The Special Theory of Relativity
A demonstration of the limits of relative motion being the speed of light. Wikipedia 2004.
Einstein’s “Theory of Relativity” actually describes two separate theories which Einstein developed from very simple concepts about
the way the world works. At sixteen years of age, Einstein had a daydream which would guide him in his thoughts about motion in
physics:
Einstein imagined himself running alongside a light beam and asked himself a fateful question: What would the light beam
look like? Like Newton visualizing throwing a rock until it orbited the earth like the moon, Einstein’s attempt to imagine such a light
beam would yield deep and surprising results. (Kaku 43)
In the year 1905, Einstein would be guided to his Theory of Special Relativity by analyzing this thought problem. Prior to Einstein,
the two pillars of physical science were Newton’s Laws of Motion and Maxwell’s Electromagnetism. In his 1905 paper “On the
Electrodynamics of Moving Bodies,” Einstein explored the contradictions between these two branches of science. While Newton’s
Laws obeyed the relativity principal, Maxwell’s did not (Wolfson 81). Newton’s principle of relativity simply stated that his laws of
mechanics were valid at all speeds. For example, one can throw a ball straight in the air while riding in an automobile, and as long
as the car maintains a constant speed, the ball will fall straight back down as if the car where not even moving. This notion is
intuitive for most of the human race, but for some reason, it did not seem to apply to electricity and magnetism. Einstein asserted in
one of the most radical statements of the 20th century that the laws of physics are the same in all uniformly moving reference
frames (Wolfson 82). He simply stated that all motion is relative and that all the laws that govern our world apply at 10, 20, and
even one million miles per hour. Now that this rule also applied to electromagnetism, Einstein predicted that light (a visible form of
electromagnetic radiation) must travel the speed of light at every speed (Wolfson 83). Therefore, shining a flashlight at ten miles per
hour or in an airplane going 800 miles per hour will yield the same result. The light will leave the flashlight at the speed of light just
as a ball would leave one’s hand at its respective speed. Maxwell’s equations state that all electricity, magnetism, and
electromagnetic radiation must travel at a defined speed which is determined by the innate properties of space. This speed is equal
to 299,792,458 meters per second or about 186,282.4 miles per second (Wikipedia, Speed of Light 1). Thus, in his “Special
Theory of Relativity,” Einstein applied relativity to not only moving objects but to electricity and magnetism.
Though the concepts that lead to the Special Theory of Relativity were intuitive, the ramifications of this discovery were incredibly
unusual and experimentally accurate. The most commonly discussed effects of the Special Theory of Relativity are the invariance of
the speed of light, time dilation, length contraction and the interchangeability of mass and energy. The first effect is a postulate
directly derived from Einstein’s premise of the laws of physics applying to all speeds. In essence this means that an observer can
watch another person racing a light beam and sees him matching the pace of the light exactly as the runner approaches the speed
of light. However, in a later interview, the runner will say that he never got close to the light and that it sped away at exactly the
speed of light. This is the most disturbing premise of the theory, however it follows directly from Einstein’s premise and is actually
proven experimentally through the testing of the next phenomena (Wolfson 88) Even Einstein was confused by the fact that two
people can see the same situation with such different perspectives. According to Kaku, while observing a clock tower from a car,
Einstein had a revelation about his theory that explained why a person racing a light beam could never catch it. “The answer was
simple and elegant: time can beat at different rates throughout the universe, depending on how fast you moved” (61). This gave
rise to the idea of “time dilation.” Time dilation says simply that “moving clocks run slow” (Wolfson 101). A better description is
that “The time between two events is shortest when measured in a reference frame where the two events occur in the same place”
(Wolfson 102). Because speed is a relation of distance divided by time, if time is to dilute and become larger than logically, Einstein
reasoned that distance must contract. Einstein had discovered a phenomenon known as length contraction. As a clock moved
faster and faster relative to an observer, not only did it appear to run slower but it also appeared to contract, becoming distorted
and squashed. If one were to speed up to this clock, it would appear normal again, ticking at a normal second interval and
lengthening to its proper proportions. Physicists use measurable quantities to describe the world, among these being distance and
time. Einstein’s Special Theory of Relativity was able to show that as an object moved faster, its mass increased:
This meant that the energy of motion was somehow being transformed into increasing mass of the object. Thus, matter and energy
are interchangeable. If you calculated precisely how much energy was being converted into mass, in a few simple lines you could
show that E=mc2. (Kaku 66)
Though these suggestions were counterintuitive for Einstein himself, they have been proven and have furthered science and
technology. The development of atomic clocks revolutionized the precision in which time could be measured and thus allowed
Einstein’s time dilation to be tested. In 1971, atomic clocks were placed on a jet plane, which was flown both East to West and
West to East. The atomic clocks, in turn, were then compared with atomic clocks that were stationary at the Naval Observatory in
Washington, D.C.” (Kaku 209) The clocks which had been flown across the United States were infinitesimally behind the stationary
clocks. Many years later, scientists would also measure small reductions in the masses of radioactive elements which radiated
energy, converting the mass of the substance into energy. These two observations confirmed Einstein’s Special Theory of Relativity,
but he would not become well known until later in his life.
Calvin and Hobbes. Bill Watterson.
This page was created by George S. Walker V. (2004)
Wikipedia 2004.