- #1
nomadreid
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- Two observables on events in a space-like separation must commute in order to ensure that causality is possible, otherwise one could be affected by the other before information could pass from one to the other. But on several sites it is stated that the vanishing of the commuter "defines" causality. I don't see the jump from possibility to necessity. Or is "causation" here defined as "possibility of causal link"?
A couple of the sites that say that the vanishing commutator defines causality:
https://www.physics.umass.edu/events/2020-02-07-causal-uncertainty-quantum-gravity
https://phys.org/news/2019-11-aspects-causality-quantum-field-theory.html
Is "define" too strong?
Or, to put it another way: cannot two events which are spacelike separated be neither causally connected nor be associated with non-commuting observables?
https://www.physics.umass.edu/events/2020-02-07-causal-uncertainty-quantum-gravity
https://phys.org/news/2019-11-aspects-causality-quantum-field-theory.html
Is "define" too strong?
Or, to put it another way: cannot two events which are spacelike separated be neither causally connected nor be associated with non-commuting observables?