Are Most Particles Gravitons?
  The number of baryons in the observable universe is of the order of $10^{80}$, as is the number of electrons. The number of photons is about nine orders of magnitude greater, $10^{89}$, as is the estimated number of neutrinos. However, the number of gravitons could be more than twenty orders of magnitude larger yet, of the order of $10^{113} r$, where $r$ is the tensor-to-scalar ratio for quantum fluctuations produced by inflation, which could be as high as $0.1$. 
Don N. Page
hep-th gr-qc