 More generally, one might step outside the framework of canonical, loop quantum gravity, and ask why one should only quantize the metric. As pointed out by Isham (1994, 2002), it may well be that the extension of quantum theory to general relativity requires one to quantize, in some sense, not only the metric but also the underlying differential structure and topology. This is somewhat unnatural from the standpoint where one begins with classical, canonical general relativity and proceeds to “quantize” (since the topological structure, unlike the metric structure, is not represented by a classical variable). But one might well think that one should start with the more fundamental, quantum theory, and then investigate under which circumstances one gets something that looks like a classical spacetime.