This Episode is sponsored by Brilliant
We often worry about humanity running out of room to grow outward, and many suggest
we might spread out to new worlds, but perhaps weâll spread vertically first. So we return to the Earth 2.0 series to conclude
our main arc by discussing Matrioshka Worlds, planets built of many concentric spherical
shells, like layers of an onion, each its own planet or layer. Weâll be drawing on many of the concepts
weâve already discussed, such as artificial islands, colonizing the depths of the oceans
or underground, bringing life to barren deserts and tundra, and even building cities floating
in the sky. Weâll also be drawing on technologies weâve
discussed in other series like the active support technologies of the upward bound series. But I thought weâd begin by reiterating
a point we made back in the Arcologies and Ecumenopolises episodes, which is that you
are unlikely to ever run out of space for people themselves on a planet, because our
real problem is coming up with the energy to support them and a way to get rid of the
heat generated in the process. Incidentally, this is going to be one of our
long episodes, or longer anyway, and one of the ones where I necessarily have to reference
previous topics weâve covered. Appropriately, for a topic involving the supersizing
of a planet and uprooting continents to hang in the sky, weâve got a lot of groundwork
to cover first, then we can get to why weâd likely want to dump a black hole into the
center of our planet and have worlds inside worlds where the time runs slower. Thereâs lots to cover so weâll be here
a while, and this would be a good time to grab a drink and a snack⌠Science fiction has examples of entire planets
given over to immense cities, what we call a Ecumenopolis, a Planet-city. A few of the best known of these are Trantor,
the capital of the First Galactic Empire of Isaac Asimovâs Foundation series, Coruscant,
the capital of the Old Republic, Galactic Empire, and New Republic in Star Wars, and
Holy Terra, the capital of the Imperium of Warhammer 40k. These boast massive populations compared to
modern Earth, but nowhere near what they should, almost like the authors flinched back from
the true scale of such places, putting it in the billions or maybe a trillion or so
people. As we saw in Ecumenopolises, even a trillion
is very low, especially if youâre cramming people into the dreary cramped lives such
places are usually described as, and points to Chris Wraight in his novel Carrion Throne
for finally giving a figure of âquadrillionsâ which would fit the scale of the world given
when you do the math. Thatâs a great book incidentally, though
showing a much more grim and dark future for Earth than weâll paint today. The key concept is you do not need more space
in and of itself, even for such an immense figure, nearly a million times our current
population. If we covered the entire planet, only one
story deep, in fairly modest individual apartments of 50 square meters per person or about 500
square feet, then Earth, with a total surface area of 500 trillion square meters, would
house 10 trillion people. Needless to say, if youâre building the
kind of immense skyscrapers we often see in such stories, a few kilometers tall, or a
thousand stories, that would give you 10 quadrillion people. In these stories, where the population is
often given as a trillion or so, but the world is nothing but mega-skyscrapers, your typical
person would feel like theyâre wandering around a deserted warehouse, not a packed
residential area. The obvious point, though, is that itâs
not people taking up all that space, itâs all the agriculture they need to be fed, and
in fact itâs not the plants taking up all that surface area, rather itâs the area
that sunlight falls on. The plants spread out to soak that in. For most of our history sunlight could be
treated, like air, as something so abundant that other scarcities like decent soil, rainfall,
and manpower to tend crops were what dominated the equation. For a high-tech culture, those begin to diminish
in importance, machinery begins to make it easier to irrigate soil, sow and harvest crops,
and science lets us improve the fertility of soil and even modify crops to be more productive,
a process that our ancestors had to do in a fairly slow and hit-or-miss fashion. Thereâs a lot of pathways to allowing more
people to survive on less land, or even removing land from the equation. Greenhouses, hydroponics, and vertical farming
really let you crank out calories per acre or hectare at levels that are vastly superior,
such that it really can support trillions of people on Earth in comfort and with full
bellies without needing to knock over any more forests or destroy any existing ecosystems. They are however, incredibly expensive, but
better energy production and automation could make them equal to or even cheaper than traditional
farming a ways down the road. Thatâs only one pathway of course. We could grow food up in space, as we discussed
in space farming, or go more artificial, either synthesizing our food, or cutting that out
in favor of cybernetic or digital existences. Or even live in life support tanks connected
to a computer and experiencing virtual reality, matrix style. And weâve discussed all these topics in
more detail previously. Whether weâre talking about space habitats
like an OâNeill Cylinder or terraforming other planets, all the living space youâre
making really has nothing to do with feeding people or giving them enough room for their
furniture once you solve two basic technological hurdles. One is abundant, reasonably clean, cheap,
and renewable power, and the other is considerably improved automation, not necessarily human-level
artificial intelligence but something smart enough to automate most factories, transport
and production chains, and construction so that they needed minimal human oversight. Truth be told, you only need one of those
technologies to basically be a post-scarcity civilization. As an example, if robots are doing most of
your mining, refining, and production, you can churn out solar panels so cheaply that
it doesnât matter how durable or efficient they are. The total of all our energy demands, from
fuel for cars and freight trucks to electricity for houses and factories is about a percent
of a percent of the sunlight hitting Earth, so even relatively inefficient panels placed
only on barren wastelands or roofs is going to cover your needs with room to spare. Thatâs hardly a breakthrough in energy technology
but it hardly matters if youâve got the power you need and can rely on the supply
lasting half of forever without being a burden on your ecology or economy. Of course those robots can do their work just
as well on the Moon and in orbit, meaning you can beam your power down and circumvent
losing any land, not needing to worry about darkness from nighttime or clouds, and not
having to mess around with giant arrays of batteries or superconductors to store and
move your energy to where and when you need it. The flipside is that if you havenât got
the smart automation but do have a revolutionary new power production method, like fusion,
then you are automatically post-scarcity because the only reason we arenât now is because
of that non-sustainable and expensive energy issue. Just the savings on electric and gas at the
personal level would result in a lot of prosperity but folks tend to forget itâs built into
everything. Even food production, since the three majors
difficulties growing everything inside climate controlled facilities is the cost to climate
control it, the cost to provide lighting or supplemental lighting, and the material cost
of building and maintaining the things. Since most of us tend to assume weâll lick
one or both of these issues, energy or automation, in the next couple of generations, we try
to factor it into our thinking for the future here at SFIA. Itâs why we often present the concept that
in the future we probably wouldnât terraform dead planets for new living space so much
as disassemble them for tons of artificially constructed habitats in orbit around those
worlds or wherever. We always note that a spinning habitat probably
only has several meters of dirt and superstructure beneath your feet, whereas a planet has a
several million, making it wasteful to basically build planets like Earth, since all that valuable
rock is merely generating gravity, which can be created much more efficiently. We have discussed building spherical shell
worlds or others shaped like discworld flat earths before, and using materials like hydrogen
or helium or even dark matter or black holes to generate most of that gravity, with a rocky
shell around it, but itâs still a lot of mass youâre using. This is where we truly lead into our topic
for today, because that is the big limitation here. By default most of us would rather live on
a sphere than inside a can, but in an economy of truly abundant energy and automation, your
economic limitation is basically on raw mass and building material, and most folks probably
would not be willing to pay a million times as much for an acre of land to have it on
a sphere instead of inside a can or ring. It takes a lot of mass to make Earth, 6x10^24
kilograms, almost a trillion tons per person living here, and enough to create the equivalent
of hundreds of thousands of square kilometers of living area per person as rotating habitats,
a modestly small nation for every living person to call their own. And so long as youâre doing a sphere with
Earth gravity on its surface, it will cost you the same mass per surface area whether
youâre making tiny planets with black holes in the middle of them for your gravity or
converting gas giants into habitable planets. Gravity falls off as the inverse square of
radius, surface area rises with the square of radius, so the two handily cancel out. However, we keep saying surface, and of course
todayâs topic is about many surfaces, spheres nested in spheres inside spheres, like a Matryoshka
Doll which is where we get the name for this approach. If your planet has many layers, they each
can get most of their gravity from the same place, so youâre not spending as much mass
per living area anymore. Build thousands of layers, each as thick as
a typical rotating habitatâs floor, and suddenly the mass cost is very different. Thereâs a general feeling that even if we
disassemble other worlds to make huge numbers of rotating habitats that we wouldnât do
it to Earth itself, and the same would likely be true of a planet that had been the early
focus of colonization in another solar system. And with such places likely being capitals
and hubs of interplanetary or even interstellar empires, the real estate is likely to be precious
on them. So this is one way to go for places like Earth. Of course, this raises a ton of other problems. How do you build such a thing? Second, how do you light the lower levels,
since natural sunlight is blocked. Third, what do you do with all the waste heat
being produced by it. Fourth, how do you build such things incrementally,
as need requires? Fifth, what exactly is the point of doing
whole new layers when you could just go the skyscraper, vertical farming, and arcology
route? And sixth, just how big can you go? How many layers can you do? Conceptually such an object is simple enough. I build a shell over the current surface of
Earth and support it somehow, we discuss the various ways in a moment. We could also go the opposite direction, hollowing
a layer out below us, and indeed it would make sense to hollow a layer out to make one
or more layers above you. You are probably thinking, correctly, that
if we build a layer above us we would have lower gravity there, being further up, and
if we dig stuff out below us and lift it up there, we will have less gravity here at the
ground level too. Now if youâre keeping your layers close
and not making very many, this can be ignored, but it will be an issue if you want to make
lots and lots of layers and keep the same gravity on each one of them. For additional layers you just need to ensure
that the extra mass of that new layer corresponds appropriately to its distance from the center. If we go up, say, 64 kilometers, to build
our next layer, that layer is 1% further out than we are and has about 2% lower gravity,
so that layer would need to mass about 2% of what Earth does to compensate for that. One built twice as high up as that would be
2% further out than original ground level, and need 4% the mass of Earth, though if weâd
built that previous layer, we can subtract its mass. It just depends on how much you care about
gravity diminishing as you go up and how much sky you want to have. You can obviously do much thinner layers and
space them a lot closer too, nor do layers all have to be at the same height as full
spherical shells. Though if you donât mind things hanging
right over head, you might as well just go the skyscraper route or live in a rotating
habitat. An important thing to remember is that a spherical
shell of mass generates no net gravity inside, not just in the dead center either but everywhere,
even right inside near the shell. So you can always ignore the levels above
for calculating gravity, though emphasis on ânetâ gravity, as itâs not really gone
and will start making clocks and time itself run slower on lower levels if you go big enough,
more on that later. Of course they canât just hang there, something
has to hold all this stuff up, right? Well yes and no, channel regulars already
know of a concept we have called active support, and itâs how we cheat when we need to keep
something heavy up and normal materials wonât let us do it. The first of these is the Atlas Pillar, basically
a particularly massive space tower whose purpose is implied by the name, it holds the sky up. Albeit in this case the sky is the underside
of another planetary layer. This type of active support works the same
as what keeps a piece of paper floating over a heat vent, nothing rigid underneath, it
just gets pushed on by hot air. See the Space Towers episode for details of
the science on that but a problem with active support is that it is active, you have to
pump power into the thing to keep it going, and it will lose that power as waste heat,
which is problematic even if you have near infinite cheap power generation. If we ever manage to make cheap superconductors,
and especially if we develop a material, probably a metamaterial, that makes for good magnetic
shielding, then hypothetically, you could make a big rod that was closed off, no new
power added or heat lost, and had ridiculously high compressive strength. Inside itâs got plenty of stuff moving around,
but since it isnât drawing power or losing it to heat, it would be an ideal building
material for stupidly big and heavy projects, like trying to hold a continent in the air. One of our other methods is the orbital ring,
which relies on standard orbital mechanics. Stuff doesnât fall down for the same reason
satellites and space stations donât, or rather they always fall down as orbiting objects
are constantly yanked on by gravity and dropping, they just are flying off to the side at just
enough speed that they wrap around a planet, constantly falling but never hitting. If a giant hand reached out and stopped the
space station, everyone floating around inside would fall to the floor as theyâre not that
high up so gravity is only a little weaker. Of course when the giant hand let go, the
station would plummet down to Earth too. However, if instead of stopping the station
our giant pushed it faster instead, then it would have to go up into a higher orbit or
even escape entirely, itâs moving faster than it falls now. Youâd have to push down on it to keep it
from flying off. What an orbital ring does is merge these. We make one ring, potentially just a long
and simple metal wire, that spins around Earth, and a tube around it doing the same. We use metal so we can generate a magnetic
field to keep the two from touching but still able to push on each other, and so that we
can use magnetics to push on them to speed or slow either one. We spin the inner ring up while slowing the
other one down, keeping their net momentum the same as a ring of equal mass to both of
them would need to stay in orbit. So long as their net momentum stays at that
value, either can be moving at very different speeds, and by default an orbital ring is
one where the outside doesnât spin at all, or no faster than the planet below it spins,
while the inner move far faster. See the Orbital Rings episode for details,
but basically you end up with a small fast ring sheathed inside a big stationary ring
you can walk around on, as gravity feels normal, or just a little lower since youâre up higher. These can handle changes of weight on that
outer sheath by just speeding up or slowing down that inner ring a bit. Incidentally, there are many ways to do this,
like using a particle accelerator instead of a metal hoop, and they do not need to be
circular either, they could be elliptical so one end actually touched the ground. One of the ways to make a space tower or Atlas
Pillar is just to take that hoop and squeeze it very narrow, so thatâs itâs basically
two straight lines spinning up from the ground to the top and falling back down on the other
side. These things can handle staggering amounts
of weight if youâre willing to invest the mass and energy into spinning it up, and you
could cocoon an entire planet in a bunch of them, made wide and tilted at angles, and
just layer over it with rock and water and air and presto, planetary shell. Same as the Atlas Pillar, if youâve got
cheap superconductors and magnetic shielding, you basically only have to pay your energy
bill once, but in both cases theyâre not nearly as power draining as youâd expect
if you have to run them with modern tech, all the interior motion is just something
flying around in a vacuum so very little energy is being lost to friction and so on. Such things always require maintenance but
that applies to every structure. Such huge projects can only be contemplated
with energy abundance and very good automation, but if you have them, theyâre not really
high tech beyond that. Theyâre quite sturdy and safe too, especially
with those rings cocooned together in case one fails. It might seem otherwise as itâs unfamiliar
but honestly itâs safer and sturdier than, say, living on a thin crust of rock floating
on top a huge ball of unpredictable molten, radioactive iron as we currently do. Also, one whose mantle tends to explode through
from time to time, which is handy for making new land but we can do better, and frankly
itâs just not tidy. Our core and mantle are like keeping radioactive
waste and explosives in your basement, not something a responsible civilization should
do, and weâll replace it with something safer like a black hole eventually. Yes, I did say a black hole. Safety, though, does encourage us to use multiple
methods and so youâd expect to see the layer built out of an orbital ring but also supported
with Atlas Pillars and many of them for redundancy. This does raise the notion of building incrementally
though, and you can do that with an Atlas Pillar, just make several of them in some
area and lay land across, like a big table. You could also have a thin orbital ring running
through that, or hang that shelf down from something, relying on tensile strength, like
a space elevator, only with much less length on the tether. You could indeed do all of the above, building
a land mass of a desired size, say a large island, that hung in the air between spherical
shell layers, which weâll call âBabylon Shelvesâ as a nod to the Hanging Gardens
of Babylon. Needless to say you could use any of the other
tricks for hanging stuff in the sky that we discussed in Cloud Cities, but this approach
lets you get away with making very heavy stuff and mobile ones too if itâs just hanging
from rings like a Chandelier City or sitting on them, though skinny Atlas Pillars could
let you walk the thing around like Baba Yagaâs Hut. I suspect youâd go both ways, above and
below, for redundancy and for ease of transport, particularly as Matrioshka Planets need a
lot more transport than just people and our personal goods and supplies. A Babylon Shelf would of course shadow whatever
it was above, but you could put lights on the bottom and of course on lower layers you
need to fake your sunlight anyway. Itâs a handy approach as you can incrementally
build many of these and expand them or lift or lower them into place on a layer youâre
building. Since orbital rings would be a central part
of your off-world economy, anytime you build a new layer youâll need to create a new
orbital ring layer to keep access to and from the planet cheap and easy. While lower layers would presumably look the
same as Earth, probably with fake sun and stars, the upper layer is likely to look like
the most massive scaffolding project in history with skeletal rings wrapping the planet and
space towers rising from it for millions of giant space freighters and passenger liners
to dock at probably domed cities hanging around, literally. What you do with all that space is hard to
say, because youâre probably not growing food on it much. You could just farm on the various levels
naturally, or have vast hydroponics complex built inside them too, but you could get away
with just importing your food from huge space farm orbiting the world further out, it will
generally cost less energy to land food than to grow it, also meaning it will produce less
heat, and you really have no need to export back your waste since you are probably constantly
adding new layers of dirt, and some of the best dirt you can get is dirt that used to
be food until someone ate it, so you might just import food. Amusingly, I often complain that Ecumenopolises
are falsely portrayed in fiction as inevitably being what tropes call a âcrapsack worldâ,
and in this case that would technically be true. One nice thing about such worlds is that unlike
a rotating habitat, you donât have your sky composed of your neighborsâ back lawn,
but actually we can double up on our layers by living upside down if we wanted. One of the incremental build methods would
be just to make a wide orbital ring like a big band around a planet, and thereâs nothing
stopping you from using the underside to produce spin, except that a spinning ring wider than
a planet would be beyond what even carbon nanotubes and graphene could handle for tensile
strength. One could spin it slower and fake lower gravity,
which might be fun, but you canât build giant ringworlds with any material existing
in known science. That is except if you cheat and use active
support. As we discussed in the Ringworlds episode,
if you have a very massive ring that doesnât spin or does so slowly, you can have another,
lighter ring just inside it spinning around very fast, by having the massive ring push
back against it; itâs the same basic concept as a normal orbital ring. Such things essentially hang there and are
too heavy, this is like holding them up from beneath, only in this case from above, and
presumably with a magnetic field so youâre not touching it. Normally this is impractical since you need
a really massive outer ring to allow this around a Sun, like a Niven-style Ringworld,
but itâs far easier when itâs just around a planet and you do have a ton of mass just
sitting there being supported, and a spinning inner ring would actually help brace it better
and give a small continent of extra living area, though you could have several. So folks could live upside down on the underside
of layers too, like some of the Hollow Earth notions, though since we need to name the
thing to avoid confusion and Iâd rather not dignify some of the crazier Hollow Earth
theories by borrowing their names, we shall name these upside down ring-shaped small continents
âAntipodean Bandsâ. What other fun options do we have? Quite a few, the skyâs the limit, at least
if you live in lower levels. Needless to say you could devote entire planetary
surfaces to being nature preserves and parks, you could have an actual âDisney Worldâ,
and there is no limitation whatsoever on how many layers you can build, except cooling
the place which is a big problem. As I mentioned, your top layer is likely to
be devoted more and more to spaceports and ongoing construction as you build ever bigger,
so you might not even bother keeping an atmosphere up there, particularly if you decide to build
one from scratch and donât want it rotating or it wasnât rotating originally because
it was a tidally locked world. So it would have no magnetosphere helping
keep the Sun from stripping your atmosphere off. Matrioshka Worlds are rather ideal for tidally
locked planets which will likely be fairly common, since those might often be around
red dwarfs, the most numerous of stars, and would often have one side baked by the Sun
and the other in eternal darkness. Since heat can only be transferred by radiation
in a vacuum, like space, you can just put a reflective coating on a planet and keep
all that sunlight off if you want to, and artificially light your lower levels. Earth, being warm and geologically active,
isnât actually the best place for making a Matrioshka World, but itâs also the best
place in the Universe for one because itâs likely to always be fairly central to a future
humanity. You can get away with adding more levels to
our world because it is Earth, even where doing it on other worlds might be easier. The problem is you canât really have very
many levels if you want to light them all. Our planetâs temperature is based on how
much light it gets from the Sun and can radiate away, and thatâs based on its radiating
surface area. If youâre doubling the light with a second
layer, but that layer is only a little bigger than Earth, youâve got a problem, your planet
is going to get rather hot, and each new layer, while slightly increasing the surface area
to radiate from, is adding far more to this heat burden. Now thatâs actually okay for a classic Ecumenpolis,
as itâs assumed youâre importing your food or growing it in optimal conditions and
light spectra, and any natural habitats are basically parks, a small minority of area. Itâs also okay to dim things in most places
as most plants donât really need full sunlight to prosper, and a big chunk of the light we
get they donât even use, or use little of, like green light, or infrared, which we canât
even see. But this only lets you do a handful of layers,
which is still quite a lot, but after that point if you want more it needs to be in darkness. Thatâs okay if you want vast subterranean
civilization or cold dark areas or just a lot of storage space, most kept in the dark,
but building a Matrioshka World with those in mind would seem like overkill. If you just want tons of storage space or
caverns, youâve no need to do huge layers, and can take the approach of just building
story after story of whatever height you want it in a particular place, like we discussed
in Dying Earth. What can we do about heat? We could build them deep in space far from
a star where theyâd already be cold, these are ideal for rogue planets, but as we mentioned
we could also just shine up the surface to reflect light away so they could work very
close to stars too, and it still doesnât let you do many more layers. Of course we might get some new technology
that violated Thermodynamics, in which case these become ideal places to live. Or we might be able to make wormholes, dumping
heat from these worlds to some other place. It may even be possible to dump waste heat
into black holes, and I did mention weâd probably want one at the center of Matrioshka
Worlds in some cases, though not principally for that reason and weâll discuss that more
in Colonizing Black Holes this summer. Barring such advances, or going the dark route,
if you want many layers you need a giant surface to radiate with, or at least a giant surface
area. Heat sinks to help cool devices are generally
all about maximizing surface area in a compact way, and we can, for instance, stick lots
of conical spikes or obelisks on the outermost layer to increase surface area, and cover
them in something reflective to infrared light, which many metals already are. That will let you squeeze out more heat and
thus more layers, but we can go further too. Such planets are likely to always be surrounded
by an immense swarm of space stations, docks and orbital habitats, what we call a Planet
Swarm, like a Dyson swarm only smaller and around a planet. Thereâs likely to be constant traffic back
and forth to those and huge skinny space towers potentially rising thousands of kilometers
over the outermost shell, indeed they might just be extensions of the Atlas Pillars holding
it up, and possibly weâd have tons of space elevators rising from that surface too, attaching
to massive counterweight habitats or space docks or farms at their far end. All along these you could have fins, like
leafs on a tree, into which heat could be moved by conduction or convection into them
and then radiated away, all arranged and coated in infrared reflective materials to spew out
heat to fly away or bounce off neighbors until it did. Same as we have electrical superconductors
that conduct electricity too, we have thermal conductive materials that move heat well and
may get a thermal superconductor one day too, in which case moving heat from a lower layer
to these radiating towers becomes easier. You want to maximize this surface area so
youâd probably make these towers or tethers or obelisks fractal in shape, at least for
their radiating leaves, and since weâre using a tree analogy, and your world would
be covered in these things potentially stretching tens or even hundreds of thousands of kilometers
off into space, we shall call them Fractal Obelisk Radiation Emitting Super Towers, or
FOREST, though the ST in these FORESTs could also be Space Tower or Space Tether I suppose. Itâs actually rather amusing since the purpose
of these FORESTs is to let us generate a lot of heat by lighting lots of forests and other
ecosystems on lower layers, and considering the sheer scale of these things, thin and
light but immense, even the massive kilometer long spaceships constantly flying around and
docking at them would just be like birds or bees flying around a normal forest. NOW we can start doing a lot more layers,
and it behooves us to space them out and up and down, as we probably donât want atmosphere
running between them, same as we mentioned in Subterranean Civilizations, dig down real
deep and the air pressure will rise from all those extra kilometers of air piled up. Though if you donât mind airlocks along
the way or barrier mountains, you could have big holes between layers people could walk
or drive directly through. You could potentially even do the equivalent
of spirals instead of concentric circles, a spherical spiral or helix with one unbroken
land surface, though I suspect youâd still need to be pumping a lot of air and water
back up to avoid it building up even if you were including a lot of chokepoints. Of course you might enjoy having a big waterfall
between layers too or massive columns of air rising back up as an eternal storm you could
hang glide between layers on. Adding to those layers, as you go up, and
as I mentioned earlier, you can maintain the same gravity on each new layer by just adding
enough mass to compensate for the decrease in gravity from being further away. However, as you do this, the density of your
entire planet is going to start dropping off inverse to its radius. Want a planet twice as wide, with four times
the surface area on the top layer, and the density of that sphere needs to be half in
order to maintain the same surface gravity. Earthâs average density is thousands of
times denser than air, so you can do a lot of layers if most of those layers are relatively
thin on dirt and water and mostly air by height. However, at a certain point, if your planet
is now dozens of times wider than Earth is, you will actually want those layers spaced
out enough that the atmosphere over each layer thins out to vacuum before the next layers. At least on the mainland, you might keep your
Atlas Pillars pressurized and make them wide with their own habitats, or include step tiers
of Babylon Shelves and Chandelier Cities. As you go down, hollowing things out though,
you will slowly slice away at your gravity, Earthâs pretty dense after all. Drop that density by hollowing things out
and gravity will drop. You could pack your center with something
ultra-dense like Osmium, but thatâs hardly super abundant so youâd either have to stop
or find something stable and far denser, cue sticking a black hole in the middle of your
planet. This is also a potentially awesome way to
power such a place too, as various possible means of power generation from black holes
are way more efficient than even the fusion that runs our Sun. Weâll save discussion of this more for another
day, but a quick mention for now of another unintentional side effect of putting layer
after layer on is that eventually, if you do enough of them, you will end up with time
dilation at the lower levels, as we discussed in Mega Earths. Clocks run slowest down at the bottom layers
and fastest up at the top and among the FORESTs and spacedocks. Considering new layers are likely to be inhabited
by new people, especially in a future with life extension technology, you might have
some very ancient folks and civilization hanging out in the depths of such worlds, especially
if you built them big enough that you were ransacking thousands of star systems to add
to your building material and made the planet so big that it qualified as a Mega Earth or
Birch Planet, where the Sun and any Dyson Swarm around it would end up instead orbiting
around that Matrioshka World. Such places would likely only ever be constructed
because they were the natural political and economic centers of their civilizations, but
if they got big enough, they might become the physical centers of such places, and indeed
regardless that the gravity on each layer might be Earth-like, the escape velocity from
such things would grow too, making it very easy to approach to bring in more material
and goods, but harder to leave, another reason for those huge forests of spacetowers rising
far away. Itâs a breathtaking project in scope, but
one that could be done over eons as need demanded, and one I could see us doing since for humanity
at least, Earth is a unique place and will stay unique even if we colonize a million
other worlds and forge a trillion space habitats. Itâs an effort that might be fueled simply
by Earth maintaining its prominence as the center of future civilizations. Itâs something that might be pushed so far
that a growing Matrioshka Earth might become a truly geocentric one, with everything literally
orbiting around us. So I could see this future happening, a many-layered
Earth able to house almost endless civilization and ecosystems, a new and greater Earth, an
Earth 2.0 We were discussing how you can achieve the
same strength of gravity on each layer of a Matrioshka World today, by carefully calculating
how much mass each layer needs based on itâs extra distance, and if youâd like learn
how to do that on your own, Iâd recommend the Forces chapter in Brilliant's Science
Essentials course. As is often the case on this channel, we introduce
the concept and folks want to create and play with it afterward, but it helps to have a
good background in science and math. Brilliant offers a lot of in-depth, fun, and
interactive courses and quizzes that let you master these topics at your own pace. With that course and others youâll gain
a greater understanding of how we can create such worlds, from their gravity to the active
support holding them up. In addition to many great courses like that,
they have fun daily problems in math, science, and engineering to encourage you to challenge
yourself everyday, and an extensive online community to help you if you get stuck. If youâd like to learn more science and
math, go to brilliant.org/IsaacArthur and sign up for free. And also, the first 200 people that go to
that link will get 20% off the annual Premium subscription, so you can view all the daily
problems in the archives and unlock every course. So I mentioned weâd be looking at Colonizing
Black Holes soon, as part of a new crossover trilogy with some of our other series, and
weâll start that next week by looking at Black Hole Ships, and many different approaches
to using black holes to move things between stars, as part of our Generation Ships and
Interstellar Colonization series. Weâll follow that up with a return to the
Outward Bound Series to look at Colonizing Black Holes, and to our Space Warfare series
with Weaponizing Black Holes. But before that, two weeks from now, weâll
be returning to the Upward Bound series to look at a different approach to launching
ships into space, to discuss Sky Platforms and other launch methods that donât start
by having a rocket launch from the ground. For alerts when those and other episodes come
out, make sure to subscribe to the channel and hit the notifications bell. And if you enjoyed this episode, hit the like
button and share it with others. Until next time, thanks for watching, and
have a Great Week!
I think a good site for a matroshka world is the planet Venus. Unlike Earth, Venus is in the wrong spot. Venus has the wrong rotation rate and nearly no axial tilt, so I say we can build six shell's around Venus. We can mine Mercury for the material to build this out of. Venus has six times as much nitrogen as the Earth does, and from this we can divide the atmosphere into sixths, place one atmosphere onto the surface of Venus itself, and then five other shell's can be made habitable as well with 1 bar atmospheres consisting of 80% nitrogen each.
Venus has a mass of 4.8675E+24 kg Mercury has a mass of 3.3011E+23 kg
The surface gravity of Venus is 0.904g If we build a shell that is 60.5 km more in radius than Venus's average radius of 6,051 km, then the gravity will be 0.9901 of Venus's surface gravity, which will make the gravity 0.895g. We need to add 1% of Venus' mass to bring the gravity back up to 0.904g. Mercury has enough mass to construct 6.7 such shell's around Venus with each shell having about 1% of the mass Venus. You can construct 6 shells, the outermost one will have a radius of 6,414 kilometers which will make it slightly larger than Earth.
The sixth shell would be open to a vacuum, it's outer surface would either have an equatorial band that is spinning at orbitAL velocity, or the entire outer surface of that shell will be rotating that fast so that it's equator is in orbit allowing ships to easily dock with it, I think more likely the former, as we need the outer shell as a radiating surface. We can then have six habitable surfaces including the original surface of Venus. If we can move that amount of material around, making oceans for each of the 5 habitable shell world's plus the original surface of Venus should be no problem.
The underside of each shell world provides illumination for the surface below it. Excess heat is removed from each she'll and radiated out through the outermost shell, and solar collectors are built with the remaining mass of Mercury to provide enough energy to illuminate all six habitable surfaces to Earth surface normal levels. We basically need one and a half times the surface area of Earth to provide enough illumination for all six habitable surfaces.
We can make each surface as "natural" as we like, have six natural unspoiled wildernesses, and then have pioneers come over from Earth, chop down trees and build log cabins. I figure we can use nanotech assembless to build these world's and the "ancient" trees in the unspoiled forests, so pioneers can chop them down and build log cabins from. Make sure that the mountains look natural and a result of fictionAL geologic processes, fake volcanoes that never erupt, fake fault lines, pretend young and old eroded mountains, and maybe some mineral deposites like gold and silver in those mountain ranges.
There's an manga and anime called Blame! which features something like this.
Sorry if I missed something obviously but why would a civilization build one a Matrioshka World instead of just continuing building vertical, as discussed in some of the previous videos?