On the purely scientific front, however, despite these disturbing failures in etiquette, Ryle’s arguments grew increasingly compelling, and by the mid-1960s, the vast majority of the astronomical community agreed that the proponents of the steady state theory had lost the battle. (Figure 30 shows, from left to right, Gold, Bondi, and Hoyle, attending a conference in the 1960s.) The discovery of extremely active galaxies, in which the accretion of mass onto central, supermassive black holes releases sufficient radiation to outshine the entire galaxy, cemented the evidence against a steady state universe. These objects, known as quasars, were luminous enough to be observed by optical telescopes. The observations allowed astronomers to use Hubble’s law to determine the distance to these sources, and to show convincingly that quasars were indeed more common in the past than at present. There was no escape from the conclusion that the universe was evolving and that it had been denser in the past. At that point, the floodgates opened, and the challenges to the steady state model kept pouring in. In particular, in 1964 scientists Arno Penzias and Robert Wilson made a discovery that to all but its diehard supporters represented the last nail in the coffin of the steady state theory.

Figure 30

Penzias and Wilson were working at the Bell Telephone Laboratories in New Jersey with an antenna built for communication satellites. To their annoyance, they were picking up some sort of pervasive background radio noise: microwave radiation that appeared to be the same from all directions. After failing to explain away this disturbing “hiss” as an instrumental artifact, Penzias and Wilson finally announced the detection of an intergalactic temperature excess of about 3 Kelvin (3 degrees above absolute zero). Lacking the necessary background, Penzias and Wilson did not realize initially what they had found. Robert Dicke of Princeton University, however, recognized the signal immediately. Dicke was in the process of building a radiometer to search for the relic radiation from the big bang, previously predicted by Alpher, Hermann, and Gamow. Consequently, his correct interpretation of the results of Penzias and Wilson literally transformed the big bang theory from hypothesis into experimentally tested physics. As the universe expanded, the incredibly hot, dense, and opaque fireball cooled down continuously, eventually reaching its present temperature of about 2.7 Kelvin.

Since then, observations of the cosmic microwave background have produced some of the most precise measurements in cosmology. The temperature of this radiation is now known to four significant figures to be 2.725 K, and its intensity changes with wavelength precisely as expected from a thermal source—confirming the predictions of the big bang. Even in the face of this overwhelming, contradictory evidence to the steady state theory, Hoyle was never convinced. He proposed that instead of representing a relic of the big bang, the cosmic microwave background is produced by some extragalactic iron “whiskers,” which absorb and scatter the infrared light of galaxies at microwave wavelengths. These iron whiskers were supposed to have condensed from metallic vapors—for instance, in the material ejected by supernova explosions.