Computer science and information theory were separate from physics. Not anymore. People realized that information had to be physical and this had profound consequences, especially in the form of quantum information/computation.
Psychology and economics were separate. Not anymore. People realized that humans were the core of economic systems and their behaviors fundamentally shape the nature of economies, even at the largest scales. Note the rise of behavioral economics.
Neuroscience and computer science were separate. Not anymore. People realized that thinking about the brain as a computer is probably the best possible abstraction to understand it.
Reality exists. There are no intrinsic boundaries in reality. All fields of study are created by humans. But these divisions seem so natural that nobody realizes that the boundaries have to dissolve. The fields have to collide. And when we realize that--or finally have the language and ideas to meaningfully talk about it--we find out all of kinds of crazy, cool stuff.
So: what collisions are we currently blind to?
Would you say the boundaries are getting lower? With increasing specialization, it seems it gets harder to connect an ever greater number of disparate fields (with a couple of choice exceptions, as you note). Of course, in nature there is no boundary (eg., between chemistry and physics), but there are limits to what fits in a human brain.
I'm not saying anything about specialization. When a collision happens, new people start specializing in the collision region. For example, now there are quantum computer scientists, behavioral economists and cognitive scientists working in AI.
I'm not even saying that all fields have to collide. For example, a historian has nothing to do with quantum physicists because there is no boundary to dissolve, implicit or explicit. But the boundary between history and sociology is a different case. I'm not saying: "Yay! Everything is connected!".
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