Astrophysics II: Cosmology Kathy Cooksey

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 …?

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 10-35-10-32 s: inflation Universe is thus homogeneous and isotropic [13,700,000,000 years: now]

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

Redshift, Speed, Distance, Time z (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

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)

Cosmic Microwave Background Strongest evidence for Big Bang theory Especially inflation 3,000 K redshifted to 2.725 K Isotropic (uniform) to one part in 100,000 Remnant of last scattering surface (when H formed) WMAP

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

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

Virgo Cluster

SDSS Fly-by

UDF Zoom

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

Dark Matter Cosmological Simulation

What is dark energy? ???

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

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