In 1935, Einstein, Podolski, and Rosen proposed a very famous thought experiment.
Later generations referred to it by their initials as the EPR experiment.
This experiment refers to preparing two particles, A and B, in a "circle" state, so that a certain property of these two particles (such as the spin angular momentum of electrons or the polarization of photons) adds up to zero, while the property of an individual particle is uncertain.
Such a pair of particles is called an "EPR pair" and belongs to the "entangled state" in quantum mechanics.
The original purpose of the EPR experiment was actually to support Einstein's own point of view, but ironically, in 1980, Aspect and others performed the EPR experiment and confirmed that the EPR phenomenon was indeed a real effect.
This is also a notable point for relentless critics of Einstein,
