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Mass-energy.

Another consequence of Einstein's theory of special relativity (see above) is that mass must be viewed as a highly concentrated form of energy. Einstein's equation representing this is the famous e = mc 2, where e is energy, m is mass, and c is the speed of light. The speed of light is so huge that to square it and multiply it by even a small amount of mass is to represent a large amount of energy (1 gram of mass equals 900 billion billion ergs of energy).

Whenever any process gives off energy, it loses a little mass; when it absorbs energy, it gains a little mass. The amount of mass lost or gained under ordinary conditions is so minute it had never been detected. That is why Lavoisier could consider mass conserved independently of energy (see 1769) and Helmholtz could consider energy conserved independently of mass (see 1847).

With the study of radioactivity, much larger energy changes per unit mass were involved, as Pierre Curie had found (see 1901). Mass-energy equivalence could then be measured and was found to be precisely as Einstein's theory required it to be. The law of conservation of energy was thus extended and made more precise by the inclusion of mass as one more form of energy. The law of conservation of mass became obsolete, or rather, was included in what is sometimes known as the law of conservation of mass-energy.

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Author:Asimov, Isaac
Publication:Asimov's Chronology of Science & Discovery, Updated ed.
Article Type:Reference Source
Date:Jan 1, 1994
Words:237
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