1. Recent Developments in Cosmology Josh Frieman Quarknet, Argonne National Laboratory, July 2002

2. Cosmology: an ancient endeavor • How did the world around us come into being? • Has it always been like this or has it evolved? • If the Universe is changing, how did it begin and what will • it be like in the future? And (how) will it end? • Early Cosmology: the Universe evolved from a beginning Babylonian cosmology: Enuma elish • Judeo-Christian cosmology: Genesis • Greek and Roman myths and philosophers • Modern cosmology:expanding Universe established 1929, • evolving Universe established in 1965 (discovery of Cosmic • Microwave Background Radiation by Penzias & Wilson, • Nobel Prize in 1978)

3. Modern Science: --The Universe is knowable through repeatable observations --The Universe can be described in terms of universal physical laws Modern Cosmology:Archaeology on the Grand Scale --We cannot (yet) create universes in the laboratory and study them --We must observe stars, galaxies, cosmic radiations, etc, and use them as `pottery shards’ to reconstruct what the Universe was like at much earlier times, to weave a coherent story of cosmic evolution based on our understanding of physical laws. Fortunately, there are surprisingly few ways (given the laws of physics) to make a Universe that looks like ours today.

4. The macroscopic Universe observed: a hierarchy of Structure...

5. Human scale: Size ~ 100 cm Mass ~ 100 kg ~ 1029 atoms Density ~ 0.6 gm/cm3 Structures organized by atomic interactions Sarah Frieman b. March 26, 2001

6. Planets: Size ~ 1010 cm~1010 cm Mass ~ 1026 kg ~ 1054 atoms Density ~ 0.6 gm/cm3 Structures determined by atomic interactions & gravity

7. Brown Dwarf Star(Planet/star transition) Ordinary Stars: Size ~ 1011 cm Mass ~ 1030 kg ~ 1057 atoms Density ~ 0.5 gm/cm3 Hot gas bound by gravity

8. M87 Nebula in Orion (star forming region in our galaxy) Interstellar gas clouds & star clusters: Size ~ 1 parsec ~ 3 light-yr ~ 3 x 1018 cm Mass ~ 105 Msun

9. An Infrared view of the Milky Way (our galaxy) Galaxies: Size ~ 1022 cm ~ 10 kiloparsec (kpc) Mass ~ 1011 Msun Self-gravitating systems of stars, gas, and dark matter

10. A Brief Tour of Galaxies Images from the Sloan Digital Sky Survey (SDSS): An on-going project to map the Universe, the SDSS will catalog roughly 70 million galaxy images and measure 3D positions for ~700,000 of them by the time it is completed in 2005

12. UGC 03214: edge-on spiral galaxy in Orion

13. NGC 1087 spiral galaxy in Aries

17. Clusters of Galaxies: Size ~ 1025 cm ~ Megaparsec (Mpc) Mass ~ 1015 Msun Largest gravitationally bound objects: galaxies, gas, dark matter

18. Cluster of Galaxies `giant arcs’ are galaxies behind the cluster, gravitationally lensed by it

19. Apparent position 2 True position 2 Apparent Position 1 True Position 1 Observer Gravitational “lens” “Looking into” the lens: extended objects are tangentially distorted... Gravitational Lensing Basically, the same effects that occur in more familiar optical circumstances: magnification and distortion Objects farther from the line of sight are distorted less.

20. Helen Frieman b. 9/20/99

21. Helen behind a Black Hole Gravitational Lens

22. Mapping the Mass in a Cluster of Galaxies via Gravitational Lensing: Most of the Mass in the Universe is Dark (it doesn’t shine) Dark Matter

23. Superclusters and Large-scale Structure: Filaments, Walls, and Voids of Galaxies 100 Million parsecs (Mpc) You Are Here `Pizza Slice’ 6 degrees thick containing 1060 galaxies: position of each galaxy represented by a single dot

24. Superclusters and Large-scale Structure: Filaments, Walls, and Voids of Galaxies 100 Million parsecs (Mpc) You Are Here

25. Superclusters and Large-scale Structure: Filaments, Walls, and Voids of Galaxies Coma cluster of galaxies 100 Million parsecs (Mpc) You Are Here

26. Early SDSS Data ~200,000 Galaxies Mapped in 3D so far

27. The Big Bang Theory:a well-tested framework for understanding the observationsand for asking new questions The Universe has been expanding isotropically from a hot, dense `beginning’ (aka the Big Bang) for about 14 billion years The only successful framework we have for explaining several key facts about the Universe: Hubble’s law of galaxy recession:expansion Uniformity (isotropy) of Microwave background Cosmic abundances of the light elements: Hydrogen, Helium, Deuterium, Lithium, cooked in the first 3 minutes

30. The Big Bang Theory Not `just a theory’, but one of the most firmly established paradigms in science: The Standard Cosmological Model

31. The Big Bang Theory The Big Bang is an idealization, a simplified description (analogous to the approximation of the Earth as a perfect sphere), and cosmologists are now occupied with mapping out/filling in the details. Even so, certain basic elements of the model remain to be understood: e.g., the natures of the Dark Matter & Dark Energy which together make up 95% of the mass-energy of the Universe These puzzles do NOT mean that the Big Bang Theory is wrong—rather, it provides the framework for investigating them.

32. The Big Bang Theory:Are there human implications?

35. (as seen on public buses and roadside billboards)

36. Spectrum of Light from Galaxies Redshift of Galaxy Emission & Absorption Lines: recession velocity v/c ≈ z = /0 (approximation for objects moving with v/c << 1) receding slowly  receding quickly

37. Hubble Space Telescope in Orbit Measured distances to galaxies using Cepheid Variable stars

38. Hubble (1929) Hubble Space Telescope (2000)

39. Modern `Hubble Diagram’ Extend to larger distances using objects brighter than Cepheids

40. The Microwave Sky: The Universe is filled with thermal radiation: Cosmic Microwave Background (CMB) COBE Map of the Temperature of the Universe On large scales, the Universe is (nearly) isotropic around us (the same in all directions): CMB radiation probes as deeply as we can, far beyond optical light from galaxies: snapshot of the young Universe (at 400,000 years old) T = 2.7 degrees above absolute zero Scale of the Observable Universe: Size ~ 1028 cm Mass ~ 1023 Msun

41. CMB (nearly) isotropic Earth not

42. The Cosmological Principle A working assumption (hypothesis) aka the Copernican Principle: We are not priviledged observers at a special place in the Universe: At any instant of time, the Universe should appear ISOTROPIC (over large scales) to All observers. A Universe that appears isotropic to all observers is HOMOGENEOUS i.e., the same at every location (averaged over large scales).

43. The Microwave Sky: COBE Map of the Temperature of the Universe Dipole anisotropy due to our Galaxy’s motion through the Universe T = 2.728 deg above absolute zero Red: 2.7+0.001 Blue:2.7-0.001 Red: 2.7+0.00001 deg Blue: 2.7-0.00001 deg

44. The Microwave Sky: COBE Map of the Temperature of the Universe Map with Dipole anisotropy removed: fluctuations of the density of the Universe (plus Galactic emission) T = 2.7 degrees above absolute zero Red: 2.7+0.001 Blue:2.7-0.001 Red: 2.7+0.00001 deg Blue: 2.7-0.00001 deg

45. Cosmology as Metaphor: From The New Yorker, March 5, 2001: `A hiss of chronic corruption suffuses the capital like background radiation from the big bang.’ --Hendrik Hertzberg `The Talk of the Town’

46. Physical Implications of Expanding Universe An expanding gas cools and becomes less denseas it expands. Run the expansion backward: going back into the past, the Universe heats up and becomes denser. Expanding Universe plus known laws of physics imply the Universe has finite age and a `singular’ (nearly infinite density and Temperature) beginning about 14 Billion years ago: THE BIG BANG

47. Big Bang Nucleosynthesis Origin of the Light Elements: Helium, Deuterium, Lithium,… When the Universe was younger than about 1 minute old, with a Temperature above ~ 1 billion degees, atomic nuclei (e.g., He4 nucleus = 2 neutrons + 2 protons bound together) could not survive: instead the baryons formed a soup of protons & neutrons. As the Temperature dropped below this value (set by the binding energy of light nuclei), protons and neutrons began to fuse together to form bound nuclei:the light elements were synthesized as the Universe expanded and cooled.

48. BBN predicted abundances h = H0/(100 km/sec/Mpc) Fraction of baryonic mass in He4 Light Element abundances depend mainly on the density of baryons in the Universe Deuterium to Hydrogen ratio Lithium to Hydrogen ratio baryon/photon ratio

49. BBN Theory vs. Observations: Observational constraints shown as boxes Remarkable agreement over 10 orders of magnitude in abundance variation Concordance region: b = 0.04 Strongest constraint comes from Deuterium. Excellent agreement w/ more recent CMB measurements b 4He

50. Recent CMB experiments: Going to smaller angular scales  higher resolution