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Topic: Dark energy

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In the News (Thu 21 Mar 19)

  Dark Energy - MSN Encarta
Using Einstein’s relationship between mass and energy, physicists can use the astronomical measurements for the acceleration rate to calculate how much dark energy there is. They calculated that dark energy contributes about 74 percent of the total density of mass and energy in the universe.
A possible explanation of dark energy that fits very simply within the framework of Einstein’s theory of general relativity is the existence of a cosmological constant.
Dark energy is not associated with matter or with electromagnetic radiation.
encarta.msn.com /encyclopedia_701835433_2/Dark_Energy.html   (1657 words)

  Dark energy - Wikipedia, the free encyclopedia
In physical cosmology, dark energy is a hypothetical form of energy which permeates all of space and has strong negative pressure.
Specifically, when the volume of the universe doubles, the density of dark matter is halved but the density of dark energy is nearly unchanged (it is exactly constant in the case of a cosmological constant).
, The Cosmological Constant, and Dark Energy and the Preposterous Universe.
en.wikipedia.org /wiki/Dark_energy   (2938 words)

 'Dark Energy' Might Not Exist Say Scientists
Not unlike dark energy, dark matter is an unseen substance that astronomers believe pervades the cosmos, but it is different.
Dark matter, which would comprise more than 90% of the weight of the universe, is thought to betray its existence through its gravitational pull on nearby objects.
The accelerated cosmic expansion, which prompted the dark energy idea, was detected in 1998 through observations of distant exploding stars known as supernovae.
www.rense.com /general69/darkenergymight.htm   (909 words)

 Dark energy star - Wikipedia, the free encyclopedia
The theory states that infalling matter is converted into vacuum energy, or dark energy as the matter falls through the event horizon.
The dark energy star is a different concept than that of a gravastar.
When the matter falls through the event horizon, the energy equivalent of some or all of that matter is converted into dark energy.
en.wikipedia.org /wiki/Dark_energy_star   (493 words)

 ZPEnergy.com - Worldwide Exclusive: 'Dark Energy' bomb more powerful than thermonuke!
The ratio of pressure to energy density is characterized by the square of the internal velocity divided by c2.
Dark energy is characterized by an "equation of state," which is the ratio w (pronounced "dubya") of its pressure to its energy density w = p/r.
That dark energy was unimportant in the past is good: This fact means the repulsive gravity of dark energy doesn't interfere with the attractive gravity of dark matter that drives the formation of cosmic structure.
www.zpenergy.com /modules.php?name=News&file=article&sid=919   (2758 words)

 CNN.com - Chandra unlocking mystery of 'dark energy' - May 18, 2004
"Dark energy is perhaps the biggest mystery in physics," said Steve Allen at the Institute of Astronomy in Cambridge, England.
According to scientists, dark energy is the force that fills the space between galaxies and drives them apart.
Chandra's probe of dark energy relies on the X-ray observations to study the hot gas in galaxy clusters.
www.cnn.com /2004/TECH/space/05/18/dark.energy/index.html?eref=sitesearch   (478 words)

 Dark Energy Fills the Cosmos   (Site not responding. Last check: 2007-08-19)
Dark energy is hardly science fiction, although no less intriguing and full of mystery for being real science.
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.
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.
www.lbl.gov /Science-Articles/Archive/dark-energy.html   (464 words)

 Dark Energy at Redshift Z=1 -- Physics News Update 802
Dark energy, the unidentified force that's pushing the universe to expand at ever faster rates, was already at work as early as nine billion years ago, scientists reported last week.
The data show that the repulsive action of dark energy was already active at that time, and are consistent with a constant energy density -- in other words, with an energy of the vacuum that does not dilute itself as the universe expands, eventually fueling an exponential growth of the universe.
For more recent ages, dark energy is known to have been constant up to a 10 percent variation.
www.aip.org /pnu/2006/split/802-1.html   (705 words)

 The Preposterous Universe   (Site not responding. Last check: 2007-08-19)
Dark matter and dark energy are not theoretical constructs which were invented by cosmologists because they seemed interesting; observational data have forced us into positing their existence.
Dark matter contributes to the total gravitational field of galaxies and clusters, which we measure by observing the velocities of nearby particles, or the deflection of light passing by.
Dark energy is smoothly distributed, but affects the geometry of spacetime itself: it makes distant galaxies appear to accelerate away from us, and it "flattens" the geometry of space, two effects which have been directly observed.
pancake.uchicago.edu /~carroll/preposterous.html   (662 words)

 Astronomy - Dark energy's long history - Provided by STScI
Dark energy is a mysterious repulsive force that causes the universe to expand at an increasing rate.
This picture of dark energy is consistent with Albert Einstein's prediction of nearly a century ago that a repulsive form of gravity emanates from empty space.
Riess led one of the first studies to reveal the presence of dark energy in 1998 and is the leader of the current Hubble study.
www.astronomy.com /asy/default.aspx?c=a&id=4675   (844 words)

 Universe Today - Chandra Furthers Understanding About Dark Energy
"Dark energy is perhaps the biggest mystery in physics," said Steve Allen of the Institute of Astronomy (IoA) at the University of Cambridge in England, and leader of the study.
Better limits on the amount of dark energy and how it varies with time are obtained by combining the X-ray results with data from NASA's Wilkinson Microwave Anisotropy Probe (WMAP), which used observations of the cosmic microwave background radiation to discover evidence for dark energy in the very early Universe.
Allen and his colleagues stress that the uncertainties in the measurements are such that the data are consistent with dark energy having a constant value.
www.universetoday.com /am/publish/chandra_furthers_dark_energy.html?1852004   (1018 words)

 Dark Energy and Dark Matter – The Results of Flawed Physics?
Dark energy and dark matter were originally conceived to explain, respectively, the accelerating expansion of the universe (despite the tendency of gravity to push matter together) and the discrepancy between the amount of matter scientists expect to observe in the universe but have not yet found.
The dark matter isn't restricted just to the visible matter and it has a rather filamentary structure, independent to galaxies shape, which refuses all the hypothesis about observable matter origin of dark matter.
By Aether Wave theory (AWT) the dark matter is the result of the shock wave collisions during inflation phase of universe evolution.
www.physorg.com /news77190620.html   (1093 words)

 3. Hark! Dark energy!
"Dark energy is a quality of flying apart, we think it's associated with a vacuum itself." Under that explanation, quantum energy found in a vacuum is somehow governing the overall shape of the universe.
In naming dark energy the science story of 2003, Science magazine, like other observers, raised a delicious irony: in 1917, Albert Einstein, invented a "cosmological constant," to help explain the overall movement of the universe.
"Dark energy could be the modern equivalent of the cosmological constant that Einstein is alleged to have called his 'greatest blunder,'" says Kirshner.
www.whyfiles.org /197dark_energy_old_gal/3.html   (1402 words)

 Astronomy - Does dark energy really exist? - Amanda Gefter
Dark energy, that stealthy ghost that lurks in the shadows of the universe, is now believed by most scientists to be a strange but significant occupant of the cosmos, an unidentified antigravity that is stretching the very fabric of space.
The fuzzy object at the center of the frame is one of the galaxy clusters observed by XMM-Newton in its investigation of the distant universe.
If dark energy is vanquished by these recent observations, cosmologists will have to rethink the perplexing universe they've grown to know and love.
www.astronomy.com /asy/default.aspx?c=a&id=2102   (636 words)

 HETDEX - Dark Energy Experiment
Dark energy is the mysterious property that consists of over 70% of the total energy in the Universe.
Although dark energy makes up 70% of the total energy in the Universe, we have no idea what it is or from where it comes.
Discovering the nature of dark energy is certainly one of astronomy's most exciting prospects for this century.
www.as.utexas.edu /hetdex   (1252 words)

 Chandra :: Photo Album :: Galaxy Clusters and Dark Energy :: 18 May 04
Dark matter, an invisible and unknown type of material, is postulated to hold clusters together.
Assuming that dark energy is responsible for the acceleration, combining the Chandra results with observations of the cosmic microwave background radiation indicates that dark energy makes up about 75% of the Universe, dark matter about 21%, and visible matter about 4%.
The new Chandra results suggest that the dark energy density may be constant.
chandra.harvard.edu /photo/2004/darkenergy   (651 words)

 Dark energy confirmed as constant presence - Space.com - MSNBC.com
While scientists are not ready to close the case, they said today that dark energy, which is thought to permeate the cosmos and work in opposition to gravity, does appear to be a constant presence as predicted.
Dark energy was conjured to explain a phenomenal discovery in 1998: Nearly all galaxies in the universe are receding from each other at an ever-faster pace.
They theorize that about 70 percent of the universe is made up of dark energy, while most of the rest is another mysterious thing called dark matter and only a small fraction is real matter like stars, planets and living entities.
msnbc.msn.com /id/4327735   (1189 words)

 Dark Energy
Furthermore, the Universe is dominated by a mysterious dark energy, which causes the cosmic expansion to accelerate.
Dark energy started its long history in 1917 and was introduced by Albert Einstein.
We do not know what the nature of dark energy is, and unveiling this mystery will most probably reveal new physics and even might shake modern particle physics to its very foundations.
www.astro.uni-bonn.de /~webiaef/outreach/posters/darkenergy   (1196 words)

 Rubber Band Invoked to Explain Dark Energy
A new theory invokes the common rubber band in an attempt to explain dark energy, a mysterious force causing the universe to expand at an ever-increasing pace.
Dark energy was conjured to explain the antigravity that must be at work.
The increasing tension is the infamous dark energy, explained Neal Weiner, a physicist at the university and another member of the study team.
www.space.com /scienceastronomy/acceleron_darkenergy_040727.html   (770 words)

 Dark energy dates back nine billion years (November 2006) - News - PhysicsWeb   (Site not responding. Last check: 2007-08-19)
To be effective, dark energy must account for about 70% of all energy in the universe -- but it has yet to be detected and physicists don’t really know if its behaviour remains constant or if it changes over time.
A consequence of the constant is that energy density of empty space is the same regardless of whether the universe was expanding.
The data suggest that the effect of dark energy was rather weak until about five to six billion years ago when it defeated gravity in a “cosmic tug of war” and the rate of expansion began to increase.
www.physicsweb.org /articles/news/10/11/16/1   (523 words)

 Unveiling the Dark Energy - The Expanding Universe
Furthermore, the data strongly suggest that an unidentified form of energy is the cause of the accelerating expansion.
The dark energy may be what Albert Einstein called the "cosmological constant," an arbitrary term he added to the general theory of relativity to make sure it described a static universe.
But its primary mission is to discover the nature of the dark energy that accelerates the expansion of the universe.
www.firstscience.com /SITE/ARTICLES/dark.asp   (1092 words)

 Dartmouth News - The next frontier for cosmologists: dark energy - 05/04/01
Ramping up the energy of colliding protons or electrons in particle accelerators (such as at Fermilab or CERN), physicists have been able to explore new phenomena that must have been prevalent at even earlier times in the universe.
Dark energy has its most direct effect on the cosmos through the rate of expansion, so measuring astrophysical phenomena like supernovae or the abundance of galaxies at different points along deep probes of space should reveal information about the evolution of the universe.
Unless the dark energy really is constant, and Caldwell doesn't think so, theorists expect to find wiggles and lumps in the distribution of the dark energy, which in turn influence both the distribution of galaxies and the temperature patterns of the cosmic microwave background (CMB).
www.dartmouth.edu /~news/releases/2001/may01/universe.html   (585 words)

 dark energy — FactMonster.com
Although dark energy is predicted in particle physics, it has never been directly observed.
It is generally agreed, however, that dark energy dominates the universe, which is projected to have a composition of c.70% dark energy, c.30%
The concept of dark energy was first proposed, and then discarded, by Albert Einstein early in the 20th cent.
www.factmonster.com /ce6/sci/A0921524.html   (359 words)

 'Dark energy' theory of universe challenged | Chron.com - Houston Chronicle
Conventional wisdom holds that the mysterious force, called "dark energy," may make up 70 percent of the universe, and could be the determining factor in whether it is eventually destroyed billions of years from now.
When he later discovered that the universe was expanding, he called the cosmological constant his "greatest blunder," but dark energy revived the idea of an anti-gravity force.
However, according to the new study, no anti-gravity factor like dark energy or cosmological constant is needed to explain the forces of the universe.
www.chron.com /disp/story.mpl/space/3097096.html   (605 words)

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