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330 BCE
Aristotle
Aristotle argued that the four elements—air, earth, fire, and water—have a natural position or place in which they travel. He further argued that objects heavier than others or those that contain more amount of earth would fall toward the ground faster and their speed would increase as they near their natural place. -
Isaac Newton published Philosophiae Naturalis Principia Mathematica
Isaac Newton publishes Philosophiae Naturalis Principia Mathematica, giving a comprehensive account of gravity. This gave astronomers an accurate toolbox for predicting the motions of planets. He argued that the orbit of the moon depended on the same type of force that causes an apple to fall on Earth. https://plato.stanford.edu/entries/newton-principia/ -
The Unknown Planet Vulcan
To explain Mercury’s odd behavior, Urbain Le Verrier proposed the existence of an unseen planet called Vulcan, which orbited closer to the sun. He suggested that the gravity from Vulcan was influencing Mercury’s orbit. But repeated observations revealed no signs of Vulcan. https://www.history.com/news/vulcan-the-famous-planet-that-never-existed -
Special Relativity
Special relativity is a theory proposed by Albert Einstein Eric Weisstein's World of Biography that describes the propagation of matter and light at high speeds. It was invented to explain the observed behavior of electric and magnetic fields. http://scienceworld.wolfram.com/physics/SpecialRelativity.html -
Einstein Predicts Gravitational Redshift
In Einstein's general theory of relativity, the gravitational redshift is the phenomenon that clocks in a gravitational field tick slower when observed by a distant observer. http://astronomy.swin.edu.au/cosmos/G/Gravitational+Redshift -
General Relativity
Albert Einstein publishes general theory of relativity. The theory also predicts the existence of black holes and gravitational waves, although Einstein himself often struggled to understand them. https://www.newscientist.com/round-up/instant-expert-general-relativity/ -
Einstein makes a theory on Stimulated Emission
Einstein publishes a paper on the quantum theory of radiation indicating stimulated emission was possible. Einstein proposed that an excited atom could return to a lower energy state by releasing energy in the form of photons in a process called spontaneous emission. https://www.rp-photonics.com/stimulated_emission.html -
Prediction of Frame Dragging
Josef Lense and Hans Thirring theorize that the rotation of a massive object in space would drag space-time around with it. https://www.space.com/456-einstein-warped-view-space-confirmed.html -
First observation of Gravitational Lensing
Gravitational lensing is the bending of light around massive objects, such as a black hole, allowing us to view objects that lie behind it. http://www.cfhtlens.org/public/what-gravitational-lensing -
First measurement of Gravitational Redshift
Walter Sydney Adams examined light emitted from the surface of massive stars and detected a red shift, as Einstein predicted. http://astronomy.swin.edu.au/cosmos/G/Gravitational+Redshift -
Prediction of a Galactic Gravitational Lensing
Swiss astronomer Fritz Zwicky proposed that an entire galaxy could act as a gravitational lens. https://arxiv.org/pdf/astro-ph/9812021.pdf -
Gravitational Redshift Verified
The theory was tested by Robert Pound and Glen Rebka by measuring the relative redshift of two sources at the top and bottom of Harvard University’s Jefferson Laboratory tower. The experiment accurately measured the tiny change in energies as photons traveled between the top and the bottom. -
Observing the existence of Black Holes
The general relativity theory gained further momentum beginning the 1960s due to the discovery of galaxies maintained by an enormous pull of black holes in the center. Gravity is responsible for this pull.
