TIME AND MATTER – SCIENCE AT NEW LIMITS

by AHMED H. ZEWAIL

Until 1800 AD, the ability to record the timing of individual steps in any process was essentially limited to time scales amenable to direct sen- sory perception – for example, the eye’s ability to see the movement of a clock or the ear’s ability to recognize a tone. Anything more fleeting than the blink of an eye (~0.1 second) or the response of the ear (~0.1 millisecond) was simply beyond the realm of inquiry. In the nineteenth century, the technology was to change drastically, resolving time intervals into the sub-second domain. The famous motion pictures by Eadweard Muybridge (1878) of a galloping horse, by Etienne-Jules Marey (1894) of a righting cat, and by Harold Edgerton (mid-1900’s) of a bullet passing through an apple and other objects are examples of these developments, with millisecond to microsecond time resolution, using snapshot photography, chronophotography and stroboscopy, respectively. By the 1980’s, this resolution became ten orders of magnitude better [see Section III], reaching the femtosecond scale, the scale for atoms and molecules in motion.

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