AAWSAP DIRD, The Space Communication Implications of Quantum Entanglement and Nonlocality, March 2010

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observer signaling (Reference 12), because one would need to deduce from the arriving
photons the polarization basis that was being used in the distant measurements. This is
an aspect of the parameter independence mentioned above. While each observer is free
to choose a parameter that specifies the polarization basis (for example, circular
right/left, linear at any angle) for the measurement, he is not free to force the photon
into a particular state of that basis, as would be required for nonlocal communication.
However, measuring polarization correlations in a system with angular momentum
constraints is not the only way to demonstrate the nonlocal connection between the
entangled separated parts of a quantum system. Below, EPR experiments that use
momentum entanglement are discussed, and the question of whether such quantum
systems might provide a better vehicle for observer-to-observer nonlocal
communication is explored, because by using momentum entanglement, an observer is
able to force the photon into particle-like or wave-like behavior.
II. The Quantum No-Signal Theorems
As Einstein implied with his well-known "spooky actions at a distance" comment,
enforcement of quantum correlations across spacelike and negative timelike intervals
by nonlocality is very counterintuitive. It appears to imply the twin possibilities of
superluminal communication and of reverse causation through back-in-time
communication between observers. However, a number of authors (Reference 13) have
presented "proofs" that such nonlocal observer-to-observer communication is
impossible within the formalism of standard quantum mechanics. These theorems
assert that in separated measurements involving entangled quantum systems, the
quantum correlations will be preserved, but there will be no effect apparent to an
observer in one sub-system if the character of the measurement is changed in the
other sub-system. Thus, it is asserted, nonlocal signaling is impossible.
As mentioned above, EPR experiments can be viewed (Reference 5, 6) as
demonstrating violations of outcome independence or parameter independence or both.
Outcome independence cannot be used for nonlocal signaling, while parameter
independence can. Thus, any test of nonlocal signaling is, in effect, a test of the
parameter independence of quantum phenomena, and the no-signal theorems are
"proofs" of parameter independence.
Do these no-signal "proofs" really have the status of mathematical theorems? Perhaps
not. Recently it has been pointed out (Reference 14) that at least some of these
"proofs" ruling out nonlocal signaling are tautological, assuming that the measurement
process and its associated Hamiltonian are local, thereby building the final conclusion of
no signaling into their starting assumptions. Standard quantum mechanical Bose­
Einstein symmetrization in systems of bosons has been raised as a counter-example,
shown to be inconsistent with the initial assumptions of some of these "proofs."
Therefore, at least from some perspectives, the possibility of nonlocal communication in
the context of standard quantum mechanics remains open and appropriate for
experimental testing.
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