Ron Garrett

Latest Observations Steal Thunder
From the Classic Big Bang Theory
On the list of cosmology's greatest hits, one that many scientists put near the top of the charts came in 1965, when astronomers at Bell Labs in New Jersey were getting pretty fed up with the constant hiss from the Labs' radio antenna.
Arno Penzias and Robert Wilson suspected it was the result of pigeon droppings in the antenna. But the noise didn't come from messy birds, they discovered. It was a whisper of energy that filled the cosmos -- and, astronomers deduced, the afterglow of a hot Big Bang that created the universe some 14 billion years ago. There was a genesis moment, the cosmic hiss implied, when space and time began.
Today, the Big Bang is facing a challenge. Since the mid-1990s, observations have required many ad hoc fixes to the theory -- so many that a few cosmologists have begun to think like homeowners with much-patched roofs: maybe it's time for a whole new structure.
A new theory of the origin of the cosmos is now being proposed by astrophysicists Paul Steinhardt of Princeton University and Neil Turok of Cambridge University: an oscillating universe that expands, stops, contracts and then bounces back in an eternal cycle. "The universe undergoes an endless sequence of cosmic epochs which begin with a bang and end in a crunch," the scientists will propose in a May issue of the journal Science. (Prof. Turok has a cool simulation of a bouncing cosmos at <a href="http://www.damtp.cam.ac.uk/user/ngt10001.)" target="_blank">www.damtp.cam.ac.uk/user/ngt10001.)</a>
The reigning theory is called the inflationary Big Bang. It says that a random blip (a "quantum fluctuation" to the cognoscenti) got things rolling, creating an infinitesimal bit of spacetime from nothingness. (This may sound like a scenario cooked up by someone smoking funny cigarettes, but pages of equations support it.) The blip expanded. That's the Big Bang part. In the next quadrillionth of a quadrillionth of a second, the nascent universe ballooned in size by a factor of 10 to the 50th power. That's the inflation part.
Since its development in the 1980s, inflation has elegantly explained mysteries such as why the universe is homogeneous, and why galaxies are scattered across the sky just so. When nonscientists asked embarrassing questions, like what came before the Big Bang, cosmologists shushed them. The Big Bang created time itself, goes the party line; there was no "before."
That left even some scientists uneasy. Worse for inflation theory, though, was that observations it never predicted kept popping up. The most dramatic came in 1998, when studies of distant exploding stars, called supernovas, suggested the universe is expanding faster as time goes by, not slowing down as a 14-billion-year-old should. The leading explanation of cosmic acceleration is that "dark energy" fills the cosmos and works like antigravity, pushing things apart and accelerating the expansion. With that, it really began to seem like cosmologists were making it up as they went along.
The current model has become too encumbered, says Prof. Steinhardt. "First there was the Big Bang, then inflation got grafted onto that, then dark energy and cosmic acceleration got added," he says. "It looks like a patchwork. Plus, it doesn't explain the beginning of time."
As he and Prof. Turok worked through equations, a possibility emerged: The universe might expand faster and faster before it stops, contracts, bounces and begins a new cycle. If they are right, we are 14 billion years into the current bounce, which will last trillions of years.
A bouncing universe replicates all the successes of the inflationary Big Bang. Even better, dark energy and cosmic acceleration emerge naturally rather than getting slapped on like mortar on a crumbling edifice. And in a bouncing universe, time neither begins nor ends. That's not to say a bouncing universe is universally embraced. "There are certainly questions in cosmology that have yet to be understood, but there are even more questions in their model," says cosmologist Andreas Albrecht of the University of California, Davis. "Like how do you collapse the universe and bounce it?"
Nature might some day reveal which account of genesis is right. Ripples in space, or gravitational waves, might look different in a cyclic universe than after a Big Bang.
But "right" in science is relative. Science lets astronomers listen to the music of the spheres, marshal the equations of physics and infer the birth of the universe. Yet even its greatest triumphs are tentative, only as good as the next observation. Right or wrong, the idea of a cyclic universe shows science at its best: It doesn't rest on its laurels.

SmashingIdols

Wow.

Just the other day I asked the question in one of the infidel forums if there was alternative theory to the Big Bang - noting that its adherants were displaying some remarkably Christian contortions in its explanation (Big Bang Apologetics)!

In any case, the best part of the article was the last sentence. And that's the way it should be.

SmashingIdols

Link to <a href="http://feynman.princeton.edu/~steinh/" target="_blank">Paul Steinhardts home-page</a>, which includes numerous PDFs, including those explaining his Cyclic Model of the Universe.

ex-robot

Cool. Do you have a link?

xr

Gooch's dad

Nice post, Ron, but the link to the simulation doesn't work.

Coragyps

Does this mean the Hindus have been right all along?

eh

Well I don't see why this must be labeled as an opponent to the big bang theory. Perhaps it is just a different explaination as to what went bang?

This theory has actually been around since this month last year, but has quickly evolved into a cyclic model. This creates the problem of infinite regress, which the BB seemed to have solved. Why must the ekpyrotic model have an infinite past? Is it not possible that these membranes were formed from a vacuum fluctuation, with a net energy of zero? If so, there needs to be a mechanism to allow a vacuum fluctuation to grow so large, and inflation sounds like a good place to start.

If that is the case, wouldn't a simpler explaination have a vacuum fluctuation inflating to a massive expanding fireball, eliminating the need for a collison completely? I don't see what this theory can explain - that inflation can't explain easier.

Any thoughts?

Ron Garrett

The physics of it all is utterly beyond me, since the last physics course I took was in 1971. The last lecture I attended on the topic was one at which Penzias spoke at U of W in the late 80's. I'm a social scientist, so this is out of my area other than curiosity. It remains fascinating to me that in a country where physicists are propounding such theories we still have some theists insisting the earth is flat and the Apollo program was a hoax.