content_image/350284.jpg content_image/350290.jpg
<img src='content_image/350284.jpg'>

<img src='content_image/350290.jpg'>

difference between the two cases is obvious at small t . We notice a divergence, or singularity, associated with the ideal non-viscous fluid, Eq. (45). The viscous fluid results in finite H even at vanishing t , as can be seen from Eq. (22). 

The scale factor a ( t ) also shows differences in both cases. a ( t ) in a Universe with an ideal and non-viscous background matter depends on t according to Eq. (46), which simply implies that a ( t ) is directly proportional to t , and a ( t ) vanishes at t = 0, which shows the existence of a singularity of H . Assuming that the background matter is described by a 

