  Given that the scale of quantum gravity is not experimentally accessible, one
naturally resorts to mathematical consistency as a measure for a good candidate
theory to replace General Relativity at high energies. Reproducing the
semi-classical results of black hole entropy has become a standard test for any
prospective theory of quantum gravity. It is often argued that another such
commonality, albeit less known, is the similar fractal behaviour. It is shown
that many, if not all, approaches to quantum gravity predict a spectral
dimension of 2 in ultraviolet regime. In this paper, by computing the heat
kernel, we show that the spectral dimension of closed bosonic string theory is
26. We discuss the implications of this disparity.
