The universe is not locally real

AI has risen Feynman from the dead, and explained Bell's theorem:

The Universe May Not Be Locally Real – Feynman Explains Bell’s Paradox

What if everything you believe about reality is wrong? In this mind-bending 23-minute exploration, Richard Feynman walks you through one of the most unsettling discoveries in the history of science — Bell's Theorem and the Nobel Prize-winning experiments that proved the universe is not locally real. From Einstein's stubborn belief in hidden variables to the groundbreaking work of Aspect, Clauser, and Zeilinger, this video breaks down quantum entanglement, the EPR paradox, and what it truly means when particles separated by miles somehow "know" what the other is doing — with no signal, no instructions, and no classical explanation.

It concludes:

[20:05] Let me bring it all together. Now we started with a simple idea that the world is locally real that things have definite properties that distant objects can't affect each other instantly. John Bell took this idea and turned it into a testable prediction. He said if local realism is true then the correlations between entangled particles must obey a mathematical limit. experiments culminating in the Nobel Prize winning work of aspect, Clauser, and Zelinger showed that the correlations exceed that limit. Local realism is violated. The universe is not locally real.

This means one of two things, or possibly both. Either particles don't have definite properties before they're measured, meaning reality isn't real in the way we thought, or distant particles can somehow affect each other instantly, meaning the universe isn't local in the way we thought. We don't know which. We don't have a complete agreed upon interpretation of quantum mechanics that resolves this.

I think we do have an agreed QM interpretation. It is the first option. Nobody thinks distant particles can somehow affect each other instantly.

The QM textbooks say that under Heisenberg uncertainty, it makes no sense for a particle to have a definite position and momentum at the same time. Particles only get definite values for position and momentum when they are measured, and you cannot measure both at the same time.

So yes, QM says particles don't have definite properties before they're measured. And I think that is what Feynman would have said, and not that this is an unsettled question.

Not everyone agrees with this, as maybe 10% of physicists subscribe to goofy interpretations like Bohm pilot wave or many worlds. But the mainstream textbook QM view is pretty clear on this point.