  A diffusion process on complex networks is introduced in order to uncover
their large scale topological structures. This is achieved by focusing on the
slowest decaying diffusive modes of the network. The proposed procedure is
applied to real-world networks like a friendship network of known modular
structure, and an Internet routing network. For the friendship network, its
known structure is well reproduced. In case of the Internet, where the
structure is far less well-known, one indeed finds a modular structure, and
modules can roughly be associated with individual countries. Quantitatively the
modular structure of the Internet manifests itself in an approximately 10 times
larger participation ratio of its slowest decaying modes as compared to the
null model -- a random scale-free network. The extreme edges of the Internet
are found to correspond to Russian and US military sites.
