The Search for Extraterrestrial Intelligence (SETI) has long been haunted by Fermi's Paradox, which questions why, given the universe's vastness and the abundance of life-sustaining elements, humanity has not encountered intelligent extraterrestrial civilizations. Notably, physicists Michael Hart and Frank Tipler proposed the Hart-Tipler Conjecture, suggesting that if advanced civilizations existed, they would have colonized the galaxy, thus explaining the lack of evidence for extraterrestrial contact. In response, astronomer Carl Sagan argued that the absence of evidence is not evidence of absence, challenging the assumptions made by Hart and Tipler. Another significant theory is the Great Filter, proposed by Robin Hanson, which posits that there are critical evolutionary steps that are highly improbable, preventing intelligent life from advancing to a stage where it can communicate or explore the galaxy. Philosopher Nick Bostrom further elaborated on this concept, describing the Great Filter as a probability barrier that must be overcome for intelligent civilizations to emerge. As SETI continues to evolve, these questions remain central to our understanding of life in the universe.