Today the awe was rekindled by xkcd and the subsequent discovery of this Frederic Perrin guy who doesn't even have his own Wikipedia page, the poor soul.
He seems to be the man for floating cities:
Perrin's illustrations are quite cool, as well as various others I have seen. What bothers me though is how this thing would work.
I see three options:
1. Resting on long pillars that extrude high in the sky
2. Hanging from something up above
3. Floating in the absence of gravity
1. Resting on long pillarsThis option gives us a plausible back story - the civilization has had to abandon the convenient, low-lying areas due to, for instance, pollution, and has built structures raised high in the sky. More importantly, this explains the vertical orientation of cities, with water falling down and trees growing in one direction - which would not be the case if we were in a situation without gravity.
With enough population, technology and raw material it's entirely feasible to build a suburb 1km high in the sky - it will definitely be easier than Burj Khalifa, that has to have inhabited floors and sophisticated elevators all the way through. Nowhere in the floating city fiction have I encountered a discussion on the technicalities of getting down to earth so I guess we're not dealing with a requirement for this to be efficient.
There's no way to have rocks floating rocks in this scenario though, so it's ruled out for all portrayals that clearly show unsuspended bodies floating around.
2. Hanging from aboveWith this scenario we're floating away from the realm of the realistic but it's still feasible in theory.
We might have a feasible designs of suspended superstructures - after all we have suspension bridges which have features raising higher than the suspended structure, with the bridge technically hanging from above.
But if we are looking at the suspended city scenario where the load-bearing structure reaches down to the ground I don't think that's fundamentally different than the 'resting on pillars' case - the more interesting thing here is to see what scenario would allow us to have a city ultimately supported from above. If we leave our imagination to run wild we can conceive some scenarios that can provide a setup for this configuration.
Large artificial satellite Future technology can allow us to produce energy in low earth orbit that's not available on earth - for instance, without the interference of the atmosphere solar panels are more efficient and we can conceivably have a arbitrarily large self-sustainable structure in orbit - provided that we have the power to put it there; after all the only energy expense is maintaining the orbit.
When in geostationary orbit this space station will hang over a specific spot on the earth surface, so some structure could hang from it, barely dipping into the atmosphere, just enough to be able to collect oxygen for breathing.
It can also work with other orbits but if it's moving too fast relative to earth (or whatever other planet it is implemented on) it won't be very practical and it will be windy all the time.
In this line of thought, why not hang something from the moon, if we have enough material?
We are not quite lucky with the choice of celestial companions - we have only this moon, which is kind of a freak case in a universe where most planets either have lots of moons or are too small to have any. If we had one that's closer to earth it would be easier to achieve - but it also better be smaller because otherwise the tides are going to be massive. On such a satellite we can potentially hang something, and then we are faced with the same problem as with non-geostationary artificial satellite - it's moving too fast over the surface!
Solution - nukes! If nuclear disarmament goes ahead both sides will be left with stockpiles of tens of thousands of nuclear warheads to be destroyed. How? Well, if we had a smaller moon nearby the nukes could have been used to slow it down to a geostationary orbit.
3. Floating in the absence of gravityThis one seems to be the most popular scenario, probably because it allows for various expressions of artistic freedom without having to bow to the constraints of gravity. Also some representations clearly show rocks floating around, which can only happen with no gravity - even the microgravity of an asteroid will quickly pull these away.
Although it's the most popular scenario the logic and physics don't quite fit - no matter how liberal use of the lack of gravity has the artist harnessed it still looks very much like our gravity-based society, with structures protruding mainly in the up direction, with some exceptions added for futuristic, outer space effect and to highlight the fact that there is no gravity. But if there is no gravity - there is not such thing as up! Why are then tree roots dangling down the bottom when there is no such thing as down?
Structures should be built mainly in direction orthogonal to the surface on which they lie, with one axis being preferred in order to make navigation and transport more efficient - and other exceptions growing in random directions for esthetic or specific practical reasons.
Most art in this sub-genre is however representing the 0-g world as pieces of civilization that was once subject to gravity which have for some reason been lifted way up in the skies, or somewhere else altogether - the place was literally torn out of somewhere, hence the dangling roots. I wonder what back stories do authors offer in such cases. The only remotely plausible explanations are:
a) That society has invented some anti-gravity mechanism, allowing them to lift chunks of a city (along with random rocks!) off the ground and release them from the burden of gravity, preserving their vertical orientation for the sake of nostalgic looks.
In Avatar they say it's unobtainium in the rocks that makes them float - sounds more plausible, although only slightly distinguishable from floating by magic.
b) This race has figured out how to transport these objects to another world, without gravity and presumably with enough breathable air so that they can float around without protective shields (or alternatively - without population, just floating about for the aesthetic effect) If we decide to speculate on a fictional universe, or if we are optimistic enough about the technological advances of human society we might as well allow for anti-gravity or teleportation of large objects, which would make both options possible. The only way I can think of for this to happen without relying on technology that has been specifically ruled out as impossible by present day scientists however is to have some gravitation cancelling arrangement in the vicinity of the home celestial body of the civilization in question. The easiest setup to utilize will be a big natural satellite in a geostationary (or planetostationary?) orbit nearby - it will have it's own gravity and there will be a region where the two forces will cancel out - the L1 Lagrangean point
Speaking about sacrificing aesthetics for practicality, a society can also drill a hole through a smaller body - a satellite or asteroid - and house a floating city at the center of masswhere gravity cancels out. A body so small to make this possible is not likely to cling to an atmosphere thick enough to allow unshielded intelligent life. And the view is going to be terrible - a city floating in a large cave instead of the open skies; kind of defeats the purpose. Who would express that on any medium?
Pierre Ferrin, apparently!
This reminds me, from today About Death, a Singularity or Nothing comes in HD!
I've always known that people are lazy and with short attention spans and are prone to freaking out when confronted with TL;DR. This made my writings in the tiny 400px columns of the old layout extremely scary.
At first I thought it's a force of good - I'm prone to delving into too much detail, so I had something to make me cut out every unnecessary word. It still looked scary though and I have enough to say to keep the scroller tiny even with a fat column like that