Reply To: Causality and quantum mechanics (Online 7/15 @ 10 p.m. to Midnight UTC-7)

[Michael B. Heaney]

Hi David,

Thank you, that is very helpful.

Suppose Alice has an excited atom that can emit a photon, and Charlie (C) has a ground state atom that can absorb the photon. Alice measures the state of her atom every minute. She finds it in the excited state (H) for the first 3 minutes, then she finds it in the ground state (T) for the next 3 minutes. Charlie finds his atom in the ground state for the first 4 minutes, then in the excited state for the next 2 minutes. So Alice measures HHHTTT and Charlie measures TTTTHH. Now repeat the experiment, but just before minute 5 Charlie puts his atom in the excited state. Now Alice measures HHHHHH and Charlie measures TTTTHH. It seems like Charlie’s action has changed the probabilities of Alice’s earlier measurements. Would you say that C is a retrocause? Or am I still misunderstanding something?

Thanks,

Michael