1. Cosmology SL - summary

2. Structure • Solar system • Galaxy • Local group • Cluster • Super-cluster Cosmological principle • Homogeneity – no edge • Isotropy – no center Structures

3. Newton’s static universe (1700) • The universe is infinite, has no beginning, no end. • Problem: Why is the night sky dark? Finite, expanding universe • Finite number of stars with finite lifetime • Finite age of universe: light has not reached us • Radiation is red-shifted; i.e. has less energy Olbers’paradox

4. Hubble red-shift: galaxies now move away from each other, so in the past they were closer together. • 1964 Penzias-Wilson: cosmic microwave background (CMB), radiation black body spectrum: remnant of the hot explosion at the beginning of time. Present value 2.7 K The Big Bang 1

5. Standard Big Bang model • Creation of space and time • About 13.7 billion years ago • Theoretical prediction: 25% helium The big Bang 2

6. Three scenarios: • Closed: the universe increases to a maximum value and collapses again; density of universe > critical density • Flat: the universe expands but the rate of expansion decreases; density of universe = critical density (≈10-26 kg.m-3) • Open: the universe expands forever; density of universe < critical density Development of the universe

7. Normal matter (4%) Dark matter: matter we can not see (23%) • Unknown neutrino mass • Weakly Interacting Massive Particles (WIMPS) • Massive Compact Halo Objects (MACHOS) Distant supernovas move away from us at increasing speeds. This is caused by dark energy (73%) = all permeating vacuum energy, producing a repulsive force which causes an accelerated expansion Mass-energy in the universe