The oldest science?

  One of the most rapidly evolving fields of modern research.

  Driven by observations and instruments

  Intersection of physics (fundamental laws) and astronomy (contents of the universe)

  Study of the Universe viewed as a whole (not a very humble field of science! Must coarse-grain and shove some details under the rug.)

  general relativity (back bone)   astronomy (supporting data)   particle physics (evolution at earliest epochs)   plasma physics (a physical system; objects)   thermodynamics (of an expanding plasma)   chemistry (late evolution; individual objects)   statistics (large scale description, initial cond’s)   mathematical physics (earliest stages)   … cosmetology (“kosmos”=“harmony”)

  ~ 80 years old (external galaxies, expansion)   ~ 40 yrs ago: CMB (hot big bang, structures)   ~ 10 yrs: Dark Energy (???)

  cf. Particle Physics: less rigorously defined open questions, puzzles are more numerous, and more fundamental

•  I. Cosmological Principle homogeneous and isotropic on large scales •  II. Expansion: kinematics expanding in a way that preserves I. → Hubble •  III. Expansion: dynamics obeys general relativity theory •  IV. Hot Big Bang hot dense state, dominated by thermal radiation •  V. Inflation(*) initial exponential (“superluminal”) expansion •  VI. The Dark Sector(**) to account for apparent acceleration + large structures

•  Galaxy Counts - follow N(>f) ∝ f -3/2 historical argument; must now disentangle space-time curvature and galaxy evolution - statistics: δN/〈N〉 vs L monotonically decreasing L ~ 30 Mpc gives δN/〈N〉 ~ 0.5 (IRAS) - more elaborate statistics: power spectra (2d,3d) low power on large scales

Super clusters and voids out to ~100 Mpc scales

No evidence for clusters of Super clusters

•  CfA Redshift Survey (mid/late1980’s) •  ~104 galaxies out to ~30 Mpc

Sloan Digital Sky Survey (SDSS)

www.sdss.org

~106 galaxies out to ~1 Gpc

•  Cosmic Microwave Background

Wilkinson Microwave Anisotropy Probe: February 13, 2003

CMB Galaxies

Distance (1pc = 3 light years)

Velo

city

(km

/s)

•  Hubble (1929): redshift vs distance to 20 galaxies (Cepheids) •  Linear expansion v=H0d → Hubble length: d=c/H0 ~ 5 Gpc

  Hubble’s constant: H0=v/r=500 km/s/Mpc

  Modern value: 72±8 km/s/Mpc (HST key project)

•  Hubble diagram extending out to > 1 Gpc

•  Hubble diagram extending out to > 1 Gpc

•  Non-linear expansion law can be explained within relativistic theory

•  But it requires a lot of “dark energy”:

Dark Energy Dark Matter Neutrinos Ordinary gas and stars

Extragalactic Background (Hauser & Dwek 2001)

•  Hot radiation from the big bang, which has cooled to ~3 Kelvin by present epoch •  Predicted in 1948 (Gamow; Alpher & Herman) → expanding universe a background for plasma/nuclear physics prediction (4K) based on light elements (D) •  Observed in 1965 (Penzias & Wilson) •  Extremely smooth, but seeds of structure discovered by COBE (1992) and WMAP (2003) •  Accounts for 3% of the static on your TV screen!

  Extremely accurately measured quantity   The most precisely measured example of a black-body spectrum

  Implies thermal equilibrium   Temperature measured to be T=2.725 ± 0.001 K   Too cold and dilute to achieve equilibrium today - real puzzle outside the big bang model - natural by-product of hot dense phase

Supports: •  Cosmological principle (isotropy) •  Laws of nature not varying even over cosmic scales •  Universe expanded •  Universe was much hotter in the past •  A puzzle: horizon problem. Inflation?

  CMB angular and frequency structures contain a wealth of cosmological information

  Amplitude of the temperature fluctuations is consistent with gravitational structure formation

  This wealth of detail (to be discussed in future lectures) is all consistent with the hot big bang + cold dark matter structure formation model

  hard feat for alternative to replicate / postdict!

•  Paradigm? Model? Picture? Principle? Scenario? Theory? Idea? Mechanism?

[you decide]

•  Solves some major problems: - flatness problem - horizon problem - monopole problem

•  No compelling competing idea for (i) starting expansion and (ii) producing inhomogeneities

•  Flat universe with critical density Ω=1.02 ±0.02

•  Scale invariant power spectrum of density fluctuations

n=dlnP/dlnk=0.99±0.04

•  Relic gravitational waves from metric perturbation (not yet observed, but future CMB experiments can detect them)

  What is the nature of dark matter ?   What is the nature of dark energy ?   Why is the Universe expanding ?   What is the origin of initial fluctuations ?   What is the physical cause of inflation ?   Is General Relativity correct in early universe ?

  Many other unsolved ‘astrophysics’ problems: - where are the baryons ? - how did galaxies form ? - what sets properties of intergalactic gas? - ….