The Race to Prove the Existence of Cosmic Microwave Background


By Emily LevesqueUniversity of Washington

The idea of a cosmic microwave background can be traced back to Ralph Alpher and Robert Herman, two American cosmologists who first proposed the idea in 1948. Working forward from the Big Bang and using Edwin Hubble’s famous equation and constant for describing the expansion of the universe, they estimated a blackbody temperature of 5 Kelvin for the background radiation of the modern universe.

Jim Peebles in 2010
Cosmologist Jim Peebles had written about how to detect and identify this radiation. (Image: Juan Diego Soler/Public domain)

The Quest for Observational Proof of the Big Bang

It would be over a decade before several scientists either rediscovered their work or made their own predictions on how this background radiation could be observed, with estimates moving ever closer to the radiation’s true temperature of 2.7 Kelvin.

Portrait of Ralph Alpher
Ralph Alpher was one of the two cosmologists who first proposed the notion of a cosmic microwave background. (Image: Alpher Papers/Public domain)

One of these scientists was a physicist named Robert Dicke, who had studied the question of the temperature of space for years and invented the most widely used microwave detector design while working at MIT. By 1964, he was at Princeton and hard at work on a painstaking scientific mission to search for, and hopefully detect, the cosmic microwave background, and with it the first robust observational proof of the Big Bang. 

Several colleagues at Princeton had joined him in the search. Jim Peebles had recently written about how to detect and identify this radiation and was preparing to publish his results, while David Todd Wilkinson and Peter Roll began building a top-notch microwave detector following Dicke’s design. This was, after all, the best design for microwave antennae in the world; a design shared by the Bell Labs antenna just up the road.

Scooping Other Scientists

Arno Penzias and Robert Wilson, who worked at Bell Labs, soon realized that what they had found at Bell Labs could potentially be this theorized cosmic microwave background and placed a call to Dicke at Princeton to learn more about the phenomenon and share what they’d found. 

It just so happened that Dicke was in a meeting with his colleagues when the call came through. After hearing what Penzias and Wilson had found, he hung up, turned to his fellow physicists, and said “Well, boys, we’ve been scooped.” To be scooped in science is to have another team discover something you’re looking for, to figuratively scoop a new result right out from under you. 

It can be a crushing disappointment to see years of effort fall short in a field where most recognition goes to the first scientists to make a discovery; or, in the case of the Princeton team, a moment of excitement when finally coming face-to-face with a much-anticipated new result that was ready to be explored and analyzed, even if they weren’t the ones to make the discovery.

This article comes directly from content in the video series Great Heroes and Discoveries of AstronomyWatch it now, on Wondrium.

Breaking News in the Scientific World

The Bell Labs and Princeton groups quickly joined forces and submitted a pair of ground-breaking papers to the Astrophysical Journal. Dicke, Peebles, Roll, and Wilkinson’s paper laid out the underlying theory and predicted properties of the cosmic microwave background; it was followed by Penzias and Wilson’s painstaking description of their microwave signal and how it was detected. Together, the two papers represented an immense leap forward in science’s understanding of our universe’s history.

Arno Penzias and Robert Wilson in front of the Bell Labs horn radio antenna
For their observation of the cosmic microwave background, Robert Wilson (left) and Arno Penzias (right) were awarded the Nobel Prize. (Image: Unknown/Public domain)

The discovery was recognized with a Nobel Prize in 1978 for Penzias and Wilson. Their observations had unarguably been the crucial catalyst that led to the cosmic microwave background’s discovery and wholly deserved the Nobel, but the prize’s limitations meant that the contribution of Robert Dicke and his group went unsung.

A Neat Theory

After its discovery, there was a surge of interest in observing the cosmic microwave background, in the hopes that the properties of this radiation could be used to untangle long-standing mysteries about our universe. At a glance, the cosmic microwave background fit wonderfully with the predictions of the Big Bang theory and physicists’ model of the universe. It seemed to be spectacularly uniform. 

Astronomers detected the same hiss in every part of the sky, and everywhere they looked this radiation corresponded to the same blackbody temperature of about 2.7 Kelvin, rather than appearing hotter in one direction and colder in another. 

This agreed wonderfully with one of the core tenets of modern physics, the cosmological principle, stating that at large scales the universe should look the same from every location—what we call homogeneity; and in every direction—what we call isotropy.

Future Challenges for Cosmologists

Penzias and Wilson’s early observations may have been enough to prove that the cosmic microwave background existed, but they didn’t capture much fine-grained detail. A detailed study of the cosmic microwave background was, in fact, crucially important, since the Big Bang theory actually did predict small inhomogeneities in the universe. 

It predicted tiny ripples in the earliest fractions of a second after the Big Bang that eventually led to the formation of the vast structures we see in the universe today: galaxy clusters and superclusters and enormous swaths of dark matter. 

The fingerprints of these little fluctuations should be observable in the cosmic microwave background as what we call anisotropies—small hot or cold patches observable in different directions in the sky.

Common Questions about the Race to Prove the Existence of Cosmic Microwave Background

Q: Who were the first cosmologists to introduce the idea of cosmic microwave background?

Ralph Alpher and Robert Herman were the two cosmologists who first proposed the idea of cosmic background radiation in 1948.

Q: What does it mean ‘to scoop’ other scientists?

In the scientific world, if one research team is able to achieve results in a specific field sooner than another team also working on the same problem, then the latter has been ‘scooped’. This is essentially what happened to Robert Dicke and his team after they found out about the discovery by the cosmologists at Bell Labs.

Q: How did the cosmic microwave background fit neatly with the predictions of the Big Bang theory?

One of the core tenets of modern physics, the cosmological principle, states that at large scales the universe should look the same from every location. In this regard, the uniformity of blackbody temperature in the universe fits with the predictions of cosmologists using their models of the universe.

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