Today, we think about multiple Christmases. The
University of Houston's College of Engineering presents
this series about the machines that make our civilization
run, and the people whose ingenuity created them.
It's been a century since Max
Planck published his famous paper introducing the quantum
theory. For a century we've tried to figure out what it
means. Every explanation takes us further from all that
common sense says about our world. We try to reject each
new violation of human intuition, but quantum mechanics
relentlessly passes every rational and experimental test.
We've learned that we live in an indeterminate world,
that two particles can be in the same place at the same
time, and that corporeal solidity is an illusion. Now
Oxford physicist David Deutsch has been giving flesh and
blood to the most bizarre notion of them all, and one
that I find very compelling.
In 1957 Hugh Everett, a graduate student at Princeton,
suggested that quantum mechanics makes sense only if
there are many parallel universes. Deutsch supports
Everett's idea by reminding us of an old experiment in
which we shine a beam of light through thin parallel
slits on to photographic film. Only every other
slit of light appears on the film. If we've arranged
things correctly, the alternate projected slits show up
only as darkness.
Earlier quantum theorists had tried to explain this by
saying that photons interact like waves and cancel one
another. But that calls for a hopeless tangle of
underlying assumptions. Deutsch points out that it can
work only if invisible shadow photons enter from a
parallel universe and obstruct the flow of light.
Bizarre as that may be, other physicists find it
increasingly inescapable. Like so many other quantum
ideas, this too appears to flow from logical necessity.
And we can't help but notice that it's one thing to
speculate about parallel universes, but here we we're
asked to admit that we interact with these other
Think about the implications: Our lives are a sequence of
choices: stand up or sit down, turn left or turn right,
strike out or forgive. If Deutsch is right, we opt into
one universe or another every time we make any free-will
choice, no matter how small. There is, after all, no room
for free will in a deterministic universe, a world of
pure cause and effect. Any free-will decision has to be
made in a place below the level of apparent cause and
effect. And that's where we touch those alternate
All our other selves are out there living lives better or
worse than our own. That wrong turn I took, umpty-ump
years ago, simply separated me from another self who took
the right turn. He's out there living out that other
life. Perhaps he found fame and riches only to suffer
some disaster six months later.
This Christmas, I'm especially touched by this notion.
For the hopes and fears of all our years truly do meet.
It's an apt time to consider that every what if
may've actually been played out. And, so, too, may every
alternate future -- in one of the universes that you and
I touch in the quiet of this winter night.
I'm John Lienhard, at the University of Houston, where
we're interested in the way inventive minds work.