Cover: The Year of Dr. Einstein

(6 of 12)

Einstein's new relativistic world, both time and distance are equally fickle and depend on the relative motion of observers. The only absolute remaining is the speed of light. Out of this theorizing emerged some bizarre conclusions about the effect of so-called relativistic speeds, those near the velocity of light. As an observer on earth, for example, watches a spacecraft move away at about 260,000 km (160,-000 miles) per second, time aboard the ship (assuming he is able to see the ship's clock) seems to him to move at only half the rate that it would on earth. The mass of the ship and everything on it appear to dou ble relative to what their mass was on earth, while all dimensions in the direction of travel seem to contract to half their earth lengths. Strangely enough, a ship board observer notices no changes aboard his craft. He thinks that it is time back on earth that is slowing, and that the masses and lengths there are changing.

These seemingly contradictory effects lead to a famous brain teaser called the Twin Paradox: If one twin goes off into space, which twin will be the older (if either is) when the brothers are reunited?

Einstein says there is a definitive answer and, therefore, no paradox. Be cause of other relativistic effects that stem from leaving and returning to earth, if one twin departs on a high-velocity space journey, he will be younger than the earth-bound brother when he returns.

Astonishing as these effects seem, they have all been verified. In designing nuclear accelerators, for example, scientists must take into account the fact that subatomic particles whipped to speeds approaching the velocity of light will appear to increase in mass. Furthermore, particles called muons, which at rest exist for only very short spans of time before decaying into other particles, are found to live far longer at high velocities.

Einstein published two other landmark reports in Annalen der Physik during 1905. One paper explained a laboratory curiosity called the photoelectric effect, which occurs when a light beam hits a metallic target and causes it to give off electrons. (This phenomenon makes possible a host of today's electronic gadgetry, ranging from electric-eye devices to TV picture tubes and solar panels for spacecraft.) In this paper Einstein borrowed from a theory by German Physicist Max Planck, who had solved a vexing problem about the radiation of heat and light from hot objects by proposing that this radiant energy is carried off or absorbed in tiny packets, or quanta. Planck himself was dissatisfied with the theory, believing it contrary to nature, but Einstein enthusiastically seized it. He introduced the very revolutionary idea that light at times has the characteristics of particles (later named photons). These particles were knocking the electrons from the metal.

Before the scientific world could even begin to digest these assertions, the journal published still another communique from the young patent examiner. Einstein had devised an equation that accounted for Brownian motion, the random, zigzagging movements of microscopic particles within liquids (named after the Scottish botanist Robert Brown, who first observed it in 1827). Einstein suggested that the specks were being jostled by molecules in the liquid, an idea that finally convinced many early 20th century skeptics of the atomic nature of