Author Topic: Elusive dark energy is real, study says  (Read 838 times)

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Offline U-238

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Elusive dark energy is real, study says
« on: September 14, 2012, 06:32:03 PM »
Dark energy, the mysterious substance thought to be accelerating the expansion of the universe, almost certainly exists despite some astronomers' doubts, a new study says.

After a two-year study, an international team of researchers concludes that the probability of dark energy being real stands at 99.996 percent. But the scientists still don't know what the stuff is.

"Dark energy is one of the great scientific mysteries of our time, so it isn’t surprising that so many researchers question its existence," co-author Bob Nichol, of the University of Portsmouth in Engalnd, said in a statement. "But with our new work we’re more confident than ever that this exotic component of the universe is real — even if we still have no idea what it consists of."

The roots of dark energy
Scientists have known since the 1920s that the universe is expanding. Most assumed that gravity would slow this expansion gradually, or even cause the universe to begin contracting one day. [8 Baffling Astronomy Mysteries]

But in 1998, two separate teams of researchers discovered that the universe's expansion is actually speeding up. In the wake of this shocking find — which earned three of the discoverers the Nobel Prize in Physics in 2011 — researchers proposed the existence of dark energy, an enigmatic force pushing the cosmos apart.

Dark energy is thought to make up 73 percent of the universe, though no one can say exactly what it is. (Twenty-three percent of the universe is similarly strange dark matter, scientists say, while the remaining 4 percent is "normal" matter that we can see and feel.)

Still, not all astronomers are convinced that dark energy is real, and many have been trying to confirm its existence for the past decade or so.

.Hunting for dark energy
One of the best lines of evidence for the existence of dark energy comes from something called the Integrated Sachs Wolfe effect, researchers said.

In 1967, astronomers Rainer Sachs and Arthur Wolfe proposed that light from the cosmic microwave background (CMB) radiation — the thermal imprint left by the Big Bang that created our universe — should become slightly bluer as it passes through the gravitational fields of lumps of matter.

Three decades later, other researchers ran with the idea, suggesting astronomers could look for these small changes in the light's energy by comparing the temperature of the distant CMB radiation with maps of nearby galaxies.

If dark energy doesn't exist, there should be no correspondence between the two maps. But if dark energy is real, then, strangely, the CMB light should be seen to gain energy as it moves through large lumps of mass, researchers said.

This latter scenario is known as the Integrated Sachs Wolfe effect, and it was first detected in 2003. However, the signal is relatively weak, and some astronomers have questioned if it's really strong evidence for dark energy after all.

Re-examining the data
In the new study, the researchers re-examine the arguments against the Integrated Sachs Wolfe detection, and they update the maps used in the original work.

In the end, the team determined that there is a 99.996 percent chance that dark energy is responsible for the hotter parts of the CMB maps, researchers said.

"This work also tells us about possible modifications to Einstein’s theory of general relativity," said lead author Tommaso Giannantonio, of Ludwig-Maximilian University of Munich in Germany.

"The next generation of cosmic microwave background and galaxy surveys should provide the definitive measurement, either confirming general relativity, including dark energy, or even more intriguingly, demanding a completely new understanding of how gravity works," Giannantonio added.

The team's findings have been published in the journal Monthly Notices of the Royal Astronomical Society.
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Offline Oceander

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Re: Elusive dark energy is real, study says
« Reply #1 on: September 15, 2012, 01:18:34 AM »
Still reminds me of the aether that Einstein dispelled.
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Offline U-238

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Re: Elusive dark energy is real, study says
« Reply #2 on: September 15, 2012, 05:41:11 PM »
Still reminds me of the aether that Einstein dispelled.

Einstein's Biggest Blunder? Dark Energy May Be Consistent With Cosmological Constant
ScienceDaily (Nov. 28, 2007) — Einstein's self-proclaimed "biggest blunder" -- his postulation of a cosmological constant (a force that opposes gravity and keeps the universe from collapsing) -- may not be such a blunder after all, according to the research of an international team of scientists that includes two Texas A&M University researchers.

The team is working on a project called ESSENCE that studies supernovae (exploding stars) to figure out if dark energy -- the accelerating force of the universe -- is consistent with Einstein's cosmological constant.

Texas A&M researchers Nicholas Suntzeff and Kevin Krisciunas are part of the project, which began in October of 2002 and is scheduled to end next month after achieving its goal of discovering and studying 200 supernovae. The team uses a 4-meter diameter telescope in Chile during the observing season of October to December to find the supernovae.

In 1917, Einstein was working on his Theory of General Relativity and was trying to come up with an equation that describes a static universe -- one that stands still and does not collapse under the force of gravity in a big crunch. In order to keep the universe static in his theory, Einstein introduced a cosmological constant -- a force that opposes the force of gravity.

Then, 12 years later, Edwin Hubble discovered that the universe is not static -- it is actually expanding. So Einstein scrapped his idea of a cosmological constant and dismissed it as his biggest blunder.

In 1998, however, two teams of scientists, one of which Texas A&M researcher Suntzeff co-founded, discovered that the universe is not only expanding, but its expansion is actually accelerating -- going faster and faster.

"So there had to be some other force that had overcome the force of gravity and is driving the universe into an exponential acceleration," Suntzeff said. This opposing force is what scientists now call dark energy, and it is believed to constitute roughly 74 percent of the universe. The other constituents of the universe are dark matter, which composes about 22 percent of the universe, and ordinary matter, which is about 4 percent.

"Eighty years later, it turns out that Einstein may have been right [about a cosmological constant]," Krisciunas said. "So he was smarter than he gave himself credit for."

The type of supernovae that the ESSENCE team studies all give off the same amount of energy and have essentially the same peak brightness. Researchers can compare the observed brightness of a supernova that they see in the sky to its known actual brightness to figure out how far away the supernova is.

Researchers also look at what is called the redshift of the supernova, which tells them how fast the universe is expanding. When scientists compare the distance of the supernova to its redshift, they can measure the acceleration of the expansion of the universe. This acceleration is caused by the force scientists call dark energy.

The ESSENCE team can then use the value of the acceleration to figure out the density of dark energy, which they then use to calculate what is called the w-parameter. For Einstein's cosmological constant to be correct, the w-parameter must equal -1, and so far, the results of the ESSENCE project seem to confirm that it is indeed very close to -1.

"The magic value is -1 exactly," Krisciunas said. "If the number turns out to be precisely -1, then this dark energy is a relatively simple thing -- it is Einstein's cosmological constant." The team won't have the final results until later next year, but right now, the measurement is coming in at -1 plus or minus 10 percent error, Suntzeff said, so the initial data seems to point to Einstein being correct.

"We can never test [dark energy] in the laboratory, so astronomers have to measure it [through observational data], and one of the ways we're measuring it is with supernovae in the ESSENCE project," Suntzeff said. "Dark energy is completely unexplained by conventional physics. Perhaps this is a manifestation of the 5th dimension from string theory. Or maybe it is a new vacuum energy density that is changing slowly in time. We have no idea, and that is what excites both physicists and astronomers."
"To do a great right, do a little wrong."(Merchant of Venice Act 4, Scene 1
“If the freedom of speech is taken away then dumb and silent we may be led, like sheep to the slaughter” – George Washington

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