What is Epr paradox: Definition and 30 Discussions

The Einstein–Podolsky–Rosen paradox (EPR paradox) is a thought experiment proposed by physicists Albert Einstein, Boris Podolsky and Nathan Rosen (EPR), with which they argued that the description of physical reality provided by quantum mechanics was incomplete. In a 1935 paper titled "Can Quantum-Mechanical Description of Physical Reality be Considered Complete?", they argued for the existence of "elements of reality" that were not part of quantum theory, and speculated that it should be possible to construct a theory containing them. Resolutions of the paradox have important implications for the interpretation of quantum mechanics.

The thought experiment involves a pair of particles prepared in an entangled state (note that this terminology was invented only later). Einstein, Podolsky, and Rosen pointed out that, in this state, if the position of the first particle were measured, the result of measuring the position of the second particle could be predicted. If, instead, the momentum of the first particle were measured, then the result of measuring the momentum of the second particle could be predicted. They argued that no action taken on the first particle could instantaneously affect the other, since this would involve information being transmitted faster than light, which is forbidden by the theory of relativity. They invoked a principle, later known as the "EPR criterion of reality", positing that, "If, without in any way disturbing a system, we can predict with certainty (i.e., with probability equal to unity) the value of a physical quantity, then there exists an element of reality corresponding to that quantity". From this, they inferred that the second particle must have a definite value of position and of momentum prior to either being measured. This contradicted the view associated with Niels Bohr and Werner Heisenberg, according to which a quantum particle does not have a definite value of a property like momentum until the measurement takes place.

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  1. Bob Walance

    I Many Worlds, EPR and ER=EPR

    This question is not intended to invoke arguments about whether Hugh Everett's theory, now referred to as the Many Worlds Interpretation of Quantum Mechanics, is feasible or not. When I heard David Wallace say that Many Worlds does away with the so-called 'spooky action at a distance' referred...
  2. E

    B How does the EPR paradox work?

    Hi, I've heard about the EPR paradox as follows: Leave two entangled particles A and B carried by scientists A' and B', with a pair of incompatible properties (eg spin up/down and left/right) in possible Green/Yellow and Blue/Red states. If one measures Yellow state (eg, particle B in spin up...
  3. Buzz Bloom

    I EPR Paradox: Exploring Uncertainty & Experimental Results

    While I have have heard about it for years, I have just read a more-or-less clear description of the EPR "paradox" in David Lindley's Where Does the Weirdness Go? (1996), page 91, "The fatal blow?". Here is a summary (paraphrasing what I read) as I understand it. A pair of particles (say A and...
  4. B

    I What is the paradox in the EPR paradox?

    Hi Which of these understandings is correct ? A stationary particle separates into 2 particles A & B Is it that : (a) One can independently measure accurately to the desired accuracy the momentum of A and the position of B and thus obtain both position AND momentum of either particle thus...
  5. S

    B Double Slit Paradox: A Wave-Particle Mystery

    Let's take a pair of particles A and B that are in a quantum entanglement state, and shoot them in different directions. Along the way, one of them will pass in the famous screen of the two slits, say B. According to the known experiment, if we put a detector in one of the slits, we will lose...
  6. S

    I What did Omnès mean with this?

    Summary: What did Omnès mean with this? I found an old article by Roland Omnès which analyzes the EPR paradox and offers a solution to it (https://www.sciencedirect.com/science/article/abs/pii/0375960189900182). At some point, the article says: "Some macroscopic systems do not satisfy the...
  7. PGaccount

    A Bohr's solution to the EPR paradox

    First, I will give my understanding of Bohr's resolution using an example that Bohr considers in his discussion. Then I will quote a passage where Bohr summarizes his resolution of the paradox. Finally, I will try to respond to John Bell's comments on this resolution. I would be interested in...
  8. victor94

    I Exploring the EPR Paradox: What Does "Simultaneous Reality" Mean?

    I'm reading the paper of the EPR paradox and I'm confused in the meaning of this: "The elements of the physical reality cannot be determined by a priori philosophical considerations, but must be found by an appeal to results of experiments and measurements......when the operators corresponding...
  9. Old Chinaman

    B Understanding the EPR Paradox - Exploring the Gamma Factor

    I am not a physicist but interested in the decade long debate between Einstein and Niels Bohr, especially in the philosophical implication of the EPR Effect. I've been wondering if anyone could explain why Einstein, Podolsky and Rosen didn't applied the Lorentz Transformation formula - the...
  10. arupel

    I Explanation of the EPR paradox

    I am not sure I understand exactly what was the situation was with the EPR paradox Example: for simplicity: two electrons are coupled. One with spin up and the other with spin down. Since they are coupled there are one state. Separate the electrons one in one galaxy and the other in another...
  11. A. Neumaier

    An abstract long-distance correlation experiment

    Inspired by stevendaryl's description of an EPR-like setting that doesn't refer to a particle concept, I want to discuss in this thread a generalized form of his setting that features a class of long-distance correlation experiments but abstracts from all distracting elements of reality and from...
  12. G

    Does quantum entanglement in fact equal a wormhole?

    So I came across this paper claiming that quantum entanglement was an as yet not understood Einstein Rosen-Bridge: http://arxiv.org/pdf/1306.0533v2.pdf I have two questions pertaining to this: 1. Does the math on this paper actually check out and is this possible? 2. Since this paper...
  13. T

    EPR paradox and time of collapse

    According to the EPR-paradox, if we have a pair of two entangled spin-1/2 fermions A and B and measure z-component of A, B collapses immediately as well(i'm using these letters for both particles and their observers). The 'canonical' solution is then to state that it is not possible to transfer...
  14. jk22

    EPR paradox and prediction time

    If we suppose we have an entangled pair in position/momentum and, following the argument, we measure position of particle A. We get a result let say xA. Then we want to predict the measurement of position of B, so up to now we have not measured particle B, but we know it's wave-function is a...
  15. D

    EPR Paradox Confusion: Understanding the Violation of Locality and Uncertainty

    Hello, I've read through several sources about the EPR Paradox but I'm not sure I'm understanding everything. I know that: -the paradox in question seems to be due to a violation of the principle of locality -there is no useful transferred faster than c regardless of which axes the two...
  16. S

    My Particularly Troublesome Version of the EPR Paradox

    In quantum physics, a wave function instantaneously collapses once an observable is measured. For instance, if an electron's angular momentum in the z direction is measured, then the angular momenta in the x and y direction immediately become indeterminate due to the Heisenberg Uncertainty...
  17. T

    Exploring the EPR Paradox: QM and Locality

    Sorry, I have 2 doubts about the EPR paradox. 1) Just check out if I am ok: What EPR proposed was that QM suggest that if two entagled particles, for example photons, prepaired in some special way, get away from each other then: a) if we measure their x-spin then one particle will get the...
  18. A

    Resolving the EPR Paradox: Exploring Signal Models and Special Relativity

    We consider a typical version of the EPR paradox where an electron and a positron are produced collinearly in the +y and -y with the spins polarized in the positive and negative z directions. The pair is emitted with zero linear and zero spin-angular momentum. If the positron is detected in the...
  19. S

    Can someone explain, simply, hidden nonlocality/locality? EPR Paradox?

    So I understand local realism (the moon is there when we aren't seeing it) and the notion that Bell's Theorem says that if local realism is true, then we could perform experiments that show observation is independent of reality and that we should expect certain probabilities to arise. But we...
  20. D

    Is action at a distance possible as envisaged by the EPR Paradox.

    Is action at a distance possible as envisaged by the EPR Paradox?
  21. T

    EPR Paradox and implications for QM

    Can somehow confirm that my understanding of the EPR Paradox is correct. Here goes... Essentially you can entangle two photons, and send them in opposite directions. If we detect one of the photons, we can find out its properties, and since the properties of the two photons are linked, also...
  22. H

    Questions on the EPR Paradox

    Hi, I am little bit lost in what is so called EPR paradox (see also http://en.wikipedia.org/wiki/EPR_paradox). It takes into account two particles A and B that have some "same" characteristics (states) and by messuring some of this characteristics of particle A implies that the same...
  23. rjbeery

    Exploring the EPR Paradox: Reconciling QM and SR

    Greetings! This is my first post so go easy. I read through the thread addressing the Sci Am article claiming that entanglement violates relativity. The article actually addresses a symptom of a larger issue that exists between QM and SR. I would like to get feedback on this issue as...
  24. M

    EPR Paradox: Examining Einstein's Challenge to QM

    was original EPR paper (as written by Einstein) contradicted uncertainty principal or was it against the copenhegon interpretation of QM? please tell me any website where original EPR paradox is discussed.
  25. T

    EPR paradox philoshophy is confusing me

    The philoshophy is confusing me. If i understand correctly, it comes down to the following: when a pion decays (which decays to an electron and positron), we can make a measurement of the spin of both resulting particles. If I measure the spin in the z-direction of the electron, I instantly...
  26. T

    Split off from EPR paradox revisited

    Apparently I didn't make clear what bothers me. I'm happy to set aside the silliness of there being two Bobs, one in each branch that occurs after Bob makes a measurement. And I concede that your idea of choosing, at random, by the Born rule, one of those branches for Bob's consciousness-token...
  27. A

    EPR paradox revisited, again. hehehe

    Simply put the EPR paradox argues that the fact QM predicts that a measurement at A affects reality at B instantaneously, means that QM is violating the speed of light limit. I ask for a clear proof or explanation of how QM does not violate the speed of light limit in EPR type experiments as...
  28. A

    No paradox in the EPR paradox

    I don't see why the EPR thought experiment would ever be concieved as a way to demonstrate anything against QM... (you can find an explanation of the EPR thought experiment here: http://en.wikipedia.org/wiki/EPR_paradox) Ok before Alice measures anything P(+z)=0.5 and P(+x)=0.5 for both...
  29. S

    Exploring EPR Paradox: Recent Experiments & Discoveries in Last 10 Years

    Hi can somebody here please give me some links or info on recent experiments (last 10 years) conducted to on the EPR paradox, for example i know of aspin's experiment, any others?
  30. DrChinese

    Question about Other Tests of EPR Paradox

    I have some questions about other possible tests of the EPR Paradox. The base of the paradox is using one entangled particle to gain information about the other. The usual setup discussed involves spin, often photon spin. But what about other measurable attributes of a particle? If we take...
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