I'm sorry if this is a stupid question. I'm a novice at physics.

I have read the article about entanglement and EPR paradox. The spin of two particles is measured when they are very far apart, and they always make opposite choices. It seems that they must be correlating faster than light, which would be spooky.

I also read the article about many worlds. And I think it solves the faster-than-light paradox. Am I correct? Has anyone already noticed this? (I tried to google it and didn't find anything).

This is why I think it solves the paradox: In order to observe the spin of the two particles you need two observers, one for each particle. To correlate the answers, the two observers need to communicate with each other (either traveling together or by sending light-speed messages to each other). According to the many worlds interpretation, both spins (clockwise and counterclockwise) are always observed by both observers. Therefore there are actually four observers. However, not all observers can communicate to each other. Only pairs of observers that exist in compatible universes are able to detect one another's communications. The discrepancies are only enforced when the two observers are near enough to each other, or enough time has past, for them to communicate. Therefore, there is no spooky faster-than-light paradox when using the many worlds interpretation.


closed as off-topic by CuriousOne, Danu, Kyle Kanos, fibonatic, ACuriousMind Jun 22 '15 at 14:57

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  • 4
    $\begingroup$ A paradox is a learning tool to teach non-trivial facts that are counterintuitive. There is nothing spooky about entanglement, it's simply a not totally obvious effect that arises from the way states are defined in quantum theory. The MWI doesn't solve anything but it creates numerous problems that do not exist in the Copenhagen interpretation and does not deal with the fact that the universe has a very broad layer of perfectly classical phenomena. Generally I would suggest that you learn to understand the standard interpretation in detail and then it will become clear why MWI is unnecessary. $\endgroup$ – CuriousOne Jun 22 '15 at 5:40
  • $\begingroup$ All you need to make the Copenhagen Interpretation work is some vigorous hand waving when it comes to the measurement problem. $\endgroup$ – user56903 Jun 22 '15 at 9:42
  • $\begingroup$ The many-worlds theory is considered to be local, as it is indicated in the chart of this article. $\endgroup$ – Moonraker Jun 22 '15 at 9:58

The MWI explains the EPR experiment without invoking any non-local influences. Each observer measures one particle. The measurement affects only the particle being measured and the measurement device. Each measurement device differentiates into two versions, one for each measurement outcome. The correlations are established only after the results are compared locally. Until that comparison is done there is no fact of the matter about the correspondence between measurement results.

This can all be described explicitly in the Heisenberg picture as explained by David Deutsch in these papers:




There exists no "spooky action at a distance" except in the mind of the bemused.

Correlation is not causation, correlation is not causation, correlation is not causation ....

I have read the article about entanglement and EPR paradox. The spin of two particles is measured when they are very far apart, and they always make opposite choices. It seems that they must be correlating faster than light, which would be spooky.

Unless you have prepared the spins in a special state of up and down your measurement will be random. It is the prior knowledge of your preparation that makes a "faster than light" recognition of the result of a correlation function.

Suppose you have a pair of twin friends, Paul and Richard, and you learn that one was sent to work in Washington DC and the other in London but your informant did not know which of the two was where. If you meet Richard in London you know faster than light that Paul is in Washington DC.

  • $\begingroup$ Which twin goes to London is decided at the airport. So you don't think a wave function has any objective reality? Which quantum interpretation do you subscribe to? $\endgroup$ – John Henckel Jun 22 '15 at 16:30
  • $\begingroup$ Does the mathematical equation of the orbit of the moon have an objective reality other than it models the position of the moon? Same is true for the wavefunction: it is a mathematical function modeling very well the probability locus of finding an electron around a proton . I am an experimentalist and am not into interpretations. I use Quantum mechanics with its postulates raw :) $\endgroup$ – anna v Jun 22 '15 at 18:02
  • $\begingroup$ You're right. I will try to live without such theological props. $\endgroup$ – John Henckel Jun 23 '15 at 16:30

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