archive: SETI [ASTRO] Scientists Conclude Anti-Gravity Force Is Accelerating

SETI [ASTRO] Scientists Conclude Anti-Gravity Force Is Accelerating

Larry Klaes ( )
Fri, 28 May 1999 12:17:34 -0400

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>Date: Fri, 28 May 1999 15:13:37 GMT
>From: Ron Baalke <>
>Subject: [ASTRO] Scientists Conclude Anti-Gravity Force Is Accelerating
Expansion of the Universe
>Reply-To: Ron Baalke <>
>Office of Communications
>Stanhope Hall, Princeton, New Jersey 08544-5264
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>Date: May 27, 1999
>Scientists Conclude Anti-Gravity Force Is Accelerating Expansion of the
>PRINCETON, N.J. -- After reviewing recent astronomical observations,
>Princeton scientists have concluded that the evidence strongly supports
>the existence of a mysterious anti-gravity force that is causing the
>expansion of the universe to accelerate.
>They presented their argument in a review article that will be published
>in the May 28 edition of the journal Science. The researchers are Neta
>Bahcall and Jeremiah Ostriker of the Department of Astrophysics and
>Paul Steinhardt of the Department of Physics, in collaboration with
>Saul Perlmutter of Berkeley National Laboratory.
>Scientists have known since the 1920s that the universe is expanding,
>and they discovered in the last year that the expansion is likely to go
>on forever. In recent months, however, evidence has emerged to suggest
>that not only will the expansion continue, it will accelerate. The only
>way to account for such acceleration is the existence of a force to
>counteract the gravitational forces that would stabilize or shrink
>the universe.
>The Princeton scientists have now bolstered that idea by reconciling
>three independent sets of data and showing that the data have a
>surprising degree of agreement. The data, some of which was generated
>at Princeton, have been used to answer three questions: How much
>matter is in the universe? Is the expansion rate slowing down or
>speeding up? And, is the universe flat? The Princeton scientists used
>a framework they call the "Cosmic Triangle," to relate the three
>questions and show for the first time how they merge into a unified
>picture of a universe that is flat, lightweight and expanding at an
>accelerating rate.
>"It's a very exciting time because we are starting to reveal the status
>of the universe and it tells us something very unexpected," says Bahcall.
>It is the acceleration idea that is most surprising, she says. Bahcall
>cautions, however, that these conjectures must be confirmed by
>further improvements in the data, which are expected to come from
>a variety of sources over the next few years.
>The expansion of the universe can be described in terms of a car
>coasting along a road as a result of a big push (the Big Bang). The mass
>of the universe, with the gravitational pull it exerts, is analogous to
>the friction and wind resistance that slow the car. In this analogy,
>there is so little resistance (gravitational tug) that the car never
>stops. The only way it could accelerate is if it were rolling downhill
>or if someone were depressing the gas pedal. The new force in the
>universe is like the downhill tug or an engine pushing the car.
>"The evidence is now getting stronger that there really is a force in
>the universe that competes with gravity and causes repulsion instead
>of attraction," says Ostriker.
>To account for this force, referred to as cosmic dark energy, scientists
>recently have revived a concept called the cosmological constant. In
>their paper, the Princeton scientists describe this cosmic dark energy
>as "a vacuum energy assigned to empty space itself, a form of energy
>with negative pressure." Einstein first introduced the cosmological
>constant in 1917, but later withdrew it, calling it the worst mistake
>of his life. Understanding the source and nature of this force poses
>deep new problems for physicists. "It's of very profound physical
>significance," says Ostriker.
>The work to explain the source of this force already has begun.
>Steinhardt, a co-author, recently introduced a possible new force
>called quintessence, which may account for the dark energy.
>Another implication of this new understanding of the universe is that
>it gives scientists a radically new picture of the future of the universe.
>It appears that the dark energy could eventually overwhelm the
>gravitational forces of matter. The density of matter in the universe
>would then become insignificant, so that the universe would approach
>an essentially uniform force field of dark energy. The researchers
>conclude that understanding dark energy, and hence the future of the
>universe, will be "one of the grand challenges of the millennium to
>Lawrence Berkeley National Laboratory
>Saul Perlmutter, (510) 486-5203,
>Paul Preuss, (510) 486-6249,
>May 25, 1999
>Dark Energy Fills The Cosmos
>BERKELEY, CA -- In an article titled "The Cosmic Triangle: Revealing the
>State of the Universe," which appears in the May 28, 1999, issue of the
>journal Science, a group of cosmologists and physicists from Princeton
>University and the Department of Energy's Lawrence Berkeley National
>Laboratory survey the wide range of evidence which, they write, "is
>forcing us to consider the possibility that some cosmic dark energy
>exists that opposes the self-attraction of matter and causes the
>expansion of the universe to accelerate."
>Dark energy is hardly science fiction, although no less intriguing and full
>of mystery for being real science.
>"The universe is made mostly of dark matter and dark energy," says Saul
>Perlmutter, leader of the Supernova Cosmology Project headquartered
>at Berkeley Lab, "and we don't know what either of them is." He credits
>University of Chicago cosmologist Michael Turner with coining the phrase
>"dark energy" in an article they wrote together with Martin White of the
>University of Illinois for Physical Review Letters.
>In the May 28 Science article, Perlmutter and Neta Bahcall, Jeremiah
>Ostriker, and Paul Steinhardt of Princeton use the concept of dark energy
>in discussing their graphic approach to understanding the past, present,
>and future status of the universe. The Cosmic Triangle is the authors'
>way of presenting the major questions cosmology must answer: "How
>much matter is in the universe? Is the expansion rate slowing down or
>speeding up? And, is the universe flat?"
>The possible answers are values for three terms in an equation that
>describes the evolution of the universe according to the general theory
>of relativity. By plotting the best experimental observations and
>estimates within the triangle, scientists can make preliminary choices
>among competing models.
>The mass density of the universe is estimated by deriving the ratio of
>visible light to mass in large systems such as clusters of galaxies, and
>in several other ways. For several decades the evidence has been building
>that mass density is low and that most of the mass in the universe is dark.
>Changes in expansion rate are estimated by comparing the redshifts of
>distant galaxies with the apparent brightness of Type 1a supernovae
>found in them. These measurements suggest that the expansion of the
>universe is accelerating.
>Curvature is estimated from measurements of the anisotropy (temperature
>fluctuation) of the cosmic microwave background radiation (CMB), a
>remnant of the Big Bang. Although uncertainty is large, current results
>suggest a flat universe.
>The Cosmic Triangle eliminates some popular models, such as a high-
>density universe that is slowing down and will eventually recollapse, as
>well as a nearly empty universe with no dark energy and low mass. While
>the evidence from galactic clusters shows that mass density is low,
>supernova evidence for acceleration shows that dark energy must be
>"These two legs of the Cosmic Triangle agree with the evidence from
>the CMB that the universe is flat," Perlmutter says, adding that "this is
>a remarkable agreement for these early days of empirical cosmology."
>Thus the Cosmic Triangle suggests that the standard inflationary
>scenario is on the right track: one of its key predictions is a flat
>Various types of dark energy have been proposed, including a cosmic
>field associated with inflation; a different, low-energy field dubbed
>"quintessence"; and the cosmological constant, or vacuum energy of
>empty space. Unlike Einstein's famous fudge factor, the cosmological
>constant in its present incarnation doesn't delicately (and artificially)
>balance gravity in order to maintain a static universe; instead, it has
>"negative pressure" that causes expansion to accelerate.
>"The term Cosmic Triangle sounds kind of New Agey," says Perlmutter,
>"but it's a good way to portray the quantities in these comparisons, and
>it's fun for people who like to plot the possibilities" -- an evolving task
>that, among other choices, will require finding an answer to "the most
>provocative and profound" issue of all, the nature of cosmic dark energy.
>The Berkeley Lab is a U.S. Department of Energy national laboratory
>located in Berkeley, California. It conducts unclassified scientific
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