  The nature of the future is completely different from the nature of the past.
When quantum effects are significant, the future shows all the signs of quantum
weirdness, including duality, uncertainty, and entanglement. With the passage
of time, after the time-irreversible process of state-vector reduction has
taken place, the past emerges, with the previous quantum uncertainty replaced
by the classical certainty of definite particle identities and states. The
present time is where this transition largely takes place, but the process does
not take place uniformly: Evidence from delayed choice and related experiments
shows that isolated patches of quantum indeterminacy remain, and that their
transition from probability to certainty only takes place later. Thus, when
quantum effects are significant, the picture of a classical Evolving Block
Universe (`EBU') cedes place to one of a Crystallizing Block Universe (`CBU'),
which reflects this quantum transition from indeterminacy to certainty, while
nevertheless resembling the EBU on large enough scales.
