In 1964 the astronomer Nikolai Kardashev proposed sorting civilizations not by age, beauty or wisdom, but by one blunt number: how much energy they can lay hands on. It is a crude measure. It is also the only one that scales. Here is the whole ladder, from where we actually stand to the rungs nobody has any business drawing yet.
Kardashev's classification: N. S. Kardashev, Transmission of Information by Extraterrestrial
Civilizations, Soviet Astronomy, 1964. The continuous version used for the figure above is
Carl Sagan's interpolation. Solar luminosity is the IAU nominal value. World energy use is
annual primary energy from the Energy Institute's Statistical Review. Every figure on this page
is either one of those published values or arithmetic on them, and the arithmetic is printed
next to the result.
Rungs beyond the second are labelled speculative because they are: no engineering exists for
them, and the numbers describe what the physics would demand, not what anyone can do.