In 1974, Robert Dennard and colleagues laid out a law that mattered. Shrink every dimension of a transistor by the same factor, and drop the supply voltage by that same factor at the same time, and the power drawn per unit of area stays exactly where it was, while density and speed alone improve. This is Dennard scaling.

It sounds like magic, and for about thirty years it actually worked. Each generation brought more transistors and faster switching, and yet the chip did not run hotter. Moore's Law kept making economic sense because it had this physical backing underneath it.