Fermilab physicists honored for uniting physics and cosmology
Three decades ago, no one had ever heard of particle astrophysics. How could the tiniest pieces of matter and the biggest objects in the universe coexist in a single field of science?
Last month, the American Institute of Physics and the American Astronomical Society honored two scientists who, more than any others, made particle astrophysics, if not a household name, a new scientific discipline.
Theoretical astrophysicists Michael Turner and Rocky Kolb won the annual Dannie Heineman Prize for Astrophysics "for their joint fundamental contributions to cosmology and their development of the field of particle astrophysics, which have resulted in a vibrant community effort to understand the early universe."
Turner and Kolb conducted much of their pioneering work at Fermilab. They were the first members of the NASA/Fermilab Theoretical Astrophysics Group, which blossomed into the realm of experiment and observation and continues today at the Fermilab Center for Particle Astrophysics. In the process, they entertained generations in the Fermilab community with a new genre of cosmic humor, astroparticle shtick.
Former Fermilab Director Leon Lederman and the late David Schramm of the University of Chicago brought the two together in 1983. John Peoples, who followed Lederman as lab director, helped them realize their plan of expanding into particle astrophysics experiments.
Turner said, "While the two of us are getting the prize, really Fermilab and the University of Chicago deserve a lot of credit for all the support they've given us and for taking chances." Not to mention auditioning their act.
For more than 25 years, the two each held joint appointments at Fermilab and the University of Chicago. Now both are professors full-time at the University of Chicago.
Taking the initiative
In the late 1970s, astrophysics had hit a wall. The standard hot Big Bang model seemed to have a problem. Neutrons and protons, the smallest known particles, were too large and interacted too strongly to allow sensible speculations about how the universe began.
Then particle physicists discovered quarks, the weakly interacting, point-like particles that make up neutrons and protons - and saved the model. Scientists could describe the early universe as a hot, primordial soup of quarks instead of a jumble of overlapping neutrons and protons.
It didn't take long for Turner and Kolb to package "Condensed Primordial Soup: A quick meal in just 4.5 billion years" in a familiar red and white can.
Now scientists could start to tackle some big questions about how the universe began and how it was shaped. But neither astrophysicists nor particle physicists could answer those questions alone.
Fermilab made a first attempt to enter the world of astrophysics in 1979, making a bid to NASA to host its Space Telescope Science Institute, which analyzes data from the Hubble Space Telescope. NASA chose the bid from Johns Hopkins University instead. Soon after, Lederman went hiking in the Dolomites with Schramm, an astrophysicist and rising star at the University of Chicago.
"I was complaining about NASA's decision," Lederman said. "Schramm said, 'You don't need to win any contests. You're the director of Fermilab. Why don't you just make yourself an astrophysics group? I'll help you.'"
The laboratory put in a new bid to NASA, this time to host a theoretical astrophysics group. This time, NASA said yes.
In 1983, Lederman hired Turner, a young assistant professor in the Astronomy Department that Schramm chaired at the University of Chicago, along with Kolb, an Oppenheimer Fellow from Los Alamos, to bring Fermilab to the cosmic frontier.
"Leon is a visionary," Peoples said. "He was always looking around for the thing nobody else had thought about."
Kolb and Turner were a perfect fit for the task, which was by no means guaranteed to succeed, Lederman said. They were good communicators; they could make people laugh. "That's a big plus," he said. "It could lighten any disaster."
Kolb and Turner had first met in 1980 at a workshop in Santa Barbara.
"We started out working on similar research, but as competitors," Turner said. "You've got a lot of testosterone when you're a young post-doc trying to make a mark. But we had a lot in common: a passion for this area of science, a similar sense of humor. It was clear to me that we would have a greater impact if we worked together - and it would be more fun."
Turner had already begun to establish himself at the University of Chicago, but he and Kolb were both in their 30s when they first came to Fermilab to head a group of about 10 post-docs and students. "I felt like I'd been given the keys to the candy store," Kolb said. "Who would allow kids like us to run something? I always thought somebody would say, 'Who's really in charge?'"
The young scientists' work paid off, Lederman said, and soon they ran the premier particle astrophysics groups in the nation. They built and studied theories of dark matter, extra dimensions, ultra-high-energy cosmic rays, superstring cosmology, the cosmic microwave background and gravitational lensing.
"We were just a little bit ahead of everybody," Lederman said. "Four of five years after our group had achieved successes, the other universities started to make those connections."
Over the years, between teaching post-docs at Fermilab and students at the University of Chicago, Kolb and Turner trained a large fraction of the people who would become the next generation of leaders in the field they began.
In 1989, Kolb and Turner published what would become the handbook for particle astrophysics: a book called "The Early Universe."
"We were so young, foolish and inexperienced, we thought it would be easy," Kolb said. "It took about three years of pretty hard work."
Around that time, they recognized that they needed to get involved in testing the theories that they had spent years developing. "We realized a purely theoretical activity is not as productive as an operation with connections to experiments and observations," Kolb said. "Even though theorists are smarter and more attractive, we do need experimentalists."
Peoples, then Fermilab's new director, supported their plan. Fermilab joined the Sloan Digital Sky Survey, the most ambitious astronomical survey ever planned; the Cryogenic Dark Matter Search experiment; and the Pierre Auger Observatory, which in 2007 identified supermassive black holes as the most likely source of the highest-energy cosmic rays.
"As a director, you have to have a few things you take a chance on," Peoples said. "If every experiment you do is successful, you're not doing anything new."
About 15 years after Turner and Kolb arrived at Fermilab, experimental results began to come in from the NASA's Cosmic Background Explorer satellite, which found patterns in the way matter and energy had been distributed soon after the universe began. The new data matched predictions based on ideas coming out of early-universe cosmology, including inflation and cold dark matter.
"The world changed on Jan. 1, 1998," Turner said. "These went from ideas to ideas supported by data. It became clear this wasn't just a bunch of airy-fairy theory."
The astrophysics group could not fully enjoy their triumph. Just days before Christmas of 1997, Schramm died in plane crash during a flight from Denver to Aspen in his private plane. He never saw the field that considered him a founder turn the corner toward widespread acceptance.
Kolb, Turner and the particle astrophysicists at Fermilab and the University of Chicago have continued the work he championed.
The Fermilab Center for Particle Astrophysics participates in the COUPP dark matter experiment, the Dark Energy Survey and GammeV. The group continues to participate in the Cryogenic Dark Matter Search, the Pierre Auger Observatory and the Sloan Digital Sky Survey. Scientists there hope to join the Joint Dark Energy Mission as well.
Since its inception, the Fermilab Theoretical Astrophysics Group has published more than 1,000 papers. The Experimental Astrophysics Group was an anchor for the SDSS and now leads the Dark Energy Survey, designed to study the acceleration of the expansion of the universe.
Turner said he has high hopes for the current search for dark matter. "We have a full-court press on dark matter. One of these methods is going to pan out."
He does not foresee solving the mystery of dark energy - a term he coined in 1998 to explain the mysterious force pushing the universe to expand at an increasing rate - anytime soon. But "I bet there'll be a surprise ahead," he said. "Each generation wants to get all the answers. After a few it gets a little more generous and says, 'We'd better save some of the big questions for the next generation.'"
Turner and Kolb are recognized as pioneers who not only brought the field new knowledge, but helped frame the questions that drive future research. And left them laughing.
"You're sure dark matter is there?" Turner once asked Kolb in a public debate on dark matter.
"I would bet your life," Kolb replied.
— Kathryn Grim