Luke_A_Somers comments on [SEQ RERUN] On Being Decoherent - Less Wrong

3 Post author: MinibearRex 18 April 2012 05:06AM

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Comment author: shminux 18 April 2012 05:42:30AM -1 points [-]

But when we humans look at the sensor, it only seems to say "LEFT" or "RIGHT", never a mixture like "LIGFT". This, of course, is because we ourselves are made of particles, and subject to the standard quantum laws that imply decoherence. Under standard quantum laws, the final state is (particle left, sensor measures LEFT, human sees "LEFT") + (particle right, sensor measures RIGHT, human sees "RIGHT").

If there are two nearly identical copies of me in the same place, why is there no further interaction between them, resulting in my seeing "LIGFT"? (Well, now that I think of it, I do see "LIGFT", if only because EY wrote it.) Yes, I know, the magical password is "decoherence". How helpful.

Comment author: Luke_A_Somers 18 April 2012 01:44:20PM 1 point [-]

Shminux, I trust you do know the actual answer to this, based on your demonstrated knowledge of QM. The essay does a qualitative job of this, here:

There are no plausible Feynman paths that end up with both LEFT and RIGHT sending amplitude to the same joint configuration. There would have to be a Feynman path from LEFT, and a Feynman path from RIGHT, in which all the quadrillions of differentiated particles ended up in the same places. So the amplitude flows from LEFT and RIGHT don't intersect, and don't interfere.

In order for the joint observer-observed system to be coherent, the two cases need to be reconcilable.

How is this a magical password? He pulls out the guts of decoherence and shows them to the reader!

Comment author: Luke_A_Somers 18 April 2012 07:26:38PM 0 points [-]

Well, part of the guts. He's given a sufficient but not necessary criterion for decoherence.

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