Alien invasion

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Lucky for us, kids have been training to ward off alien invaders since the 70's!
The woo is out there
Icon ufology.svg
Aliens did it...
... and ran away
If aliens ever visit us, I think the outcome would be much as when Christopher Columbus first landed in America, which didn't turn out very well for the Native Americans
— Stephen Hawking[1]

An alien invasion, or an a act of aggression by extraterrestrials against Earth, is a common trope in science fiction. The motivation is typically conquest, as in H.G. Wells' novel War of the Worlds, or biological assimilation, as in the 1956 film Invasion of the Body Snatchers.

Over at Wikipedia, however, the term also includes any non-military encounter between humans and extraterrestrials that occurs on Earth. Fear, rather than the more appropriate responses of curiosity or wonder, dominate the discussion,[2] probably because conventional wisdom about any such encounter has been constructed from narratives of conquest and assimilation. Thus the encounter in Arthur C. Clarke's novel Childhood's End is described as an alien invasion story despite the absence of any military operations or even the presence of many aliens on Earth once they reveal themselves.

Unfortunately, in an effort to appeal to audiences unfamiliar with hard science fiction, alien invasion stories in popular television and film are often trapped in the handful (and shrinking number) of historical metaphors familiar to the general public.[3].

Variants of this trope, more typical in literary works, include being the aliens, not the humans, the curb-stomped ones in one way or in another despite their seemingly superior technology[note 1], and/or the contact with humans being a shock for them due to cultural differences and/or changing deeply their culture[note 2].


It is unclear both what the risk is of an alien invasion of Earth, and how best to avoid or defend against it. We have little idea how many worlds may contain alien life, how many of those will have evolved interstellar technology, and how many of those will be nice. (Attempts to estimate this, such as the Drake equation, are little more than wild guesses.)

It has been proposed that the best solution is to keep as quiet as possible, and cancel projects such as SETI which attempt to contact aliens. Distinguished people such as Stephen Hawking, Elon Musk, and author David Brin have suggested this.[4][5][6] On the other hand, we unavoidably send lots of radio signals into space, so stopping SETI won't help much.[6]

Travis Taylor and Bob Boan, two defense and aerospace consultants, have published "An Introduction to Planetary Defense"; they suggested our only hope would be asymmetrical conflict, such as guerrilla warfare.[7][8] Other people have suggested imaginative tactics including blowing up satellites to intentionally create a debris field that would damage incoming spacecraft (Kessler syndrome would help); attacking craft as they enter the earth's atmosphere when sensors will be overwhelmed by the enormous heat; or threatening to blow ourselves up unless the aliens go home (which requires some major assumptions about the aliens' motives).[9]

The bullshit[edit]

From time to time some cranks using as proof texts as for example those written by Nostradamus or the Book of Revelation, or simply inventing it will claim that aliens will invade us[10]. Of course the predicted date will come and go and the only thing that will have left behind is ridiculousness for said woo-meisters.


  1. After all, interstellar travel is way beyond ours
  2. See the Worldwar series by Harry Turtledove for an excellent example.