Inexplicable Cultural Ties

""The "Parallel Worlds" concept is the key to the STAR TREK format. It means simply that our stories deal with plant and animal life, plus people, quite similar to that on earth. Social evolution will also have interesting points of similarity with ours.""

- Gene Roddenberry in his pitch for Star Trek

While distant planets in fiction are typically different from Earth in many ways (see for example Planet of Hats, Genericist Government, Single Biome Planet), they also exhibit astounding cultural similarities: aliens tend to speak English in the idiom of a 21st-century speaker of English, their written language, numerals and methods of time measurement are conveniently identical to Earth standards or can be easily converted. You might even spot European cars or Vancouver landmarks. Women will have Latin-sounding names ending in -a, wear their hair long and their heels high. Expect to come across proper names imported from Earth.

These Inexplicable Cultural Ties are caused by the fact that Most Writers Are Human and can reasonably expect you, the viewer or reader, to be human as well. Hence, some cultural similarities might be considered Acceptable Breaks From Reality (like a Translation Convention) or result from a limited budget. Others might strike you as avoidable mistakes by the creators of the fictional work.

This trope comes in vastly varying degrees. Sometimes it's just a tiny detail that catches the viewer's eye, maybe a building in the background you recognize from Real Life or a visibly branded over-the-counter prop. On the other side of the scale, the alien planet will exhibit so many implausible similarities with Earth that your Willing Suspension of Disbelief is shattered almost instantly. Extreme cases lead to Space Romans. Also, the similarities might be Hidden in Plain Sight, like a combination of social conventions that are inconspicuous precisely because they are so Earth-like but whose exact re-enactment on a distant planet is completely illogical. As this an Omnipresent Trope for Science Fiction, you might have become desensitized to it. And don't expect the characters on screen to spot Inexplicable Cultural Ties for you - odds are they're crazy Functional Genre Savvy. Instead, consult your fridge frequently.

It's difficult to avert this trope completely in live action settings for budget reasons alone, although good writing can help to pull it off. Actually, as the above quote from the original Star Trek pitch shows, use of this trope used to be a selling point to make live action Science Fiction feasible for the small screen and pull some Aesops in a Like Reality Unless Noted setting. Since then, this trope has lost some credibility due to the rise of harder science fiction and better production values and techniques conspiring to change viewer's expectations. It is something of an Undead Horse Trope, though. Of course, the whole trope is conveniently avoided in case of Aliens Steal Cable or Absent Aliens.

Animated Adaptations and Comic Book Adaptations have the potential to shift a hitherto live action franchise towards visually more alien settings, they still need good writing and design to avoid this trope. Conversely, Live Action Adaptations of animated works or comic books are likely to introduce more Inexplicable Cultural Ties to a fictional world.

Cultural counterpart to the evolutionary Human Aliens and All Planets Are Earthlike, which refers to planetary properties. See also Fantasy Counterpart Culture

Anime and Manga

 * Exaggerated by Space Adventure Cobra: The Animation, which starts with a story where Cobra eventually has to get into planet Galon, which has been isolated for 1000 years, and stop it from crashing into the sun. 1000 years notwithstanding, it has the same language, same architecture, names like Garcia, dark alleys with brick walls, earthlike clothes including hats with brims and jackets for the crooks, earthlike bars, and English writing everywhere.

Film

 * Averted by Orwellian Retcon in a A New Hope where the Death Star's English tractor beam controls have been translated into Aurebesh for the current release.
 * In Star Wars Inexplicable Cultural Ties is often played with in the blatantly Meaningful Names some characters are given, one of the worst offenders being Separatist general Whorm Loathsom. Sith names like Maul and Bane apply, too. The implication is that these names just happen to be meaningful in English or Latin by chance, while the in-universe language "Basic" just appears to be English on account of a Translation Convention.
 * Likewise, different accents and dialects of English are used to distinguish characters' affiliation, background or species to the point that a British actor in The Empire Strikes Back was given an American accent in post to conform to the Rebel-American, Empire-British pattern.

Literature
"The dragon passed like an express train, turned a somersault, and burst over Bywater with a defeaning explosion. "
 * Often played straight in classic Science Fiction novels and short stories, where Like Reality Unless Noted is in effect, for example in Nightfall by Isaac Asimov.
 * Old advice on writing science fiction usually encourages this; it might seem more exotic for alien characters to say "The podnaug is chatnik forgs away, we'll take the whekk", but that's just going to break the reader's immersion as they have to pore over your glossary. As you're translating the rest of the words anyway, you'd be better off just writing "The airport is fifty miles away, we'll take the car."
 * Philip José Farmer's Dayworld books have a minor example of this: he writes in the foreword that the future world depicted has universally adopted the metric system and the twenty-four hour clock, but Imperial measures and 12-hour time are used for the convenience of the reader.
 * Deconstructed in Ursula K. Le Guin's novelette The Pathways of Desire, where more and more suspicious resemblances to American stereotyped notions of "primitive" tribes turn up in the Human Aliens' culture. In the end.
 * Lord of the Rings: At chapter 1, a dragon is compared not only to a train, but an express train:

Live Action TV

 * The original Star Trek was very aware of this trope (as evidenced by the opening quote) but played it straight most of time. The episode Bread and Circuses actually handwaved it, citing something called "Hodgkin's Law of Parallel Planet Development", an alternative title for this trope.
 * Zig Zagged in the new Battlestar Galactica. You see,, including Vancouver, vintage Earth cars and army trucks, Classical Mythology, proper names, Bob Dylan...
 * Mostly averted on Babylon 5: the various Rubber Forehead Aliens' home worlds are usually pretty alien, especially Minbar. The Centauri, however, qualify as pre-revolutionary absolutist space Frenchmen.
 * The Centauri dress like Bourbon Frenchmen. They behave like Renaissance Italians.
 * The hat of the Minbari is tradition, and much of their behavior could be compared to a somewhat idealized(discounting that whole Kill All Humans thing, of course) version of several human cultures. It is their architecture that is alien rather then their culture.
 * Lampshaded when G'Kar mentions that, with no explanation that he has ever been able to determine, every sentient race in the galaxy has, apparently independently, come up with a dish that looks, smells, and tastes identical to what the Narn call "breen" and humans call "Swedish meatballs."
 * Justified in the Stargate Verse by means of an Ancient Astronauts premise.
 * Doctor Who oftens references many very different and alien worlds, but the ones we usually see seem pretty Earth-like, mostly due to budget reasons. Particularly of note is the Doctor's home world of Gallifrey, and the species seen in "Voyage of the Damned"; for a group coming to visit Earth's "strange and foreign culture" they certainly seemed like the British upper class.

Web Comics

 * In Homestuck, the troll civilization of the planet Alternia displays a staggering similarity to ours, notably in culture—they even have the same TV shows and a Will Smith. Justified, however, in that

Western Animation

 * Futurama plays with every kind of Science Fiction trope. This one is no exception:
 * Played for Laughs with the Yiddish-using Decapodians.
 * Inverted by George Takei's George Takei in Where No Fan Has Gone Before: "I've done enough conventions to know how to spell Melllvar." Star Trek, of course, is possibly the chief Trope Codifier.