Volume XXVII Number 1
Photo © Tyagan Miller
Artist's rendering of the Supernova/Acceleration Probe, or SNAP
The Never-ending Universe
On cool summer nights in Wyoming, I used to lie on top of my parents' green '68 Buick, staring up at the "big sky" that Montana tried to claim on its license plates, fixing on constellations sparkling in the clear depths of night. That sky thrilled me; it engaged all my senses and filled me with awe.
Steven Spielberg made Close Encounters of the Third Kind just 10 miles away from my front-yard observatory. As a fourth-grader, I made 20 bucks working as an extra for the movie. I sat in the front seat of a car all day, looking out the window at Devil's Tower National Monument as the cameras filmed that car and hundreds of others racing away from an imminent alien invasion. You can still buy key chains shaped like attenuated aliens in the tacky gift shops located just before the gates of the nation's first official monument.
I've loved the idea of space since I was a kid, but barely made it through an astronomy class in college, boggled by the math and physics. To my science teacher father's dismay, I've always been more adept at stories than story problems, more able to grasp the experiential than the exponential.
So when Stuart Mufson referred to his research as "the science fiction story I'm working on," I knew we could speak the same language. Call it a close encounter of an academic kind.
A professor of astronomy at Indiana University Bloomington, Mufson, along with colleagues in astronomy and physics, has been looking for big answers in tiny neutrinos and in heretofore unexplained dark energy that apparently makes up at least 70 percent of the universe. "The overarching scientific goal of my experiments is to understand the universe," he says. "I'm trying to do it from the very small and from the very large."
So far, the answer is not "42," as Douglas Adams jokingly suggested in The Hitchhiker's Guide to the Galaxy. But stay tuned--you never know. Until 1998, scientists thought the expansion of the universe was gradually slowing because of the gravitational attraction of matter that had been occurring since shortly after the Big Bang. The rate of deceleration, it was thought, could be used to determine the average density of matter in the universe.
Then something happened that turned everything upside down, or maybe inside out. Two different teams of scientists--from the Supernova Cosmology Project based at the Lawrence Berkeley National Laboratory and from the Mount Stromolo and Siding Spring Observatories in Australia--recorded several dozen supernovae (extremely bright, exploding stars), including some so far away that their light had started toward Earth when the universe was in its infancy. By their calculations, the universe was actually speeding up.
On its December 18, 1998, cover, Science magazine declared the accelerating universe "The Breakthrough of the Year." It was the beginning of a particularly exciting time to be an observer of the cosmos, especially because it seemed that what was making the universe accelerate--dark energy--was a scientific mystery of infinite proportions.
Cosmologists seeking to map the geometry and future of the universe had already discovered that most of the matter of the universe was unseen "dark matter" composed not of known chemical elements, but of elementary particles that do not interact with light.
"That was weird enough," says Mufson. "But dark matter isn't anything like dark energy. Dark energy is far more bizarre, and it's apparently the dominant source of energy in the universe. We're talking about a quest like the one in The Da Vinci Code, but for the Holy Grail of cosmology. There are two critical issues: what the hell is dark matter? And what in the world is dark energy?"
Consider the pie chart that Mufson shows his Astronomy A115 students: of the total energy content of the universe, a tiny sliver is visible matter and about 73 percent is dark energy. The bulk of the universe, then, is stuff that, like dark matter, does not interact with light, is gravitationally repulsive, and does not get weaker as the universe expands.
If the universe was dominated by gravitational attraction, its rate of expansion would be slowing. Acceleration requires something that opposes this attraction. "Whereas gravity pulls the chemical elements and dark matter into stars and galaxies, it pushes dark energy into a nearly uniform haze that permeates space," says an article in the January 2001 issue of Scientific American. "[Repulsive gravity] is gradually overwhelming the attractive force of ordinary matter--causing the universe to accelerate to ever larger rates of expansion."
The quest to discover the nature of dark energy is on, and Mufson and IU colleagues (Professors Chuck Bower and Jim Musser from the Department of Physics and astronomy graduate student Nick Mostek) are part of an international team of researchers working on a satellite observatory that, if built, could fulfill that quest. It's called SNAP, the SuperNova/Acceleration Probe.
The cosmologists from Berkeley and Australia who figured out that the universe was accelerating used data from approximately 80 supernovae as "standard candles" for measuring brightness over distance and time. This allowed them to postulate that the geometry of the universe is flat and thus in a state of acceleration. With a two-meter telescope and a field of view 600 times the sky area of the Hubble Space Telescope's camera, SNAP would be able to measure many more supernovae over a much wider range of distances, from nearby supernovae to very distant stars that exploded when the universe was much younger and only a third of its present size. SNAP would repeatedly image approximately 15 square degrees of the sky at a time for about three years. This would allow scientists to measure the energy spectra and brightness over time for more than 2,000 supernovae, discovering the binary star systems just after they explode.
The imaging camera on SNAP will have half a billion pixels. To grasp just how powerful the camera is, consider that the average digital camera makes images with 3 million pixels. Mufson and colleagues are looking at how LEDs (Light Emitting Diodes) may be used in onboard lamps that would calibrate SNAP's focal point detectors. The calibration device would allow researchers to make sure their equipment is making accurate measurements over the time that SNAP is in space.
Gravitational lensing, or bending of light by massive objects, will also be part of the SNAP mission and would provide "road maps" of the universe's total mass distribution, including its hidden dark matter, according the SNAP Web site (http://snap.lbl.gov).
With its supernovae and gravitational lensing data, SNAP would enable scientists to test the many theories that exist about dark energy, including, amazingly enough, the cosmological constant that Albert Einstein proposed in 1917. Einstein believed the universe was static, not contracting or expanding. To make this belief work with his general theory of relativity, however, he had to adjust the value of the constant so that its gravitational repulsion would counterbalance the gravitational attraction of matter.
"Einstein was sitting there with an equation that says the universe is expanding, and he thought it was stupid and invented his way out of it," says Mufson. "It's possible that he could have made one of the greatest predictions in scientific history."
SNAP data would also consider "inflation"--the theory that galaxies and other structures were stretched from tiny particles to cosmic size in a very brief period, resulting in a flat universe, and "quintessence"--the idea that there is a "fifth element" or a dynamic quantum field that gravitationally repels.
"Why did we see this evidence of an accelerating universe now?" Mufson muses. "The cosmological constant isn't the only way you can make it happen. Theorists are amazingly inventive. Some even say that if you make Einstein's constant big enough you accelerate so fast that there is a Big Rip--literally, space tears."
SNAP started out as a U.S. Department of Energy initiative. NASA has since joined with the DOE to sponsor a "Joint Dark Energy Mission," and SNAP is one of several proposals being considered by the JDEM initiative.
"If the SNAP project survives [the JDEM's review], presumably after three years we will turn it over to the astronomical community, and it will be the deepest and probably best mirror-free telescope they will have for the next 25 years," Mufson says.
Mufson's search for answers to the questions of the universe has also involved neutrinos, invisible particles that have no electric charge, almost no mass, and may come from colliding black holes and distant young galaxies.
"When I tell people I'm looking for the mass of a neutrino, that is a much harder concept for them to grasp," he says. "The questions are every bit as fundamental and every bit as interesting, but most people say, 'what's a neutrino?' On the other hand, I don't have to tell anyone what the universe is. If I tell them a neutrino has mass, they might say, 'Why should I pay money to care?" If, on the other hand, I say 'we're going to go off and see if the universe is going to accelerate forever and if space may just rip apart,' they're going to say, 'Wow!'"
Mufson's neutrino research tells a true-life science fiction story with dark and mysterious characters,and a Joint Dark Energy Mission seems like something Darth Vader might lead. But with a pile of his daughter's library books and a "Smarty Jones: Philly's Champ" baseball cap on his desk, the entirely genial Mufson is hardly a candidate for a Darth Vader role. He definitely enjoys the bizarre nature of the cosmology and cosmic ray physics research he conducts, though.
"If you walk up and down this hallway and asked any one of these scientists--especially the astronomers--if they were influenced by science fiction when they were kids, they'd say, 'yes, of course, absolutely,'" says Mufson. "I can look at science fiction movies and suspend my disbelief, even though I know there's no such thing as antigravity. I can watch Star Trek and love it. I grew up with Star Trek; I watched every one of them, you know?"
One of the library books on Mufson's desk is The Neverending Story, a book about a book that a little boy finds in a dusty attic. When the boy opens the book, he discovers that it is without an end, a story that keeps expanding and whose characters go on having adventures for infinity.
"I wanted to be an astronomer from the time I was in elementary school," says Mufson. "I mean, I just thought science was the coolest thing in the world."
Erika Knudson is a writer and client relations manager for the IU Office of Publications in Bloomington.