  We investigate how the overall response to a piece of information (a story or
an article) evolves and relaxes as a function of time in social networks like
Reddit, Digg and Youtube. This response or popularity is measured in terms of
the number of votes/comments that the story (or article) accrued over time. We
find that the temporal evolution of popularity can be described by a universal
function whose parameters depend upon the system under consideration. Unlike
most previous studies, which empirically investigated the dynamics of voting
behavior, we also give a theoretical interpretation of the observed behavior
using ultradiffusion.
  Whether it is the inter-arrival time between two consecutive votes on a story
on Reddit or the comments on a video shared on Youtube, there is always a
hierarchy of time scales in information propagation. One vote/comment might
occur almost simultaneously with the previous, whereas another vote/comment
might occur hours after the preceding one. This hierarchy of time scales leads
us to believe that the dynamical response of users to information is
ultradiffusive in nature. We show that a ultradiffusion based stochastic
process can be used to rationalize the observed temporal evolution.
