12. Symmetry and Phase Transitions

Applying the so called "rasor of Occam" reasoning, the scientist prefers always the simplest explanation. This simplest explanation is almost always connected to symmetry.For example the simplest explanation is that the early Universe contained matter and antimatter in equal quantities. It was uniform in all directions , etc ... So you may ask , why the universe now contains only matter and is formed by clusters of galaxies? The explanation given is the following: as the Universe temperature goes down, the universe undergoes many phase transitions that will break the initial symmetry. For this reason the universe becomes more and more asymmetric as it cools down.
How this may happen can be understood by looking at some phase transitions around us. For example the water molecules in the liquid state have no preferred direction so are in a higher symmetry state in comparison to the same molecules in ice. In this case all the molecules are aligned along the lattice directions .

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