Editing Hidden-variable theory (section)

=== Declaration of completeness of quantum mechanics, and the Bohr–Einstein debates ===
{{Main|Bohr–Einstein debates}}
Also at the Fifth Solvay Congress, Max Born and [[Werner Heisenberg]] made a presentation summarizing the recent tremendous theoretical development of quantum mechanics. At the conclusion of the presentation, they declared:{{blockquote|[W]hile we consider ... a quantum mechanical treatment of the electromagnetic field ... as not yet finished, we consider quantum mechanics to be a closed theory, whose fundamental physical and mathematical assumptions are no longer susceptible of any modification...

On the question of the 'validity of the law of causality' we have this opinion: as long as one takes into account only experiments that lie in the domain of our currently acquired physical and quantum mechanical experience, the assumption of indeterminism in principle, here taken as fundamental, agrees with experience.<ref>Max Born and Werner Heisenberg, "Quantum mechanics", proceedings of the Fifth Solvay Congress.</ref>}}Although there is no record of Einstein responding to Born and Heisenberg during the technical sessions of the Fifth Solvay Congress, he did challenge the completeness of quantum mechanics at various times. In his tribute article for Born's retirement he discussed the quantum representation of a macroscopic ball bouncing elastically between rigid barriers. He argues that such a quantum representation does not represent a specific ball, but "time ensemble of systems". As such the representation is correct, but incomplete because it does not represent the real individual macroscopic case.<ref>{{Cite arXiv |last=Einstein |first=Albert |title=Elementary Considerations on the Interpretation of the Foundations of Quantum Mechanics |date=2011 |class=physics.hist-ph |eprint=1107.3701 |quote=This paper, whose original title was “Elementare Uberlegungen zur Interpretation ¨ der Grundlagen der Quanten-Mechanik”, has been translated from the German by Dileep Karanth, Department of Physics, University of Wisconsin-Parkside, Kenosha, USA}}</ref> Einstein considered quantum mechanics incomplete  "because the state function, in general, does not even describe the individual event/system".<ref>{{Cite journal |last=Ballentine |first=L. E. |date=1972-12-01 |title=Einstein's Interpretation of Quantum Mechanics |journal=American Journal of Physics |language=en |volume=40 |issue=12 |pages=1763–1771 |doi=10.1119/1.1987060 |bibcode=1972AmJPh..40.1763B |issn=0002-9505|doi-access=free }}</ref>