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Cars are mostly 1d vehicles in practice, unless they are bumper cars. We try really hard to minimize 2d interactions between cars by stacking multiple 1d environments (lanes) and ignoring the 2nd dimension for the most part. Where we cannot ignore it we try to make it safe by adding turn lanes, roundabouts, traffic lights or building interchanges.

Quite true. Which really says a lot about what we don't want in transportation --- more degrees of freedom.

Teleportation tubes on the other hand...

>It's why even modern flight is centered around the idea of stacking multiple 2d environments (via elevation / flight levels) and then just ignoring that 3rd dimension for the most part.

Generally you want to fly at a constant altitude because climbing and descending require energy transfers. Humans have little trouble coping with the concept of 3-dimensional flight, indicated by the enduring popularity of combat flight simulators, but aircraft that aren't built for combat physically struggle (and even in those that are, such flight demands careful energy management).

The answer here is what we have in drones. Drones can stay perfectly still in the air now. A flying car or personal "jet pack" would be the same. The usable system would provide all the stabilization of a drone and your controls would be just that of a car, with a separate setting for altitude.

And just like cars, you wouldn't be flying it randomly, we'd have to build "lanes" at different heights, etc. You don't drive your car randomly through buildings. In fact, connecting to a network and having it fly for you would be the most likely scenario.

Not to say that there wouldn't be "free flight" parks around.

> It's why even modern flight is centered around the idea of stacking multiple 2d environments

That's for sharing the space. It's not only a set of stacked 2D environments, those are also divided in road-like spaces, with a limited number of junctions.

You raise some interesting points here that I had not previously considered with respect to flight/submarines vs. land vehicles/boats. That third dimension must introduce a lot of cognitive load, even before conflict of other vessels/aircraft enter the scene.

There's some sci-fi (that I cannot remember off the top of my head) that actually uses this as a plot point.

I may be misremembering, but the idea is there's a special race of humans who have continued to evolve living in low gravity (space) environment, and the terrestrial human (those living on planets) governments would hire them as space mercenaries because they're at a huge advantage when it comes to 3d combat compared to training some terrestrial guy.

Ender's game; maybe not what you're referring to (based on your description), and also uses 3d navigation as a plot point ('The enemy is down')

This was a limitation of Khan in the second Star Trek film.

There is a trilogy of books written covering Khan's life and it very subtly shows why Khan has this difficulty, but never points at it and shouts.

I had always thought of that line as metaphorical (“two dimensional thinking”), but that’s a very interesting idea, and fits well with the final battle that immediately follows it.

You don't mean The Expanse, do you?

> Humans evolutionarily think about movement with a 2 dimensional mindset because for much of our history we only needed to think about 2d movement.

That might depend on whether the aquatic ape hypothesis is true ;)

More seriously, in addition to diving and climbing, humans have been using throwing weapons for hundreds of thousands of years -- not the same as navigating one's body through 3 dimensions, but it still requires a 3 dimensional mindset because you need to work out where the trajectories will intersect with something traveling in a different plane of movement. So I'd be curious how much hard evidence there actually is for human deficiencies in 3 dimensional thinking compared to say dolphins or parrots.

> Humans evolutionarily think about movement with a 2 dimensional mindset

The humans evolved to brachiate for a lot longer than they've been wandering around savannas.

> even a kid could operate a 2d vehicle.

Trying this was a mistake and nearly got me killed. Twice.

Planes and submarines treat down as special because down is genuinely special. We would have some other abstraction if this were not the case.

It _is_ special but we cannot perceive it correctly. We do not have an absolute sense of "down" (and our absolute sense of "forward" and "backward" are based on a assuming fixed "down").

We sense "down" based on assuming that 1G of acceleration is the "down" position. This is fine if you're stationary. This is fine if you're moving in 2d. But accelerate in 3d and all of a sudden you can get completely disoriented because the "down" you're latching on to could be any acceleration vector.

We _can_ manage this, but it is an acquired skill and we need instruments to help us. Pilots (and especially fighter pilots or astronauts who truly experience a lot of 3d acceleration) need to train for years to acquire this skill.

Can you imagine training an average person years just to _use_ a jetpack? That's why we have jetpacks and yet most people don't care.

Most of the astronaut and pilot training on this, btw, is to completely ignore what our internal intuition is and use instruments and direct math - for the reason you’re talking about, but also because especially at the astronaut level ALL intuition related to speed, direction, etc. is generally wrong. for pilots it’s often only mostly wrong, but using intuition and flying IFR is not going to work for long.

For an astronaut in orbit, going ‘up’ means accelerating. Going ‘down’ means slowing down. Going sideways (in the way we typically think of it) involves changing velocity in least 2 vectors twice, etc.

They have the pointy bits forward AND treat down as a problem as well. Gravity applies equally to Roombas and Cessnas and Soyuz, but only one of those is built on planar symmetry rather than radial symmetry. Don't you agree with that and isn't that interesting, that humans seems to have something about having a forward facing Cartesian plane.

> there have been plenty of plane crashes due to this

JFK jr

The jargon term for this is spacial disorientation.

> Humans evolutionarily think about movement with a 2 dimensional mindset because for much of our history we only needed to think about 2d movement.

Citation required? If you hang out with a child you quickly discover that their world is quite three dimensional. Heck, climbing is a fast growing sport. Again, three dimensional. We're made to run, jump, and climb. Three dimensional.

From NASA: https://www.nasa.gov/audience/forstudents/9-12/features/F_Hu...

"When there is no visual input as is common in many flight situations, we rely more heavily on our vestibular sense for this information. However, in flight and in space, our vestibular system, _which is designed to work on the ground in a 1g environment_, often provides us with erroneous or disorienting information."

We have a system to somewhat understand and orient ourselves in 3d obviously, but it has quirks because evolution tuned it to work best on the ground + assuming 1G of gravity as "down".

Orienting in 3d is not intuitive for us. We can do it but we need a _lot_ of help to do it safely.

Your quote talks about 1g gravity not that 3d is not intuitive. A 3d world with 1g could be intuitive.

> __on the ground__ in a 1g

I've worked for several years with children, and have also piloted aircraft. 3D is _tough_, at least for me.

>Heck, climbing is a fast growing sport. Again, three dimensional.

Ummm… no? The surface of a mountain is still two dimensional.

A mountain surface is 2.5 dimensional. If you allow for the fractal part.

Climbing is two-dimensional, not three - on any given part of a wall or tree, you can move left-right and up-down but not in-out.

1) People, especially kids, jump between and across structures all the time.

2) Humans are great at throwing and catching objects, even with complex, changing trajectories--bouncing off walls, etc.

3) We have two innate senses that are clearly adapted to 3 dimensions: stereoscopic vision and proprioception.

What makes those behaviors relatively intuitive is constant acceleration. In a sense constant acceleration makes everything 2D. (Or 2.5D?) When humans need to track objects which independently accelerate along 3 axes, then there's a much stronger case for an environment alien to humans. (Counter point: hunting birds, though I believe hunters prefer to take their shot when birds are beginning or ending their flight. But notably the most salient characteristic there is acceleration, not merely relative movement in 3D space.)

Yeah, the more that I think about it, you get much more predictive power by emphasizing acceleration, not spatial dimensionality. And I don't think that's being pedantic; the distinction matters. When you look at studies of how the brain processes motion, constant acceleration (at least along 2 of 3 axes, unless/until hitting another object) is often one of the key assumptions that seems to be built into our cognition.

For example, tracking many objects moving independently in 3D space is pretty darned difficult for humans.[citation needed] But that probably has more to do with relative motion (and thus relative acceleration) than with the number of dimensions as a human can track two such objects surprisingly well, especially if they have a third, fixed reference independent from themselves.

Would be curious to compare & contrast studies of spatial cognition between marine animals and terrestrial animals, though.

Love this framing. Feels like the three body problem is relevant.

Kids don't act in true 3-D, they act in Doom-like 2-D. It gives the appearance of 3-D, but the Z-axis is barely off zero. Climbing swaps X and Z, but is still 2-D.

If it helps, think of what everybody else is calling "3-D" as "no obvious primary axis."