The Cosmic Hiss

Nobel Prizes in Astrophysics & Cosmology – Part 4

(A Twelve Part Series)

Arno Penzias and Robert Wilson

The Cosmic Microwave Background (CMB) is the cooled remnant of the first light that could ever travel freely throughout the Universe. This 'fossil' radiation, the furthest that any telescope can see, was released soon after the Big Bang.

- Esa

 

The horn antenna that led to CMB

The Nobel Prize is equated with the pinnacle of human achievement in both popular perception and professional esteem.  Since it was first awarded in 1901, the annual Nobel Prize for Physics has gone to major contributions in Astrophysics and Cosmology related fields only on eleven occasions. The first two awards (1967, 1974) were the subjects of earlier articles (see here 1,2). The next was in 1978, partly and jointly to Arno Penzias and Robert Wilson for their historic and serendipitous discovery of the Cosmic Microwave Background.

[This article is being posted on my blog today (10th Dec) to coincide with the annual Nobel science awards in Stockholm, Sweden, marking the death anniversary of Alfred Nobel.  Incidentally, the Nobel prize in Physics for this year is being awarded jointly to John Clarke, Michel H Devoret and John M Martinis, all three of the USA, for their ‘discovery of macroscopic quantum mechanical tunnelling and energy quantisation in an electric circuit’.]

 

The Big Bang, not pigeon poo!

Although the CMB was discovered in 1965, the idea had been predicted decades earlier. The key step was understanding that if the universe began in a hot, dense state (called the Big Bang), then as it expanded, this radiation would cool and stretch to microwave wavelengths. The major theoretical contributors to this idea were George Gamow, Ralph Alpher, and Robert Herman. In the late 1940s, they developed the theory of Big Bang nucleosynthesis, the process in the early stages after the primordial explosion that created the lightest atomic nuclei, primarily hydrogen and helium. They realized that if the temperature of the early universe was once at ~10⁹ K, the leftover radiation today should be a few degrees kelvin above absolute zero. Herman and Alpher predicted a background temperature of about 5 K. Their prediction went largely unnoticed by most astronomers. Thus, the idea of a relic radiation existed, but no one had detected it. 

Geoge Gamow

In 1964, Arno Penzias and Robert Wilson, radio astronomers at Bell Labs in New Jersey, were not looking for any cosmology. They were improving a very sensitive microwave antenna—the Holmdel Horn Antenna—for satellite communication work (as part of the Echo project). They encountered a persistent background signal: a microwave “noise” at 7.35 cm wavelength (~4.08 GHz). It was present day and night, was same in all directions, not attributable to weather, the Milky Way, urban interference, or the equipment they were working with.  They tried everything to get rid of this unwanted interference, including cooling their receivers and eliminating all known terrestrial sources. 

Suspecting pigeon poo could be the problem, they even cleaned out all pigeon droppings (which they jokingly called “white dielectric material”) inside the antenna. Yet the noise remained, with a temperature of about 3.5 K. They suspected something fundamental—but didn’t know what.

The Team That Expected the Signal: Just 60 km away, a Princeton University team led by Robert H Dicke, and including Jim Peebles, David Wilkinson and Peter Roll, was specifically trying to detect the relic Big Bang radiation predicted decades earlier. Peebles had recently rederived the theoretical expectation and concluded such radiation must exist at a few degrees kelvin. Dicke’s group was already building their own detector in search of such radiation.

Robert H Dicke

The Chance Phone Call: A mutual acquaintance, Bernard Burke, heard about the strange Bell Labs noise and realized it sounded exactly like what the Princeton group was predicting. Penzias called Dicke to describe the unexplained background. After the call, Dicke hung up and famously said to his team: “Well, boys, we’ve been scooped.” The discovery had been made—not by the group looking for the signal, but by those trying to eliminate it.

The Two Landmark Papers: In 1965, the two groups published back-to-back papers in The Astrophysical Journal. Penzias & Wilson reported the observation of a uniform noise corresponding to ~3.5 K radiation, but made no cosmological interpretation. Dicke, Peebles, Roll & Wilkinson explained that this signal was the predicted relic radiation from the early universe, and identified it as the Cosmic Microwave Background.

Jim Peebles

 

David Todd Wilkinson

Together, the two papers established the CMB as empirical evidence for the Big Bang, an event that marked the very birth of the universe. It was Penzias and Wilson who ended up being awarded the (1978) Nobel Prize in Physics for this momentous discovery. 

Why the Discovery Was Revolutionary: the CMB provided the first direct observational evidence that the universe was once hot and dense. Radiation from that epoch survives today. The universe has expanded for billions of years since the Big Bang, and is now determined to be 13.7 billion years old.

The serendipitous discovery of Penzias and Wilson transformed cosmology from speculation to precision science and decisively tipped the balance against the rival Steady State Theory. Later missions (COBE, WMAP, Planck) refined this picture with extraordinary precision.

In Summary: The CMB was predicted as early as 1948, but its detection came accidentally in 1964 when Penzias and Wilson encountered a mysterious isotropic microwave noise. At the same time, the Princeton group had been preparing to search for exactly such a signal. When the two lines of work converged, the Big Bang gained its most important observational foundation.

Arno Penzias (1933 - 2024) – A biographical sketch 

Arno Allan Penzias was born on April 26, 1933, in Munich, Germany, to a Jewish family during the rise of Nazism. When he was six, his parents recognized that survival depended on escape. In 1939, Arno and his younger brother Günther were put on a Kindertransport train—the rescue operation that brought nearly 10,000 Jewish children to the United Kingdom. After a brief stay in Britain, the boys reunited with their parents in New York City, beginning life anew with no possessions and little English. This early displacement and hardship shaped Penzias’s worldview, fostering resilience, curiosity, and a deep appreciation for scientific and intellectual freedom.

Settling in the USA, Penzias excelled academically, particularly in mathematics and the physical sciences.

·       Undergraduate: City College of New York (CCNY) — B.S. in Physics, 1954

·       Graduate School: Columbia University — Ph.D. in Physics, 1962

At Columbia, he worked under the influence of Nobel laureate I. I. Rabi’s department, which had seminal traditions in microwave spectroscopy and radio-frequency physics. This was the period when radio astronomy was becoming a premier frontier of astrophysics; Penzias was drawn toward the intersection of physics, engineering, and astronomy.

During graduate studies, he gained hands-on expertise with:

·       Microwave detection systems

·       Low-noise amplifiers

·       Radio-wave propagation

·       Precision measurement techniques

This engineering-heavy background would become crucial for the detection of the CMB.

In 1962, Penzias joined Bell Telephone Laboratories in New Jersey, a research environment famous for its freedom, cross-disciplinary collaboration, and world-leading instrumentation. Bell Labs had invented the transistor, and its radio research division had access to one of the world’s most sensitive microwave antennas: the Holmdel Horn Antenna. Here Penzias met Robert Woodrow Wilson, another young physicist who shared an interest in precision microwave measurements. They were assigned to improve the horn antenna for satellite communications and atmospheric studies. This “applied” assignment accidentally placed them in a perfect position to make one of the most profound discoveries in cosmology.

Beyond the CMB, Penzias made numerous contributions to microwave spectroscopy, satellite communication, and radio astronomy instrumentation. His career gradually evolved from pure research into scientific leadership.

Leadership roles at Bell Labs:

·       Executive Director of the Communications Sciences Division

·       Vice President for Research

·       Chief Scientist of Bell Labs

In these roles, he influenced major research programs, including digital transmission technologies, semiconductor physics, and computational systems. His approach to scientific management emphasized:

·       Interdisciplinary collaboration

·       Long-term research investment

·       Intellectual independence and curiosity-driven inquiry

These principles helped Bell Labs remain one of the world’s premier research institutions during its peak decades.

Penzias is also known for his writings on science, culture, and innovation. Two important works:

1.     Ideas and Information (1989) — reflections on communication, complexity, and information theory.

2.     Harmony: New Ideas for a Holistic World (1995) — addresses interconnected systems and global responsibility.

These books reveal Penzias as a thinker whose interests ranged far beyond physics into social systems and philosophy.

Penzias retired from Bell Labs in the 1990s but remained active as a consultant, advisor, and public speaker.

Robert Wilson (1936 - ) – A biographical sketch 

Robert Woodrow Wilson was born on January 10, 1936, in Houston, Texas. From childhood he showed an intense curiosity about measurement, engineering, and the natural world—traits that would define his career as one of the most meticulous experimental astrophysicists of the 20th century. He pursued undergraduate studies at Rice University, earning a degree in Physics in 1957. His academic interests were strongly oriented toward the emerging field of radio astronomy, a discipline that blended physics, electronics, and astronomy at a time when new microwave technology was revolutionizing observational science.

For graduate school, Wilson moved to the California Institute of Technology (Caltech), one of the world’s centers of radio astronomy under figures like Robert Leighton and the Owens Valley group. He received his Ph.D. in Physics in 1962, with a dissertation involving precise radio-frequency instrumentation, preparing him for the challenges of low-noise microwave observations.

After his Ph.D., Wilson joined Bell Telephone Laboratories in Holmdel, New Jersey—the same legendary research center where Penzias was already working. Bell Labs provided:

·       Access to cutting-edge microwave equipment

·       Freedom to pursue experimental ideas

·       A culture that encouraged cross-disciplinary innovation 

Wilson’s technical strengths (receiver design, low-noise measurements, microwave spectroscopy) complemented Penzias’s perfectly. Together they formed a partnership grounded in meticulous experimental discipline. Their primary work initially had no connection to cosmology. Instead, they were tasked with refining the Holmdel Horn Antenna, originally built for the Echo satellite communications program.

In 1964–65, while calibrating the horn antenna for low-noise atmospheric measurements, Wilson and Penzias encountered a persistent, direction-independent microwave signal corresponding to a temperature of about 3 Kelvin. Wilson’s role in this process was critical. His deep technical knowledge allowed the team to calibrate the receiver chain with unprecedented accuracy, using cold loads, ambient loads, and careful power measurements. This ensured the anomalous signal was not a calibration artifact.

Together Penzias and Wilson eliminated every plausible terrestrial and instrumental source:

·       Receiver noise

·       Antenna losses

·       Atmospheric emission

·       Galactic foregrounds

·       Scattering from nearby structures

·       Radio-frequency interference

·       Even contamination from pigeons nesting inside the horn

Wilson’s precision and engineering intuition were essential in ruling out subtle systematic errors.

When the signal could not be explained, Wilson (and Penzias) reached out to the Princeton group led by Robert Dicke, who had been searching for relic radiation predicted by Big Bang models. Wilson’s willingness to seek theoretical guidance was instrumental in connecting observation to cosmology. In 1965, the discovery was published, inaugurating the era of observational cosmology.

Wilson’s contribution was seen as a model of experimental clarity—proving that the universe carries within it an “echo” of its hot, dense origin. This detection became one of the foundational pillars of modern cosmology, analogous in significance to Hubble’s discovery of cosmic expansion.

After the CMB discovery, Wilson did not rest on cosmological fame. He turned to millimeter-wave astronomy, where his technical expertise could be applied to new scientific frontiers.

At Bell Labs and in association with Caltech, Wilson made major contributions to:

1. Molecular Astrophysics

Wilson was among the pioneers in detecting and studying interstellar molecules, including:

·       Carbon monoxide (CO) mapping of the Milky Way

·       Molecular clouds and star-forming regions

·       Rotational transitions of numerous molecular species

His work helped define molecular gas as the raw material from which stars and planetary systems form.

2. Galactic Structure

Using CO as a tracer, Wilson contributed to the modern understanding of the spiral structure of the Milky Way. His observations provided the most complete maps of molecular clouds at the time.

3. Development of Millimeter-Wave Engineering

Wilson helped advance the receivers and calibration techniques that became standard in world-class observatories such as:

·       The Owens Valley Radio Observatory

·       The Caltech Submillimeter Observatory

·      The Atacama Large Millimeter/submillimeter Array (ALMA, conceptually founded on earlier technologies)

His engineering legacy is embedded in the instrumentation of almost every major millimeter-wave telescope in operation today.

Leadership, Teaching, and Influence:  Though not a career university professor, Wilson interacted deeply with the academic community through Caltech and collaborative research. He was known for:

·       Quiet, meticulous mentorship

·       Emphasis on experimental discipline

·       A calm and deliberate approach to scientific problem-solving

While Penzias eventually moved into higher administration at Bell Labs, Wilson remained closer to hands-on science, instrumentation, and observation.

Later Recognition and Life: Wilson received numerous honors beyond the Nobel Prize, including:

·       The Henry Draper Medal (1977)

·       The Herschel Medal of the Royal Astronomical Society

·       Membership in the National Academy of Sciences

In later years, he has remained an articulate advocate for basic research, emphasizing the serendipitous nature of scientific discovery and the importance of funding “blue-sky” experiments.

Today, Wilson is widely regarded as:

·       One of the greatest experimental radio astronomers of the 20th century

·       A pioneer of millimeter-wave astrophysics

·       A model of scientific precision, humility, and integrity

 

A snapshot

 

A footnote

The Nobel Prize in Physics for 1978 was in fact divided, one half awarded to Pyotr Leonidovich Kapitsa of the (former) USSR "for his basic inventions and discoveries in the area of low-temperature physics", the other half jointly to Arno Allan Penzias and Robert Woodrow Wilson "for their discovery of cosmic microwave background radiation".