The Noise That Turned Out to Be the Universe

In the early 1960s, two physicists at Bell Labs in New Jersey were given a magnificent piece of equipment: a large horn antenna, originally built for satellite communication, now available for radio astronomy.

Arno Penzias and Robert Wilson wanted to measure radio sources. Instead they found a problem. No matter where they pointed the antenna, there was a faint, steady hiss — a low-energy noise in the microwave band, equivalent to a temperature of about 3.5 kelvin, coming from everywhere in the sky, at all hours, in all seasons.

They did what good experimentalists do. They checked the receiver. They checked the electronics. They checked for radar interference and for radiation from New York City. Then they discovered pigeons roosting inside the horn, and a layer of droppings coating the interior. They trapped the pigeons, cleaned the antenna — and, in a detail that reads as comedy, they mailed the pigeons away. The noise was still there.

Eventually they phoned Robert Dicke at Princeton, who had been theorising that the universe should be filled with leftover radiation from a hot, dense early state — a relic glow from the Big Bang, cooled by 13 billion years of expansion.

Dicke reportedly hung up and said to his colleagues: "Boys, we've been scooped."

That hiss was the cosmic microwave background. It is now the single most important piece of evidence for the Big Bang, and the map of its tiny temperature variations is the foundation of modern cosmology. Penzias and Wilson received the Nobel Prize in Physics in 1978.

They weren't looking for the origin of the universe. They were trying to get a clean signal, and they were honest enough to investigate a noise they couldn't explain instead of tuning past it. The most consequential discovery in modern cosmology arrived as an annoyance attributed to pigeons.