Or, Where is everybody?

The numbers are staggering; even in a place with little light pollution, when we star-gaze we are looking at only about 2500 stars, or a hundred-millionth of the stars in our galaxy, mostly within 1000 light-years of Earth. There are 100 to 400 billion stars in the Milky Way Galaxy, and roughly as many other galaxies in the observable universe. Although measurement is imprecise, there are likely 10^22 to 10^24 total stars in our universe. With the conservative assumption that possible life requires a sun-like star (estimated, at the low end, at 5% of total stars), that leaves us with 500 billion billion sun-like stars.

Of course, there is a debate about what percentage of such stars could foster Earth-like planets (with similar temperature conditions, and liquid water). The commonly accepted answer is at least 1-in-6. This means that roughly 1% of the sun-like stars in the Universe could have Earth-like planets orbiting them.

Assuming the mediocrity principle, the Earth (and its development of intelligent life) is not highly unusual. But even with a conservative estimate that 1% of our Earth-likes develop life, and .5% of that life achieves observable technological civilization, that would mean roughly 5 million billion civilizations in our observable universe. Even shrunk to our immediate neighborhood- the Milky Way Galaxy- there should be 50,000 communicating or traveling civilizations within it's 100,000 light year diameter.

So, where is everybody? This contradiction is known as the Fermi Paradox. A number of answers have been proposed:

Extraterrestrial life is rare or non-existent

No other intelligent species have arisen

Intelligent alien species lack advanced technology

It is the nature of intelligent life to destroy itself

It is the nature of intelligent life to destroy others

Periodic extinction by natural events

Inflation hypothesis and the youngness argument

Intelligent civilizations are too far apart in space or time

It is too expensive to spread physically throughout the galaxy

Human beings have not existed long enough

Humans are not listening properly

Civilizations broadcast detectable radio signals only for a brief period of time

They tend to isolate themselves

They are too alien

Everyone is listening, no one is transmitting

Earth is deliberately not contacted

Earth is purposely isolated (planetarium hypothesis)

It is dangerous to communicate

They are here undetected

They are here unacknowledged

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The Fermi Paradox Jam (#fermijam) is an invitation to make something (anything!) inspired by this problem. In addition to games, we welcome digital work, music, star charts, prose, comics, or things more alien. The jam will run from midnight September 2nd to midnight September 12th, 2016.

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API reference materials:

Image credit: Max Ernst and NASA