Phase Space and the Quantum Theory

We can equally well take other shapes of cells. A method which is often useful can lx, illustrated with a problem having but one coordinate q and one momentum p. Then in our two-dimensional phase space we can draw a curve of constant energy. Thus for instance consider a particle of mass m held to a position of equilibrium by a restoring force proportional to the displacement, so that its energy is 

Another illustration of this method is provided by a freely rotating wheel of moment of inertia 7. The natural coordinate to use to describe it is the angle 0, and the corresponding momentum pe is the angular momen- 

III-l Colls in phase spare, for the linear oscillator The shaded area, between two ellipses of constant energy, has an area h in the quantum theory 

as show n in Fig. III-2, lines of constant energy are straight lines at constant value of po. Since 0 goes from zero to 2ir, and then the motion 

It used to be considered possible to imagine a being of finer and more detailed powers of observation than ours, who could regulate systems on a smaller scale than we could. Such a being could reverse processes that we could not to him, the definition of a reversible process would be different from what it is to us. Such a being was discussed by Maxwell and is often called Maxwell s Dcmon., Is it possible, we may well ask, to 

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