When a cartoonist wants to show that a character is highly intelligent, there is often a thought balloon showing “E = mc2,” the famous formula that describes the essence of Albert Einstein’s relativity theories. Throughout the twentieth century the explanations of relativity in hundreds of physics classes and textbooks have befuddled many an otherwise bright student. The relativity theories, which describe how time, matter, and space interact with one another, have become known as the epitome of erudition.
Time travel, on the other hand, is usually thought of as a toy of science fiction, obviously impossible to actually implement, and totally frivolous. Einstein himself said time travel is impossible, did he not?
Well, no. In Time: A Traveler’s Guide, Clifford Pickover not only demonstrates the plausibility of moving through the fourth dimension but actually makes it enjoyable to learn how Einstein’s special and general theories of relativity work. He does so with a novel mixture of fictional lessons and scientifically sound explanations, amid a sprinkling of quotations about both the science and the philosophy of time.
Each of the book’s eighteen chapters begins with a graphically rich page of three to five brief quotations from scientists, writers, and fictional characters, along with a staff of Frédéric Chopin’s piano music. It then presents a science-fictional episode, narrated in the second person present, in which “you” are the male director of the Museum of Music in twenty-first century New York City. In each episode the director gives an informal physics lesson to two associates: the attractive young Constantia Gladkowska, who is an expert in the psychoacoustics of cello strings, and the alien “Mr. Veil,” a member of a philosopher race from the Jovian moon Ganymede. The lessons are peppered with the director’s perpetually ineffective passes at Constantia along with various bits of musical history and praise of Chopin. They make it entertaining to learn about space-time diagrams, light cones, cosmic moment lines, transcendent infinite speeds, Lorentz transformations, superluminal and ultraluminal motions, Minkowskian space-times, Goedel universes, closed timelike curves, and Tipler cylinders.
Pickover begins with an example of the relativity of simultaneity. He has Mr. Veil, in a vehicle passing along the side of the museum, use laser beams to set fire to two piles of papers at the same time. One pile is in the nose of the vehicle and the other the tail. To the observer in the museum, the beam to the nose had to catch up with the papers there, while the rear papers were catching up to the other beam, so that the nose papers caught fire a bit later that the tail papers. To Mr. Veil, however, the two flames ignited simultaneously because neither pile was moving relative to himself. Therefore, the two observers can see the same physical events and yet disagree about when they occurred. “Your present is not my present,” Pickover writes. “Your Now is not my Now.”
He then introduces the idea of a photon clock, in which a single particle of light bounces back and forth between the centers of two parallel mirrors. While the photon clock is standing still, the path of the photon forms just the same straight line, moving back and forth from one mirror to the other. It takes the photon exactly one “tick” of time to bounce once.
If the entire photon clock moves past an observer, however, the observer sees a zig-zag path as the clock bounces. During one tick in which the particle travels from the upper to the lower mirror, the clock’s motion has moved the center of the lower mirror some distance to the side, as seen by the observer. Thus, when the particle hits the lower mirror, the bounce point is no longer directly below the starting point. By the time the particle has headed back to the upper mirror, the clock has moved even farther to the side, so that the upper bounce point is no longer above the lower point. Thus, from the observer’s point of view, the photon’s path forms a zig-zag. To an observer within the photon clock, however, the photon’s path is straight up and down and therefore shorter. Each of these paths, however, has taken the same number of ticks of time.
Because the photon in a moving clock has to travel farther than a photon in a stationary clock, it seems to the observer that time has slowed down on the mobile clock. With the help of a...
(The entire section is 1831 words.)