  Interactions among units in complex systems occur in a specific sequential
order thus affecting the flow of information, the propagation of diseases, and
general dynamical processes. We investigate the Laplacian spectrum of temporal
networks and compare it with that of the corresponding aggregate network.
First, we show that the spectrum of the ensemble average of a temporal network
has identical eigenmodes but smaller eigenvalues than the aggregate networks.
In large networks without edge condensation, the expected temporal dynamics is
a time-rescaled version of the aggregate dynamics. Even for single sequential
realizations, diffusive dynamics is slower in temporal networks. These
discrepancies are due to the noncommutability of interactions. We illustrate
our analytical findings using a simple temporal motif, larger network models
and real temporal networks.
