Fifty Years of CMB Anisotropy Experiments (and Theory) ….in 15 Minutes Bruce Partridge Haverford College

A Brief History in 6 epochs Epoch to ~1970 Isotropy as one test of the cosmic origin of the CMB Flavor: “Are we right?” Spectrum: Roll and Wilkinson find T o = 3 K (and Dave later finds evidence for turn-over at spectral peak, confirmed by Boynton et al)

A Brief History in 6 epochs Epoch to ~1970 Isotropy as the other test of the cosmic origin of the CMB Flavor: “Are we right?” Isotropy: by 1967, established ΔT/T < 0.002

A Brief History in 6 epochs Epoch 2 – The epoch of upper limits Using available equipment and facilities Flavor: “What can we do with what we have?” Hunt for the dipole: definitive results by 1977 (the U2 expt.) But earlier strong hint (Conklin and Bracewell, 1971) Limitations: range of angular scale; atmosphere; detector sensitivity

A Brief History in 6 Epochs Epoch to 1992 Retrenchment Purposeful experimental design Well-grounded theoretical results (But too little interaction between the two) Flavor: “How can we do this better?” Culmination in 1992: COBE DMR detection of statistical evidence for ΔT/T ~ Limitations: range of angular scale; foregrounds made blatantly visible, but not yet limiting

A Brief History in 6 Epochs Epoch CMB anisotropy science matures Theory influences experimental design The power spectrum as THE representation of anisotropies Search for and detection of first acoustic peak Evidence for Silk damping in the high-ell tail Flavor: “We’re doing the experiments right; now to beat the systematics and foregrounds…” Limitations: foregrounds; sensitivity of single detectors; instrumental systematics Culmination: the 2003 WMAP power spectrum

From Lyman Page’s summary in Finding the Big Bang

Culmination of Epoch 4: the 2003 WMAP Power Spectrum (Actually the five year results) Figure from Dunkley et al to show that damping tail requires other results

A Brief History in 6 Epochs Epoch 5 – 2003 – 2015 (WMAP to Planck) New directions New infusion of innovation/cleverness from theorists Flavor: “How can we wring more cosmological and physical results out of the data?” Polarization (EE first detected by DASI, 2001) The richness of the damping tail (the province of SPT and ACT) Exploiting the CMB for physics as well as cosmology Limitations: now clearly foregrounds; use of arrays gets around limits on sensitivity of individual detectors (makes focal plane and optics harder); instrumental systematics

A Brief History in 6 Epochs Epoch 6 – the Future A few observations: EE and TE polarization will be firmly nailed down BB depends on which model of Inflation (a good thing) – and on control of foregrounds (a hard thing) The CMB will increasingly ne used as a background for gravitational lensing Theorists will find new ways to use the observations

Some Thanks To the organisers To George Field for teaching me cosmology (1961) To Bob Dicke (a) for hiring me (1965) and (b) for asking so many fundamental AND answerable questions (always) To Dave Wilkinson for teaching me how to care about experiments To Jim Peebles for teaching me how to care about scientific writing To so many (some here) – Martin Rees, Rod Davies, Rashid Sunyaev, Bernard Sadoulet, Paul Richards, Reno Mandolesi, Jean-Loup Puget, for teaching me that science also flourishes in foreign lands, including California To the young folks who will keep CMB science thriving