The General Theory of Relativity
Spacetime Curvature. Wikipedia 2004.
The General Theory of Relativity was developed in Einstein’s later years. Much like the popular story of Newton’s apple, Einstein
stumbled upon the idea which would not only make him a figurehead of modern physics but advance the understanding of
Gravity. According to Kaku, Einstein was working on a patent application in 1907 when he had a startling revelation:
I was sitting in a chair in the patent office at Bern when all of a sudden, a thought occurred to me: If a person falls freely, he will not
feel his own weight. I was startled. This simple thought made a deep impression on me. It impelled me toward a theory of
gravitation. (Kaku 92)
The General Theory of Relativity was Einstein’s crowning achievement because even though it did not have too many practical a
pplications, it took a large stride forward in explaining not only the how the universe works, but also its origin. Einstein also knew th
at Newton’s theory that gravity is an instantaneous force would contradict his Special Theory of Relativity because it is a force that
would travel faster than the speed of light. Also, the distance between two objects differs depending on the motion of the o
bserver relative to those objects. So if gravity’s effects depend on distance, Einstein would have to determine in which reference fr
om the distance would need to be measured. (Wolfson 175) The problem was that the Newtonian view of gravity was not at all re
lativistic. Einstein, using his startling realization of a falling body discovered the principal postulate behind his new idea of gravity.
He called this his principle of equivalence. It stated simply that the laws of physics are indistinguishable between an accelerating
and gravitating reference frame. For example, no experiment would be able to tell the difference between being in a small room
accelerating at the rate of gravity or being in a small room which is simply sitting on Earth’s surface. The converse is also true: One
would not be able to tell the difference between floating in free space or a free fall toward earth in a small room. Wolfson termed it
best by saying “The idea behind general relativity is to extend the Principle of Relativity to all reference frames, inertial or not.” (187)
Einstein considered what was termed “Tidal Forces” in a free-fall scenario in which two balls move toward or away from each other
because of their initial positions in the free fall. This takes place because the balls both want to follow straight line paths toward the
center of The Earth and because these balls are slightly apart from one another, these straight line paths create a small angle
between on another which brings them together as the balls fall with the entire system. Also if one is released above the other,
their distance apart will increase because the Newtonian force of gravity is higher upon the ball which is closer to The Earth.
(Wolfson 189) Einstein used this observation along with Tensor Calculus (Calculus using geometry on a curved surface) to develop
his ideas of curved space. His view of gravity was analogous to marbles rolling on a water bed. In this analogy the sun in our galaxy
would be replaced by a rock and the planets by marbles. Set into motion, the marbles roll around the Sun in elliptical orbits very
similar to those caused by gravity except for one difference. Instead of gravity pulling, space is pushing objects toward the large
mass of the sun. (Kaku 97) Einstein deduced that gravity was actually a distortion of space by mass. His final equation was so
simple and elegant as to be contained in an inch of text. The equation read:
(Einstein 79) This equation is beautiful when compared to monstrous eight partial differential equations which described Maxwell’s
Fields of Electricity and Magnetism.
Einstein’s Theory of General Relativity was reinforced by three early experiments. These were the bending of starlight during a solar
eclipse, the red shift, and the perihelion of Mercury. On September 22, 1919, Einstein learned that indeed, the sun bent the rays of
starlight using its immense gravity after British Scientist Arthur Eddington traveled off the coast of New Guinea to take measurements
of the stars during a solar eclipse. (Kaku 114) If gravity was different from normal acceleration and only a force that influenced
masses then the starlight would not only have remained in a straight line motion, but would not have bent at an angle very close to
Einstein’s predictions. This lent great credence to Einstein’s theory. Next an experiment in a laboratory confirmed Einstein’s
prediction that light emitted from a star loses energy as it fights gravity’s pull and thus lowers its frequency causing an effect that
would redden the suns yellow light slightly. This was called the “Red-Shift” and would become key to future speculation on the age
and origin of the universe using, instead, the light from far away galaxies. (Kaku 104) Einstein then solved the problem of Mercury’s
perihelion, which was a small deviation in the Orbit of Mercury of 43.5 seconds of arc per century. This was caused by the planet
“wobbling” in its orbit. His equations yielded the result of 42.9 seconds of arc per century, which was well within the acceptable
experimental limits. This was a difference of less than 1/2000th of a degree. (Kaku 104) Einstein was catapulted into the public eye
after these experiments conducted and showed a great degree of accuracy in his Theory.
Though the last 30 years of Einstein’s life were riddled with frustration and debate over the Unifying Field Theory (Electromagnetism
and Gravity described by one equation) with little progress, his Theory of Relativity was reshaping the foundations of Science and
Technology as well as creating a new breed of theoretical physicists.
Special relativity has explained nuclear radiation and the resulting loss of mass in the substance which is radiating. In fact, Einstein’s
equation, E=mc2, was a direct factor leading to the development of atomic power and weaponry. Years later, Einstein would
speculate on the destructive effects of his work:
All bombardments since the invention of firearms put together would be harmless child’s play compared to its destructive effects.
Assuming that it were possible to effect that immense energy release, we should merely find ourselves in an age compared to
which our coal-black present would seem golden. (Kaku 185)
Einstein’s Special Theory of Relativity, though simple in it’s development, revolutionized theoretical physics and technology.
General Relativity, however, is not so easily tested. However the study of gravity waves has yielded Nobel Prize-Winning results by
the examination of double stars which orbit each other. These stars stir through space like spoons through molasses, creating
ripples which throw off gravity waves. These gravity waves carry energy and thus the spiraling system loses energy as more and
more are created. Einstein’s theory of relativity was able to predict the decay of the orbit per revolution very accurately. According
to Kaku, “The numbers are so precise that we can conclude that general relativity is 99.7% accurate” (211). Laser detection of
gravity waves is also being developed using the original premise of the red-shift changing the frequency of light by decreasing its
energy. (Kaku 212) Telescopic research has also discovered Einstein rings, which are focused light from terrestrial objects which
bend light using gravity, focusing all the light behind it into a tight ring. Though this is interesting, the most incredible afterthought of
Einstein’s work is “dark energy.” In his equation for General Relativity, Einstein introduced a constant to account for a static universe
that was neither expanding nor contracting due to gravity. However, Hubble showed Einstein that the universe was not static but
was expanding by using a Telescope and red-shift to monitor the velocity of far away galaxies. These observations did not tell the
whole story:
Results found in 2000, however, reveal that Einstein was probably right after all: the cosmological constant not only exists, but dark
energy probably makes up the largest source of matter/energy in the entire universe. By analyzing supernovae in distant galaxies,
astronomers have been able to calculate the rate of expansion of the universe over billions of years. To their surprise, they found
that the expansion of the universe, instead of slowing down as most had thought, is actually speeding up. Thus, we can now
predict how our universe will die. (Kaku 215)
An infinitely expanding universe as the one described the revised Theory of General Relativity will spread the density of energy over
such a vast energy of space that all matter will enter a deep freeze and dissipate over infinite space.
Einstein’s insight into the physical world has not only helped to describe more accurately how motion works but has made the
analysis of gravity and electromagnetism an attractive field of study for aspiring theoretical physicists in the final search for a Unifying
Field Theory which may finally describe the dynamics of the universe.
Calvin & Hobbes. Bill Watterson 2004.
This page was created by George S. Walker V. (2004)
Wikipedia 2004.