"More than half a century after Fermi asked his question, we have still heard nothing. Despite our communication systems, no one has called. The more we explore our local neighborhood, the lonelier it seems. No concrete signs of any life, not even the simplest bacteria, have been found on the Moon, Mars, or the outer solar system planets and moons. There are no signs of interference in the light from stars that could indicate giant orbiting machines harvesting energy from them. Given the stakes, there is great attention paid to searching for extraterrestrial intelligence.