Abstract
It is generally assumed that the effects of quantum gravity will be manifest only at lengths scales comparable to or smaller than the planck length $l_p$. We argue that this belief is false; quantum gravity effects make a dramatic change to our understanding of physics on arbitrarily large length scales. The reason this can happen is that when a large number $N$ of particles are involved, the length scale of quantum gravitational effects need not be $l_p$ but $N^\alpha l_p$ for some $\alpha>0$. We explain the mechanism of `fractionation' which leads to the emergence of such a new length scale in string theory. For black holes, this new length scale turns out to be order the horizon radius, and resolves puzzles like the black hole information paradox. In the early Universe we have another situation where a large number $N$ of quanta are crushed together, and we argue that the effect of the emergent length scale is to provide an inflationary `push' to larger volumes resulting from the quantum mechanical measure term in the path integral.
Samir D. Mathur