![]() In addition to this cosmic microwave background radiation, theĮarly universe was filled with hot hydrogen gas with a density of about 1000 atoms perĬubic centimeter. Size, the cosmic microwave background was a hundred times hotter (273 degrees aboveĪbsolute zero or 32 degrees Fahrenheit, the temperature at which water freezes to form ice When the visible universe was one hundredth of its present Present size, the density of matter was eight times higher and the cosmic microwaveīackground was twice as hot. Smaller, denser and hotter in the distant past. One of the profound observations of the 20th century is that the universe is expanding. The Origin of the Cosmic Microwave Background Scales at very early times, since the radiation we see today has traveled over such a large distance. ![]() Properties of the radiation, we can learn about conditions in the universe on very large Long before stars or galaxies ever existed. The CMB radiation was emitted 13.7 billion years ago, only a few hundred thousand years after the Big Bang, They were only a few billion years after the Big Bang. Observe Andromeda, the nearest big galaxy, as it was about 2.5 million years ago.Īstronomers observing distant galaxies with the Hubble Space Telescope can see them as Thus, we see them as they were 10 to 100 years ago. Most of the stars that are visible to the naked eye in the night Since light travels at a finite speed, astronomers observing distant objects are Why study the Cosmic Microwave Background? Tried to devise alternative explanations for the source of this radiation, but none have Imagine a local source of radiation that was this uniform. Interpret the radiation as remnant heat from the Big Bang it would be very difficult to Uniform to better than one part in a thousand! This uniformity is one compelling reason to Left shows a false color depiction of the temperature (brightness) of the CMB over theįull sky (projected onto an oval, similar to a map of the Earth). Glow with a brightness that was astonishingly uniform in every direction. In fact, if we could see microwaves, the entire sky would However, it fills the universe and can beĭetected everywhere we look. Spectrum, and is invisible to the naked eye. In the microwave portion of the electromagnetic Today, the CMB radiation is very cold, only 2.725° aboveĪbsolute zero, thus this radiation shines primarily Penzias and Wilson shared the 1978 Nobel prize in physics Wilson detailing the observations, and one by Dicke, Peebles, Roll, and Wilkinson giving The result was a pair of papers in the Astrophysical Journal (vol. When they heard about the Bell Labs result they immediately realized that the CMB ![]() Coincidentally, researchers at nearby Princeton University, led by Robert DickeĪnd including Dave Wilkinson of the WMAP science team, were devising an experiment to find The radiation was acting as a source of excess noise in a radio receiver they wereīuilding. It was first observed inadvertently in 1965 byĪrno Penzias and Robert Wilson at the Bell Telephone Laboratories in Murray Hill, New The existence of the CMB radiation was first predicted by Ralph Alpherin 1948 in connection with his research on Big Bang Nucleosynthesis undertaken together with Robert Herman and George Gamow. Discovery of the Cosmic Microwave Background Thus the universe shouldīe filled with radiation that is literally the remnant heat left over from the Big Bang,Ĭalled the cosmic microwave background", or CMB. Very hot place and that as it expands, the gas within it cools. The Big Bang theory predicts that the early universe was a
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