1. COSMOLOGY SL - summary

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

3. OLBERS’PARADOX Newton’s static universe (1700)  The universe is infinite, has no beginning, no end.  Problem: Why is the night sky dark? Finite, expanding universe 1. Finite number of stars with finite lifetime 2. Finite age of universe: light has not reached us 3. Radiation is red-shifted; i.e. has less energy

4. THE BIG BANG 1  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

5. THE BIG BANG 2 Standard Big Bang model  Creation of space and time  About 13.7 billion years ago  Theoretical prediction: 25% helium

6. DEVELOPMENT OF THE UNIVERSE Three scenarios: 1. Closed: the universe increases to a maximum value and collapses again; density of universe > critical density 2. Flat: the universe expands but the rate of expansion decreases; density of universe = critical density (≈10 -26 kg.m -3 ) 3. Open: the universe expands forever; density of universe < critical density

7. MASS-ENERGY IN THE UNIVERSE 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