Parallel Worlds (7 page)

As revolutionary
as Einstein was, he could not believe that the universe could be in motion.
Like Newton and legions of others, Einstein believed in a static universe. So
in 1917, Einstein was forced to introduce a new term into his equations, a
"fudge factor" that produced a new force into his theory, an
"antigravity" force that pushed the stars apart. Einstein called this
the "cosmological constant," an ugly duckling that seemed like an
afterthought to Einstein's theory. Einstein then arbitrarily chose this
antigravity to cancel precisely the attraction of gravity, creating a static
universe. In other words, the universe became static by fiat: the inward
contraction of the universe due to gravity was canceled by the outward force
of dark energy. (For seventy years, this antigravity force was considered to
be something of an orphan, until the discoveries of the last few years.)

In 1917, the
Dutch physicist Willem de Sitter produced another solution to Einstein's
theory, one in which the universe was infinite but was completely devoid of any
matter; in fact, it consisted only of energy contained in the vacuum, the
cosmological constant. This pure antigravity force was sufficient to drive a
rapid, exponential expansion of the universe. Even without matter, this dark
energy could create an expanding universe.

Physicists were
now faced with a dilemma. Einstein's universe had matter, but no motion. De Sitter's
universe had motion, but no matter. In Einstein's universe, the cosmological
constant was necessary to neutralize the attraction of gravity and create a
static universe. In de Sitter's universe, the cosmological constant alone was
sufficient to create an expanding universe.

Finally, in
1919, when Europe was trying to dig its way out of the rubble and carnage of
World War I, teams of astronomers were sent around the world to test Einstein's
new theory. Einstein had earlier proposed that the curvature of space-time by
the Sun would be suf-

In
1919, two groups confirmed Einstein's prediction that light from a distant star
would bend when passing by the Sun. Thus, the position of the star would appear
to move from its normal position in the presence of the Sun. This is because
the Sun has warped the space-time surrounding it. Thus, gravity does not
"pull." Rather, space "pushes."
ficient to bend starlight that is
passing in its vicinity. Starlight should bend around the Sun in a precise,
calculable way, similar to the way glass bends light. But since the brilliance
of Sun's light masks any stars during the day, scientists would have to wait
for an eclipse of the Sun to make the decisive experiment.

A group led by
British astrophysicist Arthur Eddington sailed to the island of Principe in the
Gulf of Guinea off the coast of West Africa to record the bending of starlight
around the Sun during the next solar eclipse. Another team, led by Andrew
Crommelin, set sail to Sobral in northern Brazil. The data they gathered
indicated an average deviation of starlight to be 1.79 arc seconds, which
confirmed Einstein's prediction of 1.74 arc seconds (to within experimental error).
In other words, light did bend near the Sun. Eddington later claimed that
verifying Einstein's theory was the greatest moment in his life.

On November 6,
1919, at a joint meeting of the Royal Society and the Royal Astronomical
Society in London, Nobel laureate and Royal Society president J. J. Thompson
said solemnly that this was "one of the greatest achievements in the
history of human thought. It is not the discovery of an outlying island but of
a whole continent of new scientific ideas. It is the greatest discovery in
connection with gravitation since Newton enunciated his principles."

(According to
legend, Eddington was later asked by a reporter, "There's a rumor that
only three people in the entire world understand Einstein's theory. You must
be one of them." Eddington stood in silence, so the reporter said,
"Don't be modest, Eddington." Eddington shrugged, and said, "Not
at all. I was wondering who the third might be.")

The next day,
the London
Times
splashed the
headline: "Revolution in Science—New Theory of the Universe—Newton's Ideas
Overthrown." The headline marked the moment when Einstein became a
world-renowned figure, a messenger from the stars.

So great was
this announcement, and so radical was Einstein's departure from Newton, that it
also caused a backlash, as distinguished physicists and astronomers denounced
the theory. At Columbia University, Charles Lane Poor, a professor of celestial
mechanics, led the criticism of relativity, saying, "I feel as if I had
been wandering with Alice in Wonderland and had tea with the Mad Hatter."

The reason that
relativity violates our common sense is not that relativity is wrong, but that
our common sense does not represent reality.
We
are the oddballs of the universe. We inhabit an unusual piece of real estate,
where temperatures, densities, and velocities are quite mild. However, in the "real
universe," temperatures can be blisteringly hot in the center of stars, or
numbingly cold in outer space, and subatomic particles zipping through space
regularly travel near light-speed. In other words, our common sense evolved in
a highly unusual, obscure part of the universe, Earth; it is not surprising
that our common sense fails to grasp the true universe. The problem lies not in
relativity but in assuming that our common sense represents reality.

THE FUTURE OF THE UNIVERSE

Although
Einstein's theory was successful in explaining astronomical phenomena such as
the bending of starlight around the Sun and the slight wobbling of the orbit of
the planet Mercury, its cosmolog- ical predictions were still confusing.
Matters were greatly clarified by the Russian physicist Aleksandr Friedmann,
who found the most general and realistic solutions of Einstein's equations.
Even today, they are taught in every graduate course in general relativity. (He
discovered them in 1922, but he died in 1925, and his work was largely
forgotten until years later.)

Normally,
Einstein's theory consists of a series of extraordinarily difficult equations
which often require a computer to solve. However, Friedmann assumed that the
universe was dynamic and then made two simplifying assumptions (called the
cosmological principle): that the universe is isotropic (it looks the same no
matter where we look from a given point), and that the universe is homogeneous
(it is uniform no matter where you go in the universe).

Under these two
simplifying assumptions, we find that these equations collapse. (In fact, both
Einstein's and de Sitter's solutions were special cases of Friedmann's more
general solution.) Remarkably, his solutions depend on just three parameters:

1.
    
H,
which determines the rate of
expansion of the universe. (Today, this is called Hubble's constant, named
after the astronomer who actually measured the expansion of the universe.)

2.
   
Omega,
which measures
the average density of matter in the universe.

3.
  
Lambda,
the energy
associated with empty space, or dark energy.

Many
cosmologists have spent their entire professional careers trying to nail down
the precise value of these three numbers. The subtle interplay between these
three constants determines the future evolution of the entire universe. For
example, since gravity attracts, the density of the universe Omega acts as a
kind of brake, to slow the expansion of the universe, reversing some of the
effects of the big bang's rate of expansion. Think of throwing a rock into the
air. Normally, gravity is strong enough to reverse the direction of the rock,
which then tumbles back to Earth. However, if one throws the rock fast enough,
then it can escape Earth's gravity and soar into outer space forever. Like a
rock, the universe originally expanded because of the big bang, but matter, or
Omega, acts as a brake on the expansion of the universe, in the same way that
Earth's gravity acts as a brake on the rock.

For the moment,
let's assume that Lambda, the energy associated with empty space, equals zero.
Let Omega be the density of the universe divided by the critical density. (The
critical density of the universe is approximately 10 hydrogen atoms per cubic
meter. To appreciate how empty the universe is, the critical density of the
universe corresponds to finding a single hydrogen atom within the volume of
three basketballs, on average.)

If Omega is less
than 1, scientists conclude that there is not enough matter in the universe to
reverse the original expansion from the big bang. (Like throwing the rock in
the air, if Earth's mass is not great enough, the rock will eventually leave
Earth.) As a result, the universe will expand forever, eventually plunging the
universe into a big freeze until temperatures approach absolute zero. (This is
the principle behind a refrigerator or air conditioner. When gas expands, it
cools down. In your air conditioner, for example, gas circulating in a pipe
expands, cooling the pipe and your room.)

If Omega is
greater than 1, then there is sufficient matter and gravity in the universe to
ultimately reverse the cosmic expansion. As a result, the expansion of the
universe will come to a halt, and the universe will begin to contract. (Like
the rock thrown in the air, if Earth's mass is great enough, the rock will
eventually reach a maximum height and then come tumbling back to Earth.)
Temperatures will begin to soar, as the stars and galaxies rush toward each
other. (Anyone who has ever inflated a bicycle tire knows that the compression
of gas creates heat. The mechanical work of pumping air is converted into heat
energy. In the same way, the compression of the universe converts gravitational
energy into heat energy.) Eventually, temperatures would become so hot that all
life would be extinguished,

The evolution of the universe has three possible histories.
If Omega is less than 1 (and Lambda is 0), the universe will expand forever
into the big freeze. If Omega is greater than 1, the universe will recollapse
into the big crunch. If Omega is equal to 1, then the universe is flat and will
expand forever. (The WMAP satellite data shows that Omega plus Lambda is equal
to 1, meaning that the universe is flat. This is consistent with the
inflationary theory.)

as the universe
heads toward a fiery "big crunch." (Astronomer Ken Croswell labels
this process "from Creation to Cremation.")

A third
possibility is that Omega is perched precisely at 1; in other words, the
density of the universe equals the critical density, in which case the universe
hovers between the two extremes but will still expand forever. (This scenario,
we will see, is favored by the inflationary picture.)

And last, there
is the possibility that the universe, in the aftermath of a big crunch, can
reemerge into a new big bang. This theory is referred to as the oscillating
universe.

Friedmann showed
that each of these scenarios, in turn, determines the curvature of space-time.
If Omega is less than 1 and the universe expands forever, Friedmann showed that
not only is time infinite, but space is infinite as well. The universe is said
to be "open," that is, infinite in both space and time. When
Friedmann computed the curvature of this universe, he found it to be negative.
(This is like the surface of a saddle or a trumpet. If a bug lived on the
surface of this surface, it would find that parallel lines never meet, and the
interior angles of a triangle sum up to less than
180
degrees.) If
Omega is larger than 1, then the universe will eventually con-

tract into a big
crunch. Time and space are finite. Friedmann found that the curvature of this
universe is positive (like a sphere). Finally, if Omega equals 1, then space is
flat and both time and space are unbounded.

Not only did
Friedmann provide the first comprehensive approach to Einstein's cosmological
equations, he also gave the most realistic conjecture about Doomsday, the
ultimate fate of the uni- verse—whether it will perish in a big freeze, fry in
a big crunch, or oscillate forever. The answer depends upon the crucial
parameters: the density of the universe and the energy of the vacuum.

But Friedmann's
picture left a gaping hole. If the universe is expanding, then it means that
it might have had a beginning. Einstein's theory said nothing about the instant
of this beginning. What was missing was the moment of creation, the big bang.
And three scientists would eventually give us a most compelling picture of the
big bang.

The universe is not only queerer
than we suppose, it is queerer than we can suppose.

—J. B. S. Haldane

What we humans are looking for in a creation story is a way
of experiencing the world that will open to us the transcendent, that informs
us and at the same time forms ourselves within it. That is what people want.
This is what the soul asks for.

—Joseph Campbell