In the final part of his series on the connections between developments in physic and music, the late Ian Johnston, physicist from The University of Sydney, explores developments in the twentieth century. In physics, communications technology saw valves come, and go, replaced by transistors, then silicon chips, leading to increased capacity and miniaturisation. In music, accepted conventions of harmony came under attack and composers experimented with more freedom. Musical styles developed using new electronic instruments offering new sounds and capability. In the end, Ian Johnston says the desires of music and physics are the same – both search for harmony.