The Significance of Shear Stress in Cosmology

The concept of shear stress forms a fundamental base for meteorology and oceanography, which is the heritage of classical physics. In this paper, we show by well understood physical reasoning that it is also fundamental to cosmology although this link has not been previously recognised. The key physical model is that of the sea surface where two fluids (air and water) of high density contrast interact giving rise to a constant shear stress layer and wave breaking.

In cosmology, we show that two analogous, equal and opposite stress layers, due respectively to the formation of galaxies on the large scale and to their destruction by black holes on the small scale, constitute the physical model for the Universe, in which the mean shear stress is zero. The consequences of this condition for the expanding Universe are shown in a simple model. Two comparative images are also presented which illustrate the similarity between stress fields observed in a laboratory experiment and in the cosmos.