Parallel Worlds (8 page)

The cover of
Time
magazine on March 6, 1995, showing the great spiral galaxy
M100, claimed "Cosmology is in chaos." Cosmology was being thrown
into turmoil because the latest data from the Hubble space telescope seemed to
indicate that the universe was younger than its oldest star, a scientific
impossibility. The data indicated that the universe was between 8 billion and
12 billion years old, while some believed the oldest star to be as much as 14
billion years old. "You can't be older than your ma," quipped
Christopher Impey of the University of Arizona.

But once you
read the fine print, you realized that the theory of the big bang is quite
healthy. The evidence disproving the big bang theory was based on a single
galaxy, M100, which is a dubious way of conducting science. The loopholes were,
as the article acknowledged, "big enough to drive the Starship Enterprise
through." Based on the Hubble space telescope's rough data, the age of the
universe could not be calculated to better than 10 to 20 percent accuracy.

My point is that
the big bang theory is not based on speculation but on hundreds of data points
taken from several different sources, each of which converge to support a
single, self-consistent theory. (In science, not all theories are created
equal. While anyone is free to propose their own version of the creation of the
universe, it should be required that it explain the hundreds of data points we
have collected that are consistent with the big bang theory.)

The three great
"proofs" of the big bang theory are based on the work of three
larger-than-life scientists who dominated their respective fields: Edwin
Hubble, George Gamow, and Fred Hoyle.

EDWIN HUBBLE, PATRICIAN ASTRONOMER

While the
theoretical foundation of cosmology was laid by Einstein, modern observational
cosmology was almost single-handedly created by Edwin Hubble, who was perhaps
the most important astronomer of the twentieth century.

Born in 1889 in
the backwoods of Marshfield, Missouri, Hubble was a modest country boy with
high ambitions. His father, a lawyer and insurance agent, urged him to pursue a
career in law. Hubble, however, was enthralled by the books of Jules Verne and
enchanted by the stars. He devoured science fiction classics like
Twenty Thousand Leagues Under the Sea
and
From the Earth to the Moon.
He was also an
accomplished boxer; promoters wanted him to turn professional and fight the
world heavyweight champion, Jack Johnson.

He won a
prestigious Rhodes scholarship to study law at Oxford, where he began to adopt
the mannerisms of British upper-crust society. (He started wearing tweed
suits, smoking a pipe, adopting a distinguished British accent, and speaking of
his dueling scars, which were rumored to be self-inflicted.)

Hubble, however,
was unhappy. What really motivated him was not torts and lawsuits; his romance
was with the stars, one that had started when he was a child. He bravely
switched careers and headed for the University of Chicago and the observatory
at Mount Wilson, California, which then housed the largest telescope on Earth,
with a 100-inch mirror. Starting so late in his career, Hubble was a man in a hurry.
To make up for lost time, he rapidly set out to answer some of the deepest,
most enduring mysteries in astronomy.

In the 1920s,
the universe was a comfortable place; it was widely believed that the entire
universe consisted of just the Milky Way galaxy, the hazy swath of light that
cuts across the night sky resembling spilt milk. (The word "galaxy,"
in fact, comes from the Greek word for milk.) In 1920, the "Great
Debate" took place between astronomers Harlow Shapley of Harvard and
Heber Curtis of Lick Observatory. Entitled "The Scale of the
Universe," it concerned the size of the Milky Way galaxy and the universe
itself. Shapley took the position that the Milky Way made up the entire visible
universe. Curtis believed that beyond the Milky Way lay the "spiral
nebulae," strange but beautiful wisps of swirling haze. (As early as the
1700s, the philosopher Immanuel Kant had speculated that these nebulae were
"island universes.")

Hubble was
intrigued by the debate. The key problem was that determining the distance to
the stars is (and still remains) one of the most fiendishly difficult tasks in
astronomy. A bright star that is very distant can look identical to a dim star
that is close by. This confusion was the source of many great feuds and
controversies in astronomy. Hubble needed a "standard candle," an
object that emits the same amount of light anywhere in the universe, to resolve
the problem. (A large part, in fact, of the effort in cosmology to this day
consists of attempting to find and calibrate such standard candles. Many of the
great debates in astronomy center around how reliable these standard candles
really are.) If one had a standard candle that burned uniformly with the same
intensity throughout the universe, then a star that was four times dimmer than
normal would simply be twice as far from Earth.

One night, when
analyzing a photograph of the spiral nebula Andromeda, Hubble had a eureka
moment. What he found within

Andromeda was a
type of variable star (called a Cepheid) which had been studied by Henrietta
Leavitt. It was known that this star regularly grew and dimmed with time, and
the time for one complete cycle was correlated with its brightness. The
brighter the star, the longer its cycle of pulsation. Thus, by simply measuring
the length of this cycle, one could calibrate its brightness and hence
determine its distance. Hubble found that it had a period of 31.4 days, which,
much to his surprise, translated to a distance of a million light- years, far
outside the Milky Way galaxy. (The Milky Way's luminous disk is only 100,000
light-years across. Later calculations would show that Hubble in fact
underestimated the true distance to Andromeda, which is closer to 2 million
light-years away.)

When he
performed the same experiment on other spiral nebulae, Hubble found that they
too were well outside the Milky Way galaxy. In other words, it was clear to him
that these spiral nebulae were entire island universes in their own right—that
the Milky Way galaxy was just one galaxy in a firmament of galaxies.

In one stroke,
the size of the universe became vastly larger. From a single galaxy, the
universe was suddenly populated with millions, perhaps billions, of sister
galaxies. From a universe just 100,000 light-years across, the universe
suddenly was perhaps billions of light-years across.

That discovery
alone would have guaranteed Hubble a place in the pantheon of astronomers. But
he topped even that discovery. Not only was he determined to find the distance
to the galaxies, he wanted to calculate how fast they moved, as well.

DOPPLER EFFECT AND THE EXPANDING UNIVERSE

Hubble knew that
the simplest way of calculating the speed of distant objects is to analyze the
change in sound or light they emit, otherwise known as the Doppler effect.
Cars make this sound as they pass us on the highway. Police use the Doppler
effect to calculate your speed; they flash a laser beam onto your car, which
reflects back to the police car. By analyzing the shift in frequency of the
laser light, the police can calculate your velocity.

If a star, for
example, is moving toward you, the light waves it emits are squeezed like an
accordion. As a result, its wavelength gets shorter. A yellow star will appear
slightly bluish (because the color blue has a shorter wavelength than yellow).
Similarly, if a star is moving away from you, its light waves are stretched,
giving it a longer wavelength, so that a yellow star appears slightly reddish.
The greater the distortion, the greater the velocity of the star. Thus, if we
know the shift in frequency of starlight, we can determine the star's speed.

In 1912,
astronomer Vesto Slipher had found that the galaxies were moving away from
Earth at great velocity. Not only was the universe much larger than previously
expected, it was also expanding and at great speed. Outside of small
fluctuations, he found that the galaxies exhibited a redshift, caused by
galaxies moving away from us, rather than a blue one. Slipher's discovery
showed that the universe was indeed dynamic and not static, as Newton and
Einstein had assumed.

In all the
centuries that scientists had studied the paradoxes of Bentley and Olbers, no
one had seriously considered the possibility that the universe was expanding.
In 1928, Hubble made a fateful trip to Holland to meet with Willem de Sitter.
What intrigued Hubble was de Sitter's prediction that the farther away a galaxy
is, the faster it should be moving. Think of an expanding balloon with galaxies
marked on its surface. As the balloon expands, the galaxies that are close to
each other move apart relatively slowly. The closer they are to each other, the
slower they move apart. But galaxies that are farther apart on the balloon
move apart much faster.

De Sitter urged
Hubble to look for this effect in his data, which could be verified by
analyzing the redshift of the galaxies. The greater the redshift of a galaxy,
the faster it was moving away, and hence the farther it should be. (According
to Einstein's theory, the redshift of a galaxy was not, technically speaking,
caused by the galaxy speeding away from Earth; instead, it was caused by the expansion
of space itself between the galaxy and Earth. The origin of the redshift is
that light emanating from a distant galaxy is stretched or lengthened by the
expansion of space, and hence it appears reddened.)

HUBBLE'S LAW

When Hubble went
back to California, he heeded de Sitter's advice and looked for evidence of
this effect. By analyzing twenty-four galaxies, he found that the farther the
galaxy was, the faster it was moving away from Earth, just as Einstein's
equations had predicted. The ratio between the two (speed divided by distance)
was roughly a constant. It quickly became known as Hubble's constant, or
H.
It is perhaps the single most important constant in all of
cosmology, because Hubble's constant tells you the rate at which the universe
is expanding.

If the universe
is expanding, scientists pondered, then perhaps it had a beginning, as well.
The inverse of the Hubble constant, in fact, gives a rough calculation of the
age of the universe. Imagine a videotape of an explosion. In the videotape, we
see the debris leaving the site of the explosion and can calculate the velocity
of expansion. But this also means that we can run the videotape backward, until
all the debris collects into a single point. Since we know the velocity of
expansion, we can roughly work backward and calculate the time at which the
explosion took place.

(Hubble's
original estimate put the age of the universe at about 1.8 billion years, which
gave generations of cosmologists headaches because that was younger than the
reputed age of Earth and the stars. Years later, astronomers realized that
errors in measuring the light from the Cepheid variables in Andromeda had given
an incorrect value of Hubble's constant. In fact, the "Hubble wars"
concerning the precise value of the Hubble constant have raged for the past
seventy years. The most definitive figure today comes from the WMAP satellite.)

In 1931, on
Einstein's triumphant visit to the Mount Wilson

Observatory, he first met Hubble. Realizing that the universe
was indeed expanding, he called the cosmological constant his "biggest
blunder." (However, even a blunder by Einstein is enough to shake the
foundations of cosmology, as we will see in discussing the WMAP satellite data
in later chapters.) When Einstein's wife was shown around the mammoth
observatory, she was told that the gigantic telescope was determining the
ultimate shape of the universe. Mrs. Einstein replied nonchalantly, "My
husband does that on the back of an old envelope."

THE BIG BANG

A Belgian
priest, Georges Lemaitre, who learned of Einstein's theory, was fascinated by
the idea that the theory logically led to a universe that was expanding and
therefore had a beginning. Because gases heat up as they are compressed, he
realized that the universe at the beginning of time must have been
fantastically hot. In 1927, he stated that the universe must have started out
as a "superatom" of incredible temperature and density, which
suddenly exploded outward, giving rise to Hubble's expanding universe. He
wrote, "The evolution of the world can be compared to a display of
fireworks that has just ended: some few red wisps, ashes and smoke. Standing on
a well-chilled cinder, we see the slow fading of the suns, and we try to recall
the vanished brilliance of the origin of worlds."

(The first
person to propose this idea of a "superatom" at the beginning of time
was, once again, Edgar Allan Poe. He argued that matter attracts other forms of
matter, therefore at the beginning of time there must have been a cosmic
concentration of atoms.)

Lemaitre would
attend physics conferences and pester other scientists with his idea. They
would listen to him with good humor and then quietly dismiss his idea. Arthur
Eddington, one of the leading physicists of his time, said, "As a
scientist, I simply do not believe that the present order of things started off
with a bang . . . The notion of an abrupt beginning to this present order of
Nature is repugnant to me."