Despite an observable universe sprinkled with several trillion galaxies, each stuffed with a trillion planets, we see no evidence of anyone. No signals, no megastructures, no interstellar rockets. While astronomers routinely uncover puzzling objects in the sky, these always turn out to be manifestations of natural phenomena.
When you consider that age of the Universe – 13.8 billion years by our most recent counts – and that which is “observable” to us measures about 27.6 billion light years in diameter, you begin to wonder why we haven’t found signs of extra-terrestrial intelligence (ETI) beyond our Solar System. To paraphrase Enrico Fermi, the 20th century physicists who advanced the famous Fermi Paradox – “where the heck are all the aliens?”