Most SF isn't written by scientists, but it helps if the scientific content is accurate or at least vaguely plausible. Some classic howlers follow, leading up to a recent novel with thrilling new depths of scientific bollocks.
Yes, SF often uses magic science like force fields, but we still need common sense. Look at L. Ron Hubbard's Battlefield Earth, featuring a stack of atomic bombs encased in an "impenetrable" force screen. The first bomb dramatically goes off, converting everything inside into white-hot radioactive plasma – and the force field just barely holds. Then, with mounting tension, the second bomb (which was sitting next to the first, and just got vaporized) explodes. Then the third ...
Judith Merril's The Tomorrow People featured a helicopter flying on the Moon, in near-vacuum. Anne McCaffrey managed a subtler boo-boo with All the Weyrs of Pern, where – again in the hard vacuum of space – things are held together by suction cups. Fritz Leiber's The Wanderer not only features that old favourite, laser beams visible in airless space, but describes them as staying visible, zooming away to infinity, for minutes after the firing stops.
Larry Niven slipped badly in the first edition of Ringworld (which is thus quite valuable, like a misprinted stamp with the Queen's ears upside down): he has Earth rotating the wrong way. Even better, Brian Aldiss's short 'His Seventieth Heaven' describes a satellite that 'orbited Earth once every twenty-four hours, three thousand two hundred kilometres above the centre of the Earth ...' That is, over 3,000 kilometres below the surface. Philip E.High showed off his geometry homework in Twin Planets: 'The alien device was a blank, black cube about a foot high and three feet long.'
My latest, treasured source of scientific codswallop is Jeff Long's The Descent, whose blockbuster concept is that Hell is real, a worldwide labyrinth of deep tunnels packed with cannibal horrors, whose countless entrances were overlooked until just now. I didn't mind Long bending known facts about plate tectonics, or temperatures and pressures miles underground, but other bits made me gibber.
One scene features a Bosnian mass grave that's being disturbed by nasties and 'therefore' emits gales of nitrogen (methane maybe, ammonia maybe, but nitrogen?), so much that helicopter engines stall for lack of oxygen (oh dear), and when someone who's breathed this nitrogen gets a reviving whiff of oxygen he instantly dies of the bends – caused only by decompression. Blimey.
Meanwhile, humanity's underground relatives the 'hadals' have evolved super nocturnal vision, and their weird environment causes knobby growths of calcium, i.e. horns. Therefore, when a soldier who hasn't been down the tunnels sees some hadals, he promptly develops super nocturnal vision and horns.
Then the Turin Shroud bizarrely enters the plot, and we learn how its image was really formed. A small statue coated in 'a low grade isotope, newtonium' (not in my Periodic Table) is held over a blank test shroud. Without even introducing the unlikelihood of a lens that focuses hard rays, an image of the statue appears: 'The radiation heats and weakens the fabric on one side, creating an image. If I hold my statue here long enough, the cloth will turn dark. If I hold it higher, the image will be larger.' Argh!
Best silly remark about the Shroud image in Long's book: 'He's too anatomically correct to have been created by an artist.' Which reminds me of Erich von Daniken's argument in The Gold of the Gods that because our ancestors carved accurate human skeletons in stone, they must have been taught anatomy by alien visitors: 'As we know, Roentgen did not discover X rays until 1895!'
Radio also goes pear-shaped in The Descent – a message from the deeps is delayed because 'the transmission bounced off the upper mantle and came back up through basalt that was folded. In short, the transmission was lost in stone for five weeks.' It must have been rather faint by then, after travelling back and forth for nearly a thousand billion kilometres. On other occasions, and for no apparent reason, radio signals slip backwards in time.
Let's be fair: Jeff Long's book works, more or less, as a paranoid and over-the-top horror novel. Pity he mucks this up with grotesque chunks of pretend science – reminiscent of famous Dean R. Koontz describing lasers in his early, wisely forgotten SF epic Star Quest: 'Laser cannon erupted like acid-stomached giants, belching forth corrosive froth ...'
David Langford only belches corrosive froth after a vindaloo.