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Unit 1The Theories of Relativity |
In 1905 Albert Einstein developed the Special Theory of Relativity to explain the null results of the Michelson-Morley experiment, and in 1915 he developed the General Theory of Relativity in order to extend his concept to include the phenomenon of gravitation. More specifically, he realized that Newtonian physics could not account for the fact that the speed of light was always measured to be the same universal constant regardless of the motion of the observer. So he developed a theory of space and time that was consistent with the properties of light. Then he realized that Newtonian gravitation was not consistent with his new theory, so he developed an even newer theory consistent with the properties of gravity.
The Special Theory of Relativity is that branch of modern physics that pertains to objects moving at extremely high speeds - speeds comparable to the speed of light. It is based upon a single, simple assumption called the Principle of Relativity. This principle asserts that the laws of physics are the same in every inertial frame of reference. In other words, no one is special. Everyone has an equally valid view of reality. The most fundamental properties of the universe are independent of whoever observes them. Or, the laws of nature are the same everywhere and every when.
When this Principle of Relativity is applied to the properties of light, the results is Special Relativity. More specifically, when one develops the simplest possible theory of space and time consistent with the experimental fact that the speed of light is the same universal constant relative to all observers, one obtains the Special Theory of Relativity. Einstein was the first person to do this. But anyone who develops such a theory will obtain the same result: a theory that demonstrates that space and time are no longer independent variables, but interdependent aspects of the flat, four-dimensional spacetime in which we live.
The General Theory of Relativity is that branch of modern physics that pertains to extremely strong gravitational fields - fields so strong that they actually warp the very fabric of space and time. It is based upon the assumption that the spacetime in which we live is not really flat, but curved, with the amount of curvature depending upon the distribution of matter in the universe. In essence, Einstein assumed that mass curves spacetime and that curved spacetime determines how things move. This is in contrast to Newtonian gravitation which assumes that mass causes forces and that forces determine how things move.
Needless to say because of the Correspondence Principle,
both Special Relativity and General Relativity reduce to Newtonian physics in
the proper limits. When velocities are small, Special Relativity reduces to
Newtonian mechanics, and when gravitational fields are small, General
Relativity reduces to Newtonian gravitation.
Questions:
Q1. The Principle of Relativity
asserts that the laws of physics are the same (A) for all observers, (B) in all
frames of reference, (C) in every inertial frame. (D) More than one of these.
(E) None of these.
Q2. Under what circumstances does
the Correspondence Principle assert that General Relativity reduces to
Newtonian physics? (A) Small Particles, (B) Many Particles, (C) Fast Speeds,
(D) Slow Speeds, (E) Weak Gravity.
Q3. Which of the following assumes
that mass causes forces and forces determine how things move? (A) Newtonian
Physics, (B) Special Relativity, (C)General Relativity, (D) Quantum Mechanics,
(E) Statistical Physics.
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