A new
optical experiment provides further proof that quantum mechanics is not hiding
some classical framework beneath its veneer of context-dependent observations.
The
contrast with classical expectations is one of the most intriguing features of
quantum mechanics. It can be illustrated by playing a classic “guessing game”
with quantum rules. In this case, the answer to one question will depend on the
other questions being asked and the order chosen. This dependence on the
context does not conform to our everyday experience, but we may have to live
with it, as theorists have shown that we can’t just assume that there exists a
hidden answer sheet that is unaffected by the choice of questions. However, designing
a generic test of quantum contextuality in the lab has been difficult, so far.