->"[[IfMyCalculationsAreCorrect If our calculations prove to be correct]], this will be the most frightening discovery of all time."\\
-- '''Dr. Bronson'''

''When Worlds Collide'' is a 1951 sci-fi film produced by George Pal (of ''DestinationMoon'' fame) and directed by Rudolph Mate. Based upon the 1933 novel by Philip Wylie and Edwin Balmer, it follows a group of astronomers who discover that a star is on a collision course with Earth. They work to build a spaceship to carry a small group of humans to a passing planet in an effort to save humanity.

This is often considered the first true impact event film and one of George Pal's best works.

The story was slated for [[TheRemake a remake]] in 2012, to be produced by Creator/StevenSpielberg.

!!When Tropes Collide!
* AdaptationNameChange. Bronson Alpha and Beta from the book become Bellus and Zyra.
* AcePilot: Randall. It actually becomes important only in one particular plot point (see Plot Tailored, below).
* AmericaSavesTheDay: Dr. Hendron's rocketship, which will take a grand total of forty people to their new world. Mention is made of other rockets being built around the world, but we never see any of them, nor learn if they were completed, launched and/or landed successfully.
** Until the sequel novel, ''After Worlds Collide,'' published a year later, in which we learn that multiple rockets, launched from multiple nations, reached Beta.
* ColonyDrop / TheEndOfTheWorldAsWeKnowIt / EarthShatteringKaboom: Whether Bronson Alpha / Bellus is a star, a not-quite-stellar Brown Dwarf, or merely a humongous, rogue gas giant, the end is the same for Earth.
* CorruptCorporateExecutive: Stanton. While we never see any evidence of his actual business practices, he has a rather unpleasant personality.
* BetaCouple: Eddie and Julie. The kicker: [[spoiler:his number comes up for evacuation, hers does not, and he rejects his winning number to stay and die with his beloved. Both are given passage at the last minute, though at a very steep cost (see HeroicSacrifice below).]]
* DieselPunk: A [[http://en.wikipedia.org/wiki/Differential_analyser differential analyzer]] (admittedly at the cusp of its own obsolescence in 1951) is used to calculate Bellus's course.
* EvilCannotComprehendGood: Stanton, who freely admits to being completely selfish, expects that the human race will [[TakingYouWithMe tear itself apart in an attempt to escape the disaster]]. "It's dog eat dog -- the law of the jungle!"
** GoodCannotComprehendEvil: By way of contrast, Dr. Hendron firmly believes that humanity will reveal its noble side as they FaceDeathWithDignity.
** In the end, [[spoiler:Hendron]] admits that [[spoiler:Stanton]] was right.
* ExtraExtraReadAllAboutIt: After Hendron is laughed out of the UN, we see a newsboy announcing the latest news.
* {{Genre Bust|ing}}er: Generally considered a SpeculativeFiction story, but the film is more a human drama, studying and tracing out people's psychological reactions to TheEndOfTheWorldAsWeKnowIt.
* HeroicSacrifice: [[spoiler: Hendron keeps himself and Stanton]] from boarding the rocket in order to lighten the load. As it turns out, their sacrifice was crucial as the fuel still runs out too soon.
* IfMyCalculationsAreCorrect: invoked nearly word for word.
* IgnoredExpert: When Dr. Hendron first takes his warning of the impending ColonyDrop to the U.N., they literally laugh him out of the room.
* IKnowYouKnowIKnow: Toyed with; Randall initally must bring some data from one Dr. Bronson to Dr. Hendron for analysis and confirmation, but he (Randall) has no clue what the data is, much less [[ColonyDrop what it means]]. When Joyce Hendron meets Randall, she assumes he already knows the details and speaks candidly to him; he plays this up in hopes that she will [[YouJustToldMe let slip what's going on]].
* InfantImmortality: The little boy is one of three people who doesn't need to Lottery his way onto the ship. Which, given the situation, is probably entirely justified.
* IWantMyBelovedToBeHappy: [[spoiler:Tony]] steps aside nobly and gracefully (well, eventually) when it becomes clear that Joyce loves [[spoiler:David]].
* {{Jerkass}}: Sydney Stanton, the wheelchair-bound financier.
* LotteryOfDoom: Only forty people can fit onto the rocket and thus escape the end of the world. A few seats are reserved for the expedition leaders (Dr. Hendron, Joyce, Tony, Dr. Frye) and a couple of select passengers (Randall, Stanton, the little boy and his dog).
* MoneyToBurn: David does this after learning the world is ending.
* OnlyInItForTheMoney: Randall, at first.
* PlotTailoredToTheParty: Played with and/or invoked; Joyce manages to cajole the evacuation into including Randall despite the fact (as even he readily admits) that he has no skills necessary to the trip -- until it is pointed out that [[spoiler:should something happen to the ship's pilot, only Randall could fly it]].
* TheProfessor: Dr. Hendron, Dr. Bronson.
* RaygunGothic
* RetroRocket: The Ark, although it's not a tail-sitter (it launches from a gigantic ramp).
* RomanticFalseLead: Tony
* SceneryGorn: Planet Zyra's close call with Earth causes massive earthquakes, typhoons, tsunamis, volcanic eruptions and all other manner of StockFootage.
* SciFiWritersHaveNoSenseOfScale: Dr. Hendron says that Bellus is exactly three billion miles from Earth. That is precisely the orbit of Neptune, and it is hard to imagine that a star heading for Earth wouldn't be seen long before getting that close.
** The opening line of the film says that Bellus and Zyra have moved a million miles in two weeks. Later, upon hearing they are three billion miles away, David laughs and says people will need to worry in a hundred years. At that speed and from that distance, it ''would'' take a hundred years to hit Earth, not the eight months that pass in the film.
* ScrewTheMoneyIHaveRules: Dr. Hendron [[EnforcedTrope enforces this]] upon Stanton, who wants to finance the rocket in exchange for complete control.
* TechnologyPorn: The differential analyser (a digital/mechanical computer) and the helicopter (still new to audiences in TheFifties) get a lot of visual emphasis.
* ThrowingOffTheDisability: Stanton gets off his wheelchair and stumbles a few steps away from it [[spoiler:to bid the rocket --that is launching without him-- goodbye]].
* WhatHappenedToTheMouse: In the first half of the film, there are passing mentions that similar rockets are being built in other nations. However, after the passing of Zyra, there is absolutely no mention of whether these ships were completed and made it off the planet.
** The book's sequel described the fate of the other ships: the French ship crashed in the Alps on takeoff, the British ship landed in a lake on the new planet, and the broad Asian ship lands successfully and tries to claim the new world as its own.