The Great Silence
In 1961, Frank Drake wrote an equation to estimate the number of active civilizations ($N$) in our galaxy. $$ N = R* cdot fp cdot ne cdot fl cdot fi cdot fc cdot L $$
The Variables
- Stars ($R_*$): The galaxy is full of them (100 Billion+).
- Planets ($f_p$): We now know almost every star has planets.
- Life ($f_l$): Life seems to start easily on Earth...
- Intelligence ($f_i$): ...but it took 4 billion years to get to humans.
- Communication ($L$): This is the bottleneck. How long does a civilization last before it destroys itself with nukes or AI?
The Great Filter
We haven't met anyone yet. This implies one of two things: 1. Rare Earth: Life is incredibly rare, and we are special. 2. The Filter Ahead: Advanced civilizations inevitably commit suicide quickly (The Great Filter), so nobody is out there to talk to.