Blasts from the past
How can the significance or usefulness of a scientific paper be measured? One way to do this is to count the number of times that a given paper has been included in the reference lists of other papers. This citation approach can be applied to individual papers or scientists, and also to journals, areas of science and whole countries. However, the number of citations cannot easily be equated with the overall significance or usefulness of a paper. This is true for recent papers, the long-term significance of which may not yet be clear, and also for many older papers that are not cited because their results are now so well known that they appear in textbooks. It would be easy to theorize and speculate about these matters, but there is a much more satisfactory way to proceed: as is always the case in physics, the best way to make progress is to collect and analyse data.