For the last couple of decades, astronomers and astrophysicists have generally searched for extraterrestrial life by looking for biosignatures — such as water, oxygen or chlorophyll — on other planets. That seems like a sound strategy in general; after all, life has existed on Earth for around 3.7 billion years, while industrial civilization has only existed for 200.
But now, some astronomers think perhaps we have been searching for alien life by following the wrong clues. The reason has to do with the power of our telescopes, and the fact that the signals from technologically advanced civilizations may be much easier to detect than the traces of unsophisticated biological life.
