Parallel Worlds (3 page)

(Over the years,
one of the most embarrassing facts plaguing cosmology has been that the age of
the universe was often computed to be younger than the age of the planets and
stars, due to faulty data. Previous estimates for the age of the universe were
as low as 1 to 2 billion years, which contradicted the age of Earth [4.5
billion years] and the oldest stars [12 billion years]. These contradictions
have now been eliminated.)

The WMAP has
added a new, bizarre twist to the debate over what the universe is made of, a
question that the Greeks asked over two thousand years ago. For the past
century, scientists believed that they knew the answer to this question. After
thousands of painstaking experiments, scientists had concluded that the
universe was basically made of about a hundred different types of atoms,
arranged in an orderly periodic chart, beginning with elemental hydrogen. This
forms the basis of modern chemistry and is, in fact, taught in every high
school science class. The WMAP has now demolished that belief.

Confirming
previous experiments, the WMAP satellite showed that the visible matter we see
around us (including the mountains, planets, stars, and galaxies) makes up a
paltry 4 percent of the total matter and energy content of the universe. (Of
that 4 percent, most of it is in the form of hydrogen and helium, and probably
only 0.03 percent takes the form of the heavy elements.) Most of the universe
is actually made of mysterious, invisible material of totally unknown origin.
The familiar elements that make up our world constitute only 0.03 percent of
the universe. In some sense, science is being thrown back centuries into the
past, before the rise of the atomic hypothesis, as physicists grapple with the
fact that the universe is dominated by entirely new, unknown forms of matter
and energy.

According to the
WMAP, 23 percent of the universe is made of a strange, undetermined substance
called dark matter, which has weight, surrounds the galaxies in a gigantic
halo, but is totally invisible. Dark matter is so pervasive and abundant that,
in our own Milky Way galaxy, it outweighs all the stars by a factor of i0.
Although invisible, this strange dark matter can be observed indirectly by
scientists because it bends starlight, just like glass, and hence can be
located by the amount of optical distortion it creates.

Referring to the
strange results obtained from the WMAP satellite, Princeton astronomer John
Bahcall said, "We live in an implausible, crazy universe, but one whose
defining characteristics we now know."

But perhaps the
greatest surprise from the WMAP data, data that sent the scientific community
reeling, was that 73 percent of the universe, by far the largest amount, is
made of a totally unknown form of energy called dark energy, or the invisible
energy hidden in the vacuum of space. Introduced by Einstein himself in i9i7
and then later discarded (he called it his "greatest blunder"), dark
energy, or the energy of nothing or empty space, is now re-emerging as the
driving force in the entire universe. This dark energy is now believed to create
a new antigravity field which is driving the galaxies apart. The ultimate fate
of the universe itself will be determined by dark energy.

No one at the
present time has any understanding of where this "energy of nothing"
comes from. "Frankly, we just don't understand it. We know what its
effects are [but] we're completely clueless . . . everybody's clueless about
it," admits Craig Hogan, an astronomer at the University of Washington at
Seattle.

If we take the
latest theory of subatomic particles and try to compute the value of this dark
energy, we find a number that is off by 10
¹²⁰
(that's the number 1
followed by 120 zeros). This discrepancy between theory and experiment is far
and away the largest gap ever found in the history of science. It is one of our
greatest embarrassments—our best theory cannot calculate the value of the
largest source of energy in the entire universe. Surely, there is a shelf full
of Nobel Prizes waiting for the enterprising individuals who can unravel the
mystery of dark matter and dark energy.

INFLATION

Astronomers are
still trying to wade through this avalanche of data from the WMAP. As it sweeps
away older conceptions of the universe, a new cosmological picture is
emerging. "We have laid the cornerstone of a unified coherent theory of
the cosmos," declares Charles L. Bennett, who led an international team
that helped to build and analyze the WMAP satellite. So far, the leading theory
is the "inflationary universe theory," a major refinement of the big
bang theory, first proposed by physicist Alan Guth of MIT. In the inflationary
scenario, in the first trillionth of a trillionth of a second, a mysterious
antigravity force caused the universe to expand much faster than originally
thought. The inflationary period was unimaginably explosive, with the universe
expanding much faster than the speed of light. (This does not violate
Einstein's dictum that nothing can travel faster than light, because it is
empty space that is expanding. For material objects, the light barrier cannot
be broken.) Within a fraction of a second, the universe expanded by an unimaginable
factor of 10
⁵⁰
.

To visualize the
power of this inflationary period, imagine a balloon that is being rapidly
inflated, with the galaxies painted on the surface. The universe that we see
populated by the stars and galaxies all lies on the surface of this balloon,
rather than in the interior. Now draw a microscopic circle on the balloon. This
tiny circle represents the visible universe, everything we can see with our
telescopes. (By comparison, if the entire visible universe were as small as a
subatomic particle, then the actual universe would be much larger than the visible
universe that we see around us.) In other words, the inflationary expansion was
so intense that there are whole regions of the universe beyond our visible
universe that will forever be beyond our reach.

The inflation
was so enormous, in fact, that the balloon seems flat in our vicinity, a fact
that has been experimentally verified by the WMAP satellite. In the same way
that the earth appears flat to us because we are so small compared to the
radius of Earth, the universe appears flat only because it is curved on a much
larger scale.

By assuming that
the early universe underwent this process of inflation, one can almost
effortlessly explain many of the puzzles concerning the universe, such as why
it appears to be flat and uniform. Commenting on the inflation theory,
physicist Joel Primack has said, "No theory as beautiful as this has ever
been wrong before."

THE MULTIVERSE

The inflationary
universe, although it is consistent with the data from the WMAP satellite,
still does not answer the question: what caused inflation? What set off this
antigravity force that inflated the universe? There are over fifty proposals
explaining what turned on inflation and what eventually terminated it, creating
the universe we see around us. But there is no universal consensus. Most physicists
rally around the core idea of a rapid inflationary period, but there is no
definitive proposal to answer what the engine behind inflation is.

Because no one
knows precisely how inflation started, there is always the possibility that the
same mechanism can take place again—that inflationary explosions can happen
repeatedly. This is the idea proposed by Russian physicist Andrei Linde of
Stanford University—that whatever mechanism caused part of the universe to
suddenly inflate is still at work, perhaps randomly causing other distant
regions of the universe to inflate as well.

According to
this theory, a tiny patch of a universe may suddenly inflate and
"bud," sprouting a "daughter" universe or "baby"
universe, which may in turn bud another baby universe, with this budding
process continuing forever. Imagine blowing soap bubbles into the air. If we
blow hard enough, we see that some of the soap bubbles split in half and
generate new soap bubbles. In the same way, universes may be continually
giving birth to new universes. In this scenario, big bangs have been happening
continually. If true, we may live in a sea of such universes, like a bubble
floating in an ocean of other bubbles. In fact, a better word than
"universe" would be "multiverse" or "megaverse."

Linde calls this
theory eternal, self-reproducing inflation, or "chaotic inflation,"
because he envisions a never-ending process of continual inflation of parallel
universes. "Inflation pretty much forces the idea of multiple universes
upon us," declares Alan Guth, who first proposed the inflation theory.

This theory also
means that our universe may, at some time, bud a baby universe of its own.
Perhaps our own universe may have gotten its start by budding off from a more
ancient, earlier universe.

As the
Astronomer Royal of Great Britain, Sir Martin Rees, has said, "What's
conventionally called 'the universe' could be just one member of an ensemble.
Countless other ways may exist in which the laws are different. The universe in
which we've emerged belongs to the unusual subset that permits complexity and
consciousness to develop."

All this
research activity on the subject of the multiverse has given rise to
speculation about what these other universes may look like, whether they harbor
life, and even whether it's possible to eventually make contact with them.
Calculations have been made by

scientists at Cal Tech, MIT, Princeton, and other centers of
learning to determine whether entering a parallel universe is consistent with
the laws of physics.

M-THEORY AND THE ELEVENTH DIMENSION

The very idea of
parallel universes was once viewed with suspicion by scientists as being the
province of mystics, charlatans, and cranks. Any scientist daring to work on
parallel universes was subject to ridicule and was jeopardizing his or her
career, since even today there is no experimental evidence proving their
existence.

But recently,
the tide has turned dramatically, with the finest minds on the planet working
furiously on the subject. The reason for this sudden change is the arrival of a
new theory, string theory, and its latest version, M-theory, which promise not only
to unravel the nature of the multiverse but also to allow us to "read the
Mind of God," as Einstein once eloquently put it. If proved correct, it
would represent the crowning achievement of the last two thousand years of
research in physics, ever since the Greeks first began the search for a single
coherent and comprehensive theory of the universe.

The number of
papers published in string theory and M-theory is staggering, amounting to tens
of thousands. Hundreds of international conferences have been held on the
subject. Every single major university in the world either has a group working
on string theory or is desperately trying to learn it. Although the theory is
not testable with our feeble present-day instruments, it has sparked enormous
interest among physicists, mathematicians, and even experimentalists who hope
to test the periphery of the theory in the future with powerful gravity wave
detectors in outer space and huge atom smashers.

Ultimately, this
theory may answer the question that has dogged cosmologists ever since the big
bang theory was first proposed: what happened before the big bang?

This requires us
to bring to bear the full force of our physical knowledge, of every physical
discovery accumulated over the centuries. In other words, we need a
"theory of everything," a theory of every physical force that drives
the universe. Einstein spent the last thirty years of his life chasing after
this theory, but he ultimately failed.

At present, the
leading (and only) theory that can explain the diversity of forces we see
guiding the universe is string theory or, in its latest incarnation, M-theory.
(M stands for "membrane" but can also mean "mystery,"
"magic," even "mother." Although string theory and
M-theory are essentially identical, M-theory is a more mysterious and more
sophisticated framework which unifies various string theories.)

Ever since the
Greeks, philosophers have speculated that the ultimate building blocks of
matter might be made of tiny particles called atoms. Today, with our powerful
atom smashers and particle accelerators, we can break apart the atom itself
into electrons and nuclei, which in turn can be broken into even smaller
subatomic particles. But instead of finding an elegant and simple framework, it
was distressing to find that there were hundreds of subatomic particles
streaming from our accelerators, with strange names like neutrinos, quarks,
mesons, leptons, hadrons, gluons, W-bosons, and so forth. It is hard to believe
that nature, at its most fundamental level, could create a confusing jungle of
bizarre subatomic particles.

String theory
and M-theory are based on the simple and elegant idea that the bewildering
variety of subatomic particles making up the universe are similar to the notes
that one can play on a violin string, or on a membrane such as a drum head.
(These are no ordinary strings and membranes; they exist in ten- and eleven-
dimensional hyperspace.)

Traditionally,
physicists viewed electrons as being point particles, which were
infinitesimally small. This meant physicists had to introduce a different point
particle for each of the hundreds of subatomic particles they found, which was
very confusing. But according to string theory, if we had a supermicroscope
that could peer into the heart of an electron, we would see that it was not a
point particle at all but a tiny vibrating string. It only appeared to be a
point particle because our instruments were too crude.