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Just because we perceive time as flowing in one direction, does that
mean there really is a difference between the past and future? This old
question has been re-examined by Huw Price of the University of Sydney in
the context of quantum mechanics. He concludes that the idea that the past
is not influenced by the future is an illusion, a ‘projection of our own
temporal asymmetry’.

If signals from the future play a part in determining the outcome of
quantum experiments, Price says he can resolve all the puzzles and paradoxes
of the quantum world. This approach has a long history, but the implications
have never been spelt out as clearly as Price has spelt them in an article
to be published in the journal Mind.

It is one of the curiosities of Maxwell’s equations of electromagnetism,
for example, that they allow two sets of solutions for the effect of a moving
electric charge. One describes an electromagnetic wave moving out from the
particle into the future at the speed of light (a retarded wave) and the
other describes waves from the future converging on the particle at the
speed of light (an advanced wave). The advanced wave solutions have been
largely ignored but a few physicists, including John Wheeler, Richard Feynman
and Fred Hoyle, have considered the implications of taking such waves to
be physically real.

More recently, the idea has been investigated in a quantum context
by the American researcher John Cramer. He envisages a quantum entity such
as an electron that is about to be involved in an interaction sending out
an ‘offer’ wave into the future. The particle that the electron is about
to interact with picks up the offer wave, and sends a response echoing
backwards in time to the electron. The advanced and retarded waves combine
to create a ‘handshake’ between the two particles which, in a sense atemporally,
determines the outcome of the interaction at the instant the electron starts
to make the offer.

According to Price, this kind of approach solves the classic quantum
puzzles, such as the electron faced with two holes in a screen, ‘deciding’
which hole to go through. Experiments show that, even though an individual
electron can only go through one hole, its behaviour is affected by whether
or not the second hole is open or closed. The offer wave goes out through
both holes, but the echo comes back only through one hole, the one the electron
then goes through. So the handshake process does take account of both holes,
even though the electron only goes through one of them.

Many physicists find such ideas abhorrent. They would, for example,
encourage speculations such as those of Henry Stapp that our own minds can
influence things that have already happened (New Å®ÉúСÊÓƵ, Science, 27
August). However, Price’s approach offers a framework for understanding
how the world can include both forward and backward causation at a fundamental
level, but appear to have a unique direction of time from a human perspective.

His argument is complex, but it boils down to the view that the reason
why the things we do in the present do not seem to have altered the past
is that the past has already taken account of what we are doing. If we decide
to do something different, the past already knows, so ‘to say that if we
suppose the present to be different, while the past remains the same, it
will follow that the past is different . . . is untrue, of course, but simply
on logical grounds. No physical asymmetry is required to explain it.’

For the mathematically inclined, Price discusses John Bell’s famous
inequality, in which two widely separated quantum systems seem to be connected
by what Einstein called a ‘spooky action at a distance’. The action at a
distance is real, in this picture, and is essentially a version of Cramer’s
handshaking process. But what are the implications for us? There is, according
to Price, no limitation on free will. We are free to make any decisions
we please. The past already knows what those decisions will be, but that
does not affect our freedom in making them, and ‘we shouldn’t expect to
‘see’ backward influence in action,’ which may be bad news for Stapp, after
all. ‘It is time,’ says Price, ‘that this neglected approach (to quantum
mechanics) received the attention it so richly deserves.’