2011 © University of Cambridge. Not to be quoted or reproduced without permission.
Physical Cosmology
Dr Ian Parry Tel: 01223 337092 Room: H57 E-mail: [email protected] Lectures: Mon 10am, Thurs 10am 2011 © University of Cambridge. Not to be quoted or reproduced without permission. HANDOUTS
• www.ast.cam.ac.uk/~irp/teaching • Username: intro • Password: dotzenblobs 2011 © University of Cambridge. Not to be quoted or reproduced without permission. Physical Cosmology Course Schedule 2011 © University of Cambridge. Not to be quoted or reproduced without permission. What is cosmology about?
Cosmology from Greek s world s word, reasoning, theory
Physical Cosmology studies the Universe as a whole, draws on many branches of Physics.
It tries to explain the following properties of the Universe:
• geometry, dynamics • content (baryons, photons, neutrinos, dark matter, dark energy) • spatial distribution • time evolution (thermal history, growth of structure, galaxy formation) 2011 © University of Cambridge. Not to be quoted or reproduced without permission.
Text books 2011 © University of Cambridge. Not to be quoted or reproduced without permission. 2011 © University of Cambridge. Not to be quoted or reproduced without permission.
http://http://www.nap.edu/readingroom/books/cosmologywww.nap.edu/readingroom/books/cosmology 2011 © University of Cambridge. Not to be quoted or reproduced without permission.
Sequence of events
• At z=1100 the Universe has cooled down to 3000K . Hydrogen becomes neutral (“Recombination”). • At z <~ 20 the “first” star (clusters)/small galaxies form. • At z ~ 6-10 these gradually photo-ionize the hydrogen in the IGM (“Reionization”). • At z<6 galaxies form most of their stars and grow by merging. • At z<1 massive galaxy clusters are assembled. 2011 © University of Cambridge. Not to be quoted or reproduced without permission.
The whole sky as seen by WMAP
WMAP = Wilkinson Microwave Anisotropy Probe 2011 © University of Cambridge. Not to be quoted or reproduced without permission. 2011 © University of Cambridge. Not to be quoted or reproduced without permission. The Standard Model 2011 © University of Cambridge. Not to be quoted or reproduced without permission. Cosmology – early history “The Greeks” Aristotle (384-322 BC) geocentric cosmology heavenly bodies move on spheres Ptolemy (100-170) epicycles
“The Renaissance” Copernicus (1473-1543) Earth not at the centre of the Universe (Copernican principle) Brahe (1546-1601) detects supernova, measures planetary motion Kepler (1571-1630) elliptic planetary motion, Kepler’s laws Galileo (1546-1642) observes planets with telescope detects moons of Jupiter Newton (1643-1727) calculus, Newton’s laws, mechanics, deterministic cosmology 2011 © University of Cambridge. Not to be quoted or reproduced without permission. Cosmology – history continued 1683 Newton’s Principia 1927 George Lemaitre proposed the “primeval atom”: expansion implies 1750 Structure of Milky Way a singularity in the past (Wright, Kant, Herschel) 1948 Nucleosynthesis of light elements in early universe and prediction of the 1915 Einstein’s General relativity CMB (Gamow, Alpha, Herman)
1916/7 Relativistic Cosmologies 1948 Steady-state theory proposed (Einstein, Friedman, Lemaitre, (Hoyle, Bondi, Gold) de Sitter) 1949 Hoyle coins phrase “big bang”
1920 Curtis/Shapley debate on 1957 Nucleosynthesis of heavy elements galaxies (Burbidge, Burbidge, Hoyle, Fowler) 1924 Hubble establishes Andromeda 1965 Cosmic microwave background nebula to be extragalactic (CMB) discovered (Penzias, Wilson) Late Expansion of Universe 1920’s established, Hubble’s law 2011 © University of Cambridge. Not to be quoted or reproduced without permission. Cosmology – recent history
1980’s Hot/Cold Dark Matter; Large Scale Structure in galaxy distribution measured 2003 announcement of results of WMAP satellite 1992 Detection of CMB fluctuations by COBE satellite late increasing observational evidence 1990s for cosmological constant/dark energy, e.g. from type Ia supernovae
2000 Detection of “acoustic peaks” in CMB power spectrum by balloon experiments 2011 © University of Cambridge. Not to be quoted or reproduced without permission. 2011 © University of Cambridge. Not to be quoted or reproduced without permission. 2011 © University of Cambridge. Not to be quoted or reproduced without permission. 2011 © University of Cambridge. Not to be quoted or reproduced without permission. 2011 © University of Cambridge. Not to be quoted or reproduced without permission. 2011 © University of Cambridge. Not to be quoted or reproduced without permission.
The cosmic microwave background photons were last scattered when the Universe was only 380 000 years old. 2011 © University of Cambridge. Not to be quoted or reproduced without permission. 2011 © University of Cambridge. Not to be quoted or reproduced without permission. 2011 © University of Cambridge. Not to be quoted or reproduced without permission. Scales/Distances
7 Earth 1.3 x 10 m 1 parsec =3.08 x 1016 m Moon 3.6 x 106 m Sun 1.4 x 109 m pc, kpc, Mpc, Gpc distance to k kilo 103 11 Sun 1.5 x 10 m M Mega 106 centauri 4.0 x 1016 m G Giga 109 Galactic centre 2.6 x 1020 m M31 Andromeda 2.2 x 1022 m Virgo cluster 4.6 x 1023 m Hubble radius 1.4 x 1026 m 2011 © University of Cambridge. Not to be quoted or reproduced without permission. Cosmological Principles
• Copernican Principle: Earth is not at the centre of the Universe
• Perfect Cosmological Principle: The Universe is homogeneous, isotropic and static .
• Anthropic Principle: The Universe must have conditions which are compatible with our existence Multiverses
• The Cosmological Principle (agreed upon by most): The Universe is homogeneous and isotropic 2011 © University of Cambridge. Not to be quoted or reproduced without permission. homogeneous: the same everywhere no point special isotropic: no preferred direction
isotropic everywhere homogeneous
homogeneous isotropic