Especially important was Fine's critical reading of the Einstein-Schrödinger correspondence of 1926, which prefigures their exchanges nine years later about nonlocality and nonseparability, following Einstein's epoch-making EPR paper in 1935.

Fine traces the Einstein's debates in the late 1920's about interpretations of the "new" quantum mechanics with Bohr, Heisenberg, Schrödinger, and Max Born, among others. Fine shows that the standard attacks on Einstein as not understanding their ideas, that he is senile, are completely inappropriate. In particular, their portrayal of Einstein as hoping to restore determinism and objecting to Heisenberg's uncertainty principle is misplaced.

Fine shows that Einstein had five objections to the new quantum mechanics, even before Heisenberg formulated his uncertainty principle in mid-1927.

(1) the equations of the theory are not relativistically invariant;

(2) it does not yield the classical behavior of macroscopic objects to a good approximation;

(3) it leads to correlations among spatially separated objects that appear to violate action-by-contact principles;

(4) it is an essentially statistical theory that seems incapable even of describing the behavior of individual systems;

and (5) the scope of the commutation relations may not in fact be so broad as the theory supposes.

(The Shaky Game, p.28)

Fine is correct that Einstein held these views in early 1927. But we have shown that he suspected many of them (especially 1, 3) as early as 1905. That chance is involved he saw clearly in 1916, so alternative possibilities exist with calculable probabilities. Quantum mechanics is a statistical theory that applies to ensembles of identical systems. It does not describe individual systems.

Sometime, likely before 1920, Einstein described the Führungsfeld and the Gespensterfeld to Max Born and others. For Einstein, these wave fields are the probabilities of finding a light quantum. Born wrote in his 1926 paper on atomic collisions

I shall recall a remark that Einstein made about the behavior of the wave field and light quanta. He said that perhaps the waves only have to be wherever one needs to know the path of the corpuscular light quanta, and in that sense, he spoke of a “ghost field.” It determines the probability that a light quantum - viz., the carrier of energy and impulse – follows a certain path; however, the field itself is ascribed no energy and no impulse

(Quantum mechanics of collision processes (Quantenmechanik der Stoßvorgänge), Zeitschrift für Physik, 38 (1926), 803-827)

Einstein made his probability view explicit in 1927 at the Solvay Conference where he said

|ψ|² expresses the probability that there exists at the point considered a particular particle of the cloud, for example at a given point on the screen.

(Quantum Theory at the Crossroads: Reconsidering the 1927 Solvay Conference, G. Bacciagaluppi and A. Valentini, 2009. pp.440-442)