This chapter traverses a terrain of "computers" - the abstract ideas of Turing and Church, the physical computers envisaged by Deutsch and hence quantum computation, the relationship between what computers can do and what mathematics makes possible and ultimately what people can explain and why the universe and reality broadly is comprehensible. We look at the science, the physics and the philosophical consequences of all of this. An inspiring chapter about technology, people and the unbounded possibility of coming to understand reality ever better and thus the physical possibility of always being able to solve problems and make progress.