Does The Universe Exist If We're Not Looking?
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DOES THE UNIVERSE EXIST IF WE'RE NOT LOOKING?
By Tim Folger
DISCOVER Vol. 23 No. 6 (June 2002)
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
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
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.
But when the photon detectors are removed, something weird occurs. One would
expect to see two distinct clusters of dots on the film, corresponding to
where individual photons hit after randomly passing through one slit or the
other. Instead, a pattern of alternating light and dark stripes appears.
Such a pattern could be produced only if the photons are behaving like
waves, with each individual photon spreading out and surging against both
slits at once, like a breaker hitting a jetty. Alternating bright stripes in
the pattern on the film show where crests from those waves overlap; dark
stripes indicate that a crest and a trough have canceled each other.
The outcome of the experiment depends on what the physicists try to measure:
If they set up detectors beside the slits, the photons act like ordinary
particles, always traversing one route or the other, not both at the same
time. In that case the striped pattern doesn't appear on the film. But if
the physicists remove the detectors, each photon seems to travel both routes
simultaneously like a tiny wave, producing the striped pattern.
Wheeler has come up with a cosmic-scale version of this experiment that has
even weirder implications. Where the classic experiment demonstrates that
physicists' observations determine the behavior of a photon in the present,
Wheeler's version shows that our observations in the present can affect how
a photon behaved in the past.
To demonstrate, he sketches a diagram on a scrap of paper. Imagine, he says,
a quasar a very luminous and very remote young galaxy. Now imagine that
there are two other large galaxies between Earth and the quasar. The gravity
from massive objects like galaxies can bend light, just as conventional
glass lenses do. In Wheeler's experiment the two huge galaxies substitute
for the pair of slits; the quasar is the light source. Just as in the
two-slit experiment, light photons from the quasar can follow two
different paths, past one galaxy or the other.
Suppose that on Earth, some astronomers decide to observe the quasars. In
this case a telescope plays the role of the photon detector in the two-slit
experiment. If the astronomers point a telescope in the direction of one of
the two intervening galaxies, they will see photons from the quasar that
were deflected by that galaxy; they would get the same result by looking at
the other galaxy. But the astronomers could also mimic the second part of
the two-slit experiment. By carefully arranging mirrors, they could make
photons arriving from the routes around both galaxies strike a piece of
photographic film simultaneously. Alternating light and dark bands would
appear on the film, identical to the pattern found when photons passed
through the two slits.
Here's the odd part. The quasar could be very distant from Earth, with light
so faint that its photons hit the piece of film only one at a time. But the
results of the experiment wouldn't change. The striped pattern would still
show up, meaning that a lone photon not observed by the telescope traveled
both paths toward Earth, even if those paths were separated by many
light-years. And that's not all.
By the time the astronomers decide which measurement to make whether to pin
down the photon to one definite route or to have it follow both paths
simultaneously the photon could have already journeyed for billions of
years, long before life appeared on Earth. The measurements made now, says
Wheeler, determine the photon's past. In one case the astronomers create a
past in which a photon took both possible routes from the quasar to Earth.
Alternatively, they retroactively force the photon onto one straight trail
toward their detector, even though the photon began its jaunt long before
any detectors existed.
It would be tempting to dismiss Wheeler's thought experiment as a curious
idea, except for one thing: It has been demonstrated in a laboratory. In
1984 physicists at the University of Maryland set up a tabletop version of
the delayed-choice scenario. Using a light source and an arrangement of
mirrors to provide a number of possible photon routes, the physicists were
able to show that the paths the photons took were not fixed until the
physicists made their measurements, even though those measurements were made
after the photons had already left the light source and begun their circuit
through the course of mirrors.
Wheeler conjectures we are part of a universe that is a work in progress; we
are tiny patches of the universe looking at itself and building itself.
It's not only the future that is still undetermined but the past as well.
And by peering back into time, even all the way back to the Big Bang, our
present observations select one out of many possible quantum histories for
Does this mean humans are necessary to the existence of the universe? While
conscious observers certainly partake in the creation of the participatory
universe envisioned by Wheeler, they are not the only, or even primary, way
by which quantum potentials become real. Ordinary matter and radiation play
the dominant roles. Wheeler likes to use the example of a high-energy
particle released by a radioactive element like radium in Earth's crust. The
particle, as with the photons in the two-slit experiment, exists in many
possible states at once, traveling in every possible direction, not quite
real and solid until it interacts with something, say a piece of mica in
Earth's crust. When that happens, one of those many different probable
outcomes becomes real. In this case the mica, not a conscious being, is the
object that transforms what might happen into what does happen. The trail of
disrupted atoms left in the mica by the high-energy particle becomes part of
the real world.
At every moment, in Wheeler's view, the entire universe is filled with such
events, where the possible outcomes of countless interactions become real,
where the infinite variety inherent in quantum mechanics manifests as a
physical cosmos. And we see only a tiny portion of that cosmos. Wheeler
suspects that most of the universe consists of huge clouds of uncertainty
that have not yet interacted either with a conscious observer or even with
some lump of inanimate matter. He sees the universe as a vast arena
containing realms where the past is not yet fixed.
Wheeler is the first to admit that this is a mind-stretching idea. It's not
even really a theory but more of an intuition about what a final theory of
everything might be like. It's a tenuous lead, a clue that the mystery of
creation may lie not in the distant past but in the living present. "This
point of view is what gives me hope that the question How come existence?
can be answered," he says.
William Wootters, one of Wheeler's many students and now a professor of
physics at Williams College in Williamstown, Massachusetts, sees Wheeler as
an almost oracular figure. "I think asking this question How come
existence? is a good thing," Wootters says. "Why not see how far you can
stretch? See where that takes you. It's got to generate at least some good
ideas, even if the question doesn't get answered. John is interested in the
significance of quantum measurement, how it creates an actuality of what was
a mere potentiality. He has come to think of that as the essential building
block of reality."
In his concern for the nature of quantum measurements, Wheeler is addressing
one of the most confounding aspects of modern physics: the relationship
between the observations and the outcomes of experiments on quantum systems.
The problem goes back to the earliest days of quantum mechanics and was
formulated most famously by the Austrian physicist Erwin Schrödinger, who
imagined a Rube Goldberg-type of quantum experiment with a cat.
Put a cat in a closed box, along with a vial of poison gas, a piece of
uranium, and a Geiger counter hooked up to a hammer suspended above the gas
vial. During the course of the experiment, the radioactive uranium may or
may not emit a particle. If the particle is released, the Geiger counter
will detect it and send a signal to a mechanism controlling the hammer,
which will strike the vial and release the gas, killing the cat. If the
particle is not released, the cat will live. Schrödinger asked, What could
be known about the cat before opening the box?
If there were no such thing as quantum mechanics, the answer would be
simple: The cat is either alive or dead, depending on whether a particle hit
the Geiger counter. But in the quantum world, things are not so
straightforward. The particle and the cat now form a quantum system
consisting of all possible outcomes of the experiment. One outcome includes
a dead cat; another, a live one. Neither becomes real until someone opens
the box and looks inside. With that observation, an entire consistent
sequence of events the particle jettisoned from the uranium, the release of
the poison gas, the cat's death at once becomes real, giving the appearance
of something that has taken weeks to transpire. Stanford University
physicist Andrei Linde believes this quantum paradox gets to the heart of
Wheeler's idea about the nature of the universe: The principles of quantum
mechanics dictate severe limits on the certainty of our knowledge.
"You may ask whether the universe really existed before you start looking at
it," he says. "That's the same Schrödinger cat question. And my answer would
be that the universe looks as if it existed before I started looking at it.
When you open the cat's box after a week, you're going to find either a live
cat or a smelly piece of meat. You can say that the cat looks as if it were
dead or as if it were alive during the whole week. Likewise, when we look at
the universe, the best we can say is that it looks as if it were there 10
billion years ago."
Linde believes that Wheeler's intuition of the participatory nature of
reality is probably right. But he differs with Wheeler on one crucial point.
Linde believes that conscious observers are an essential component of the
universe and cannot be replaced by inanimate objects.
"The universe and the observer exist as a pair," Linde says. "You can say
that the universe is there only when there is an observer who can say, Yes,
I see the universe there. These small words it looks like it was here for
practical purposes it may not matter much, but for me as a human being, I do
not know any sense in which I could claim that the universe is here in the
absence of observers. We are together, the universe and us. The moment you
say that the universe exists without any observers, I cannot make any sense
out of that. I cannot imagine a consistent theory of everything that ignores
consciousness. A recording device cannot play the role of an observer,
because who will read what is written on this recording device? In order for
us to see that something happens, and say to one another that something
happens, you need to have a universe, you need to have a recording device,
and you need to have us. It's not enough for the information to be stored
somewhere, completely inaccessible to anybody. It's necessary for somebody
to look at it. You need an observer who looks at the universe. In the
absence of observers, our universe is dead."
The short answer: The cat's fate is undecided until the moment someone
observes the experiment. Will Wheeler's question How come existence? ever
be answered? Wootters is skeptical."I don't know if human intelligence is
capable of answering that question," he says. "We don't expect dogs or ants
to be able to figure out everything about the universe. And in the sweep of
evolution, I doubt that we're the last word in intelligence. There might be
higher levels later. So why should we think we're at the point where we can
understand everything? At the same time I think it's great to ask the
question and see how far you can go before you bump into a wall."
Linde is more optimistic.
"You know, if you say that we're smart enough to figure everything out, that
is a very arrogant thought. If you say that we're not smart enough, that is
a very humiliating thought. I come from Russia, where there is a fairy tale
about two frogs in a can of sour cream. The frogs were drowning in the
cream. There was nothing solid there; they could not jump from the can. One
of the frogs understood there was no hope, and he stopped beating the sour
cream with his legs. He just died. He drowned in sour cream. The other one
did not want to give up. There was absolutely no way it could change
anything, but it just kept kicking and kicking and kicking. And then all of
a sudden, the sour cream was churned into butter. Then the frog stood on the
butter and jumped out of the can. So you look at the sour cream and you
think, 'There is no way I can do anything with that.' But sometimes,
unexpected things happen.
"I'm happy that some people who previously thought this question How come
existence? was meaningless did not stop us from asking it. We all learned
from people like John Wheeler, who asks strange questions and gives strange
answers. You may agree or disagree with his answers. But the very fact that
he asks these questions, and suggests some plausible and implausible
answers, it has shaken these boundaries of what is possible and what is
impossible to ask."
And what does the oracle of High Island himself think? Will we ever
understand why the universe came into being?
"Or at least how," he says. "Why is a trickier thing." Wheeler points to the
example of Charles Darwin in the 19th century and how he provided a simple
explanation evolution through natural selection for what seemed an utterly
intractable problem: how to explain the origin and diversity of life on
Earth. Does Wheeler think that physicists might one day have a similarly
clear understanding of the origin of the universe?
"Absolutely," he says. "Absolutely."
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