Entanglement is the idea that particles can be linked in such a way
that changing the quantum state of one instantaneously affects the
other, even if they are light years apart. I'm always interested in
"spooky action at a distance", or any serious blow to our conception
of how the world works. In 1964, physicist John Bell calculated a
mathematical inequality that encapsulated the maximum correlation
between the states of remote particles in experiments in which three
"reasonable" conditions hold: that experimenters have free will in
setting things up as they want; that the particle properties being
measured are real and pre-existing, not just popping up at the time of
measurement; and that no influence travels faster than the speed of
light, the cosmic speed limit. Many experiments since have shown that
quantum mechanics regularly violates Bell's inequality, yielding
levels of correlation way above those possible if his conditions hold.
That pitches us into a philosophical dilemma. Do we not have free
will, meaning something, somehow predetermines what measurements we
take? That is not anyone's first choice. Are the properties of quantum
particles not real - implying that nothing is real at all, but exists
merely as a result of our perception? That's a more popular position,
but it hardly leaves us any the wiser. Or is there really an
influence that travels faster than light? In 2008 physicist Nicolas
Gisin and his colleagues at the University of Geneva showed that, if
reality and free will hold, the speed of transfer of quantum states
between entangled photons held in two villages 18 kilometres apart was
somewhere above 10 million times the speed of light (Nature, vol 454,
p 861).
This is not the science that lets us build stuff, but I do feel some
kind of buzz about not being quite so trapped by the rather crude
inevitability of being stuck with the limitations of the speed of
light.
