Anne Leckie’s Translators. Aliens so alien that the only way we can have any shred of common ground is by them taking a few humans and rebuilding them specifically to be their ambassadors, with interesting results.

The Uplift Series is a gem. Copied directly from Wiki because it's succinct yet thorough:

The Five Galaxies are filled with alien races, all of whom were "uplifted" into sentience by another race through the use of directed breeding. As "payment" for being made sentient, the uplifted races are subservient to their uplifters for a period of time. All existing races have reached sentience through this process, and follow a common evolution in which the races become free of their uplifters, enter a period of independent power, and then fade and eventually disappear.

The arrival of a human ship at a populated star upsets the established races as humanity reached sentience on their own. This had been believed to be impossible, nothing of the sort is known in the eons-old galactic library. This leads to great arguments among the alien powers. Humanity begins to uplift other species on Earth, including chimpanzees and dolphins, but does not demand subservience.

my favorite trope that i dont see enough of in movies is realistic galactic travel and all the tech that would require.. travel to another star system.. usually multi-generational attempts. feels like there is a lot of this in books.

you often see a brief glimpse, or some hand waiving with hibernation techniques. not much feels real.

This is a bit of a general one, but I have a fondness for very large space structures. A number of my favorite scifi stories take the premise of "exploring a (usually abandoned or tech-regressed) alien megastructure".

Dyson spheres and ringworlds and stellar engines and the like are the obvious candidates, but honestly I like smaller (but still huge) ideas like oneill cylinder colonies just as much, because what I like in them is a function of both size and how close to understood physics they follow, and the latter tend to be easier to make plausible.

There's a certain sense of inspiration that comes of someone describing something almost incomprehensibly huge, explaining that it is designed by intelligent entities, and then justifying it with enough real science as to convince you that something at least somewhat like it really could exist, someday, or maybe already does somewhere out in the vastness of the universe.

The book writing technique of the D'ni from Myst. It was not magic, it was essentially math and virtual reality. It just was in hand written books you could enter by placing your hand on a window instead of walking into a big room like the holodecks of Star Trek.

In Doctor who spin-off media there exists a voodoo time-travelling cult called faction paradox. They wear bones and skulls. To obtain these they find a species, hunt them, then go back in time and prevent that species from ever having existed in the first place

So they’re wearing the real bones of creatures who never evolved and never existed

That’s pretty cool

A couple from from Douglas Adams' Hitchhiker's Guide to the Galaxy series have always stood out to me:

The Infinite Improbability Drive is used to propel a spaceship by means of increasing improbability to infinity. It ramps up improbability at your departure point until you are literally everywhere at once since everything is possible, then ramps it back down leaving you at your destination. The offshoot being a whole lot of highly improbable other things happen in the vicinity.

The Total Perspective Vortex is a machine that upon entering gives one a perfect sense of perspective of the entirety of existence (which it derives from a piece of cake.) No one emerges sane. It was invented by a guy to get his wife to stop nagging him.

Speaking of Alastair Reynolds, concept of Pattern Jugglers - benign algae-like pools that oscillate in strange image-like patterns and can physically connect, read, and modify human brains. A person entering the Pattern Juggler could experience someone else's life, temporarily gain skills or knowledge, or... die.

In Ursula LeGuin's Left Hand Of Darkness, I love the idea of society without war. There is still violence and murder, but fighting on someone else's behalf must be viewed as incredibly absurd and unacceptable.

Department Of Truth comics are based around the idea "what if what we believe becomes true?". So cryptids, UFOs, and conspiracies exist because enough people believe in them.

The depth and mechanics of Orogenes in N.K. Jemisin's Fifth Season / Broken Earth. It's not just "I cast frost", it's heat and energy manipulation, with sense, direction, and geometry.

I can't remember what book it came from, maybe one of Peter F. Hamiltons, but portals was a thing. So naturally the superrich had houses where rooms were not on the same planet. The doors between the rooms looked normal, but was portals to the next room somewhere else.

Especially the toilet tickled me. That was situated on an open raft on a deserted ocean covered planet.

The evolved species in Adrian Tchaikovsky's "children of time" series. So much thought and detail went into them and he's a fantastically descriptive storyteller. His command of language is superb.

I don't want to spoiler too much beyond that but it's easily my favourite series.

"We're going on an adventure"

Elite Dangerous's Frame Shift Drive having both modes of operation with the standard Alcubierre drive which allows you to do FTL by contracting spacetime around your ship (hence frame shift) or near instant system travel by creating a wormhole to travel through.

The catch is that while supercruise has been around for a long time and works just as you expect, the wormhole hyperjump is new reverse engineered tech by captured Thargoid technology.

The drive uses mass to guide the ship to the destination, meaning it can only work by locking onto primary stars of a system. You can only make wormhole jumps between systems but must use supercruise to get to where you actually need within the system.

Also that mass affects its operation:

Being close to any mass will affect the FSD charge time. While being next to a heavier ship will merely make it charge slower, the FSD will get mass-locked should the ship be next to something extremely massive (station, asteroid field, etc.) and will be unable to charge at all.

The wormhole network of the Nasqueron Dwellers in "The Algebraist."

Niling d-sinks, from Peter F Hamilton's Commonwealth novels.

The Planet Express ship from Futurama (it would take too much energy to move the ship at FTL, so it moves the universe instead.)

Since I read Stranger in a Strange Land long ago. I keep coming back to the idea of an indoor lawn.

It's an idea that seems fairly complicated when you get into the details, but also there's no real reason it can't be done.

My current favorite topic is the idea of a world ark, a self-contained world adrift in space containing the remnants of life from a doomed world, and the inhabitants aren't aware of it. Intetestingly it has been featured in two different games: SOMA and Genshin Impact. I'm currently working on a TTRPG campaign within such a world.

I love science and technology vs. the supernatural. I think it started with Ghostbusters when I was a kid.

Any time any movie or TV show attempts to battle the supernatural with technology I am glued to the screen. Anything from movies like Oculus where you try to confront an ancient evil with real-life modern tech to inverse movies like Event Horizon where oops...my future tech unleashed evil.

I don’t recall which book. But there was one with truth in advertising laws. I feel like it was Larry Niven. Anyway, the laws were the result of improved sucsess rates for organ transplants. It's really only a side point, but I loved how they were connected.

piers anthony has a series called I think kirilian quest. There is no ftl and the law of physics as we know them can't be circumvented (I think its been awhile but maybe its real difficult and rarely used). Anyway all civilizations eventually realize astral projection is possible and time and space make no difference. Thing is it takes two types of people to work. People with strong auras can project and people with weak auras can be possesed. Its not a requirement but more it will work better and last longer. Anyway people with the strongest auras get jobs traveling and people with the lowest get jobs as vessels. This is how communication between societies in an intergalactic culture communicate and interact.

Okay, absolutely not realistic, but one of my favorites is XANA and Lyoko from Code Lyoko. XANA an AI contained in a nuclear powered supercomputer and is evil. Lyoko is a virtual world within the computer and the only way to stop it. Basically, a group of students at a nearby school have to head over to an abandoned factory where the supercomputer is located and go virtualize themselves into the digital world in order to guide someone who can stop XANA attacks.

XANA is a pretty unrealistic AI villain since it can take control of non-electronic things, control gasses, and even control living creatures. It's a deadly menace that in one episode turned lamp posts into antigravity devices. That kind of unrealistic, yet terrifying AI villain because of just how dangerous it is.

Always fun to come up with horrifying ways that XANA could destroy the world if the main characters ever failed. Or if it was real.

I really like sci fi settings where there is one major leap of physics that has ramifications across the rest of the setting.

Mass Effect is my prime example with the discovery of mass effect fields that allow the manipulation of how much mass things have. This is the basis for local interstellar travel after using a mass relay, as the mass of the ship is reduced for acceleration greater than the speed of light. Artificial gravity is created by increasing the mass of the floor. Guns work by electromagnetically accelerating bullets through a reduced mass field for greater acceleration, while shields work by emitting repulsive mass effect fields.

In The Expanse, the only technological breakthrough that doesn’t feel like a natural extension of modern technology is the Epstein Drive. The only thing it does is make propulsion engines fuel efficient enough that they can burn nonstop between destinations, which allows a ship to constantly accelerate to its destination instead of reaching a maximum velocity then floating the rest of the way there. It cuts down travel times between planets from months/years to weeks, and allows the society presented to exist.

I'm boring and I really like rotating megastructures. I think what I find fascinating is they're feasible for us to make IRL if we somehow figure out refining on the moon and mass drivers (ignoring the economics too lol) since they use conventional materials even for relatively large ones.

Everyone is always focused on terraforming or colonizing distant planets. A rotating habitat is engineered to be exactly what we need better than any planet we can colonize.

Life on Mars would be demonstrably worse. You need to bury your habs under meters of regolith to not kill your colonists from radiation. Going outside is a space walk with a laundry list of items you need to attend to with little to no time to enjoy being outdoors (you're in a suit regardless which means it sucks to some extent no matter what)

A rotating Hab means you can live much closer to how you live on Earth

I think my favourite is just when they play with the unknowable. Things so different from humans they operate on different principles and see the world differently.

Sure you see this in fantasy and horror a lot with like the house in House of Leaves or Cthulhu but I'm also thinking the TechnoCore and Shrike in Hyperion, maud'dib in Dune, or the black stuff in the Expanse series. I just like alien stuff that's, well, alien

Wormholes always kinda rubbed me wrong in sci-fi. They're always depicted in a way that screams fantasy, not science, with only one exception that comes to mind, which was Interstellar's depiction of a wormhole as a sphere, even taking the time to explain why it looks that way.

The only got it half right though, since as soon as they enter the sphere it's straight back to the fantasy BS with the blue tunnel. That scene could have been a really cool transition of entering the one 'side' of the sphere while exiting the other simultaneously. Cut from the crew's perspective seeing lens-like distortion of the stars, to an external view of the ship moving into the sphere.

I kinda feel like that's how they intended to do that scene, with the whole buildup about the sphere, but decided to throw a nod to oldschool science fantasy for some reason.

Oh well. They got it half right, and that half was pretty fucking sick - it was the first presentation of a wormhole that didn't instantly yoink me out of suspension of disbelief. Until the blue tunnel ofc, at which point, yoink.

To answer OP's question, I guess for me it's less a specific concept as it is presenting something possible only in theory in a believable way. The whole lens-distortion style transition would have been way less flashy, but less can be more.

I love the dying earth trope. Its earth, but millions if not billions of years after present day. I love thinking about what the humanity of today might leave to be discovered by whatever comes next. I think the first real exposure I had to it in media was that Artificial Intelligence movie from 2001. Its been around in fiction a lot longer, but that was the first time I really "got" it. Its so neat to me to think about how an alien (or a distantly removed human) might interpret the present day.

It's so hard to choose just one. Relevan to OP's post is a part of Revelation Space where someone is pushed into a long elevatr shaft on a lighthugger, and she uses the Conjoiner engines to stop her fall relative to the ship, and ends up beating her assailant to death with the floor and ceiling as she adjusted the ship speed back and forth at 10g.

In Adrian Taichovsky's "Alien Clay", there is a planet inhabited by symbionts. Everything is symbiotic with everything else. You'll have a creature, but it's made up of a critter that can digest food, a critter that can see, a critter that can move, a critter that can defend itself, etc.

Neal Asher's "Polity" books depict a future where AI has taken over, and it's a good thing, because humans are such murderous evil dipshits.

"A World Out Of Time" had a guy who was frozen, woke up in the future, was forced into becoming a bussard ramjet pilot, and his attempt to get away from this situation landed him in another, weirder situation. There was a weapon mentioned in this book that would make you wish for death. "If you lie to me, you will take your own life. When I let you."

The Well World, divided up into hexagons, each hex having an entirely different climate, ecology, and technological rules.

"A Deepness in the Sky" by Vernor Vinge had a space faring civilization that didnt use hours, minutes, years, etc. Everything was seconds. Centiseconds, kiloseconds, megaseconds. It made sense for these people who were always in space, always on ships.

Another thing I like is all the various propulsion methods that different authors come up with. Conjoiner engines, is just one example. Niven wrote about a type of hyperspace that moves at exactly one speed, (Or another, faster speed) and looking outside the ship will drive you mad. Alderson drives work instantly, but you have to be in exactly the right spot for it to work. The rest of the time you're stuck with fusion rockets accelerating as fast as the humans on board can stand.

A tardis from Dr who. It's a living spaceship + time machine.

It also has some insane features like:

1. It's bigger on the inside. In fact it has infinite rooms and storage.

2. It also has access to all knowledge across time.

3. It can instantly translate all languages telepathically. So everything you hear and see will automagically be in your language.

4. It can take any form physically. On both the inside and outside. It has a chameleon circuit which makes it blend perfectly into the surroundings.

It's said that it's destiny to be chosen by a tardis. It reads your thoughts and takes you where you want to go or where you are needed.

You might be interested in browsing through this site:

https://projectrho.com/public_html/rocket/

It talks about a lot of sci fi tropes from a hard science perspective, and goes over FTL specifically:

https://www.projectrho.com/public_html/rocket/fasterlight.php

It's kind of a downer site in some respects because it does a lot of "here's why your favorite sci fi series is unrealistic", but in that discussion there's a lot of looking at interesting tropes and concepts. There's also a good explainer for FTL specifically here:

https://www.physicsmatt.com/blog/2016/8/25/why-ftl-implies-time-travel