- A new theory of the universe suggests that space and
time may not have begun in a big bang, but may have always existed in an
endless cycle of expansion and rebirth.
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- Princeton physicist Paul Steinhardt and Neil Turok of
Cambridge University described their proposed theory in an article published
April 25 in an online edition of Science.
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- The theory proposes that, in each cycle, the universe
refills with hot, dense matter and radiation, which begins a period of
expansion and cooling like the one of the standard big bang picture. After
14 billion years, the expansion of the universe accelerates, as astronomers
have recently observed. After trillions of years, the matter and radiation
are almost completely dissipated and the expansion stalls. An energy field
that pervades the universe then creates new matter and radiation, which
restarts the cycle.
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- The new theory provides possible answers to several longstanding
problems with the big bang model, which has dominated the field of cosmology
for decades. It addresses, for example, the nagging question of what might
have triggered or come "before" the beginning of time.
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- The idea also reproduces all the successful explanations
provided by standard picture, but there is no direct evidence to say which
is correct, said Steinhardt, a professor of physics. "I do not eliminate
either of them at this stage," he said. "To me, what's interesting
is that we now have a second possibility that is poles apart from the standard
picture in many respects, and we may have the capability to distinguish
them experimentally during the coming years."
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- The big bang model of the universe, originally suggested
over 60 years ago, has been developed to explain a wide range of observations
about the cosmos. A major element of the current model, added in the 1980s,
is the theory of "inflation," a period of hyperfast expansion
that occurred within the first second after the big bang. This inflationary
period is critical for explaining the tremendous "smoothness"
and homogeneity of the universe observed by astronomers, as well as for
explaining tiny ripples in space that led to the formation galaxies.
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- Scientists also have been forced to augment the standard
theory with a component called "dark energy" to account for the
recent discovery that the expansion of the universe is accelerating.
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- The new model replaces inflation and dark energy with
a single energy field that oscillates in such a way as to sometimes cause
expansion and sometimes cause stagnation. At the same time, it continues
to explain all the currently observed phenomena of the cosmos in the same
detail as the big bang theory.
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- Because the new theory requires fewer components, and
builds them in from the start, it is more "economical," said
Steinhardt, who was one of the leaders in establishing the theory of inflation.
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- Another advantage of the new theory is that it automatically
includes a prediction of the future course of the universe, because it
goes through definite repeating cycles lasting perhaps trillions of years
each. The big bang/inflation model has no built-in prediction about the
long-term future; in the same way that inflation and dark energy arose
unpredictably, another effect could emerge that would alter the current
course of expansion.
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- The cyclic model entails many new concepts that Turok
and Steinhardt developed over the last few years with Justin Khoury, a
graduate student at Princeton, Burt Ovrut of the University of Pennsylvania
and Nathan Seiberg of the Institute for Advanced Study.
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- "This work by Paul Steinhardt and Neil Turok is
extraordinarily exciting and represents the first new big idea in cosmology
in over two decades," said Jeremiah Ostriker, professor of astrophysics
at Princeton and the Plumian Professor of Astronomy and Experimental Philosophy
at Cambridge.
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- "They have found a simple explanation for the observed
fact the universe on large scales looks the same to us left and right,
up and down -- a seemingly obvious and natural condition -- that in fact
has defied explanation for decades."
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- Sir Martin Rees, Royal Society Research Fellow at Cambridge,
noted that the physics concerning key properties of the expanding universe
remain "conjectural, and still not rooted in experiment or observation."
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- "There have been many ideas over the last 20 years,"
said Rees. "Steinhardt and Turok have injected an imaginative new
speculation. Their work emphasizes the extent to which we may need to jettison
common sense concepts, and transcend normal ideas of space and time, in
order to make real progress.
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- "This work adds to the growing body of speculative
research which intimates that physical reality could encompass far more
than just the aftermath of 'our' big bang."
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- The cyclic universe theory represents a combination of
standard physical concepts and ideas from the emerging fields of string
theory and M-theory, which are ambitious efforts to develop a unified theory
of all physical forces and particles. Although these theories are rooted
in complex mathematics, they offer a compelling graphic picture of the
cyclic universe theory.
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- Under these theories, the universe would exist as two
infinitely large parallel sheets, like two sheets of paper separated by
a microscopic distance. This distance is a extra, or fifth dimension, that
is not apparent us. At our current phase in the history of the universe,
the sheets are expanding in all directions, gradually spreading out and
dispersing all the matter and energy they contain. After trillions of years,
when they become essentially empty, they enter a "stagnant" period
in which they stop stretching and, instead, begin to move toward each other
as the fifth dimension undergoes a collapse.
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- The sheets meet and "bounce" off each other.
The impact causes the sheets to be charged with the extraordinarily hot
and dense matter that is commonly associated with the big bang. After the
sheets move apart, they resume their expansion, spreading out the matter,
which cools and coalesces into stars and galaxies as in our present universe.
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- The sheets, or branes, as physicists call them, are not
parallel universes, but rather are facets of the same universe, with one
containing all the ordinary matter we know and the other containing "we
know not what," said Steinhardt. It is conceivable, he said, that
a material called dark matter, which is widely believed to make up a significant
part of the universe, resides on this other brane. The two sheets interact
only by gravity, with massive objects in one sheet exerting a tug on matter
in the other, which is what dark matter does to ordinary matter.
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- The movements and properties of these sheets all arise
naturally from the underlying mathematics of the model, noted Steinhardt.
That is in contrast to the big bang model, in which dark energy has been
added simply to explain current observations.
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- Steinhardt and Turok continue to refine the theory and
are looking for theoretical or experimental ideas that might favor one
idea over the other.
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- "These paradigms are as far apart as you can imagine
in terms of the nature of time," said Steinhardt. "On the other
hand, in terms of what they predict about the universe, they are as close
as you can be up to what you can measure so far.
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- "Yet, we also know that, with more precise observations
that may be possible in the next decade or so, you can distinguish them.
That is the fascinating situation we find ourselves in. It's fun to debate
which ones you like better, but I really think nature will be the final
arbiter here."
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- For further information and a graphic animation of the
cyclic scenario, see http://feynman.princeton.edu/~steinh/
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- Editor's Note: The original news release can be found
at http://www.princeton.edu/pr/pwb/02/0506/0506-cyclicuniverse.htm
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- Note: This story has been adapted from a news release
issued by Princeton University for journalists and other members of the
public. If you wish to quote from any part of this story, please credit
Princeton University as the original source. You may also wish to include
the following link in any citation: http://www.sciencedaily.com/releases/2002/04/020429080540.htm
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