Characterization of microstates for confined systems and associated scale-dependent continuum fields via Fourier coefficients

The phase space description of a system of N point masses confined to a rectangular box is shown to be equivalent to knowledge of a minimal set of 6N complex Fourier coefficients associated with the discrete distributions of matter and momentum. The corresponding real-valued truncated Fourier series yield continuum densities of particle number and momentum at a specific length scale, min . Continuum descriptions at any scale >min correspond to further truncation of these series. Attention is drawn to the relevance of the results to recent investigations of reproducible macroscopic behaviour, at a given pair and - of length time scales, using projection operator methodology.