Re: The 1920s onwards
Actually the 1780s to 1800. Programmable power looms, then in 1800 we entered the Electrical Age (Steam was well established), due to Volta's battery. Hence Shelly's Frankenstien's Monster 1821 approx (there were revisions). Before the end of 1800s there was telegraph, lead acid batteries, dry cells, fax, voice telephony, radio, cars (Steam, Battery Electric, Petrol and Diesel), typewriters, punch card census analysis (Hollerith = IBM), Gestetner's Rotary Duplicator, photography, cine, phonograph & gramophone, hearing aids using carbon mic/moving iron, amplifier module, torpedoes. HG Wells WOTW "warships" were already obsolete.
Maxwells famous equations only a hair's breadth from relativity than showed speed of light a constant (Einstein credited him) and the Michelson–Morley experiment was performed over the spring and summer of 1887.
The modern novel is mostly an 18th C development. (Jane Austin rather famous now)
Boolean Algebra for computers and the special non-Euclidian geometry need by Einstein for his 2nd Relativity equation.
Improved vacuum pumps and the CRT (UK and Germany).
Though SF can be argued to seriously start with Lucian's True Stories (about 150 AD?) they really took off due to 19th C industrialisation, science, mathematics and tech. Verne's 20,000 leagues was all based on EXISTING tech, he'd been inspired by a model of a French military submarine.
Books were still only for well off people. Most people in 1830s to 1850s saw theatre productions of Frankenstein rather than book. London had many theatres with up to 5,000 people a night.
The whole Victorian pre-Raphelite, neo-pagan, Celtic literature (English translations) and thus Fantasy writing took off in Victorian age, which fed into SF. Dracula (based on the Irish myths & lenann shee more than central Europe, he was Irish), McDonald's Lilith and many otthers without which SF would be rather boring (how much a debt does Hellconia owe to Fantasy?).
Tolkien new all the Victorian stuff, though LOTR is more based on Celtic, Teutonic and Norse myth. & legend.
EE "Doc" Smith in late 1920s "invents" Space Opera (he puts impossible "jokes", he knew science and that Iron is the lowest state were Fusion and Fission end, so the spacecraft powered on Iron is an "in joke").
By the 1980s SF had seriously gone off and is now most is too Transhumanist "religion" and indulgent fantasy (Nano everything that's really just magic, immortality, General AI, resurrection clones and mind transfer to computers, the stuff of the comic end of SF in the 1940s).
I like Aldiss's earlier works.
Biting the hand that feeds IT
