  The exponential increase in the number of scientific publications raises the
question of whether the sciences are expanding into a fractured structure,
making cross-field communication difficult. On the other hand, scientists may
be motivated to learn extensively across fields to enhance their innovative
capacity, and this may offset the negative effects of fragmentation. Through an
investigation of the distances within and clustering of cross-sectional
citation networks, this study presents evidence that fields of science become
more integrated over time. The average citation distance between papers
published in the same year decreased from approximately 5.33 to 3.18 steps
between 1950 and 2018. This observation is attributed to the growth of
cross-field communication throughout the entire period as well as the growing
importance of high impact papers to bridge networks in the same year. Three
empirical findings support this conclusion. First, distances decreased between
almost all disciplines throughout the time period. Second, inequality in the
number of citations received by papers increased, and as a consequence the
shortest paths in the network depend more on high impact papers later in the
period. Third, the dispersion of connections between fields increased
continually. Moreover, these changes did not entail a lower level of clustering
of citations. Both within- and cross-field citations show a similar rate of
slowly growing clustering values in all years. The latter findings suggest that
domain spanning scholarly communication is partly enabled by new fields that
connect disciplines.
