Fugitive of Time — E.C. Tubb

Starships are grounded, interrupting vital inter-stellar commerce, all the highly-developed industries have stopped, man turns to the primitive sources of animal fat and wood for light and heat. With civilization waning, the young scientist Kleon, sentenced to death for using precious conserves of power in an attempt to generate vast energy from dead matter, makes a spectacular bid for the freedom of the whole universe.