Carl Sagan once asked this question, “What does it mean for a civilization to be a million years old? We have had radio telescopes and spaceships for a few decades; our technical civilization is a few hundred years old… an advanced civilization millions of years old is as much beyond us as we are beyond a bush baby or a macaque.” Now imagine if you will a truly advanced civilizations – sheer speculation, of course, but how would the laws of quantum field theory, general relativity, thermodynamics, etc. be fairly well-established, physics apply to these civilizations? This is no longer just an idle question and we may soon have the existential shock as Kepler and others find planets with habitable zones and hundreds of earth-sized planets, which are almost identical twins of our celestial homeland. Are there really hundreds of earth-like planets out there? It seems so….
Although it is impossible to predict the precise features of such advanced civilizations, they still must obey the iron laws of physics, which are now advanced enough to explain everything from sub-atomic particles to the large-scale structure of the universe. In a paper published in 1964 in the Journal of Soviet Astronomy, Russian astrophysicist Nicolai Kardashev theorized that advanced civilizations should, therefore, be grouped according to three types: Type I, II, and III, which have mastered planetary, stellar and galactic forms of energy, respectively. He calculated that the energy consumption of these three types of civilization would be separated by a factor of many billions. But how long will it take to reach Type II and III status?
Physics of Type I, II, and III Civilizations
Specifically, we can rank civilizations by their energy consumption, using the following principles:
1) The laws of thermodynamics. Even an advanced civilization is bound by the laws of thermodynamics, especially the Second Law, and can hence be ranked by the energy at their disposal.
2) The laws of stable matter. Baryonic matter (e.g. based on protons and neutrons) tends to clump into three large groupings: planets, stars and galaxies. (This is a well-defined by product of stellar and galactic evolution, thermonuclear fusion, etc.) Thus, their energy will also be based on three distinct types, and this places upper limits on their rate of energy consumption.
3) The laws of planetary evolution. Any advanced civilization must grow in energy consumption faster than the frequency of life-threatening catastrophes (e.g. meteor impacts, ice ages, supernovas, etc.). If they grow any slower, they are doomed to extinction. This places mathematical lower limits on the rate of growth of these civilizations.