In this world, there exists a type of material that has mass, but is incredibly buoyant in atmosphere. 1 kg of this material attached to 1 kg of any other material will be neutrally buoyant at sea level and act more like a beach ball than a large clod, excepting wind takes a lot longer to accelerate this mass(it takes a lot of force to move much more mass than a beach ball).

This material is available everywhere thanks to its incorrigible habit of bonding structurally and mixing with other materials(think clay) and it is as common as most other forms of earth. Its buoyancy is logarithmic with respect to elevation so that even at the treeline on mountains it still retains something like 95% buoyancy, but achieves neutral buoyancy approximately in the range storm and rain clouds form and pass through, bringing it back to earth with the water cycle and re-bonding it to the now wet earth (this seems like a good way to keep it from both permanently floating up to where humans can't use it and from forming an opaque layer in the atmosphere, killing all plant life).

We'll call it floatstone.

Since this material is everywhere, and mixing with everything, rocks and earth don't always weigh what their mass suggests they should. Many clods of earth and rocks are possibly buoyant in the atmosphere and many more can be as they have large chunks of floatstone underneath them, they just need to be separated from or removed from under other dirt and rocks close by. Assuming an Earth-like planet and climate systems, these buoyant boulders will be bashing and battering beasts and buildings alike, buffeted along by breezes.

All Alliteration aside, how could this be stopped from a creation mechanics perspective, or created as is, how could this be dealt with by the inhabitants of this world?

  • $\begingroup$ "material that has mass" - how much mass? $\endgroup$ – Alexander Jul 16 '19 at 21:31
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    $\begingroup$ When a person is struck by this material, does the material absorb into the person, like a sponge, when it bonds? Or does it bond with the outer layer of the person, forming a sort of patina which is opaque to floatstone bonding, after which they are pushed along by the rest of the floatstone? Or does it just strike them like a regular stone? How long does the bonding process take, and how well does it permeate a material which it is bonding to? $\endgroup$ – boxcartenant Jul 16 '19 at 21:35
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    $\begingroup$ I'm just wondering how much of the dirty rain actually reaches the ground, and how much just falls to a point where the mixture has neutral buoyancy, is slowed down by air resistance, and then ultimately just bobs around in standing banks of filthy fog. $\endgroup$ – Admiral Jota Jul 16 '19 at 22:16
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    $\begingroup$ @AdmiralJota If floatstone breaks apart from itself when wet, would the pieces eventually get small enough that this is a non-issue? The rain carries what are essentially dust particles. This might mean a lot of fog after 'accidents' release a lot of it into the air, but it would eventually all fall back down. $\endgroup$ – Vashkarzas Jul 16 '19 at 22:35
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    $\begingroup$ How does the water cycle bring the float stone down? You would need 1KG of water to lower 1KG of floatstone, but depending on the size, this would be basically impossible. The water also can't break the float stone apart, because you will have issues recombining it, since it bonds to almost everything and dirt will basically be the first thing it bonds with making it a giant dust ball, so maybe its some chemical reaction that prevents float stone from floating? $\endgroup$ – Shadowzee Jul 17 '19 at 1:02

Some initial handwaving of mechanics to use as a basis:

We'll assume that the material in question can react with a limited range of other materials, and undergoes an excessive density change during its phase change from a liquid to a solid. Kind of like how liquid water has a density change when it freezes and turns to a solid, but we're upping this mechanic by several orders of magnitude. This allows it to cycle through the environment kind of like water, and doesn't just end up forming the upper atmosphere.

We'll really want that "limited range of other materials" mentioned earlier, simply to handwave what that kind of matter might do to living plant life... Complex life forms might struggle to evolve on a planet where getting rained on might cause parts of them to balloon in volume at random and float away.

  • Probably safe to assume that forms of carbon common in life disrupt the reaction in some manner, otherwise life is going to be really awkward if this stuff isn't super super rare: And where would the fun be if it wasn't at least somewhat common?

The density of air being about 1.225Kg/m^3 should actually help us keep much of the worst case scenarios to a minimum, because "Full on Floating bits" are probably unlikely to manage to stay in single massive chunks for long after getting slammed into trees and against exposed rocks. Anything really big that does manage to gather will stand a high chance of cracking into smaller bits, so our towns and cities probably don't have to worry about having whole mountains blunder into them on a regular basis.

Having the material expansion based on phase change from a liquid to a solid will also aid in limiting the size of chunks: As float-rain hits material it can react with, it will start expanding on the top of the material, eventually breaking the expanded low-density stuff off from the material below. This will cause floatstone based erosion to mostly flake off in layers, or more likely sort of corn kernel or mushroom shapes as reaction regions try to expand in all directions, but will take the path of least resistance: Up and out.

Temperature limitations on the reaction will also help keep things 'interesting'. Such as a minimum temperature and endothermic reaction would help more material saturate and bind with the float-rain before reacting to become full on floatstone. Larger chunks could stay together longer before 'lift-off', and the liquid could reach deeper into the ground before the reaction begins.

Locals may be terrified of "very hot summers" as it means lots of land suddenly erupting at random and fresh floatstone nodules hit their thermal tripping point and expand... but the endothermic nature of said reaction would naturally put a brake on too much going too far in a very short time.

Having it slowly break down in sunlight, shedding more of its 'non-floaty-mass' in dust like volumes would mostly keep boulders from falling out of the sky, and also give it a mechanic for returning back to float-rain/vapour status: It sticks to clumps of non-float-matter, or forms with pockets of it inside, but is naturally far less dense than air: Once enough mass is shed it shifts to higher in the atmosphere, where it breaks down the rest of the way and phase changes back to liquid when it runs out of 'reaction matter' to hang on to.

But all this brings us back around to the important part of the question:

So how would we best want to deal with low density floating stones?

  • Deflection is likely our best bet.

Successful settlements are probably going to be on the leeward side of hills, and hiding in holes during hurricanes is highly advised.

  • Long, low sloping rooflines, such that blown floatstone is likely to roll up and over buildings, sounds like a good idea.
  • Large vertical glass windows are probably not going to be popular.
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