Dark Energy is Real, Say Astronomers

Dark energy, a mysterious substance thought to be speeding up the expansion of the Universe is really there, according to a team of astronomers at the University of Portsmouth and LMU University Munich.

A visual impression of the data used in the study. The relevant extra-galactic maps are represented as shells of increasing distance from Earth from left to right. The closest thing seen is our Milky Way galaxy, which is a potential source of noise for the analysis. After this are six shells containing maps of the millions of distant galaxies used in the study. These maps are produced using different telescopes in different wavelengths and are colour-coded to show denser clumps of galaxies as red and under-dense regions as blue. There are holes in the maps due to data quality cuts. The last, largest shell shows the temperature of the cosmic microwave background from the WMAP satellite (red is hot, blue is cold), which is the most distant image of the Universe seen, some 46 billion light-years away. The team have detected (at 99.996% significance) very small correlations between these foreground maps (on the left) and the cosmic microwave background (on the right).(Credit: Earth: NASA/BlueEarth; Milky Way: ESO/S. Brunier; CMB: NASA/WMAP)
A visual impression of the data used in the study. The relevant extra-galactic maps are represented as shells of increasing distance from Earth from left to right. The closest thing seen is our Milky Way galaxy, which is a potential source of noise for the analysis. After this are six shells containing maps of the millions of distant galaxies used in the study. These maps are produced using different telescopes in different wavelengths and are colour-coded to show denser clumps of galaxies as red and under-dense regions as blue. There are holes in the maps due to data quality cuts. The last, largest shell shows the temperature of the cosmic microwave background from the WMAP satellite (red is hot, blue is cold), which is the most distant image of the Universe seen, some 46 billion light-years away. The team have detected (at 99.996% significance) very small correlations between these foreground maps (on the left) and the cosmic microwave background (on the right).(Credit: Earth: NASA/BlueEarth; Milky Way: ESO/S. Brunier; CMB: NASA/WMAP)

After a two-year study led by Tommaso Giannantonio and Robert Crittenden, scientists conclude that the likelihood of its existence stands at 99.996 per cent. Their findings are published in the Monthly Notices of the Royal Astronomical Society.

Professor Bob Nichol, a member of the Portsmouth team, said: "Dark energy is one of the great scientific mysteries of our time, so it isn't surprising that so many researchers question its existence.

"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."

Over a decade ago, astronomers observing the brightness of distant supernovae realised that the expansion of the Universe appeared to be accelerating. The acceleration is attributed to the repulsive force associated with dark energy now thought to make up 73 per cent of the content of the cosmos. The researchers who made this discovery received the Nobel Prize for Physics in 2011, but the existence of dark energy remains a topic of hot debate.

Many other techniques have been used to confirm the reality of dark energy but they are either indirect probes of the accelerating Universe or susceptible to their own uncertainties. Clear evidence for dark energy comes from the Integrated Sachs Wolfe effect named after Rainer Sachs and Arthur Wolfe.

The Cosmic Microwave Background, the radiation of the residual heat of the Big Bang, is seen all over the sky. In 1967 Sachs and Wolfe proposed that light from this radiation would become slightly bluer as it passed through the gravitational fields of lumps of matter, an effect known as gravitational redshift.

In 1996, Robert Crittenden and Neil Turok, now at the Perimeter Institute in Canada, took this idea to the next level, suggesting that astronomers could look for these small changes in the energy of the light, or photons, by comparing the temperature of the radiation with maps of galaxies in the local Universe.

In the absence of dark energy, or a large curvature in the Universe, there would be no correspondence between these two maps (the distant cosmic microwave background and relatively closer distribution of galaxies), but the existence of dark energy would lead to the strange, counter-intuitive effect where the cosmic microwave background photons would gain energy as they travelled through large lumps of mass.

The Integrated Sachs Wolfe effect was first detected in 2003 and was immediately seen as corroborative evidence for dark energy, featuring in the 'Discovery of the year' in Science magazine. But the signal is weak as the expected correlation between maps is small and so some scientists suggested it was caused by other sources such as the dust in our galaxy. Since the first Integrated Sachs Wolfe papers, several astronomers have questioned the original detections of the effect and thus called some of the strongest evidence yet for dark energy into question.

In the new paper, the product of nearly two years of work, the team have re-examined all the arguments against the Integrated Sachs Wolfe detection as well as improving the maps used in the original work. In their painstaking analysis, they conclude that there is a 99.996 per cent chance that dark energy is responsible for the hotter parts of the cosmic microwave background maps (or the same level of significance as the recent discovery of the Higgs boson).

"This work also tells us about possible modifications to Einstein's theory of General Relativity," notes Tommaso Giannantonio, lead author of the present study.

"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."

Comments

We haven't even gotten out of the solar system, barely out of Earth and we are already pretending to know it all about the Universe? We're just like the Greek, creating a whole mythology out of nothing without really knowing.

Why is the shape of the known Universe so even in the big picture, but with high concentrations of galaxies in some places, that background radiation is not portraying such variations in galactic mass/distribution, is it? What if we're detecting something else, closer to us than we think? I don't see a scientific mind in this article but a new sect in science, sorry.

The shape of the known universe is so obscenely vast that the shape is based on the evidence we have available to us. The evidence that we have available is the sky as we can see it from Earth and the extrapolation of the data from what we can see into what would be possible. The shape is even only because it's a rendering of the idea of the galaxy, rather than an exact picture of the edges.

As to why there are higher concentrations of galaxies in some places as compared with others, just consider the Big Bang itself. When the explosion that would be the universe occurred, it was an explosion in every sense of the word. It was not a uniform dispelling of matter all across the universe. Also, after the initial explosion, things began to group together as a result of gravity pulling things together with massive objects collecting the smaller objects that they're in close enough proximity to and (possibly) dark energy causing the universe to expand. So between the push and pull of these two forces, you have collections that might appear random to the naked eye, but there is clearly nothing random going on. There are very specific physical principles governing all of this, which is not to say that we fully understand them all but there are clearly measurable forces at work. We just haven't figured out how to quantify them yet.

We know a heck of a lot about stars thanks to being able to see them at various distances. When we've gone from one generation of space telescopes to another, the findings become progressively more detailed. There is an obvious progression that is simply too profound, too detailed and too consistent to not be representative of a larger universe.

Just because we can't get out of the universe yet (if at all), does not mean that the universe is not unbelievably vast, nor does it even suggest it. Whether or not we can get out of the universe does not in any way shape or form dictate evidence for your claim and extraordinary claims require extraordinary evidence.

extraordinary claims require extraordinary evidence.

there is a man, with a white beard, sitting on a cloud, beyond the edge of the universe. he's keeping a list, checking it twice. he's knows if i've been naughty or nice.

at what point does science become faith? i'd like to know. i love these science articles, but i would like sources cited, please, so that i can seek them out. instrument error is a confounding thing...

Absolutely logical Alfredo, absolutely!

It is understood among the scientific community that any scientific claims, particularly in physics, correspond only to the best current measurements, the well-established theories, and correct mathematics. The 99.9996 certainty corresponds only to such measurements and theories, and it is not a pretense to "know" with such certainty what "really is". The fact that we haven't left out heliosphere doesn't mean we don't have a pretty good model of what stars are made of, their lifespans, their energies and so forth. Physics cannot be dismissed with the argument "what do you know? Have you been there yourself? Have you touched the stuff?". Such attitude shows a deep ignorance of how science works and what it's claims relate to, and it is very un-TZM-ish.

Before we understood what comprised wind, we could feel it's effects. We knew the wind existed based on how it effected the trees, oceans and even ourselves. From my understanding is that scientists call it dark energy because they can "see" the effects of it, they can measure to a certain extent how much force it exerts yet we can't see it. Maybe one day we'll be able to understand it like we now understand the wind. We now know that even though we can't "see" wind with our eyes, we know it has mass (the molecules that make up air) and we know what causes it (pressure gradients, temperature gradients etc).

Same goes for electricity, we were manipulating it before we could see the electrons move about.

Some day we may be able to harness dark energy (we may even call it something else once we understand it) to make cars/trains levitate, or spaceships travel vast distances.

Scientists aren't saying they know what dark energy is, but they're saying with 99.9996% certainty that it exists.