SANTA BARBARA, Calif. — The word “crisis” hung in the air from the very beginning of the meeting.
In a room just steps from the ocean in Santa Barbara, astronomers and physicists shifted restlessly in their chairs. Sunshine and sea breezes beckoned, but the scientists had cloistered themselves to debate one of the biggest quandaries in physics: how fast the universe is expanding.
Estimates based on exploding stars, or supernovas, had suggested that the universe is growing approximately 10 percent faster than indicated by light emitted just after the Big Bang, about 13.8 billion years ago. Now, a measurement based on observations of luminous objects called quasars had pushed the problem beyond a statistical benchmark known as five sigma, denoting that the issue was something to take seriously.
At the front of the room on July 15, two Nobel-winning physics titans debated the appropriate level of alarm. Cosmologist Adam Riess of the Space Telescope Science Institute in Baltimore queried theoretical particle physicist David Gross: How would particle physicists refer to a discrepancy this large?