spaceConsole

Communicate with space aliens using a weatherized hardware console attached to a 13.41 meter light beacon installed at about 3907' (in altitude) in a high desert.

Requires 4800 ws2815b RGB LED pixels.

The genetic algorithm

To find the best patterns for communicating with space aliens, we use a genetic algorithm that requires people called burners to rank how much they like the pattern they are currently looking at on a scale of 1-5.

pattern (n) A unique combination of motion, colors, and pretty blinky lights displayed on the beacon.

burner (n) A passerby covered in alkaline dust.

Here's how it works.

• A sequence (n) is a 32 bit unsigned long that strictly defines the exact light show that the beacon will display. Every part of the 32 bit number affects some part of the pattern that will be displayed. The same sequence always produces the same pattern.

• Sequences can be shown to burners in the form of 16-letter strings using only the letters A, C, G, and T, such that A = 00, C = 01, G = 10, and T = 11. This helps burners intuit what is going on even without an artist (n) to explain it to them.

We maintain a breeding pool in EEPROM of 120 sequences.

• The number 120 is chosen because a sequence is typically displayed for about 30 seconds, so on average we work through a pool in about an hour.

• Each sequence has an associated fitness score from 1-5.

• When the artist resets the EEPROM, the breeding pool is initialized to 120 completely random sequences, each with a fitness score of 1.

• The EEPROM is rewritten only every time 10 changes have been made to the pool, to avoid burning it out.

Choosing the next sequence

The algorithm chooses a sequence to show to the burners by breeding two existing sequences from the pool as follows:

• Choose two parent sequences at random, however

  • Sequences with fitness 5 are 20x as likely to be chosen
  • Sequences with fitness 4 are 10x as likely to be chosen
  • Sequences with fitness 3 are 3x as likely to be chosen
  • Sequences with fitness 2 are 2x as likely to be chosen
  • Sequences with fitness 1 are 1x as likely to be chosen

• Generate a child sequence by assigning each bit, in sequence, to the value of either

  • The mommy sequence with probability 0.49
  • The daddy sequence with probability 0.49
  • A random number with probability 0.02 (mutation)

• Show this child to the burner

Responding to ranking

The burner will rank (v) using shiny brightly colored buttons that are fun to push, to indicate their preference for the new sequence. That rank then becomes the fitness of that sequence.

• If there is no rank at all (burner is drunk or high), nothing happens (the new sequence is discarded).

• If the rank is very low the sequence is quickly replaced with a new sequence.

• If the rank is high, the sequence runs for a bit longer.

• Once the rank is recorded, the new sequence tries to displace another sequence in the pool that has the lowest fitness score. In other words, we first displace all the 1-fitness sequences from the pool, then all the 2-fitness ones, etc.

• However, we never displace a sequence with a lower fitness than our own fitness. So for example if the pool is already full of 3-, 4-, and 5-fitness sequences, and the new sequence received a rank of 2, it is discarded.

• Thus the sum of all the fitnesses in the pool is monotonically increasing as fast as possible.

• Theoretically, the pool will be filled with only fitness 5 sequences as soon as 120 5-ranks have been received.