EPR thought experiment

Main Question or Discussion Point

the source from where i read about the above experiment also mentioned that the outcome is favoured for bohr's point of view( mathematically equations by bell)......
if that's true____


why relativity limit of speed of light?
 

Answers and Replies

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Almost all EPR type experiments to date violate Bell's inequalities. This means that the results can not be explained by a theory that is both realistic and local. In this context a realistic theory is one that can be explained by classical physics and a local theory is one that is restricted to information in the past light cone. i.e local means no communications at greater than the speed of light. However, it turns out that even if we assume that some form of instantaneous communication does occur between quantum entangled particles at the microscopic level, there is no way to use this to transfer information at the macroscopic level. This means a non local quantum theory does not contradict Special Relativity at the macroscopic level. However, if we insist that the speed of light is the limit that information can transferred at both the macroscopic and microscopic level so preserving locality in all situations, then violation of Bells's inequalities has to be explained by a non realistic theory such as the Many Worlds Interpretation (MWI). Unless someone can prove that the MWI explanation is flawed, EPR experiments by themselves can not conclusively prove that quantum transactions are non local. There are many other quantum phenomena such as observed in dual slit experiments, quantum tunnelling and quantum erasure and if it can be shown that MWI fails to explain any one of these, then we would be forced to accept a non local explanation. Even if that was the case, it would not be a disaster for SR. We would just have to more carefully define what we mean by communications and transfer of "meaningful" information and more carefully delineate the boundary between microscopic and macroscopic systems.
 
consider a situation where we can possibly create a vaccum chamber,now we have an option for capturing one of the pair of particles from that void and then accelerating the other pair at speed near that of light,due to time dilation if true will also slow down it's interaction with it's pair,then finally wecheck for epr validity then............................

it's spooky to use both relativity and epr at the same time but it gonna work,probably
don't u think yuiop
 
think in direction by considering our defination of term information,it's perception!!!!!!1
 
i gave u a thought experiment above


what u would say in for that?____________________dalespam
 
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QED is compatible with SR, so why would you expect that experiment to do anything other than confirm both?
 
in QED events between participators occur at speed nearer to speed of light but if u force one of the particle to b a that speed and other at very slow then u may resolve the text
 
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QED is compatible with SR, so why would you expect that experiment to do anything other than confirm both?
Hi Dale, does that mean you prefer the non-realistic explanations to the non-local explanations? Do you consider non-local explanations to be ruled out?
 
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in QED events between participators occur at speed nearer to speed of light but if u force one of the particle to b a that speed and other at very slow then u may resolve the text
"resolve the text" what are you talking about?

Do you understand that it is mathematically impossible for an experiment to be consistent with QED and inconsistent with SR.
 
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Hi Dale, does that mean you prefer the non-realistic explanations to the non-local explanations? Do you consider non-local explanations to be ruled out?
When it comes to QM I am of the "shut up and calculate" school. I am rather uninterested in the explanations/interpretations, only in the equations and predictions. Those are fully compatible with SR.
 
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DrChinese
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QED is compatible with SR, so why would you expect that experiment to do anything other than confirm both?
This is accurate. As far as I know, there are no predictions of one which are inconsistent with the other. It is only the physical interpretations where issues arise.
 
Ken G
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I would offer a slightly different interpretation of the meaning of the term "nonlocal" than that which yulop gave (relevant information can only appear in the past light cone of some event). I agree that the issue is often expressed as an issue of whether we will relax locality or realism, but in my view, it is really only the combination of the two that we can clearly define-- when we deviate from that combination, it can be hard to pinpoint which one we relaxed!

I would say that the combination of locality and realism is the statement that the way any particle behaves is determined by information that is "carried with" the particle, so it resides both spatially and temporally with that particle at the time the particle is asked to participate in an experiment. Since the particle can only have visited its own past light cone, and any particle coming into interaction with that particle as well, that restriction includes the restriction given by yulop. (There is a detail-- virtual particles are not limited by special relativity, but their effects are, every superrelativistic influence by virtual particles has to cancel out).

Where we find a difference is if we relax the local realism, and say that the information that is required to determine an experimental outcome (or its probability) is not entirely contained in the particle involved, then we have the potential for entanglement and various other well-known quantum mechanical effects. I'm never sure why entanglement gets so much press-- there is a much more common effect that exhibits violation of local realism, and that's the Pauli exclusion principle. There is no direct interaction between particles that generates the exclusion principle-- it strictly requires a holistic treatment of a system of particles, such that the information needed cannot be carried by any of the particles themselves. Is the exclusion principle nonlocal, or nonrealistic?

I would say neither-- it is holistic. So to me, the key issue is not whether quantum mechanics violates locality or realism, because a holistic treatment is neither strictly local, nor strictly realistic, in the sense that realism here means the ability to dissect the system into independent parts that make it up. A many-particle wave function is inherently not realistic unless only the entire system is regarded as "real," and if you do that, there's no concept of locality of an entire system. So I would say that realism and locality are simply incompatible concepts in quantum mechanics, and there is no need to ask which is the one that breaks down-- it would be like asking which side of a stick breaks from the other when you snap it in half.
 
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I think I missed the part that prevents a detector from converting a particles spin to an electronic one or zero.
 
Ken G
Gold Member
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Can you expound on your meaning?
 
This question is for all


Why is there a time delation in relativity?..
I want answer in term of interactions
 
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Why is there a time delation in relativity?..
Because the fundamental laws of physics all seem to be symmetric under the Poincare group.

I want answer in term of interactions
Time dilation is present even in the absence of an interaction.
 
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consider a situation where we can possibly create a vaccum chamber,now we have an option for capturing one of the pair of particles from that void and then accelerating the other pair at speed near that of light,due to time dilation if true will also slow down it's interaction with it's pair,then finally wecheck for epr validity then. it's spooky to use both relativity and epr at the same time but it gonna work,probably
don't u think yuiop
nitin_zilch,

I don’t quite understand the question you asked on Monday. You have 1 particle here and one moving away at nearly the speed of light. What kind of measurements are you doing and at what time? I’m not sure how keeping 1 particle here changes the experiment. Keep in mind that it’s probably not a good idea to imagine some kind of communication between the particles since there are several untestible explanations for the results that Bell gets. Each interpretation of QM comes with a different explanation.
This question is for all. Why is there a time delation in relativity? I want answer in term of interactions
As for time dilation, I'm not sure how to answer in terms of interactions. Einstein started with to postulates. 1 – The speed of light is constant (in a vacuum). The direction doesn’t matter. 2 – The rules of physics stay the same no matter how fast you’re moving. Now ask yourself if 2 people pass each other at a million miles a minute just as a light flashes, how can they both see themselves in the center of that flash? For the answer, go to http://casa.colorado.edu/~ajsh/sr/paradox.html. It has a very easy explanation. When you’re done absorbing that, read about photon clocks and the Lorentz transformation. If you prefer videos, watch episodes 41, 42 and 43 of http://www.learner.org/resources/series42.html. Once you’re done with those you’ll understand that the limit is on the speed of time! Not light. If you have more questions about relativity, you’re best off asking in forum on relativity at https://www.physicsforums.com/forumdisplay.php?f=70.
 
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