[OT] Destroying all human life on Earth AT THE SAME TIME

[Gregor Richards]

You want to destroy all life on Earth. However, you don't want people 
panicking as this could alter the result, so you want all humans to die 
at the same instant. To do this, you're creating nano-robots. A single 
nano-robot cannot control a persons mind: Seven are required (three in 
each half of the brain and one in the brain stem). Nano-robots can 
harvest material from their host to build new nano-robots, but the host 
will die after approximately twenty nano-robots-worth of material has 
been harvested (they require particular rare particles that can only be 
harvested from the heart and lungs). Nano-robots may communicate with 
one-another via broadcast, but the range is limited to 1 mile. 
Nano-robots do not have unique identification globally, but do have 
unique identification within a body (that is, nano-robots in the same 
body can distinguish each other, but broadcast messages from a 
nano-robot in one human cannot implicitly be distinguished from 
broadcasts from another). These broadcasts travel at the speed of light 
(seeing as that they are light). Nano-robots harvest energy from their 
host, and as such can survive indefinitely. A nano-robot in a dead host 
survives long enough that this variable is not relevant for this problem.

Robots can only be spread by direct physical contact from an infected 
host to an uninfected one, and the process of transferring one 
nano-robot destroys two nano-robots (that is, the infected host loses 
three robots in the process but the new host only gains one).

Devise an algorithm for these nano-robots that will destroy all human 
life on Earth in a minimum amount of time, but with which all humans 
will be destroyed within five minutes of each other. That is, minimize 
the time from deploying the first nano-robot to the initial human life 
being exterminated, and minimize the time from the initial human life 
being exterminated to all human life being exterminated. You may assume 
a maximum of twelve degrees of separation between average industrialized 
people and that even the most remote tribe is connected by at least one 
human to the industrialized world.

Bonus: How would you change this algorithm if you wanted to destroy all 
animal life? All life? How would you change it if astronauts were 
considered?

  - Gregor Richards