1. Naomi Pequette

2. Background Information

3. History  Predicted -- George Gamow (1948) and Ralph Alpher and Robert Herman (1950)  Detected-- Arno Penizas and Robert Wilson (1965) Dave Wilkinson and Robert Dicke - Released papers on observation and cosmological significance  Penzias and Wilson received Nobel Prize in 1978

4. Cosmic Microwave Background Radiation (CMBR)  Peaks in microwave part of spectrum at 2.75K  Was formed 380,000 years after Big Bang  Protons and electrons combine to form neutral hydrogen  Photons interact very weakly with the matter of early universe

5.  The early universe is like the clouds in the Earth’s atmosphere.  You can’t see the tops of the clouds, only the bottoms.  Maps of the CMB temperatures are of the surface of the scattering

6. WMAP  Launched in 2001 as replacement for COBE

7. OpticsDual Gregorian; 1.4 m x 1.6 m primaries ThermalPassively cooled with radiators, solar array shades instrument; MLI and gamma-alumina cylinder isolates spacecraft from instrument RedundancyPrimary Single String StructureComposite / aluminum Lifetime27 months; fuel limit > 3 years Frequencies22 30 40 60 90 Wavelengths (mm)13.6 10.0 7.5 5.0 3.3 Number of Channels4 4 8 8 16 Resolution (FWHM, degrees)0.93 0.68 0.53 0.35 <0.23

8. Fundamental Sound Wave Mapping this—Angular Power Spectrum Causes of the Anisotropies

9. The Fundamental Sound Wave  Random fluctuations (Gaussian) due propagated throughout early universe  Waves oscillating in time instead of space  Fixed by distance sound could travel before recombination

10. Fundamental Sound Wave  As sound wave propagates region of max. positive displacement would go toward av. temp (min. displacement) to min. temperature (max. neg. displacement)  Fundamental Tone  Harmonics (overtones) oscillate quicker, and cause smaller regions to reach max. displacement  Can be understood by breaking up into harmonics or modes

11. From “Four Keys to Cosmology” in Scientific American

13. Fourier Decomposition  Basic wave can be decomposed into fundamental harmonics  CMB Anisotropies can be expanded into terms of multipoles

14. Multipoles  Each mode is like a particular instrument and the whole sky map is the sound of the cosmic symphony  Each multipole labeled by number ( l = 1,2,3…)  The higher the l, the smaller the features the multipole describes  The amplitude of each mode is like the volume of each instrument

15. Monopole ( l = 0)  Lowest note in the cosmic note  Entire sphere pulses as one  At average temperature of CMBR  Fundamental tone

16. Dipole ( l = 1)  Next lowest note  Temperature goes up in one hemisphere and down in the other  Dominated by Doppler shift of solar system’s motion relative to CMBR  Sky appears hotter in direction sun is traveling

17. Other Multipoles Quadropole subtends about 90 degrees Octopole subtends about 60 degrees

18. WMAP’s View of the CMBR

19. Angular Power Spectrum  Plot the magnitude of temperature variations against sizes of hot and cold spots  Greatest variations ~1 degree  First and highest peak = fundamental wave  Second = 1 st harmonic

20. What Does this Tell Us? Angular Power Spectrum

21. What Does This Tell Us?  Shape of the Universe  Composition of the Universe  Effects of Dark Energy and Dark Matter  Cosmic Neutrino Abundance

22. Geometry of the Universe  Information from the fundamental frequency and strengths of overtones  CMBR gives us angular size of most intense temperature variation  This tells us frequency of fundamental sound wave  Given this and speed of sound, can determine size of wave  This information + knowing distance CMBR photons traveled to earth—know information about triangle formed by wave

23. Note!  The distance to the CMBR depends on the peaks of the angular power spectrum  This distance depends on the curvature of space-time and the history of dark energy (expansion of the universe)  This cosmic radius is not infinite, but is certainly larger than the radius of the currently visible universe

24. Geometry continued  Knowing the triangle—can see if angles add up to 180 degrees  Test of spatial curvature  Indeed—angles add up to 180 degrees  We live in a flat universe!!!  The fact that it is a flat universe implies average energy density is close to critical density (10 -29 g/cm 3 )  Geometry depends on energy density

25. Geometry continued  Another way to determine this using WMAP is the size of the features in the CMBR  The largest variations are ~1º  Flat Universe  Now know this with 2% accuracy

26. Composition of the Universe  Information from the amplitude of the second peak in power spectrum  Sound waves in early universe modified by gravity  Both ordinary and dark matter provide mass and enhance gravitational pull  BUT only baryonic matter undergoes sonic compressions and rarefactions.

27. Composition of the Unviverse  First overtone—gravity attempting to compress plasma while gas pressure trying to expand it  Thus why temp. variations are less pronounced and second peak is lower  By compare heights of two peaks  Baryons had same energy density as photons— thus constitute about 4.6% of critical density today

28. Dark Matter  Abundance of cold dark matter is needed for gravitational potential wells to be sufficiently deep  By measuring ratios of heights of first 3 peaks— can determine the density of CDM  About five times that of the baryon density  23% of the universe today is CDM!!!  Likely composed of one or more species of sub- atomic particles  interact very weakly with ordinary matter

29. Dark Energy  However, 72% of critical density is unspecified…..  Lets call the leftovers Dark Energy  Its influence has grown as universe expands \  It explains many observed phenomena

30. Cosmic Neutrinos (5 year results)  5 year data determines the temperature fluctuations at small angles more precisely  Theoretical prediction of the third peak in the angular power spectrum  Only matches the data if the very early universe was bathed in a vast number of neutrinos which would have smoothed out the density perturbations very slightly.  The neutrino background was first inferred in 2005  But first time measured solely from WMAP data

31. What Does this Tell Us? Polarization of the CMBR

32. Polarization  Peaks in angular power spectrum that correspond to small scales should be dampened in specific way  As predicted by standard model of cosmology  Dampening causes radiation to gain polarization  Where dampening occurs (on small scales) photons can travel w/ little scattering  Retain directional information = polarization

33. Polarization Cont.  Scattered light is often polarized  The electron-photon scattering cross-section depends upon polarization of incoming photon  This effect allows scientist to investigate the properties of the electrons that the photons were scattered off of

34. Polarization, cont. Image from WMAP website

35. Constraints on Inflation  From polarization, three year results were able to put tight limitations on the spectral index of the fluctuation (α)  This is the main parameter that inflation describes  Three year results—α<1  Five year results α = 0.960 ± 0.014  Rules out a lot of inflationary models

36. Constraints on Inflation, cont.  One of the greatest tests of inflation would be to detect gravitational wave relics  If inflation occurred at “grand unification scale”— could be detected by CMBR polarization  Vortex-like pattern created by gravity waves  If α is indeed greater than 0.95, then ratio of the gravitational-wave and density contributions to the CMB anisotropy needs to be greater than 0.01 for inflation to past test  Five Year--Gravity waves no more than 20% to total temperature anisotropy –many models ruled out

37. Origins of Stars and Galaxies  Ionizing material affects polarization  Provides an idea of when the “cosmic dark ages” ended and the first stars begin to shine  For polarization signal to be as large as we see it—stars need to have started forming earlier than first billion years  Three year results –first stars start to form around 400 million years  Quasars formed later—so universe partially neutral around 1 billion years  “lighting up” probably long process

38. Even More Parameters

39. The Age of the Universe  The First peak in the angular power spectrum:  Know acoustic size: r s = 147 ± 2 Mpc  Known redshift: z dec = 1089 ± 1  Then, after determining the geometry of the universe (flat) and CMB light travel time over distance determined by decupling surface (d a = 14 + 0.2 or -0.3 Gpc)…  We find the age of the universe is t 0 = 13.73 ± 0.12 Gyr (5 year result)

40. Hubble Constant  We now have determined the age of the universe and matter density  Can use this to determine the Hubble Constant  The five year results find H 0 = 70.1 ± 1.3 km/s/Mpc  This measurement is consistent with the values from the HST Key Project, gravitational lens timing, and measurements of the Sunyaev-Zeldovich Effect

41. Optical Depth and Reionization  With longer integration of the large-scale polarization anisotropy, there has been a significant improvement in the measurement of the optical depth to reionization  τ = 0.0870 ± 0.017  We also know the redshift of reionization z reion = 10.8 ± 1.4  This measurement suggests that the re- ionization of the universe took place very gradually

42. From CMBR to Galaxy Clusters

43. The Characteristic Length  Often called the acoustic scale  Distance a point source traveled from just after inflation to decoupling  Hubble expansion has expanded the universe a thousand fold  The radius of that sound sphere is 480 million light years  After decoupling—acoustic scale constant coming separation of 480Mly

44. Creation of Clustering  Primordial fluctuation seen now as clustering of galaxies  Fluctuations and regions of “over density” were seeds for gravitational wells that grow larger and denser with time.  The real cosmic density is a superposition of spherical wave shells  The spatial correlation of galaxies is still enhanced at a commoving distance corresponding to the size of the shell at decoupling (480 Mlyr)

45. Mapping Effects of Primordial Sound Wave  Galaxy redshift surveys map out the universe in three dimensions  From this, can map galaxy correlation function  Excess probability of finding one galaxy a particular distance from another

46. Mapping Effects of Primordial Sound Wave  The peak--the excess probability of finding galaxies 480 Mly from another  Predicted by WMAP  This single peak corresponds to all the harmonic peaks in the CMBR power spectrum. That is the primordial sound wave!!!

47. Structure Formation Simulation  http://www.youtube.com/watch?v=8C_dnP2f vxk http://www.youtube.com/watch?v=8C_dnP2f vxk

48. Cosmic Distances  Because this length scale of the baryon acoustic peak can be calculated from known physics and quantities, it gives us a cosmic distance scale  The more distant a galaxy is from Earth, the smaller angle the commoving separation subtends on the sky.  By measuring the angular correlations within a large-enough cluster of galaxies, one can determine how far away it is.