Page "EPR paradox" Paragraph 17

Quantum theory and quantum mechanics do not provide single measurement outcomes in a deterministic way.

According to the understanding of quantum mechanics known as the Copenhagen interpretation, measurement causes an instantaneous collapse of the wave function describing the quantum system into an eigenstate of the observable state that was measured.

Einstein characterized this imagined collapse in the 1927 Solvay Conference.

He presented a thought experiment in which electrons are introduced through a small hole in a sphere whose inner surface serves as a detection screen.

The electrons will contact the spherical detection screen in a widely dispersed manner.

Those electrons, however, are all individually described by wave fronts that expand in all directions from the point of entry.

A wave as it is understood in everyday life would paint a large area of the detection screen, but the electrons would be found to impact the screen at single points and would eventually form a pattern in keeping with the probabilities described by their identical wave functions.

Einstein asks what makes each electron's wave front " collapse " at its respective location.

Why do the electrons appear as single bright scintillations rather than as dim washes of energy across the surface?

Why does any single electron appear at one point rather than some alternative point?

The behavior of the electrons gives the impression of some signal having been sent to all possible points of contact that would have nullified all but one of them, or, in other words, would have preferentially selected a single point to the exclusion of all others.