ASTR 1102-0022008 Fall Semester

Joel E. Tohline, Alumni ProfessorOffice: 247 Nicholson Hall

[Slides from Lecture23]

Chapter 26: Cosmologyand

Chapter 27: Exploring the Universe

Implications of Big Bang

• Era of “recombination” and “Cosmic Microwave Background (CMB)”

• Origin of the Elements

• Non-uniformities in the Early Universe and the Origin of Galaxies

At the time of recombination, the temperature wasa few thousand degreeseverywhere!

But from our point ofview “now,” this radiation has been significantly redshifted(due to expansion ofthe universe) so the spectrum should looklike a “black-body” ofa much cooler temperature.

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At the time of recombination, the temperature wasa few thousand degreeseverywhere!

But from our point ofview “now,” this radiation has been significantly redshifted(due to expansion ofthe universe) so the spectrum should looklike a “black-body” ofa much cooler temperature.

From Einstein’s theory,Dicke & Peebles (Princeton University)predict T = 3 K.

At the time of recombination, the temperature wasa few thousand degreeseverywhere!

But from our point ofview “now,” this radiation has been significantly redshifted(due to expansion ofthe universe) so the spectrum should looklike a “black-body” ofa much cooler temperature.

From Einstein’s theory,Dicke & Peebles (Princeton University)predict T = 3 K.

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What would a 3 K spectrum look like?

Penzias & Wilson discover CMB radiation; awarded 1978 Nobel Prize

Uniformity of CMB• COBE satellite measurements (which

improved on discovery of Penzias & Wilson) show …– CMB temperature is 2.725 K

– Exactly the same temperature no matter which direction you look in the sky! at the time of recombination, the universe was extremely uniform

– Slight Doppler shift due to Earth’s motion through space

– Otherwise, only very tiny fluctuations; smaller than 200 micro-Kelvin (K)

Uniformity of CMB• COBE satellite measurements (which

improved on discovery of Penzias & Wilson) show …– CMB temperature is 2.725 K

– Exactly the same temperature no matter which direction you look in the sky! at the time of recombination, the universe was extremely uniform

– Slight Doppler shift due to Earth’s motion through space

– Otherwise, only very tiny fluctuations; smaller than 200 micro-Kelvin (K)

Uniformity of CMB• COBE satellite measurements (which

improved on discovery of Penzias & Wilson) show …– CMB temperature is 2.725 K

– Exactly the same temperature no matter which direction you look in the sky! at the time of recombination, the universe was extremely uniform

– Slight Doppler shift due to Earth’s motion through space

– Otherwise, only very tiny fluctuations; smaller than 200 micro-Kelvin (K)

Uniformity of CMB• COBE satellite measurements (which

improved on discovery of Penzias & Wilson) show …– CMB temperature is 2.725 K

– Exactly the same temperature no matter which direction you look in the sky! at the time of recombination, the universe was extremely uniform

– Slight Doppler shift due to Earth’s motion through space

– Otherwise, only very tiny fluctuations; smaller than 200 micro-Kelvin (K)

Uniformity of CMB• COBE satellite measurements (which

improved on discovery of Penzias & Wilson) show …– CMB temperature is 2.725 K– Exactly the same temperature no matter which

direction you look in the sky! at the time of recombination, the universe was extremely uniform

– Slight Doppler shift due to Earth’s motion through space

– Otherwise, only very tiny fluctuations; smaller than 200 micro-Kelvin (K) – confirmed by WMAP spacecraft

Implications of Big Bang

• Era of “recombination” and “Cosmic Microwave Background (CMB)”

• Origin of the Elements

• Non-uniformities in the Early Universe and the Origin of Galaxies

Implications of Big Bang

• Era of “recombination” and “Cosmic Microwave Background (CMB)”

• Origin of the Elements

• Non-uniformities in the Early Universe and the Origin of Galaxies

Origin of the Elements

• Looking back even further in time – before recombination – the universe was even hotter

• At a sufficiently early epoch it was too hot for any atomic nuclei heavier than Hydrogen to have existed!

• When did the first elements form; and which ones were able to form? ANS: In the “first 3 minutes”; and only Helium!

Origin of the Elements

• Looking back even further in time – before recombination – the universe was even hotter

• At a sufficiently early epoch it was too hot for any atomic nuclei heavier than Hydrogen to have existed!

• When did the first elements form; and which ones were able to form? ANS: In the “first 3 minutes”; and only Helium!

Origin of the Elements

• Looking back even further in time – before recombination – the universe was even hotter

• At a sufficiently early epoch it was too hot for any atomic nuclei heavier than Hydrogen to have existed!

• When did the first elements form; and which ones were able to form?

Origin of the Elements

• Looking back even further in time – before recombination – the universe was even hotter

• At a sufficiently early epoch it was too hot for any atomic nuclei heavier than Hydrogen to have existed!

• When did the first elements form; and which ones were able to form? ANS: In the “first 3 minutes”; and only Helium!

How Do We Measure 0 ?

• Measure (count up) all the matter density in the universe (0) and compare the value to c.

• Measure distances and redshifts of even more distant galaxies and look for deviations in the Hubble diagram.

Modern Hubble Law implies:

0 = m +