Ever since the invention of the microscope, one of the great trends of modern science has been toward resolving ever-finer detail in the study of matter. Since small objects generally move quickly (which simply follows from the dependence of inertia on mass), high spatial resolution alone is not sufficient to image such objects (for example, to take a magnified photograph of them with a camera). A short-duration flash of light (or fast shutter) is also necessary to prevent blurring of the image. While the millisecond duration of an ordinary camera is sufficient to freeze the action of a person running (meter-scale length), a strobe light with ultrashort pulse duration (1 femtosecond or 10⁻¹⁵ s) is required in order to resolve a moving atom (10⁻¹⁰-m-scale length).