Cosmic cats and nuclear blasts: the strange history of interstellar messages

From Sagan to Tesla, scientists have long puzzled over how to talk to extraterrestrial intelligence

So you've received a message from an extraterrestrial intelligence. Congratulations! You are now at the centre of one of the most important events in human history. But now comes the hard part: what do you say in return - and, more importantly, how do you say it?

For the past 200 years, the problem of interstellar communication with an extraterrestrial intelligence has vexed some of the world's greatest scientists and mathematicians. Carl Friedrich Gauss, the mathematician and inventor of the heliotrope, suggested using a large array of mirrors; Guglielmo Marconi and Nikola Tesla, pioneers of wireless communication, found a solution in radio waves; and John McCarthy and Marvin Minsky, the progenitors of artificial intelligence, wanted to send computers into space as our extraterrestrial envoys.