"Physics has generally accepted that the quantum world flouts "local realism", but in 2003,
Anthony Leggett of the University of Illinois at Urbana-Champaign tried to restore realism
by sacrificing locality. If two entities can arrange their correlations through instantaneous
communication, then perhaps it is still possible that they each have definite properties.
Leggett’s real but non-local scenario passes the Bell test, but could it really describe the
Four years later, physicists in Austria, Switzerland and Singapore answered with data.
Instead of measuring the linear polarization states used to violate Bell’s inequality they
looked for correlations between elliptical polarizations – combinations of linear and circular
states. Even assuming that entangled photons could respond to one another instantly, the
correlations between polarization states still violated Leggett’s inequality. The conclusion
being that instantaneous communication is not enough to explain entanglement and
realism must also be abandoned.
This conclusion is now backed up by Sonja Franke-Arnold and collegues at the University
of Glasgow and University of Strathclyde who have performed another experiment
showing that entangled photons exhibit entangled photons show stronger correlations
than allowed for particles with individually defined properties – even if they would be
allowed to communicate constantly. But rather than polarization, they studied the
properties of each photon’s orbital angular momentum."
Thanks to Saul-Paul Sirag for alerting me to this.
In the case of Bohm's particle mechanics, does violation of Leggett's inequality mean that definite particle trajectories cannot exist?