With the development of nuclear physics, the formula became a symbol of the dangers inherent in the modern era
Amit Hagar
E = mc2
The last paper that Einstein published in 1905 was a short paper on one of the interesting derivatives of special relativity, which he had first formulated three months earlier. The article included an equation, albeit a short one, that has become a cultural icon over the years.E=mc2, Einstein wrote to express the conclusion derived from the theory of relativity regarding the "parallel" between the mass of a body and the energy stored in it, but with the development of nuclear physics, the sign became a symbol of the inherent dangers in the modern era.
In the last article of "The Year of Wonder", Einstein analyzes how two observers, one at rest relative to an object with mass and the other moving at a constant speed relative to that object, would describe the innocent phenomenon of light emission by that object. Since, according to the principle of relativity, the laws of physics are the same whether we are at rest or moving at a constant speed, the law of conservation of energy holds in both these descriptions. In other words, the two observers must agree that the total energy of the physical system in question (which in this case is the sum of the energy of the light radiation and the kinetic energy of the object) remains the same before and after the emission of the light.
According to Einstein's thought experiment, the observer who describes the object as emitting light will discover, following the emission, a decrease in the object's kinetic energy (and this as compensation for the "addition" of the energy of the light radiation to the system). The kinetic energy is the product of the mass multiplied by half the square of the velocity, therefore a decrease in the kinetic energy can be interpreted either as a change in velocity or as a change in mass. However, according to the principle of relativity, the object "moves" only relative to the observer, and a parallel and physically identical description can be described by the passive observer, a description in which the object does not move at all (that is, a description in which its velocity is zero).
If the change in kinetic energy cannot be the result of a change in speed, since it changes depending on the point of view chosen (and can even be zeroed out), it must be the result of a change in mass, Einstein concluded. According to Einstein, the mass of a body is apparently a measure of its energy content, and the equation connecting the two can be formulated as E=mc2 (in the original article, Einstein wrote a more complicated formula, and the famous expression is actually a simplification of that formula).
With the birth of nuclear physics and the discovery of the processes of fission and fusion, the situation that Einstein discussed turned from a thought experiment into a field of fruitful research and application, and Einstein's equation received a literal interpretation whose far-reaching consequences largely shaped the history of the 20th century. Today, when in every particle accelerator it is possible to observe the "conversion" of matter particles into energy, and vice versa, the claim that "energy is a form of mass" has become commonplace, and can be found in popular scientific literature and even in textbooks.
According to one interpretation, shared by Einstein in 1905, the last article of "The Year of Wonder" provides an "exchange rate" for the conversion between energy and mass, thereby claiming that mass and energy are actually two sides of the same "thing", just as ice and vapor are actually a form of water. Another, deeper interpretation, which Einstein proposed a little later, is to say that following the theory of relativity, another law of the Newtonian world picture - the law of conservation of mass, according to which the mass of a body, which is a measure of its resistance to the forces acting on it, always remains constant - was removed from the shelf. If, as Einstein showed, nature "compensates" for a change in mass with the help of a change in energy, then the physical quantity that is kept constant in physical processes is not mass alone or energy alone, but the "welding" of both into a new size: mass-energy.
Hence, the best way to interpret the most famous formula in the history of science is simply to say that according to the theory of relativity, physical quantities that until now we have treated as objective, absolute quantities, such as mass and energy or distance and time, are not actually such. The "really" objective quantities according to special relativity are the quantities that remain unchanged in the transition from one point of view to another, from one description of a physical system to another. According to the theory of relativity, mass or energy are not absolute quantities but relative quantities, dependent on description: in Einstein's thought experiment, for example, the two observers - the one at rest and the one in constant motion - will think a different amount of mass "turns" into energy. In contrast, the absolute quantity, the one that remains unchanged regardless of our point of view, is mass-energy, or more precisely momentum-energy (momentum is mass multiplied by velocity).
The distinction that energy is not a "form of mass" (as ice, for example, is a form of water) is a critical distinction that many and good people tend to forget. This forgetfulness characterizes a significant part of the interpretations received by the theory of relativity during the 20th century. In the history of science, quite a few cases are known in which physical theory became a magnet for myths and baseless hypotheses. For example, the second law of thermodynamics inspired the myth of the death of the universe that prevailed in the middle of the 19th century, and quantum mechanics provided (and still provides) inspiration for dozens of pseudo-scientific discussions about the connection between body and mind or about the equivalence between philosophies of the Far East and modern physics.
Relativity surpasses all of these. Einstein's discoveries in the "year of wonder" and in the years that followed caused great excitement, and this caused philosophers and thinkers to bring the theories of relativity (special and general, which was formulated about a decade later) as support for almost any ideology imaginable. The truth is that the moral of the theories of relativity is that concepts and categories that until Einstein were considered separate, such as space and time, or momentum and energy, or space and time and matter, were welded together into one piece. The theories of relativity do not imply that coordinate systems or even geometry are merely arbitrary conventions; It is not implied that time is the "fourth dimension" in any sense that is not trivial or self-evident (that is, a sense in which time is not simply another axis in addition to the three axes of space); And it certainly doesn't mean that everything is relative.
Tomorrow: General Relativity
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