What Happened Before the Big Bang? (Forwarded)

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Eberly College of Science
Pennsylvania State University
University Park, Pennsylvania

CONTACTS:
Martin Bojowald: (+1) 814-865-3502
Barbara K. Kennedy (PIO): (+1) 814-863-4682

1 July 2007

What Happened Before the Big Bang?

New discoveries about another universe whose collapse appears to have
given birth to the one we live in today will be announced in the early
on-line edition of the journal Nature Physics on 1 July 2007 and will be
published in the August 2007 issue of the journal's print edition. "My
paper introduces a new mathematical model that we can use to derive new
details about the properties of a quantum state as it travels through the
Big Bounce, which replaces the classical idea of a Big Bang as the
beginning of our universe," said Martin Bojowald, assistant professor of
physics at Penn State. Bojowald's research also suggests that, although it
is possible to learn about many properties of the earlier universe, we
always will be uncertain about some of these properties because his
calculations reveal a "cosmic forgetfulness" that results from the extreme
quantum forces during the Big Bounce.

The idea that the universe erupted with a Big Bang explosion has been a
big barrier in scientific attempts to understand the origin of our
expanding universe, although the Big Bang long has been considered by
physicists to be the best model. As described by Einstein's Theory of
General Relativity, the origin of the Big Bang is a mathematically
nonsensical state -- a "singularity" of zero volume that nevertheless
contained infinite density and infinitely large energy. Now, however,
Bojowald and other physicists at Penn State are exploring territory
unknown even to Einstein -- the time before the Big Bang -- using a
mathematical time machine called Loop Quantum Gravity. This theory, which
combines Einstein's Theory of General Relativity with equations of quantum
physics that did not exist in Einstein's day, is the first mathematical
description to systematically establish the existence of the Big Bounce
and to deduce properties of the earlier universe from which our own may
have sprung. For scientists, the Big Bounce opens a crack in the barrier
that was the Big Bang.

"Einstein's Theory of General Relativity does not include the quantum
physics that you must have in order to describe the extremely high
energies that dominated our universe during its very early evolution,"
Bojowald explained, "but we now have Loop Quantum Gravity, a theory that
does include the necessary quantum physics." Loop Quantum Gravity was
pioneered and is being developed in the Penn State Institute for
Gravitational Physics and Geometry, and is now a leading approach to the
goal of unifying general relativity with quantum physics. Scientists using
this theory to trace our universe backward in time have found that its
beginning point had a minimum volume that is not zero and a maximum energy
that is not infinite. As a result of these limits, the theory's equations
continue to produce valid mathematical results past the point of the
classical Big Bang, giving scientists a window into the time before the
Big Bounce.

Quantum-gravity theory indicates that the fabric of space-time has an
"atomic" geometry that is woven with one-dimensional quantum threads. This
fabric tears violently under the extreme conditions dominated by quantum
physics near the Big Bounce, causing gravity to become strongly repulsive
so that, instead of vanishing into infinity as predicted by Einstein's
Theory of General Relativity, the universe rebounded in the Big Bounce
that gave birth to our expanding universe. The theory reveals a
contracting universe before the Big Bounce, with space-time geometry that
otherwise was similar to that of our universe today.

Bojowald found he had to create a new mathematical model to use with the
theory of Loop Quantum Gravity in order to explore the universe before the
Big Bounce with more precision. "A more precise model was needed within
Loop Quantum Gravity than the existing numerical methods, which require
successive approximations of the solutions and yield results that are not
as general and complete as one would like," Bojowald explained. He
developed a mathematical model that produces precise analytical solutions
by solving of a set of mathematical equations.

In addition to being more precise, Bojowald's new model also is much
shorter. He reformulated the quantum-gravity models using a different
mathematical description, which he says made it possible to solve the
equations explicitly and also turned out to be a strong simplification.
"The earlier numerical model looked much more complicated, but its
solutions looked very clean, which was a clue that such a mathematical
simplification might exist," he said. Bojowald reformulated quantum
gravity's differential equations -- which require many calculations of
numerous consecutive small changes in time -- into an integrable system --
in which a cumulative length of time can be specified for adding up all
the small incremental changes.

The model's equations require parameters that describe the state of our
current universe accurately so that scientists then can use the model to
travel backward in time, mathematically "un-evolving" the universe to
reveal its state at earlier times. The model's equations also contain some
"free" parameters that are not yet known precisely but are nevertheless
necessary to describe certain properties. Bojowald discovered that two of
these free parameters are complementary: one is relevant almost
exclusively after the Big Bounce and the other is relevant almost
exclusively before the Big Bounce. Because one of these free parameters
has essentially no influence on calculations of our current universe,
Bojowald concludes that it cannot be used as a tool for back-calculating
its value in the earlier universe before the Big Bounce.

The two free parameters, which Bojowald found were complementary,
represent the quantum uncertainty in the total volume of the universe
before and after the Big Bang. "These uncertainties are additional
parameters that apply when you put a system into a quantum context such as
a theory of quantum gravity," Bojowald said. "It is similar to the
uncertainty relations in quantum physics, where there is complimentarity
between the position of an object and its velocity -- if you measure one
you cannot simultaneously measure the other." Similarly, Bojowald's study
indicates that there is complementarity between the uncertainty factors
for the volume of the universe before the Big Bounce and the universe
after the Big Bounce. "For all practical purposes, the precise uncertainty
factor for the volume of the previous universe never will be determined by
a procedure of calculating backwards from conditions in our present
universe, even with most accurate measurements we ever will be able to
make," Bojowald explained. This discovery implies further limitations for
discovering whether the matter in the universe before the Big Bang was
dominated more strongly by quantum or classical properties.

"A problem with the earlier numerical model is you don't see so clearly
what the free parameters really are and what their influence is," Bojowald
said. "This mathematical model gives you an improved expression that
contains all the free parameters and you can immediately see the influence
of each one," he explained. "After the equations were solved, it was
rather immediate to reach conclusions from the results."

Bojowald reached an additional conclusion after finding that at least one
of the parameters of the previous universe did not survive its trip
through the Big Bounce -- that successive universes likely will not be
perfect replicas of each other. He said, "the eternal recurrence of
absolutely identical universes would seem to be prevented by the apparent
existence of an intrinsic cosmic forgetfulness."

The research was sponsored, in part, by the National Science Foundation.

IMAGE CAPTION:
[http://www.science.psu.edu/alert/ima...BounceGold.jpg (166KB)]
Spreading through a bounce: A state that initially has small fluctuations
(left) bounces and develops larger fluctuations (right). Time proceeds
along the horizontal axis, with the volume plotted vertically.

Credit: Martin Bojawald, Penn State