User:Zojj/e=mc2

My take on how the intro should look for mass-energy equivalence.

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In physics, mass–energy equivalence is the concept that the mass of a body is a measure of its energy content. This means that energy has mass. Albert Einstein proposed mass–energy equivalence in 1905 in one of his Annus Mirabilis papers entitled "Does the inertia of a body depend upon its energy-content?" The equivalence is described by the famous equation:
 * $$E = mc^2 \,\!$$

where E is energy, m is mass, and c is the speed of light in a vacuum.

A gram of mass has the same "weight" as 89,875 GJ of energy. Scientists are divided on whether it is a fair statement that mass may be "converted" to energy. A loose analogy would be to compare energy to sand, and mass to a clump of sand. In a nuclear reaction, the mass of the reactants (the starting sand clump) is the same as the products (smaller clumps) plus the mass of the released energy (sand that goes flying off). All energy and mass (sand) is conserved. Similarly, when a particle is decays (i.e. a neutron), other particles and radiation are created with so much speed and energy that their combined energy "weighs" the same as the original particle. Tests measuring these reactions have shown mass-energy equivalence to 0.0004% accuracy.