Entanglement and observations

[michael879]

I just had one of those lightbulb thoughts a few minutes ago reading someones post. Does observing some particle in an superposed state entangle you with that particle? It makes perfect sense to me right now..

Its definitely like entanglement, even if it isnt. Observing the first observers reaction instantly gives you the state of the particle (and vise versa). Wouldnt this mean superposition is relative depending on whos observing? For example if someone did a quantum coin flip to determine whether to spread a deadly virus or not Then everyone on Earth would be in a superposition of dead and alive to the rest of the universe, right?

 

[jostpuur]

I just had one of those lightbulb thoughts a few minutes ago reading someones post. Does observing some particle in an superposed state entangle you with that particle? It makes perfect sense to me right now..

Its definitely like entanglement, even if it isnt. Observing the first observers reaction instantly gives you the state of the particle (and vise versa). Wouldnt this mean superposition is relative depending on whos observing? For example if someone did a quantum coin flip to determine whether to spread a deadly virus or not Then everyone on Earth would be in a superposition of dead and alive to the rest of the universe, right?

I agree with this mostly. I've come to the same conclusions.

Isn't the many world interpretation also part of this? I don't see how it could make sense to say that the observer is in superposition of having measured different outcomes without the many world interpretation. The observer doesn't see himself being in superposition, so there should be, from the observer's point of view, different worlds where he has obtained different results. Only from the point of view of somebody who has not been involved in the measurement, does it make sense to say that the observer is in superposition.

 

[rasgar]

The act of observation destroys the state of entanglement. This is why entanglement is so good for quantum cryptography. The act of receiving the data that an entangled particle has is a process in itself (generally requiring multiple entanglements). Also entanglement works at the speed of light. By the time that process is complete, the state is unknown. And by the time your brain perceives the sensory information that tells you about the particles state, it will be even further along its path. Here's an interesting link I found on it: <http://calitreview.com/2007/03/30/the-strange-world-of-quantum-entanglement/>

 

[genneth]

Yes -- this is the basis of the relational interpretation. We say that reality is defined by what observers can agree on when they exchange/compare information. Note that this is strictly a weaker definition of reality than the usual Copenhagen interpretation. Thus, measurement is nothing more or less than simply entangling yourself with the system. A 2nd observer can see that you've entangled yourself, but could still not know anything about the system, except that if she were to measure you and the system separately, there would be a correlation.

See http://plato.stanford.edu/entries/qm-relational/

I think this is the easiest view for those who are skeptical of absolute reality to begin with. Notice that it doesn't say *everything* is subjective -- different observers will agree with each others' observations when they interact/communicate (which is a quantum process itself -- mutual observation).

My personal crackpot theory is that the probabilistic nature of QM is due to the impossibility of knowing one's own state, plus a lower limit to how much you much disturb a system if you want to gain information about it (the nature scale set by \hbar).

 

[michael879]

The act of observation destroys the state of entanglement. This is why entanglement is so good for quantum cryptography. The act of receiving the data that an entangled particle has is a process in itself (generally requiring multiple entanglements). Also entanglement works at the speed of light. By the time that process is complete, the state is unknown. And by the time your brain perceives the sensory information that tells you about the particles state, it will be even further along its path. Here's an interesting link I found on it: <http://calitreview.com/2007/03/30/the-strange-world-of-quantum-entanglement/>[/QUOTE]
no kidding. However what I am saying is that observation only destroys the state of superposition/entanglement for the observer. The fact that observing a state entangles you with it explains this perfectly. Now in macroscopic systems, you observe a particle and become entangled with it. Then all the air around u gets entangled with you and the particle and etc until everything in the world is entangled with this particle. Therefore it seems like the act of observation simply decoheres a system when it fact it only decohers it for the observer and the observers of the observer.

 

[rasgar]

In this debate you have to be weary of what 'observe' means. When quantum physicists talk about observation, they talk about the small amount of energy exerted on a physical system that is needed to extract the information, such as a photon bouncing off a phosphorous atom and breaking down the rhodopsin in your photo receptors which is then transferred as an ionic impulse into your brain. Now entanglement is a very delicate event that is destroyed by entropy, which is why it's rare (actually only entanglement that lasts for a while is rare, entanglement for small fractions of a second is very common). For the laboratory superposition that is what I assume you're talking about, there must be virtually no interaction between the entangled particles, otherwise superposition only lasts a few seconds (or less).If everything in the world was entangled, there would be a violation in the laws of thermodynamics (specifically the second one that deals with entropy). For a system to maintain entanglement, energy must be exerted to reduce entropy, which in turn increases entropy is some distant system. An over simplification of the process to find out what the state of an entangled system is that there must be more than one system entangled with it. Thus, only one aspect of system is compromised when energy is exerted onto it. The act of entangling other particles with it once more exerts energy, which could potentially destroy the system, so there is a limited amount of times that you can extract the data. Also, increasing the distance increases the entropy since once more, energy is exerted onto the system, adding further complications.

 

[mn4j]

You guys are all kidding right? I see how you guys are going off into metaphysics and I wonder if you are serious."entanglement" is really mutual exclusivity disguised in weird language. Let's take an example. If you know that Mr Smith has two children, one a boy and the other a girl, the the children are "entangled". What this means is that if you meet one of the children who turns out to be a boy, you will immediately be able to tell that the other is a girl.

Before you meet the first child, if you were to calculate the probability that the child is boy or girl, it would be 50:50 (boy:girl) provided you have no other information. However the probability that the second child will be a girl is not independent of the probability of the first observation, because both are not mutually exclusive. Some how QM decided to invent it's own term "entanglement" which get's a lot of people really confused.

The probability of one of random children being boy or girl is 50:50 irrespective of if it's the first observation, or the second observation, simply because we have no information to "entangle" them in our minds. By knowing that the two kids are from the same parent who has only one boy and one girl, entangles them.

The same applies to quantum systems. Two photons from the same source will be entangled by the property of the source they share.

Coming to think of it, "entanglement" is a clever way of hiding the hidden variable shared by both systems when we have no idea about the nature of the hidden variable.

 

[rasgar]

Quantum entanglement is a quantum mechanical event that causes two particle to essentially be part of one entity. Read the link I posted.

 

[mn4j]

Quantum entanglement is a quantum mechanical event that causes two particle to essentially be part of one entity. Read the link I posted.

First, quantum entanglement is not an event, it is a description.
Second, saying the two particles are part of one entity is misleading. Siblings can be part of an entity called a family, yet they are separate individuals. Two particles being entangled is analogous to two people being related. In reality all that is happening is that the two particles have common or correlated properties.

Quantum entanglement is essentially equivalent to a hidden variable theory since Bell's theorem has been effectively shown to be wrong.

 

[cesiumfrog]

since Bell's theorem has been effectively shown to be wrong.

mn4j, rather than debate off-topic technical issues, I think we can both agree that the claims you are making contradict mainstream modern physics, yes? As such, can you understand why such claims are inappropriate (i.e., anti-conducive to others understanding modern physics) in threads not specifically intended to investigate alternative views?

 

[michael879]

yea I think your just wrong about this mn4j. What your describing is a classical view of entanglement. Quantum entanglement is defined as a multi-particle superposition. i.e. |0>|0> + |1>|1> is an entanglement between two qubits where they have equal values. The system is in a superposition between |0>|0> and |1>|1>, it isn't in one or the other.

As for the entropy argument, I am not sure that disproves what I am saying. If you view the Earth as isolated, any quantum measurement that effected everything on Earth would put Earth into an entangled state with what was being measured relative to everything outside the earth. If you don't like assuming the Earth is isolated from the rest of the universe, imagine a sphere around the Earth whose radius grows with the speed of light. Nothing outside of the Earth could possibly know the outcome of the measurement.

looking at this from the MWI, the area of the universe that is affected by the measurement splits while the rest of the universe doesnt. In our localized sphere, the 2nd law of thermodynamics isn't violated, since from our point of view the particle has been measured and we have been effected by that measurement (we split into one of the possible universes).

 

[mn4j]

mn4j, rather than debate off-topic technical issues, I think we can both agree that the claims you are making contradict mainstream modern physics, yes? As such, can you understand why such claims are inappropriate (i.e., anti-conducive to others understanding modern physics) in threads not specifically intended to investigate alternative views?

Apparently you are not following the literature very much. It is a fact that Bell's theorem has been disproved, maybe your textbook does not say that yet.

Hess and Philipp (2000) Bell's theorem and the problem of decidability between the views of Einstein and Bohr, PNAS vol.98 no.25 pp14228-14233
The authors find that:

We argue that the mathe-matical model of Bell excludes a large set of local hidden variables
and a large variety of probability densities. Our set of local hidden
variables includes time-like correlated parameters and a general-
ized probability density. We prove that our extended space of local
hidden variables does permit derivation of the quantum result and
is consistent with all known experiments.

In case you don't recall, Bell's theorem was supposed to prove that Quantum Entanglement was not the same as a hidden variable theorem. This paper shows that Bell's theorem is wrong.

I've quoted just one example, there are several others in case you are still in doubt.

If by mainstream physics you mean "the religion of blindly following ideas without any due diligence on their historical basis" then you are right. I'm not mainstream.

 

[mn4j]

yea I think your just wrong about this mn4j. What your describing is a classical view of entanglement. Quantum entanglement is defined as a multi-particle superposition. i.e. |0>|0> + |1>|1> is an entanglement between two qubits where they have equal values. The system is in a superposition between |0>|0> and |1>|1>, it isn't in one or the other.

I think you are wrong. Quantum superposition is a an epistemological property not an ontological one. By trying to make it an ontological one, you are committing the mind-project fallacy -- the most prevalent error of reasoning in modern physics.

Using epistemological statements ontologically, makes absolutely no sense and is equivalent to saying:

What happens if I boil my political opinions to 50 degrees and subtract my love for cigarettes?.

A good example is:
"I don't know the exact state of the system, therefore the system exists in all possible states at once"

In case you don't see it yet, and are tempted to agree with the above statement, remember that by saying the system exists in all possible states at once, you are saying that the system has no specific state and by definition, any attempt to measure a state of the system is a contradiction. This is only made worse by then positing that by observing "the state" (which we've established is meaningless), the system collapses into a particular state. What has essentially happened is that the individual has projected a deficiency of his brain (ignorance of the particular state of the system), to a deficiency of nature (indeterminacy of the state of the system), and has projected a change in his brain (obtaining new information about the state of the system) to an actually physical process happening in nature (the indeterminate system collapsing into a singular value). --- The mind-projection fallacy at it's best or rather worst.

I'll encourage anyone here to investigate for themselves the difference between "epistemological statements" and "ontological statements"


The best article I have found on the subject particularly as applied to QM is the following:
Jaynes, E. T., 1990, Probability in Quantum Theory
http://bayes.wustl.edu/etj/articles/prob.in.qm.pdf

 

[cesiumfrog]

Apparently you are not following the literature very much. It is a fact that Bell's theorem has been disproved[.. by] Hess and Philipp

Refuted (http://www.pnas.org/cgi/content/abstract/99/23/14632).

the difference between "epistemological statements" and "ontological statements"

That difference is basically moot (or philosophical) since physicists are always open to the possibility that new experiments will disprove their current theories, and as such, stating "the universe is a Lorentzian four-manifold" is merely shorthand for "measurements agreed with a Lorentzian four-manifold model".

 

[mn4j]

Refuted (http://www.pnas.org/cgi/content/abstract/99/23/14632).

The original authors rebutted that 'refutation' three years ago. Neither Gill nor anyone else has attempted a response.

http://www.pnas.org/cgi/content/full/101/7/1799
PNAS | February 17, 2004 | vol. 101 | no. 7 | 1799-1805

We show that the known proofs of Bell's inequalities contain algebraic manipulations that are not appropriate within the syntax of Kolmogorov's axioms for probability theory without detailed justification. Such justification can be achieved by a variant of the techniques used in Bell-type proofs but only for a subclass of objective local parameter spaces. It cannot be achieved for an extended parameter space that is still objective local and that includes instrument parameters correlated by both time and setting dependencies.

 

[michael879]

mn4j, according to QM (which is experimentally proven) superposition and entanglement are fundamentally different than hidden variables.

"I don't know the exact state of the system, therefore the system exists in all possible states at once"

Superposition is proven by the fact that a particle can interfere with itself, not by the fact that we can't predict its properties.

Either way, can you please take this argument to another thread because my original question hasn't been answered and I think this is completely irrelevant. I am asking for what quantum mechanics says on the topic, not your personal view. Especially when it has been shown that no hidden variable theory works.

 

[mn4j]

mn4j, according to QM (which is experimentally proven) superposition and entanglement are fundamentally different than hidden variables.

QM is not a physical theory but a mathematical model. If you have a theory with an infinite number of variables, you can fit any experimental data through it. That does not mean the data has validated the theory.

If only you'll get over your religious beliefs and read the articles on Bell's theorem, you'll see for yourself that Quantum superposition is in effect a hidden variable theorem. Quantum superposition hangs on the validity of bell's theorem. Bell's theorem IS the supposed proof that no hidden variable theorem works. The articles I posted prove that Bell's theorem is wrong. Therefore, Quantum superposition hangs on thin air.

Superposition is proven by the fact that a particle can interfere with itself, not by the fact that we can't predict its properties.

There has NEVER been an experiment proving that a particle can interfere with itself. It is simply a postulate.

Either way, can you please take this argument to another thread because my original question hasn't been answered and I think this is completely irrelevant. I am asking for what quantum mechanics says on the topic, not your personal view. Especially when it has been shown that no hidden variable theory works.

Your question has been answered. The answer is "The question is a meaningless mix of ontological and epistemological statements"

 

[michael879]

theres nothing wrong with the question. Its simply does an observer entangle with the observed state. The observer could be a photon or w/e, it doesn't have to be a macroscopic object.

how can you say the double slit experiment with electrons DOESNT prove that a particle can interfere with itself? Unless your just being a pain and trying to say that experimental evidence is different from a proof, I don't understand what you mean by that.

Also, Ill admit I didn't read the papers you posted (havnt had time). However that other guy posted saying those papers have been refuted:
http://www.pnas.org/cgi/content/abstract/99/23/14632
(I havnt read that either).

Also, how can you equate believing in a generally accepted scientific theory to religion? I know that scientists accept these theories, and I know that scientists require proof (or experiment evidence). Its also ridiculous to expect someone to verify every single theory they read about. Other than the simple experiments they teach in school, I don't have time to try to reprove quantum mechanics (if I had time Id do it). I've read enough about it to believe its "true" (like you said its a mathematical model it doesn't explain what's actually going on). However as far as a particle interfering with itself, I don't see how any other conclusion can be drawn from observing an interference pattern when sending single electrons through a double slit.

 

[mn4j]

theres nothing wrong with the question. Its simply does an observer entangle with the observed state. The observer could be a photon or w/e, it doesn't have to be a macroscopic object.

how can you say the double slit experiment with electrons DOESNT prove that a particle can interfere with itself? Unless your just being a pain and trying to say that experimental evidence is different from a proof, I don't understand what you mean by that.

Clearly you need a paradigm shift to be able to see what I'm talking about. And when you do see it, you will understand why most of the things you are posting here make no sense at all. Let me try to illustrate to you the difference between ontological statements and epistemological statements.

Imagine I call you up on the phone and tell you I have a coin in my hand and I'm going to toss it. Then I toss it. You actually hear as the coin drops and settles to a stop. Then I ask you, what is the outcome, heads or tails? What will you say. The correct answer will be to say you don't know, which is exactly the same thing but more precise to say that there is a 0.5 probability that the outcome is heads and 0.5 probability that the outcome is tails.

If you say it is "both heads and tails", or "neither heads no tails", I would think you are just being stupid because I look down and see clearly the state of the coin. This clearly tells you that there is a difference between epistemological statements and ontological ones. For the person who has observed the outcome, their observation is an ontological statement. For the person who is yet to observe the outcome, their statement is epistemological.

- epistemological: the probability of the outcome being a "head" is 0.5
- ontological: the outcome IS a "head", or the probability of the outcome being a "head" is 1.0

As you see, the two statements appear to contradict each other but they are both correct in their contexts. It would be wrong for a person who has not observed the outcome and thus is making an epistemological statement, to suggest without any extra information that the probability for "head" is 1.0, even though ontologically that is the correct answer. Therefore, it is nonsensical to interpret a statement that was made epistemologically in an ontological manner.

Every time somebody says the "the coin IS in a superposition of head and tails" that is what they are doing. It makes absolutely no difference whether you are talking about macroscopic objects, or photons and electrons. Every time a person uses wavefunction collapse as a real physical process happening at observation, that is, with the unstated assumption that something is actually happening to the coin or photon when it is observed, they commit the same error. Everytime somebody says there are two universes such that in one the coin is heads and the other is tails, commits this error.

This is so fundamental, I dare say your future as a scientist (as opposed to a phenomenologist) hangs on you understanding this difference.

Also, Ill admit I didn't read the papers you posted (havnt had time). However that other guy posted saying those papers have been refuted:
http://www.pnas.org/cgi/content/abstract/99/23/14632
(I havnt read that either).

You've got the sequence wrong.

In the first paper, the authors showed that Bell's theorem was inaccurate.
In the second paper, the authors attempted a rebuttal to the first paper.
In the third paper, the original authors showed that the rebuttal in the second paper was based on fautly mathematics and reiterated more clearly their position showing exactly where the second paper's authors as well as Bell himself were wrong.
It's been 4 years, since and nobody has attempted a response to the third paper, not even the authors of the second paper.

Also, how can you equate believing in a generally accepted scientific theory to religion?

Because it is not scientific and is mostly vain speculation.

I know that scientists accept these theories, and I know that scientists require proof (or experiment evidence). Its also ridiculous to expect someone to verify every single theory they read about.

You should read some physics history. There are a lot of things that are commonly accepted but are unscientific. Unfortunately, you have to read the articles and be convinced by them rather than accept the claims at face value.

Other than the simple experiments they teach in school, I don't have time to try to reprove quantum mechanics (if I had time Id do it).

You don't have to, there are many renowned scientists that have successfully challenged some of these commonly accepted dogma. You don't have to accept their claims at face value. You have to read it for yourself.

I've read enough about it to believe its "true" (like you said its a mathematical model it doesn't explain what's actually going on). However as far as a particle interfering with itself, I don't see how any other conclusion can be drawn from observing an interference pattern when sending single electrons through a double slit.

The mathematical system of "epicycles" was developed 1000s of years ago to explain the motion of the planets and the solar system. It appeared to work, some people like Galileo, Kepler, Corpernicus challenged it, and many thought they were crazy for rejecting a commonly accepted theory. It turns out they were right.

QM and QED are analogous to epicycles. They are mathematical tools that appear to work but are far from describing what actually happens. The sooner you realize this the sooner you can put your mental effort to an attempt at developing something better.

As far as concerns an electron interfering with itself, you claim that sending electrons through a slit system one at a time and obtaining a pattern means the electron interferes with itself? It doesn't, a single electron produces a single spec on the screen not a diffraction pattern. The ensemble of electrons passing through the slits, produce the diffraction pattern. The only thing this experiment proves is that the slits sort out the ensemble of electrons passing through them into a pattern. It says nothing about the mechanism of the sorting although it is evident that the sorting is based on a property of the electrons themselves. There is no evidence of any "interference".

 

[di1026]

A new question

If one particle is entangled with a second particle, then the second particle is entangled with another one, then what is the relationship between the first particle and the third one?If the answer is just entanglement, then what is the essential function of quantum repeater?
Thanks for replying:)

 

[cesiumfrog]

QM and QED are analogous to epicycles.

lol :rofl: Let us know when you've got a better theory, we'll be all ears. Remember that the reason we no longer believe in epicycles is the existence of hard experimental data which agreed better with Kepler's description than it did with any epicycle theory of comparable complexity (plus Newton and Einstein correctly predicted new phenomena that would not otherwise have been expected). So far all you have is a small controversy (over which particular classes of theory have been proven unworkable) not a working alternative to the complete mainstream theory.

[..] If the answer is just entanglement, then what is the essential function of quantum repeater?

Is that to teleport a quantum state further than you can transport it?

 

[mn4j]

lol :rofl: Let us know when you've got a better theory, we'll be all ears.

I will, since it is obvious that while you are religiously believing that the "epicycles" of QM and QED are the REALTHING, there'll no possibility for you to contribute to this "better theory".

Remember that the reason we no longer believe in epicycles is the existence of hard experimental data which agreed better with Kepler's description than it did with any epicycle theory of comparable complexity

Remember also that the people who were castigating Galileo and Kepler such as the Pope were not the ones who came up with the hard experimental data.

(plus Newton and Einstein correctly predicted new phenomena that would not otherwise have been expected). So far all you have is a small controversy (over which particular classes of theory have been proven unworkable) not a working alternative to the complete mainstream theory.

Epicycles was also a mainstream theory.

Like I've told you before, you don't need a new theory to be able to see the flaws of a present one, but you need to see the flaws of the present theory to be able to develop a new one as has be proven time after time again throughout the history of physics.

 

[Cthugha]

You've got the sequence wrong.

In the first paper, the authors showed that Bell's theorem was inaccurate.
In the second paper, the authors attempted a rebuttal to the first paper.
In the third paper, the original authors showed that the rebuttal in the second paper was based on fautly mathematics and reiterated more clearly their position showing exactly where the second paper's authors as well as Bell himself were wrong.
It's been 4 years, since and nobody has attempted a response to the third paper, not even the authors of the second paper.

This is wrong.
David N. Mermin gave a response in Foundations of Physics, Volume 35, Number 12, December 2005 , pp. 2073-2077(5) (http://www.technion.ac.il/~peres/mermin.pdf).

 

[mn4j]

This is wrong.
David N. Mermin gave a response in Foundations of Physics, Volume 35, Number 12, December 2005 , pp. 2073-2077(5) (http://www.technion.ac.il/~peres/mermin.pdf).

Thanks for mentioning this. I wasn't aware of this paper as they only cite the original paper in a footnote( difficult to track). However, this paper is hardly a rebutt. I'll characterise it as a "musing". After reading this paper I believe the author has misunderstood the work of Hess and Philipp, probably based on a basic misunderstanding of probability theory. The author claims he is working on a detailed rebutt of Hess and Philipp. I'm waiting to read that.

There have however been other disproofs of Bell's theorem independent of Hess and Philipp:
* Disproof of Bells theorem by Clifford Algebra Valued Local Variables. http://arxiv.org/pdf/quant-ph/0703179.pdf
* Disproof of Bell's Theorem: Reply to Critics. http://arxiv.org/pdf/quant-ph/0703244.pdf
* Disproof of Bell's Theorem: Further Consolidations. http://arxiv.org/pdf/0707.1333.pdf

 

[Demystifier]

Mn4j, we already had a discussion of the Clifford algebra valued local variables at this forum. My opinion is that a Clifford algebra valued variable contradicts the basic idea of a true physical variable. I cannot imagine how a Clifford valued variable could possibly be measured.

Considering refutations of the Bell theorem, I am not surprised that many people believe that they can refute it, given the fact that the Bell proof is a rather indirect proof against possibility of local hidden variables. But there are also more direct proofs, which seem impossible to refute, like the Hardy proof. Are you familiar with this?

 

[mn4j]

Mn4j, we already had a discussion of the Clifford algebra valued local variables at this forum. My opinion is that a Clifford algebra valued variable contradicts the basic idea of a true physical variable. I cannot imagine how a Clifford valued variable could possibly be measured.

Could you point me to the thread in which this was discussed. Needless to say I disagree with that opinion.

Considering refutations of the Bell theorem, I am not surprised that many people believe that they can refute it, given the fact that the Bell proof is a rather indirect proof against possibility of local hidden variables.

Bell's theorem allegedly lays out rules which local hidden variable theorem's must obey. And since the predictions of QM contradict Bell's theorem, it it was inferred that the phenomena described by the QM formalism must be non-local. Disproofs of Bell's theorem only go to show that the rules for local hidden variable theorems suggested by Bell, are inaccurate, and some local variable theorems do produce the same results as predicted by the QM formalism, which has profound implications for non-local interpretations of the QM formalism.

But there are also more direct proofs, which seem impossible to refute, like the Hardy proof. Are you familiar with this?

I'm not intimately familiar with the Hardy proof although a quick review of it reveals that it still suffers from the same misunderstandings of probability theory known as the conjugation fallacy and the inverse fallacy. See section 2 of (http://xxx.lanl.gov/pdf/0708.3948)

 

[Micha]

As far as concerns an electron interfering with itself, you claim that sending electrons through a slit system one at a time and obtaining a pattern means the electron interferes with itself? It doesn't, a single electron produces a single spec on the screen not a diffraction pattern. The ensemble of electrons passing through the slits, produce the diffraction pattern. The only thing this experiment proves is that the slits sort out the ensemble of electrons passing through them into a pattern. It says nothing about the mechanism of the sorting although it is evident that the sorting is based on a property of the electrons themselves. There is no evidence of any "interference".

How come, that the slit is sorting out the ensemble of electrons just in a pattern,
as if a wave was passing through both slits and would interfere with itself?
Accident? Some deep reason, we missed? God playing a trick on us?
An irrelevant question althogether, because not fitting into the scheme of
allowed questions?

 

[mn4j]

How come, that the slit is sorting out the ensemble of electrons just in a pattern,
as if a wave was passing through both slits and would interfere with itself?
Accident? Some deep reason, we missed? God playing a trick on us?
An irrelevant question althogether, because not fitting into the scheme of
allowed questions?

Hypothetical Scenario 1:
Let's assume for a moment that the hidden property of the photon on which the sorting is based is the angular momentum. The angular momentum of a photon is quantized, so it can not be a continuum of values. Thus, the angle at which the re-emitted photon leaves is based on conservation of angular momentum of the photon and the electron with which it interacts. In this case, you won't need any sort of interference. The slits just sort out the electrons such that the resulting diffraction pattern is a function of the angular momentum distribution of the photons impinging on the slits.

I propose an experiment to verify this hypothesis. Create a photon source such that you can influence the angular momentum content of the produced photons. If this hypothesis is true, you should see something on your detecting screen.

Alternatively, manipulate the electrons in the slits in such a way that you can influence their angular momentum. Then you should be able to see effects on the detecting screen.


Hypothetical scenario 2:
Lets assume that diffraction happens as follows: consider any two photons A and B impinging on an electron on the slits. A arrives at a given time before B on the same electron. The electron absorbs A and starts oscillating in a certain manner determined by the phase with which the photon hit the electron. Then a short time after (shorter than time required for the electron to re-emit A), B arrives at the same electron. The effect of B on A is such that it affects the angle at which A is re-emitted, and that angle is based on the phase with which photon impinged on the electron etc. This hypothesis is more difficult to test.

These are the ideas I'm currently working on to explain what happens ontologically.
Note a few things in my hypotheses:
a) only photons that 'touch' the slits are re-emitted at an angle. Thus a single slit has two diffracting surfaces and a double slit has 4 diffracting surfaces.
b) if (a) is true, then the diffraction pattern from a single electron bi-prism, should be similar profile to diffraction of a photon from a single slit, because even though the bi-prism has two slits, only one edge of each slit is diffracting, which makes the bi-prism effectively a single slit. I have not verified this my self as I just thought of it while replying to you.

As concerns the question of why it is similar to waves passing through two slits, I would ask you back a similar question. Why is the circumference of any circle equal to 2*pi*radius? Does that mean God is playing dice with us? I think the answer is that wave-like behaviour has certain characteristics, just like circles.

 

[Micha]

Hi mn4j,
hypothetical scenario 2 is already ruled out by experiment.
The textbooks say, that the diffraction pattern, which you get
at the end, stays exactly the same, no matter, how low the intensity is.

I think, hypothetical scenario 1 can be easily ruled out by showing, that the angular momentum change needed for the diffraction pattern is much bigger than hbar,
which is the quantization required by QM.

Generically these and other scenarios are ruled out by Bell's theorem, of course.
I understand that you do not accept Bell's theorem, but honestly, based on the
scenarios, you present, I don't think, you have a valid disproof of Bell's theorem in your hands.

 

[f95toli]

Mn4j: Quantum computing and other forms of QIP are perhapse the most "non-classical" type of experiments one can perform since they completely rely on superpositions of states. You are not seriously suggestion that all the experiments done so far (of which there are many) can be explained using only "statistics", are you?

Also, how do you explain Rabi-splitting of spectroscopic lines when a two-level system couples to a cavity, as in e.g. cavity-QED? Note that this is a steady-state result, there is nothing preventing you from looking at both peaks at once.

 

[mn4j]

Hi mn4j,
hypothetical scenario 2 is already ruled out by experiment.
The textbooks say, that the diffraction pattern, which you get
at the end, stays exactly the same, no matter, how low the intensity is.

Then the textbooks are wrong. Let's take the intensity down to the point where you get a single photon on the screen. Do you get a diffraction pattern? Of course NOT! You get a single speck. Experiment in fact proves that the diffraction pattern is built up slowly from individual specks and you need a significant number of photons/electrons to start noticing the appearance of a pattern.

I think, hypothetical scenario 1 can be easily ruled out by showing, that the angular momentum change needed for the diffraction pattern is much bigger than hbar,
which is the quantization required by QM.

I think you are sorely mistaken. The angular momentum transfer happens per photon, which as we already agree does not produce a diffraction pattern. Now try to explain HOW the angular momentum transfer required to deviate the trajectory of the photon is more than hbar.

Generically these and other scenarios are ruled out by Bell's theorem, of course.
I understand that you do not accept Bell's theorem, but honestly, based on the
scenarios, you present, I don't think, you have a valid disproof of Bell's theorem in your hands.

Apparently you have not read any of the articles I posted on Bell's theorem. When you do, then I can entertain your doubt.

Take a look at the following completely classical experiment:
http://docto.ipgp.jussieu.fr/IMG/pdf/Couder-Fort_PRL_2006.pdf

It proves that non-locality is not necessary to obtain diffraction patterns. So much for Bell's theorem.

 

[mn4j]

Mn4j: Quantum computing and other forms of QIP are perhapse the most "non-classical" type of experiments one can perform since they completely rely on superpositions of states. You are not seriously suggestion that all the experiments done so far (of which there are many) can be explained using only "statistics", are you?

Probability not statistics.

 

[f95toli]

I wrote "statistics" because you seem to think it is very important that we tend to meausre ensembles. But nevermind, probabilities then?
Can you explain how Shor's algorithm works using only probability?
Or, a simpler case, the abovementioned Rabi-splitting?

 

[Cthugha]

Then the textbooks are wrong. Let's take the intensity down to the point where you get a single photon on the screen. Do you get a diffraction pattern? Of course NOT! You get a single speck. Experiment in fact proves that the diffraction pattern is built up slowly from individual specks and you need a significant number of photons/electrons to start noticing the appearance of a pattern.

Nevertheless your scenario 2 is ruled out. Even if the time interval between the arrival of two photons is much longer than the timescale you mentioned, in which an electron absorbs and reemits a photon, you will notice an interference pattern after enough photons hitting the screen.

Apart from that interference patterns are always created by ensembles of photons. Whether you have one or more photons on your screen is a question of the temporal resolution of your photo diode or streak camera or whatever you use to detect photons. Intensity is a time averaged quantity. It does not even make sense to speak of intensity after having detected just one photon. So the textbooks are quite right. Mentioning intensity means automatically that you are having a look at an ensemble of photons.

 

[vanesch]

I just had one of those lightbulb thoughts a few minutes ago reading someones post. Does observing some particle in an superposed state entangle you with that particle? It makes perfect sense to me right now..

Its definitely like entanglement, even if it isnt. Observing the first observers reaction instantly gives you the state of the particle (and vise versa). Wouldnt this mean superposition is relative depending on whos observing? For example if someone did a quantum coin flip to determine whether to spread a deadly virus or not Then everyone on Earth would be in a superposition of dead and alive to the rest of the universe, right?

This is exactly the basis of the many worlds interpretation.

As to other points in this thread, whether observation is "irreversible entanglement" or "destroys entanglement" depends on the interpretation one takes up. If one takes up an "all quantum" many worlds view, then observation is irreversible entanglement ; if one takes up a collapse view, then observation destroys entanglement.

But what matters is that in both cases, interference between different outcomes is not possible anymore ; in the collapse view, this is simply because the other term has disappeared, in the irreversible entanglement case, this is because the interference term appears in a product with the in-product of the two (orthogonal) observer+environment states, which is zero. So in both cases, the interference term is suppressed.

As such, both views yield identical experimental predictions.