Suppose you had two entangled particles light-years distance apart.
Observer A observes one entangled particle at a spin up. At the same time, Observer B observes particle B at a spin down.
Observer A's observation of a spin up means observer B must see a spin down. However, the two observers are restricted at the speed of light to communicate this to each other.
It would initially seem like there is a instantaneous causal impact based on observer A's observation. But that's not the case.
I tend to think it was predestined what each observer see, but that leads to all sorts of philosophical questions.
I hope I did this topic justice, I find it quite interesting but have no background in it.
But isn't superdeterminism still possible? I thought that was implied by the article's first assumption that physics was loathe to abandon, that the experimenters had free will, so to speak.
None of the interpretations of quantum mechanics are. By design, they all predict exactly the same outcome for any conceivable experiment. The subject is entirely philosophical, not scientific.
They make predictions, which can be falsified. They even make different predictions---Scott Aaronson agrees that WF poses problems for the standard Copenhagen interpretation. Sean Carroll is on record somewhere saying that e.g. objective collapse models predict an in principle measurably different evolution of a system's entropy than many worlds.
I suppose I should have asked what predictions SD actually makes.
Copenhagen Interpretation and MWI don't make different predictions from each other, but there are other theories that do. For example, pilot-wave theory makes different predictions. There are also some superdeterminist theories that make new predictions (Gerard T'Hooft is one advocate of such theories, I believe). Unfortunately I don't know of any concrete examples. Here is some more information on the subject from Sabine Hossenfelder:
Global hidden variables are the predestined effect. The argument against global hidden variables is that it requires a godlike meddling in the whole universe to populate an infinite amount of arbitrary asymmetric details.
Observer A observes one entangled particle at a spin up. At the same time, Observer B observes particle B at a spin down.
Observer A's observation of a spin up means observer B must see a spin down. However, the two observers are restricted at the speed of light to communicate this to each other.
It would initially seem like there is a instantaneous causal impact based on observer A's observation. But that's not the case.
I tend to think it was predestined what each observer see, but that leads to all sorts of philosophical questions.
I hope I did this topic justice, I find it quite interesting but have no background in it.