Parallel Worlds (38 page)

The Greek
philosopher Democritus, who hypothesized the existence of atoms, wrote,
"There are worlds infinite in number and different in size. In some there
is neither sun nor moon. In others, there are more than one sun and moon. The
distances between the worlds are unequal, in some directions there are more of
them . . .

Their
destruction comes about through collision with one another. Some worlds are
destitute of animal and plant life and of all moisture."

By 2002, in
fact, astronomers had discovered one hundred extra- solar planets that were
orbiting other stars. Extrasolar planets are being discovered at the rate of
one every two weeks or so. Since ex- trasolar planets do not give off any light
of their own, astronomers identify them via various indirect means. The most
reliable is to look for the wobbling of the mother star, which moves back and
forth as its Jupiter-sized planet circles around it. By analyzing the Doppler
shift of the light emitted from the wobbling star, one can calculate how fast
it is moving and use Newton's laws to calculate the mass of its planet.

"You can
think of the star and the large planet as dance partners, spinning around while
clasping their outstretched hands. The smaller partner on the outside is moving
greater distances in a larger circle, while the larger inside partner only
moves his or her feet in a very small circle—the movement around the very small
inner circle is the 'wobble' that we see in these stars," says Chris
McCarthy of the Carnegie Institution. This process is now so accurate that we
can detect tiny variations in velocity of 3 meters per second (the speed of a
brisk walk) in a star hundreds of light-years away.

Other, more
ingenious methods are being proposed to find even more planets. One is to look
for a planet when it eclipses the mother star, which leads to a slight decrease
in its brightness as the planet passes in front of the star. And within fifteen
to twenty years, NASA will send its interferometry space satellite into orbit,
which will be able to find smaller, Earth-like planets in outer space. (Since
the brightness of the mother star overwhelms the planet, this satellite will
use light interference to cancel out the mother star's intense halo, leaving
the Earth-like planet unobscured.)

So far, none of
the Jupiter-sized extrasolar planets we've discovered resembles our Earth, and
all are probably dead. Astronomers have discovered them in highly eccentric
orbits or in orbits extremely close to their mother star; in either case, an
Earth-like planet within a Goldilocks zone will be impossible. In these solar
systems, the Jupiter-sized planet would cross the Goldilocks zone and fling
any small Earth-sized planet into outer space, preventing life as we know it
from forming.

Highly eccentric
orbits are common in space—so common, in fact, that when a "normal"
solar system was discovered in space, it made headlines in 2003. Astronomers in
the United States and Australia alike heralded the discovery of a Jupiter-sized
planet orbiting the star HD 70642. What was so unusual about this planet
(about twice the size of our Jupiter) was that it was in a circular orbit in
roughly the same ratio as Jupiter is to our sun.

In the future,
however, astronomers should be able to catalog all the nearby stars for
potential solar systems. "We are working to place all 2,000 of the nearest
sun-like stars under survey, all the sunlike stars out to 150
light-years," says Paul Butler of the Carnegie Institution of Washington,
who was involved in the first discovery of an extrasolar planet in i995.
"Our goal is two-fold—to provide a reconnaissance—a first census—of our
nearest neighbors in space, and to provide the first data to address the
fundamental question, how common or how rare is our own solar system," he
says.

COSMIC ACCIDENTS

In order to
create life, our planet must have been relatively stable for hundreds of
millions of years. But a world that is stable for hundreds of millions of
years is astonishingly difficult to make.

Start with the way
atoms are made, with the fact that a proton weighs slightly less than a
neutron. This means that neutrons eventually decay into protons, which occupy
a lower energy state. If the proton were just i percent heavier, it would decay
into a neutron, and all nuclei would become unstable and disintegrate. Atoms
would fly apart, making life impossible.

Another cosmic
accident that makes life possible is that the proton is stable and does not
decay into an antielectron. Experiments have shown that the proton lifetime is
truly astronomical, much longer than the lifetime of the universe. For the
purpose of creating stable DNA, protons must be stable for at least hundreds of
millions of years.

If the strong
nuclear force were a bit weaker, nuclei like deuterium would fly apart, and
none of the elements of the universe could have been successively built up in
the interior of stars via nucleosynthesis. If the nuclear force were a bit
stronger, stars would burn their nuclear fuel too quickly, and life could not
evolve.

If we vary the
strength of the weak force, we also find that life once again is impossible.
Neutrinos, which act via the weak nuclear force, are crucial to carry the
energy outward from an exploding supernova. This energy, in turn, is responsible
for the creation of the higher elements beyond iron. If the weak force were a
bit weaker, neutrinos would interact hardly at all, meaning that supernovae
could not create the elements beyond iron. If the weak force were a bit
stronger, neutrinos might not escape properly from a star's core, again
preventing the creation of the higher elements that make up our bodies and our
world.

Scientists have,
in fact, assembled long lists of scores of such "happy cosmic
accidents." When faced with this imposing list, it's shocking to find how
many of the familiar constants of the universe lie within a very narrow band
that makes life possible. If a single one of these accidents were altered,
stars would never form, the universe would fly apart, DNA would not exist,
life as we know it would be impossible, Earth would flip over or freeze, and so
on.

Astronomer Hugh
Ross, to emphasize how truly remarkable this situation is, has compared it to a
Boeing 747 aircraft being completely assembled as a result of a tornado
striking a junkyard.

THE ANTHROPIC PRINCIPLE

Again, all the
arguments presented above are lumped together under the anthropic principle.
There are several points of view one can take concerning this controversial
principle. My second-grade teacher felt that these happy coincidences implied
the existence of a grand design or plan. As physicist Freeman Dyson once said,
"It's as if the universe knew we were coming." This is an example of
the strong anthropic principle, the idea that the fine-tuning of the physical
constants was not an accident but implies a design of some sort. (The weak
anthropic principle simply states that the physical constants of the universe
are such that they make life and consciousness possible.)

Physicist Don Page has summarized the various forms of the
an- thropic principle that have been proposed over the years:

weak anthropic principle: "What we observe about the
universe is restricted by the requirement of our existence as observers."

strong-weak anthropic principle: "In at least one world
... of the many-worlds universe, life must develop."

strong anthropic principle: "The universe must have the
properties for life to develop at some time within it."

final anthropic principle:
"Intelligence must develop within the universe and then never die
out."

One physicist
who takes the strong anthropic principle seriously, and claims that it is a
sign of a God, is Vera Kistiakowsky, a physicist at MIT. She says, "The
exquisite order displayed by our scientific understanding of the physical
world calls for the divine." A scientist who seconds that opinion is John
Polkinghorne, a particle physicist who gave up his position at Cambridge
University and became a priest of the Church of England. He writes that the
universe is "not just 'any old world,' but it's special and finely tuned
for life because it is the creation of a Creator who wills that it should be
so." Indeed, Isaac Newton himself, who introduced the concept of immutable
laws which guided the planets and stars without divine intervention, believed
that the elegance of these laws pointed to the existence of God.

But the
physicist and Nobel laureate Steven Weinberg is not convinced. He acknowledges
the appeal of the anthropic principle: "It is almost irresistible for
humans to believe that we have some special relation to the universe, that
human life is not just a more-or-less farcical outcome of a chain of accidents
reaching back to the first three minutes, but that we were somehow built in
from the beginning." However, he concludes that the strong anthropic
principle is "little more than mystical mumbo jumbo."

Others are also
less convinced about the anthropic principle's power. The late physicist Heinz
Pagels was once impressed with the anthropic principle but eventually lost
interest because it had no predictive power. The theory is not testable, nor is
there any way to extract new information from it. Instead, it yields an endless
stream of empty tautologies—that we are here because we are here.

Guth, too, dismisses
the anthropic principle, stating that, "I find it hard to believe that
anybody would ever use the anthropic principle if he had a better explanation
for something. I've yet, for example, to hear an anthropic principle of world
history . . . The anthropic principle is something that people do if they can't
think of anything better to do."

MULTIVERSE

Other
scientists, like Sir Martin Rees of Cambridge University, think that these
cosmic accidents give evidence for the existence of the multiverse. Rees believes
that the only way to resolve the fact that we live within an incredibly tiny
band of hundreds of "coincidences" is to postulate the existence of
millions of parallel universes. In this multiverse of universes, most universes
are dead. The proton is not stable. Atoms never condense. DNA never forms. The
universe collapses prematurely or freezes almost immediately. But in our universe,
a series of cosmic accidents has happened, not necessarily because of the hand
of God but because of the law of averages.

In some sense,
Sir Martin Rees is the last person one might expect to advance the idea of
parallel universes. He is the Astronomer Royal of England and bears much
responsibility for representing the establishment viewpoint toward the
universe. Silver-haired, distinguished, impeccably dressed, Rees is equally
fluent speaking about the marvels of the cosmos as about the concerns of the
general public.

It is no
accident, he believes, that the universe is fine-tuned to allow life to exist.
There are simply too many accidents for the universe to be in such a narrow
band that allows for life. "The apparent fine-tuning on which our
existence depends could be a coincidence," writes Rees. "I once
thought so. But that view now seems too narrow . . . Once we accept this,
various apparently special features of our universe—those that some theologians
once adduced as evidence for Providence or design—occasion no surprise."

Rees has tried
to give substance to his arguments by quantifying some of these concepts. He
claims that the universe seems to be governed by six numbers, each of which is
measurable and finely tuned. These six numbers must satisfy the conditions for
life, or else they create dead universes.

First is Epsilon,
which equals 0.007, which is the relative amount of hydrogen that converts to
helium via fusion in the big bang. If this number were 0.006 instead of 0.007,
this would weaken the nuclear force, and protons and neutrons would not bind
together. Deuterium (with one proton and one neutron) could not form, hence the
heavier elements would never have been created in the stars, the atoms of our
body could not have formed, and the entire universe would have dissolved into
hydrogen. Even a small reduction in the nuclear force would create instability
in the periodic chart of the elements, and there would be fewer stable
elements out of which to create life.

If Epsilon were
0.008, then fusion would have been so rapid that no hydrogen would have
survived from the big bang, and there would be no stars today to give energy to
the planets. Or perhaps two protons would have bound together, also making
fusion in the stars impossible. Rees points to the fact that Fred Hoyle found
that even a shift as small as 4 percent in the nuclear force would have made
the formation of carbon impossible in the stars, making the higher elements
and hence life impossible. Hoyle found that if one changed the nuclear force
slightly, then beryllium would be so unstable that it could never be a
"bridge" to form carbon atoms.

Second is N,
equal to io3
⁶
, which is the strength of the electric force divided
by the strength of gravity, which shows how weak gravity is. If gravity were
even weaker, then stars could not condense and create the enormous temperatures
necessary for fusion. Hence, stars would not shine, and the planets would
plunge into freezing darkness.