1. Astrophysics II: Cosmology
Kathy Cooksey

2. Concept Question:
How do you think the Universe began and evolved to its present state?
What have you heard about in class or in the news or …?

3. Big Bang Timeline
0 s: Big Bang--beginning of physics, of time, of space
10-43 s: gravity separates from electromagnetic and nuclear forces
10-35 s: Inflation begins
Strong force separates from weak and EM forces
s: inflation
Universe is thus homogeneous and isotropic
[13,700,000,000 years: now]

4. z: Redshift Speed of light c = 3105 km/s = 186,000 mi/s
Hubble’s constant H0 = 70 (km/s)/Mpc
Distance D
(1 Mpc = 3.3106 light-year)
Wavelength 
Velocity v

5. Redshift, Speed, Distance, Timez
(v/c)
D (Mpc)
tB (Myr)
0.01 42
137
0.05
0.049
209
665
0.1
0.095
413
1,290
0.5
0.385
1,880
5,020 1
0.6
3,320
7,730 3
0.882
6,460
11,500 5
0.946
7,940
12,500 10
0.984
9,660
13,200
Infinity
14,600
13,700
Look-back time tB

6. Beyond Big Bang Remaining story is of Expansion and cooling
Cosmic microwave background
400,000 year after Big Bang
First stars light up
z ~ 10 (500,000 years after)
Reionization complete
z ~ 6 (1 Myr after)

7. Cosmic Microwave Background
Strongest evidence for Big Bang theory
Especially inflation
3,000 K redshifted to K
Isotropic (uniform) to one part in 100,000
Remnant of last scattering surface (when H formed)
WMAP

8. Matter and Energy E = m c2 Big Bang nucleosynthesis
<1% Li
Actual energy budget
5% baryons
25% dark matter
70% dark energy

9. What is ordinary matter (baryons)?
Let’s see pretty pictures in motion

10. Virgo Cluster

11. SDSS Fly-by

12. UDF Zoom

13. Driver behind structure formation
What is dark matter?
Driver behind structure formation

14. Dark Matter Cosmological Simulation

15. What is dark energy?
???

16. Dark Energy Not known Originally mistakenly predicted by Einstein
Cosmological constant
Currently two hypotheses
Cosmological constant or “vacuum energy”
Fills space homogeneously
Scalar fields
Varies with time
Looks like cosmological constant

17. Summary Universe is 13.7 Gyr old Universe is “flat” but expanding
Expected to expand forever at decreasing rate
Structure formation is bottom-up
Large structure fragments into smaller
Universe is isotropic and homogeneous
Dark energy rules
Dark matter is governor
Regular matter is peon