Jan_24 - The Early Universe Thursday, January 24...

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The Early Universe The Early Universe Thursday, January 24 (planetarium show tonight: 7 pm, 5 th floor Smith Lab)
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Hot, dense, opaque objects emit light. Color (or wavelength) of light depends on object’s temperature.
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Temperature is inversely proportional to wavelength. red-hot iron = red-hot iron = 1000 K 1000 K lightbulb filament = lightbulb filament = 2900 K 2900 K Sun’s surface = Sun’s surface = 5800 K 5800 K
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Early universe was hot, dense, and opaque: it emitted light. In 1965, two astronomers (Penzias & Wilson) discovered faint “static” in their microwave antenna.
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This static was the “leftover light” from hot, dense, opaque early universe. Its spectrum peaks at λ ≈ 1 mm; this is microwave microwave radiation. Scientists call the “leftover light” the Cosmic Microwave Microwave Background (CMB). Intensity
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Temperature implied by CMB spectrum is T ≈ 3 K. (That’s COLD!)
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The universe became transparent at a temperature T ≈ 3000 K . But…objects at T ≈ 3000 K produce visible & infrared visible & infrared light (think “lightbulb filament”), not microwave microwave light.
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How did the cosmic background change from visible & infrared visible & infrared light (λ ≈ 0.001 mm) to microwave microwave light (λ ≈ 1 mm)? How did its temperature drop from 3000 K 3000 K to 3 K 3 K ?
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The universe is expanding. The universe is expanding. Distance between galaxies increases.
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This note was uploaded on 07/17/2008 for the course ASTRO 294 taught by Professor Ryden during the Winter '08 term at Ohio State.

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Jan_24 - The Early Universe Thursday, January 24...

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