[brianfitz]

TL;DR: There was a loophole found in an older thought experiment that indicated that at the quantum level, nothing is real until it is observed.

A discovery was recently made that found a way to add an unknown variable into the mix such that an expiriment where the future seems to affect the past was possibly explained away by a classical model.

However, a new experiment was proposed to show whether the new classical model actually was the explanation — and it turns out this classical “loophole” can not explain it.

So we’re now back to the beginning where it once again appears that nothing is real until observed at a quantum level which is also referred to as “anti-realism”.

[seppel]

> nothing is real until it is observed.

What do the terms "real" and "observed" mean in this sentence?

[Diggsey]

Pretty sure local hidden variable theories were ruled out as an explanation of quantum mechanics a long time ago. What's new here?

[21]

Wikipedia says that this is the conclusion of Wheeler's experiment:

> Any explanation of what goes on in a specific individual observation of one photon has to take into account the whole experimental apparatus of the complete quantum state consisting of both photons, and it can only make sense after all information concerning complementary variables has been recorded. Our results demonstrate that the viewpoint that the system photon behaves either definitely as a wave or definitely as a particle would require faster-than-light communication. Because this would be in strong tension with the special theory of relativity, we believe that such a viewpoint should be given up entirely.

[Diggsey]

Local hidden variable theories were disproved by violations of Bell's inequality, not by a thought experiment.

https://en.wikipedia.org/wiki/Bell_test_experiments

Are you saying that all of these experiments were flawed in some way?

[21]

No, I'm saying that the Wheeler experiment seems to be more concerned with the wave/particle duality, not with the hidden variables.

And as this article shows, the Wheeler experiments are not thought experiments, they are very real ones.

[brianfitz]

Wheeler’s delayed choice excitement is referred to as a thought expirement both by the physicists in the article as well as the first line in its Wikipedia entry. Like Einstein, he worked through many thought excitements that suggested an outcome, but couldn’t be tested at the time. However, many of Einstein’s proposed experiments that have since been observed are still referred to as his thought expiriments.

We may be saying the same thing, but worth making the distinction.

For the other poster (diggsey), it will be difficult to answer your question about the novelty of these newly run expiriments without a full read of the article.

[naasking]

Local hidden variables are only ruled out if you reject superdeterminism. At least one Nobel prize winning physicist is developing a superdeterministic theory of QM.

And of course, non-local classical theories like de Broglie-Bohm are just fine, once again.

[Ygg2]

They weren't. There was an error or oversight in the proof.