Is all research connected via citations?
When looking at the paper-is-cited-by-paper binary relation in an undirected manner: Is all research connected to each other or will there be clusters?


First, it's possible to have an unconnected paper. Unlikely, but possible, to write something that has no citations and is never cited. This is clearly an edge case, but you did say all.

Second, all research can connect, but there can still be clusters. The two are not mutually exclusive - fields will cluster, presumably, but there will then be some links between fields. My suspicion, from personal experience, is that these papers will be methodological in focus primarily.


  In other words: Is there a way from a, say, computer science paper to a chemistry paper by walking along the citation graph?


Third, yes, you could get from a CS paper to a Chemistry paper. I know this because I can trace that tree in my own work, and the work my work cites. The path isn't even all that convoluted or exciting.