IL NUOVO CIMENTO Vol. ?, N. ? ? CMB Anisotropies: Their Discovery and Utilization George F. Smoot Lawrence Berkeley National Laboratory and Berkeley Center for Cosmological Physics Physics Department, University of California, Berkeley CA 94720 Summary. ��� This article is a written and modified version of a talk presented at the conference ���A Century of Cosmology��� held at San Servolo, Venice, Italy, in August 2007. The talk focuses on some of the cosmology history leading to the discovery and exploitation of Cosmic Microwave Background (CMB) Radiation anisotropies. We have made tremendous advances first in the development of the techniques to observe these anisotropies and in observing and interpreting them to extract their contained cosmological information. CMB anisotropies are now a cornerstone in our understanding of the cosmos and our future progress in the field. This is an outcome that Dennis Sciama hoped for and encouraged. 1. ��� Introduction It was a privilege to be invited to give a talk at this San Servolo meeting celebrating ���A Century of Cosmology��� and commemorating Dennis Sciama. Perhaps the most conclusive (and certainly among the most carefully examined) piece of evidence for Big Bang Cosmology is the existence of an isotropic radiation bath that permeates the entire Universe, known as the���cosmic microwave background��� (CMB). The word ���isotropic��� means the same in all directions. In 1964, two young radio astronomers, Arno Penzias and Robert Wilson, working at Bell Laboratories discovered the CMB using a well-calibrated horn antenna. They soon determined that the radiation was diffuse, emanated uniformly from all directions in the sky, and had a temperature of approximately 3 Kelvin (i.e. 3���C above absolute zero). Initially, they could find no satisfactory explanation for their observations, and considered the possibility that their signal may have been due to some undetermined systematic effect or noise. Their careful work soon eliminated alternative possibilities. Then MIT radio astronomer Bernie Burke drew their attention to Robert Dicke and Jim Peebles of Princeton who were considering the existence of a potential relic radiation and they had encouraged colleagues Peter Roll and David Wilkinson to begin constructing an instrument and start a program to search for this relic radiation. Eventually they learned that this background radiation had in fact been predicted years earlier by George Gamow[1] and colleagues Ralph Alpher and c Societ`a Italiana di Fisica 1 arXiv:0801.2563v1 [astro-ph] 16 Jan 2008

2 GEORGE F. SMOOT Fig. 1. ��� Photos of Robert Wilson and Arno Penzias in front of the Bell Labs Homdel antenna used for their observations and discovery of the CMB, David Wilkinson, and Dennis Sciama. Second row shows author George Smoot with Jim Peebles and Joe Silk. Third row shows Rainer Sachs with student Chris Reed and Art Wolfe. Fourth and bottom row shows Stephen Hawking, Neil Turok, Alan Guth and Paul Steinhardt, Alexi Starobinskii.