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What Is Dark Energy? How the Universe Has Cooled

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What Is Dark Energy? How the Universe Has Cooled National Aeronautics and Space Administration Age of the Universe: Size of the Universe: 13.7 Billion Years Cosmic Times 94 Billion Light Years 2006 Faster Walk On The Dark Side Journey Seeds of Modern Universe There is fresh evidence for the existence of Here’s how the ISW effect works. Gravity is dark energy, a peculiar entity that is hastening a property of matter, so matter exists in “gravity the expansion of the cosmos. Dark energy wells” in space-time. More matter makes a to Cosmos’ amazingly comprises almost three-quarters of deeper well. If there is no change in the depth the universe. It appears to be accelerating the of a well while a photon crosses it, the well has distances between galaxies and working against no effect on the photon’s energy. But if dark Dark Heart energy stretches out deep wells of gravity into gravity, but its nature is still unknown. Scientists are gearing up to shed some light mere shallow dents, then CMB photons crossing The new evidence is the discovery of an on the darkest mystery in the universe: dark the well will change their energy. The recent effect dark energy has on photons of light from energy. observations of these subtle changes in the CMB the earliest universe. This ancient light began NASA and the US Department of Energy have provides further evidence for the existence of moving across the universe just 380,000 years selected three concept studies for consideration dark energy. after the Big Bang, and its initial energy has to become their Joint Dark Energy Mission This additional evidence is good news to been shifted into the microwave part of the (JDEM). JDEM is slated for launch as early as astronomers who first detected a gravity-defying energy spectrum in the 13 billion years since. 2013. We see the light today as what scientists call dark energy in 1998. At that time, two teams JDEM’s goal is to sharpen and double- of astronomers were measuring the retreat of a Teams Science WMAP Credit: COBE and the cosmic microwave background (CMB) check the distance measurements to Type Ia collection of very distant Type Ia supernovae. radiation. The detection of an effect in the CMB supernovae. This, in turn, should reveal critical A sky map of the temperature fluctuations in the Cosmic Microwave Background as measured by the Wilkinson These supernovae are created by the explosion called Integrated Sachs-Wolfe (ISW) confirms clues to how fast the universe has expanded at Microwave Anisotropy Probe. The dark blue regions are only a few millionths of a degree cooler than the red of a white dwarf. The teams from the Supernova regions. Astronomers analyzing these fluctuations have determined the percentages of matter and energy in the that dark energy had an additional influence on different points in cosmic history. Cosmology Project at Lawrence Berkeley universe. those photons. Type Ia’s are considered a standard of National Lab and the High-Z Supernova Search ISW was named after Rainer Kurt Sachs and comparison used to determine the distance to Cosmic researchers now have the sharpest work out the energy composition. They find nor- had intended to measure the rate at which Arthur Michael Wolfe, who first described it in other astronomical objects. By observing a large focus ever of the universe’s early structure. This mal matter comprises 4% of the universe, dark the universe’s expansion was slowing down. 1967. But its influence on the CMB was recently number of these “standard candle” supernovae better view comes in the form of super-sensi- matter is 23% of the universe, and the energy is Instead, they found that the distance between verified by an international collaboration of in galaxies far and near, researchers hope to find tive temperature data of the sky-filling cosmic 73%. Rather nicely, the energy needed falls right Earth and these supernovae was growing, and researchers: Stephen Boughn (Haverford out just how quickly those galaxies are flying microwave background (CMB) collected by in the range of the amount of gravity-repulsing at an increasingly faster rate. Starting about College) and Robert Crittenden (University of away from us. the Wilkinson Microwave Anisotropy Probe dark energy discovered by astronomers in 1998. five billion years ago, some unexplained “dark” Portsmouth), Charles Bennett’s (NASA) WMAP The three proposed concepts are the Supernova (WMAP). The CMB is the afterglow of the Big WMAP has also, for the first time, detected energy began to overwhelm the force of gravity team, and a collaboration of astronomers from Acceleration Probe (SNAP), the Advanced Dark Bang. the polarization of light in the CMB across the and push galaxies apart. the Sloan Digital Sky Survey and the Institut Energy Physics Telescope (ADEPT), and the WMAP has vastly improved on the fuzzier, entire sky. This is important because it helps The researchers chose to name it dark energy, d’Astrophysique de Paris. Dark Energy Space Telescope (Destiny). Each but groundbreaking first image of the CMB work out details of what happened during the not to be confused with dark matter, which is Their conclusions result from efforts to pull would look at the supernovae in a different way. unveiled in 1993 from NASA’s Cosmic Back- first split second after the Big Bang. That’s when another confounding problem in cosmology. together a treasure trove of data, on the large- SNAP would use a 1.8-meter optical/infrared ground Explorer satellite (COBE). the universe puffed up like a hyperactive lump As for what dark energy is, that’s anybody’s scale structures of the universe and on light telescope with a CCD (charge-coupled device) What WMAP has now confirmed are the of bread dough. It’s that moment of what as- guess right now. While there are at least a half from the newborn universe. The data included light detector like those in digital cameras. But acoustic “peaks” of the undulating Big Bang tronomers call inflation which allowed for tiny dozen theories, none seem very close to an observations from visible light, x-ray, radio and with a billion pixels, SNAP’s detector beats any shockwaves in the CMB. These were first ob- fluctuations in the original Big Bang to translate authoritative answer. microwave telescopes. handheld camera by a factor of a thousand. SNAP served in 1999 and 2000 with ground-based in- into huge, but subtle differences in temperature would spot about 2,000 Type Ia supernovae each struments, leading to the conclusion that the ge- seen in the CMB. And those differences, in turn, year over a wide range of distances – about 200 ometry of the universe is flat. What that means, are now thought to be the seeds of today’s gi- times more supernovae than are now detected among other things, is that on a large scale, par- gantic clusters of galaxies . each year. allel lines would stay parallel. Researchers are now comparing and combin- ADEPT would use a 1.1-meter near-infrared WMAP’s measurement of these acoustic ing the new WMAP data with a range of other telescope to locate 100 million galaxies and peaks gives the amount of normal matter and cosmic measurements – vast surveys of stars, 1,000 Type Ia’s. Its data would be compared with dark matter in the universe. Because WMAP has galaxy clustering, hydrogen gas clouds, super- that of the minute temperature differences in the nailed down the flatness of the universe, astron- novae, and others – to uncover a new unified un- cosmic microwave background. The mission omers know what the overall matter and energy derstanding of the universe’s past, present and would reveal how well the earliest (most distant) composition of the universe must be. Knowing future. galaxies match up with the earliest clumps of the matter composition, they have been able to matter, and how dark energy has altered the distribution since then. Destiny would have a 1.65-meter near- infrared telescope, designed to detect 3,000 Type Ia supernovae over two years. It would ‘First Light’ spend an additional year surveying, in detail, 1,000 square-degrees of sky. This would gather Wins Nobel Credit: NASA / WMAP Science Teams Teams Science WMAP / Credit: NASA new readings on changes in the large-scale Astrophysicists John Mather and George Smoot have been awarded the 2006 Nobel Prize WMAP data reveals that the universe’s contents include 4% atoms, the building blocks of stars and planets. Dark distribution of matter in the cosmos since the Big in Physics. It was presented for their 1992 dis- matter comprises 23% of the universe. This matter, different from atoms, does not emit or absorb light. It has only Bang. Both phases of Destiny’s mission would been detected indirectly by its gravity. 73% of the universe, is composed of “dark energy”, that acts as a sort of an improve on the sensitivity of similar ground- coveries about the cosmic microwave back- anti-gravity. This energy, distinct from dark matter, is responsible for the present-day acceleration of the universal based observations by a factor of about 10. ground (CMB), the light from the beginning of expansion. the universe as we see it today. According to the Nobel jury, “These mea- surements also marked the inception of cosmol- ogy as a precise science.” Using data from the space-based Cosmic Biggest Mystery: Background Explorer (COBE), a team led by Mather and Smoot teased out the details of What is Dark Energy? how the universe has cooled. They measured The further we look into the cosmos, the cal constant an annoying fudge factor, without the spectrum of light from this background and Credit: Johns Hopkins, Lawrence Berkeley Lab, NASA/DOE found that it matched predictions from the Big more puzzled we are.
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