and other major theories of modern cosmology.If the colossal fireball known as the Big Bang really marked the birth of our universe, as most astronomers believe, then things would have been very hot back in the early days, when unfathomable amounts of energy had not yet expanded to the vast reaches now observed.
The idea of a Big Bang is supported by Edwin Hubble's discovery, in the 1920s, that the universe is
| An Expanding Balloon |
| To imagine an expanding universe, think of a balloon with spots on itssurface. As the balloon is inflated, the spots grow farther apart. If you stoodwithin one of these spots, you'd see all the others moving away from you, and the most distant spots would move appear to move the fastest. |
As gas from the Big Bang expanded over the last 10 billion to 15 billion years, the idea goes, it would have cooled, leaving present-day space the relatively frigid place it is at 2.726 Kelvin (minus 454.8 degrees Fahrenheit, or minus 270 degrees Celsius).
And if all this is true, then scientists should be able to look far away, and therefore back in time, to find evidence of a warmer universe.
That's what Raghunathan Srianand, of the Inter University Center for Astronomy and Astrophysics in Pune, India, and colleagues did. They studied light from a distant quasar, one of the most luminous objects in the universe. To be more precise, they actually studied the light as it passed through an ancient cloud of gas and dust back when the universe was only about 3 billion years old.
The results show that the cosmic background radiation temperature around the cloud must have been between 6 and 14 Kelvin (minus 449 to minus 434 degrees Fahrenheit, or minus 262 to minus 259 degrees Celsius).
"Our measurement demonstrates for the first time that the cosmic radiation exists at earlier times and has a higher temperature than today," the researchers reported in the December 20 issue of the journal Nature.
The value is consistent with an estimate of 9 Kelvin (minus 436 degrees Fahrenheit, or minus 260 degrees Celsius), predicted by the Big Bang theory to be the cosmic background radiation temperature at the position of the cloud, said John Bahcall of Princeton University's Institute for Advanced Study. "This is three times as high as its temperature near Earth (2.73 Kelvin), as expected."
Bahcall, who was not involved in the research, said the report represents a "landmark result," writing in an accompanying analysis in Nature.
The researchers studied both visible and ultraviolet light from the quasar, using the European Southern Observatory's Paranal observatory in Chile. The light was absorbed by carbon atoms and hydrogen molecules. Cosmic background radiation heated up the atoms and molecules in the cloud in a way that allows the temperature of the gas to be estimated.
Bahcall said the team was lucky to find a space cloud with the right clues.
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