Soon a fourth ’charm’ quark was proposed, providing an elegant solution to some problems in the description of weak interactions (the theory that underlies radioactive decay). Most hadrons could be explained as combinations of just two quarks, dubbed ‘up’ and ‘down’, while a class of so-called ‘strange’ hadrons with anomalously long lifetimes could fit into the model by postulating a third ‘strange’ quark. In the 1960s, physicists Murray Gell-Mann and George Zweig proposed that most of these particles were actually made up of combinations of two or three fundamental constituents, which they called ‘quarks’ (pronounced to rhyme either with ‘Mark’ or ‘York’). Murray Gell-Mann, one of the proposers of the quark model and recipient of the Nobel Prize in Physics in 1969, visiting the ATLAS experiment in 2012. As in Mendeleev’s periodic table, these particles could be arranged by their properties into intriguing patterns, which had their roots in a branch of mathematics called ‘group theory’. The debris from such collisions consisted not only of familiar protons, neutrons and electrons, but an ever-expanding ‘zoo’ of heavier and more exotic particles (collectively called ‘hadrons’) that would appear fleetingly and then rapidly decay into lighter, more familiar particles. The rich structure of the periodic table can be explained by fundamental building blocks of electrons, protons and neutrons, and the ways in which they interact and fit together.Īfter the Second World War, increasingly powerful particle accelerators allowed protons or electrons to be boosted to high energies and smashed into dense material targets or, later, into other accelerated particles in head-on collisions. The number and allowed arrangements of the electrons (governed by the laws of quantum mechanics) determine all the element’s chemical properties whether it is stable or reactive, acid or alkaline, metal or non-metal etc. Each chemical element has a characteristic number of electrons, equal to the number of protons in its nucleus. The disparate chemical elements are all made of the same building blocks: a compact ‘nucleus’ made of similar numbers of protons and neutrons, surrounded by a cloud of orbiting electrons. Thomson, Ernest Rutherford, Marie and Pierre Curie, James Chadwick and others, the modern ‘periodic table’ we know from school chemistry was born. With subsequent discoveries and insights from Antoine Becquerel, J.J. In the 19th century, Russian chemist Dimitri Mendeleev noticed that the properties of approximately 100 known chemical elements showed distinct patterns when arranged in a table according to their mass.
One of the most successful paradigms in physics is to try to understand complex phenomena in terms of simpler building blocks.
0 kommentar(er)
