A Theory Of Everything?
Page 9
PARALLEL UNIVERSES
One of the principles of quantum cosmology is that we must treat the
entire universe just like we treat a quantum particle, and the simplest
particle is the electron. As students learn in chemistry class, we never
know for certain which energy level an electron is in; quantum
fluctuations are always bouncing an electron into various energy levels
simultaneously.
Similarly, once we treat the universe like an electron, then we are
forced to conclude that the universe can exist in several different
states simultaneously, i.e. parallel universes.
The simplest analogy is that of boiling of water, which is a quantum
mechanical effect. Tiny bubbles constantly form in the water, which then
expand very rapidly. If we treat the universe like a bubble, then we see
that our universe co-exists with an infinite sea of other bubbles. Our
universe, then, may be nothing but a quantum bubble, a quantum
fluctuation in an infinite ocean frothing with universes, which is
constantly generating new universes, called the "multiverse." In this
picture, Big Bangs are constantly taking place, each representing a
quantum fluctuation in the vacuum. (Treating the universe as a quantum
fluctuation was first proposed by Prof. Edward Tryon of Hunter College).
Creating universes out of Nothing may seem to violate cherished
conservation principles, until we realize that it takes no energy to
create a universe. If the universe is closed like a bubble, then the
energy content of its matter is positive, while the energy of its
gravity is negative: the sum is exactly zero. Thus, it takes no net
energy to create new bubbles, which are constantly being created in the
sea of Nothing.
[To visualize negative energy, think of the earth in the solar system,
or a dog stuck in a hole. In each case, we have to add (italicize "add")
energy to pull the earth out of the solar system into deep space, or the
dog out of the hole. Since we define deep space and the ground outside
the hole to have zero energy, both the earth and the dog originally have
negative gravitational energy).
Universes are for free. There is a free lunch, after all, and it is
called a universe. (This doesn't help if you are trying to create a
universe in the laboratory. As Alan Guth, originator of the
"inflationary universe," has pointed out, one would have to heat up
matter to l,000 trillion trillion degrees to create a "baby universe" in
your basement! The net energy of this system, however, might still be
zero, since the gravitational energy is negative and cancels the
positive energy of the system).
Andre Linde of Stanford University, one of the pioneers of the
inflationary universe, believes that these bubbles are constantly
churning and peeling off other bubbles. Writing in the cover article in
the Nov. issue of Scientific American, he said, "If my colleagues and I
are right, we may soon be saying good-bye to the idea that our universe
was a single fireball created in the Big Bang."
GENESIS OR NIRVANA?
This new picture of cosmology creates a new twist on religious
mythology. In theology, most myths concerning the origin of the universe
fall into one of two categories: the Judeo-Christian myth of Genesis (or
the Cosmic Egg), which describes a definite instant called Creation, or
the Hindu-Buddhist myth of Nirvana, which states that the universe is
endless, with no beginning in time or space. In this new picture, we are
combining these two mythologies into one coherent picture: We have a
constant genesis, or boiling of universes, being born in an ocean of
cosmic Nothing or Nirvana.
I was once interviewed on Australian Broadcasting Co. along with Nobel
laureate Steve Weinberg and cosmologist Paul Davies. When I mentioned
this picture of millions of Big Bangs constantly emerging from Nothing,
Weinberg said, "I find this an attractive picture and [it's] certainly
worth thinking about very seriously. An important implication is that
there wasn't a beginning; that there were increasingly large Big Bangs,
so that the [multiverse] goes on forever - one doesn't have to grapple
with the question of it before the Bang. The [multiverse] has just been
here all along. I find that a very satisfying picture."
Weinberg cautioned, however, that there may not be life in these other
universes. Most of them, in fact, are probably dead universes, where the
proton lifetime is less than, say, 10 billion years, the minimum time
necessary to create stable organic chemicals, DNA, and life itself.
These other universes may be lifeless, consisting of a sea of neutrinos,
photons, and electrons, incapable of combining to form life. Our
universe, in fact, may be one of the few universes that are compatible
with life.
ANTHROPIC PRINCIPLE REVISITED
This compelling picture of Creation emerging from quantum cosmology may
also solve the curious puzzle of the "anthropic principle." Cosmologists
have long noticed a remarkable observation, that the fundamental
constants of the universe fall within an exceedingly narrow band which
is compatible with life. Is life, therefore, a special property of the
universe? As Freeman Dyson of the Institute for Advanced Study has said,
"It's as if the universe were expecting us." For example, if the
electric charge or the gravitational constant were changed slightly,
then stable DNA molecules would not be possible. The "strong anthropic
principle," in fact, concludes that this proves the existence of a
divine entity or God.
Some physicists have objected to the anthropic principle, stating that
it can never be tested, i.e. it cannot be falsified, and therefore is
not a scientific principle. Perhaps. But this does not explain the
origin of this remarkable "coincidence."
In quantum cosmology, however, we have a simple explanation; perhaps
there are an infinite number of possible universes, with different
physical constants. We just happen to live in the one that is compatible
with life. That is why we are here to discuss the question in the first
place. So it is not an accident at all that the physical constants are
compatible with life; we co-exist with plenty of dead universes where
the physical constants are not compatible with stable DNA-type
molecules.
LIFE IN A PARALLEL UNIVERSE
But if most of the universes are dead universes, this raises the
ticklish question of whether some of the universes might look just like
ours. Some of them, in fact, may be carbon copies of our own universe,
except with a tiny quantum twist.
There is the story of a Russian physicist visiting the United States for
the first time, asking to be taken to Las Vegas. Considering him to be a
seasoned gambler, his American hosts were curious to learn what his
gambling strategy might be. The Russian said that he would put all his
money, every penny, on the first bet. But, his hosts protested, "That's
a ridiculous strategy." "Yes," he replied, "but in one parallel
universe, I shall be rich beyond my wildest imagination!"
Strange, but perhaps true. In millions of other universes, however, he
will be broke!
This raises another delicate question: can we visit these parallel
universes? Can we walk down Main Street one day, only to find a hole in
space emerging in front of us, leading us to another dimension or
universe, like some episode of the Twilight Zone? Or can we wake up one
morning finding ourselves in a world where our loved ones never heard o
walk down Main Street one day, only to find a hole in space emerging in
front of us, leading us to another dimension or universe, like some
episode of the Twilight Zone? Or can we wake up one morning finding
ourselves in a world where our loved ones never heard of us?
So in principle, the answer is yes, wormholes connect our universe with
others. But don't worry about falling into one. After performing a rough
back-of-the-envelope estimate of the probability of such an event, I
find that it won't happen within the lifetime of the known universe!
THE 10TH DIMENSION
There is still, however, an important defect in this picture, which is
still largely qualitative. Once we try to mathematically calculate these
quantum fluctuations that give rise to new universes, the answer blows
up, i.e. the theory becomes meaningless. Simply splicing Einstein's
general theory of relativity with the quantum theory is too crude. The
problem of constructing a true, rigorous quantum theory of gravity -
i.e. a unification of quantum theory with general relativity - has, in
fact, frustrated the finest minds of the 20th century, including
Einstein.
Once, Nobel laureate Wolfgang Pauli presented his proposal for a theory
of everything while Niels Bohr was in the audience. Bohr was not
impressed. He raised his hand and said, "We in the audience are all
agreed that your theory is crazy. But what divides us is whether your
theory is crazy enough."
All the "sane" proposals for a theory of everything have been shown to
be mathematically inconsistent. We are forced, in fact, to go to a
higher theory, which unifies both general relativity and the quantum
theory into a coherent whole. At present, the only (I repeat: only)
candidate for a theory of everything is the superstring theory.
Superstring theory is certainly crazy enough. It postulates that the
particles we see in the universe, including the atoms in our bodies, are
composed of tiny, vibrating strings. The resonances or "notes" of the
strings determine the particle "zoo" (electrons, quarks, photons, etc.).
The universe is a symphony of vibrating strings, and the laws of harmony
are the known laws of physics.
Einstein once asked the question, "Did God have any choice in making the
universe?" Apparently not. The principles of general relativity and the
quantum theory are so alien to each other that any theory which melds
them into a coherent whole must not only have enormous power, it must
also be highly constrained.
A theory of everything must satisfy two important criteria
a) at large distances, it must reproduce Einstein's theory of gravity,
but at small distances, it must reproduce the quantum theory of
particles.
b) it must be simple conceptually
These conditions are so stringent that there may be only one solution to
them.
What is surprising, however, is that superstring theory is so
constrained that it fixes the dimension of space and time to be 10! The
unique feature of superstring theory is that these tiny strings (about
100 billion billion times smaller than a proton) can only vibrate in 10
dimensional space-time.
Mystics, charlatans, philosophers, and science fiction writers have
always been fascinated by higher dimensions. But we now have a
mathematical reason for believing in 10 dimensional space-time: only in
that dimension do we have "enough room" to accommodate both the quantum
theory and Einstein's theory! (If we write down superstring theories in,
say, 11 or 12 dimensions, the theory becomes mathematically
inconsistent. A universe starting out in these dimensions is apparently
not stable and will decay down to 10 dimensions.)
This gives us a startling new picture of quantum cosmology. These
bubbles are actually 10 dimensional bubbles, but they are unstable. Our
bubble, soon after itactually 10 dimensional bubbles, but they are
unstable. Our bubble, soon after its creation, "fissioned" in half, into
four and six dimensional universes. The six dimensional universe
collapsed, these dimensions are so "curled up" (they are 10 trillion
trillion times smaller than an atom) we can't see them. But the collapse
of the six dimensional universe allowed our four dimensional universe to
expand, giving us the expanding universe that we see today.
This also means that there may be bubbles which fission into 5, 6, 7,
etc. dimensions. However, once again one can show that these bubbles are
probably not compatible with life. Physics tells us that stable solar
systems, atoms, and protons can probably only exist in our four
dimensional universe. Our universe is four dimensional because if it
weren't, we probably wouldn't be here to debate the question in the
first place.
TESTING THE UNTESTABLE
There is a fundamental difference, however, between religious mythology
and quantum cosmology. Mythology makes no pretense of being scientific;
it fails the test of being "falsifiable," i.e. there is no experiment
which can rigorously exclude the possibility of miracles, angels, etc.
which are not (by definition) reproducible. Quantum cosmology, however,
may eventually be verified or falsified. But we do not have to wait
until we fall into a parallel universe to test these ideas.
For example, the COBE satellite detected tiny ripples in the otherwise
uniform microwave background radiation. This is significant, because
these ripples most likely correspond to quantum fluctuations that
existed at the instant of the Big Bang. We are, in fact, "children" of
these ripples. The quantum fluctuations at the beginning of time
gradually grew in size over billions of years, becoming the galaxies,
stars, and planets that we see today.
Other "tests" of this scenario may come from dark matter. Numerous
observations have conclusively verified the existence of a mysterious,
new form of matter which makes up perhaps 90% of the mass of the
universe. For example, our own Milky Way Galaxy is so lightweight that
it would have disintegrated billions of years ago if it weren't held
together by a large hollow sphere that extends several hundred thousand
light years beyond the edge of our galactic disk, weighing 10 times as
much as the stars in our galaxy. One of the leading candidates for dark
matter is a new form of matter called "sparticles" (short for super
particles), which are some of the lowest frequency vibrations of the
superstring. Early in the next century, we should be able to identify
the precise nature of dark matter, which in turn should verify or rule
out many of the conjectures in superstring theory and quantum cosmology.
Looking further ahead, we may one day even detect a new form of "relic"
radiation left over from the Big Bang, the neutrino background (see
"Curtains at the Edge of the Universe," November 1995). If this
notoriously elusive radiation can be detected, then we will have a snap
shot of the universe when it was only 3 seconds old! Then "ripples" on
the neutrino background will give us a breathtaking look into the cosmic
fireball itself.
So what's the farthest object in the multiverse? Probably something
floating in a bubble-universe and dimension far, far away. As the
British philosopher J.B.S. Haldane once said, "Our universe is not only
queerer than we suppose, it is queerer than we can suppose."
Send mail to Dr. Kaku at [email protected]
Sheila Na Gig
Send e-mail to [email protected]
Copyright © 1999 Sheila Na Gig.
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