The H _ { 0 } \hbox { - } \Omega diagram is resurrected to dramatically illustrate the nature of the key problems in physical cosmology today and the role that nuclear physics plays in many of them .
In particular it is noted that the constraints on \Omega _ { baryon } from big bang nucleosynthesis do not overlap with the constraints on \Omega _ { vis } nor have significant overlap with the lower bound on \Omega from cluster studies .
The former implies that the bulk of the baryons are dark and the later is the principle argument for non-baryonic dark matter .
A comparison with hot x-ray emitting gas in clusters is also made .
The lower bound on the age of the universe from globular cluster ages ( hydrogen burning in low mass stars ) and from nucleocosmochronology also illustrates the Hubble constant requirement H _ { 0 } \leq 66 { km / sec / Mpc } for \Omega _ { 0 } = 1 .
It is also noted that high values of H _ { 0 } ( \sim 80 { km / sec / Mpc } ) even more strongly require the presence of non-baryonic dark matter .
The lower limit on H _ { 0 } ( \geq 38 { km / sec / Mpc } ) from carbon detonation driven type Ia supernova constrains long ages and only marginally allows \Omega _ { baryon } to overlap with \Omega _ { cluster } .
Diagrams of H _ { 0 } \hbox { - } \Omega for \Lambda _ { 0 } = 0 and \Lambda _ { 0 } \neq 0 are presented to show that the need for non-baryonic dark matter is independent of \Lambda .