Cosmic Background Radiation

In 1965 astronomers announced that they had detected an “echo” of the Big Bang — the event in which our universe is believed to have been born. Cosmic background radiation.

Cosmic Background Radiation 1

This is for Sunday, July 1 — with a landmark in 20th century science. On today’s date in 1965, scientists announced strong evidence that our universe was created in a Big Bang. Tune your radio between stations, and you’ll hear a hiss. Part of it is human-made static — part of it comes from the sun. But a tiny fraction of the static on your radio dial is believed to be left over from the birth of our universe. It’s called the “cosmic background radiation.”

Radio astronomers Arno Penzias and Robert Wilson discovered the cosmic background radiation accidentally in the year 1965. They wanted to use a satellite-tracking antenna in New Jersey for astronomy — but they couldn’t eliminate a faint background hiss. It didn’t seem to be an antenna problem. It seemed to come from everywhere. Penzias and Wilson spoke to Princeton University astronomers — and learned that the hiss was predicted by Big Bang theory.

Cosmic Background Radiation 2In the mid-1960s, this theory was still controversial. Princeton astronomers were preparing their own search for the cosmic background radiation when Penzias and Wilson discovered it first. Today most astronomers believe our universe was created in a Big Bang. For their discovery, Penzias and Wilson shared the Nobel Prize for physics in 1978.

Author notes:

Big Bang theory is the prevailing theory today of how our universe began. According to this theory, the universe was born in an inconceivably dense fireball — a primordial explosion in which space, time and matter all came simultaneously into being.

The “hiss” detected by Penzias and Wilson is believed to be a remnant of the Big Bang. In other words, as space expanded, the fireball cooled. Matter came together to form galaxies, stars, and planets — and eventually human beings. But all the while — through billions of years of evolution — the universe has been expanding. This expansion caused the frequency of the cooling fireball to slide down the spectrum from heat to radio waves. At last it became the faint hiss first heard by Penzias and Wilson.

Penzias and Wilson submitted their paper on the 3.5 K unexpected signal received by their antenna in the form of a letter to the editor of the Astrophysical Journal Letters on May 13, 1965. The letter appeared on July 1, 1965, along with a companion letter by the Princeton scientists Robert Dicke, James Peebles, Peter Roll, and David Wilkinson tying the antenna signal to the cosmic background radiation. In the meantime, the New York Times had announced the discovery prominently on the front page on May 21, 1965.

Other names play prominent roles in the story of the discovery of cosmic background radiation. In 1927, Georges Lemaitre used Einstein’s General Theory of Relativity to predict that the universe would be found to be expanding, and that the motion of galaxies might be used to confirm this.

In 1929, Edwin Hubble announced that galaxies are moving apart at great speeds. Their motion implied that once they were together in a small space.

In 1949, George Gamow described the conditions that must have prevailed as the universe began its explosive expansion, and predicted the faint hiss Penzias and Wilson heard in 1965. Robert Dicke at Princeton told Penzias and Wilson what the hiss meant.

The horn-shaped antenna at Holmdel Penzias and Wilson used to detect the cosmic background radiation was built by Bell Laboratories to bounce radio signals off the early Echo satellites. After that, it was used to measure signals from Telstar. It’s said that Wilson took his job at Bell Labs primarily to get access to the antenna for astronomy after it completed its satellite tracking duties. In 1990 the National Park Service designated the Holmdel antenna a National Historic Landmark.


  • John Gribbin, Companion to the Cosmos Weidenfeld Nicolson, 1996, pp. 38-41.
  • Donald Goldsmith, Einstein’s Greatest Blunder? Harvard, 1995, pp. 71-75.
  • Matt Roos, Introduction to Cosmology Wiley Sons, 1994, pp. 95-99.
  • “Footprints of Creation: Discovery of the Cosmic Background Radiation,”
  • “A Science Odyssey: People and Discoveries,” –
  • AT T News Release, June 12, 1990.

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