In the International System of Units (abbreviated SI from the French Système International), the kilogram is the basic unit of mass, the metre is the basic unit of length, the second is the basic unit of time, and the ampere is the basic unit of electric current. Mass, length, time, and electric current are never defined but the standard units used to measure them are always defined. Physicists assume the existence of mass, length, time and electric current and then define (give the meaning of) all other physical quantities in terms of these basic units. Physics is the study of energy and matter in space and time and how they are related to each other. People like Werner Heisenberg, Erwin Schrödinger, and Paul Dirac continued to work on quantum mechanics and eventually we got the Standard Model. ![]() Quantum mechanics applies for very small things like the electrons, protons, and neutrons that make up an atom. Max Planck came up with quantum mechanics to explain why metal releases electrons when you shine a light at it, and why matter emits radiation. His view of space-time replaced the ancient idea that space and time were quite separate things. Einstein predicted that the speed of electromagnetic radiation through empty space would always be the same. This was predicted by Albert Einstein's theory of special relativity. Modern physicsĪs research progressed, scientists found things that classical mechanics did not explain.Ĭlassical mechanics predicted that the speed of light varied, but experiments showed the speed of light stayed the same. Isaac Newton used Galileo's ideas to put together his three laws of motion. And although he did not invent the telescope, he noticed that the stars and planets were not perfect. Galileo's experiments helped to create classical physics. Physics became a separate field of study after the scientific revolution. In The Book of Optics, Ibn Al-Haitham rejects previous Greek ideas and comes up with a new theory about vision. ![]() Scientists like Ibn Sahl, Al-Kindi, Ibn al-Haytham, Al-Farisi and Avicenna worked a lot on optics and vision. They also developed an early form of the scientific method. Islamic scholars continued to study Aristotelian physics during the Islamic Golden Age. Leucippus and his student Democritus suggested the idea of the atom around this period. Natural philosophy started in Greece around 650 BC when some philosophers rejected superstition and decided things had to happen for a reason. ![]() Most names for constellations came from Greek astronomers. A lot of astronomy comes from Mesopotamia, Babylonia, Ancient Egypt, and Ancient Greece.
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