So we return today to the Megastructures series, a bit unexpectedly, for a look at Hoopworlds.
Hypothetical megastructures that are shaped like donuts or hoops.
Donut Planet seems insufficiently dignified, so the term Hoopworld has stuck.
I’ve heard them called Toroidal worlds too but that’s not entirely accurate.
A Toroid is any object created by taking a surface and revolving it around a circle so
you end up with this sort of ring shape.
A Torus is where that’s a circle and even it has some non-obvious versions.
A torus has two types of radius.
The Major Radius, which is what you rotated around to get the shape, and a minor radius,
which the radius of this circle inscribing the Torus.
That can have some unexpected versions, like the Spindle Torus, where the major radius
is smaller than the minor radius, more of an apple shape, and would be a sphere if the
major radius was 0.
And a Horn Torus, which is when the major and minor radius are equal.
Our interest is in the Ring Torus, and specifically where the major radius is not just larger
than the minor radius but much larger, and Hoop fits that idea just fine.
Now it is actually possible, highly improbable but still possible, for a planet shaped like
this to naturally occur, either beginning as a double planet, our subject for next week
in the Habitable Planet Series, or as a very fast rotating ellipsoid planet that disintegrates
into a hoop.
Take that Spindle Torus for instance, that’s already very close to what a very fast spin
planet might look like.
I’ve seen some interesting discussions of such world forming naturally but this is the
Megastructures series so Nature can go jump off a skyscraper, which also aren’t naturally
occurring.
If you’ve already seen the Shell Worlds and Discworlds video then you’re familiar
with the concept of Active Supports Structures like Orbital rings, and you can make a Hoopworld
using those same basic principles.
Using orbiting mass that is spinning quite quickly to provide our inertia to keep things
from falling together while magnetically levitating a non-spinning stationary layer above it we
can build our fake planet on, which I will call the Sheath.
Now if you’ve just entered this video without seeing prior ones, the megatructures series
is not really a self-contained one, we reference a lot of prior concepts, especially in this
episode so you might want to go back and watch those first.
In some ways it’s actually easier because your sheath for a hoopworld is already pretty
close to stable.
A hoopworld isn’t really a stable natural planet design but its pretty close so our
artificial version only needs a little extra effort to make sure it stays stable.
You’re essentially building a big ring whose centrifugal force of orbit is cancelling out
the gravity that wants to collapse back together again.
This is no different than a planetary ring like Saturn has, only denser and much more
massive.
Usually about a dozen times more so than Earth, in terms of both mass and living area.
Planetary Rings, especially big ones like Saturn’s, aren’t terribly stable on astronomical
timelines as collisions and perturbations from gravity tend to slowly deplete the ring.
Saturn hasn’t always had such a big one and won’t always have it.
Earth has probably had one several times, probably a much thicker one then Saturn before
some of it coalesced into the Moon and the rest fell back down to earth or got flung
off out of our gravity well.
In many respects a hoopworld is simply ones of these, only made solid and stabilized.
In fact this would be a pretty good approach to terraform Neptune or Uranus mass gas giant,
using their rocky metallic cores as your exterior sheath and the gaseous part as your filler
material, generating gravity to hold people to the sheath while simultaneously keeping
that sheath from collapsing.
This would also, if you configured it with this in mind, generate one heck of a magnetic
field to protect the world from a lot of the nastier types of radiation and keep the atmosphere
on there.
As we discussed back in the Terraforming video, if you want a place to be livable in the long
term you need to either have a strong magnetic field generated by it, create an artificial
one around it, or not have an exposed atmosphere, like rotating habitats where everything is
sealed inside.
A hoopworld with a molten core or high speed filler material would have a very impressive
magnetic field more than capable of withstanding more volatile suns and the least hospitable
regions of the galaxy.
So while Hoopworlds at first seem even more ostentatious and impractical then Discworlds,
let alone Spherical Shellworlds, there’s quite a few circumstances where these would
have massive advantages.
Also like the Shellworld, but unlike the Discworld, it not only has seasons if tipped on its axis
toward the sun but also has tropical, temperate, and cold regions.
Also right down the middle you can have an object bobbing up and down, though it’s
periods more closely resemble those of a moon then a sun, like the Alderson Disc this is
not a great setup spot for a fake sun to light the place, the ‘day length’ it would take
to bob up, down, and back again is too long if it needs to get up high enough to provide
any light to the outer area of the hoop.
Just fine for a moon though, although it would need stabilization especially if the hoop
were tilted on its axis to the sun, which it needs to be or you’d have no light to
the inner sections.
But it would let you have a moon and tides.
Interestingly, the maps used in a lot of old video games, where if you went too far east
or west, north or south, and just emerged on the other side, at the same position, actually
corresponds to a torus shape.
If you played a lot of those old Nintendo RPGs you’d probably remember that but what’s
always amused me is some of them hade an extra Underworld below, and while you can have those
on a Shell World, there up is your up, they not flipped upside down like in Hollow Earth
models.
The cool thing about a hoopworld is you can actually do that flipped over version, using
a long interior rotating habitat, sort of miniature version of the Topopolis we discussed
near the end of that video.
Connecting the two is pretty easy, you just make sure the connecting shafts let you build
up speed, so that at the bottom of it you’ve matched speeds with the rotating section,
then climb up through any airlock mechanism in what would be its floor.
Of course you’d have too artificial light this underworld, but tis double your land
space.
Also just like the shell world, if you’re doing artificial lighting you can do additional
nested layers for your hoop.
And if you’re using lots of active support structures anyway, you can make some fairly
huge conglomerations of these hoopworlds, like a chain.
There’s no gravity in the center of these, and it’s very weak as you move out from
the center, so you could but your hoops there, or do an even more classic chain setup if
you put some sort of thin frictionless strip around the equators and slammed in a sturdy
atlas pillar, like we discussed last time, of great strength to keep the world from bumping,
and you could then create a long chain all the way around a star.
A Chainworld if you would.
Now we need to talk about both gravity and seasons.
Gravity is pretty tricky.
All symmetric objects will have zero gravity in their exact center, but only for a hollow
sphere is gravity zero everywhere inside it.
For a ring or Torus, as you move radially outward from the center gravity begins pulling
on you more and more toward the nearest part of the ring.
That’s why getting a moon in there is very tricky since it could be very easily perturbed
and crash into the ring.
If you go up or down from the center gravity points back to the middle but only straight
toward the middle if you’re up or down from the center.
Now gravity on or near the ring points basically in the right direction, down to the ring,
but it’s weaker on the inside than the outside and stronger at the poles.
There’s no simple equation for doing this and it will vary on how big the major and
minor radius are to each other, but keeping it just conceptual, here on the inner equator,
because our hoopworld spins to have night and day, gravity is somewhat stronger than
on the outer equator because of centrifugal force.
The hoop is spinning, on the inside that centrifugal force pushes in the same direction as gravity,
on the outside it is in the opposite direction and makes you lighter.
Gravity is stronger near the poles and especially on the inner side where centrifugal force
adds rather than subtracts to normal gravity.
Here’s a model Anders Sandberg created of that gravity, for a Hoopworld best approximating
Earth conditions, he did a nice article one the subject from the standpoint of naturally
occurring hoopworlds over on ANDART, which is linked in the video description, and is
another of the old hands over at Orion’s Arm, which is the group that basically inspired
this entire series and to which I’m an infrequent contributor.
Sandberg is also a neuroscientist and one of the leading minds on transhumanism so I’ll
be referencing a lot his work in the upcoming video on that subject.
I’ve heard it suggested that hoopworlds will probably have very spectacular aurorae
and it’s also worth noting that it’s the nature of such an object, already have a huge
radius, that it’s geostationary orbit is going to be very low, so space elevators on
these are pretty simple to build and about an order of magnitude shorter than one for
Earth would be.
And while the central point of the ring isn’t terribly stable you can build elevators out
to that and stabilize it by just having three lines running up to a central port, which
since pi is about 3 and the circumference is pi times the diameter is as many as you’d
probably want to build to expedite movement around the ring.
Okay, weather.
First we can tilts these just like Earth is to have seasons.
As the planet orbits the sun the side tilted toward it gets more light, same as the north
and south hemispheres get more light for half the year each, though I guess it would be
hemi-hoop here.
Second, unlike the discworld and like other normal spherical worlds there is a temperature
difference between the equator and… well we can’t call them poles, northern and southern
rings I suppose.
But it is what you’d expect, equator warmer than northern and southern regions, but only
the outer equator, the inner equator is colder since it doesn’t get as much light.
Weather for a hoop is hard to predict, because gravity varies significantly too with latitude,
and because a hoop has so much more centrifugal and Coriolis force driving its weather.
So it would be pretty volatile, but on the whole plausibly Earth-like, and so long as
the hoop spins once every 24 hours you could find places congruous to our native habitats.
There is a lot more to this concept, but that’s where we’ll wrap it for today, Sandberg’s
attached article covers a lot more of the nuts and bolts if you want to learn more.
Next time in the Megastructures series we’ll be taking our first look at star encompassing
megastructures with Shkadov Thrusters, a technique for moving entire stars, the simplest form
a Dyson Sphere to build.
We touched on Dyson Sphere concepts in the Dyson Dilemma video and its remake but we
didn’t do anything like properly explore it and that’s where we’ll be heading next
in the Megastructures series, starting with the Shkadov Thruster.
But before that we’ll be skipping back to the Habitable Series for a look at Double
Planets, which as mentioned is two of the routes in nature which could conceivably produce
a naturally occurring hoopworld.
As always, questions and comments are welcome, like and share the video if you enjoyed it,
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In the meantime you can try these other playlists, and we’ll see you next time.