''[[ExactlyWhatItSaysOnTheTin When Worlds Collide]]'' is a SpeculativeFiction novel co-written by Philip Wylie (who also wrote the [[UnbuiltTrope proto-superhero novel]] ''Literature/{{Gladiator}}''.) and Edwin Balmer. It was first published as a six-part serial between September 1932 and February 1933 in the "King of the Pulps", the magazine ''Blue Book''.

In South Africa, astronomer Sven Bronson discovers a pair of rogue planets speeding towards the solar system from the depths of interstellar space. The smaller Bronson Beta will enter a stable orbit around the Sun, but the gas giant Bronson Alpha [[SignsOfTheEndTimes will cause apocalyptic damage to the Earth through its gravitational influence]], swing around the Sun, [[TheEndOfTheWorldAsWeKnowIt and finish off ol' Terra by smashing into it on its way out]]. It looks like humanity is doomed. But if "The League of the Last Days" can [[InterplanetaryVoyage cross the gulf of space between Earth and Bronson Beta]], some small fraction of the human race might just survive...

…and naturally, they do, since the sequel, ''After Worlds Collide'', was also serialized between November 1933 and April 1934.

In 1951 producer George Pal followed up ''DestinationMoon'' [[{{Film/WhenWorldsCollide}} with an adaptation]].

There was also a syndicated newspaper comic strip, ''[[http://strippersguide.blogspot.com/2011/01/obscurity-of-day-speed-spaulding.html Speed Spaulding]]'', that loosely followed the plot of the first novel; it ran from January 1940 to March 1941.

!!The first novel included the following tropes:

* ApocalypseHow: Bronson Alpha's first approach causes planetary societal collapse through massive tidal waves, earthquakes and volcanic activity. It wipes out the planet entirely on its second pass.
* AmericaSavesTheDay: Zig-zagged. The US government does a magnificent job of moving people and resources away from the vulnerable coasts; unfortunately, the devastation from Bronson Alpha's first pass is so comprehensive that the President can only radio his good wishes to the League from his devastated Midwestern redoubt, and wait for the second pass to finish off the planet.
* DisasterScavengers: People are picking through abandoned New York City even as the streets flood due to Bronson Alpha's tidal effects.
* {{Egopolis}}: The encroaching planets are called Bronson Alpha and Bronson Beta after the scientist who discovers them.
* FrenchJerk: Professor Duquesne, although maybe [[{{Determinator}} that's the type of person you need to be to decide you own countrymen's efforts are doomed to failure and cross the Atlantic and half a continent]] in order to arrive at the Ark [[JustInTime thirty minutes before it launches]].
* HopeSpot: As the first Ark views the impending collision of Earth with Bronson Alpha, they briefly think it may only suffer a glancing blow and survive. They quickly learn that when you're talking planets, [[EarthShatteringKaboom a glancing blow is]] ''[[EarthShatteringKaboom quant. suff.]]''
* ILoveNuclearPower
* LoveTriangle: Between [[AcePilot Dave Randsell]], [[NiceGuy Tony Drake]], and [[MadScientistsBeautifulDaughter Eve Hendron]].
* NextSundayAD: The story takes place "in the middle third of the twentieth century", which would qualify for a book written in 1932.
* NoPlansNoPrototypeNoBackup: Averted; the League of the Last Days launches several test vehicles to try out their atomic engines, and when they complete the first Ark early, they immediately start work on a second, larger one for the rest of the construction team. In addition, other countries are building their own ships.
* PhlebotinumBreakdown: Without the {{Unobtanium}} available to the US team, the atomic engines of the French Ark melt down in mid-flight and it crashes back to Earth.
* TheArk: Five of them - two American, one British, one {failed) French, and one Japanese/Russian/German cooperative effort.
* TwoDSpace: Semi-averted; the Bronson bodies approach the solar system from below the ecliptic. However, when Bronson Beta settles into its new orbit, it seems to be in more-or-less the same plane as the rest of the planets.
* {{Unobtainium}}: The massive tectonic disruptions from Bronson's first pass force a seam of exotic metal from the deep mantle all the way to the surface; [[ContrivedCoincidence it just happens to be exactly what the League needs to line the Ark's engine tubes]].
* UnintentionalPeriodPiece: The plates on which the Bronson bodies were discovered are being shipped to the United States. By oceanliner. There was telegraph and telephone at the time, but this was ''right'' before television or other means of quickly transmitting images.
* WeaponizedExhaust: When a crazed army of survivors attacks the Ark construction site, things look bleak until Randsell starts up the almost-complete first Ark, sets the engine to "1 G", and floats over the attacking hordes in blowtorch mode.
* WeirdMoon: The Moon's orbit is severely altered by Bronson Alpha before it is ultimately destroyed.

!!The second novel included the following tropes:

* AfterTheEnd
* AlienSky: The atmosphere of Bronson Beta contains a higher proportion of noble gases (including neon) than Earth's; consequentially, there are often spectacular aurorae at night. In addition, the daytime sky is blue-green; it is later discovered that this is caused by algae that float into the sky as spores, develop miniature hydrogen balloons, and eventually fall back to the surface as "green rain".
* AncientTomb: Averted; after all, the Vanished People [[ShapedLikeItself vanished]].
* ApocalypseHow: Bronson Beta was also a victim of planetary depopulation, since it held a thriving civilization before it was ejected out of its own solar system by Alpha and its original star.
* ApocalypticLog: After the survivors move into one of the cities, they find written records from the Vanished People that describe the centuries between their discovery that a star was heading for them and its arrival. Apparently they voluntarily reduced their population over time, [[SequelHook but their ultimate fate is unrevealed]].
* BecomingTheMask: [[InscrutableOriental Kyto]] came to the US as a secret agent for ImperialJapan but learned to love its culture and eventually revealed [[CommieNazis the Dominion's]] plan to build their own Ark.
* CallASmeerpARabbit: One of the biologists [[AltumVidetur comes up with elaborate scientific names for the native life]], but eventually they just name them after their closest Earthly analogues.
* CommieNazis: The Dominion of Asian Realists, a group of "fanatical Japanese, Russians and [[ANaziByAnyOtherName 'certain Germans']]" who built their own ship in Manchuria and made it to Bronson Beta.
* CurbStompBattle: After the Dominion sleep-gasses the second Ark's settlement, they fly in troop transports to occupy it and enslave the people. Unfortunately for them, people from the first Ark show up beforehand, find a warning message left by one of the locals, and rig a RayGun out of the Ark's atomic engines. They burn every one of the Dominion's flyers out of the sky.
* DomedHometown: The cities of the Vanished People.
* HarmlessFreezing: The entire biosphere of Bronson Beta seems to come back to life without any problem after it thaws out under the influence of the Sun; in addition, the domed cities and all the equipment, food, and machinery within them are just fine.
* HumanAliens: While exploring the city of the Vanished People/Million Years Dead, they find a picture of one on a wall. She looks perfectly human. Later video and audio recordings confirm this trope. Their clothes fit the humans, but the shoes don't quite work.
* InstantSedation: One of the people from the second Ark's settlement barely has time to write a warning note about the Dominion's sleep gas attack before they fall unconscious.
* NoBiochemicalBarriers: Soon after arrival, a mysterious disease sweeps through the first Ark's people that sickens many and causes a couple of deaths. Later on, the find that the massive stockpiles of grains and meats they discover in the domed cities are perfectly edible.
* PassingTheTorch: The chapter is even titled ''"Tony, I pass the torch to you!"''
* [[FantasyWorldMap Science Fiction World Map]]: The book includes a chart of the rearranged solar system and a map of the Arks' landing area on Bronson Beta.
* RagnarokProofing: The cities are not only still in pristine shape, but repair themselves.
* SequelHook: The book leaves open the possibility that the Vanished People may reappear (did they die off, fly off into space or go into cryogenic suspension somewhere?), but no third book was produced.