  Our current societies increasingly rely on electronic repositories of
collective knowledge. An archetype of these databases is the Web of Science
(WoS) that stores scientific publications. In contrast to several other forms
of knowledge -- e.g., Wikipedia articles -- a scientific paper does not change
after its "birth". Nonetheless, from the moment a paper is published it exists
within the evolving web of other papers, thus, its actual meaning to the reader
changes. To track how scientific ideas (represented by groups of scientific
papers) appear and evolve, we apply a novel combination of algorithms
explicitly allowing for papers to change their groups. We (i) identify the
overlapping clusters of the undirected yearly co-citation networks of the WoS
(1975-2008) and (ii) match these yearly clusters (groups) to form group
timelines. After visualizing the longest lived groups of the entire data set we
assign topic labels to the groups. We find that in the entire Web of Science
multidisciplinarity is clearly over-represented among cutting edge ideas. In
addition, we provide detailed examples for papers that (i) change their topic
labels and (ii) move between groups.
