put Bob's particle out of singlet. Either there is a spooky action at a distance or there isn't, regardless of what time the data was collected. You obviously believe there is such a spooky action.

Emphasis added. Correct. (Although I would use the word "measured" instead of "knew"; the former is what affects the particles, the latter is just a consequence.)

Now, there are two explanations of the data: mine, which does not include spooky action at a distance; and yours, which includes the spooky action at a distance.

Occam's razor says, choose the simplest one.

Right. All other things being equal, your explanation as stated above would be simplest. But all other things are not equal. In your explanation, you are only able to reject "action at a distance" in a tradeoff by introducing a number of additional, unnecessary complexities. To wit, to make your argument work, you have invented ad-hoc the new concept of a single-particle "singlet" state, which you haven't rigorously defined, and which has no sensible definition according to the ordinary rules of QM. You've also allowed conservation of total angular momentum to be violated, in spite of yourself. If Alice measures spin-up, then according to your explanation, Bob's particle does not "really" carry spin-down until Bob measures it. Therefore, Bob could choose not to ever measure it, and according to your reasoning, the total spin has increased by +hbar/2. More singlets could be prepared, and Bob could look over Alice's shoulder, and choose to never measure his particle when Alice's measurement obtains +hbar/2, but always measure otherwise. In this way, your explanation implies that Alice and Bob could conspire to increase the total spin of the universe indefinitely. (The reasoning is even more straightforward if you consider the simpler case where Alice can do both measurements, without Bob.)

Those unnecessary and self-contradictory complexities are absent from my (orthodox) explanation. Therefore, in total, accepting "action at a distance" is the simplest tradeoff.

 

[zaybu]

Emphasis added. Correct. (Although I would use the word "measured" instead of "knew"; the former is what affects the particles, the latter is just a consequence.)

Right. All other things being equal, your explanation as stated above would be simplest. But all other things are not equal. In your explanation, you are only able to reject "action at a distance" in a tradeoff by introducing a number of additional, unnecessary complexities.

I don't have to reject spooky action at a distance. I'm showing that the data can be explained without it.

Put it this way, to explain the data in both scenarios:

(Z) Zaybu's explanation ( no spooky action at a distance)
(S) Spinkles explanation ( with spooky action at a distance)

(Z) explanation: two sets of data in both scenarios:

1. Observing the spin of each particle. Both Alice and Bob do that. Explanation of data, why 50% up, 50% down, comes from QM that spin is quantized along a certain direction and there's only two possibilities.
2. Correlation between data collected from Alice and Bob. Explanation: conservation of angular momentum

(S) explanation: convoluted arguments with singlet states, spooky action at a distance.

To wit, to make your argument work, you have invented ad-hoc the new concept of a single-particle "singlet" state, which you haven't rigorously defined, and which has no sensible definition according to the ordinary rules of QM.

I don't need to define a singlet in either scenarios under discussion the way you do it because it's not part of my explanation of the data (see (Z)from above). I don't need the construction of any singlet in my explanation of the data, but it is part of yours ( see (S) from above). So you have to invent spooky action to justify that a singlet turns into a down- spin at Bob's end, even though Bob's hasn't made his measurement.

You've also allowed conservation of total angular momentum to be violated, in spite of yourself.

The conservation of total angular momentum is violated in (S) but not in (Z). (HINT: I don't need the construction of any singlet in my explanation of the data)

If Alice measures spin-up, then according to your explanation, Bob's particle does not "really" carry spin-down until Bob measures it. Therefore, Bob could choose not to ever measure it, and according to your reasoning, the total spin has increased by +hbar/2. More singlets could be prepared, and Bob could look over Alice's shoulder, and choose to never measure his particle when Alice's measurement obtains +hbar/2, but always measure otherwise. In this way, your explanation implies that Alice and Bob could conspire to increase the total spin of the universe indefinitely. (The reasoning is even more straightforward if you consider the simpler case where Alice can do both measurements, without Bob.)

All of that is part of (S). (HINT: I don't need the construction of any singlet in my explanation of the data)

Those unnecessary and self-contradictory complexities are absent from my (orthodox) explanation. Therefore, in total, accepting "action at a distance" is the simplest tradeoff.

Still part of (S).

....................................................................................................................................................................................................................................

We're back to square one:

To explain the data in both scenarios -


(Z) Zaybu's explanation ( no need to use singlet, no spooky action at a distance)
(S) Spinkles' explanation ( need to invent convoluted singlet, with spooky action at a distance)

And I maintain that your spooky action at a distance is superfluous.

 

[Mr Spinkles]

(S) explanation: convoluted arguments with singlet states, spooky action at a distance.

Nice straw man.

(Z) Zaybu's explanation ( no need to use singlet, no spooky action at a distance)

You are wriggling around and contradicting yourself, again. You said in post #244: "If Bob makes no measurement, his particle stays in a singlet state."

Even after Alice measures? Be clear, yes or no.

 

[idav]

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.

The interpretation of the experiment results are the question. My position fits what the link describes as the realist position. That the particle was always at C and qm couldnt determine it until measurement.

 

[zaybu]

Nice straw man.

You are wriggling around and contradicting yourself, again. You said in post #244: "If Bob makes no measurement, his particle stays in a singlet state."

Because I was making counter-arguments within your contorted explanation ( HINT: the one in which you need to invent convoluted singlet, with spooky action at a distance). And the reality is for your explanation to make sense: you not only have to fabricate a singlet state, which is not needed, but also fabricate a spooky action at a distance to maintain the fabrication of your explanation.

However, within my explanation: there are no singlet states, and no spooky action at a distance, and the data can be explained.

Even after Alice measures? Be clear, yes or no.

That question makes sense only in your contorted explanation (S) of convoluted singlet with spooky action at a distance. (HINT: I don't need the construction of any singlet in my explanation of the data, so your question makes no sense in (Z))

Just in case you've already forgotten:

(Z) Zaybu's explanation ( no need to use singlet, no spooky action at a distance)
(S) Spinkles' explanation ( need to invent convoluted singlet, with spooky action at a distance)


(Z) explanation: two sets of data in both scenarios:

1. Observing the spin of each particle. Both Alice and Bob do that. Explanation of data, why 50% up, 50% down, comes from QM that spin is quantized along a certain direction and there's only two possibilities.
2. Correlation between data collected from Alice and Bob. Explanation: conservation of angular momentum

(S) explanation: convoluted arguments with singlet states, spooky action at a distance.