Microwave Static: Identifying the ‘Hiss’


By Emily LevesqueUniversity of Washington

In 1964, Arno Penzias and Robert Wilson were frustrated. Like Karl Jansky more than 30 years prior, they were physicists working at Bell Labs. Like Jansky, they were working on a new, cutting-edge radio antenna. And, like Jansky, they were having trouble getting rid of a faint but persistent hiss in their data. That hiss, that microwave static, proved to be an incredible discovery.

Aerial view of old Bell Labs Holmdel Complex in New Jersey
Arno Penzias and Robert Wilson started their work together at Bell Labs in New Jersey. (Image: MBisanz/Public domain)

Jansky, Penzias, and Wilson

A black and white photo of Karl Jansky
Karl Jansky had also picked up radio waves with his radio antenna, microwave static that he did not know the source of. (Image: Saber1983/Public domain)

Jansky had picked up radio waves emitted by the center of the galaxy with his radio antenna, a discovery that marked the beginning of radio astronomy. Penzias and Wilson had found something even more extraordinary: their radio antenna was detecting light that had been traveling through the universe since shortly after the Big Bang.

Arno Penzias was born in Munich, Germany in 1933, and his life may well have been saved by a radio signal. At age six he and his brother were among the 10,000 Jewish children evacuated to the United Kingdom, a rescue operation known as Kindertransport after a broadcast was sent out via BBC radio asking for foster homes for children fleeing Nazi-occupied parts of Europe just before the start of World War II. 

His family was eventually reunited in New York City, where he earned an undergraduate degree in physics from the City College of New York and a doctorate from Columbia University. Robert Wilson, a few years younger than Penzias, was born and raised in Houston, Texas, spending time in the oil fields where his father worked as a chemical engineer. 

He described himself as a middling student in high school, but followed his father’s footsteps at Rice University, he earned a degree in physics before moving to Caltech for his Ph.D.

Bell Labs, the Best Place for Researching Microwave Static

Karl Jansky at a conference
Arno Penzias (above) was already working at Bell Labs when he met Robert Wilson at a conference in 1962. (Image: Kartik J/Public domain)

Penzias and Wilson met at a conference in 1962 when Penzias was already working as a physicist for Bell Labs in New Jersey. In the decades since Karl Jansky’s discovery, Bell Labs had remained a top-notch site for physics research, driven by its overarching goal of pushing the limits of long-distance communication. 

Wilson joined Penzias at Bell Labs, and the two began working with the Horn antenna, a 20-foot radio detector built atop Crawford Hill in New Jersey. It had originally been used to capture radio signals from an early NASA communications satellite. When that communication project ended, Penzias and Wilson took over the use of the antenna. They hoped to repurpose it for radio astronomy and study how radio signals interacted with Earth’s atmosphere.

However, when Penzias and Wilson first started pointing the New Jersey antenna at empty patches of sky—a standard step to calibrate the detector—they kept picking up the same background noise, a kind of microwave static. What’s more, unlike Karl Jansky’s detection of radio waves from the center of our galaxy, this static hiss seemed to be coming from everywhere, popping up in their data no matter where they pointed the telescope.

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Was It the Pigeons?

Astronomers are used to this sort of static. Everything from car engines to fluorescent lights can produce radio signals that interfere with telescopes. Penzias and Wilson immediately began examining their antenna and its surroundings, suspecting that their persistent microwave signal was actually just some local signal interfering with their work. 

They ruled out cars on the Garden State Parkway and stray signals from a nearby military base. They even questioned the local birds. Two pigeons had set up house in their antenna, leaving behind what Penzias politely referred to as a ‘white dielectric substance’. The two physicists gamely climbed into the telescope and wiped it clean. Still, the microwave static remained.

The Discovery That Was Yet to Come

They looked for variations in the static across the sky and found none. They measured the static for an entire year, in summer and winter, but to no effect. This microwave static appeared to be clear, consistent, and real. But what was it? 

Ironically, just about 30 miles west, another team of physicists at Princeton University had recently begun building a microwave detector with the sole goal of finding and measuring the exact signal that was plaguing Bell Labs. 

Drawing on nearly two decades of research and theories, they dreamed of finding a faint, consistent microwave hiss, in the hopes that it would prove to be a long-predicted signal that we know today as the cosmic microwave background.

What began as a faint hiss that could have come from pigeon droppings has now become one of the most crucial signals being studied in astronomy today. Work on the cosmic microwave background has shaped our understanding of the entire universe, from its size and age and earliest beginnings to the way it works today.

Common Questions about the Microwave Static

Q: How did Arno Penzias and Robert Wilson meet?

When Penzias was already working for Bell Labs, the two met at a conference. Wilson later joined Penzias, and together they started work at the Holmdel Horn antenna in New Jersey, the same antenna that would help them discover a kind of background microwave static.

Q: What was the Holmdel Horn antenna used for prior to Penzias and Wilson working with it?

The Holmdel Horn antenna’s original purpose was to capture signals from a NASA communication satellite.

Q: What did Penzias and Wilson first think the reason behind the background noise their radio antenna picked up was?

Penzias and Wilson suspected that this kind of microwave static had some local source that was interfering with their research. They ruled out nearby traffic and the nearest military airbase. They even cleaned the telescope to get rid of two pigeons, but the background noise persisted.

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