What Do Alien Civilizations Look Like? The Kardashev Scale
The observable universe is a big place that has been around for more than 13 billion years. Up to two trillion galaxies made up of something like 20,000 billion billion stars surround our home galaxy. In the milky way alone scientists assume there are some 40 billion earth like planets in the habitable zone of their stars. When we look at these numbers it is hard to imagine that there is nobody else out there.
An interesting idea I’ve heard is that the universe simply isn’t old enough to have produced a type 3 or even type 2 civilization. This has to do with rare elements only produced by supernovas. Basically, planets substantially older than Earth won’t have enough gold, uranium, etc to support an advanced civilization because there wasn’t enough of it in the universe at the time those planets formed.
