The theory of relativity formulated by the famous Albert Einstein is perhaps one of the greatest scientific advances of humanity. At present, and since it was originated or formulated, it continues to be an essential formula for many processes. But do you know what it corresponds to exactly? Let’s now learn more about Albert Einstein’s theory of relativity: what it is, summary and examples.
Albert Einstein’s theory of relativity: what it is, summary and examples
Albert Einstein published in 1905 the first of two important studies on the theory of relativity , Electrodynamics of moving bodies, in which he denied the existence of absolute motion . In fact, Einstein argued that no object in the universe could represent a fixed absolute and universal frame of reference with respect to the rest of space . In addition, any organism could be considered a good reference system for the study of the laws of the motion of bodies.
For Einstein, motion was a relative concept , which could be described in any inertial frame of reference: all observers who describe physical phenomena in the frame of reference arrive at the same laws of nature. This is the fundamental hypothesis (Principle of Relativity) of all Einstein’s theory: for two observers moving with each other at constant speed, the same laws of nature apply. Newton had already established Einstein’s observations, according to which “absolute rest cannot be determined by observing the position of bodies in our region of space.”
The Theory of Relativity in Simple Words
The novelty introduced by Einstein consists in having established that the speed of propagation of light with respect to any observer is always the same : 300,000 km / s. The concept of the invariance of the speed of light was determined using Maxwell’s equations, according to which the speed of propagation of electromagnetic waves is considered a “natural constant” that does not change if the phenomena are described in different frames of reference. According to Einstein, two observers moving with each other measure the same speed of light, as demonstrated by the experiments of Michelson and Morley.
Einstein’s hypothesis was in stark contrast to classical physics , according to which only one of the observers could be considered at rest, while the other would have made a measurement error due to the Lorentz-Fitzgerald contraction. For Einstein , on the contrary, both observers could be considered at rest and each could make its own measurement correctly, taking as reference its own coordinate system: in fact, the coordinates are connected to each other through appropriate mathematical equations, the transformations by Lorentz.
Meaning and forms of energy
As a consequence of the impossibility of defining an absolute motion, Einstein questioned the possibility of defining an absolute time and mass . The Lorentz transformations predicted that a clock moving relative to an observer would appear slower, while material objects appeared to have a greater mass. Therefore, the principle of absolute time of Newtonian mechanics was replaced by the principle of invariance of the speed of light with respect to the state of motion of the observer.
The discovery of the electron a few years earlier also provided the possibility of verifying the accuracy of the Lorentz transformations: electrons emitted by radioactive substances, in fact, have speeds similar to that of light. The experiments confirmed Einstein’s hypothesis: the mass of an electron with speeds similar to those of light is greater than the rest mass, exactly as expected. The increase in the mass of the electron was due to the conversion of kinetic energy into mass, according to the formula E = mc2.
Einstein’s theory was also confirmed by experiments on the speed of light in moving bodies of water and on magnetic forces in moving substances. The abandonment of the concept of simultaneity means that two events recorded as simultaneous by an observer are not so for a second observer in motion with respect to the first. The evolution of every particle or object in the universe is described by a line called universal in four-dimensional space, called spacetime . The distance (or interval) between any two events can be described by a combination of intervals of space and time.
Theory of general relativity
In 1915 Einstein formulated the theory of general relativity, also valid for systems in accelerated motion with each other . The need for this theory came from the apparent contrast between the laws of relativity and the law of gravitation. To resolve these conflicts, Einstein developed a new approach to the concept of gravity, based on the principle of equivalence. In the new formulation, the forces associated with gravity are equivalent to those produced by acceleration. Therefore, it is theoretically impossible to distinguish the two types of forces. The analogy between the two relativities is obvious: the special theory of relativity established that a person, inside a car at constant speed on a smooth road, could in no way know whether he was at rest or in uniform rectilinear motion.
However, the theory of general relativity stated that a person, inside the machine in accelerated, decelerated or curvilinear movement, could not establish whether the forces that determined the movement were of gravitational origin or if they were accelerating forces activated by other mechanisms.
Theory of special relativity
According to Einstein’s theory, Newton’s law of gravitation was an unnecessary hypothesis. In fact, Einstein considered all forces, including gravitational, to be the effects of an acceleration. Newton’s hypothesis, according to which two objects attract each other with a force proportional to their masses, has been replaced in general relativity by the hypothesis that spacetime curves in the vicinity of massive bodies. Einstein’s law of gravitation consists in synthesis in the statement that the universal line of a body is a curve that joins the different points in space according to the shortest path.
A theory that seems easier to understand than the theory of general relativity that has a complex mathematical formulation, based on the application of tensor algebra and Riemannian geometry. The famous claim that only ten people in the world understood Einstein’s general relativity alludes to the difficulty of the mathematical concepts that form the backbone of the theory’s formalism. In contrast, special relativity is based on simple calculations, which everyone can understand.
How Einstein’s Theory of Relativity Has Evolved and How It Is Applied
Since its introduction, Einstein’s relativity has found many experimental confirmations. After 1915, the theory of general relativity was expanded by Einstein himself and developed by scientists such as James Jeans, Arthur Eddington, Edward Arthur Milne, Willem de Sitter, and Hermann Weyl. Much of his work was aimed at expanding the theory to include electromagnetic phenomena. Many studies subsequent to the formulation of the theory have been devoted to the creation of a relativistic quantum mechanics. Furthermore, physicists have studied the cosmological consequences of the theory of general relativity: many lines of development were in fact possible in the scheme of axioms established by Einstein. For example, the theory of relativity implied the possibility that the universe was expanding. Hypothesis that seemed confirmed by the experimental results.
