There's a yardstick people toss out periodically, which states an approximation of the doubling of human knowledge over time. It lumps together all books written prior to, I think, 1 AD and calls that "one." Based on their metrics, it didn't double until the printing press was invented in 1436, after the invention of the printing press, it doubled in something like 500 years, and then doubled again in 50 years, and we'll soon be reaching the point where its doubling every year/minute/second (I'm going from memory here, so the details aren't exact).Certainly, its probably *not* highly accurate, but it does give people something to talk/blovate about.I got to thinking, though, what about the demands for energy by humanity? For a good portion of our existence, humans used only their own strength to accomplish tasks. IIRC, a human is good enough to light a 60 watt bulb, so that gives us a bit of a baseline to work with. The discovery of fire would have more than doubled that, I'm sure, so would the domestication of animals.The use of wind and water would probably have doubled that as well. It seems to me that things would have fairly stabilized at this point, until the Industrial Revolution began in the late 1700s, then it would have jumped dramatically. It also would have jumped dramatically with the invention of electricity and the adoption of petroleum.I am at a loss, however, how one would calculate all of this (and in poking around on WolframAlpha, I can't find anything handy to give me the data). Surely someone out there has tackled the concept and put the information (or at least their best guess) online. Anybody have any clues?