  Theoretical studies have shown that electron-electron (e-e) and electron-hole
(e-h) interactions play important roles in many observed quantum properties of
graphene making this an ideal system to study many body effects. In this report
we show that spectroscopic ellipsometry can enable us to measure this
interactions quantitatively. We present spectroscopic data in two extreme
systems of graphene on quartz (GOQ), an insulator, and graphene on copper
(GOC), a metal which show that for GOQ, both e-e and e-h interactions dominate
while for GOC e-h interactions are screened. The data further enables the
estimation of the strength of the many body interaction through the effective
fine structure constant, $\alpha_{g}^{*}$. The $\alpha_{g}^{*}$ for GOQ
indicates a strong correlation with an almost energy independent value of about
1.37. In contrast, $\alpha_{g}^{*}$ value of GOC is photon energy dependent, is
almost two orders of magnitude lower at low energies indicating very weak
correlation.
