Math Mutation 68: The Bogus Bang?
We're all used to the Big Bang theory by now, the standard
model of cosmology that says our universe started out with a
infinitely hot, dense point and suddenly expanded outward. You've
also probably heard of superstring theory, which I've mentioned a few
times before in this podcast. Among other things, this predicts that
the universe actually contains 11 dimensions, not just the three we
can see, and in fact we are living on some kind of gigantic
three-dimensional membrane, or "brane", floating within this
higher-dimensional space. These two theories don't seem to
inherently contradict each other, to a layman at least, but in fact
there are a lot of details of the Big Bang, especially the way it
describes the first moments of our universe, that have made some
physicists nervous. Recently I was intrigued to read in Rudy Rucker's
blog about a new theory, created a few years ago by physicists Paul
Steinhardt of Princeton and Neil Turok of Cambridge, that uses this
new view of the multidimensional nature of our universe to replace the
Big Bang model with something a bit different.
The basic idea is that if we are living on a three-dimensional
membrane floating around a multidimensional space, why should it be
the only one? Suppose there are other, similar branes floating
around. What happens when a pair collide? Steinhardt and Turok
investigated this question, and spent over a year trying to work on
the equations that would describe this situation. They discovered
that when two of these membranes get close, they would begin to ripple
and distort. Then at some point, the peaks of a pair of ripples would
collide, and create an effect very similar to the Big Bang! The
force of the impact would cause a burst of energy and a rapid
expansion of space, just as in the Big Bang theory, and due to the
various peaks and valleys in the ripples, there would be hot and cold
spots after the collision. These hot and cold spots correspond to
what we actually observe in the universe. This new model is known as
the "ekpyrotic" model, from the Greek word for conflagration.
What's even more interesting, though, is the long-term future in
this model. Currently, with the expansion of the universe
accelerating, the Big Bang theory predicts that our universe will
slowly become essentially empty as all particles of matter accelerate
away from each other. But in the new theory, the nearby neighbor
brane that we originally collided with will still be out there,
floating in multidimensional space-- and eventually, there will be
another collision between the two now-empty branes, that will form
another Big Bang-like explosion and start the cycle of matter all over
again. So, insteead of just being on a long path to emptiness, this
says we live in a cyclic universe, which will eventually renew itself
and start again.
As with any new theory, though, there is quite a bit of
controversy. Like the Big Bang theory, this theory still suffers from
a singularity, that is a point where its equations break down, at the
very beginning of the universe. And even Steinhardt has a disclaimer
on his web page that this idea is based on unproven ideas in string
theory. There is work underway to try to find evidence one way or the
other, in the form of gravity waves that would exist in the Big Bang
but not the ekpyrotic theory, but results will be a long way off.
Still, it's fascinating to think that, as professor David
Spergel of Princeton has said, maybe "everything that astronomers
have ever observed is just a speck within the higher dimensions, and
all of history since the Big Bang is but an instant in the infinity of
time."
And this has been your Math Mutation for today.
References:
BBC
article summarizing the ekpyrotic model
Discover
magazine article on the new theory
Professor
Steinhardt's introduction to ekpyrotic models
Rudy Rucker's blog entry on this topic