Light and waves
1965
The afterglow of the Big Bang
Arno Penzias and Robert Wilson
What is the oldest light you can see?
Two radio engineers could not get rid of a faint hiss in their antenna, coming from every direction. It was the cooled leftover light of the hot early universe, now about 2.7 degrees above absolute zero, predicted years earlier.
How they figured it out
In 1964 at Bell Labs in New Jersey, Arno Penzias and Robert Wilson had a large horn-shaped antenna and an annoying problem: a faint hiss coming from every direction, day and night. They suspected pigeon droppings, cleaned the antenna and removed the pigeons. The hiss stayed.
Meanwhile, about 50 km away at Princeton, Robert Dicke’s team was building an instrument to search for exactly this: the leftover glow of a hot early universe. When Dicke heard about the Bell Labs hiss, he reportedly told his team, “Boys, we’ve been scooped.”
The equation
The universe’s oldest light has been stretched by expansion until it is cold microwaves.
See it in real life
A cooling stove
Switch off an electric stove ring and its glow fades from orange to dull red to invisible warmth. The universe’s glow has done the same, cooling from about 3,000 degrees to 2.7 degrees above absolute zero and stretching into microwaves.
Where engineers use it
Noise engineering
Penzias and Wilson found it by chasing antenna noise; low-noise receiver design is an engineering field of its own.
Where it came from
- The expanding universe 1922–1929
Led to
If the universe expanded, it was once hot and dense, and that heat should still glow.