Penzias and Wilson's Discovery is One of the Century's Key Advances

Murray Hill, N.J. -- When the intellectual history of the 20th century is written, a few achievements will tower over all. Einstein's theory of general relativity will be one; the laws of quantum mechanics will be another. The so-called Big Bang Theory of the origin of the universe will be a third.

The discovery in 1963 by Arno Penzias and Robert Wilson of the cosmic microwave background of the Big Bang set the seal of approval on the theory, and brought cosmology to the forefront as a scientific discipline. It was proof that the universe was born at a definite moment, some 15 billion years ago.

Wilson and Penzias with their historic horned antenna at Crawford Hill, N.J.

Dan Stanzione, then Bell Labs president and Lucent's chief operating officer when Penzias retired, said Penzias "embodies the creativity and technical excellence that are the hallmarks of Bell Labs." He called him a Renaissance figure who "extended our fragile understanding of creation, and advanced the frontiers of science in many important areas."

Scientists acknowledge that the discovery that Penzias and Wilson made was one of the century's key scientific advances.

Said Michael Turner, a well-known cosmologist at the University of Chicago who recently gave a talk here, "The discovery of the cosmic microwave background by Penzias and Wilson transformed cosmology from being the realm of a handful of astronomers to a 'respectable' branch of physics almost overnight."

Two conflicting theories

In the 1950s, there were two theories to the origin of the universe. The first was called the Steady State Theory. It had been put forward by Hermann Bondi, Thomas Gold and Fred Hoyle and held that the universe was homogeneous in space and time and had remained like that forever -- essentially, that the universe existed in "a steady state."

The rival, more controversial theory sought to incorporate the expansion of the universe into its framework. Edwin Hubble had shown in 1929 that galaxies are moving away from one another at remarkable speeds, implying that the space between galaxies is constantly expanding. A few physicists led by George Gamow had taken this notion and argued that the separation between galaxies must have been smaller in the past.

If one stretched the idea to the limit, it meant that the universe had been infinitely dense at one point sufficiently back in time. Using the laws of physics, Gamow and his colleagues were able to show that the point -- which was also infinitely hot -- corresponded to the moment of creation. Everything in the universe had emerged from this incredibly dense and hot state in a cataclysmic event astronomers call "the Big Bang."

Dispute settled by radio noise

The conflict between the theories was resolved by Penzias and Wilson in 1965.

They had been using an ultra-sensitive microwave receiving system to study radio emissions from the Milky Way when they found an unexpected background of radio noise with no obvious explanation. It came from all directions and, after repeated checks, it appeared to emanate from outside the Galaxy.

Penzias and Wilson consulted with Princeton physicist Robert H. Dicke, who had theorized that if the universe was created according to the Big Bang theory, a background radiation at 3-degree Kelvin would exist throughout the universe. Dicke visited Bell Labs and confirmed that the mysterious radio signal Penzias and Wilson detected was, indeed, the cosmic radiation that had survived from the very early days of the universe. It was proof of the Big Bang.

As John Huchra, a professor of astronomy at Harvard University and a leading observational cosmologist, put it, "The discovery of the 2.7 degree background was the clincher for the current cosmological model, the hot Big Bang. It opened a window on the Universe at a very, very early time, enabling astronomers and physicists to see the initial conditions from which the beauty of the present-day cosmos sprang."

'Why do such a thing?'

Reflecting back on Penzias's early days at Bell Labs, Ivan Kaminow, one of his colleagues at Holmdel, recalled a round-faced, enthusiastic scientist who arrived with a small dish antenna to conduct radio astronomy. "I had no idea why anyone would want to do such a thing, but we spent many lunch hours walking through the fields discussing the present and future," Kaminow said.

He joked that Penzias was an unusually lucky guy. "Arno Penzias and Bob Wilson were trying to find the source of excess noise in their antenna, where pigeons were roosting," he said. "They spent hours searching for and removing the pigeon dung. Still the noise remained, and was later identified with the Big Bang."

He laughed, "Thus, they looked for dung but found gold, which is just opposite of the experience of most of us."

A turning point for cosmology

The cosmic microwave background hails from the earliest observable event in the history of the universe, some 300,000 years after its birth. Although the original temperature of the cosmic microwave background was much higher, the expansion of the universe has cooled it to its present value of 2.7 degrees Kelvin.

More than three decades after Penzias and Wilson's discovery, the significance of their finding remains as great. It provided a new tool for exploring the early universe.

A few years ago, NASA sent the Cosmic Microwave Background Explorer (COBE) satellite into orbit to investigate the cosmic microwave background in great detail. The principal scientist of the COBE mission, George Smoot, said, "There is no doubt that Penzias and Wilson's discovery of the cosmic background radiation marked a turning point in cosmology."

Understanding the universe's origin

Tony Tyson at Bell Labs concurred, saying it was one of the greatest breakthroughs in our understanding of the universe's origin. "Its precise black-body spectrum and uniformity over the sky have ruled out many theories of the evolution of the Universe," he noted.

Experiments to analyze the small irregularities in the cosmic background radiation are under way today, in the effort to increase our understanding of the early universe. "This faint microwave radiation continues to be a wellspring of cosmological discovery," he said.

John Bahcall, a leading astrophysicist and professor of natural sciences at the Princeton Institute for Advanced Study, said, "The discovery of the cosmic microwave background radiation changed forever the nature of cosmology, from a subject that had many elements in common with theology to a fantastically exciting empirical study of the origins and evolution of the things that populate the physical universe."

He called it the most important achievement in astronomy since Hubble's discovery of the expansion of the universe.

(May, 1998; Rev. Feb., 2001)

See Also

• Nobel Laureate Arno Penzias Retires After 37 Years at Bell Labs
• Arno Penzias' Homepage