Big Bang's Shadow: How 2 Guys Accidentally Uncovered the Universe's Echoes
The cosmic microwave background, depicted here from nine years of data from NASA's WMAP telescope, was the key to proving the validity of the Big Bang theory.
Credit: NASA/WMAP Science Team

Paul Sutter is an astrophysicist at The Ohio State University and the chief scientist at COSI Science Center. Sutter is also host of Ask a Spaceman, RealSpace, and COSI Science Now

It's not often that you can get promoted, commended and even awarded for failing to do your job. Usually, it's the exact opposite. So how exactly did Arno Penzias and Robert Wilson — two who-the-heck-are-those-guys at Bell Labs in the 1960s — win a free trip to Stockholm and a shiny golden Nobel medal?

First, a little setup. At the time, the Big Bang theory wasn't the high-and-mighty, universal champ model to explain the end-all and be-all in the cosmos that it is today. Far from it: while a strong contender for the title, it had some powerful rivals, especially the Steady State theory.

See, Edwin Hubble had correctly pointed out two fantastic facts about our universe: it's very, very, very large, and it seems to be getting bigger. Or at least, it looks like every galaxy is getting farther away from every other galaxy (on average, of course, not counting a few mergers here and there). We live in a large, expanding universe. [The Universe: Big Bang to Now in 10 Easy Steps]

With this mind-blowing knowledge, theorists hurried to come up with explanations. In the heady days of the '20s and '30s, two models emerged. In one corner: The Big Bang (although it didn't get that cool name until later), which posited that the universe used to be small, hot and very dense, and over time has mellowed out to become the staid, mature character we know and love today. It was a pretty simple, and pretty popular, idea.

In the opposite corner: Steady State, heavily promoted by astronomer Fred Hoyle because — well, maybe he just wanted to stick it to the establishment. In this view, the universe is roughly the same throughout all of space and throughout all of time. Matter is continually generated and then pushed out in a never-ending cosmic cycle. (Learn more about the Steady State model in the below video.)

For a few decades, these two theories wouldn't budge. The Big Bang had some slight advantages when it came to real-world observations, but couldn't explain everything. At the time, cosmology (the study of the entire universe as a whole) wasn't even really its own scientific discipline; it was just a side hobby for otherwise reasonable astronomers. Folks were much more interested in solar nuclear physics and white dwarfs and other cool stuff. 

Without a lot of additional brainpower or telescope time, there simply wasn't enough data to sway our understanding to Big Bang or the Steady State conclusively.

But a few physicists had started to make some interesting predictions regarding the Big Bang theory. If the universe was hot and dense a long time ago, then it must have been a plasma: a state of matter where all the electrons are ripped from their nuclei and swim around freely.

But at some point in that early state, the universe must have cooled to the point that stable atoms could form. Instead of being ripped off violently by some high-energy bit of light, electrons could snuggle up safely next to protons and form the first hydrogen. 

The universe went from "stew" to "soup," and light could travel freely. At the time, the light was white-hot, but over the eons that primordial light would get diluted and stretched by the expansion of the universe. (I describe the effect in this video.)

That light should still permeate the universe today, cooled down from its rambunctious childhood to just a few calm and collected degrees above absolute zero — putting it in the microwave band.

"Hmmmm," these physicists reasoned, "we should be able to…you know, see it. Maybe we should build a microwave detector or something?"

The Cosmic Microwave Background (CMB) radiation tells us the age and composition of the universe and raises new questions that must be answered. <a href="">See how the Cosmic Microwave Background works and can be detected here</a>.
The Cosmic Microwave Background (CMB) radiation tells us the age and composition of the universe and raises new questions that must be answered. See how the Cosmic Microwave Background works and can be detected here.
Credit: Karl Tate, Infographics Artist

Enter a couple jokers from Bell Labs. After successfully building a fancy new microwave detector — unbeknownst to most other scientists — Penzias and Wilson had a problem. No matter what, they couldn't get rid of a constant background hiss.

Point it at a different part of the sky? Nope, still there.

Wait a few weeks? Nope, still there.

Ask the nearby Army base if they were doing anything fancy? Nope, still there.

Scrape off all the pigeon poop? Nope, still there.

They had one job — to get the darn antenna to work right — and they couldn't do it. No matter what, the sky seemed to be filled with microwave radiation, just a few degrees Kelvin above absolute zero. A cosmic microwave background, if you will.

They eventually got hooked up with the physicists studying the early universe, and both groups came to the same conclusion: The errant signal they were detecting might possibly be the leftover light from the early universe.

But who got The Big Prize? The scientists who had labored over decades to predict the signal and start to investigate how to detect it — or the two random dudes from Bell Labs? 

Despite who got the glory, it was a big win for the Big Bang. The Steady State model — with its assumption that the universe has been unchanging for eternity — simply couldn't account for the cosmic microwave background. All other explanations for the radiation couldn't work, either: The Big Bang model predicted a cold, fantastically uniform wash of microwaves across the sky, and that's exactly what Penzias and Wilson accidentally found. Everything else in the universe is just too dang lumpy to make something so smooth. [Images: Peering Back to the Big Bang & Early Universe]

The discovery of the cosmic microwave background sent ripples of excitement through the scientific community. Cosmology came into its own as a full-fledged scientific discipline. The universe was different in the past, and will be different in the future. It became experimentally clear that things change — at the very largest scales — with time. 

And the Big Bang theory had its first major piece of evidence. That's what matters most: if you want to sway a skeptical scientific community, you can begin and end with the evidence. Before 1964, we had no reason to believe the Big Bang theory. But the universe itself, in a subtle whisper of microwaves, is telling us we ought to. 

Learn more by listening to the episode "What is the Cosmic Microwave Background?" on the Ask A Spaceman podcast, available on iTunes and on the web at Thanks to Arlington T., Jeffrey B., Edward J., Jason A., Ernie J., Rea N., Chris L. and Randy B.for the questions that led to this piece! Ask your own question on Twitter using #AskASpaceman or by following Paul @PaulMattSutter and Follow us @Spacedotcom, Facebook and Google+. Original article on