Cosmology in a nutshell

 Minimalist "Cosmology in a Nutshell"

Things "every astronomer should kind-of know"; HWR - very undigested list

Space and the overall evolution of the Universe is described by a metric

• it's the Robertson-Walker metric; cosmological principle puts all interesting stuff into a(t)
• a(t) depends on mass-energy-density of the Universe; and an expansion scale factor H(t); (1+z)~1/a
• a(t), which depends on O_M, O_L, O_R, determines the dependence of fluxes and sizes on redshift, which in turn constrains the "Omegas"

An expanding Universe goes through distinct thermal phases: T ~ 1/a

• there are 10^9x more photons in the Universe, but rho_phot ~ a^-4; while rho_mass~a^-3; the two are equal at z~15.000
• after three minutes, kT ~ DeltaE (proton - neutron) --> He forms
• at z~1300 T~4000K recombination P+e- --> H
• "surprising" in light of 13.6EV <--> 20.000K
• scattering off free electrons (Thompson) disappears --> long-mean-free path
• ==> CMB: photons from "surface of last scattering" elsewhere, reaching us now
• CMB bizarrely uniform on large scales
• small-scale temperature fluctuations (10^-4.5) reflect initial density fluctuations (in complex ways)
• at z~9, discrete UV light sources (hot stars, accretion disks) re-ionize the Universe
• making it (partially) transparent in UV

Structure grows, eventually forming galaxies, etc..

• initial fluctuations seeds in inflationary epoch (frozen quantum fluctuations)
• grow happens in competition between gravitational instability and expansion never faster than linear delta ~ a. <-- therefore structure growth depends on (and constrains) the Omegas
• eventually some fluctuations become no-linear --> gran. collapse --> halos

We now know the Omegas and Ho at the % level

• from all the above