Universe Born
In Fire
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Essay
posted by
The Centaur
~ April 30, 2002
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In the Beginning.
According to Genesis, the world was created
in six days - but according to modern astronomers, it didn't
even take six minutes. The Big Bang, a jazzy name for the idea
that the entire universe expanded rapidly out of a single
point, is orthodox astronomy's current creation myth. Even when astronomers
realized the Big Bang had big problems, they corrected it with a
new idea called "inflation" that is just another story about how the universe
expanded from a single point.
But now the
unthinkable has happened: a new theory has arisen that explains the
origin of the universe not by inflating points but by colliding
universes. This new "ekpyrotic model" is exotic, imagining vast
"branes" moving and colliding in five dimensional space, but might
solve some of the problems of the origin of the universe ... and in
so doing, shed light on the fundamentals of time and space.
First, A Little Background.
The power of the Big Bang model is that it explains the
extraordinary fact that the stars are rushing away from us in terms
of our understanding of how things fall down. Albert Einstein,
exploring the consequences of his new theory of gravity called
general relativity, was shocked to find that his equations predicted
the universe would expand. Astronomers did not believe
the stars were rushing away, so Einstein added a special
"cosmological constant" to his equations to make the unwanted
expansion go away.
But Einstein was too hasty. As telescopes and
methods improved, astronomers soon found that stars in distant
galaxies appeared to be receding from us, in
direct proportion to their distance. They tried for decades to
account for this expansion with a vast range of theories ranging
from fantastic antimatter explosions to steady state creation of
matter. The Big Bang at first seemed a long shot, predicting that
space should expand and that the sky should glow with the
aftereffects of the explosion. But this prediction proved
correct: the sky does glow, faintly, with microwaves called the
cosmic background radiation
. And so, emboldened by both theory
and evidence, astronomers settled upon the Big Bang as the best
available explanation.
But there's
a big problem with the Big Bang: the universe appears to be too
damn flat --- more homogenous than milk at truly astronomical
distances. That's fine for milk --- the molecules in the milk can
mix freely until the milk reaches smoothness, or equilibrium --- but
not fine for the universe. The universe's parts are too separated
and the speed of light too slow for the universe to smooth itself
out in the time it's had to expand. SO, if the Big Bang happened as
predicted, there would be "hot spots" in both the distribution of
matter and in the cosmic background --- which we don't see. A big
mystery. Astrophysicists like mysteries --- they're paid to figure
them out. So a lot of people began thinking very hard about the
problem.
Inflating the Universe.
Enter a man named Guth, who came up with the leading
contender to fix this problem: inflation theory . The idea, you see,
is to smooth out the hot spots by blowing them up. At a very early
point in its history, the universe was very hot, very dense, very
small and --- you guessed it, very homogeneous, in effective
equilbrium. Guth proposed that the physics of the hot-dense-small
universe caused it to expand violently, suddenly, expansively, under
the influence of a force called inflaton. A region smaller than a
proton blew up to a size greater than the entire visible universe,
making the universe appear, as far as light can shine, to be almost
completely flat.
Now the
challenge: making the physics of inflation work. For this,
astrophysicists, the surveyors of the unimaginably large, turned to
particle physicists, probers of the preturnaturally small.
Physicists have been plugging away for quite some time trying to
come up with a simple description of the universe that can fit on a
T-shirt --- for aesthetic or marketing reasons no one can say.
Maxwell did it for electricity and magetism in the 1800s, and a trio
of bright particle physicists did it in the 1960's for
electromagetism and the so-called "weak" force that governs certain
kinds of radioactivity. But gravity --- Einstein's baby, "matter
tells space how to bend and bent space tells matter how to move" ---
and the "strong force" --- which binds the nuclei of atoms together
--- resisted physicists' advances.
Tying Up A Few Loose Ends.
The best luck was had by a German mathematician called
Kaluza, who in the mid 1920's wrote Einstein's equations down in
five dimensions instead of four and found that --- voila! ---
electromagnetism just "fell out". Of course, the extra dimension was
a bit worrisome, and no-one paid attention to another German
mathematician, Klein, who pointed out that we could make the extra
dimension go away by "rolling it up" --- just in the same way that
the surface of a garden hose is 'effectively' one dimensional
because its second dimension a short small circuit insignificant
with respect to its great length.
Fast forward
fifty years. In the absence of a unified theory, a lot of bright
people, including luminaries like Richard Feynman, worked to
reconcile electromagnetism, the strong force, relativity and quantum
mechanics with the virtual zoo of particles flying out of modern
particle accelerators --- pions, mesons, the W, the Z --- and
produced another alphabet soup of theories called QED and QCD and so
on. As they did so, a few people began to realize that the old ideas
of Kaluza and Klein didn't look so crazy after all. If you imagined
that this zoo of particles were not points, but strings, then all of
forces could easily be unified and all particles easily accounted
for. True, the mathematics required extra dimensions, just as Kaluza
predicted --- but now instead of five dimensions, it was ten or even
sixteen --- yet the mathematics practically demanded that most of
these dimensions roll up into invisibility, just as Klein predicted.
Dozens,
hundreds of versions of these "string" and "gauge" theories
proliferated --- SO(32) symmetry, heterotic strings, bosonic
strings, and so on. Many of these theories were of very great
delight to astrophysicists, providing them with candidate sources
for the "inflaton" field. Many of these theories were of very great
disappointment to particle physicists, experimental physicists, and
Richard Feynman, because while the theories were mathematically very
pretty, there was no known way to test them.
Enter the Branes. One
candidate for a unified theory proposed an unusual configuration of
all those rolled up dimensions: two universes, living "side by
side", unable to influence each other at all, or at the very most
through gravity alone. Our universe is like the surface of an ocean,
its four-dimensional physics determined by a five-dimensional
reality beneath the waves; out there may be other surfaces parallel
to our own that we never see. Elegant, yes; but as unprovable as all
other string and gauge theories. Nothing distinguished this theory
from a dozen others --- until a man named Ovrut and a group of
physicists working with him realized that these surfaces, these
"branes" could collide, and violently --- producing a universe not
entirely unlike the Big Bang that we see.
The
Ekpyrotic Model of the origin of the universe postulates that our
universe was a vast, formless void, virtually empty of matter and
life until it "collided" with another brane in a unvisualizable
space of higher dimensions. The collision heated the universe
intensely over a vast period of time, triggering the expansion we
now call the Big Bang. The latest version of the model, proposed by
Steinhardt and Turok, turns this expansion into a cycle: the
universe continues to expand until all matter has cooled and all
particles are separated, leaving a vast formless void, virtually
empty of matter and life, awaiting a collision with another brane
that will start the whole process over again.
So in one
sense the ekpyrotic model is nothing new. It is based on known
mathematics. It predicts the traditional Big Bang. And it takes its
very name from the ancient Greek idea that the universe was created
in a vast conflagration of fire. Yet there is one key difference -
the ekypyrotic model makes predictions. Testable
predictions about how the matter in the early universe will be
distributed --- similar enough to what is known to be interesting,
but different enough from the inflationary model that they can be
told apart.
In other
words, if the ekpyrotic model is true, we will be able to see the
signature of the theory of everything written in the very background
of the sky.
With
Microwave Eyes. And with that, we can see the excitement.
Astrophysicists, fighting for years to explain unnatural smoothness,
at last found a theory from particle physics that just might explain
what they see. Particle physicists, struggling for years to explain
nature with exceptional elegance, at last found an elegant theory
that can be tested against evidence. And as a result, the universe
is stranger than we imagined. It is more than length and width and
depth and time: it has a strange fifth dimension separating us from
a world which is a mirror of our own --- a fifth dimension which we
can never see, except when we look close at each particle running
through its tiny subatomic courses; and a mirror world we can never
know, except when we look up at the sky with microwave eyes and
wonder at the heavens' unnatural calm.
-The Centaur
Renaissance Engineer