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A
lbert Einstein’s general
theory of relativity has
been called the greatest
act of thought about nature ever
to take place in a person’s head.
It explains gravity, motion, matter,
energy, space and time, the
formation of black holes, the Big
Bang, and possibly dark energy.
Einstein developed the theory over
more than a decade at the start
of the 20th century. It went on to
inspire Georges Lemaître, Stephen
Hawking, and the LIGO team,
which searched for the gravitational
waves predicted by the theory.
The theory of relativity arose from
a contradiction between the laws of
motion described by Isaac Newton
and the laws of electromagnetism
defined by Scottish physicist
James Clerk Maxwell. Newton
described nature in terms of matter
in motion governed by forces that
act between objects. Maxwell’s
theories concerned the behavior
of electric and magnetic fields.
Light, he said, was an oscillation
through these fields, and he
predicted that the speed of light
was always constant, regardless
of how fast the source was moving.THE THEORY OF RELATIVITY
IN CONTEXT
KEY ASTRONOMER
Albert Einstein (1879 –1955)BEFORE
1676 Ole Rømer shows that
light speed is not infinite.1687 Isaac Newton publishes
his laws of motion and
universal law of gravitation.1865 James Clerk Maxwell
shows that light is a
wave moving though an
electromagnetic field at
a constant speed.AFTER
1916 Karl Schwarzschild uses
Einstein’s equations to show
how much matter warps space.1919 Arthur Eddington
provides evidence for the
warping of spacetime.1927 Georges Lemaître shows
that a relativistic universe can
be dynamic and constantly
changing, and proposes the
Big Bang theory.Measuring the speed of light is
not an easy thing to do. Danish
astronomer Ole Rømer tried in 1676
by measuring the time delay in the
light arriving from Jupiter’s moons.
His answer was 25 percent too
slow, but he did show that light’s
speed was finite. By the 1850s,
more accurate measurements
had been made. However, in a
Newtonian universe, there must
also be changes in the speed
of light to account for the relative
motion of its source and observer.
Try as researchers might, no such
differences could be measured.The speed of light
is always constant
even when observers
are moving.This must mean that
moving through space
makes the flow of
time slower.A person undergoing
acceleration cannot tell
if this is due to gravity or
another force. Their body
could be thought of as
moving, or the universe
around it could be thought
of as changing.Time and space and gravitation have
no separate existence from matter.Mass exists not
just in space but in
spacetime. Mass itself
distorts spacetime.The slowing of time
makes an object’s
mass increase.Gravity is best described
as the result of spacetime
being warped by mass.