  This is an essay sketching the line of thinking which has led the present
author to propose the constituent or atomic model of gravitation more than a
decade ago. It turns out that viewing the problem of gravitation as a quantum
many body problem could be quite useful when addressing some old unsolved
problems such as the cosmological constant problem. I have applied this idea in
1996 to the problem of the largest cold gravitating system, the finite Universe
itself. The result was the prediction of a small, positive vacuum energy
density, now known, after its experimental discovery in 1998, as `dark energy'.
The smallness of this quantity was understood as the finite size effect in the
cold quantum many body system, and I quote here from \cite{Ma96}, {\it `` The
smallness of the cosmological constant in natural Planck units is a result of
an almost perfect thermodynamical limit. This is to say that the smallness of
the cosmological constant is an effect due to an enormous number $N$ of
hypothetical \textsf{gravitational} \textsf{atoms}. The present upper bound on
the cosmological constant $\Lambda$ allows us to draw the conclusion about the
lower bound on a number of \textsf{gravitational} \textsf{atoms} in the
observed Universe, $N\sim 10^{122}$. ...''}. The old cosmological constant
problem is a man-made problem because the vacuum energy density has nothing to
do with the quartic divergences (zero point energies) in the interacting
relativistic quantum field theories (i.e. in the Standard Model of elementary
particles). The actual value of the vacuum energy density of the vacuum finite
size de Sitter Universe is $\frac{E_{0}}{V}$, where $E_{0}$ is the ground state
energy of $N$ \textsf{gravitational} \textsf{atoms}, which are spin-zero bosons
of mass $M\sim M_{_{Pl}}$, contained in the finite volume $V$.
