Gnomes hail from a parallel dimension very like this one. The main difference between the two planes is the amount of magic floating about. In the Gnomish homeland, there is an awful lot of it. Arcane energies are a pervasive part of everyday life for the gnomes; their reality, therefore, is somewhat less concrete than others’.
In our own dimension, the gnomes’ strong magical affinities are undiminished. The manipulation of arcane energies, especially those pertaining to illusion and the nature of reality, comes to them as easily as breathing.
There is a theory that the powerful magical energy inhabiting the gnomish home plane is a direct result of the lack of deities thereupon. It is certainly true that there are no gnome gods. Moreover, the land does seem to reshape itself of its own accord sometimes.