Science fiction writers foresee the inevitable, and although problems and catastrophes may be inevitable, solutions are not. - Isaac Asimov

Balcy had left the City and could not re-enter. The City was
no longer his; the Caves of Steel were alien. This had to be; and
it would be so for others and Earth would be bom again and reach
outwards.

His heart beat madly and the noise of life about him sank to an
unheard murmur.

He remembered his dream on Solaria and he understood it at
last. He lifted his head and he could see through all the steel and
concrete and humanity above him. He could see the beacon set in
space to lure men outwards. He could see it shining down — the
naked sun.

I think what we need to do here is to make use of Thargola's Sword. You know what that is, Beenay?" "Of course, sir. The principle of parsimony. First put forth by the medieval philosopher Thargola 14, who said, 'We must drive a sword through any hypothesis that is not strictly necessary,

En la Era Primitiva los derivados del petróleo natural constituían el origen de la energía y la goma natural protegía las ruedas. Desde luego, eso no se aplicaba a ninguno de los Siglos posteriores.