August 20, 2004  


SSI Special Report: The Quigg Challenge

By Shawne Neeper and Davide Castelvecchi

Chris Quigg (Photo by Shawne Neeper)

In his opening address for the SLAC Summer Institute (SSI) entitled Nature’s Greatest Puzzles, theorist Chris Quigg of Fermilab set the tone for two weeks’ worth of exploration into ten of nature’s greatest physics questions. First, he challenged attending scientists to describe how their current work relates to one of the ten great questions—or is otherwise irresistibly fascinating. Second, propose the eleventh puzzle.

“The spirit of those opening remarks was partly that I’m uncomfortable with the idea of ‘great questions’,” Quigg said. On the one hand, he argued, it’s often by asking small questions that scientists find clues to sweeping ideas—as hot-air balloonist Hess’s curiosity about air conductivity led him to propose the existence of cosmic radiation. “These people had no idea they were answering a great question. They were just curious about a small thing.”

On the flip side, Quigg sought to stir SSI attendees’ imaginations about the broad implications of their own experiments. “It’s very easy, especially when you’re a student and are doing things because someone else told to you, to not think about why the work is so interesting or important.”

Enter the Quigg challenge. As homework, Quigg asked attendees to explain their work’s importance to a Great Question in only a paragraph or two. Science writers could be lurking behind any tree, Quigg warned; scientists had best be prepared. He was right. Many participants later found themselves facing a reporter’s notebook at SSI functions, and most had done their homework.

“The world is made of matter but not antimatter [Question 8] for no apparent reason,” said SUNY Stonybrook graduate student Ilektra Christidi of her experiments in rare particle decays. “So we want to explain how it happened” by examining how different flavors of particles mix.

2004 SSI Topics:
Nature’s Greatest Puzzles

1. Where and what is dark matter?

2. How massive are neutrinos?

3. What are the implications of the neutrino mass?

4. What are the origins of mass?

5. Why is there a spectrum of Fermion masses?

6. Why is gravity so weak?

7. Is nature supersymmetric?

8. Why is the Universe made of matter and not anti-matter?

9. Where do ultra-high-energy cosmic rays come from?

10. Did the Universe inflate at birth?


“If inflation occurred at all [Question 10], it was at energies that we wouldn’t be able to probe with present [high-energy physics] technologies,” said Caltech graduate student Tristan Smith. His thesis project explores how future experiments in NASA’s Beyond Einstein program could measure faint ripples in the geometry of space—proof that inflation did take place. “That would tell you how the large-scale structures of the universe—galaxies, clusters of galaxies—formed.”

One of the mysteries of neutrinos is exactly how heavy they are [Question 2]. University of Kentucky’s Susan Gardner is trying to improve estimates on their mass by looking at tritium decay. The ultimate goal? “There is an intrinsic joy in human understanding,” she said, quoting Latin poet Lucretius: “Happy is he who understands the nature of things.”

The next leap in understanding nature was the focus of the second—but also eleventh—challenge. In his opening address, Quigg presented a list of ten great physics puzzles, from CP violation to the flat universe, and challenged his audience to come up with an eleventh. Quigg received 37 entries from SSI’s array of physicists, students, university faculty and someone claiming to be George Bush.

The winning entry won neutrino theorist Yasaman Farzan a bottle of Iron Horse Brut California sparkling wine, signed by SLAC director Jonathan Dorfan and other physics noteworthies. Honorable mention and a copy of Peter Galison’s Einstein’s Clocks, Poincare’s Maps: Empires of Time went to Marco Zanetti, a student at Padova University in Italy, for his question about time, and to Thomas Topel, a Colorado State graduate student, for his question about symmetry breaking in grand unified theories.

On August 11, Farzan presented an 11-minute talk on her eleventh great question, Is the Lorentz invariance exact? Lorentz invariance—a principle of special relativity—states that laws of physics are identical for observers moving at constant velocity relative to each other. “Hopefully in the future we will learn that this is not the final word, and we will find something even stranger,” said Farzan, who will defend her Ph.D. thesis at the Sissa Institute in Trieste, Italy in October, “and this will help us to revolutionize physics again.”

For further information on SSI, see:

For more on the 11th Challenge entries, see:



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Last update Thursday August 19, 2004 by Emily Ball