In 1974 a group of scientists beamed a message into space. The message, meant to be received by an intelligent alien species, described life on Earth.
Written in simple binary code, and using the most powerful radio telescope on the planet, the message was broadcast to a dense cluster of stars in the constellation of Hercules.
This exercise was just ceremonial; a way to demonstrate new technology in radio astronomy.
Nobody was really expected to receive it. And even if they did, it wouldn't be any time soon. The nearest star in the direction of the broadcast is 25,000 light-years away.
So, the telescope was tuned to 2380 Megherz, aimed at Hercules, and fired up. The scientists congratulated each other, shook hands, and went on with their lives.
But 27 years later, something very unexpected happened with that message beamed into deep space.
We got a reply.