Parallel Worlds (9 page)

But, over the
years, his persistence gradually wore down the resistance of the physics
community. The scientist who would become the most important spokesman and popularizer
of the big bang theory would eventually provide the most convincing proof of
the

GEORGE GAMOW, COSMIC JESTER

While Hubble was
the sophisticated patrician of astronomy, his work was continued by yet another
larger-than-life figure, George Gamow. Gamow was in many respects his opposite:
a jester, a cartoonist, famous for his practical jokes and his twenty books on
science, many of them for young adults. Several generations of physicists
(myself included) were raised on his entertaining and informative books about
physics and cosmology. In a time when relativity and the quantum theory were
revolutionizing science and society, his books stood alone: they were the only
credible books on advanced science available to teenagers.

While lesser
scientists are often barren of ideas, content to merely grind through mountains
of dry data, Gamow was one of the creative geniuses of his time, a polymath who
rapidly spun off ideas that would change the course of nuclear physics,
cosmology, and even DNA research. It was perhaps no accident that the
autobiography of James Watson, who with Francis Crick unraveled the secret of
the DNA molecule, was titled
Genes, Gamow, and Girls.
As his colleague Edward Teller recalled, "Ninety
percent of Gamow's theories were wrong, and it was easy to recognize that they
were wrong. But he didn't mind. He was one of those people who had no
particular pride in any of his inventions. He would throw out his latest idea
and then treat it as a joke." But the remaining 10 percent of his ideas
would go on to change the entire scientific landscape.

Gamow was born
in Odessa, Russia, in 1904, during that country's early social upheavals. Gamow
recalled that "classes were often suspended when Odessa was bombarded by
some enemy warship, or when Greek, French, or British expeditionary forces
staged a bayonet attack along the main streets of the city against entrenched,
White, Red, or even green Russian forces, or when Russian forces of different
colors fought one another."

The turning
point in his early life came when he went to church and secretly took home some
communion bread after the service. Looking through a microscope, he could see
no difference between the communion bread, representing the flesh of Jesus
Christ, and ordinary bread. He concluded, "I think this was the
experiment which made me a scientist."

He was educated
at the University of Leningrad and studied under physicist Aleksandr
Friedmann. Later, at the University of Copenhagen, he met many of the giants of
physics, like Niels Bohr. (In 1932, he and his wife tried unsuccessfully to
defect from the Soviet Union by sailing on a raft from the Crimean to Turkey.
Later, he succeeded in defecting while attending a physics conference in
Brussels, which earned him a death sentence from the Soviets.)

Gamow was famous
for sending limericks to his friends. Most are unprintable, but one limerick
captures the anxieties cosmologists feel when they face the enormity of
astronomical numbers and stare infinity in the face:

There was a young fellow from Trinity

Who took the square root of infinity

But the number of digits

Gave him the fidgits;

He dropped Math and took up Divinity.

In the 1920s in
Russia, Gamow scored his first big success when he solved the mystery of why
radioactive decay was possible. Thanks to the work of Madame Curie and others,
scientists knew that the uranium atom was unstable and emitted radiation in
the form of an alpha ray (the nucleus of a helium atom). But according to
Newtonian mechanics, the mysterious nuclear force that held the nucleus together
should have been a barrier that prevented this leakage. How was this possible?

Gamow (and R. W.
Gurney and E. U. Condon) realized that radioactive decay was possible because
in the quantum theory, the uncertainty principle meant that one never knew
precisely the location and velocity of a particle; hence there was a small
probability that it might "tunnel" or penetrate right through a
barrier. (Today, this idea of tunneling is central to all of physics and is used
to explain the properties of electronic devices, black holes, and the big
bang. The universe itself might have been created via tunneling.)

By analogy,
Gamow envisioned a prisoner sealed in a jail, surrounded by huge prison walls.
In a classical Newtonian world, escape is impossible. But in the strange world
of the quantum theory, you don't know precisely where the prisoner is at any
point or his velocity. If the prisoner bangs against the prison walls often
enough, you can calculate the chances that one day he will pass right through
them, in direct violation of common sense and Newtonian mechanics. There is a
finite, calculable probability that he will be found outside the gates of the
prison walls. For large objects like prisoners, you would have to wait longer
than the lifetime of the universe for this miraculous event to happen. But for
alpha particles and subatomic particles, it happens all the time, because
these particles hit against the walls of the nucleus repeatedly with vast
amounts of energy. Many feel that Gamow should have been given the Nobel Prize
for this vitally important work.

In the 1940s,
Gamow's interests began to shift from relativity to cosmology, which he viewed
as a rich, undiscovered country. All that was known about the universe at that
time was that the sky was black and that the universe was expanding. Gamow was
guided by a single idea: to find any evidence or "fossils" proving
that there was a big bang billions of years ago. This was frustrating, because
cosmology is not an experimental science in the true sense of the word. There
are no experiments one can conduct on the big bang. Cosmology is more like a
detective story, an observational science where you look for "relics"
or evidence at the scene of the crime, rather than an experimental science
where you can perform precise experiments.

NUCLEAR KITCHEN
OF THE UNIVERSE

Gamow's next
great contribution to science was his discovery of the nuclear reactions that
gave birth to the lightest elements that we see in the universe. He liked to
call it the "prehistoric kitchen of the universe," where all the
elements of the universe were originally cooked by the intense heat of the big
bang. Today, this process is called "nucleosynthesis," or calculating
the relative abundances of the elements in the universe. Gamow's idea was that
there was an unbroken chain, starting with hydrogen, that could be built by simply
adding successively more particles to the hydrogen atom. The entire Mendeleev
periodic chart of the chemical elements, he believed, could be created from the
heat of the big bang.

Gamow and his
students reasoned that because the universe was an incredibly hot collection of
protons and neutrons at the instant of creation, then perhaps fusion took place,
with hydrogen atoms being fused together to produce helium atoms. As in a
hydrogen bomb or a star, the temperatures are so hot that the protons of a
hydrogen atom are smashed into each other until they merge, creating helium
nuclei. Subsequent collisions between hydrogen and helium would, according to
this scenario, produce the next set of elements, including lithium and
beryllium. Gamow assumed that the higher elements could be sequentially built
up by adding more and more subatomic particles to the nucleus—in other words,
that all of the hundred or so elements that make up the visible universe were
"cooked" in the fiery heat of the original fireball.

In typical
fashion, Gamow laid out the broad outlines of this ambitious program and let
his Ph.D. student Ralph Alpher fill in the details. When the paper was
finished, he couldn't resist a practical joke. He put physicist Hans Bethe's
name on the paper without his permission, and it became the celebrated
alpha-beta-gamma paper.

What Gamow had
found was that the big bang indeed was hot enough to create helium, which makes
up about 25 percent of the universe, by mass. Working in reverse, one
"proof" of the big bang can be found by simply looking at many of the
stars and galaxies of today and realizing that they are made of approximately
75 percent hydrogen, 25 percent helium, and a few trace elements. (As David
Spergel, an astrophysicist at Princeton, has said, "Every time you buy a
balloon, you are getting atoms [some of which] were made in the first few
minutes of the big bang.")

However, Gamow
also found problems with the calculation. His theory worked well for the very
light elements. But elements with 5 and 8 neutrons and protons are extremely
unstable and hence cannot act as a "bridge" to create elements that
have a greater number of protons and neutrons. The bridge was washed out at 5
and 8 particles. Since the universe is composed of heavy elements with a great
many more than 5 and 8 neutrons and protons, this left a cosmic mystery. The
failure of Gamow's program to extend beyond the 5-particle and 8-particle gap
remained a stubborn problem for years, dooming his vision of showing that all
the elements of the universe were created at the moment of the big bang.

MICROWAVE BACKGROUND RADIATION

At the same
time, another idea intrigued him: if the big bang was so incredibly hot,
perhaps some of its residual heat is still circulating around the universe
today. If so, it would give a "fossil record" of the big bang itself.
Perhaps the big bang was so colossal that its aftershocks are still filling up
the universe with a uniform haze of radiation.

In 1946, Gamow
assumed that the big bang began with a superhot core of neutrons. This was a
reasonable assumption, since very little was known about subatomic particles
other than the electron, proton, and neutron. If he could estimate the
temperature of this ball of neutrons, he realized he could calculate the amount
and nature of radiation that it emitted. Two years later, Gamow showed that
radiation given off by this superhot core would act like "black body radiation."
This is a very specific type of radiation given off by a hot object; it absorbs
all light hitting it, emitting radiation back in a characteristic way. For
example, the Sun, molten lava, hot coals in a fire, and hot ceramics in an oven
all glow yellow-red and emit black body radiation. (Black body radiation was
first discovered by the famed maker of porcelain, Thomas Wedgwood, in 1792. He
noticed that when raw materials were baked in his ovens, they changed in color
from red to yellow to white, as he raised the temperature.)

This is
important because once one knows the color of a hot object, one also knows
roughly its temperature, and vice versa; the precise formula relating the
temperature of a hot object and the radiation it emits was first obtained by
Max Planck in 1900, which led to the birth of the quantum theory. (This is, in
fact, one way in which scientists determine the temperature of the Sun. The Sun
radiates mainly yellow light, which in turn corresponds to a black body
temperature of roughly 6,000 K. Thus we know the temperature of the Sun's
outer atmosphere. Similarly, the red giant star Betelgeuse has a surface
temperature of 3,000 K, the black body temperature corresponding to the color
red, which is also emitted by a red-hot piece of coal.)

Gamow's 1948
paper was the first time anyone had suggested that the radiation of the big
bang might have a specific characteristic— black body radiation. The most
important characteristic of black body radiation is its temperature. Next,
Gamow had to compute the current temperature of black body radiation.

Gamow's Ph.D.
student Ralph Alpher and another student, Robert Herman, tried to complete
Gamow's calculation by computing its temperature. Gamow wrote,
"Extrapolating from the early days of the universe to the present time, we
found that during the eons which had passed, the universe must have cooled to
about 5 degrees above the absolute temperature."

In 1948, Alpher
and Herman published a paper giving detailed arguments why the temperature of
the afterglow of the big bang today should be 5 degrees above absolute zero
(their estimate was remarkably close to what we now know is the correct
temperature of 2.7 degrees above zero). This radiation, which they identified
as being in the microwave range, should still be circulating around the
universe today, they postulated, filling up the cosmos with a uniform
afterglow.

(The reasoning
is as follows. For years after the big bang, the temperature of the universe
was so hot that anytime an atom formed, it would be ripped apart; hence there
were many free electrons that could scatter light. Thus, the universe was
opaque, not transparent. Any light beam moving in this super-hot universe would
be absorbed after traveling a short distance, so the universe looked cloudy.
After 380,000 years, however, the temperature dropped to 3,000 degrees. Below
that temperature, atoms were no longer ripped apart by collisions. As a
result, stable atoms could form, and light beams could now travel for
light-years without being absorbed. Thus, for the first time, empty space
became transparent. This radiation, which was no longer instantly absorbed as
soon as it was created, is circulating around the universe today.)