The Bell laboratories had built a huge horn antenna that looks much like a ear-trumpet for a giant. It was used for long-distance communication: In 1960, Bell Labs and NASA had launched a large plastic balloon into orbit (called “Echo”) that worked only as a passive reflector, so this antenna was used as a transmitter. But in 1962, they launched Telstar, the first communication satellite that had its own transmitter, so this antenna becomes obsolete.
The good thing was, they gave it to two scientists to work with. German born Arno Penzias (of course, yet another brilliant scientist who had to flee the Nazis, this one as a child) and Robert Wilson started working with the antenna to look out into the universe! They listened to the radio signals transmitted from space, and to reduce all background noise, the receiver on the antenna was cooled with liquid helium! The noise of an antenna is measured as antenna noise temperature, that is the actual temperature of the receiver. So, for liquid helium, the noise temperature should have been about 3K. Still, taking away all known sources of noise, they still had 3K too much noise!
At first, they thought it might be a sophisticated systematic error (bird shit), but when they removed this error the noise remained. The spent days cleaning out the systematic error, but of course the birds came back. The birds were pigeons, so they drove them to a trader who didn’t want them and they just set them free. A few days later, the pigeons were back. The problem was resolved by someone with a rifle and them looking the other way…
So, they had 3K to explain. After talking to Princeton theorists, they solution came fast: The Big Bang model of the universe would force some kind of afterglow of the universe, which is now called the cosmic microwave background radiation, which was theoretically expected, and was expected to be at 3K (that means, that the universe is not excatly cold, even in the directions where there is really nothing. It still radiates like a perfect black body emitting at 3K!) - Penzias and Wilson found it! This supports the Big Bang model of the universe, and the two bird hunters received the Nobel Prize in Physics in 1978.
The antenna was declared a historic landmark in 1990, together with the pigeon traps. Later, it became part of the “Exploring the Universe” exhibition at the Smithsonian National Air and Space Museum. Here is the online exhibition page for the pigeon trap!
For a short explanation of CMBR, look here.
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