(October 18, 2021 at 4:23 pm)Jehanne Wrote: In particular, this:
Wikipedia -- Abraham–Lorentz force, Signals from the Future.
I hadn't known about this classical derivation, but in Quantum mechanics, the future affects our interpretation of the history of the past.
For instance, when a photon passes through an absorbing gas, the correct interpretation is that the photon forms a superposition with all gas molecules. Future measurements may show that a particular one actually did the absorbing, but this event is farther down the causal chain, after we have completed a macroscopic measurement.
Once we find that one molecule did the absorbing, none of the other molecules can possibly have been found to be effected. They didn't gain any momentum or energy from the interaction. It is like it never happened to them. Only the one molecule gains energy and momentum.
This isn't retro-causality, but the Transactional Interpretation of quantum mechanics makes use of this "our interpretation of the past must be consistent with the measurements of the present or future". It posits that advance waves travel from now into the future, and into the past, and that only transactions that complete a handshake (a consistent causal chain) are considered to have really happened.
It is a useful idea. For instance, one can stop an atom from emitting radiation by preventing it from coupling to external radiation modes. There are only two ways to model this. You either say that the atom radiates, but when the radiation can't couple to the external world, it sends a wave back in time to cancel the whole thing. Or, you say that a pre-emission vacuum fluctuation probes the entire system, and that the atom only emits when the electric field perturbation from the vacuum field fluctuation has gone on for enough time to ensure a radiation mode.
Quantum mechanics guarantees consistency. It doesn't say we really know what happens all the time.