  Science is a growing system, exhibiting ~4% annual growth in publications and
~1.8% annual growth in the number of references per publication. Combined these
trends correspond to a 12-year doubling period in the total supply of
references, thereby challenging traditional methods of evaluating scientific
production, from researchers to institutions. Against this background, we
analyzed a citation network comprised of 837 million references produced by
32.6 million publications over the period 1965-2012, allowing for a temporal
analysis of the `attention economy' in science. Unlike previous studies, we
analyzed the entire probability distribution of reference ages - the time
difference between a citing and cited paper - thereby capturing previously
overlooked trends. Over this half-century period we observe a narrowing range
of attention - both classic and recent literature are being cited increasingly
less, pointing to the important role of socio-technical processes. To better
understand the impact of exponential growth on the underlying knowledge network
we develop a network-based model, featuring the redirection of scientific
attention via publications' reference lists, and validate the model against
several empirical benchmarks. We then use the model to test the causal impact
of real paradigm shifts, thereby providing guidance for science policy
analysis. In particular, we show how perturbations to the growth rate of
scientific output affects the reference age distribution and the functionality
of the vast science citation network as an aid for the search & retrieval of
knowledge. In order to account for the inflation of science, our study points
to the need for a systemic overhaul of the counting methods used to evaluate
citation impact - especially in the case of evaluating science careers, which
can span several decades and thus several doubling periods.
