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Relativity--the
start of it all!
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An Old Idea Seen In a New Way!
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What is "Relativity"?
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Relativity is the observation
of motion of an object by two different observers in two different frames
of reference moving relative to each other.
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Aristotle's
Theory of Relativity
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Aristotle (384-322 BC) presented
the earliest recorded statement of relativity. He stated that the Earth
was at absolute rest as the center of the universe. All the rest of
the objects in the universe move relative to the planet Earth. Because
of the immense prestige of this philosopher/scientist, this theory was
accepted many hundreds of years until Galileo questioned it.
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Galileo's Theory of Relativity
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Galileo (1564-1642) proposed
the idea of relative motion for objects on the Earth. He used the example
of a boat moving forward at constant speed and constant direction.
He suggested that if a ball were thrown upward by someone on the moving
boat the ball would follow the same path to the person on the boat just
as if the person threw the ball straight upward on the shore. He maintained
that there is no difference between "at rest" and "motion
at a constant velocity". This was part of his ill-fated observations
that the Earth was not the "at rest" center of the universe.
But that is another story.
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THE
POSTULATES OF SPECIAL RELATIVITY-- Albert Einstein --1905
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In Einstein's "new
physics", moving
clocks run slowly, a moving meter stick contracts in the direction
of motion, and events that appear simultaneous in one frame may not
appear so in another moving frame of reference!
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At the
base of understanding The
Special Theory of Relativity is understanding the two postulates
upon which it is framed.
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POSTULATE
1
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The laws of physics are
invariant (have the same form) in all frames of motion moving at constant
velocity with respect to each other.
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NOTE: This means it is impossible
for observers to identify differences between "at rest" and
"constant velocity" by any way or any method. Such a constant
motion frame is referred to as "inertial"!
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POSTULATE
2
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The speed of light in
a vacuum is the same --c-- regardless of the speed of the observer.
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Early support for this observation
was the famous
Michelson-Morley experiment. This experiment
disproved the existance of the ether and measured the speed of light
to be the same regardless of the orientation
of the experiment with regard to the Earth's speed in space.
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