The Saga of General Relativity and Arthur Eddington: How a British Astronomer Proved Einstein's Theory
In the year 1905, commonly known as Albert Einstein’s miracle year, Einstein achieved recognition among some famous Physicists such as Max Planck; as, Einstein laid out his famous theory of special relativity, successfully explained Brownian motion, the Photoelectric effect, and won the Nobel Prize in Physics in 1927 for photon theory of light.
EINSTEIN’S HAPPIEST THOUGHT: A Man Falling from a Building
Einstein’s journey to general relativity began in November 1907 when he was struggling to meet his deadline for a science yearbook article explaining the special theory of relativity. The limitations of it still bothered him: the theory only dealt with uniform velocity motions and it did not incorporate Newton’s theory of gravitation. Einstein himself recalled:” I was sitting in a chair in the patent office at Bern when all of a sudden a thought occurred to me, if a person falls freely he will not feel his weight”. The realization startled him and set him on an eight-year journey to generalize his special theory of relativity and impelled him toward a theory of gravitation that would answer the question that even Newton could not answer. The question of how gravity works. (Isaacson, 2007, Chapter 12)
Isaac Newton in his book ‘Philosophiæ Naturalis Principia Mathematica’ stated that
“Hitherto we have explained the phenomena of the heavens and our sea by the power of gravity, but have not yet assigned the cause of this power. This is certain, that it must proceed from a cause that penetrates to the very centers of the sun and planets,”, (Newton, 1846, pp. 939-942)
GRAVITY AND ACCELERATION EQUIVALENCE
The young Einstein took this challenge and started to work with calculations and thought experiments to explain the true nature of gravity, formulating an Equivalence Principle.
Gravity and acceleration equivalence is the idea that the effects of gravity can be indistinguishable from the effects of acceleration. In other words, if you were in a closed box without any external reference points, you would not be able to tell whether the box was accelerating through space or whether it was sitting on the surface of a massive planet with gravity pulling you towards it.
The equivalence principle plays a crucial role in general relativity because it suggests that the curvature of space-time caused by massive objects is intimately related to the effects of acceleration. In other words, gravity and acceleration are two sides of the same coin. This insight led Einstein to develop his theory of general relativity, which has been extremely successful in explaining many of the observed phenomena in the universe, including black holes, gravitational waves, and the large-scale structure of the universe.
In his book The Fabric of the Cosmos, Brian Greene explains that "the central message of general relativity is that gravity is not a force between masses, but a curvature of space and time created by the presence of mass and energy".(Greene, 2004, p. 158).
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Einstein spent eight years developing the foundation of the theory and creating the necessary mathematical equations in 1915. It then took four more years for his prediction about gravity bending light to be confirmed through observations, but this vision set him on a path toward one of physics' most remarkable accomplishments: The General Theory of Relativity. (Isaacson, 2007, Chapter 7)
PROPOSITIONS:
One of the consequences of the equivalence principle is that a beam must bend when subjected to gravitational influence. When a beam of light passes close to the Sun, it bends slightly due to the Sun's gravity, that bending of light is known as deflection; which was predicted by Einstein to be around 0.83 seconds of arc (Isaacson, 2007, Chapter 9). Einstein even proposed a test for astronomers to find any experimental evidence for this theory that during a solar eclipse, the stars in the near parts of the sky would be visible so there is a chance that the consequences of it would be visible.
Erwin Freundlich, a young astronomer at Berlin University Observatory read the paper and became excited to test it but it would not be possible without a solar eclipse and proposed to measure the deflection of starlight by Jupiter’s gravity as it has greater gravitational influence than any other planet in our Solar System. Einstein once joked about it to Freundlich, saying “if only we had a truly larger planet than Jupiter…But nature did not deem it her business to make the discovery of her laws easy for us” (Isaacson, 2007, Chapter 9).
ARTHUR EDDINGTON:
Arthur Eddington was a British astronomer, physicist, and mathematician who made significant contributions to the development and popularization of Einstein's theory of General Relativity. Born in Kendal, England in 1882, Eddington earned his degrees in mathematics and physics from Trinity College, Cambridge. He was one of the few scientists who fully grasped the significance of Einstein's theory of relativity when it was first introduced.
In 1919, two British expeditions were sent to observe a solar eclipse, one to Sobral,” Brazil” and one to Principe, led by Arthur Eddington from Cambridge. The purpose was to test Einstein's theory of general relativity, which predicted that gravity would bend light. Three telescopes were used to photograph the star field near the Sun during the eclipse, and the images were compared to photographs of the same star field taken at nighttime.
After months of meticulous measurement and calculations, Eddington's hard work paid off with a positive result that proved Einstein's theory of relativity. He was ecstatic, declaring it the greatest moment of his life and recognizing that this new outlook on scientific thought must prevail. Eddington presented his findings to a packed room at the Royal Society, where his announcement met with much excitement and praise, with the president of the Royal Society hailing it as one of the highest achievements in human thought. The Times headline the next day proclaimed a "Revolution in Science." (“The Man Who Made Einstein World-Famous,” 2019).
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Eddington's expedition made accurate measurements of light bending around the sun, and as a result, Einstein became an overnight sensation, rising from an obscure academic to an international scientific icon (“The Man Who Made Einstein World-Famous,” 2019). Einstein himself was thrilled to learn that his theory had been verified, but he was also puzzled by the sudden media frenzy that engulfed his life. Without Eddington, relativity would have remained unproven, and Einstein would never have become a genius icon. Despite not meeting until years after the war's end, Eddington and Einstein's collaboration was critical not only to the birth of modern physics but also to the survival of science as an international community during the darkest days of World War 1 (“The Man Who Made Einstein World-Famous,” 2019).
General relativity has had numerous implications in modern times, including GPS technology, Televisions, Radars, black holes and gravitational waves, cosmology, space exploration, energy production, gravitational lensing, quantum gravity, and the philosophy of science. It has challenged the traditional notion of absolute space and time, leading to a better understanding of the true nature of space and time. This theory has revolutionized our understanding of the universe, opening new avenues for scientific research and technological advancement. Without this theory and its empirical confirmation, science would have continued to rely on outdated theories, and our current world would have been deprived of the amazing breakthroughs and discoveries made possible by general relativity. (TVs, Radar Guns and Other Technologies Linked to Einstein’s Theories of Relativity, 2015)
SUGGESTIONS:
Those who want to understand GR may head to the following leads.
Demonstration of the Equivalence principle and General Relativity by Brian Greene: https://youtu.be/0jjFjC30-4
Albert Einstein and Theory of Relativity Full Documentary: https://youtu.be/Qzm947lBqnE
REFERENCES
Greene, B. (2004). The Fabric of the Cosmos: Space, Time, and the Texture of Reality. Knopf Doubleday Publishing Group.
Isaacson, W. (2007). Einstein: His Life and Universe. Simon and Schuster.
BBC News. (n.d.). The man who made Einstein world famous. Retrieved from The man who made Einstein world-famous - BBC News
Eddington, A. S. (1887). Space, time, and gravitation. ratio, 61, 4.
Newton, I. (n.d.). Philosophiæ Naturalis Principia Mathematica. Retrieved from https://archive.org/details/newtonspmathema00newtrich/page/n13/mode/2up
TV Radar Guns and Other Technology Linked to Einstein's Theories of Relativity. (2015, November 25). PBS NewsHour. Retrieved from TVs, radar guns and other technologies linked to Einstein’s theories of relativity | PBS NewsHour
