FREE ESSAY ON EINSTEIN'S THEORY OF SPECIAL RELATIVITY

EINSTEIN'S THEORY OF SPECIAL RELATIVITY

The Rise of Einsteinian Special Relativity
In 1905, Einstein's Theory of Special Relativity was proposed. The reason that it is so
"special" is because it was part of the more complex and extensive Theory of General
Relativity, which was published in 1915. His theory reshaped the world of physics when it
contradicted all previous laws of motion erected by Galileo and Newton. By mathematically
manipulating these previous laws of motion, physicists in the nineteenth century were
able to explain such phenomena as the flow of the ocean, the orbits of planets around the
sun, the fall of rocks, and the random behavior of molecules in gases. At first, Einstein
faced great opposition when he came up with his radical new theory because the previous
laws of motion proposed by Galileo and expanded upon by Newton had remained valid for
over two hundred years. However, it wouldn't be long before the "cement" in the
foundation of Newtonian and Galilean physics would begin to crumble.
Galileo had determined in 1608 that merely addition and subtraction could calculate
relative speeds. Suppose that an observer stands on the side of the highway, and they
watch two cars approach each other at 30 and 40 miles per hour. If they were to ask the
question, "how fast is the 40 mile per hour car moving relative to the 30 mile per hour
car?" They could solve the problem easily by adding the two speeds of the cars, which
would equal 70 miles per hour. This means that the 40 mile per hour car sees the 30 mile
per hour car advance at a speed of 70 miles per hour and vice versa. 
At the core of Newtonian physics was the fact that space and time were absolute. Newton's
absolute space was the space of everyday experience with its three dimensions: east-west,
north-south, and up-down. This space gives us our sense of length, breadth, and height;
according to Newton. We all, regardless of our motion, will agree on the length, breadth,
and height of an object, so long as we make sufficiently accurate measurements. Newton's
absolute time was the time that flows inexorably forward as we age. It is a time whose
flow is experienced in common by all humanity.
The maximum speeds of birds in nature are regulated by air. No matter what direction a
bird flies, it always has the same maximum speed. Newton had proposed something similar
for light, which he referred to as the aether. He theorized that it was omnipresent and
that it regulated the speed of light in any direction. Furthermore, since the aether was
at rest in absolute space (according to Newtonian physics), anybody who is stationary
will measure the same light speed in all directions, while anybody in motion will measure
different light speeds.
Newton and Galileo would have assumed that like the speeds of the two cars in the
previous example, the velocity of light could be calculated in the same fashion. For
example: If a car is moving at a speed of 25 meters per second with its headlights on,
what is the speed of the light emitted by the headlights? Newton and Galileo would have
thought, "25 meters per second for the car plus 299,792,458 meters per second for the
speed of light equals 299,792,483 meters per second for the speed of the light emitted by
the headlights of the car."
This method of thinking would have been acceptable up until 1881. At this time, an
experiment took place that would change physics forever. Albert Michelson wanted to test
Newton's idea of variable speeds of light due to the existence of the aether. He knew
that since the Earth moves in absolute space, that the speed of light should be measured
differently in January than six months later in June when it is moving in an opposite
direction in its orbit. This is because the speed of light and Earth would be additive.
The difference, according to Newton and Galileo, would only be about 1 part in 10,000
since the earth moves slowly relative to the speed of light.
Michelson set up an extremely accurate test using a special device that he developed
called an interferometer, which measured very small distances using the wave properties
of light. After he performed a battery of tests, he was astonished to find that the speed
of light is the same in all directions and seasons. This means that in the previous
example, the speed of light would still be 299,792,458 meters per second, regardless of
the speed and direction of the car. Therefore, Galileo's relative motion theories, which
had been accepted for over two hundred had been definitively proven not to apply to
light.
Einstein soon heard of the results of the Michelson experiment. Although a lot of
physicists at the time were skeptical about the validity of the results due to their
great ramifications, Einstein took the data from the experiment at face value. He
concluded that Newtonian physics was flawed. Although Einstein forced to reject Newtonian
Physics, he also came to two revolutionary principles that forever changed the world of
physics. The principle of relativity states that the laws of physics are the same for
observers in all uniformly moving reference frames. In Einstein's Theory of Special
Relativity, a reference frame is simply the platform or framework from which one makes
observations. This first postulate was already widely accepted by the physics world. The
only difference between it and what Newton had proposed is that now Einstein is referring
to reference frames instead of motion in general. For instance, if an observer was to
study the motion of billiard balls in a rocket that is passing them, they would have to
take into account the speed of the rocket. The principle of the absoluteness of the speed
of light states that whatever the nature of space and time are, they must be constituted
as to make them the same in all directions, and absolutely independent of the motion of
the person who is measuring it. This theory is in agreement with the Michelson
experiment, and no matter how accurate measuring devices may become in the future, the
speed of light will always be the same. The second postulate is simply an exception to
the first because it says that space and time must exist in a way that the speed of light
is the same in all directions.
Einstein began writing his paper on Special Relativity by thinking what his two
postulates implicated about motion. He knew that motion is described by using
acceleration and speed. Speed is an example of how much distance is covered per unit
time; therefore, in order to obtain speed, one needs distance and time. The ability to
quantify motion with speed and time is rooted in the measurement of space and time, which
Theory of Special Relativity in intimately connected with.
The results of Einstein's postulates are described in terms of three effects, called the
relativity of simultaneity, time dilation, and length contraction. Although these effects
are all related, they are easiest to construe individually.
In order to explain simultaneity, once again, a hypothetical situation will be used. Adam
is standing on a platform of a railroad station while a train passes. It just so happens
that two lightning bolts strike the train; one strikes the front and one strikes the
rear. The lightning bolts leave burn marks on both ends of the train and analogous marks
on the platform where Adam is standing. At this point, he makes an assessment of the
situation. He realizes that the lightning bolts both reached him at the same instant in
time, and that the distances between him and the burn marks on the platform are the same.
Thus, Adam is equidistant from both burn marks on the platform. From this, he can
conclude the time that it took the light to travel from each burn mark on the platform is
the same.
Now, lets look at this same series of events from an observer inside the car. This person
will be Brett, who is positioned precisely at the center of the train. Because Brett is
moving with the train, he is moving towards the light signal that is traveling to him
from the front of the train, and away from the light signal that is traveling to him from
the rear of the train. Because of this, he first sees the light signal from the front of
the train, then the light signal from the rear of the train. Brett now notices that he is
an equal distance from the two burn marks on the train. From this, he concludes that he
is equidistant from the two burn marks, and the speed of light experienced by him is the
same as Adam experienced. Because the light from the front of the train reached Brett
first, and light travels at the same speed all the time; Brett concludes that the
lightning bolt that struck the front of the train occurred before the lightning bolt that
struck the rear of the train.
Einstein's answer to this situation is that both Adam and Brett are correct in their
observations. This is due to Einstein's postulate of the relativity of simultaneity. This
postulate states that the same event is not necessarily experienced the same way in two
different moving reference frames.
Simultaneity is also connected with two other space and time effects called time dilation
and length contraction. Time dilation means that an observer will see a clock on a rocket
recording time slower than if it were stationary. Suppose that the Earth and rocket
clocks are synchronized as the rocket whizzes around Earth at 2:00 P.M. An hour later,
when the clock on Earth reads 3:00 P.M.; the clock on the rocket would read less than
3:00 P.M., depending on how fast the rocket was traveling. The faster the rate of travel,
the more time is slowed down. Also, if someone in the rocket were to read the Earth clock
when the clock on the rocket read 3:00 P.M., they would see it read slower than 3:00 P.M.
Thus, this slowing in time works both ways. Each observer in a different frame of
reference traveling at a different speed will see the other's clock slowed down.
Finally, length contraction is apparent whenever an object is in motion. For instance, an
observer on the Earth would measure the length of the rocket to be shorter when it is
moving at its high speed as compared to its length at rest.
Simultaneity, time intervals, and length must all be relative. Two events that are
observed to be simultaneous in one reference frame will not be simultaneous in any other
reference frame that is moving with respect to the first frame.
If Newtonian physics is so flawed, then why is it still used today? The answer is very
simple. When traveling at speeds that are far from the speed of light i.e. speeds typical
of human experience, effects such as time dilation and length contraction are so minute,
it's not practical to use Einstein's more complex equations of Special Relativity in
place of Newton's for these motions. The fastest a human being has ever gone in a
spacecraft in space is nowhere remotely near the awesome speed of light. Perhaps in the
future, when spacecraft capable of traveling just under speed of light is developed, will
we encounter this phenomenon in a substantial quantity.