Microscopic World

An invisible world of astonishing complexity is all around you. A world so small you can't see it with the naked eye. A world so crowded that its population staggers the mind. A world in which you participate every day—often without even knowing it. The inhabitants of this world are trillions of bacteria, viruses, fungi, and other organisms, collectively known as microbes. Hundreds of thousands could fit on the period at the end of this sentence. And many play a powerful role in your life, from the bacteria in your stomach that help you digest food to the pathogens that make you sick.

One day in 1900, German physicist Max Planck told his son that he had made a breakthrough as important as Isaac Newton's discovery of the workings of the universe. Planck had reached the surprising conclusion that light behaves as if it is packaged in discrete amounts, or quanta, a seemingly simple observation that would lead to a powerful new field of physics called quantum mechanics.