Did Erdős Save Western Civilization?

Abstract

If you stand on the famous Chain bridge in Budapest, you will see below you the broad sweep of the Danube. But this broad river arose from the confluence of many small streams. Indeed, there is a point near St. Moritz, where if a rain drop happens to fall a few centimeters to the north, it will make its way into the Rhine, and so to the North Sea. If it falls a little to the west, it will join the Adda and the Po, and end up in the Adriatic, whereas to the east it would run Into the Inn, the Danube, and the Black Sea. An apparently negligible movement at the start can make a difference of hundreds of kilometers later on.