The results reported on Monday emerged after researchers peered into the faint light that remains from the Big Bang of nearly 14 billion years ago.
The discovery "gives us a window on the universe at the very beginning," when it was far less than one-trillionth of a second old, said theoretical physicist Lawrence Krauss of Arizona State University, who was not involved in the work.
Marc Kamionkowski, a theoretical physicist at Johns Hopkins University who did not participate in the research, said the finding is "not just a home run. It's a grand slam."
Monday's findings were announced by a collaboration that included researchers from the Harvard-Smithsonian Center for Astrophysics, the University of Minnesota, Stanford University, the California Institute of Technology and NASA's Jet Propulsion Laboratory.
Astronomers scanned about 2 percent of the sky for three years with a telescope at the South Pole, where the air is exceptionally dry, to find 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 rapid growth, known as inflation.
The researchers say the light-wave pattern was caused by gravitational waves, which are ripples in space and time. If verified, 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.