David Wallace
speaker
1,940 appearances
2 recordings
1 series
first heard May 2025
last heard 20 Jul
David Wallace’s voice in public audio — every appearance, attributed to the second.
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Appearances
Um but in the Everetsian framework, of course, all of these measurements are physical processes.
What's all that's actually going on is some complicated set of unitary interactions between the system being measured and the stuff measuring it.
And
one and the same physical process might be considered to be many
And
Formal quantum measurements.
And one and the same formal quantum measurement might correspond to many different physical processes.
So suppose for instance I'm measuring uh the spin of an electron, say, or that's the spin of a silver atom, but in uh in a Stern Gurlach framework.
So if you're just being axiomatic about it, you'll say, fine, this is a spin measurement.
And my spin measurement is um
uh represented by these projectors onto the spin up.
um subspace and onto the spin down subspace.
And there'll be a separate thing you might do, which is a position measurement, which is gonna be represented by some
You know.
Can you cash it out?
Some's c some kind of collection of projectors onto coarse grained.
regions of position space and all of that will just be primitive.
It'll just just stipulate that that's what those things are.
If you've got a dynamical story about measurement, if you ask how do I actually measure spin, for instance, well a way to do it is I've got an inhomogeneous magnetic field and I separate the um the beams so that um some of the particles, the ones that spin up go in classical terms, the ones that spin up go uh towards the top of the apparatus, and the ones that spin down go towards the bottom of the apparatus, and then I measure where they are by slamming them into a screen or something.
So
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