OAS Lecture on Interstellar Communication by Roger O’Brien on 27 September 2023
Review by Andrew Ramsay
In little more than an hour Roger O’Brien demolished decades of expectations and hopes raised by science fiction. He began with a review of the science behind the ill-fated SETI (Search for Extraterrestrial Intelligence) – and the slim chances of an electromagnetic signal being strong enough to detect over light years of space. Pausing briefly to dismiss Dyson spheres as a practical way to harness the power of a star he debunked our own civilisation’s tentative attempts to communicate with distant entities. Roger touched on the immense distances that actual spacecraft needed to cover to stand a hope of delivering a message, and the structural failure of the Arecibo radio telescope in 2020, which finally aborted the attempt to send a primitive signal towards M13 (misaligned, as it turned out).
We were invited to consider the immense problems of sailing a tiny probe across light years using solar or laser power – not least the impossibility of slowing it down anywhere near the destination. The sort of people-carrying spaceships envisaged by Arthur C Clarke seemed unlikely to be able to achieve more than a fraction of light speed, condemning them to aeons of travel in order to get to our nearest star systems.
Rather than waiting 50,000 years for a reply, Roger suggested we considered ourselves as authors like Aristotle and Homer who had managed to communicate over millennia without the possibility of interrogation. If we absolutely had to send a signal, Roger suggested a series of earth-sized disks on an orbit perpendicular to the solar system which could interrupt the sun’s rays with a primitive “anomalous modulation” which could attract attention.