E = mc^2
Date: Around 1993
What does e=mc^2 mean?
By itself, this equation tells us that, when a quantity "m" of
matter is converted to energy, the amount produced is equal to m*c^2, where c
is the speed of light. One way this equation can be obtained: when Einstein
developed the special theory of relativity, he found it predicted that mass
increases with speed. When this is applied to a calculation for the kinetic
energy KE of a moving object traveling with speed v, one obtains the result KE
= (m - m0)*c^2 where m is the (increased) mass of the object when its speed is
v, and m0 is the mass of the object when it is at rest. Thus, an increase in
kinetic energy is accompanied by an increase in mass. Furthermore, this
suggests that, even when the object is not moving, there is a "rest-mass"
energy m0*c^2 associated with it.Then the total energy (kinetic + rest-mass
energy) is given by E=mc^2 . It was Einstein's great insight to assert that
matter and energy in general are, in essence, equivalent and interchangeable.
There was other evidence for such an assertion at that time. An experiment
done in 1890 confirmed that radiation exerts a pressure when it hits and is
absorbed by an object. Interpreted in the context of relativity, one is led
to the conclusion that when an object absorbs electromagnetic radiation of
energy E, its mass is increased by E/c^2. Thus, it seems reasonable to assign
an equivalent mass to radiation. Since then, the correctness of the E=mc^2
equation, as well as the mass- energy equivalence that underlies it, has been
widely confirmed by experiment.
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Update: June 2012