A Tribute Article To Stephen Hawking - R.I.P. (1942-2018)
Corps Obscura
The idea that there might be stars from which light can not escape was first suggested in 1783 by the British geologist and clergyman, John Michell. In a meeting of the Royal Society of London held on November 27, 1783, he predicted that dark stars might exist if they were small enough that their escape velocity exceeded the speed of light. Light could then not escape.
In 1796, Pierre Simon Laplace made a similar prediction in his book Le Systeme du Monde. Laplace referred to these objects as "corps obscura". Laplace either thought of the idea independently or did not give proper credit because he made no reference to Michell's earlier work.
By the early 19th century, experiments showed that light had wave-like properties. Because scientists thought that waves, unlike particles, would not be affected by gravity the idea of corps obscura fell out of favor.
In the early 20th century we learned that light exhibits both wave and particle properties (from quantum mechanics) and that light is affected by gravity (general relativity), perhaps paving the way for the idea's return.
Schwarzschild's Solution to Einstein's Equations
Einstein's theory of general relativity predicts the possibility of black holes, but Einstein did not make the prediction himself. Karl Schwarzschild set the stage for black holes.
Einstein's paper on general relativity appeared in 1915 during the height of World War I. Schwarzschild, a loyal German citizen, served in the German army despite being above the normal age for military service. While serving on the Russian front, he read Einstein's paper in the November issue of the Proceedings of the Prussian Academy of Sciences. Einstein had used only an approximate solution to his gravitational field equations.
Schwarzschild found an exact solution in a few days. By confining the problem to an idealized star that was perfectly spherical and not rotating, he found the gravitational field outside the star. Einstein read the resulting paper on Schwarzschild's behalf at the January 1916 meeting of the Prussian Academy of Sciences. Schwarzschild continued working and in a few weeks calculated the gravitational field inside the star. Again Einstein presented the paper on his behalf at the February meeting of the Prussian Academy.
Unfortunately for science, and especially for Schwarzschild, he was not able to continue his groundbreaking work. He died on the Russian front within a few months, and Einstein had the sad task of presenting Schwarzschild's obituary at the June meeting of the Prussian Academy.
Schwarzschild's Prediction
Schwarzschild did not actually predict the existence of black holes because he did not consider the possibility that such exotic collapsed stars might exist. However the possibility of stars collapsed to the point that light can not escape is a direct consequence of his solutions to Einstein's gravitational field equations. Because Einstein's special theory of relativity predicts that nothing can travel faster than light any star collapsed to the point that its escape velocity exceeds the speed of light allows nothing to escape.
Schwarzschild's work lay dormant for a while. In the 1960s, interest in these stars revived. John Wheeler coined the descriptive term "black hole" to describe them. They are black because light can not escape. The fact that nothing else can escape either makes them like a hole. One can fall in but can not climb back out.
Author Paul Nchemba
Corps Obscura
The idea that there might be stars from which light can not escape was first suggested in 1783 by the British geologist and clergyman, John Michell. In a meeting of the Royal Society of London held on November 27, 1783, he predicted that dark stars might exist if they were small enough that their escape velocity exceeded the speed of light. Light could then not escape.
In 1796, Pierre Simon Laplace made a similar prediction in his book Le Systeme du Monde. Laplace referred to these objects as "corps obscura". Laplace either thought of the idea independently or did not give proper credit because he made no reference to Michell's earlier work.
By the early 19th century, experiments showed that light had wave-like properties. Because scientists thought that waves, unlike particles, would not be affected by gravity the idea of corps obscura fell out of favor.
In the early 20th century we learned that light exhibits both wave and particle properties (from quantum mechanics) and that light is affected by gravity (general relativity), perhaps paving the way for the idea's return.
Schwarzschild's Solution to Einstein's Equations
Einstein's theory of general relativity predicts the possibility of black holes, but Einstein did not make the prediction himself. Karl Schwarzschild set the stage for black holes.
Einstein's paper on general relativity appeared in 1915 during the height of World War I. Schwarzschild, a loyal German citizen, served in the German army despite being above the normal age for military service. While serving on the Russian front, he read Einstein's paper in the November issue of the Proceedings of the Prussian Academy of Sciences. Einstein had used only an approximate solution to his gravitational field equations.
Schwarzschild found an exact solution in a few days. By confining the problem to an idealized star that was perfectly spherical and not rotating, he found the gravitational field outside the star. Einstein read the resulting paper on Schwarzschild's behalf at the January 1916 meeting of the Prussian Academy of Sciences. Schwarzschild continued working and in a few weeks calculated the gravitational field inside the star. Again Einstein presented the paper on his behalf at the February meeting of the Prussian Academy.
Unfortunately for science, and especially for Schwarzschild, he was not able to continue his groundbreaking work. He died on the Russian front within a few months, and Einstein had the sad task of presenting Schwarzschild's obituary at the June meeting of the Prussian Academy.
The Masai Mara National Reserve In Kenya
Ultimate Africa Tour Destination In Kenya
Schwarzschild's Prediction
Schwarzschild did not actually predict the existence of black holes because he did not consider the possibility that such exotic collapsed stars might exist. However the possibility of stars collapsed to the point that light can not escape is a direct consequence of his solutions to Einstein's gravitational field equations. Because Einstein's special theory of relativity predicts that nothing can travel faster than light any star collapsed to the point that its escape velocity exceeds the speed of light allows nothing to escape.
Schwarzschild's work lay dormant for a while. In the 1960s, interest in these stars revived. John Wheeler coined the descriptive term "black hole" to describe them. They are black because light can not escape. The fact that nothing else can escape either makes them like a hole. One can fall in but can not climb back out.
Author Paul Nchemba
Comments