  In the early-mid 20$^{\rm th}$ century Dirac and Zel'dovich were among the
first scientists to suggest an intimate connection between cosmology and atomic
physics. Though a revolutionary proposal for its time, Dirac's Large Number
Hypothesis (1937) adopted a standard assumption of the day, namely, the
non-existence of the cosmological constant term ($\Lambda = 0$). As a result,
its implementation necessitated extreme violence to the theory of general
relativity -- something few physicists were prepared to sacrifice in favour of
`numerology' -- requiring a time-dependent gravitational coupling of the form
$G(t) \sim 1/t$. Zel'dovich's insight (1968) was to realise that a small but
nonzero cosmological term ($\Lambda > 0$) allowed the present day radius of the
Universe to be identified with the de Sitter radius, $r_{\rm U} \simeq l_{\rm
dS} \simeq 1/{\sqrt{\Lambda}}$, which removed the need for time-dependence in
the fundamental couplings. Thus, he obtained the formula $\Lambda \simeq
m^6G^2/\hbar^4$, where $m$ is a mass scale characterising the relative
strengths of the gravitational and electromagnetic interactions, which he
identified with the proton mass $m_{\rm p}$. In this paper, we review a number
of recent arguments which, instead, suggest the identification $m = m_{\rm
e}/\alpha_{\rm e}$, where $m_{\rm e}$ is the electron mass and $\alpha_{\rm e}
= e^2/\hbar c \simeq 1/137$ is the usual fine structure constant. We note that
these are of a {\it physical} nature and, therefore, represent an attempt to
lift previous arguments \emph{{\` a} la} Dirac from the realm of numerology
into the realm of empirical science. If valid, such arguments suggest an
intimate connection, not only between the macroscopic and microscopic worlds,
but, perhaps even more surprisingly, between the very essence of "dark" and
"light" physics.
