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Articles: Devotion | In quest of infinity - 9
- Prof. venkata ramanamurty mallajosyula
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The short answer to this question is: Symmetry breaking. This is a very important concept and indeed a corner stone of modern physics. The idea may be understood by considering the solidification of a liquid. As we are all aware, when water is cooled from a high temperature to below 0 degrees Centigrade, it freezes; what we get is ice, which is crystalline. Whereas the liquid is absolutely uniform and homogenous, crystalline ice though very geometric, is actually “grainy” compared to water. We say that this “graininess” is due to “loss of symmetry” and that solidification occurs because of “symmetry breaking”. I know I have greatly slurred over a beautiful [but technical] point but that is enough for the present. With this background, we may rephrase the question posed above: “Can one understand the change from one state to another in terms of symmetry breaking?” Yes we can, and that is what I shall now consider.
In discussing the point we are now considering, we must first note that physical systems always like to be in the lowest possible energy state. Sometimes, they may be prevented from doing so by some constraint [constraint is a check; in real life for example, the parents of a girl might not like their daughter getting married to a certain chap!]; but given a chance, a system would seek that state which has the lowest energy. Keep this important guiding principle in mind.
Now let us look at the figures presented below.
The energy of the system varies with the “state” of the system. Nature is such that systems always choose that state which has the lowest energy. Curve (a) is typical of water [above the freezing point], while curve (b) applies to ice [produced when water is cooled below the freezing point]. Note that in (b), the minimum energy state [i.e., the state with zero energy] is different from that in (a); it is this difference that drives freezing. Later, we shall use the word order parameter, which is more precise while charactering different “states”.
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