For their research, astronomers scanned about 2 percent of the sky for three years with a telescope at the South Pole, chosen for its very dry air to aid in the observations.
They were looking for a specific pattern in light waves within the faint microwave glow left over from the Big Bang. The pattern has long been considered evidence of the rapid growth spurt, known as inflation. Kovac called it "the smoking gun signature of inflation."
The scientists say the light-wave pattern was caused by gravitational waves, which are ripples in the interweaving of space and time that sprawls through the universe. If confirmed, the new work would be the first detection of such waves from the birth of the universe, which have been called the first tremors of the Big Bang.
Arizona State's Krauss cautioned that it's possible that the light-wave pattern is not a sign of inflation, although he stressed that it's "extremely likely" that it is. It's "our best hope" for a direct test of whether the rapid growth spurt happened, he said.
Krauss and other experts said the results must be verified by other observations, a standard caveat in science.
Marc Kamionkowski, a theoretical physicist at Johns Hopkins University who didn't participate in the work, called the detection of the light-wave pattern "huge news" for the study of the cosmos.
"It's not every day you wake up and learn something completely new about the early universe," he said.
Malcolm Ritter can be followed at http://www.twitter.com/malcolmritter