Starship Asterisk*

Dark energy, the mysterious cosmic force thought to be the fuel behind the accelerating expansion of the universe, is real, according to an Anglo-German team of astronomers.

After a two-year study, scientists at the University of Portsmouth in the United Kingdom and LMU University Munich in Germany have concluded that the likelihood of dark energy's existence stands at 99.996 percent.']

That's the same level of certainty as this year's celebrated discovery of the Higgs boson, or a subatomic particle that looks very much like it, by scientists at the CERN research center near Geneva.

A 2009 simulation of dark matter in the Universe: Researcher now say they are (almost) certain it exists.

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Although accepted by many scientists as the best explanation for why the universe is expanding at an ever-faster rate, the theory of dark energy has its skeptics.

Astronomers studying the brightness of distant supernovae over a decade ago won the 2011 Nobel Prize for Physics for their conclusion that the expansion of the universe was accelerating.

But some scientists argue this is an illusion, caused by the relative movement of Earth in relation to the rest of the cosmos.

Others suggest shortcomings in our understanding of gravity are more likely responsible than dark energy.

'Dark energy is one of the great scientific mysteries of our time, so it isn't surprising that so many researchers question its existence,' said Bob Nichol, a member of the Portsmouth team involved in the research, which was published in the academic journal Monthly Notices of the Royal Astronomical Society.

'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.

Dark energy DOES exist and it's increasingly driving our universe apart, scientists claim

Einstein proved right over universe: It is expanding at EXACTLY the speed he predicted - driven by 'dark energy'

A basic premise of modern cosmology is that the visible universe of stars, planets and gases makes up about 4 percent of the cosmos and is sitting like flotsam in a massive sea of unknown material referred to as dark energy.

Dark energy is thought to make up 73 percent of the cosmos, while the slightly less mysterious dark matter comprises the remaining 23 percent.

One of the strongest pieces of evidence for dark energy is in the so-called Integrated Sachs Wolfe effect.

In 1967, Rainer Sachs and Arthur Wolfe theorized that light from the radiation from the heat left over from the Big Bang, would become slightly more blue as it passed through the gravitational fields of lumps of matter in the universe, an effect known as gravitational redshift.

The existence of dark energy would cause light from this residual radiation to gain energy as it travels through large lumps of mass.

In 1996, astronomers Robert Crittenden and Neil Turok suggested overlaying a map of the local universe on the picture of the residual cosmic radiation could provide clues about where to look for the effect. In 2003, it was spotted, albeit weakly.

Researchers have spent decades investigating the phenomenon - but have never been able to prove it actually exists.

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It was seen as supporting evidence for dark energy and hailed as the 'Discovery of the Year' in Science magazine.
But some scientists argued it could have been caused by cosmic dust and questioned the discovery.

The Anglo-German team that carried out the latest study was led by Crittenden and Tommaso Giannantonio.

They re-examined all the arguments against the detection and have improved the maps used in the original work.

They conclude that dark energy is almost certainly responsible for the hotter parts of the cosmic microwave background.

'We have methodically addressed all of these issues and concluded none of them can explain the observations we see,' Nichol told Reuters. ']

'In the end, the only remaining explanation is dark energy - if it walks like a duck and quacks like a duck, it's probably a duck.'

Radio telescopes like the huge Square Kilometre Array that will be sited in remote areas in South Africa and Australia, should improve the tricky process of measuring distances in the universe and give more definitive data, he said.

"What dark energy could be, theoretically, is another question," Nichol said.

geckzilla wrote:Why is that article all about dark energy but then it has a picture with a caption about dark matter? Confused writer?

geckzilla wrote:
Why is that article all about dark energy but then it has a picture with a caption about dark matter? Confused writer?

A basic premise of modern cosmology is that the visible universe of stars, planets and gases makes up about 4 percent of the cosmos and is sitting like flotsam in a massive sea of unknown material referred to as dark energy.

geckzilla wrote:

A basic premise of modern cosmology is that the visible universe of stars, planets and gases makes up about 4 percent of the cosmos and is sitting like flotsam in a massive sea of unknown material referred to as dark energy.

:incredulous:

neufer wrote:

geckzilla wrote:
Why is that article all about dark energy but then it has a picture with a caption about dark matter? Confused writer?

Actually, dark matter is an important part of the discussion in the dark energy article
(but the writer is no doubt confused as well).

In 1967, Rainer Sachs and Arthur Wolfe theorized that light from the radiation from the heat left over from the Big Bang, would become slightly more blue as it passed through the gravitational fields of lumps of matter in the universe, an effect known as gravitational redshift.

Ann wrote:
I was confused at this:

In 1967, Rainer Sachs and Arthur Wolfe theorized that light from the radiation from the heat left over from the Big Bang, would become slightly more blue as it passed through the gravitational fields of lumps of matter in the universe, an effect known as gravitational redshift.

Surely a gravitational redshift wouldn't cause light to become bluer?

• Photons are "surfing" the modulated gravitational wells:

http://en.wikipedia.org/wiki/Sachs%E2%80%93Wolfe_effect wrote:

<<The Sachs–Wolfe effect, named after Rainer Kurt Sachs and Arthur Michael Wolfe, is a property of the cosmic microwave background radiation (CMB), in which photons from the CMB are gravitationally redshifted, causing the CMB spectrum to appear uneven. This effect is the predominant source of fluctuations in the CMB for angular scales above about ten degrees. The non-integrated Sachs–Wolfe effect is caused by gravitational redshift occurring at the surface of last scattering. The effect is not constant across the sky due to differences in the matter/energy density at the time of last scattering.

The integrated Sachs–Wolfe (ISW) effect is also caused by gravitational redshift, however it occurs between the surface of last scattering and the Earth, so it is not part of the primordial CMB. It occurs when the Universe is dominated in its energy density by something other than matter. If the Universe is dominated by matter, then large-scale gravitational potential energy wells and hills do not evolve significantly. If the Universe is dominated by radiation, or by dark energy, though, those potentials do evolve, subtly changing the energy of photons passing through them.

There are two contributions to the ISW effect. The "early-time" ISW occurs immediately after the (non-integrated) Sachs–Wolfe effect produces the primordial CMB, as photons course through density fluctuations while there is still enough radiation around to affect the Universe's expansion. Although it is physically the same as the late-time ISW, for observational purposes it is usually lumped in with the primordial CMB, since the matter fluctuations that cause it are in practice undetectable.

The "late-time" ISW effect arises quite recently in cosmic history, as dark energy, or the cosmological constant, starts to govern the Universe's expansion. Unfortunately, the nomenclature is a bit confusing. Often, "late-time ISW" implicitly refers to the late-time ISW effect to linear/first order in density perturbations. This linear part of the effect entirely vanishes in a flat universe with only matter, but dominates over the higher-order part of the effect in a universe with dark energy. The full nonlinear (linear + higher-order) late-time ISW effect, especially in the case of individual voids and clusters, is sometimes known as the Rees–Sciama effect, since Martin Rees and Dennis Sciama elucidated the following physical picture.

Accelerated expansion due to dark energy causes even strong large-scale potential wells (superclusters) and hills (voids) to decay over the time it takes a photon to travel through them. A photon gets a kick of energy going into a potential well (a supercluster), and it keeps some of that energy after it exits, after the well has been stretched out and shallowed. Similarly, a photon has to expend energy entering a supervoid, but will not get all of it back upon exiting the slightly squashed potential hill.

A signature of the late-time ISW is a non-zero cross-correlation function between the galaxy density (the number of galaxies per square degree) and the temperature of the CMB, because superclusters gently heat photons, while supervoids gently cool them. This correlation has been detected at moderate to high significance.

In May 2008, Granett, Neyrinck & Szapudi showed that the late-time ISW can be pinned to discrete supervoids and superclusters identified in the SDSS Luminous Red Galaxy catalog. Their ISW detection is arguably the clearest to date, producing an image of the mean effect supervoids and superclusters have on the CMB.>>