Grabby Aliens

Why do we humans appear (apparently) so early in the universe? This is the way (the controversial but always inspiring) Robin Hanson reframes the obsessive Fermi Paradox in a working paper published this week.

Back on Dec. 16, he envisioned the basic “grabby aliens” model, and found a simple math model to express its key symmetries. Then he went “in manic mode”, recruited three collaborators (Daniel Martin, Calvin McCarter, Jonathan Paulson), and they together have written a working paper to share with the world.

Our grabby aliens model can explain a striking but neglected empirical puzzle: why do we humans appear so early in the universe?

What is a grabby civilization? They think there are two main types of aliens: quiet and loud. Quiet aliens are harder to see, and therefore could be quite common, or not. Loud aliens, in contrast, could be quite noticeable if they exist in any substantial number per Hubble volume.

Grabby aliens:

  • never die alone
  • expand the volumes they control at the same speed
  • clearly change the look of their volumes (relative to uncontrolled volumes), and
  • are not born within grabby civilization controlled volumes.

To study those aliens the model needs only three free parameters:

  1. The rate at which grabby civilizations are born.
  2. The (assumed universal) speed at which grabby civilizations expand.
  3. The effective number of  “hard steps” in the “great filter” process by which simple dead matter evolves to become a grabby civilization

Hanson’s grabby aliens model resolves the (Fermi) puzzle by denying a key assumption in other models: that the birth of some advanced life has no effect on the chances that others are born at later dates.

Our grabby alien model instead embodies a selection effect: if grabby aliens will soon grab all the universe volume, that sets a deadline by which others must be born, if they are not to be born within an alien volume. So we can explain why we are early via the twin assumptions that (a) we could see but do not see alien controlled volumes, and (b) some of our descendants may soon become grabby.

In other words, by the time we noticed grabby aliens, it would already be nearly too late. Robin’s and co. grabby model is disturbing, and very much in line with perhaps the most well-known storyline in science-fiction cinema: the alien invasion.

Just another good reason to take a deep breath before opening your window and looking at the sky.


Featured Image: 10 Cloverfield Lane


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