Entropy of the Universe and Hierarchical Dark Matter
  We discuss the relationship between dark matter and the entropy of the
universe with the premise that dark matter exists in the form of primordial
black holes (PBHs) in a hierarchy of mass tiers. The lightest tier are
intermediate-mass PIMBHs within galaxies including the Milky Way. Supermassive
black holes at galactic centres are in the second tier. We are led to speculate
that there exists a third tier of extremely massive PBHs, more massive than
entire galaxies. We discuss future observations by the Rubin Observatory and
James Webb Space Telescope.
