John Archibald Wheeler,
high priest of quantum mysteries,
suspects that
reality exists not
because of physical particles but
rather because of the act
of
observing the universe. "Information
may not be just what we learn
about the world," he says. "It may
be what makes the world."
The world seems to be putting itself together piece by piece on this
damp gray morning along the coast of Maine. First the spruce and white
pine trees that cover High Island materialize from the fog, then the
rocky headland, and finally the sea, as if the mere act of watching has
drawn them all into existence. And that may indeed be the case. While
this misty genesis unfolds, the island's most eminent resident
discusses notions that still perplex him after seven decades in
physics, including his gut feeling that the very universe may be
constantly emerging from a haze of possibility, that we inhabit a
cosmos made real in part by our own observations.
John Wheeler,
scientist and dreamer, colleague of Albert Einstein and Niels Bohr,
mentor to many of today's leading physicists, and the man who chose the
name "black hole" to describe the unimaginably dense, light-trapping
objects now thought to be common throughout the universe, turned 90
last July. He is one of the last of the towering figures of
20th-century physics, a member of the generation that plumbed the
mysteries of quantum mechanics and limned the utmost reaches of space
and time. After a lifetime of fundamental contributions in fields
ranging from atomic physics to cosmology, Wheeler has concerned himself
in his later years with what he calls "ideas for ideas."
"I
had a heart attack on January 9, 2001," he says, "I said, 'That's a
signal. I only have a limited amount of time left, so I'll concentrate
on one question: How come existence?'"
Why does the universe
exist? Wheeler believes the quest for an answer to that question
inevitably entails wrestling with the implications of one of the
strangest aspects of modern physics: According to the rules of quantum
mechanics, our observations influence the universe at the most
fundamental levels. The boundary between an objective "world out there"
and our own subjective consciousness that seemed so clearly defined in
physics before the eerie discoveries of the 20th century blurs in
quantum mechanics. When physicists look at the basic constituents of
reality— atoms and their innards, or the particles of light called
photons— what they see depends on how they have set up their
experiment. A physicist's observations determine whether an atom, say,
behaves like a fluid wave or a hard particle, or which path it follows
in traveling from one point to another. From the quantum perspective
the universe is an extremely interactive place. Wheeler takes the
quantum view and runs with it.
As Wheeler voices his thoughts,
he laces his fingers behind his large head, leans back onto a sofa, and
gazes at the ceiling or perhaps far beyond it. He sits with his back to
a wide window. Outside, the fog is beginning to lift on what promises
to be a hot summer day. On an end table near the sofa rests a large
oval rock, with one half polished black so that its surface resembles
the Chinese yin-yang symbol. "That rock is about 200 million years
old," says Wheeler. "One revolution of our galaxy."
Although
Wheeler's face looks careworn and sober, it becomes almost boyish when
he smiles, as he does when I extend a hand to help him from the couch
and he says, "Ah, antigravity." Wheeler is short and sturdily built,
with sparse white hair. He retains an impish fascination with
fireworks— an enthusiasm that cost him part of a finger when he was
young— and has on occasion lit Roman candles in the corridors of
Princeton, where he became a faculty member in 1938 and where he still
keeps an office. At one point a loud bang interrupts our interview.
Wheeler's son, who lives on a cliff a few hundred yards away, has fired
a small cannon, a gift from Wheeler.
Wheeler is gracious to a
fault; one colleague describes him as "a gentleman hidden inside a
gentleman." But that courtly demeanor also hides something else: one of
the most adventurous minds in physics. Instead of shying away from
questions about the meaning of it all, Wheeler relishes the profound
and the paradoxical. He was an early advocate of the anthropic
principle, the idea that the universe and the laws of physics are
fine-tuned to permit the existence of life. For the past two decades,
though, he has pursued a far more provocative idea for an idea,
something he calls genesis by observership. Our observations, he
suggests, might actually contribute to the creation of physical
reality. To Wheeler we are not simply bystanders on a cosmic stage; we
are shapers and creators living in a participatory universe.
Wheeler's
hunch is that the universe is built like an enormous feedback loop, a
loop in which we contribute to the ongoing creation of not just the
present and the future but the past as well. To illustrate his idea, he
devised what he calls his "delayed-choice experiment," which adds a
startling, cosmic variation to a cornerstone of quantum physics: the
classic two-slit experiment.
Seeing Double (Click here to enlarge)
In his delayed-choice thought experiment,
Wheeler suggests that a single photon
emitted from a distant quasar (far right) can
simultaneously follow two paths
to Earth,
even if those paths are separated by many
light-years. Here one
photon travels past two
different galaxies, with both routes deflected
by the
gravitational pull of the galaxies. Stranger
still, Wheeler theorizes, the observations
astronomers make on Earth today decide the
path the photon took
billions of years ago.
Graphic by Matt Zang
That experiment is exceedingly strange in its own right, even without
Wheeler's extra kink thrown in. It illustrates a key principle of
quantum mechanics: Light has a dual nature. Sometimes light behaves
like a compact particle, a photon; sometimes it seems to behave like a
wave spread out in space, just like the ripples in a pond. In the
experiment, light— a stream of photons— shines through two parallel
slits and hits a strip of photographic film behind the slits. The
experiment can be run two ways: with photon detectors right beside each
slit that allow physicists to observe the photons as they pass, or with
detectors removed, which allows the photons to travel unobserved. When
physicists use the photon detectors, the result is unsurprising: Every
photon is observed to pass through one slit or the other. The photons,
in other words, act like particles.
