Perhaps the next big thing, but grounded in some older principles. Chapter 3 attempts to put Reactive into some historical context. The actor model goes back to 1973, and there is a bit about what has happened since then.
The book is intended for developers who have some experience in distributed development and want to extend their knowledge into Reactive design. Most of the examples in the book are in
Java and Scala, with a few nods to JavaScript along the way. If you are a greenhorn in the sense that you do not know either of those languages or do not have any distributed systems experience, I think you will find the book difficult. The concepts cross languages but sometimes seeing a bit of code is what it takes to reach understanding.