The oldest light we can see
In 1964 two engineers at Bell Labs spent months trying to remove a persistent hiss from a horn antenna. They cooled the receiver, checked the wiring, and evicted a pair of pigeons. The noise stayed.
The accident
The hiss came from every direction equally and did not change with the seasons. Forty kilometres away at Princeton, a group was building an instrument to look for exactly that signal — the cooled afterglow of a hot early universe. The two teams talked, and a stubborn instrument problem became a Nobel Prize.
What the light is
For 380,000 years the universe was an opaque plasma: photons scattered off free electrons and got nowhere. When it cooled enough for atoms to form, the fog lifted and that light has been travelling since. Expansion has stretched it from visible into the microwave band, at a temperature of 2.725 K.
Reading the wrinkles
The glow is smooth to about one part in 100,000. Those tiny variations are the whole story — they are the seeds of every galaxy that exists. Mapping them precisely gives us:
- the age of the universe: 13.8 billion years
- its geometry: flat, to within measurement error
- the split of contents: roughly 5% ordinary matter, 27% dark matter, 68% dark energy
A small part of the static on an untuned analogue television was this same light. That is no longer true, which is a minor loss for science teaching.
Cover image: NASA/Goddard/WMAP Science Team — Public domain (source).
