b'modern era can be considered another way: It took 200,000 years for the human population to reach 1 billion and then just 200 more years to pass 7 billion. Today, were on the cusp of 8 billion. Litanies of accom-panying growth in resource use and pollutioneverything from carbon emissions, energy, plastic and synthetic chemicals to glaciers melting and lead in the Greenland ice capare legion. Out of all this tumult, the worlds first few thousand billionaires made their way to center stage.Jeremy Grantham, widely respected on Wall Street and whose hedge fund has more than $60 billion in assets, has been arguing for years that the compound growth rate assumed by modern finance is unsustainable:I was talking to a group of super quants, mostly PhDs in math-ematics, about finance and the environment. I used the growth rate of the global economy back then4.5% for two years, back to backand I argued that it was the growth rate to which we now aspired. To point to the ludicrous unsustainability of this compound growth I suggested that we imagine the Ancient Egyptians (an example I had offered in my July 2008 Letter) whose gods, pharaohs, language, and general culture lasted for well over 3,000 years. Starting with only a cubic meter of physical possessions (to make calculations easy), I asked how much physical wealth they would have had 3,000 years later at 4.5% compounded growth. Now, these were trained mathematicians, so I teased them: Come on, make a guess. Internalize the general idea. You know its a very big number. And the answers came back: Miles deep around the planet. No, its much bigger than that, from here to the moon. Big quantities to be sure, but no one came close. In fact, not one of these potential experts came within one billionth of 1% of the actual number, which is approx-imately 10 57 , a number so vast that it could not be squeezed into a billion of our Solar Systems. Go on, check it. If trained mathe-maticians get it so wrong, how can an ordinary specimen of Homo sapiens have a clue? Well, he doesnt. 55 GMO Newsletter, April 201153'