Wouldn't they follow similar engineering principles? What forces them to create weirdly shaped structures in movies/games?
You appear to have a perspective problem. In this case, that can be taken quite literally. After all, we have some really weird structures on Earth that were designed that way. A thing is weird only because it's not encountered on a regular basis.
Architecture is also a very subjective thing. It's as much an art as a science. An architect is just as often concerned with the appearance of a design/structure as with its functionality, and there have been plenty of architects who create fantastic and functional structures. So what humans consider to be a weird design could be an accepted norm for an alien species.
There's also a difference in species. An alien species may not have the same spatial needs as a human and their structures are designed towards those needs.
Environment also plays a role in determining the design of a structure. One wouldn't want to put a square building in a location with high winds; a rounded structure would better resist the wind. Sloped roofs are preferred in snowy regions, to prevent the snow from building up and collapsing the roof.
Finally, and maybe critically, there's the Rule of Cool. People go to the movies to see extraordinary things, not to be reminded of the places they live or work.
As always, the answer is "Lots of reasons"
For storytelling purposes, having a clear visual difference between cultures or species is very important. It provides an immediate, intuitive way to identify different groups at a glance. We're limited in our interaction with most media - we can't smell, taste, or touch the aliens, only see and hear them, so storytellers need to use design to show these differences.
In-universe, it's not entirely certain to what extent our own designs are independent of our psychology. While humans may make a clear distinction between "Inside" and "Outside", another species might not see the world the same way, weaving inside and outside together. If they think more three-dimensionally than we do, they may have structures built that blend what we would see as different floors together much more completely. A collectivist species would probably not understand the concept of having different buildings for different activities at all, or having 'personal space'.
Then there are physical differences. Design can be an excellent way to show physical differences between species, even when they're played by the same human actors in different rubber forehead prosthetics. Compare these weapons from Star Trek:
While the configurations are similar, notice that the grip of the cardassian weapon extends from the body at pretty close to 90 degrees, an angle that a human would find very uncomfortable. The bajoran weapon has a much more familiar angle to its grip. This fits the fact that cardassians are intended to be an enemy species that look very different from humans, while bajorans just have bumpy noses. The design in this case is intended to suggest that different species not only have different rubber prosthetics, but that their limbs are hooked on differently.
So, while all species face the same structural design considerations, the goal they're trying to reach with their structures and technology can be very different, and they may be working with different physical needs - all of which can justify some very different designs, and keep concept artists fully employed.
Other people explain this well, so I'll just leave pictures. Short answer, is that there is more than one way to accomplish the same task. Consider the differences between United States and Russian crewed spacecraft:
Now I'm over simplifying a little. These crafts were made in different eras, for different purposes (general Low Earth Orbit vs Moon missions), but you can see that there is a clear aesthetic difference between the two. Engineering can be done many different ways and still accomplish the same task. When all of the engineering constraints have been met, you have to just do aesthetic design on what is left, and that is informed by budget, culture, resources, and more. As far as movies/tv/other medium are concerned, it provides an easy way for the audience to tell the different factions apart.
Form follows function
Why are modern cubesats made with 90° angles, as opposed to cylinders like you normally picture rockets and modules to be?
For inhabited modules, roundness is best for holding air. For equiptment racks, stackable blocks are best.
Seagoing vessles are an excellent study of how shape plays a role in function. The streamlining or the bulb-nose; outriggers, pontoons, or hydrofoils; all are engineering features with function and reflect different approaches.
An alien ship will look like it does because of the technology used, plus other issues such as launching support and to cope with any special environments it encounters.
Solar sails or microwave wisps have characteristic looks for the tech. Pressurized modules look like propane tanks anywhere in the galaxy.
Form follows building tecnique
Future and/or alien tech may look like vegetables, not boxes, because they are “grown”. Systems that hook up using superconductive flux pinning may end up with distinctive protrusions because of the material located right there to guide the flux. Ships built using a nanofab with a 1-meter orifice will end up looking like a tangled ribbon.
Boils down to aesthetics. We tend to gravitate towards symmetry as our general design, and much of what is natural on earth follows a pattern of symmetry. However, the fact that we as a culture see that as "beautiful" we try to design a structure for something that is alien to that viewpoint. The assumption is that the thinking of other life elsewhere will NOT be like our own, which results in buildings we might find ugly, highly inconvenient to build, aesthetically irregular, etc. Purely because if we built them in the image of our own designs it wouldn't "feel" alien.
There is an opposite point on this that I'd like to suggest as well. Most of the time we view alien life as more advanced than our own. Therefore their ability to design seemingly impossible and strikingly beautiful structures can also be factored in. In this respect art is a highlight of intelligence and so it might follow an advanced being might actually have a superior aesthetic pallet compared to our own.
Lastly, taking into consideration material on hand, gravitational differences, technology, air and water quality, geology, etc. Building sky scrapers might not be feasible or could be far simpler (on lower gravity planets). So on a large planet you might see many squat buildings, or underground facilities because larger buildings might have too much stress to stand. And on small planets you might have spidery, fragile-looking buildings that would otherwise collapse here on Earth.
I'm going to throw my two cents into this. Every other answer on here makes good points, and several touch a little on this idea, but none quite spell it out.
The in-universe reasons for these differences, if they are even explained at all, are almost always just the result of being shoehorned in to fit an aesthetic, say something about the species/faction, or give an excuse to just have them look different.
Whatever the case, 9 times out of 10 it is simply a means to an end. When building a universe, it behooves the creator to design other species or factions markedly different from what we're used to for several reasons. Here are just a few examples:
- Visual differences allow the viewer to easily distinguish between groups.
- Extreme ("alien") differences create intrigue and sometimes fear or other emotions depending on the design. Just think, what's more intriguing: An aircraft hovering by using rotor blades, or a solid, featureless sphere that hovers with no visible source of power?
- If the aliens had design aesthetics that resemble our own, it would create an immediate amount of sympathy with them. The viewer would on some level relate to the aliens, and therefore they would seem less "alien" and more like a long-lost sister species.
And that's just for starters. But the point is this:
TL;DR Aliens looking different from us is usually just a device to affect the viewer's impression of the species. Any in-universe explanations for this almost always are designed to fit the aesthetic, not the other way around.
I think there are two completely different questions here. "Why do movies and games depict alien engineering as weird-looking?" and "Would alien engineering really look weird?"
The first question is easy to answer. They design it that way so that it looks distinctive and cool. That's what we watch movies and play games for: new experiences that are cool. Designers can make things whatever shapes they want; the only constraint is that they don't break the suspension of disbelief for most people. And when you tell them it's alien, most people shut their brains right off.
The second question is much harder. But I think the answer is it would look a lot less weird than most people think. Engineers need to make things that work. They are constrained by things like math and physics, which are universal.
For example, human engineering uses lots of squares and right angles. This is not an arbitrary choice. Rectilinear shapes are easy to treat mathematically (computing areas and volumes, constructing the angles and so on) and they pack easily in two- and three-dimensional Euclidean space. We should expect alien engineers to show the same preference for rectilinear shapes because they would get the same advantages from them.
Even aesthetic concerns aren't as arbitrary as you might think. For example, we happen to like simple geometric symmetries. But that's not a construction of our culture; people all over the world and all through history have shown a fondness for geometrical symmetry. Turns out it's an evolutionary adaptation: symmetrical structures are easier to balance. And engineers continue to use symmetry, because it works. We should expect alien engineers to favor symmetry also, for exactly the same reasons.
They only real reason for alien engineering to be different from ours is if they're solving a different set of problems. The aliens might live on a different scale from us (either spacially or temporally). They might require a drastically different environment. (I hesitate to think how hard it would be to conduct a space program for an aquatic species.) Even these differences are limited though. No one's ever thought of a plausible basis for life other than water and carbon. (I mean, maaaaaybe hydrogen fluoride and carbon, but HFl is rare and water is the second most abundant molecule in the universe.)
DL;DR: H. P. Lovecraft felt it was mere arrogance to believe that our human ideas of engineering, biology and morality were universal. But it turns out that stuff is a lot less arbitrary than we thought in the 1930s.
If you want a answer as a person watching the movie/playing the game, it attracts people. It's the same reason aliens look weird. It gives them a more exotic look, more interesting, and makes you want to take more interest in their culture and behavior because if they were to build homes like us and look like us they wouldn't be as interesting.
If you want an answer as a person inside that movie/game - they don't have to follow similar engineering principals. The aliens probably sense the universe differently, so perhaps that could be one of the reasons. They could have different senses, a different way of seeing, etc. which makes every alien community different but with similar aspects. Perhaps their behavior and senses make them think of different things as beautiful (or safer as they also may have different building materials) than us humans.
It often doesn't matter. When you're actually in space, there are a couple shapes that are useful and many more that are serviceable.
A sphere minimizes the surface area to volume ratio. So if minimal surface area is important, a sphere is the way to go.
A cylinder or ring allows for gravity simulation by rotation. So if you expect your spaceship to spend a lot of time in free fall but want an up and down, you need to pick one of those shapes.
If you're going to land your ship, you may find an aerodynamic shape with wings that allow gliding to be important.
Beyond those though, it doesn't really matter what shape you choose. Perhaps your ship will never land, will always be under acceleration (or you have a better form of artificial gravity), and you don't care about minimizing surface area. Then you can choose whatever shape you find attractive.
For those shapes, it's going to be aesthetics, not function, that drives the choices that you make. Aliens are likely to have a very different idea of aesthetic beauty than humans.
And conveniently enough that works with the out-of-universe reason: alien ships should look alien so that we can tell them from the non-alien ships.
We are used to earth-bound structures. Aliens came from different part of the space.
- The have different aesthetics. When two nations on one planet have different tastes why to expect the aliens have the same style as [culture X, age Y]?
- They came from different planet. They may come from heavier planet than the Earth is and thus their structures tends to be touher. If they came from ligter plant they structures may be ligter. If they came from planet with wild atmosphere, their design would be more aerodynamic and tough, if they came from calm planet their design may be more "artistic".
- They have different body shapes and ergonomics. Everything they build is to suit their needs, not ours.
Why are alien buildings/ships unusual looking?
Because otherwise they'd be too familiar, boring and just plain not evil enough. Alien cultures are "supposed to be evil" so that "killing them all" is giving you a "nice and warm feeling".
For further study, the movie "Spaceballs" makes fun of this in such an "obvious and childlike manner" that most people (which includes those without any sense of humor (ooh, incorrect generalization)) can't even see the philosophical, political, sociological and artistic comment that is being made.
It's called Art Direction. It's telling you how to feel about the story and the situation. It's an associative visual language. Art direction is telling the viewer how to feel about the story through visual cues.
If an alien city's buildings all look like Ancient Rome, we can make assumptions about their society, their government, how they will react to strangers. We'll fill in the blanks about their culture and their fundamental values. You don't need to waste time explaining their political landscape or religious history. In Star Wars, it doesn't take long to understand the Space Nazis are bad. In Alien, you know the wrecked spaceship is a spooky bad place full of scary deaths – in fact you know it long before the characters know it. You see it through the art direction.
Unfortunately cookie-cutter production and audience expectations for the familiar often make a mess of it. Too many Hollywood projects mindlessly imitate other Hollywood projects, and too many over-produced films are just CGI-salad to begin with.
Pffft you meatbags with your crude understanding of physics and primitive euclidian geometries.
The underlying assumption that all physical laws is constant across all time and space, or that different forms of life could not have reached different conclusions in mathematics and physics, which could be right, wrong or just different is far less believable than idea that they could have, especially given humanity's limited understanding of the universe.
To demonstrate, take a simple bit of information theory.
- Suppose every decision that is involved in engineering something boils down to a yes or no question (or a range of tolerances which represent a boolean expression).
- Each yes or no decision is 1 bit (or shannon) of information, the nature of which would be decided by the alien environment and the race's empirical observations.
- Suppose for the sake of argument there are only 64 necessary design choices (e.g. straight or curvy, sleek or rough, metal or plastic). Obviously you would have to be more specific, so the real number is significantly higher.
- Now each bit of information is in either the off (no) or on (yes) state that allows for 2^64 states.
In other words for just small number of design choices the possible shapes of ships are an astronomical ~18,000,000,000,000,000,000. The likelihood of an alien ship being anywhere similar to something a human would think up are astronomically different.