Jan_29 - VERY Early Universe Tuesday, January 29...

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VERY Early Universe Tuesday, January 29 Tuesday, January 29 (planetarium show tonight: 7 pm, 5 (planetarium show tonight: 7 pm, 5 th th floor floor
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It’s about time! Different calendars have different starting times (birth of Christ, hijra to Medina, etc.) The Big Bang (start of expansion) provides an absolute zero absolute zero for time.
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Universe started expanding at a time t = 0 t = 0 . What is the current current time t = t t = t 0 0 ? (That is, how much time has elapsed since the Big Bang?) We’ve already answered that question (approximately).
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1/H 0 , called the “ Hubble Hubble time time ”, is the approximate age of the universe in the Big Bang Model. At a finite time in the past (t ≈ 1/H 0 ), the universe began in a very dense state. Flashback slide!
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The Hubble time, 1/H 0 , is approximately equal to t 0 (time elapsed since Big Bang). If expansion has been slowing down slowing down , the universe is younger younger than 1/H 0 . If expansion has been speeding up speeding up , the universe is older older .
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Redshift (z) of a distant object: measure of how much the universe has expanded since light was emitted. Since universe has been expanding continuously, each z z corresponds to a unique time t t .
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Looking at the Cosmic Microwave Background: z ≈ 1000, t ≈ 350,000 years
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As time (t) increases, density and temperature decrease decrease .
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the the temperature of the early universe”? Today, the universe is full of things
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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_29 - VERY Early Universe Tuesday, January 29...

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