- #1
J O Linton
- 67
- 8
- TL;DR Summary
- By analysing a simple experiment involving entangled photons I wish to explore which, if any, of the various interpretations of QT violate locality (i.e. involve spooky action at a distance)
By analysing a simple experiment involving entangled photons I wish to explore which, if any, of the various interpretations of QT violate locality (i.e. involve spooky action at a distance)
Consider the following idealised scenario: A source S produces entangled pairs of photons A and B such that the plane of polarisation is random but the two photons are at right angles. Photon A impinges on a vertical polaoid P1 placed 1m from the source, a short distance behind which is a detector D1. Photon B impinges on a similar vertical polaroid P2 placed 2 m from the source behind which is a second detector D2. We are interested in the times and circumstances under which both detectors respond together.
I believe that I am right in saying that if the photons were purely classical (i.e. not entangled) both detectors would fire 12½% of the time but since the two photons are entangled and their planes of polarisation are at right angles, QT predicts that the two detectors will never fire together.
On a very simplistic interpretation of QT this effect may be explained as follows: When the two photons leave the source they are in a superposition of an infinite number of states with their polarisation planes in all possible directions (but always at right angles to each other); when photon A reaches P1 a 'measurement' of its plane of polarisation is made and the wavefunction partially collapses into just two possible states with equal propbability: in one, photon A passes through P1 with it plane of polarisation vertical while photon B is absorbed because its plane of polarisation is horizontal; in the other, photon A is absorbed and photon B passes through P2. Later when the detectors are examined, the wavefunction collapses still further into one or other of these possibilities.
To my mind, this interpretation does not violate locality because all that happens when photon A passes through or is absorbed by P1 is that a large number of alternative possibilities are simply ruled out. No information is passed from A to B.
First, is my analysis of the situation correct and second, how would the experiment be explained by an adherent of the Many Worlds interpretation or indeed any other popular interpretation of QT?
Consider the following idealised scenario: A source S produces entangled pairs of photons A and B such that the plane of polarisation is random but the two photons are at right angles. Photon A impinges on a vertical polaoid P1 placed 1m from the source, a short distance behind which is a detector D1. Photon B impinges on a similar vertical polaroid P2 placed 2 m from the source behind which is a second detector D2. We are interested in the times and circumstances under which both detectors respond together.
I believe that I am right in saying that if the photons were purely classical (i.e. not entangled) both detectors would fire 12½% of the time but since the two photons are entangled and their planes of polarisation are at right angles, QT predicts that the two detectors will never fire together.
On a very simplistic interpretation of QT this effect may be explained as follows: When the two photons leave the source they are in a superposition of an infinite number of states with their polarisation planes in all possible directions (but always at right angles to each other); when photon A reaches P1 a 'measurement' of its plane of polarisation is made and the wavefunction partially collapses into just two possible states with equal propbability: in one, photon A passes through P1 with it plane of polarisation vertical while photon B is absorbed because its plane of polarisation is horizontal; in the other, photon A is absorbed and photon B passes through P2. Later when the detectors are examined, the wavefunction collapses still further into one or other of these possibilities.
To my mind, this interpretation does not violate locality because all that happens when photon A passes through or is absorbed by P1 is that a large number of alternative possibilities are simply ruled out. No information is passed from A to B.
First, is my analysis of the situation correct and second, how would the experiment be explained by an adherent of the Many Worlds interpretation or indeed any other popular interpretation of QT?