Re: local gauge symmetries and particle histories

verdigris wrote:
A local symmetry is one in which a transformation can be performed in
one region of space without affecting another region of space.I can
change the polarization of a photon in a certain local region of space
and not affect what happens in another local region.Sometimes photon
polarizations are coupled and I could change the polarization of a
photon in one region of space and instantaneously change another,
correlated, photon polarization, over a big distance.

No. You cannot "change" the spin of a photon at all. What you can do: for a coupled pair, by _measuring_ the spin of one photon you can _discover_ what the other's must be, independent of their spatial separation. That is _quite_different_ from "changing" either spin.

Those photons' spins are _correlated_, but correlation is not causation, and your description in terms of "change" (causation) is invalid.


How accurate a reflection of nature can a
local symmetry be?

Experiments show it is not a good model for all phenomena. But for most activities it is an exceedingly good approximation.


Clearly a local symmetry can be destroyed depending
on the history of the photons involved (coupled or uncoupled).

You assume that two coupled photons still obey a local symmetry. They don't.


Does
this mean, in general,that local symmetries and associated
conservation laws should take into account the history of the
particles under consideration,and not just introduce particles on an
ad hoc basis?

No. It means that naive notions of locality are not valid in the universe we inhabit.


I would think that to distinguish a coupled photon pair from an
uncoupled pair,in a symmetry theory, would require that individual
photons have some property when they are coupled that is different
from when they are uncoupled.This property would, according to Bell's
Theorem, be a "hidden variable" and its existence would mean that
instantaneous action at a distance (Einstein called it
spukhaftefernwirkung - ghostly action at a distance - to emphasise
that he thought it was not a real phenomenon) in quantum mechanics is
wrong.

Quantum mechanics accurately describes the experiments, with no such hidden variables, and no "spooky action at a distance". The situation is far more subtle than you describe.


Tom Roberts

.

Relevant Pages

  • Re: I dont understand EPR
    ... a property that photon 1 and photon 2 have in ... that common property is polarization. ... In the combined context, which includes ... wrt the determination of coincidental detection ...
    (sci.physics.research)
  • Re: A Look at Quantum "Spookiness"
    ... Einstein, Podalsky, and Rosen because quantum theory seemed to ... polarization angle of one of the "paired photons" were changed, ... not in any individual measurement. ... photon was vertically polarised), he merely measured it. ...
    (sci.physics.particle)
  • Re: A Look at Quantum "Spookiness"
    ... polarization angle of one of the "paired photons" were changed, ... not in any individual measurement. ... known at another point connected by quantum entanglement. ... photon was vertically polarised), he merely measured it. ...
    (sci.physics.particle)
  • Re: Quantum entanglement and information transfer
    ... you would need to know the emission-produced polarization. ... For accurately predicting coincidence rates in the combined ... >> Wrt this scenario, in the combined context, the only variable ... There may, for instance, be more photon ...
    (sci.physics.research)
  • Re: Two EPR questions
    ... My understanding is that paired detection attributes in, say, ... It's not the combination of the polarization of photon 1 wrt polarizer ...
    (sci.physics.research)