Parallel Worlds (24 page)

And say which grain will grow and which will not,

Speak then to
me .. .

(act I, scene 3)

Shakespeare
wrote these words in 1606. Eighty years later, another Englishman, Isaac
Newton, had the audacity to claim that he knew the answer to this ancient
question. Both Newton and Einstein believed in the concept called determinism,
which states that all future events can be determined in principle. To Newton,
the universe was a gigantic clock wound up by God at the beginning of time.
Ever since then, it's been ticking, obeying his three laws of motion, in a
precisely predictable way. The French mathematician Pierre Simon de Laplace,
who was a scientific advisor to Napoleon, wrote that, using Newton's laws, one
could predict the future with the same precision that one views the past. He
wrote that if a being could know the position and velocity of all the particles
in the universe, "for such an intellect, nothing could be uncertain; and
the future just like the past would be present before his eyes." When
Laplace presented Napoleon with a copy of his masterwork,
Celestial Mechanics,
the emperor said, "You have
written this huge work on the heavens without once mentioning God."
Laplace replied, "Sire, I had no need of that hypothesis."

To Newton and
Einstein, the notion of free will, that we are masters of our destiny, was an
illusion. This commonsense notion of reality, that concrete objects that we
touch are real and exist in definite states, Einstein called "objective
reality." He most clearly presented his position as follows:

I am a determinist, compelled to act as if free will existed,
because if I wish to live in a civilized society, I must act responsibly. I
know

philosophically a murderer is not responsible for his crimes,
but I prefer not to take tea with him. My career has been determined by various
forces over which I have no control, primarily those mysterious glands in which
nature prepares the very essence of life. Henry Ford may call it is his Inner
Voice, Socrates referred to it as his daemon: each man explains in his own way
the fact that the human will is not free . . . Everything is determined . . .
by forces over which we have no control . . . for the insect as well as for the
star. Human beings, vegetables, or cosmic dust, we all dance to a mysterious
time, intoned in the distance by an invisible player.

Theologians have
also wrestled with this question. Most religions of the world believe in some
form of predestination, the idea that God is not only omnipotent (all-powerful)
and omnipresent (exists everywhere), but also omniscient (knows everything,
even the future). In some religions, this means that God knows whether we will
go to heaven or hell, even before we are born. In essence, there is a
"book of destiny" somewhere in heaven with all of our names listed,
including our birth date, our failures and triumphs, our joys and our defeats,
even our death date, and whether we will live in paradise or eternal damnation.

(This delicate
theological question of predestination, in part, helped to split the Catholic
Church in half in 1517, when Martin Luther tacked the ninety-five theses on the
church at Wittenberg. In it, he attacked the church's practice of selling
indulgences—essentially bribes that paved the journey to heaven for the rich.
Perhaps, Luther seemed to say, God does know our future ahead of time and our
fates are predestined, but God cannot be persuaded to change his mind by our
making a handsome donation to the church.)

But to
physicists who accept the concept of probability, the most controversial
postulate by far is the third postulate, which has given headaches to
generations of physicists and philosophers. "Observation" is a
loose, ill-defined concept. Moreover, it relies on the fact that there are
actually two types of physics: one for the bizarre subatomic world, where
electrons can seemingly be in two places at the same time, and the other for
the macroscopic world that we live in, which appears to obey the commonsense
laws of Newton.

According to
Bohr, there is an invisible "wall" separating the atomic world from
the everyday, familiar macroscopic world. While the atomic world obeys the
bizarre rules of the quantum theory, we live out our lives outside that wall,
in the world of well-defined planets and stars where the waves have already
collapsed.

Wheeler, who
learned quantum mechanics from its creators, liked to summarize the two schools
of thought on this question. He gives the example of three umpires at a
baseball game discussing the finer points of baseball. In making a decision,
the three umpires say:

Number 1: I calls 'em like I see 'em.

Number 2: I calls 'em the way they
are.

Number 3: They ain't
nothing
till I calls 'em.

To Wheeler, the
second umpire is Einstein, who believed there was an absolute reality outside
human experience. Einstein called this "objective reality," the idea
that objects can exist in definite states without human intervention. The third
umpire is Bohr, who argued that reality existed only after an observation was
made.

TREES IN THE FOREST

Physicists
sometimes view philosophers with a certain disdain, quoting from the Roman
Cicero, who once said, "There is nothing so absurd that it has not been
said by philosophers." The mathematician Stanislaw Ulam, who took a dim
view of giving lofty names to silly concepts, once said, "Madness is the
ability to make fine distinctions on different kinds of nonsense."
Einstein himself once wrote of philosophy, "Is not all of philosophy as
if written in honey? It looks wonderful when one contemplates it, but when one
looks again it is all gone. Only mush remains."

Physicists also
like to tell the apocryphal story supposedly told by a university president who
became exasperated looking at the budget for the physics, math, and philosophy
departments. He supposedly said, "Why is it that you physicists always
require so much expensive equipment? Now the Department of Mathematics requires
nothing but money for paper, pencils, and waste paper baskets and the
Department of Philosophy is better still. It doesn't even ask for waste paper
baskets."

However,
philosophers may yet get the last laugh. The quantum theory is incomplete and
rests on shaky philosophical grounds. This quantum controversy forces one to
reexamine the work of philosophers like Bishop Berkeley, who in the eighteenth
century claimed that objects exist only because humans are there to observe
them, a philosophy called solipsism or idealism. If a tree falls in the forest
but no one is there to see it, then it does not really fall, they claim.

Now we have a
quantum reinterpretation of trees falling in the forest. Before an observation
is made, you don't know whether it has fallen or not. In fact, the tree exists
in all possible states simultaneously: it might be burnt, fallen, firewood,
sawdust, and so on. Once an observation is made, then the tree suddenly springs
into a definite state, and we see that it has fallen, for instance.

Comparing the
philosophical difficulty of relativity and the quantum theory, Feynman once
remarked, "There was a time when the newspapers said that only twelve men
understood the theory of relativity. I do not believe there was ever such a
time . . . On the other hand, I think I can safely say that nobody understands
quantum mechanics." He writes that quantum mechanics "describes nature
as absurd from the point of view of common sense. And it fully agrees with
experiment. So I hope you can accept nature as she is— absurd." This has
created an uneasy feeling among many practicing physicists, who feel as if they
are creating entire worlds based on shifting sands. Steven Weinberg writes,
"I admit to some discomfort in working all my life in a theoretical
framework that no one fully understands."

In traditional
science, the observer tries to keep as dispassionately detached from the world
as possible. (As one wag said, "You can always spot the scientist at a
strip club, because he is the only one examining the audience.") But now,
for the first time, we see that it is impossible to separate the observer from
the observed. As Max Planck once remarked, "Science cannot solve the
ultimate mystery of Nature. And it is because in the last analysis we ourselves
are part of the mystery we are trying to solve."

THE CAT PROBLEM

Erwin
Schrodinger, who introduced the wave equation in the first place, thought that
this was going too far. He confessed to Bohr that he regretted ever proposing
the wave concept if it introduced the concept of probability into physics.

To demolish the
idea of probabilities, he proposed an experiment. Imagine a cat sealed in a
box. Inside the box, there is a bottle of poison gas, connected to a hammer,
which in turn is connected to a Geiger counter placed near a piece of uranium.
No one disputes that the radioactive decay of the uranium atom is purely a
quantum event that cannot be predicted ahead of time. Let's say there is a 50
percent chance that a uranium atom will decay in the next second. But if a
uranium atom decays, it sets off the Geiger counter, which sets off the hammer
that breaks the glass, killing the cat. Before you open the box, it is
impossible to tell whether the cat is dead or alive. In fact, in order to
describe the cat, physicists add the wave function of the live cat and the dead
cat—that is, we put the cat in a nether world of being 50 percent dead and 50
percent alive simultaneously.

Now open the
box. Once we peer into the box, an observation is made, the wave function
collapses, and we see that the cat is, say, alive. To Schrodinger, this was
silly. How can a cat be both dead and alive at the same time, just because we
haven't looked at it? Does it suddenly spring into existence as soon as we
observe it? Einstein was also displeased with this interpretation. Whenever
guests came over to his house, he would say: look at the moon. Does it suddenly
spring into existence when a mouse looks at it? Einstein believed the answer
was no. But in some sense, the answer might be yes.

Things finally
came to a head in 1930 in a historic clash at the Solvay Conference between
Einstein and Bohr. Wheeler would later remark that it was the greatest debate
in intellectual history that he knew about. In thirty years, he had never heard
of a debate between two greater men on a deeper issue with deeper consequences
for an understanding of the universe.

Einstein, always
bold, daring, and supremely eloquent, proposed a barrage of "thought
experiments" to demolish the quantum theory. Bohr, who mumbled
incessantly, was reeling after each attack. Physicist Paul Ehrenfest observed,
"It was wonderful for me to be present at the dialogues between Bohr and
E. E, like a chess player, with ever new examples. A kind of perpetuum mobile
of the second kind, intent on breaking through uncertainty. Bohr always, out of
a cloud of philosophical smoke, seeking the tools for destroying one example
after another. Einstein like a jack-in-a-box, popping up fresh every morning.
Oh, it was delightful. But I am almost unreservedly pro Bohr and contra E. He
now behaves toward Bohr exactly as the champions of absolute simultaneity had
behaved toward him."

Finally,
Einstein proposed an experiment that he thought would give the coup de grace to
the quantum theory. Imagine a box containing a gas of photons. If the box has
a shutter, it can briefly release a single photon. Since one can measure the
shutter speed precisely, and also measure the photon's energy, one can
therefore determine the state of the photon with infinite precision, thereby violating
the uncertainty principle.

Ehrenfest wrote,
"To Bohr, this was a heavy blow. At the moment he saw no solution. He was
extremely unhappy all through the evening, walked from one person to another,
trying to persuade them all that this could not be true, because if E was right
this would mean the end of physics. But he could think of no refutation. I will
never forget the sight of the two opponents leaving the university club.
Einstein, a majestic figure, walking calmly with a faint ironical smile, and
Bohr trotting along by his side, extremely upset."

When Ehrenfest
later encountered Bohr, he was speechless; all he could do was mumble the same
word over and over again, "Einstein . . . Einstein . . . Einstein."

The next day,
after an intense, sleepless night, Bohr was able to find a tiny flaw in
Einstein's argument. After emitting the photon, the box was slightly lighter,
since matter and energy were equivalent. This meant that the box rose slightly
under gravity, since energy has weight, according to Einstein's own theory of
gravity. But this introduced uncertainty in the photon's energy. If one then
calculated the uncertainty in the weight and uncertainty in the shutter
speed, one found that the box obeyed the uncertainty principle exactly. In
effect, Bohr had used Einstein's own theory of gravity to refute Einstein! Bohr
had emerged victorious. Einstein was defeated.

When Einstein
later complained that "God does not play dice with the world," Bohr
reportedly fired back, "Stop telling God what to do." Ultimately,
Einstein admitted that Bohr had successfully refuted his arguments. Einstein
would write, "I am convinced that this theory undoubtedly contains a piece
of definitive truth." (Einstein, however, had disdain for physicists who
failed to appreciate the subtle paradoxes inherent in the quantum theory. He
once wrote, "Of course, today every rascal thinks he knows the answer, but
he is deluding himself.")