įermi was not the first to ask the question. However, there is no convincing evidence that this has happened.Since many of the stars similar to the Sun are billions of years older, Earth should have already been visited by extraterrestrial civilizations, or at least their probes.Even at the slow pace of currently envisioned interstellar travel, the Milky Way galaxy could be completely traversed in a few million years.Some of these civilizations may have developed interstellar travel, a step humans are investigating now.If the Earth is typical, some may have developed intelligent life long ago. Many of these stars, and hence their planets, are much older than the Sun.With high probability, some of these stars have Earth-like planets in a circumstellar habitable zone.There are billions of stars in the Milky Way similar to the Sun.The following are some of the facts and hypotheses that together serve to highlight the apparent contradiction: 5.7 Alien life is already here unacknowledged.5.6.4 Earth is deliberately isolated (planetarium hypothesis).5.6.1 Everyone is listening but no one is transmitting.
5.4.2 It is cheaper to transfer information than explore physically.5.4.1 Lack of resources needed to physically spread throughout the galaxy.5.3.4 Alien species may isolate themselves from the outside world.5.3.3 Alien species may not live on planets.5.3.2 Alien species may have only settled part of the galaxy.5.3.1 Colonization is not the cosmic norm.5.2.4 Civilizations only broadcast detectable signals for a brief period of time.5.2.3 It is the nature of intelligent life to destroy others.5.2.2 It is the nature of intelligent life to destroy itself.5.2.1 Intelligent alien species have not developed advanced technologies.5.1.3 Periodic extinction by natural events.5.1.2 Extraterrestrial intelligence is rare or non-existent.5.1.1 Extraterrestrial life is rare or non-existent.5 Hypothetical explanations for the paradox.4.4 Searches for stellar-scale artifacts.4.3 Conjectures about interstellar probes.This suggests that at universe time and space scales, two intelligent civilizations would be unlikely ever to meet, even if many developed during the life of the universe. There have been many attempts to explain the Fermi paradox, primarily suggesting that intelligent extraterrestrial beings are extremely rare, that the lifetime of such civilizations is short, or that they exist but (for various reasons) humans see no evidence. The conversation moved on to other topics, until during lunch Fermi blurted out, "But where is everybody?" (although the exact quote is uncertain). While walking to lunch, the men discussed recent UFO reports and the possibility of faster-than-light travel. Italian-American physicist Enrico Fermi's name is associated with the paradox because of a casual conversation in the summer of 1950 with fellow physicists Edward Teller, Herbert York, and Emil Konopinski. As a 2015 article put it, "If life is so easy, someone from somewhere must have come calling by now." The Fermi paradox is the conflict between the lack of clear, obvious evidence for extraterrestrial life and various high estimates for their existence. A graphical representation of the Arecibo message, humanity's first attempt to use radio waves to actively communicate its existence to alien civilizations
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