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fermi
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- 5
Recently a student brought the following to my attention from Weinberg’s Quantum Theory of Fields, Volume I, from page 177, which I must admit that it stumped me. Here Weinberg introduces the concept of Cluster Decomposition: “It is one of the fundamental principles of physics (indeed, of all science) that experiments that are sufficiently separated in space have unrelated results…” The quantum entanglement a la EPR paradox, however, tells us that the measurement of the polarization of a photon from a [itex]{\pi}^o[/itex] decay measured a year later will determine the polarization of the other photon (two light years away from this measurement.) This is because the decay photons from a [itex]{\pi}^o[/itex] are entangled forever, no matter how far apart they may be. This sort of thing was discussed and dissected endlessly in the past fifty years, but today we simply accept this non-local entanglement as part of Quantum Mechanics.
So back to Weinberg: what is he saying here then? If you were to restate his words a little more precisely, how would you restate the cluster decomposition?
So back to Weinberg: what is he saying here then? If you were to restate his words a little more precisely, how would you restate the cluster decomposition?