科学家发现宇宙膨胀的证据

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　　WASHINGTON, March 17 (Xinhua) -- U.S. astronomers¹ announced Monday they have captured the first images of gravitational waves, or ripples² in space-time described as the "first tremors³"" of the Big Bang in which the universe came into existence 14 billion years ago.

　　The researchers believed that the results represent the first direct evidence of cosmic inflation, a theory that say the universe expanded by 100 trillion trillion times in less than the blink of an eye in the first fleeting⁴ fraction of a second after the Big Bang.

　　"This work offers new insights into some of our most basic questions: Why do we exist? How did the universe begin?" Harvard- Smithsonian Center for Astrophysics theorist Avi Loeb said in a statement.

　　Scientists find first direct evidence of cosmic inflation

　　"These results are not only a smoking gun for inflation, they also tell us when inflation took place and how powerful the process was," Loeb said.

　　These groundbreaking results came from observations by the BICEP2 telescope at the South Pole of the cosmic microwave background, a faint glow left over from the Big Bang. Tiny fluctuations⁵ in this afterglow provide clues to conditions in the early universe. For example, small differences in temperature across the sky show where parts of the universe were denser⁶, eventually condensing into galaxies⁷ and galactic clusters.

　　But as theorized, inflation should also produce gravitational waves, ripples in space-time propagating throughout the universe. Observations from the BICEP2 telescope at the South Pole now demonstrate that gravitational waves were created in abundance during the early inflation of the universe.

　　On Earth, light can become polarized by scattering⁸ off surfaces, such as a car or pond, causing the glare that polarized sunglasses are designed to reduce. In space, the radiation of the cosmic microwave background, influenced by the squeezing of gravitational waves, was scattered⁹ by electrons, and became polarized, too.

　　Because gravitational waves have a "handedness," they can have both left- and right-handed polarizations and leave behind a characteristic pattern of polarization on the cosmic microwave background known as B-mode polarization.

　　"The swirly¹⁰ B-mode pattern of polarization is a unique signature of gravitational waves," said collaboration¹¹ co-leader Chao-Lin Kuo of Stanford University. "This is the first direct image of gravitational waves across the primordial¹² sky."

　　The team traveled to the South Pole to take advantage of its cold, dry, stable air to examine spatial¹³ scales on the sky spanning about one to five degrees, two to ten times the width of the full Moon.

　　"The South Pole is the closest you can get to space and still be on the ground," said John Kovac of the Harvard-Smithsonian Center for Astrophysics, project co-leader and BICEP2 principal investigator¹⁴. "It's one of the driest and clearest locations on Earth, perfect for observing the faint microwaves from the Big Bang."

　　They were "surprised" to detect a B-mode polarization signal " considerably¹⁵ stronger than many cosmologists expected."

　　The researchers said they analyzed¹⁶ their data for more than three years in an effort to rule out any errors. They also considered whether dust in our galaxy¹⁷ could produce the observed pattern, but the data suggest this is "highly unlikely."

　　Several physicists¹⁸ noted¹⁹ that this could be a Nobel Prize level discovery.

　　"This certainly would rank with the most important discoveries in cosmology over the past 25 years, two of which have already won Nobel Prizes," Lawrence Krauss, professor of Arizona State University, wrote in an email to Xinhua.

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