Understanding Einstein's Paradox: The Answer Revealed

[kashiark]

an atom goes through a particular nuclear reaction and emits a left-handed and right-handed particle. after the particles have traveled to opposite sides of the universe, if you measure the handedness of one you instantly know the other's which is information moving faster than the speed of light. what was the answer to this paradox?

 

[DrChinese]

an atom goes through a particular nuclear reaction and emits a left-handed and right-handed particle. after the particles have traveled to opposite sides of the universe, if you measure the handedness of one you instantly know the other's which is information moving faster than the speed of light. what was the answer to this paradox?

I believe you are referring to the EPR paradox (Einstein is the E, Podolsky and Rosen are the other 2). The short answer to the paradox is that their intuition about reality did not hold up. They thought that QM could not be a complete theory because it led to "spooky" predictions. However, modern tests show that these spooky things happen.

I might point you to my page on Bell's Theorem which discusses the 1935 EPR paper.

 

[ThomasT]

They thought that QM could not be a complete theory because it led to "spooky" predictions. However, modern tests show that these spooky things happen.

That's one way of looking at it.

EPR's conclusion was that the quantum theory was an incomplete theory of physical reality -- and, depending on what one takes 'physical reality' to mean, then it either is or isn't. For EPR, physical reality included a causal reality underlying instrumentation and detection -- and in this sense quantum theory is an incomplete theory of physical reality.

But quantum theory includes everything that's known wrt the physical reality revealed to our senses via the instrumental data. So, wrt that physical reality it's a complete theory. It accurately predicts statistical probabilities and correlations without a complete accounting of the underlying dynamics.

If by "modern tests show that these spooky things happen" you mean that quantum experimental phenomena are somewhat mysterious in that the underlying structures and causal dynamics are not fully understood, then I agree. If you mean that 'instantaneous-action-at-a-distance' and/or ftl propagations have been experimentally demonstrated, then I disagree.

an atom goes through a particular nuclear reaction and emits a left-handed and right-handed particle. after the particles have traveled to opposite sides of the universe, if you measure the handedness of one you instantly know the other's which is information moving faster than the speed of light. what was the answer to this paradox?

There's no paradox because as far as anybody knows there's no information moving faster than the speed of light.

For each individual biparticle emission trial:
If you know that the filters-detectors are aligned, then if you know the result at one end of the universe, then you can deduce (~instantaneously) the result at the other end.

If you don't know how they're aligned, or if you know that they're not aligned, or even if you know how they're not aligned, then if you know the result at one end of the universe, then all you can say about the result at the other end is that it has 1/2 chance of being a detection and a 1/2 chance of being a non-detection.

For accumulations of large numbers of individual trial results:
If you know how they're not aligned, then the accuracy of the qm prediction regarding the frequency of coincidental detection increases as the size of the data set increases.

 

[DrChinese]

EPR's conclusion was that the quantum theory was an incomplete theory of physical reality -- and, depending on what one takes 'physical reality' to mean, then it either is or isn't. ...

I think the OP needs a starting point on the subject before getting into the interpretations. I wasn't trying to make any comment on those by using the word "spooky".

OP: Learning about EPR, Bell and Aspect would be a good starting point for you before continuing the discussion. Googling those terms should be a good start too.

 

[Ilja]

But quantum theory includes everything that's known wrt the physical reality revealed to our senses via the instrumental data. So, wrt that physical reality it's a complete theory. It accurately predicts statistical probabilities and correlations without a complete accounting of the underlying dynamics.

Physical reality is what exists independent of our possibility to observe it. QM does not even make claims what is this reality. Is the wave function real or not? What else, if anything, is real too? These questions are simply not answered. Thus, it does not make sense to claim that QM is in some sense a complete description of reality.

In realistic theories, we make guesses about it (all our theories are such guesses, so there is nothing wrong for a theory being understood as a guess).

If you mean that 'instantaneous-action-at-a-distance' and/or ftl propagations have been experimentally demonstrated, then I disagree.

There's no paradox because as far as anybody knows there's no information moving faster than the speed of light.

What "everybody knows" is not relevant.

Fact is, there are simple realistic explanations of the violations of Bell's inequality in terms of realistic hidden variables and hidden FTL information transfer. But there is no realistic explanation of the violations of Bell's inequality without FTL. Moreover, we have a theorem, that there cannot be such explanations without FTL.

This is the ideal situation of falsification of a theory. No theory can be falsified in a more rigorous way. Instaed, usually almost every theory can be saved, given some falsification, by some (at least formally realistic) ad hoc explanation. But here there is no such ad hoc explanation - no realistic explanation is possible in principle.

 

[Dmitry67]

But here there is no such ad hoc explanation - no realistic explanation is possible in principle.

No single-history realistic explanation is possible,

 

[Ilja]

No single-history realistic explanation is possible,

MWI is something I do not count as an explanation. As well as "God's will is unexplanable". (Is there a difference between the two?)

 

[Dmitry67]

It is newbies question so its is not the place for MWI vs CI.
I just wanted to say that based on the recent polls, MWI is now #1 - the mainstream interpretation, or at least it is as popular as CI, so you can hate MWI if you want, but let's play fair and give info about all interpretations.

You need to sacrifice something: determinism, realism, causality, single history. If you can sacrifice single history then you can use MWI - it is realistic and deterministic, and only sacrifice is a single history.

 

[jms5631]

It is newbies question so its is not the place for MWI vs CI.
I just wanted to say that based on the recent polls, MWI is now #1 - the mainstream interpretation, or at least it is as popular as CI,

Hey Dmitry, I wonder which polls you are referring to, and what demographics of the physics community they represent, because MWI is surely not the most accepted interpretation in the enitre working physicist community. I'm aware of a single poll from a specific sampling of theorists that gives this result and several others that give opposite results, with MWI placing second and even last. I'm just say the MWI adherants should guard against being overzealous.

 

[alxm]

I suspect the real #1 'interpretation' is the one I adhere to: the "Who the heck needs a damn interpretation?" interpretation.

 

[Dmitry67]

I suspect the real #1 'interpretation' is the one I adhere to: the "Who the heck needs a damn interpretation?" interpretation.

That interpretation already have a name:
http://en.wikipedia.org/wiki/Copenhagen_interpretation

Many physicists have subscribed to the null interpretation of quantum mechanics summarized by the sentence "Shut up and calculate!". While it is sometimes attributed to Paul Dirac[17] or Richard Feynman, it is in fact due to David Mermin.

 

[Dmitry67]

Hey Dmitry, I wonder which polls you are referring to, and what demographics of the physics community they represent, because MWI is surely not the most accepted interpretation in the enitre working physicist community. I'm aware of a single poll from a specific sampling of theorists that gives this result and several others that give opposite results, with MWI placing second and even last. I'm just say the MWI adherants should guard against being overzealous.

http://en.wikipedia.org/wiki/Many-worlds_interpretation#Acceptance_among_physicists

"Many worlds"-like interpretations are now considered fairly mainstream within the quantum physics community. For example, a poll of 72 leading physicists conducted by the American researcher David Raub in 1995 and published in the French periodical Sciences et Avenir in January 1998 recorded that nearly 60% thought many worlds interpretation was "true". Max Tegmark also reports the result of a poll taken at a 1997 quantum mechanics workshop.[36] According to Tegmark, "The many worlds interpretation (MWI) scored second, comfortably ahead of the consistent histories and Bohm interpretations."

There was also a poll on this forum in 2005 but I don't remember exactly the name of the thread - I tried to find it but got too many results...

 

[Ilja]

You need to sacrifice something: determinism, realism, causality, single history. If you can sacrifice single history then you can use MWI - it is realistic and deterministic, and only sacrifice is a single history.

You don't need to sacrifice anything from your list: The pilot wave interpretation is deterministic, realistic, causal, and has a single history.

What is sacrificed is not in your list: It is the speculative idea of Minkowski that a particular symmetry, which appears as an effective symmetry in every wave equation, should be fundamental.

 

[Demystifier]

No single-history realistic explanation is possible,

Is there a theorem that proves this statement? I don't think so because there is a counterexample to this (Bohm).

 

[Dmitry67]

You don't need to sacrifice anything from your list: The pilot wave interpretation is deterministic, realistic, causal, and has a single history.

Ooops, I forgot about it - for me this is worst interpretation: pure handwaving, plus even not relativistic. I was thinking it had been proven to be false a long tie ago:

http://en.wikipedia.org/wiki/Bohm_interpretation#Comparison_with_experimental_data

An important prediction of the Bohm theory, made in Bohm's original 1952 paper, is that the electron in the ground state of a hydrogen atom is in rest (cf. equation (3) above - s states have spherical symmetry and thus have constant phase), as the quantum force introduced by Bohm balances the classical electromagnetic potential.

Any measurement of the momentum of a ground state electron will give a non-zero result as predicted by quantum mechanics, but Bohm's theory argues that the act of measuring the momentum disturbs the electron at rest, resulting in a non-zero expection value. [3]

Experimental observation of the decay rates of muons bound in exotic atoms has shown, however, that ground state electrons are in fact in motion. Because of their mass, muons captured in higher states rapidly cascade to the ground state, and about 99 percent of the bound muons decay from the 1S state. If the atomic number of the hydrogen-like atom is high enough, the muon motion will be relativistic, and subject to time dilation. The data show that for moderate Z atoms, the observed lengthening of the muon decay time can be attributed to the relativistic time dilation.[4]

Since the motion of the muon has been demonstrated without any disturbance of the atom, it cannot be explained by disturbances related to the measurement process as with conventional measurements of the momentum of ground state electrons. An important conceptual prediction of the Bohm model, namely that ground state electrons are at rest, would seem to be contradicted by experimental evidence.

 

[Dmitry67]

Is there a theorem that proves this statement? I don't think so because there is a counterexample to this (Bohm).

Sorry, I forgot to add "hidden variables-free"

 

[Demystifier]

Since the motion of the muon has been demonstrated without any disturbance of the atom, it cannot be explained by disturbances related to the measurement process as with conventional measurements of the momentum of ground state electrons. An important conceptual prediction of the Bohm model, namely that ground state electrons are at rest, would seem to be contradicted by experimental evidence.

This is nonsense. The measurement of motion of the muon disturbs the MUON, so the Bohm model predicts that the muon moves when its motion is measured, in agreement with experiments.

 

[Demystifier]

Ooops, I forgot about it - for me this is worst interpretation: pure handwaving, plus even not relativistic.

First, as I repeated many times, it can be made relativistic. Second, I don't know what do you mean by "handwaving", but all new features of Bohmian mechanics are strictly DERIVED from postulating one additional EQUATION. If you call it "handwaving", then all the best theories in physics are "handwaving" too.

 

[Dmitry67]

This is nonsense. The measurement of motion of the muon disturbs the MUON, so the Bohm model predicts that the muon moves when its motion is measured, in agreement with experiments.

No, you just measure the lifetime of muonium, you don't measure the muon itself.

 

[Ilja]

Ooops, I forgot about it - for me this is worst interpretation: pure handwaving, plus even not relativistic. I was thinking it had been proven to be false a long tie ago:

http://en.wikipedia.org/wiki/Bohm_interpretation#Comparison_with_experimental_data

Of course, not. Have you ever heard about such things like equivalence theorems? There is one which proves that the predictions of pilot wave theories in quantum equilibrium agree with the predictions of standard QT.

Note, this is not handwaving, but a theorem. The only nontrivial assumption used there is that the pilot wave beables allow to distinguish macroscopically different states.

And the "not relativistic" is also only pure polemics. There are a sufficient number of variants of pilot wave theories for relativistic field theory. With the same equivalence proof working as well.

Whenever you meet some claim about "BM falsified by observation": Crackpot alert. There is a theorem of equivalence with QT. So, the title would be (if BM would really be falsified) "QT falsified by observation". If a paper claiming experimental differences does not explain in detail what is wrong with the equivalence theorem, it should be put into the folder with trisections of angles, quadratures of the circle, perpetuum mobile constructions and other constructions which violate well-known theorems.

 

[ThomasT]

Physical reality is what exists independent of our possibility to observe it. QM does not even make claims what is this reality. Is the wave function real or not? What else, if anything, is real too? These questions are simply not answered.

Thus, it does not make sense to claim that QM is in some sense a complete description of reality

Physical reality also refers to our objective records. For those who think of QM as being only about the objective records, then it's a complete theory. For those who think of QM as being about an underlying reality, then it's an incomplete theory.

But I agree with you that there is no sense in which QM is a complete description of reality.

It's true that QM doesn't make any formal claims about an underlying reality. But the language surrounding it, and the incorporation of concepts from classical physics can lead one to believe that it does.

Fact is, there are simple realistic explanations of the violations of Bell's inequality in terms of realistic hidden variables and hidden FTL information transfer. But there is no realistic explanation of the violations of Bell's inequality without FTL. Moreover, we have a theorem, that there cannot be such explanations without FTL.

This is the ideal situation of falsification of a theory. No theory can be falsified in a more rigorous way. Instaed, usually almost every theory can be saved, given some falsification, by some (at least formally realistic) ad hoc explanation. But here there is no such ad hoc explanation - no realistic explanation is possible in principle.

I agree that there are no 'realistic' explanations of violations of Bell inequalities. The inequalities aren't realistic constructions. They're logical constructions. Bell's 'theorem' is that a certain lhv ansatz is incompatible with the mathematical structure of QM (of course he goes a bit further than that and says that any lhv formulation must conform to the salient characteristic of this ansatz which is the separability of the variables to be correlated).

If the ansatz also doesn't correspond to physical reality (or some aspect thereof, such as the experimental design and preparation), then experimental violations of inequalities based on it would be expected. The ansatz assumes an independence between data accumulators in entanglement preparations. The inequalities incorporate this assumption. But the experiments are designed to produce statistical dependence. So the inequalities are violated. These experimental violations can therefore be used as indicators of the presence of entanglement. And that's all they tell us about physical reality, afaik.

For those who want to explain entanglement using ftl propagations, or instantaneous actions at a distance, or gods or whatever, then fine, but it remains for them to demonstrate this, because Bell's theorem, and experimental violations of inequalities based on it, don't imply or require this.

So I'll stand by my statement to the OP, kashiark, that there's no paradox because as far as anybody knows the statistical dependencies produced in entanglement experiments are not due to ftl propagations.

 

[Demystifier]

No, you just measure the lifetime of muonium, you don't measure the muon itself.

But in your previous post you said that "motion of the muon has been demonstrated". How measuring the lifetime of the muonium demonstrates the motion of the muon?

 

[Dmitry67]

But in your previous post you said that "motion of the muon has been demonstrated". How measuring the lifetime of the muonium demonstrates the motion of the muon?

If the lifetime of muonium is longer then the lifetime of muon itself then it can be explained by the time dilation of the muon

Fineprint: (but we should be careful, for example, lifetime of Deuterium is infinite while lifetime of free neutron is half an hour, but it explained not by the movement but by the fact that binding force is very strong and neutron is 'lighter' in nuclei then a free one).

 

[Demystifier]

If the lifetime of muonium is longer then the lifetime of muon itself then it can be explained by the time dilation of the muon

I see. But it looks as a classical explanation. On the other hand, lifetimes should be calculable from standard quantum mechanics, irrespective of the interpretation. In other words, this difference of the lifetimes should be encoded in properties of the wave function, which by itself says nothing about particle motions. Therefore, since the Bohmian interpretation uses the same wave functions as standard quantum theory, and since there is a GENERAL THEOREM stating that all measurable predictions are the same, the Bohmian interpretation also must explain this effect. To see in detail how exactly this happens in the Bohmian interpretation, I would need first to see an explanation with standard QM. If standard QM could not explain it (which I am convinced that it can), then yes, it would be a failure of the Bohmian interpretation, but moreover, it would be a failure of standard QM as well.