In 1964, physicists Arno Penzias and Robert Wilson at the Bell Telephone Laboratories in New Jersey were investigating interference that was affecting a horn-shaped antenna built for satellite communications. Their analysis suggested it was emanating from an incredibly feeble source of heat, amounting to just a few degrees above absolute zero (-273°C) – and bizarrely, it seemed to be coming from everywhere in the sky at once.
When the pair described their findings to astrophysicists at nearby Princeton University, the truth emerged: Penzias and Wilson had detected the heat left over from the Big Bang. The momentous discovery garnered the pair a share of the Nobel Prize for physics in 1978.
But by then, it was clear they weren’t the first to detect this primordial heat. In 1940, Canadian astronomer Andrew McKellar found molecules in space whose properties revealed the temperature of their surroundings. He showed that these suggested the whole of space was a few degrees warmer than absolute zero, but the significance of this was missed because theorists had yet to work out the consequences of the Big Bang in detail. Sadly, McKellar never lived to see his claim vindicated: he died in 1960, aged just 50.