QUANTUM METAPHYSICS - E-thesis

Einstein presented the EPR paradox in 1935 in collaboration with his young colleagues Boris
Podolsky and Nathan Rosen. 540 They presented a thought experiment which was taken to
demonstrate that the statistical predictions of quantum mechanics did not address all the
elements of reality, and thus the theory could not be complete. In simple terms, the EPR paradox
can be presented as follows. Particles are being examined in an experiment which breaks them
into two parts of equal size. In accordance with the laws of conservation of energy and
momentum, the resulting particles fly in opposite directions at equally-great velocities. When
either the position or momentum of one of the particles is measured, the corresponding property
of the other particle becomes known. According to quantum mechanics, a system’s properties do
not have precise values before they are measured. Einstein considered that this assumption had to
be incorrect as it would be absurd to presume that measuring one of the particles could instantly
give birth to the corresponding property in the other particle.
Einstein’s argumentation was not accepted by Bohr, who considered quantum theory to be
complete and emphasised the indivisibility of quantum phenomena and the fact that the whole
experimental system should taken into account. 541 Correlation phenomena between particles
which had once belonged to the same system were understandable by thinking that the particles
in some way also at a later
point in time were connected together. The problem was struggled over for a long time. There
was no desire to abandon the requirement for classical locality, even though matching this to
quantum theory had been problematical from the very beginning. In 1964, John Bell succeeded
in casting new light on the EPR situation and presumptions of locality. He started from the
traditional realistic assumption that a local objective reality existed and worked out a specific
formula concerning the correlation between particles flying in opposite directions, something
which experimental observations should confirm, if the initial assumptions were correct. When
quantum mechanics gave different predictions for correlation, local hidden-variable theories and
quantum mechanics could be tested against each other.
540 A more-detailed description of the paradox can be found, for example, in the introductory chapter of J.T.
Cushing and E. McMullin (ed.) Philosophical Consequences of Quantum Theory, Reflections on Bell´s Theorem or
in Bell’s article Indeterminism and Nonlocality in Mathematical Undecidability and the Question of the Existence of
God (Ed. A. Driessen and A. Suarez)1997, 83-93.
541 For Bohr’s account of the discussions, see Bohr 1949, 32-66.
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