.Einstein’s Theory Energy from Mass

Advertisement

.Einstein’s Theory
Energy is something with which everyone is familiar. It appears in many different forms, including electricity, light, heat, chemical energy, and motional (or kinetic) energy. An important scientific discovery in the 19th century was that energy is conserved. This means that energy can be converted from one form to another, but the total amount of energy must stay the same. Mass is also very familiar, though sometimes it is referred to, rather inaccurately, as weight. On the Earth’s surface, mass and weight are often thought of as being the same thing, and they do use the same units—something that weighs 1 kilogram has a mass of 1 kilogram—but strictly speaking weight is the force that a mass experiences in the Earth’s gravity. An object always has the same mass, even though in outer space it might appear to be weightless. Mass, like energy, is conserved.

      Photograph of Albert Einstein in 1921—the year in which he received the Nobel
Prize in Physics. Einstein (1879–1955) had graduated in 1901 and had made a number of applications for academic jobs, without success. He eventually got a job as technical expert, third class, in the Swiss patent office in Berne, which meant that he had to do all his research in his spare time.

The extraordinary idea that mass and energy are equivalent was proposed by Albert Einstein in a brief three-page paper published in 1905. At that time, Einstein was a young man who was virtually unknown in the scientific world. His paper on the equivalence of mass and energy was followed soon after by three seminal papers—on the photoelectric effect, on Brownian motion, and on special relativity—all published in the same year. Henri Becquerel had discovered radioactivity 10 years previously. Using simple equations and application of the laws of conservation of energy and momentum, Einstein argued that the atom left after a radioactive decay event had emitted energy in the form of radiation must be less massive than the original atom. From this analysis he deduced that “If a body gives off the energy E in the form of radiation, its mass diminishes by E/c2.” He went on to say, “It is not impossible that with bodies whose energy content is variable to a high degree (e.g., radium salts) the theory may be successfully put to the test.” Einstein’s deduction is more commonly written as E  mc2, probably the most famous equation in physics. It states that mass is another form of energy and that energy equals mass multiplied by the velocity of light squared. Although it took a long time to get experimental proof of this entirely theoretical prediction, we now know that it was one of the most significant advances ever made in science.

Advertisement