Parallel Worlds (5 page)

Newton not only
gave us the eternal laws of motion; he also overturned our worldview, giving
us a radically new picture of the universe in which the mysterious laws
governing celestial bodies were identical to the laws governing Earth. The
stage of life was no longer surrounded by terrifying celestial omens; the same
laws that applied to the actors also applied to the set.

BENTLEY'S PARADOX

Because
Principia
was such an ambitious work, it raised the first disturbing
paradoxes about the construction of the universe. If the world is a stage, then
how big is it? Is it infinite or finite? This is an age-old question; even the
Roman philosopher Lucretius was fascinated by it. "The Universe is not
bounded in any direction," he wrote. "If it were, it would
necessarily have a limit somewhere. But clearly a thing cannot have a limit
unless there is something outside to limit it . . . In all dimensions alike, on
this side or that, upward or downward throughout the universe, there is no
end."

But Newton's
theory also revealed the paradoxes inherent in any theory of a finite or
infinite universe. The simplest questions lead to a morass of contradictions.
Even as Newton was basking in the fame brought to him by the publication of
Principia,
he discovered that his theory of gravity was necessarily
riddled with paradoxes. In i692, a clergyman, Rev. Richard Bentley, wrote a
disarmingly simple but distressing letter to Newton. Since gravity was always
attractive and never repulsive, wrote Bentley, this meant that any collection
of stars would naturally collapse into themselves. If the universe was finite,
then the night sky, instead of being eternal and static, should be a scene of
incredible carnage, as stars plowed into each other and coalesced into a fiery
superstar. But Bentley also pointed out that if the universe were infinite,
then the force on any object, tugging it to the left or right, would also be
infinite, and therefore the stars should be ripped to shreds in fiery
cataclysms.

At first, it
seemed as if Bentley had Newton checkmated. Either the universe was finite (and
it collapsed into a fireball), or it was infinite (in which case all the stars
would be blown apart). Either possibility was a disaster for the young theory
being proposed by

Newton. This
problem, for the first time in history, revealed the subtle but inherent
paradoxes that riddle any theory of gravity when applied to the entire
universe.

After careful
thought, Newton wrote back that he found a loophole in the argument. He
preferred an infinite universe, but one that was totally uniform. Thus, if a
star is tugged to the right by an infinite number of stars, this is canceled
exactly by an equal tug of another infinite sequence of stars in the other
direction. All forces are balanced in each direction, creating a static
universe. Thus, if gravity is always attractive, the only solution to Bentley's
paradox is to have a uniform, infinite universe.

Newton had
indeed found a loophole in Bentley's argument. But Newton was clever enough to
realize the weakness of his own response. He admitted in a letter that his
solution, although technically correct, was inherently unstable. Newton's
uniform but infinite universe was like a house of cards: seemingly stable, but
liable to collapse at the slightest disturbance. One could calculate that if
even a single star is jiggled by a tiny amount, it would set off a chain
reaction, and star clusters would immediately begin to collapse. Newton's
feeble response was to appeal to "a divine power" that prevented his
house of cards from collapsing. "A continual miracle is needed to prevent
the Sun and the fixt stars from rushing together through gravity," he
wrote.

To Newton, the
universe was like a gigantic clock wound up at the beginning of time by God
which has been ticking away ever since, according to his three laws of motion,
without Divine interference. But at times, even God himself had to intervene
and tweak the universe a bit, to keep it from collapsing. (In other words,
occasionally God has to intervene to prevent the sets on the stage of life from
collapsing on top of the actors.)

OLBERS' PARADOX

In addition to
Bentley's paradox, there was an even deeper paradox inherent in any infinite
universe. Olbers' paradox begins by asking why the night sky is black.
Astronomers as early as Johannes Kepler realized that if the universe were
uniform and infinite, then wherever you looked, you would see the light from
an infinite number of stars. Gazing at any point in the night sky, our line of
sight will eventually cross an uncountable number of stars and thus receive an
infinite amount of starlight. Thus, the night sky should be on fire! The fact
that the night sky is black, not white, has been a subtle but profound cosmic
paradox for centuries.

Olbers' paradox,
like Bentley's paradox, is deceptively simple but has bedeviled many
generations of philosophers and astronomers. Both Bentley's and Olbers'
paradoxes depend on the observation that, in an infinite universe,
gravitational forces and light beams can add to give infinite, meaningless
results. Over the centuries, scores of incorrect answers have been proposed.
Kepler was so disturbed by this paradox that he simply postulated that the
universe was finite, enclosed within a shell, and hence only a finite amount of
starlight could ever reach our eyes.

The confusion
over this paradox is so great that a 1987 study showed that fully 70 percent of
astronomy textbooks gave the incorrect answer.

At first, one
might try to solve Olbers' paradox by stating that starlight is absorbed by
dust clouds. This was the answer given by Heinrich Wilhelm Olbers himself in
1823 when he first clearly stated the paradox. Olbers wrote, "How
fortunate that the Earth does not receive starlight from every point of the
celestial vault! Yet, with such unimaginable brightness and heat, amounting to
90,000 times more than what we now experience, the Almighty could easily have
designed organisms capable of adapting to such extreme conditions." In
order that the earth not be bathed "against a background as brilliant as
the Sun's disk," Olbers suggested that dust clouds must absorb the
intense heat to make life on earth possible. For example, the fiery center of
our own Milky Way galaxy, which should by rights dominate the night sky, is
actually hidden behind dust clouds. If we look in the direction of the
constellation Sagittarius, where the center of the Milky Way is located, we
see not a blazing ball of fire but a patch of darkness.

But dust clouds
cannot genuinely explain Olbers' paradox. Over an infinite period of time, the
dust clouds will absorb sunlight from an infinite number of stars and
eventually will glow like the surface of a star. Thus, even the dust clouds
should be blazing in the night sky.

Similarly, one
might suppose that the farther a star is, the fainter it is. This is true, but
this also cannot be the answer. If we look at a portion of the night sky, the
very distant stars are indeed faint, but there are also more stars the farther
you look. These two effects would exactly cancel in a uniform universe, leaving
the night sky white. (This is because the intensity of starlight decreases as
the square of the distance, which is canceled by the fact that the number of
stars goes up as the square of the distance.)

Oddly enough,
the first person in history to solve the paradox was the American mystery
writer Edgar Allan Poe, who had a long-term interest in astronomy. Just before
he died, he published many of his observations in a rambling, philosophical
poem called
Eureka: A Prose Poem.
In a remarkable
passage, he wrote:

Were the
succession of stars endless, then the background of the sky would present us an
uniform luminosity, like that displayed by the Galaxy—
since
there could be absolutely no point, in all that background, at which would not
exist a star.
The only mode, therefore, in which, under such a
state of affairs, we could comprehend the
voids
which our
telescopes find in innumerable directions, would be by supposing that the
distance of the invisible background [is] so immense that no ray from it has
yet been able to reach us at all.

He concluded by
noting that the idea "is by far too beautiful not to possess Truth as its
essentiality."

This is the key
to the correct answer. The universe is not infinitely old. There was a
Genesis. There is a finite cutoff to the light that reaches our eye. Light from
the most distant stars has not yet had time to reach us. Cosmologist Edward Harrison,
who was the first to discover that Poe had solved Olbers' paradox, has written,
"When I first read Poe's words I was astounded: How could a poet, at best
an amateur scientist, have perceived the right explanation i40 years ago when
in our colleges the wrong explanation . . . is still being taught?"

In 1901,
Scottish physicist Lord Kelvin also discovered the correct answer. He realized
that when you look at the night sky, you are looking at it as it was in the
past, not as it is now, because the speed of light, although enormous by earth
standards (i86,282 miles per second), is still finite, and it takes time for
light to reach Earth from the distant stars. Kelvin calculated that for the
night sky to be white, the universe would have to extend hundreds of trillions
of light-years. But because the universe is not trillions of years old, the sky
is necessarily black. (There is also a second, contributing reason why the
night sky is black, and that is the finite lifespan of the stars, which is
measured in billions of years.)

Recently, it has
become possible to experimentally verify the correctness of Poe's solution,
using satellites like the Hubble space telescope. These powerful telescopes,
in turn, allow us to answer a question even children ask: Where is the farthest
star? And what lies beyond the farthest star? To answer these questions,
astronomers programmed the Hubble space telescope to perform a historic task:
to take a snapshot of the farthest point in the universe. To capture extremely
faint emissions from the deepest corners of space, the telescope had to
perform an unprecedented task: to aim at precisely the same point in the sky
near the constellation Orion for a total of several hundred hours, which
required the telescope to be aligned perfectly for four hundred orbits of
Earth. The project was so difficult that it had to be spread out over four
months.

In 2004, a
stunning photograph was released which made frontpage headlines around the
world. It showed a collection of ten thousand infant galaxies as they
condensed out of the chaos of the big bang itself. "We might have seen the
end of the beginning," declared Anton Koekemoer of the Space Telescope
Science Institute. The photograph showed a jumble of faint galaxies over i3
billion light-years from Earth—that is, it took over i3 billion years for their
light to reach Earth. Since the universe itself is only 13.7 billion years old,
this means these galaxies were formed roughly half a billion years after
creation, when the first stars and galaxies were condensing out of the
"soup" of gases left over from the big bang. "Hubble takes us to
within a stone's throw of the big bang itself," said astronomer Massimo
Stivavelli of the Institute.

But this raises
the question: What lies beyond the farthest galaxies? When peering at this
remarkable photograph, what is quite apparent is that there is only blackness
between these galaxies. This blackness is what causes the night sky to be
black. It is the ultimate cutoff for light from the distant stars. However,
this blackness in turn is actually the background microwave radiation. So the
final answer to the question of why the night sky is black is that the night
sky is not really black at all. (If our eyes could somehow see microwave
radiation, and not just visible light, we would see radiation from the big bang
itself flooding the night sky. In some sense, radiation from the big bang
comes out every night. If we had eyes able to see microwaves, we could see that
beyond the farthest star lies creation itself.)

EINSTEIN THE REBEL

Newton's laws
were so successful that it took over two hundred years for science to take the
next fateful step, with the work of Albert Einstein. Einstein started his
career as a most unlikely candidate for such a revolutionary. After he
graduated with a bachelor's degree from the Polytechnic Institute in Zurich,
Switzerland, in 1900, he found himself hopelessly unemployable. His career was
sabotaged by his professors, who disliked this impudent, cocky student who
often cut classes. His pleading, depressing letters show the depths to which he
descended. He considered himself to be a failure and a painful financial burden
on his parents. In one poignant letter, he confessed that he even considered
ending his life: "The misfortune of my poor parents, who for so many years
have not had a happy moment, weighs most heavily on
me
...
I am nothing but a burden to my relatives ... It would surely
be better if I did not live at all," he wrote dejectedly.

In desperation,
he thought of switching careers and joining an insurance company. He even took
a job tutoring children but got into an argument with his employer and was
fired. When his girlfriend, Mileva Maric, unexpectedly became pregnant, he
realized sadly that their child would be born illegitimate because he did not
have the resources to marry her. (No one knows what eventually happened to his
illegitimate daughter, Lieseral.) And the deep, personal shock he felt when his
father suddenly died left an emotional scar from which he never fully
recovered. His father died thinking his son was a failure.