From David Roffey, London, UK
Schulze-Makuch and Bains mention economist Robin Hanson's idea of a “Great Filter” that makes truly advanced life very rare. It seems likely that the harder thing for intelligent life to pass through is the “Green Filter”: can it get past the phase of energy overuse and pollution without destroying itself or devastating its home? If we do make it to star-faring and visit exoplanets, will we find shards of broken civilisations who didn't make it?
