Paul Steinhardt's universe is a lot like the workaday world of many people, a
cycle of early vigor, spent energy, exhausted return, and new beginnings.
However, in Steinhardt's universe, there is absolutely no end to the cycle.
The Princeton physicist and his colleague, Neil Turok of Cambridge
University, have developed a whole new theory for how the universe came to be.
Their proposal seeks to explain recently uncovered flaws in the scientifically
accepted model for the origin and evolution of all known things. It describes a
series of big bangs and equally significant crunches that form a never-ending
cycle of rejuvenation and destruction.
In this universe -- our universe -- time never ends.
The current leading theory for the universe holds that it emerged from a
single Big Bang sometime around 12 billion to 15 billion years ago, undergoing
an early and rapid period of inflation. That much remains widely accepted.
"However, the standard model has some cracks," Steinhardt and Turok write in
a paper published today in the online version of the journal Science.
Astronomers have in recent years learned that the universe is not just
expanding, but is doing so at an ever-increasing pace. This can't be explained
given the known matter and energy that exists. To account for the acceleration,
theorists have conjured a product they call
,
which supposedly repels things rather than attracting, as gravity does.
No one has seen this dark energy, and scientists don't even know what it is.
But they say it's all around us.
More important, it shouldn't be there.
"The recent discoveries of cosmic acceleration and gravitationally
self-repulsive dark energy were not predicted and have no particular role in the
standard model," Steinhardt and Turok argue. "Furthermore, the standard model
does not explain the ‘beginning of time,' the initial conditions of the
universe, or what will happen in the long-term future."
So to patch some of the theoretical cracks, Steinhardt and Turok envision a
universe based on perpetual expansion and contraction.
Here's how it works, and keep in mind we're jumping into the middle of the
explanation: A big bang sends everything outward. Matter and radiation develop.
Dark energy drives an expansion -- as is presently underway -- that lasts
trillions of years. Finally, the matter, radiation, and even black holes are
"diluted away," leaving the universe smooth, empty, and flat.
Then everything contracts in a so-called big crunch, and a fresh cycle
begins.
"In this picture, space and time exist forever, Steinhardt says. "The big
bang is not the beginning of time. Rather, it is a bridge to a pre-existing
contracting era."
Curiously, the cyclic universe, as it is called, puts the origin of some
present-day structures and events prior to the Big Bang.
While existing theory states that galaxies and large clusters of galaxies
developed from lumps and filaments that formed in the otherwise smooth fabric of
space and time shortly after the Big Bang, Steinhardt thinks the seeds of galaxy
formation were created by instabilities that arose during the last contraction,
before the crunch that led to "our" bang.
The new model "turns the conventional picture topsy-turvy," he says.
The cyclic universe has roots in even more complex thoughts like so-called
superstring theory, which suggests there are as many as 10 spatial dimensions,
not just the three we know of. The seemingly inexplicable physics of a big
crunch and a big bang might be explained with the aid of these extra dimensions,
which are otherwise invisible to us, several theorists believe.
In fact, Steinhardt, Turok and others proposed last year that our universe
might have sprung from the collapse of an extra dimension, an idea they called
the
