Exploring the Cosmos: Evolution from Recombination to CMB

1. ASTR 1102-0022008 Fall Semester Joel E. Tohline, Alumni Professor Office: 247 Nicholson Hall [Slides from Lecture23]

2. Chapter 26: CosmologyandChapter 27: Exploring the Universe

3. 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

8. At the time of recombination, the temperature was a few thousand degrees everywhere! But from our point of view “now,” this radiation has been significantly redshifted (due to expansion of the universe) so the spectrum should look like a “black-body” of a much cooler temperature.

9. Remember “Black body spectrum” from Chapter 5

10. At the time of recombination, the temperature was a few thousand degrees everywhere! But from our point of view “now,” this radiation has been significantly redshifted (due to expansion of the universe) so the spectrum should look like a “black-body” of a much cooler temperature. From Einstein’s theory, Dicke & Peebles (Princeton University) predict T = 3 K.

11. At the time of recombination, the temperature was a few thousand degrees everywhere! But from our point of view “now,” this radiation has been significantly redshifted (due to expansion of the universe) so the spectrum should look like a “black-body” of a much cooler temperature. From Einstein’s theory, Dicke & Peebles (Princeton University) predict T = 3 K.

12. Remember “Black body spectrum” from Chapter 5 What would a 3 K spectrum look like?

13. Penzias & Wilson discover CMB radiation; awarded 1978 Nobel Prize

16. 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 (mK)

17. 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 (mK)

19. 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 (mK)

20. 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 (mK)

24. 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 (mK) – confirmed by WMAP spacecraft

27. 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

32. 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

33. 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!

36. 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!

38. 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?

41. 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!

44. How Do We Measure W0 ? • Measure (count up) all the matter density in the universe (r0) and compare the value to rc. • Measure distances and redshifts of even more distant galaxies and look for deviations in the Hubble diagram.

49. Modern Hubble Law implies: W0 = Wm + WL