Newswise — When the moon threw its shadow on the Department of Energy’s SLAC National Accelerator Laboratory during the Aug. 21 partial solar eclipse, it created the perfect backdrop for the 45th annual SLAC Summer Institute (SSI). This year, the program was all about the fascinating universe. The two-week summer institute attracted an international crowd of 123 participants, mostly graduate students and postdoctoral researchers, who discussed “cosmic opportunities” in particle physics and astrophysics research with world-renowned experts in the field.

An intense program of lectures, talks and discussions focused on what we know – and don’t know – about the life of our universe, from its birth 14 billion years ago to its future evolution. Topics included the standard model of cosmology; the production of particles after the Big Bang; the oldest light in the universe, known as the cosmic microwave background; the formation of large structures such as galaxies and galaxy clusters; invisible dark matter, which is the scaffold for this structure formation; mysterious dark energy, which causes space to expand at an ever increasing rate; and alternative theories of gravity.

A series of talks also covered experiments at the forefront of particle physics and cosmology, such as searches for new physics not explained by the standard theory of particle physics; attempts to detect hypothetical dark matter particles; analyses of recently discovered gravitational waves; studies of the nature of elementary neutrinos and their role in the evolution of the universe; and sky surveys that look deeper into the universe than ever before.

“One of the great things about the summer institute was its wide range of topics, which helped me see the larger context of my own work,” said Danny Brooker, a graduate student at the University of Florida who studies cosmic inflation, a period of exponential expansion believed to have occurred shortly after the Big Bang. “SSI was also a lot of fun and an excellent opportunity to meet great speakers and other students.”

Gongjun Choi, a graduate student in theoretical particle physics at Stony Brook University, said, “I’m interested in research at the interface of elementary particle physics and cosmology, and how this field could tell us more about potential physics beyond the Standard Model of particle physics. Two weeks of SSI provided more information about basic concepts, hot topics and future directions than I could have possibly learned in two or three months of reading papers.”

Participants also worked on projects designed to engage them more deeply with topics related to the institute’s theme.

“We had six teams working on different projects during SSI and giving reports at the end,” said Thomas Rizzo, head of the theory group in SLAC’s Elementary Particle Physics Division and lead SSI organizer. “We were very impressed with the amount and quality of their work and with the ideas they came up with.”

The team selected for best presentation, for example, developed ideas for new experiments that could support or reject the hypothesis that massive black holes created in the very early universe are a source of dark matter.

Tanvi Karwal, a graduate student at Johns Hopkins University who studies the expansion history of the universe with cosmic microwave background data, said, “SSI was a great experience. It was particularly valuable to hear first-hand accounts from researchers collecting and analyzing cosmological data obtained with different methods. I learned things that I hadn’t considered in my work before, which will be very helpful in developing a better plan for my future research.”

Training the next generation of scientists in developing fresh ideas has always been a key objective of SSI. Particle astrophysics and cosmology are particularly fertile ground for exploration. Although researchers already have a relatively good grasp of many aspects of the universe’s fundamental physics, there is no shortage of unanswered important questions: Why is there any matter at all? Did the expanding universe undergo a period of inflation? What exactly is dark matter? Does dark energy change over time? Do we live in one of many universes?

“I won’t give you any answers,” said Roger Blandford, a faculty member of SLAC’s and Stanford University’s Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), addressing SSI participants in the event’s closing lecture. “But you should be thinking about all these things and make up your own mind.”

For photos of the event check out the SSI Facebook page.           

SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, Calif., SLAC is operated by Stanford University for the U.S. Department of Energy's Office of Science. For more information, please visit

SLAC National Accelerator Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit