Bird flocks, bacterial swarms, and even crowds move according to interaction rules that appear to break one of physicsβ most fundamental principles: Newtonβs law of action and reaction. Birds can see much of what is happening around them, but when flying in a flock, they respond only to birds beside them or ahead of them. [...]
The Upper Colorado River on the Grand Canyon last month. About 40 million people and 5.5 million acres of cropland depend on the Colorado for drinking water and irrigation.
A talk on rising energy costs on Capitol Hill hosted by Democrats, from left, Sen. Martin Heinrich of New Mexico, Senate Minority Leader Chuck Schumer and Sen. Sheldon Whitehouse of Rhode Island, in March.