Exploring the Paradoxical Einstein-Podolsky-Rosen Experiment

[guguma]

I saw this Einstein, Podolsky, Rosen paradox in one of my textbooks and it is very interesting. The paradox simply challenges the Copenhagen (Orthodox) Interpretation of Quantum Mechanics by using the constancy of the speed of light.

It simply states that if we observe a pi meson decay into a positron and an electron, then wait long enough that

{delta}x >> ct

and measure the spin of the electron, we are going to collapse both the wavefunction of the electron and the positron. If we find the electron spin to be +1/2 the positron spin will be -1/2.

Thus it is claimed that then information will be carried over much faster than the speed of light which is not possible, so they conclude that the electron and the positron had definite spins prior to the measurement.

What do you make of that?

P.S. I would also be glad if someone would provide me a good source showing how Schroedinger came up with the Schroedinger Equation, I have looked at a bunch of books and could not find one, I am really curious about that.

P.S. How do you implement latex code in your messages?

Thanks.

 

[DrChinese]

I saw this Einstein, Podolsky, Rosen paradox in one of my textbooks and it is very interesting. The paradox simply challenges the Copenhagen (Orthodox) Interpretation of Quantum Mechanics by using the constancy of the speed of light.
...

Thus it is claimed that then information will be carried over much faster than the speed of light which is not possible, so they conclude that the electron and the positron had definite spins prior to the measurement.

What do you make of that?

Welcome to PhysicsForums!

The EPR paper was the first in a series of 3 critical papers on this subject. It raised questions, but did not provide firm answers that were likely to change opinions. No experimental tests were proposed.

The second was the 1964 paper by J.S. Bell called "On the Einstein Podolsky Rosen paradox" which demonstrated that the EPR explanation was inconsistent with Quantum Mechanics: No physical theory of local Hidden Variables can ever reproduce all of the predictions of Quantum Mechanics. An experimental test was imagined to resolve the issue.

The third part was a series of experimental tests of the CHSH version of Bell's Inequality (derived from Bell's paper) which provided results consistent with Quantum Mechanics, but inconsistent with EPR.

You might be interested in this page from my web site:

EPR, Bell and Aspect: The original References[/URL]

 

[peter0302]

What do you make of that?

I'm not sure exactly what kinds of responses you're looking for, but the EPR issue inidcates to me that there is something fundamental about the relationship between quantum mechanics and spacetime that we do not fully understand.

 

[faen]

This video may be an answer to your question:



However i have another question regarding this youtube vid:



Its the double slit experiment and shows that when we observe particles the wavefunction collapses and behave as particles. Some philosophers say it has to be an intelligent being observing the particle in order to collapse the wave function. But this wouldn't make any sense to me. In the video they show an eyeball watching the particles as a way of measuring it. However I would picture it as a device interfering with the particles, and showing the measurements on a screen.

So the question is: If a person does not look at the screen to see the results of measurements, would the particles still create an interference pattern or behave as particles when measured right before they pass the slits?

If answer is the wavefunction still collapses those philosophers would be wrong because no intelligent being observed its position.

 

[peter0302]

Some philosophers say it has to be an intelligent being observing the particle in order to collapse the wave function

I've never heard any reputable physicist say they believe that. Most theories I've heard either don't attempt to define wavefunction collapse, or hold something along the lines of a wavefunction collapse being caused by a thermodynamically irreversible interaction. Anyone who thinks that there needs to be an intelligent being involved is, for lack of a better word, nuts.

 

[guguma]

This video may be an answer to your question:



However i have another question regarding this youtube vid:



Its the double slit experiment and shows that when we observe particles the wavefunction collapses and behave as particles. Some philosophers say it has to be an intelligent being observing the particle in order to collapse the wave function. But this wouldn't make any sense to me. In the video they show an eyeball watching the particles as a way of measuring it. However I would picture it as a device interfering with the particles, and showing the measurements on a screen.

So the question is: If a person does not look at the screen to see the results of measurements, would the particles still create an interference pattern or behave as particles when measured right before they pass the slits?

If answer is the wavefunction still collapses those philosophers would be wrong because no intelligent being observed its position.

I am sorry to say this but neither my question is about the double slit experiment nor these videos have any truth value in them. One of the clips are from "what the bleep do we know" (a movie) and the other is an animation made by infamous Dr. Quantum "Fred Allen Wolf". These guys are Zen Cultists and they have no idea of what they are talking about and all of it is just bullcrap.

Collapse of the wavefunction is just the localization of a probabilistic ensamble whose physical properties are defined by the Schroedinger Equation, it has nothing to do with consciousness or looking. But measurement is a different process because measurement picks out a value (by disturbing the system thus changing the physical constitution of the system) thus collapsing the probability of other values rather than the observed to zero.

 

[peter0302]

These guys are Zen Cultists and they have no idea of what they are talking about and all of it is just bullcrap.

Even though those clips have nothing to do with your question, I'm glad I got a chance to watch another one. I still see absolutely nothing wrong with those movies if they are considered as intended to a general or young audience. They clearly DO know what they are talking about. That second clip is a dumbed down version of the first chapter of volume III of the Feynman lectures.

 

[faen]

Well the first video does indicate that all the particles are connected to each other, even at distant positions. This may be how the positron knows to pick the oposite spin state of the electron after a pi meson decay without having to be predetermined.

I agree that the videos are decieving. Crazy philosophers make crazy ideas based on the deceptive/missinterpreted arguments from the dr quantum vid.

A proof of that these philosophers are wrong, is if the wavefunction collapses without being observed/perceived in the mind. That is all I am asking.

In my physics book it just says a measurement causes it to collapse, but what is that? A force from a charged particle? If it is the force from a charged particle, why isn't a wave function collapsed all the time while traveling through air? How long does the collapse last?

 

[guguma]

Even though those clips have nothing to do with your question, I'm glad I got a chance to watch another one. I still see absolutely nothing wrong with those movies if they are considered as intended to a general or young audience. They clearly DO know what they are talking about. That second clip is a dumbed down version of the first chapter of volume III of the Feynman lectures.

It may be similar, but they are right out of target, by showing an eye looking at a particle and basketballs jumping around the space. If you want to make a young audience interested
you should at least mention the disturbance of the system and not get into the consciousness part.

The basketball argument shows complete "n" basketballs occupying the whole space and than collapsing into only one basketball?

The videos thus are neither raising interest nor showing the truth, Feynman's "Nature of Physical Law" for example is directed towards a general or young audience (it has the double slit of volume III too) and it is not misleading.

Misleading creates pseudo-science and pseudo-science is no more tame but dangerous.
eg. scientology.

 

[peter0302]

OMG. Now you're comparing that to scientology! This is paranoia.

You wanted a video directed to kids to mention "disturbance of the system"? First of all, the uncertainty principle doesn't care whether the system was disturbed at all so your point isn't even valid.

Anyone who thinks that video is malicious or dangerous really needs to chill out and stop thinking themselves to be the Magisterium of all things quantum.

 

[guguma]

In my physics book it just says a measurement causes it to collapse, but what is that? A force from a charged particle? If it is the force from a charged particle, why isn't a wave function collapsed all the time while traveling through air? How long does the collapse last?

I read this from one of Heisenberg's books once, I do not remeber the exact quotation but still I will try to put it in my own words:

"What quantum mechanics taught us is that we can only talk about the interactions of two physical systems, because an isolated standing alone system need to be interacted by another one to "look" (measure, observe whatever) inside it but when this interaction occurs both systems are disturbed by their effect on each other and in the end we can only talk about this interaction"

I will give a crude example of collapse. Let's say I am running on a straight line and your eyes are closed and you have a catapult. You estimate that I am confined in a 100m line running back and forth and you start throwing rocks at me. When one rock hits me and sends you a signal that it hit me at +25.3m on the x axis, you have collapsed my wave function on top of this +25.3 at the instant. But I am disturbed too and after a while when I recover from the concussion I will continue running along the line again and if you wait long enough the only knowledge you have about me will be that I am confined in a 100m line. Now if the effect of the disturbance was "big" say you broke my leg my wavefunction will be different than the first 100m confining function.

Now this maybe a bit misleading too but think of this as picking a photon by a geiger counter, it clicks at a certain point but if the interaction between the counter and the photon somehow reduced or increased the total energy of the photon it will behave differently later on.

 

[Doc Al]

You wanted a video directed to kids to mention "disturbance of the system"? First of all, the uncertainty principle doesn't care whether the system was disturbed at all so your point isn't even valid.

Anyone who thinks that video is malicious or dangerous really needs to chill out and stop thinking themselves to be the Magisterium of all things quantum.

For someone who obviously hasn't watched this crackpot movie, you're quite the fan. Go and rent it! (As childish as those clips might have seemed, the movie is not directed towards kids.)

Enough already.

 

[faen]

Well i like the vids, but the thing with the eyeball makes it unnecessary missleading. That part has convinced many non physicists that things don't exist before we see them etc.

 

[JesseM]

Well i like the vids, but the thing with the eyeball makes it unnecessary missleading. That part has convinced many non physicists that things don't exist before we see them etc.

As I understand it, basically any thermodynamically irreversible interaction with the outside environment will cause the quantum system to behave as if it has been "measured", although the details of what variable the environment will act as if it is measuring will depend on the details of the interaction (in most cases I think the environment acts like it's measuring position).

 

[faen]

"What quantum mechanics taught us is that we can only talk about the interactions of two physical systems, because an isolated standing alone system need to be interacted by another one to "look" (measure, observe whatever) inside it but when this interaction occurs both systems are disturbed by their effect on each other and in the end we can only talk about this interaction"

I will give a crude example of collapse. Let's say I am running on a straight line and your eyes are closed and you have a catapult. You estimate that I am confined in a 100m line running back and forth and you start throwing rocks at me. When one rock hits me and sends you a signal that it hit me at +25.3m on the x axis, you have collapsed my wave function on top of this +25.3 at the instant. But I am disturbed too and after a while when I recover from the concussion I will continue running along the line again and if you wait long enough the only knowledge you have about me will be that I am confined in a 100m line. Now if the effect of the disturbance was "big" say you broke my leg my wavefunction will be different than the first 100m confining function.

Now this maybe a bit misleading too but think of this as picking a photon by a geiger counter, it clicks at a certain point but if the interaction between the counter and the photon somehow reduced or increased the total energy of the photon it will behave differently later on.

As I understand it, basically any thermodynamically irreversible interaction with the outside environment will cause the quantum system to behave as if it has been "measured", although the details of what variable the environment will act as if it is measuring will depend on the details of the interaction (in most cases I think the environment acts like it's measuring position).

Thanks, now i understand it :)

 

[peter0302]

For someone who obviously hasn't watched this crackpot movie, you're quite the fan. Go and rent it! (As childish as those clips might have seemed, the movie is not directed towards kids.)

Enough already.

I haven't seen the whole "crackpot" movie. I've only seen those two youtube clips. I'm really immensly curious what is so bad about it, but I'm reluctant to rent it becuase I fear I will continue to not see what the big deal is and just get myself more worked up.

 

[JesseM]

I haven't seen the whole "crackpot" movie. I've only seen those two youtube clips. I'm really immensly curious what is so bad about it, but I'm reluctant to rent it becuase I fear I will continue to not see what the big deal is and just get myself more worked up.

Those "Dr. Quantum" clips aren't actually in the movie, I guess they were DVD extras or something. The one on the double-slit experiment didn't strike me as too bad except for at the end where they implied a conscious observer was needed to collapse the interference pattern, and the clip on entanglement isn't so bad except that "do something to one and the other responds instantly" has the potential to be pretty misleading, making people think entanglement could be used for FTL communication or something (and the part about everything still being entangled since they were together at the big bang would be controversial, although it could be seen as correct in the many-worlds interpretation). But the actual movie is a lot more new-agey then these Dr. Quantum clips, and I think that one clip on the double-slit experiment basically conveys more meaningful physics info than the entire movie.

 

[peter0302]

Ok.

Well here's my point. As a lawyer and ex-poly sci guy I can nit Schoolhouse Rock's song about how a bill becomes a law till I'm blue in the face, but at the end of the day it's a cute cartoon that conveys mainly correct information in an entertaining way. Sure the Dr. Quantum thing takes some liberties but not outrageous ones, and the liberties it does take are designed to spark more interest or wonder in the subject, NOT to mislead. After all - what do they possibly have to GAIN by making people think that "everything is connected" or that an "eyeball" implies human intervention. It is utterly harmles and might actually do some good.

As for this You Don't Know Bleep film, if these Dr.Q clips aren't even in the film then I really don't understand why everyone's in an uproar over it. I thought the uproar was over the Dr. Quantum stuff. I'm slightly relieved it's not.

Do people here really think that anything that doesn't cover a subject comprhensively and technically perfectly should be banned literature? If so we need to throw out every elementary or even high school science book because none of them can live up to that standard and still be comprhensible or remotely interesting to their audience.

 

[Doc Al]

The "Dr Quantum" clips were certainly in the version of the movie I saw. The double slit cartoon was the best part of the movie! The problem I have with those clips in the context of the movie was that they were used to provide the illusion of "scientific support" for the many outrageous crackpot claims made in the movie. I discussed these claims in a previous thread--and even provided links to detailed reviews of the content of the film.

 

[faen]

Sure the Dr. Quantum thing takes some liberties but not outrageous ones, and the liberties it does take are designed to spark more interest or wonder in the subject, NOT to mislead. After all - what do they possibly have to GAIN by making people think that "everything is connected" or that an "eyeball" implies human intervention. It is utterly harmles and might actually do some good.

Well it is the case that the liberties they take make a huge difference. Dr quantum basically tells that you have to perceive a particle with your mind to collapse the wave function, and that is very strange and what makes ppl think its an interresting movie. They gain a lot of viewers with this cheat, and it leads to retarded theories which quantum physics in reality does not support. People think that the quantum indetermacy is connected to the mind. If they had explained it correctly it would be obvious that the particle position is decided by hidden variables.

 

[JesseM]

If they had explained it correctly it would be obvious that the particle position is decided by hidden variables.

That isn't standard quantum theory either! Only in the Bohm interpretation do particles have well-defined positions which are determined by hidden variables.

 

[peter0302]

Well it is the case that the liberties they take make a huge difference. Dr quantum basically tells that you have to perceive a particle with your mind to collapse the wave function, and that is very strange and what makes ppl think its an interresting movie.

That is absolutely NOT what the clip said - anywhere. You are completely reading that into it.

Now, I read a little more about the main film and it indeed sounds as wacky as others have said. The Dr. Quantum clips _themselves_ however, are not nearly as bad as some of the responses here have suggested.

 

[faen]

That is absolutely NOT what the clip said - anywhere. You are completely reading that into it.

Now, I read a little more about the main film and it indeed sounds as wacky as others have said. The Dr. Quantum clips _themselves_ however, are not nearly as bad as some of the responses here have suggested.

It does show an eyeball observing the particle causing its wave function to collapse. Hence it does say that it requires to be seen with the eye (and not the truth which is that interaction with another physical system causes the wave function to collapse). The eye leads the info to the brain/mind. This is what most people read into that movie, and how it pretty much lies. Other than the eyeball thing i can't think of anything that wrong with the movie though.

 

[peter0302]

Ever heard of METAPHOR?

 

[JesseM]

Ever heard of METAPHOR?

But in the context of the rest of the movie, it's pretty unlikely they meant it as a metaphor.

 

[faen]

Ever heard of METAPHOR?

Metaphor or not, its how the audience interpret the movie which is relevant. Everyone watching the movie have the impression that the wavefunction collapses because the mind perceived it. Thats the obvious way to interpret the movie, and that is how i observed other people i know have interpreted it.

Anyway, how can it be a metaphor? The observation through the eye, and disturbance of physical systems are two entirely different concepts.

 

[JesseM]

Anyway, how can it be a metaphor? The observation through the eye, and disturbance of physical systems are two entirely different concepts.

Not really, one way of observing the electron is to bounce light off it as it passes through the slits and measure the light, which is pretty much what the eye does. I think it could easily be interpreted as a metaphor in a different context, but in the context of that movie (whose main theme was the power of the mind to create reality) I feel pretty confident the creators didn't intend it as a metaphor.

 

[faen]

Not really, one way of observing the electron is to bounce light off it as it passes through the slits and measure the light, which is pretty much what the eye does. I think it could easily be interpreted as a metaphor in a different context, but in the context of that movie (whose main theme was the power of the mind to create reality) I feel pretty confident the creators didn't intend it as a metaphor.

Yeah one can say its the eye which observes it through light, but its not the eye which collapsed the wave function, it was the photon.

 

[guguma]

Not really, one way of observing the electron is to bounce light off it as it passes through the slits and measure the light, which is pretty much what the eye does. I think it could easily be interpreted as a metaphor in a different context, but in the context of that movie (whose main theme was the power of the mind to create reality) I feel pretty confident the creators didn't intend it as a metaphor.

Our eyes do not radiate high energy photons enough to be able to hit onto electrons and reabsorb the photon. And leave that aside our brain is only able to interpret wavelengths through the visible spectrum. Otherwise you would be seeing electrons everywhere and we would not need LHC to look into subatomic particles.

 

[JesseM]

Our eyes do not radiate high energy photons enough to be able to hit onto electrons and reabsorb the photon. And leave that aside our brain is only able to interpret wavelengths through the visible spectrum.

What makes you think the photons would have to be "high energy" or outside the visible spectrum? I believe any wavelength of light can be used to detect on electron, although the light's wavelength needs to be smaller than the separation between the slits if you want to determine which slit it went through.

Otherwise you would be seeing electrons everywhere and we would not need LHC to look into subatomic particles.

Well, anytime you look at any solid object you're seeing the light scattered by many electrons in the atoms that make up its surface. But at low light levels the nerve cells in your retina actually can be triggered by very small numbers of photons, possibly even individual photons--see this page along with this one (which notes that we won't consciously see anything if a single retinal nerve fires, but it's thought that we can consciously see collections of 5 to 9 photons)

Also, the point of particle colliders like the LHC isn't to help us see preexisting particles with more sensitive photodectors, it's about creating particles that don't normally exist freely through high-energy collisions!

 

[JesseM]

Yeah one can say its the eye which observes it through light, but its not the eye which collapsed the wave function, it was the photon.

Yes, you're right about that--if a photon interacts with an electron in such a way that there is the potential to pinpoint the electron's position by measuring the photon, that enough should be enough to make the electron act as if its position had been "observed". Although I don't think that all photon-electron interactions would qualify (I vaguely remember something about it depending on whether the scattering was inelastic or elastic, maybe because one is thermodynamically irreversible while the other is not, although I could be misremembering).

 

[Doc Al]

no insults please

(Folks: Please resist the temptation to insult each other. You are better than that. Rather than delete the posts I will edit out the insulting remarks.)

 

[vanesch]

Everyone watching the movie have the impression that the wavefunction collapses because the mind perceived it. Thats the obvious way to interpret the movie, and that is how i observed other people i know have interpreted it.

I would like to say first that I haven't seen either the movie, nor the clips.

But I can assure you that the viewpoint (although it is only that: a possible viewpoint) that there is a link between "subjective observation" on one hand, and "collapse of the wavefunction" on the other, is not a crazy concept: certain interpretations of quantum mechanics are based on exactly that idea. However, this does NOT mean some telepathic "mind force" or whatever, no, it means that *relative to a subjective observer* is *appears* as if the wavefunction collapsed. So it is not "by the power of the mind" or other BS that some *objective* wavefunction collapses, but rather that the interactions with whatever is the material support for a subjective experience (say, a brain) give rise to a perception of a collapsed wavefunction.

There are two "interpretational" schemes based on that concept: "many worlds" (of course ) and also the "relational interpretation" by Rovelli.

It is one of the possible "philosophical solutions" to the fundamental dilemma of the interpretation of quantum theory. Because you have to know that a photon-electron interaction does NOT collapse the wavefunction, nor of the photon, nor of the electron, but simply ENTANGLES them, according to quantum theory. It is because nobody knows a *physical* process that gives rise to a *collapse* (all elementary physical processes - except gravity - are described by quantum mechanical unitary operators), that one ended up resorting to this kind of stories.

 

[peter0302]

Anyway, I don't know how we diverged from a question about EPR to a debate over whether an eyeball is a metaphor for a conscious observer or not, but the fact is many, many discussions of quantum mechanics, including statements from Heisenberg, emphasize the importance of the observer. The clip using a ROBOTIC EYE, which the narrator explicitly calls a "measuring device", does not imply consciousness. It simply implies MEASUREMENT, which is totally in line with mainstream theories.

About wavefunction collapse - there should be no physical difference between interaction of a photon-electron and the observation of a human eye other than complexity, assuming one doesn't buy into the "conscious observer" requirement. So, if it is complexity that gives rise to "collapse," whereas simple interactions give rise to "entanglement," "collapse" must be nothing more that entanglement that is too complex to be measurable, and thus the near-infinitely entangled wavefunction of the system becomes indistinguishable from a "collapsed" wavefunction. That's about the same as saying a "thermodynamically irreversible measurement" if I'm not mistaken, right?

 

[Ken G]

About wavefunction collapse - there should be no physical difference between interaction of a photon-electron and the observation of a human eye other than complexity, assuming one doesn't buy into the "conscious observer" requirement. So, if it is complexity that gives rise to "collapse," whereas simple interactions give rise to "entanglement," "collapse" must be nothing more that entanglement that is too complex to be measurable, and thus the near-infinitely entangled wavefunction of the system becomes indistinguishable from a "collapsed" wavefunction.

Yes, I think that's exactly the issue-- the complexity comes from all the untraceable noise modes, which when you give up on tracing explicitly, induce a random "decohering" effect on the interferences between the amplitudes of the different outcomes. I would say that "wavefunction collapse" proceeds in two steps: the first is the real guts of it, which is the process of getting quantum systems to behave classically, and that is best accomplished by actual coupling to systems that we already know behave classically. It is only this first step that has anything to do with quantum mechanics, and the wavefunction is already collapsed, we just don't know how yet. The second step is "looking at the result", but we also do that in classical physics, so it's not really an important step at all! It was our intention to induce the classical behavior so that we could use the familiar tools of science on the outcome, that is at the core of collapse, not consciousness.