Bring up aliens and a lot of people will scoff. But not everyone is laughing. Around the turn of the century, 3.8 million people banded together in a real-time search for aliens -- with screensavers.

If so, why haven’t they said hello? The humble residents of this pale blue dot have been on a quest to find an alien civilisation for more than a century. First, it was the “canals” of Mars. Then ...