PHYS 005 Lecture Notes - Lecture 17: Reionization, Cosmic Microwave Background, Baryon
5 Jul 2018
School
Department
Course
Professor
5/14 Session 17 (session 19) The Universe before Recombination
Cosmic Microwave Background
Present temp should be microwave-like temp
Beginning of universe- only hydrogen
●Cont.s EXPANDING w. Universe
Stars release helium (after fusion in core)
Microwave noise- particles fr. beginning of universe- Penzias & Wilson
●Checkmark- BB is true
Dicke- universe’s high temps (photons) should become low energy microwaves by now
●To explain where all the other heliums come from (other than stars)
Densities
We can calc how dense universe was in past v. now
●Given temp of photons of cosmic microwave background
●prad= 4.6 x 10 ^-31 kg/m^3
Difficult to determine amt of dark matter in Universe
●Use hot gas in CLUSTERS of galaxies
○Make gravitational lenses
●Gravity fr dark matter & regular matter ARE IN EQUILIBRIUM
○Radiation pressure from hot gas emits x-rays
Avg density of matter (baryonic + dark) in Universe is
●pm= 2.4 x 10^ -27 km/m^3
Observable universe- 13.4 billion ly? That we can see
●Avg of 1 atom of hydrogen/m^3
●Versus our atm… A LOT more
MATTER DOMINATES THE PRESENT UNIVERSE
●Matter is 5,200x MORE ABUNDANT than radiation in Universe
●For every 6 atoms of matter
○1 is baryonic, 5 is dark matter
●Dark matter is MORE EVENLY DISTRIBUTED than baryonic matter
○Baryonic matter clumps into stars
Document Summary
5/14 session 17 (session 19) the universe before recombination. Microwave noise- particles fr. beginning of universe- penzias & wilson. Dicke- universe"s high temps (photons) should become low energy microwaves by now. To explain where all the other heliums come from (other than stars) We can calc how dense universe was in past v. now. Given temp of photons of cosmic microwave background. Difficult to determine amt of dark matter in universe. Use hot gas in clusters of galaxies. Radiation pressure from hot gas emits x-rays. Gravity fr dark matter & regular matter are in equilibrium. Avg density of matter (baryonic + dark) in universe is. Matter is 5,200x more abundant than radiation in universe. 1 is baryonic, 5 is dark matter. Dark matter is more evenly distributed than baryonic matter. **matter did not always dominate the universe- before- radiation dominated. We need matter to dominate to create gravity & form things. 1 million x more photons > atoms.
