DanielLC comments on Can You Prove Two Particles Are Identical? - Less Wrong

32 Post author: Eliezer_Yudkowsky 14 April 2008 07:06AM

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Comment author: DanielLC 01 October 2011 10:46:02PM 0 points [-]

From what I understand, what's known is that a given configuration will have exactly the same probability as the same configuration with two particles swapped. This is enough to show you can't test it. If you had a detector go off when you show it photon a, it would have to also go off when you switch it out with photon b, or it would break the symmetry laws. This means that, if there are multiple photons, it's an epiphenomenon. If you believe that they can, in principle exist, like a particle that doesn't interact with any of the other particles and isn't correlated with them, then there might still be more than one photon.

Also, for what it's worth, while the probability must be the same, the amplitude can be different. With photons it will be the same, but if you swap two electrons it multiplies by negative one. The square of the magnitude is the same, so you're just as likely to see it, but this still would seem to suggest something fundamentally different.