Alexander If you search for “fluctuations” OR “fluctuations” on google, it will give you about 97 Million entry points. For the last 23 years I have been tracing through these kinds of searches to see exactly what people are doing with terms like “fluctuations”. As you can imagine, this particular term, “fluctuations” has lots of groups who use it in many different ways.
“fluctuations” “quantum” gives 38.3 Million entries, so your intuition that it (“fluctuations”) is often connected to “quantum” is right. But if you want to find the core of where the term comes from, how it is measured, what you can do with it — you probably want to look at “statistical mechanics”, “aerodynamics”, “thermodynamics”, “electromagnetics”, “gravitational”, “vacuum”, “fluid dynamics”, “circulation”, “vorticity” and related terms.
My general recommendation, if you want to treat “fluctuations” seriously, is to look where it is measured, or where its properties affect performance and applicability of some system. One good problem is to reduce noise and “fluctuations” in plasmas, during combustion , in engines of all type, in pipelines, in flows of fluids and energy. I routinely look at millions of pages on the Internet. It is a classic problem. People say “review article” and they have read a few hundred papers, or a few dozen books. Then I look at my daily logs of what I have covered, and see where I have had to look at, try to understand thousands of groups, with millions of individuals – usually every one of them working hard on some facet of something like “fluctuations”. So, to me, it is not a five minute or five day or five year topic, but rather something that consumes million of human hours each year. Almost always everyone doing their own thing, not sharing, not working toward anything consciously.