Eminent physicist John Wheeler says he has only enough time left to work on 
one idea that human consciousness shapes not only the present but the past 
as well.  -- By Tim Folger

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.


Click on image to enlarge (14K)
Seeing Double
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.

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 
the universe.

Birthday Bash
Andrei Linde, top, one of the principal architects of inflationary theory, 
helps celebrate John Wheeler's pre-91st birthday at a gathering at Princeton 
University. Linde is using his hands to illustrate that our universe may 
have been paired with another when it was born. Wheeler, with glass in hand 
(bottom), chats with Ravi Ravindra, a professor emeritus of comparative 
religion at Dalhousie University in Nova Scotia.

Photographs by Brian Finke 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."

Schrödinger's Cat

Erwin Schrödinger, a founding father of quantum mechanics, asked what would 
happen to a cat locked in a box with a radioactive element that may or may 
not trigger the release of poison gas during the experiment. 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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RELATED WEB SITES

Geons, Black Holes & Quantum Foam A Life in Physics by John Archibald 
Wheeler with Kenneth Ford. New York W. W. Norton & Company, 1998. Also 
check out Andrei Linde's Web site http//physics.stanford.edu/linde.