"It's the most curious thing I ever saw in my life!" Alice
thought to herself when she saw a Cheshire cat disappear and
leave only its grin behind. It is not only in Wonderland,
however, that properties of objects can exist independently of
the objects themselves. That is the conclusion of a group of
physicists from Israel and the UK, which has shown how the
strange laws of quantum mechanics permit a photon to be in one
place and its circular polarization in another.  This
counterintuitive result was achieved thanks to the quantum-
mechanical concept of post-selection. In classical physics, the
initial conditions of a set of particles and the rules governing
the behaviour of those particles are in principle enough to
determine the properties of the particles at any arbitrary point
in the future. That is not the case in quantum mechanics, in
which a particle's evolution is inherently probabilistic. So
while the results of a measurement carried out on a set of
particles will have a known probability distribution