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Entangled quantum states and non-locality. A branching space-time resolution of the problem

Storrs McCall

Let F be a two-photon entangled state where measurement by parallel polarization analyzers always yields opposite outcomes + and - for the left and right photons. If the analyzers are not parallel but oriented at an angle of 30o to each other, the probability of obtaining the joint result ++ or -- on left and right is no longer zero but 1/2sin230o = 1/8, and if oriented at an angle of 60o the probability of ++ or -- is 1/2sin260o = 3/8. In the Aspect experiment two entangled photons leave a source S and at the last instant are directed to one of two different analyzers:

				 A						B

				 0o						30o




30o 60o

Obviously if makes a difference to (say) the left photon when it is passing through analyzer B whether (i) its twin is passing through B or C, and (ii) what the outcome of the twin's measurement is. If it passes through B and emerges +, then the left photon cannot pass +, but if it passes through C and emerges + then the left photon should exhibit a probability 1/8 of being measured +.


Question: How is the behaviour of the left photon influenced by the distant measurement outcome of its twin? This is the famous problem of non-locality. Does nature permit faster-than-light signalling as a means of coordinating the outcome probabilities of the two photons? A physical branching space-time mechanism is described which permits a negative answer to this question. This mechanism explains the distant correlations of the Aspect experiment without recourse to local hidden variables, i.e. "instruction sets" for the two photons which tell them how to react when encountering analyzers set at various angles. 



Date: Wednesday, October 25, 2006

Time: 5:00 PM

Place: Concordia University, Loyola Campus, Science Pavilion (Building SP), 7141 Sherbrooke Street West, 3rd Floor 

Room: SP 365.01

Contact: 514-848-2424 ext 2595


Note: There are regular shuttle buses traveling between Sir George Williams Campus (1455 de Maisonneuve Blvd. W.) and Loyola Campus; see Shuttle bus schedule.


Wednesday, 25 December, 2013 - 17:00
Seminar Location: 
Concordia University, Loyola Campus, Science Pavilion (Building SP), 7141 Sherbrooke Street West, 3rd Floor, SP 365.01

Groupe de Physique des particules
​Université de Montréal
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