Liron comments on No Individual Particles - Less Wrong

15 Post author: Eliezer_Yudkowsky 18 April 2008 04:40AM

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Comment author: Liron 22 April 2008 06:55:25PM 0 points [-]

Hey Eliezer, your explanations are incredible but I don't understand why we are folding the amplitude distribution over that diagonal line. I do understand that the folded distribution is unfactorable, but what is the motivation behind the folding operation?

Comment author: Cecil 01 December 2009 06:43:48AM *  3 points [-]

I believe the idea here is that because particle A and B are indistinguishable, the probability assigned to the case where particle A is "before" B can be equivalently assigned to the opposite case.

In the same manner that a train schedule with cities across the top and side needs only one entry per cityA / cityB pairing.

Comment author: Liron 01 December 2009 10:35:02PM 0 points [-]

I see

Comment author: ec429 17 September 2011 08:37:28PM 0 points [-]

I was also having a problem with this, but I think it can be resolved by saying that every operator is symmetric in A and B. Therefore, whenever we take a measurement, we will fail to distinguish between a blob at (1,0) and a blob at (0,1). More fundamentally, any interaction with a third particle will be the same whether the blob is at (1,0) or (0,1).

Even more important is that a blob at (0,1) plus a blob with the opposite phase at (1,0) can have a subtractive effect, even cancelling out entirely if both have the same amplitude.

In a sense, then, factoring the topology of configuration-space by the identity A==B causes the symmetry of operators to be an unavoidable consequence of the topology, rather than some freakish coincidence.