What do penicillin, nuclear fission, and microwave ovens have in common?

Not a lot. But they do happen to all be things that scientists discovered by accident.

We have this image of scientists going out to prove a thing, all focused and purposeful. And yeah, that definitely does happen. But there are also dozens of discoveries in science that happened totally randomly.

Take the Big Bang for example. For a long time, it was just an idea and there wasn’t much good evidence to support it. That changed in 1964 … by accident.

Astronomers Arno Penzias and Robert Wilson were setting up their large horn antenna — basically a giant microwave detector. To their surprise, the detector seemed to be picking up a bunch of static, like the snow and hiss on an old-fashioned TV. Their first thought was that they must have messed something up, and they tried everything to fix it — including getting rid of a flock of pigeons roosting inside the detector.

It didn’t even occur to them that they might have found evidence for the most important event in the history of the universe: the Big Bang. According to the Big Bang theory, all the matter in the universe was once squashed together into an incredibly dense, hot point. It then exploded outwards in … well, a bang, forming the universe we know today.

One of the predictions of the Big Bang is that all the radiation that was produced in that super hot state should still be around today — just really hard to detect. As the universe expands, everything moves away from everything else, which causes electromagnetic waves like light to stretch out in what’s known as redshift. And the electromagnetic radiation from the big bang has redshifted so much over the last 13.8 billion years that it’s now in the microwave part of the spectrum.

That’s the static that Penzias and Wilson were picking up with their detector. But it took a while for them to realize what they’d discovered, because they were using their huge horn antenna for a totally different reason. They were looking for faint sources of radiation in the Milky Way that might damage communications satellites.

In fact, the horn antenna was built to help develop those satellites. It was first used to detect microwaves bouncing off of what were basically giant metal balloons — the first try at making something like a communications satellite. So this was all very important work, but for their experiment they had to remove all other sources of interference.

That meant that when they detected a weird background static, in every direction, non-stop, day and night, it was a huge pain in the butt. They had to find out what it was and get rid of it, and they had to do it ASAP. They started out by cooling their detector down to 4 degrees above absolute zero using liquid helium, which wiped out most possible sources of static.

But the background noise was still there. Next, they wondered if it could be coming from human sources, so they pointed their detector at New York City to see if the static would get worse. But nope: it didn’t change.

Finally, they did some calculations to show that it couldn’t be from a military source, either. Eventually, they concluded that the static couldn’t be coming from Earth, or from the Milky Way galaxy. Then one day, they noticed something in the antenna: bird droppings.

It turned out pigeons had been roosting inside their antenna, and they thought they’d finally found the source of the static. They cleaned out the droppings and did everything they could to get rid of the birds, but the pigeons kept coming back. Finally they just shot the birds.

An instant death for sure, but they still felt pretty bad about it. They probably felt even worse when they turned on the detector, and the static hadn’t gone away. So if it wasn’t in the detector, and it wasn’t from the Earth, and it wasn’t from the Milky Way, that left only one possibility: the static had to be coming from outside our galaxy.

But they had no idea what would cause such a thing. Around this time, Penzias was chatting with a colleague who happened to mention that a group of scientists at Princeton were getting ready to look for a microwave background signal to help learn more about the Big Bang. Suddenly Penzias realized how important that background static might be after all.

He contacted the scientists from Princeton, and invited them to see the detector. The signal looked exactly like what they were looking for. They’d found cosmic microwave background radiation, confirming a key prediction of the Big Bang.

They ended up publishing a joint paper, and just like that, the Big Bang theory went straight to the forefront of physics, earning Penzias and Wilson a Nobel Prize in 1978. It was a great story for Penzias and Wilson, even though it wasn’t so great for the birds. But at least the pigeons gave their lives for a good cause: they helped us learn more about how the entire universe came to exist.

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