The Antenna Hiss That Turned Out to Be Echoes of the Early Universe

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In the 1960s, two Bell Labs radio astronomers were trying to make a large horn antenna sensitive enough for precise radio observations. Instead, they kept detecting a faint, steady hiss that seemed to come from everywhere. They checked ordinary sources of interference, including signals from nearby cities and other radio sources, but the mystery remained. They even investigated pigeons nesting inside the antenna and cleaned away accumulated droppings, yet the unwanted signal refused to disappear. The clue turned out to be much bigger than a faulty instrument or dirty equipment. The signal was cosmic microwave background radiation, a faint afterglow from the hot early universe that has been traveling through space for billions of years. The discovery provided powerful evidence for the Big Bang model. The radiation is now understood as light released when the early universe had cooled enough for atoms to form and light to travel freely. As the universe expanded, that ancient light was stretched into the microwave part of the electromagnetic spectrum. The unexpected finding became one of the landmark discoveries of modern cosmology. The two researchers shared half of the 1978 Nobel Prize in Physics for discovering the cosmic microwave background radiation. Later experiments measured the background in far greater detail, revealing tiny variations that help scientists study the early universe and its evolution.