| Themes > Science > Physics > About Physics, Generalities > A Brief History and Philosophy of Physics > The Unification of Physical Phenomena |
The work of Maxwell represents the first great theoretical unification of physical phenomena, in this case the integration of magnetic, electrical and optical theory into one all-encompassing framework. Again, this must be seen as desirable under Ockham's Razor, which argues for economy of understanding. Such economy is the strength of modern analytical science, which emphasizes the logical description of a vast range of physical phenomena from a few basic principles, rather than the memorization of a large number of isolated facts or formulae. The former approach enables the user to predict effects not seen previously, to invent, whereas the latter restricts one to what already is known. Other great unifications that have taken place in physics include the integration of classical mechanics, quantum physics and heat in the development of statistical mechanics. This subject assumes that the properties of large systems, such as gases or solids, can be calculated by working out the average of the properties of all their constituent particles. For example, the relationship between the temperature and pressure of a gas can be calculated by treating the gas as being made up of a very large number of independent molecules, and calculating the average force they produce as they collide with the container walls, using Newtonian mechanics for the particles. This approach was followed for gases by Maxwell and Ludwig Boltzmann (1844-1906). Boltzmann also showed that Clausius' entropy could be interpreted as a measure of the disorder of a system. In particular, he proved that the value for entropy can be obtained from a knowledge of the total number of different states in which a system can be found. That, in turn, depends on the number of different potential configurations of all the particles which comprised the system. This statistical approach has led to the development of "quantum statistics", the application of statistical mechanics to quantum phenomena. Perhaps the greatest such unification that has taken place in this century is the integration of electromagnetism and quantum mechanics, in quantum electrodynamics (QED). This feat earned Richard Feynman, Julian Schwinger, and Sin-itiro Tomonaga the Nobel Prize for physics in 1965. It is capable of predicting the spin g-factor of the electron with a numerical accuracy of 1 part in 1010! In 1979, Sheldon Glashow, Abdus Salam, and Stephen Weinberg were given the Nobel Prize for their "electroweak theory" that unified the electromagnetic and weak nuclear forces. Attempts have also been made to form a quantum theory of the strong nuclear force. Because of its similarity to QED, it has been called quantum chromodynamics (QCD). "Chromo" comes from the Greek word for colour, and refers to the fact that the quarks that make up neutrons and protons come in several varieties that have been given the names red, blue and green, and their antiparticles. (These names have been chosen in analogy to light. These three colours can be combined to give white light; the three quarks combine to give a "colourless" particle.) The combination of electroweak theory and QCD comprises what is called the "Standard Model". Attempts are still under way to integrate QCD and electroweak theory into a single "Grand Unified Theory" (GUT). Much effort has also gone into trying to unify electromagnetism and gravitation. In fact, Einstein spent most of the latter part of his life trying to create a quantum form of the general theory of relativity. As can be seen from these few examples, the nineteenth-century belief that the main theoretical work of physicists was over could not have been further from the truth! |
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