Since the universe is very old and really big, most scientists posit a high probability that a small percentage of planets are homes to intelligent life and civilizations. Some of these civilizations would be older and more technologically advanced than ours.
If this is the case, many have wondered, why haven’t we seen any real evidence or scientific proof of their presence? Wouldn’t they have visited us by now? Wouldn’t we have detected their movements?
“Where is everybody?” asked the physicist Enrico Fermi back in 1950 while having lunch with Edward Teller and two other scientists at Los Alamos National Laboratory. The topic of UFOs had come up in the conversation, Fermi posed his question, and a lively debate ensued to which no satisfactory answer could be conjectured.
The debate still goes on.
The Fermi paradox is the apparent conflict between the probability of intelligent extraterrestrial life and the complete lack of evidence for it.
Fermi estimated that there could be as many as 10,000,000,000,000,000 intelligent civilizations in the observable universe. As old as the universe is, at least some of these civilizations should by now have achieved the art of long-distance space travel. This, in short, is the Fermi paradox.
Scientists have been grappling with the paradox for decades, and have come up with some hypothetical explanations for the paradox. In this infographic from futurism.com, these possible solutions to the Fermi paradox are presented in simple language. Click the infographic to enlarge.