Why Can't We Find Extraterrestrials?

The report of liquid water on Mars, and the increased probability that life will be found on the planet, reminded me of this old article hoping humans are alone in the universe because the alternative is too terrifying. The search of extraterrestrial intelligence (SETI) has been going on for decades will no success. Why?

We're Too Dumb

There are intelligent creatures on Earth - apes, dolphins, elephants, ravens. While we can train them to understand us and even teach them languages so they can communicate with us, we have never been able to understand their languages. If we can't understand dolphinese in the wild how can we hope to understand an extraterrestrial. Evidence of extraterrestrials may be all around us but we are too stupid to recognize it. This is the most likely answer.

They Killed Themselves

This is the Great Filter theory mentioned by Nick Bostrom. Any civilization that achieves interstellar travel would have to be both aggressively expansionist and an aggressive user of resources. Aggressive species are, necessarily, warrior species. Like humanity, a dominate warrior species will likely develop weapons capable of destroying their planet's ecosystem. Likewise, rapacious consumption of resources can deplete the planet and collapse the civilization before space travel can be achieved.

Why Leave?

Civilizations that don't want to kill each other or rape their planet live in Nirvana. What would motivate them to venture into the vast emptiness of a hostile galaxy? If they are not seeking to pillage and conquer, why go anywhere?

God Zaps Them

The universe is a dangerous place. The other Great Filter barrier is the universe smites planets every few billion years. An advanced civilization might be able to defend itself from asteroids or super volcanoes, but there are things that no civilization can survive. Take Gamma Ray bursts. When a star goes supernova it releases a beam of gamma rays that, quite literally, will fry any planet in its path. Gamma rays travel at the speed of light, there is no seeing it coming. Estimates are they happened in the Milky Way some 5,000 times since the Earth was formed. It is suggested a gamma ray burst struck the Earth 450 million years ago causing a mass extinction.

Or...
Reptilian shape-shifting extraterrestrials are among us now and Barack Obama is their king.