Real Estate e Fiscal Advisor: dr. Michelangelo Ferraro
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In brief, the argument is this. Separability implies that spacelikeseparated systems have associated with them independent real states ofaffairs. A second postulate, locality, implies that the events in oneregion of spacetime cannot physically influence physical reality in aregion of spacetime separated from the first by a spacelikeinterval. Consider now an experiment in which two systems, A and B,interact and separate, subsequent measurements on each correspondingto spacelike separated events. Separability implies that A and B haveseparate real physical states, and locality implies that themeasurement performed on A cannot influence B's real physicalstate. But quantum mechanics ascribes different theoretical states,different wave functions, to B depending upon that parameter that ismeasured on A. Therefore, quantum mechanics ascribes differenttheoretical states to B, when B possesses, in fact, one real physicalstate. Hence quantum mechanics is incomplete.
Cartoon by Nick D Kim (, used by permission).
The postulate of spatial separability as that which undergirds theontic independence and, hence, individual identities of the systemsthat physics describes was an important part of Einstein's thinkingabout the foundations of physics since at least the time of his veryfirst paper on the quantum hypothesis in 1905 (Einstein 1905a; formore detail on the early history of this idea in Einstein's thinking,see Howard 1990b). But the true significance of the separabilityprinciple emerged most clearly in 1935, when (as hinted in thejust-quoted remark) Einstein made it one of the central premises ofhis argument for the incompleteness of quantum mechanics (see Howard1985 and 1989). It is not so clearly deployed in the published versionof the Einstein, Podolsky, Rosen paper (1935), but Einstein did notwrite that paper and did not like the way the argument appearedthere. Separability is, however, an explicit premise in all ofEinstein's later presentations of the argument for the incompletenessof quantum mechanics, both in correspondence and in print (see Howard1985 for a detailed list of references).
into the world essay introduction
Einstein does not explicitly commend Schlick's defense ofsimplicity, but he also in no way objects in the course of a longcorrespondence during the late 1910s, wherein he strongly commendsSchlick's general philosophical orientation and carefully records allpoints of disagreement (for more detail, see Howard 1984). Moreoverthe principle underlying Schlick's defense of simplicity, the ideathat it is the non-arbitrary elements of our theories that representthe real, played a deep and enduring role in Einstein's philosophy ofscience.