Bell Labs Found the Echo of the Big Bang and First Suspected It Was Pigeon Droppings
In 1964, two engineers at Bell Labs in New Jersey were trying to debug a strange persistent hum in their radio antenna. They cleaned every cable. They climbed inside the horn-shaped antenna and scrubbed out a layer of pigeon droppings. The hum stayed. They had stumbled on the cosmic microwave background — the leftover heat from the Big Bang. It is the strongest direct evidence we have for the origin of the universe.
In 1964, two radio engineers at Bell Labs in Holmdel, New Jersey, were trying to debug a stubborn problem in their antenna. The antenna was a large horn-shaped instrument originally built to communicate with the early Echo balloon satellites. Arno Penzias and Robert Wilson wanted to repurpose it for radio astronomy, and were trying to characterize its noise floor.
They could not get rid of a faint persistent hum. The hum had three peculiar properties. It was the same brightness in every direction they pointed the antenna. It was the same at every time of day and through every season of the year. And it corresponded to a temperature of roughly three degrees above absolute zero, regardless of where they looked.
They worked through every plausible source of the noise. They checked their connections. They eliminated city interference. They climbed inside the horn and scrubbed out the pigeon droppings that had accumulated, what Wilson later described in conversation as 'a white dielectric material.' They evicted the pigeons themselves.
The hum was still there.
A few miles away, at Princeton, a group of physicists led by Robert Dicke was working through a different problem. They had calculated that if the Big Bang had really happened — at the time, a contested cosmological model — it should have left behind a faint, uniform glow of microwave radiation, observable everywhere on the sky at a temperature of a few degrees above absolute zero. They were building an antenna to look for it.
Penzias and Wilson, hearing about the prediction through a chain of mutual contacts, made a phone call. The two groups compared their notes. The hum was not equipment noise. It was the cosmic microwave background — the residual thermal radiation from the early universe, redshifted into the microwave range by 13 billion years of cosmic expansion.
The 1978 Nobel Prize in Physics went to Penzias and Wilson. The thing they had been trying to remove from their data was the strongest piece of evidence ever found for how the universe began.