Life in the Universe:
Life in the Universe:
The Fermi Paradox
The Fermi Paradox
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In 1950, the Nobel Prize-winning nuclear physicist Enrico Fermi posed this question:
Where is everybody?
Where is everybody?
He was referring to intelligent extraterrestrial civilizations.
His question frames what has become known as the Fermi Paradox.
The logical sequence of assumptions leading to the paradox are outlined below.
Enrico Fermi (1901-1954 CE; Italian-American), circa 1943-1949.
Credit: United States Department of Energy; available in the holdings of the National Archives and Records Administration, cataloged under the National Archives Identifier (NAID) 558578 [link]There are billions of Sun-like stars in the Milky Way Galaxy.
Many of these stars are up to billions of years older than the Sun, so whatever processes have happened in our Solar System will have had plenty of time to play out around other Sun-like stars.
Some of these stars probably almost certainly have Earth-like planets.
If Earth is typical of Earth-like planets, then at least some of these planets will have evolved intelligent life.
Some of these intelligent civilizations will have developed interstellar travel (Earth's civilization is at the beginning of this now).
Even at the slow pace of interstellar travel, the entire Milky Way Galaxy could be explored and colonized in a few million years - that is a long time compared to the history of human civilization (about 10,000 years) but not compared to the age of our Galaxy (more than 10 billion years).
Thus, we should have been visited by intelligent extraterrestrials many times by now, and see obvious evidence of advanced civilizations all around us.
Where is everybody?
What can we look for?
What can we look for?
Technosignatures of an advanced civilization.
Technosignatures of an advanced civilization.
Credit: Kander10 Designs/Forbes [link]
Where is everybody?
Where is everybody?
Here are some possible answers to that question...
Here are some possible answers to that question...
Lonely Galaxy: Life is (much) more rare than we think.
Time Is Not On Our Side: A few million years is a blink in the 13 billion year history of our Galaxy. Other civilizations might have lived and died billions of years ago, or we might be the first.
Stupid Galaxy: Life might be common, but intelligent life not so much…
Stay At Home: Other civilizations have not developed advanced technology or are not interested in exploration.
Prime Directive: Other civilizations do not contact us on purpose to protect us or themselves (see Red Flag #2).
Aliens Are Weird: Extraterrestrial life might be drastically different than life on Earth. Their thought processes might proceed orders of magnitude slower or faster than ours. They might not recognize us as intelligent or even as life. And so on…
Indistinguishable From Magic: Other civilizations might have advanced so far beyond us that they don’t consider us worth contacting (why would you want to talk to bacteria?)
Red Flag #1: Civilizations do not last long enough to travel very far (or at all) into the Galaxy.
Red Flag #2: Advanced civilizations tend to destroy each other when they meet.
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