My friend Harlan sent this to me. A video basically explaining doubling time or rule of 72 (or 70 or 69) in real-world examples that don't have to do with money. It's pretty simple, but cool to watch especially seeing rule of 72 in areas other than money. Total length is ~75 minutes, but you can watch any number of the videos and get some good info.
Here's the equation:
70 / % of growth per unit of time = doubling period per unit of time
Examples:
70 / 5 (% per year) = in 14 years it will double
70 / 4 (% per year) = in 17.5 years it will double
70 / 35 (% per minute) = in 2 minutes it will double
Try it yourself with a compound interest calculator.
The approximation that you can do in your head of course is only accurate within a certain range (lower numbers). One can see as we approach 70:
70 / 70 (% per year) = in 1 year it will double
Well this is obviously not true.
I don't entirely agree with the conclusion he comes to about population growth being beyond problematic; I don't dispute the numbers though. As far as population and energy problems I think the biggest thing that is ignored is rate of innovation (not only new technology, but the different ways people can live [vertically?]) and supply and demand. One cannot ignore the bacteria example though in that we are just one unit of time away from doubling once we reach that point of fullness (example: if we fill up this planet to the maximum even if we discover another planet that is habitable (or make it habitable) we will fill it up (double) in just one more unit of time.
