ASTR 108 - Does Extraterrestrial Intelligence Exist?

Most arguments for the existence of extraterrestrial intelligence (ETI) rest on the Principle of Mediocrity, which asserts that on the cosmic scale there is nothing special about either the earth or the human beings who inhabit it- so intelligent extraterrestrials ought to exist. We will discuss the possibility of finding them by radio searches currently in progress, or by direct contact via future space exploration. If we're nothing special, then ETIs should have developed millions of solar systems long before ours did and the presence should already be known to us. Yet, we've never seen a single shred of evidence to support the existence of ETI, so where are they? This seemingly innocuous question represents a paradox whose scientific and philosophical implications will be fully explored. We will make reasonable estimates of the number of ETIs that co-inhabit our galaxy based upon our current understanding of cosmology, stellar and planetary evolution, anthropology, the nature of life, and evolutionary processes that have produced the human species, the probable sociology and philosophy of intelligent civilizations, and the possible evolution of noncarbon-based ETI. If we conclude that the number of ETIs is small then we must explain the uniqueness of our existence, given the Principle of Mediocrity. But, if we conclude that the number is large, then we must ask the question, so where are they? Either conclusion has profound consequences for the continued existence of the human species. All speculation is based on sound scientific principles and current theories and facts drawn from a highly diverse set of scientific principles.