Big Bang Background Radiation Found — 62 Years Ago

A Hiss That Changed Cosmology

In 1964, radio astronomers Arno Penzias and Robert Wilson were working at Bell Labs in New Jersey, trying to use a large horn-shaped antenna for satellite communication. No matter where they pointed it, they detected a faint, persistent microwave hiss coming from every direction in the sky equally. They checked everything — cleaned out pigeon droppings from inside the antenna, checked the equipment repeatedly — and could not eliminate the noise. Meanwhile, nearby physicists at Princeton had predicted that the Big Bang should have left behind exactly this kind of faint radiation, now cooled to just a few degrees above absolute zero.

What the Signal Means

The Cosmic Microwave Background (CMB) radiation is the afterglow of the Big Bang — light released about 380,000 years after the universe began, when it had cooled enough for atoms to form and became transparent for the first time. The CMB fills the entire universe uniformly, coming from all directions with the same temperature: about 2.7 Kelvin (minus 270 degrees Celsius). Tiny variations in that temperature, measured by later satellites, show the seeds of structure — the slight density differences that eventually grew into galaxies, stars, and planets. The CMB is a snapshot of the infant universe.

Confirming the Big Bang

Penzias and Wilson won the Nobel Prize in Physics in 1978 for their discovery. The CMB became the strongest evidence that the universe began in an extremely hot, dense state about 13.8 billion years ago and has been expanding and cooling ever since. Subsequent satellite missions — COBE, WMAP, and the Planck satellite — mapped the CMB in increasing detail, measuring the age, geometry, and composition of the universe with remarkable precision. The accidental discovery of a persistent hiss in a satellite dish turned out to be the echo of creation itself.