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How did Arno Penzias and Robert Wilson discover the cosmic microwave background by accident?

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Examine the observable universe's place within the whole universe — Cosmology Learn about defining and measuring the observable universe within the “whole” universe.

In 1965, Arno Penzias and Robert Wilson discovered the cosmic microwave background (CMB) while working at Bell Laboratories in New Jersey.12

The discovery was accidental. The pair were using a 6-metre horn antenna, originally intended for communications satellite research, to monitor radio emissions from the Milky Way Galaxy. During their observations, they detected a persistent, uniform radio noise that seemed to come from every direction in the sky.321

To identify the source, Penzias and Wilson meticulously eliminated potential causes of interference, including circuit noise and even removing pigeons that had been roosting in the antenna. Despite these efforts, the signal remained constant. They eventually consulted with Robert Dicke at Princeton University, who realized they had detected the residual thermal radiation from the early universe—a phenomenon predicted by the big-bang model. This discovery provided critical evidence for the big-bang theory and earned Penzias and Wilson a share of the 1978 Nobel Prize for Physics.213