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Relativity's
history does not start with Einstein.
The
Speed of Light is Constant
Several
important figures in the study of electromagnetic phenomena suspected
that something was wrong with the newtonian view of the universe.
In Newton's universe, everything was a particle, or made up of particles.
But Hans Christian Ørsted, Michael Faraday, and James Clerk Maxwell
noticed wave-like behaviors that moved at a constant speed (about
300,000 km/s) inconsistent with Newtonian physics.
In 1878
Albert Abraham Michelson determined himself to accurately measure
the speed of light. In 1880 he traveled to Europe where he began
to build a very useful device called an interferometer. This instrument
was designed to split a single beam of light into two separate beams
that traveled perpendicular to each other. The Interferometer then
rejoined to two beams and if one beam of light had traveled a greater
distance or had traveled more slowly, the two beams would be "out
of phase", meaning they would constructively and destructively
interfere with each other, creating visible bands of light. By measuring
and studying these bands one could determine how much out of phase
the two beams were, thus what the velocities of the beams were,
relative to each other.
In 1887
Michelson and Edward Williams Morley, with Michelson's interferometer,
set out to determine how fast the Earth moved through the "ether",
a theoretical substrate through which light was conducted. They
reasoned that since Earth was moving through this ether, the speed
of light in the same direction as the Earth's path would be the
velocity of light plus the velocity of the Earth, whereas the speed
of light at a right angle to the Earth's path would simply be the
speed of light. After all, this is what Newtonian physics predicted.
This wasn't so. There were no bands, thus it appeared that either
the Earth's velocity was zero, or the speed of light was constant.
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The
Foundations of Relativity
In 1889
George Francis FitzGerald developed the notion "localized time",
that time flowed at different rates in different places (Einstein
was 10 years old). 1895 Hendrik Antoon Lorentz, in an effort to
explain the odd outcome of the Michelson-Morley experiment, independently
developed the same concept. They both also discovered that objects,
as they approach the speed of light, contract in the direction of
motion. This is now called Lorentz-FitzGerald contraction. By 1904
Lorentz had a complete set of equations that accurately described
the skewing of length, time, and mass. (See the Twin
Paradox Illustration and Why Relativity
Works.)
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Relativity
is Born
1905 is
called the "Annus Mirabilis", Einstein's Miracle Year, in which
he, at age 26, published his special theory of relativity, related
it to mass and energy to get  ,
developed a quantum theory of light, and proved molecules exist,
all while working 40 hours a week at a patent office. Two years
later he applied his special theory to gravity and determined that
acceleration and gravity were equivalent.
In 1915
Einstein developed his general theory of relativity which described
gravity as a curvature of space-time itself in a fourth dimension.
What is perceived as the force of gravity is actually the tendency
of an object to take the path of least resistance through a four-dimensional
universe.
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