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There is a more precise concept of causality in physics that is very much fundamental part of all modern theories.
by uecker 2y ago
There is a more precise concept of causality in physics that is very much fundamental part of all modern theories.
- layer8 2y agoAnd what concept would that be?
- uecker 2y agoEinstein causality, i.e that no physical effect propagates faster than light. In QFT it it is modeled by the rule that space-like separated measurements commute.
- layer8 2y agoThat merely equates the term "causality" to propagating waves. It doesn't introduce any new concept. Ontologically, there are only quantum fields in space-time. The physical laws governing them imply from their mathematics that they cannot contain any propagations faster than c. But attaching the term "causality" to it doesn't really add anything here.
- uecker 2y agoThis does not equate causality with propagating waves. I also did not claim it is a new concept. Instead I said physics has a precise and fundamental concept of causality.
- layer8 2y agoHow is it fundamental? You can do all the physics without reference to it. It is a consequence of the equations, not a premise. Edit: It is not actually a complete consequence, because cause and effect imply a directonality that the equations do not have, being time-symmetric. At the same time, this directionality or asymmetry has no derivable consequences for the practical physics, meaning having the asymmetry doesn't add anything. This is one of the conceptual troubles that introducing "causality" here brings.
- uecker 2y agoPhysicists put this into the theories as an assumption at a fundamental level, e.g. they put it as an axiom into axiomatic QFT. This is why it is fundamental. Also arrow of time is something else than Einstein causality.
- niemandhier 2y agoIt is used in theories that discuss particles with imaginary mass, such as tachyons, that travel backwards in time. Theories that violate causality are considered unphysical, whereas theories in which measuring such time traveling particle, cannot be distinguished from creating a particle that moves forward in time are not.