Andrew Yee
May 16th 06, 03:30 AM
Office of Public Information
Eberly College of Science
Penn State
University Park, Pennsylvania
SCIENCE CONTACTS:
Abhay Ashtekar (by phone after 1 June), (+1)814-863-9601
Tomasz Pawlowski (by phone before 1 June), (+1)865-2924
Parmpreet Singh (by phone before 1 June), (+1)865-2924
PIO CONTACT:
Barbara Kennedy, (+1)814-863-4682
12 May 2006
Penn State Researchers Look Beyond the Birth of the Universe
According to Einstein's general theory of relativity, the Big Bang
represents The Beginning, the grand event at which not only matter but
space-time itself was born. While classical theories offer no clues about
existence before that moment, a research team at Penn State has used quantum
gravitational calculations to find threads that lead to an earlier time.
"General relativity can be used to describe the universe back to a point at
which matter becomes so dense that its equations don't hold up," says Abhay
Ashtekar, Holder of the Eberly Family Chair in Physics and Director of the
Institute for Gravitational Physics and Geometry at Penn State. "Beyond that
point, we needed to apply quantum tools that were not available to
Einstein." By combining quantum physics with general relativity, Ashtekar
and two of his post-doctoral researchers, Tomasz Pawlowski and Parmpreet
Singh, were able to develop a model that traces through the Big Bang to a
shrinking universe that exhibits physics similar to ours.
In research reported in the current issue of Physical Review Letters, the
team shows that, prior to the Big Bang, there was a contracting universe
with space-time geometry that otherwise is similar to that of our current
expanding universe. As gravitational forces pulled this previous universe
inward, it reached a point at which the quantum properties of space-time
cause gravity to become repulsive, rather than attractive. "Using quantum
modifications of Einstein's cosmological equations, we have shown that in
place of a classical Big Bang there is in fact a quantum Bounce," says
Ashtekar. "We were so surprised by the finding that there is another
classical, pre-Big Bang universe that we repeated the simulations with
different parameter values over several months, but we found that the Big
Bounce scenario is robust."
While the general idea of another universe existing prior to the Big Bang
has been proposed before, this is the first mathematical description that
systematically establishes its existence and deduces properties of
space-time geometry in that universe.
The research team used loop quantum gravity, a leading approach to the
problem of the unification of general relativity with quantum physics, which
also was pioneered at the Penn State Institute of Gravitational Physics and
Geometry. In this theory, space-time geometry itself has a discrete 'atomic'
structure and the familiar continuum is only an approximation. The fabric of
space is literally woven by one-dimensional quantum threads. Near the
Big-Bang, this fabric is violently torn and the quantum nature of geometry
becomes important. It makes gravity strongly repulsive, giving rise to the
Big Bounce.
"Our initial work assumes a homogenous model of our universe," says
Ashtekar. "However, it has given us confidence in the underlying ideas of
loop quantum gravity. We will continue to refine the model to better portray
the universe as we know it and to better understand the features of quantum
gravity."
The research was sponsored by the National Science Foundation, the Alexander
von Humboldt Foundation, and the Penn State Eberly College of Science.
IMAGE CAPTION:
[http://www.science.psu.edu/alert/images/AshtekarFigure.jpg (27KB)]
The figure represents our expanding universe as the right branch of the arc.
Our time now is located at the 1.8 grid mark on the right side of the
drawing. According to Ashtekar's team's calculations, when looking backward
throughout the history of the universe, 'time' does not go to the point of
the Big Bang but bounces to the left branch of the drawing, which describes
a contracting universe. Singh explains, "The state of the universe depicted
by its wavefunction is shown in space (mu) and time(phi). The big bang
singularity lies where space vanishes (goes to zero). Our expanding phase of
the universe is shown by the right branch which, when reversed backward in
time, bounces near the Big Bang to a contracting phase (left branch) and
never reaches the Big Bang."
Eberly College of Science
Penn State
University Park, Pennsylvania
SCIENCE CONTACTS:
Abhay Ashtekar (by phone after 1 June), (+1)814-863-9601
Tomasz Pawlowski (by phone before 1 June), (+1)865-2924
Parmpreet Singh (by phone before 1 June), (+1)865-2924
PIO CONTACT:
Barbara Kennedy, (+1)814-863-4682
12 May 2006
Penn State Researchers Look Beyond the Birth of the Universe
According to Einstein's general theory of relativity, the Big Bang
represents The Beginning, the grand event at which not only matter but
space-time itself was born. While classical theories offer no clues about
existence before that moment, a research team at Penn State has used quantum
gravitational calculations to find threads that lead to an earlier time.
"General relativity can be used to describe the universe back to a point at
which matter becomes so dense that its equations don't hold up," says Abhay
Ashtekar, Holder of the Eberly Family Chair in Physics and Director of the
Institute for Gravitational Physics and Geometry at Penn State. "Beyond that
point, we needed to apply quantum tools that were not available to
Einstein." By combining quantum physics with general relativity, Ashtekar
and two of his post-doctoral researchers, Tomasz Pawlowski and Parmpreet
Singh, were able to develop a model that traces through the Big Bang to a
shrinking universe that exhibits physics similar to ours.
In research reported in the current issue of Physical Review Letters, the
team shows that, prior to the Big Bang, there was a contracting universe
with space-time geometry that otherwise is similar to that of our current
expanding universe. As gravitational forces pulled this previous universe
inward, it reached a point at which the quantum properties of space-time
cause gravity to become repulsive, rather than attractive. "Using quantum
modifications of Einstein's cosmological equations, we have shown that in
place of a classical Big Bang there is in fact a quantum Bounce," says
Ashtekar. "We were so surprised by the finding that there is another
classical, pre-Big Bang universe that we repeated the simulations with
different parameter values over several months, but we found that the Big
Bounce scenario is robust."
While the general idea of another universe existing prior to the Big Bang
has been proposed before, this is the first mathematical description that
systematically establishes its existence and deduces properties of
space-time geometry in that universe.
The research team used loop quantum gravity, a leading approach to the
problem of the unification of general relativity with quantum physics, which
also was pioneered at the Penn State Institute of Gravitational Physics and
Geometry. In this theory, space-time geometry itself has a discrete 'atomic'
structure and the familiar continuum is only an approximation. The fabric of
space is literally woven by one-dimensional quantum threads. Near the
Big-Bang, this fabric is violently torn and the quantum nature of geometry
becomes important. It makes gravity strongly repulsive, giving rise to the
Big Bounce.
"Our initial work assumes a homogenous model of our universe," says
Ashtekar. "However, it has given us confidence in the underlying ideas of
loop quantum gravity. We will continue to refine the model to better portray
the universe as we know it and to better understand the features of quantum
gravity."
The research was sponsored by the National Science Foundation, the Alexander
von Humboldt Foundation, and the Penn State Eberly College of Science.
IMAGE CAPTION:
[http://www.science.psu.edu/alert/images/AshtekarFigure.jpg (27KB)]
The figure represents our expanding universe as the right branch of the arc.
Our time now is located at the 1.8 grid mark on the right side of the
drawing. According to Ashtekar's team's calculations, when looking backward
throughout the history of the universe, 'time' does not go to the point of
the Big Bang but bounces to the left branch of the drawing, which describes
a contracting universe. Singh explains, "The state of the universe depicted
by its wavefunction is shown in space (mu) and time(phi). The big bang
singularity lies where space vanishes (goes to zero). Our expanding phase of
the universe is shown by the right branch which, when reversed backward in
time, bounces near the Big Bang to a contracting phase (left branch) and
never reaches the Big Bang."