On November 25, 1915, Albert Einstein’s research on the General Theory of Relativity was published. Today, General Relativity is regarded as the most comprehensive theory describing gravitation in modern physics.
I. Historical Background of the General Theory of Relativity
The brilliant physicist Albert Einstein presented his work on the General Theory of Relativity on November 25, 1915, before the Prussian Academy of Sciences in Berlin. In March 1916, the study was published in the scientific journal Annalen der Physik. This event is considered a major turning point in human history, marking a significant leap beyond Isaac Newton’s Law of Universal Gravitation, which was formulated in 1687.
Figure 1: The scientist Albert Einstein (1879–1955).
At present, the General Theory of Relativity is regarded as the most comprehensive theory describing gravitation in modern physics. For researchers not only in physics but also in other scientific fields, since its publication, General Relativity has brought about a true revolution in humanity’s scientific understanding.
Earlier, in 1905, Albert Einstein proposed the Special Theory of Relativity. In this theory, he described the distortion of time and space caused by an object moving at a speed close to that of light. Combined with other laws of physics, Einstein formulated the famous equation
E = mc²
(E: energy, m: mass, c: the speed of light), which expresses the equivalence and mutual convertibility of mass and energy. This equation fundamentally changed previous assumptions that mass and energy were unrelated quantities.
II. Explanation of the General Theory of Relativity
The General Theory of Relativity explains gravitation through the geometric curvature of spacetime, determined by the following principles:
- Matter and energy curve the spacetime around them.
- An object in free fall under the influence of a gravitational field moves along a geodesic between two points in spacetime.
Four-dimensional spacetime in Special Relativity is already difficult to visualize; curved spacetime is therefore an even greater challenge for researchers studying General Relativity. In a simplified interpretation, if the number of dimensions of spacetime is reduced, analogous descriptions can be made using images of two-dimensional curved surfaces.
For example, suppose two vehicles start at the equator and move northward. Initially, their directions are parallel. Even without being acted upon by any force, the two vehicles will eventually meet at the North Pole. An observer watching their motion, if unaware that the Earth’s surface is curved, might conclude that a force has drawn the vehicles toward each other.
This is a typical example of a purely geometric phenomenon; consequently, gravity in General Relativity is sometimes referred to as a fictitious force. Because the geodesic connecting two points in spacetime does not depend on the properties of the freely falling object in a gravitational field—a phenomenon first discovered by the physicist Galileo Galilei—two objects released from the same height will fall at the same rate. In Newtonian mechanics, this implies that an object’s inertial mass and gravitational mass must be equivalent. This principle also forms the foundation of the General Theory of Relativity.
Figure 2: Curvature of spacetime caused by a massive object.
Albert Einstein later stated that the motivation for developing the General Theory of Relativity stemmed from his dissatisfaction with the privileged role of inertial motion in Special Relativity. He believed that a theory encompassing other states of motion (including accelerated motion) would be more complete. Therefore, in 1908, he wrote a paper on acceleration within the framework of Special Relativity, in which he also observed that free fall is, in fact, an inertial motion. For an observer in free fall, the principles of Special Relativity should still apply. This assertion is known as the Equivalence Principle. Within the same paper, Einstein also predicted the phenomenon of gravitational time dilation.
In 1911, Einstein published another paper extending his 1907 work, introducing the effect of the deflection of light caused by massive objects when light passes nearby. General Relativity is a theory of gravitation developed by Albert Einstein between 1907 and 1915, with the assistance of Marcel Grossmann. According to this theory, the mutual attraction between objects arises from the curvature of spacetime produced by matter and energy.
III. Differences Between General Relativity and the Law of Universal Gravitation
Before the advent of General Relativity, Newton’s Law of Universal Gravitation had been accepted for more than 200 years and successfully described the gravitational force between objects, although Newton himself did not claim that his theory fully explained the true nature of gravitation. In astronomy, numerous careful observations revealed discrepancies between theoretical predictions and actual observations that could not be explained by Newtonian theory. According to Newton’s model, gravitation is an attractive force between objects; although the nature of this force was not clearly understood, the theory fundamentally succeeded in describing the motion of the planets.
Figure 3: Formula in General Relativity.
However, experiments and observations have shown that Einstein’s model is related to several effects that remain unexplained in Newton’s framework, such as the small anomalies in the motion of Mercury and other planets. General Relativity also predicts many unusual gravitational phenomena, such as gravitational waves, gravitational lensing, and a gravity-induced effect on time known as gravitational time dilation. Many of these predictions have been experimentally confirmed, while several topics within the theory are still under active investigation. For example, although there is indirect evidence for gravitational waves, direct experimental confirmation of their existence is still being sought by numerous scientific organizations, including projects such as LIGO and GEO 600.
General Relativity has developed into a fundamental tool in modern astrophysics. It provides essential insights into black holes, regions of spacetime where gravity is so strong that not even light can escape. Their presence is revealed through the intense radiation emitted by astronomical objects, such as active galactic nuclei and quasars. General Relativity is also a key component of the standard Big Bang model, which describes the origin of the universe.
Source: GenK.vn
M.Sc. Hồ Quốc Bảo, Faculty of Engineering Technology, Van Hien University
References
[1]. Chandrasekhar. S (1998), The Mathematical Theory of Black holes, Oxford University press – reprinted.
[2]. D’inverno (1998), Introducting Einstein’s Relativity, Oxford University press – reprinted.
[3]. Hugshton LP and Tod . K (1999), Introduction to General Relativity, Cambridge University press – reprinted.
[4]. Lawden D.P (1982), Introduction to Tensor Caculus, Relativity and Cosmology, Wiley – New York – reprinted.
[5]. Landau and Lifshits (1967), The Classical Theory of Fields, Scientific Press – Moscow.
[6]. Lim Yung Kuo (edi) (1995), Problems and Solutions on Solid State Physics and Relativity, World Scientific – reprinted.
[7]. Misner C – Thorne K Wheeler J (1999), Gravitation, Freeman – San Francisco- reprinted.
[8]. Schutz B.F (1999), First Course in General Relativity, Cambridge University press – reprinted.
[9]. Stephani (2001), General Relativity, Cambridge University Press – reprinted.
[10]. Wasserman .R.H (1992), Tensors and Manifolds with Applications to Mechanics and Relativity, Oxford University press – reprinted.
[11]. Weinberg (1975), Gravitation and Cosmology, Wiley & Sons Inc.