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20 21 BAsic stuff symmetries at the heart of matter Toward the end of the 19th century the pioneering physicist Pierre Curie stated what he felt to be a universal principle of physics, to the effect that symmetric causes will necessarily lead to equally symmetric effects. Now, as a general principle he was quite wrong, for symmetries are not always linked in the way that he implied. But his intuition of symmetric continuity is certainly true at the more basic levels of matter. The highly ordered world of the crystalline state, exposed to view by Xray crystallography 1, is entirely determined by the underlying symmetries of the atomic and subatomic realms. Mendeleevs Periodic Table, which placed the elements into a rational series, was one of the great milestones of 19thcentury, classical physics. But early on in the 20th century it became clear that the properties of the elements were, in fact, reflecting regularities within the internal structures of their component atoms. As atomic theories developed further it became apparent that all chemical properties derived from the numbers of protons and electrons in their respective atomic structures, allowing them to group in orderly molecular arrangements 2. By the 1960s it was realised that although the orbiting electrons 3 were indeed fundamental particles, the protons and neutrons of the nucleus 4 were made up of yet smaller componentshadrons and leptons. The hadrons, in turn, are combinations of quarks which come together in the beautiful symmetries of the famous 8fold way 5. Above Xray diffraction tehniques enabled scientists to peer into the intensely ordered world of crystals. Right When atoms are close together their positively charged nuclei and negatively charged electrons pull together to form molecules Above The symmetries of the eightfold way classification of hadrons for an octet and decuplet of hadrons. Left Neutrons and protons behaving like spinning tops in the nucleus. 3. Probability distribution patterns of electrons around a nucleus 4. 5. 2. 1.
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