All Those People
It seems that everyone has their own example of the effects of exponential growth, so here is mine:
Let us accept the biblical account that all human beings descended from one original couple, and biblical scholars' estimates of the date of creation as being 4004 BC. If every couple throughout history had exactly two children who lived to reproduce, then the population of human beings would remain stable and would never increase, since each couple would merely be replacing themselves. So let's assume that the reproduction rate of human beings has been steady throughout the history of the earth, and that couples have averaged three children per generation (who lived to reproduce again), with an average generation time of 20 years.
If the population of the earth has grown as described in this scenario, without any other constraints or disturbances, what would be the total mass (or weight) of the combined human population today, if we assume that the average human being weighs 150 pounds?
Answer:
Equal to the mass of 1.53 billion billion trillion earths!
Calculation: 4004 B.C. + 2011 A.D. = 6015 years. Dividing this by 20 equals: 6013/20 = 300 generations. Having three children means that each succeeding generation is 1 1/2 times as large as the previous one. If you use a spreadsheet to start with 2, and multiply by 1 1/2, 300 times, you will get a population of 1.34 x 1053 (whatever that might be!). Multiplying this by 150 pounds, and then dividing by 2000 pounds to get tons, gives us a total mass of 1.01 x 1052 tons (whatever that might be!). The mass of the Earth, as given in a textbook that I own, is 6.59 x 1021 tons, obviously a much smaller number (as huge as it is!) than the mass/weight that we just obtained. Dividing this mass into the mass we calculated for the human population, gives us 1.53 x 1030. That is the number 153 followed by 28 zeros, or 1.53 billion billion trillions!
Would you like to calculate the population of the earth if it had grown under a scenario that you designate?