, a phenomenon where the apparent motion of celestial bodies about their locations was dependent on the velocity of the observer.
In addition, tests performed on the speed of light in water (the Fizeau experiment) indicated that light traveling through a moving medium would be dragged along by the medium, but not nearly as much as expected. This supported other experiments – such as Fresnel’s partial aether-drag hypothesis and the experiments of Sir George Stokes – which proposed that the aether is either partially or entirely carried along by matter.
Einstein’s theory of special relativity was groundbreaking in that he argued that the speed of light is the same in all inertial reference frames, and introduced the idea that major changes occur when things move close the speed of light. These include the time-space frame of a moving body appearing to slow down and contract in the direction of motion when measured in the frame of the observer.
Known as Einstein’s Theory of Special Relativity, his observations reconciled Maxwell’s equations for electricity and magnetism with the laws of mechanics, simplified the mathematical calculations by doing away with extraneous explanations used by other scientists, and made the existence of an aether entirely superfluous. It also accorded with the directly observed speed of light and accounted for the observed aberrations.
Naturally, Einstein’s theory met with mixed reactions from the scientific community, and would remain controversial for many years. With his one equation, E=mc², Einstein had vastly simplified the calculations necessary to understand how light propagates. He also suggested, in effect, that space and time (as well as matter and energy) were merely different expressions of the same thing.
Between 1907 and 1911, while still working at the patent office, Einstein began considering how special relativity could be applied to gravity fields – what would come to be known as the Theory of General Relativity. This began with an article titled, “On the Relativity Principle and the Conclusions Drawn from It“, published in 1907, in which he addressed how the rule of special relativity might also apply to acceleration.
In short, he argued that free fall is really inertial motion; and for the observer, the rules of special relativity must apply. This argument is also known as the Equivalence Principle, which states that gravitational mass is identical to inertial mass. In the same article, Einstein also predicted the phenomenon of gravitational time dilation – where two observers situated at varying distances from a gravitating mass perceive a difference in the amount of time between two events.
In 1911, Einstein published “On the Influence of Gravitation on the Propagation of Light“, which expanded on the 1907 article. In this article, he predicted that a box containing a clock that was accelerating upwards would experience time faster than one that was sitting still within an unchanging gravitational field. He concludes that the rates of clocks depend on their position in a gravitational field, and that the difference in rate is proportional to the gravitational potential to first approximation.
In the same article, he predicted that the deflection of light would depend upon the mass of the body involved. This proved to be especially influential, because for the first time, he had offered a testable proposition. In 1919, German astronomer Erwin Finlay-Freundlich urged scientists around the world to test this theory by measuring the deflection of light during the solar eclipse of May 1929.
Einstein’s prediction was confirmed by Sir Arthur Eddington, who’s observations were announced shortly thereafter. On Nov. 7th, 1919, the The Times published the results under the headline: “Revolution in Science – New Theory of the Universe – Newtonian Ideas Overthrown”. General Relativity has since developed into an essential tool in modern astrophysics. It provides the foundation for the current understanding of black holes, regions of space where gravitational attraction is so strong that 