The Physics of Star Trek Read Online Free Page A

since has been to determine what if any “physical
     grounds” exist that would rule out the possibility of time travel, which the form of the
     equations of general relativity appears to foreshadow. To discuss such things will require
     us to travel beyond the classical world of general relativity to a murky domain where
     quantum mechanics must affect even the nature of space and time. On the way, we, like the
    
    
     Enterprise,
    
    
     will encounter black holes and wormholes. But first we ourselves must travel back in time
     to the latter half of the nineteenth century.
    The marriage of space and time that heralded the modern era began with the marriage, in
     1864, of electricity and magnetism. This remarkable intellectual achievement, based on the
     cumulative efforts of great physicists such as AndrŽ-Marie Amp�re, Charles-Augustin de
     Coulomb, and Michael Faraday, was capped by the brilliant British physicist James Clerk
     Maxwell. He discovered that the laws of electricity and magnetism not only displayed an
     intimate relationship with one another but together implied the existence of
     “electromagnetic waves,” which should travel throughout space at a speed that one could
     calculate based on the known properties of electricity and magnetism. The speed turned out
     to be identical to the speed of light, which had previously been measured.
    Now, since the time of Newton there had been a debate about whether light was a wavethat
     is, a traveling disturbance in some background mediumor a particle, which travels
     regardless of the presence of a background medium. The observation of Maxwell that
     electromagnetic waves must exist and that their speed was identical to that of light ended
     the debate: light was an electromagnetic wave.
    Any wave is just a traveling disturbance. Well, if light is an electromagnetic
     disturbance, then what is the medium that is being disturbed as the wave travels? This
     became the hot topic for investigation at the end of the nineteenth century. The proposed
     medium had had a name since Aristotle. It was called the aether, and had thus far escaped
     any attempts at direct detection. In 1887, however, Albert A. Michelson and Edward Morley,
     working at the institutions that later merged in 1967 to form my present home, Case
     Western Reserve University, performed an experiment guaranteed to detect not the aether
     but the aether's effects: Since the aether was presumed to fill all of space, the Earth
     was presumed to be in motion through it. Light traveling in different directions with
     respect to the Earth's motion through the aether ought therefore to show variations in
     speed. This experiment has since become recognized as one of the most significant of the
     last century, even though Michelson and Morley never observed the effect they were
     searching for. In fact, it is precisely because they failed to observe the effect of the
     Earth's motion through the aether that we remember their names today. (A. A. Michelson
     actually went on to become the first American Nobel laureate in physics for his
     experimental investigations into the speed of light, and I feel privileged to hold a
     position today which he held more than a hundred years ago. Edward Morley continued as a
     renowned chemist and determined the atomic weight of helium, among other things.)
    The nondiscovery of the aether did send minor ripples of shock throughout the physics
     community, but, like many watershed discoveries, its implications were fully appreciated
     only by a few individuals who had already begun to recognize several paradoxes associated
     with the theory of electromagnetism. Around this time, a young high school student who had
     been eight years old at the time of the Michelson-Morley experiment independently began to
     try to confront these paradoxes directly. By the time he was twenty-six, in the year 1905,
     Albert Einstein had solved the