Theories of Relativity-Sandeep K Chhabra

The laws of Newton's movement

Scientists propose theories to explain the known phenomena of nature and predict future results. An important aspect of the study of natural phenomena is the idea of ​​strength. Scientists study the body's reaction under the influence of force. This study received a major boost in 1687 when Newton published his book "Philosophiae Naturalis Principia Mathematica", which contained the three laws of motion. The first and second laws of the movement define the concept of force respectively qualitatively and quantitatively. The three laws of motion have defined mechanics, which is itself the first chapter of physics.

Law of universal gravitation

Scientists like to describe nature with as few laws as possible, especially to reduce the number of types of forces. Newton proposed the universal law of gravitation which was the first significant unification of the laws of force, believing that the same gravitational force that governs the motion of planets also governs the movement of bodies on the earth. At the present time, there are more than two fundamental forces, namely weak electro and strong nuclear. All other forces are manifestations of it. Scientists apply mathematical models and techniques to analyze natural phenomena. Newton has contributed to the development of Calculus, the most widely used branch of mathematics in physics. All of this cemented Newton's position as the father of classical physics. His laws explained almost all known observations, were simple to understand, and brought science closer to our vision of common sense.

4 papers of Einstein

In 1905, Einstein published 4 articles that challenged the basic assumptions of physics itself. He estimated the size of the molecule based on the observation of a simple phenomenon, the Brownian motion, just as Newton began to work on the law of gravitation after seeing a simple event, namely the fall of an apple. He provided a correct explanation of the photoelectric effect based on a particle model of light, which also contributed to the idea that nature was more easily explained if we applied different mathematical models in different circumstances rather than using a model to explain all observations. It was also his greatest contribution to quantum mechanics

Special theory of relativity

However, it was his equivalence equation of theory of relativity and mass energy that rewrote the laws of physics. The theory of special relativity is based on an unusual assumption that the speed of light is the same regardless of the movement of the source or the observer, a hypothesis that breaks with the idea of ​​relative motion. classical physics.

He predicts that mass, length and time are not constant but depend on the speed of the body. In classical physics, these are absolute quantities. As at least one of these quantities appears in all the formulas of physics, explicitly or implicitly, this has consequences for almost all branches of physics. It replaces Newton's law of motion, which is the basic equation of mechanics. One of the most used equations of physics, F = ma, is not valid according to the theory of special relativity. This is not a theory of mechanics and it has been proposed to explain the discrepancies between the laws of electromagnetism.

His predictions defy common sense. He says nothing can go faster than the speed of light in a free space. He suggests that clocks slow down in a mobile frame of reference (temporal dilation), body masses increase and lengths contract. Another prediction of the special theory of relativity concerns simultaneity, that is, two space-separated events occurring at the same time in a frame of reference seem to occur at different times in a frame. moving relative to the first.

The assumption that the speed of light is constant was used to define the unit of length, that is to say the meter. It is now defined as a distance traveled by the light in a certain period of time. Previously, it was defined by marks on a bar that was almost impossible to maintain at constant length. No experiments have been made so far that contradict the theory of special relativity, but other results such as Twin's paradox or paradox of the pole in paradox, etc. are still considered very difficult experiences to physically check. The fact that it has an impact on almost all branches of physics, making it virtually impossible to assert the validity of the theory is a matter for all circumstances. Partly because of this and partly for historical reasons, we speak of theory, although it is more precise than Newton's laws of motion, called laws.

Energy equivalence of mass

One of the articles published by Einstein in 1905 refers to the formula of mass and energy equivalence, namely E = mc2, sometimes called the most famous equation of the physical. In writing this formula, Einstein pursued the process of unification by reducing the two different concepts of mass and energy to one. Although the formula was known in a different format before, Einstein derived it on the basis of the theory of special relativity. If the theory is not valid, then this formula is not valid. The formula governs all the energy training of the Universe. The energy of the earth comes from the sun, from the inside and from the radio activity. All 3 mentioned sources draw their energy from the destruction of the mass.

General theory of relativity

In 1916, Einstein published the general theory of relativity and assumed that the gravitational and inertial masses were the same. The first refers to the mass that appears in Newton's law of gravitation and creates a force while the second appears in Newton's second law and is an attribute of the body due to force. The theory removes the restriction of inertial frames of reference used in the theory of special relativity and further incorporates the effect of gravitation. It is therefore called the general theory.

Although it predicts the movement of particles under the influence of gravitation, it is not written in the form of a law of force where the word force appears on the left side of l & # 39; equation. In fact, rather than force, the theory is written in terms of distortion of the space-time curvature near the masses. It is a complex mathematical theory based on field equations that relate spatio-temporal curvature to energy (and thus to the masses). The approach of gravitation is completely different from that of Newton's law. Although he does not replace it directly, he predicts things, eg. dilation of time, bending of light due to gravitational fields etc. that Newton's law does not do. Some of them, for example red gravitational displacements or lenses, etc., are used to detect various objects in the Universe by detecting frequency changes or light trajectories when it is detected. crosses intense gravitational fields. He predicts the formation of black holes, the stars with intense gravitational force that pull everything in them, including the light,

Like the theory of special relativity, the theory of general relativity was in advance. One of his predictions of gravitational waves that are distortions of displacement in space – time. They were first detected by the LIGO experiment in December 2015 and announced in June 2016. Up to now, the laboratory has detected 4 gravity waves, the last one in September 2017. In fact, the US scientists Rainer Weiss, Barry Barish and Kip Thorne won the 2017 Nobel Prize for Physics for their pioneering role in the detection of gravitational waves. Although regarded as a fundamental theory of astrophysics, its predictions are slowly being verified. Partly because of this, its historical connotations and its mathematical complexity, we speak of theory although it is more precise than Newton's law of gravitation, called law.

Modern physics

The year 2005 was declared the Year of Physics to highlight the immense contribution of the four articles published by Einstein in 1905 in favor of physics. Relativity and quantum mechanics are the two pillars of modern physics. The first explains things more precisely when bodies move at a speed comparable to the speed of light and later when their sizes are on the atomic scale. It is Einstein's insight that his theories of relativity are still verified and qualified as theories although they explain the observations better than Newton's laws. Scientists often discover something contradictory to these theories, but only end up retracting later. A recent example being that in 2011, CERN scientists discovered that neutrinos were moving faster than the speed of light. However, further analysis canceled the results. Einstein also contributed to quantum mechanics, notably by explaining the photoelectric effects, Bose Einstein statistics, and so on.

Tomorrow, the theories of relativity could become laws or theories that could explain the phenomena with even more precision could emerge. However, Einstein's contribution to relativity and quantum mechanics has strengthened his position as a father of modern physics.