Today's post, Relative Configuration Space was originally published on 26 May 2008. A summary (taken from the LW wiki):

 

Maybe the reason why we can't observe absolute speeds, absolute positions, absolute accelerations, or absolute rotations, is that particles don't have absolute positions - only positions relative to each other. That is, maybe quantum physics takes place in a relative configuration space.


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A simple relative configuration space is done in degree-track freshman physics (and maybe a good general freshman physics course) : extracting center of mass motion from orbital motion or two bodies connected by springs, to get the reduced mass and relative motion only. So relative configuration spaces are nearly universally known among physicists. Either Galileian or Special Relativity contains Mach's principle for position and velocity, so I'd expect those bits to be near-universal too.

The notion that there is no such thing as absolute rotation - well, since there's so much stuff out there, when it comes down to doing problems, we always end up doing our problems as a system isolated from a background of stuff. This makes Mach's principle a bit less applicable in the contexts that require different backgrounds. Physicists are not universally taught GR.

(edited to correct to 'rotation' from 'position', which I'd just discussed)

This is a lead-up to the timeless physics post series, which bounces between Barbourism ("look, ma, no time!") and New Age ("it's beautiful because it's timeless!"), to eventually emerge discussing a useful cognitive problem, the dissolution of the free will question. I am not sure why EY could not have skipped this whole block-like universe thing, none of the relevant arguments rely on it.