  It is well-known that Bell's Theorem and other No Hidden Variable theorems
have a "retrocausal loophole", because they assume that the values of
pre-existing hidden variables are independent of future measurement settings.
(This is often referred to, misleadingly, as the assumption of "free will".)
However, it seems to have gone unnoticed until recently that a violation of
this assumption is a straightforward consequence of time-symmetry, given an
understanding of the quantization of light that would have seemed natural to
Einstein after 1905. The new argument shows precisely why quantization makes a
difference, and why time-symmetry alone does not imply retrocausality, in the
classical context. It is true that later developments in quantum theory provide
a way to avoid retrocausality, without violating time-symmetry; but this escape
route relies on the "ontic" conception of the wave function that Einstein
rejected. Had this new argument been noticed much sooner, then, it seems likely
that retrocausality would have been regarded as the default option for hidden
variables theories (a fact that would then have seemed confirmed by Bell's
Theorem and the No Hidden Variable theorems). This paper presents these ideas
at a level intended to be accessible to general readers.
