On a hot June Illinois afternoon, a celebratory atmosphere prevails at Kuhn Barn, a holdover from Fermi National Accelerator Laboratory’s agricultural past and also a popular cookout spot. Doctoral student Guillermo Moroni works the grill, proudly serving lamb chops and hamburgers to his scientific collaborators—other postdocs, technicians, scientists and graduate students. The smell of roasted corn floats across picnic tables littered with cakes, pies and brownies. The gathering is more than a simple celebration of the start of summer; it marks a tipping point. The Dark Energy Camera, the first device specifically designed to search for dark energy, is on the brink of completion. Project manager Brenna Flaugher—who organized the cookout—and her colleagues are about to see the project they’ve been preparing for the past eight years transition from dream to reality. This fall, scientists will fire up DECam, as it’s affectionately known, on a mountaintop in Chile and see their hard work pay off. “It’s going to be very exciting for all of us to open the shutter for the first time,” Flaugher says. “Who knows what we’ll see?” What they hope to see are signs of the invisible, mysterious force that seems to pull the universe apart—a force that has never been directly observed.

T. Abbott and NOAO/AURA/NSF. Curtis Weaverdyck, University of Michigan Curtis Weaverdyck, University of Michigan Curtis Weaverdyck, University of Michigan Curtis Weaverdyck, University of Michigan Curtis Weaverdyck, University of Michigan Fermilab Fermilab Curtis Weaverdyck, University of Michigan NASA/Andy Fruchter/ERO team Previous Next

The mystery of dark energy Physicists have known about cosmic expansion since the 1920s, when Edwin Hubble found that the light spectrum of distant objects was shifted to higher wavelengths in a phenomenon called redshift. But dark energy has been on their minds only since 1998, when two independent studies of type 1a supernovae revealed the bright, exploding stars to be fainter than expected, hinting that the expansion of the universe is speeding up. Scientists previously thought that, under Einstein’s Theory of General Relativity, the expansion of the universe would slow as time went on due to the pull of gravity. The 1998 finding suggested otherwise. It seems that about 5 billion years ago, the universe started expanding at an accelerating pace. Before that, gravity had been the dominant force in the universe, but then something else took over, relentlessly pushing parts of the cosmos away from one another. Theorists postulate that if we really understand how gravity works, then some unforeseen, invisible force—a dark energy—must be responsible. “The universe was matter-dominated when it was slowing down,” Flaugher says. “And then this slowing down stopped—and now we’re in a dark-energy dominated universe because the expansion is winning over the gravitational pull of everything.” Four different views of the universe After first light in September, DECam will enable the most comprehensive search for dark energy yet. As currently understood, dark energy is pushing galaxies and other large objects in the cosmos away from each other. Exactly how it does that or where it came from is unknown. The Dark Energy Survey collaboration, which built DECam and will use it to carry out a new survey of the universe, is hoping their instrument will provide some answers. Using DECam, the Dark Energy Survey will measure the history of the expansion of the universe as well as the development of large-scale cosmic structures over time. To accomplish these goals, the survey will look to the skies for four pieces of evidence. First are type 1a supernovae, the phenomena that first tipped scientists off to the presence of dark energy. DES will identify 4000 supernovae whose brightnesses will indicate how fast the universe was expanding at different times in the past. Another piece of evidence, a count of tens of thousands of galaxy clusters, will provide data on the rate at which these large groupings of galaxies formed. As dark energy came to dominate the universe, it is thought to have shut off the formation of such massive structures. Weak gravitational lensing, the warping of light from 200 million distant galaxies due to the gravity of astronomical objects in the foreground, gives another indicator of how structures formed and evolved over time. Finally, baryon acoustic oscillations, large-scale ripples in the proton and neutron sea of the early universe, provide information about the rate of expansion of the universe. Each of these pieces of evidence can help elucidate changes in that rate and in the clustering of matter in the universe. “The combination of these four different ways to probe dark energy really became the hallmark of the project,” says Josh Frieman, the director of the Dark Energy Survey.

Dark Energy Camera Construction Timelapse Video of Dark Energy Camera Construction Timelapse