Einstein’s Theory of General Relativity was published on November 25th, 1915. The theory, in simple terms, explains that gravity is not only an invisible force that pulls objects to each other, but gravity is instead a curving and warping of space-time.
This discovery, which was proved to be true by many scientists, has become the cornerstone of our understanding of the universe.
Theory Explained
In Classical Newtonian Mechanics, Sir Isaac Newton hypothesized that gravity is a force of attraction that pulls objects towards each other. However, Einstein explains gravity as the curvature of spacetime caused by massive objects. The curvature subsequently affects the movement of objects through space and time. This curvature of spacetime directly relates to the energy and momentum of the matter and/or radiation present.
The theory also considers unifying space and time as a four-dimensional continuum, making the continuum called spacetime.
Further into the research, it was discovered by Einstein that objects with a higher mass cause more of a distortion in spacetime. For example, when a large object is placed in the center of the trampoline, it will cause the trampoline to dimple and create a U shape. If a marble is then rolled along the circumference of the trampoline, the marble will continue to roll along a circular path as it spirals towards the inner body.
As shown in Figure 1, there are 9 cubes, in which a ball (planet) with mass is orbiting around the large cube. As the ball travels, the vectors that form the cube are bent, showing how the mass of an object interacts with the spacetime continuum.
Figure 1: 3D demonstration of General Relativity
Another peculiar phenomenon is the bending of light under a gravitational field. Intuitively, light waves take the shortest path, which should be a straight line. However, the shortest path on Earth is not a straight line. On Earth, the proper shortest path will always involve curvature as the particle has to traverse through the Earth’s curvature while reaching its destination. As shown in Figure 2, the subsequent shortest path due to the bending is a curved line, not a straight line.
Figure 2: 2D demonstration of spacetime curvature
Applications
The Theory of General Relativity has brought along many accurate cosmological predictions of planets and black holes. For example, the prediction of black holes—regions of space in which space and time are distorted that not even light, can escape from them.
The theory also predicts gravitational lensing, which describes the bending of light that occurs due to the sufficient curvature of spacetime for the path of light to be visibly bent.
Impact and Significance
The aspects that form general relativity allowed scientists to understand the orbits around Mercury and other planets demonstrated by the mathematical equation below.
In addition, the framework of the theory also enables talks about the history of the universe, providing modern frameworks for cosmology, as well as aiding the development of the different theories as to how the universe formed. The Big Bang and cosmic microwave background radiation were both subsequently discovered.
Fun Facts
Time slows down in strong gravitational fields…
General relativity is incompatible with quantum mechanics…
The Theory of Special Relativity describes more about the relationship between space, time, and mass. General relativity adds gravity to the picture.
Works Cited
1ucasvb (2016). General Relativity - Conceptual illustration of time and space distortion. [online] www.youtube.com. Available at: https://www.youtube.com/watch?v=H8h1c7ToC9w [Accessed 17 Mar. 2023].
Arvin Ash (2020). General Relativity Explained simply & visually. [online] YouTube. Available at: https://www.youtube.com/watch?app=desktop&v=tzQC3uYL67U [Accessed 30 Jun. 2024].
Hom, T. (2023). 13 Extraordinary Facts About General Relativity. [online] Facts.net. Available at: https://facts.net/science/physics/13-extraordinary-facts-about-general-relativity/ [Accessed 30 Jun. 2024].
Hubble, E. (1929). A relation between distance and radial velocity among extra-galactic nebulae. Proceedings of the National Academy of Sciences, 15(3), pp.168–173. doi:https://doi.org/10.1073/pnas.15.3.168.
Tillman, N.T., Bartels, M. and Dutfield, S. (2022). Einstein’s theory of general relativity. [online] Space.com. Available at: https://www.space.com/17661-theory-general-relativity.html.
Webb, R. (n.d.). General relativity. [online] New Scientist. Available at: https://www.newscientist.com/definition/general-relativity/.
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