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: Photons have zero rest mass, but they are not at rest. A reference is given for the deflection of light as predicted by relativity theory. So the article seems to be correct about the bending of light. [[User:RSchlafly|RSchlafly]] 12:41, 12 May 2009 (EDT)
: Photons have zero rest mass, but they are not at rest. A reference is given for the deflection of light as predicted by relativity theory. So the article seems to be correct about the bending of light. [[User:RSchlafly|RSchlafly]] 12:41, 12 May 2009 (EDT)
== Non-Locality and Quantum Field Theory ==
There is no action at a distance, nor non-locality, in quantum mechanics nor field theory. None. You're confusing two different subjects.
First, action at a distance: True, in Newton's gravity, there is action at a distance. But this is totally different from anything to be found in QM or field theory, which have no action at a distance. All Hamiltonians in the standard models of field theory (QED, electroweak, QCD) are strictly local Hamiltonians. Forces are exerted by passing virtual bosons back and forth in space, like footballs. Interactions (like electron/photon, then photon/electron) are all 100% local.
The fact that Newton's theory assumed action at a distance (without proof) does not mean that ALL theories require action at a distance. Why should that follow? Why should modern theories be limited by Newton's unproved assumptions? Quantum field theory is immensely more accurate, measured objectively, than Newton's gravity force ever was. QED (with special relativity built in) predicted the anomalous magnetic moment of the electron accurate to one part in a TRILLION. Newton's theory was never even close to that level of accuracy! Newton could never accurately compute the orbit of Mercury or gravitational lensing to one part in a trillion! Or billion. By objective criteria, field theory is more accurate than Newton.
Second, non-locality: non-locality is not the same as action at a distance. Action at a distance requires exertion of a FORCE. Nothing in QM is in fact non-local. The only thing non-local about QM is the Copenhagen interpretation of wavefunction collapse, which is not a part of the equations, but a way of visualizing the effect of observation a QM system.
You have mentioned quantum entanglement as a supposed example of non-locality. Entanglement, and phenomena like quantum teleportation, do not exert FORCES, so they are not actiona at a distance! Further, quantum entanglement can never be used to transmit information faster than the speed of light. Hence, there's no contradiction between QM and SR. Field theory has SR built in. There is no experiment, in quantum teleportation nor Bell's inequality, that can possibly transmit information FTL. Describe one experiment, just one entanglement experiment, that can supposedly transmit info FTL. I dare you. Just one.
So what is this supposed "non-locality" then? The Copenhagen interpretation of QM says that the wavefunction should "collapse" (revert to a single eigenfunction) everywhere simultaneously when an observation is made. If this really happened, it would be a problem for SR, because in SR, simultaneity is relative to the observer. But, two problems. First, this supposed "collapse" can never be observed and can never be used to transmit info FTL. Second, the Copenhagen interpretation is deeply flawed because it never defined what an "observation" was. It is no longer the most popular interpretation; among physicists, the Many Worlds interpretation is more popular now, because it precisely defines what observation means, in terms of quantum decoherence, so MWI connects better to macroscopic thermodynamics.
If you want to (groan) argue the point, you can argue that Copenhagen and Many Worlds are both non-local, but so what? They're visualizations, not equations, and certainly not forces, nor "actions"!! When neither visualization scheme can be used to transmit info FTL, nor exert a force, this is no problem for SR at all!
The only big problem here is that field theory is incompatible with GR, not SR. True. Everybody knows this is the biggest problem in physics. No one knows whether the flaw is in GR, field theory, or both. However, either way, there is no problem between field theory and SR. Field theory has SR built in, and is (objectively measured) the most precise scientific theory in history. If you argue this, I'll swamp you with experimental proofs. [[User:Cuddlytakun|Cuddlytakun]] 15:53, 18 May 2009 (EDT)