AT THE SMITHSONIAN

How Two Pigeons Helped Scientists Confirm the Big Bang Theory

For decades, astronomers had debated how the universe began. Then, in 1964, they had their “Eureka!” moment

February 19, 2014

Pigeon Trap — A pigeon trap, on view at the Air and Space Museum, used by Nobel Prize winners Penzias and Wilson to remove the birds roosting in the radio antenna's large horn. NASM/SI, Loan from Robert Wilson

In 1964, when Robert W. Wilson and Arno A. Penzias initially heard those astonishing radio signals that would lead to the first confirmed proof for the Big Bang Theory, they wondered if they had made a mistake. Was the signal actually radio noise from nearby New York City? Was it the after-effects of a nuclear bomb test that had been conducted over the Pacific several years earlier? Could it be a signal from the Van Allen belts, those giant rings of charged radiation circling the Earth?

Or maybe, the hissing sound was the result of a defect in their instrument?

“I had a lot of experience fixing practical problems in radio telescopes,” Robert Wilson now says. He and his wife Betsy Wilson still live in Holmdel, New Jersey, not far from hilltop where the tests were run. “We looked for anything in the instrument or in the environment that might be causing the excess antenna noise. Among things, we searched for radiation from the walls of the antenna, especially the throat, which is the small end of the horn. We constructed a whole new throat section and then tested the instrument with it.”

At one point, new suspects emerged. Two pigeons had set up housekeeping inside the guts of the antenna. Maybe their droppings were causing the noise? Wilson and Penzias had the birds trapped and then cleaned the equipment, but the signals continued.

After a year of experiments, the scientists concluded that they’d detected the cosmic background radiation, an echo of the universe at a very early moment after its birth.

“We started out seeking a halo around the Milky Way and we found something else,” notes Dr. Wilson. “When an experiment goes wrong, it’s usually the best thing. The thing we did see was much more important than what we were looking for. This was really the start of modern cosmology.” In fact, Wilson and Penzias were awarded the Nobel Prize in Physics in 1978 for determining that the hiss they were hearing wasn't pigeon poop at all, but the faint whisper of the Big Bang, or the after glow that astronomers call the cosmic microwave background.

Visitors to the Smithsonian Air and Space Museum have long been able to view an unassuming artifact of that Nobel Prize-winning discovery. On the first floor in the "Exploring the Universe" gallery that metal trap built to capture the squatting pigeons, can be seen, along with some other instrumentation of that propitious moment 50 years ago. The pigeon trap is on loan from Robert Wilson.

Other artifacts survive. Arno Penzias, who’d come to the United States as a child refugee from Nazi Germany, sent the radio receiver and its calibration system to the Deutsches Museum of Munich, the city of his birth.

As for the giant horn antenna, it still stands tall on Holmdel Road, where it can be seen by the public.

On Thursday, February 20 at 7:30, Wilson will be joined in a panel discussion by cosmologist Alan Guth and astronomers Robert Kirshner and Avi Loeb at the Harvard-Smithsonian Center for Astrophysics, in celebration of the 50th anniversary of the confirmation of the Big Bang Theory. Watch the discussion live on YouTube.