  While the modern science is characterized by an exponential growth in
scientific literature, the increase in publication volume clearly does not
reflect the expansion of the cognitive boundaries of science. Nevertheless,
most of the metrics for assessing the vitality of science or for making funding
and policy decisions are based on productivity. Similarly, the increasing level
of knowledge production by large science teams, whose results often enjoy
greater visibility, does not necessarily mean that "big science" leads to
cognitive expansion. Here we present a novel, big-data method to quantify the
extents of cognitive domains of different bodies of scientific literature
independently from publication volume, and apply it to 20 million articles
published over 60-130 years in physics, astronomy, and biomedicine. The method
is based on the lexical diversity of titles of fixed quotas of research
articles. Owing to large size of quotas, the method overcomes the inherent
stochasticity of article titles to achieve <1% precision. We show that the
periods of cognitive growth do not necessarily coincide with the trends in
publication volume. Furthermore, we show that the articles produced by larger
teams cover significantly smaller cognitive territory than (the same quota of)
articles from smaller teams. Our findings provide a new perspective on the role
of small teams and individual researchers in expanding the cognitive boundaries
of science. The proposed method of quantifying the extent of the cognitive
territory can also be applied to study many other aspects of "science of
science."
