Gigastructures, Terastructures, and beyond

[Xannari Ferrows]

Okay, to start smaller, a Megastructure is easy to visualize. A very large structure usually compared to a dam or something. Dams aren't too absolutely huge, even though they are quite towering; it's easy to put their sizes into perspective.

But... What's the next step up? A gigastructure can be a little more difficult, but let's go take a look at some larger things.

Let's see the island of Palm Jebel Ali, a man-made island! This thing is absolutely huge, and while not the largest thing ever built, it is the largest island ever "built". Standing upright, this thing would tower over the Hoover Dam, at only 220 meters. It would stand a crazy 8 Kilometers tall! It's not breaking any records in distance or anything, though, so let's go further, dubbed temporarily, a Terastructure.

Take a look at the Great Barrier Reef. Although not manmade and technically not one object, it's designated length is a crazy 2.6 Megameters. That's a lot... But if you want something man-made, look at the next thing: The Great Wall of China. This thing is nuts, and while it doesn't have a very moral origin story, it's a fascinating structure, stretching for 8.85 Megameters. Distances like this are still fairly sedate when you remind yourself it was built by people.

However, it get's weirder. What would qualify as the next step up would be something the size of Uranus! [i swear, if anyone takes that out of context...]

Nothing even remotely close to this had been built, but if you believe that a structure doesn't have to be man-made, look to planets for this answer.

That's a massive structure, obviously beyond our capabilities for the time being. This isn't where the journey ends, though.

If you've ever heard of a Dyson Sphere, you'll know something this huge would be bigger than our entire solar system, encapsulating even Pluto, and if we really wanted to go all the way, even Sedna [not likely]. Something this size would be... Just, ginormous. There's no other word for it. It would be worthy of the title as an Exastructure, and if we wanted to capture Sedna, maybe even a Zettastructure.

Speaking of Zettastructures, I'm not even sure something this huge could exist. Theoretically? It would have to be extremely sophisticated, and advanced at the same time. Something this huge, at at least 150 Terameters in diameter, would be much longer than a light day. If this object were to pop into existence right now, it would be able to stretch from Voyager 1 to the sun, and back...

757 times... As of right now, that is. This distance can only grow larger. Don't worry, it gets scarier.

Now in the realm of something I consider impossible, but would enjoy being proven wrong on, the Yottastructure. This is a structure that would be so huge, it would span the distance from Proxima Centauri to Alpha Centauri A. Anyone that knows the number of that distance would have their jaw on the floor right now. Not quite the distance of Gomez's Hamburger [Mmmm... Delicious] from end to end, but still ridiculously impressive.

This is the realm of impossibility right here. An unofficial term for something bigger than a Yottabyte was created, and named the Brontobyte, which I think is clever. Regardless, what would be a Brontostructure? How big would that be? ...Well, how do I explain this...

A structure following the rhythm of it's defined namesake, a structure that would be classified as a Brontostructure would... Well, first of all be impossible, and secondly, be the size of the Tarantula Nebula, the largest known nebula, and the size of what would qualify as a Dwarf Galaxy I think. That's larger than an Exameter by far, which is already a distance difficult to appreciate! Nothing this big can really exist as a single, joined object, but maybe we could go back to the Great Barrier Reef, and make a system of intercommunicating objects. That sounds like a fun school project.

If you want to look at the largest object in existence, take a look at the Hercules-Corona Borealis Great Wall. Stretching a mind-blowing 3 Gigaparsecs in average diameter, it's length is only trumped by one thing: The distance from Earth to the Hubble Deep Field, which is an incredible 3.85 Gigaparsecs! Distances like this are just too big for our minds to comprehend. I mean, come on. The only thing bigger than this distance to measure within the observable universe IS the observable universe! If you want to get into distances much larger than 93 billion lightyears, look up Teraparsecs, and Petaparsecs. If you really want to give your brain a run for it's money, go beyond with Exaparsecs, Zettaparsecs, and Yottaparsecs even! I'm starting to sound like I'm advertising or something...

Regardless, these are huge structures. How big can we build?

Edited September 18, 2015 by Xannari Ferrows

[Bill Phil]

Depends on our total energy production. The Great Wall is long, but not very thick. And now we have more energy available.

[shynung]

We need more than energy to build structures, we also need materials. Concrete, rebars, I-beams, cables, and struts are the most common basic materials. Along with all that, we also need labor, as in someone/something to actually assemble them into usable structures.

To expand, it depends on our energy production capability, access to building materials, and the amount of workers we can afford to have at any one time.

Edited September 18, 2015 by shynung

[Bill Phil]

We need more than energy to build structures, we also need materials. Concrete, rebars, I-beams, cables, and struts are the most common basic materials. Along with all that, we also need labor, as in someone/something to actually assemble them into usable structures.

To expand, it depends on our energy production capability, access to building materials, and the amount of workers we can afford to have at any one time.

But it requires energy to get the materials.

[magnemoe]

Depends on our total energy production. The Great Wall is long, but not very thick. And now we have more energy available.

Yes, in fact the great wall is more like a highway or an railway, its long, thin and build over time. Both are far longer, you can take the train or drive from china to Europe.

[shynung]

But it requires energy to get the materials.

Sure. What I'm saying is that pure energy alone won't do the job.

[Bill Phil]

Sure. What I'm saying is that pure energy alone won't do the job.

Yes, but energy determines the amount of material that can be moved/ acquired and used.

[shynung]

Yes, but energy determines the amount of material that can be moved/ acquired and used.

Yes, I agree. But we can't build anything without piles of material that we can actually use. There isn't so much we could do with just power stations alone.

[kerbiloid]

Any building is just a structurized region of space, a grid of potentioal barriers.

Different sub-regions (in human slang - "rooms") are separated by (electromagnetic) potential barriers (so called "walls").

The "wall" which prevents you from transition into the state with lower potential energy is also called "floor".

The "wall" which prevents some objects with higher potentional energy to enter you place is called "ceiling".

Why to structurize any space larger than several km in height and several km in diameter at all?

Population density of a city, say, 3000 humans/km².

Binocular vision range - several meters, so a ceiling of a large atrium (say, of a large cathedral) is on "visual infinity" and doesn't "press" you visually from above, as also the sky doesn't.

So, we can slice a city into layers each 100 m height with virtual "sky with clouds" and city people won't see much difference.

In this layered city we have 100·1000 / 3000 = 33 m³/human.

The biological studies of 60s gave a result: a spaceship would provide 27 m³ per human to let this human feel enough comfortable in long flight.

This number is close to what we have gotten above.

So, let it be 50 m³/human to feel more or less happy.

One billion people = 50 bln m³ = 50 km³

50^1/3 = 3.7 km.

So, a building 5x5x5 km is enough to let one billion people live as in usual city.

How many people anybody can imagine to use those Dyson spheres and other megalomania?

[PB666]

We need more than energy to build structures, we also need materials. Concrete, rebars, I-beams, cables, and struts are the most common basic materials. Along with all that, we also need labor, as in someone/something to actually assemble them into usable structures.

To expand, it depends on our energy production capability, access to building materials, and the amount of workers we can afford to have at any one time.

Those are surface mats, however in space you want to build light, you will be using carbin fiber and other organic chem mats.

Let me give a example supposse we wanted to create a is launching system using centrpedal force around a star, you could build such a structure in orbit around the star using say spiders silk, however as you accelerated your force would increase and it would stretch. The same is true if you built along the normal of the orbit, except after a few degrees your object would cave in. Inertia is a big killer in space, you need to have a high strucural integretity to weight ratio. Particular good stretch resistence. The diamond reference i gave is a good example of stretch resistence. the basic problem is that all the lightstuff is in the outer solar system, we need to get it and bring it back toward the star, metals are useful, carbon is not particularly resilient to Ionizing radiation.

[Pipcard]

So, a building 5x5x5 km is enough to let one billion people live as in usual city.

But what about everything that would support them, like farms?

[Nuke]

i think a more important question might be why? what function would such structures serve?

one thing i can think of is a dyson sphere network. individual spheres would generate power and this would be beamed through space using microwave, lasers or whatever. receiving dishes would probibly need to be very large themselves. the huge amount of energy this would create could be used for interstellar travel. have power stations with a receiving dish and powerful lasers for beamed power for your engines (they could act as energy repeaters to refocus the beam). have them placed throughout various trade routes. you could also ride the beams directly with solar sails, perhaps have an accelerator beam in one direction and a decelerator beam in the other almost in parallel with each other. accelerate in one and maneuver into the other lane when you get to the half way point.

you could also build smaller spheres or rings around white dwarfs for really long term settlements. you could take advantage of the compact nature of these stars to make construction a bit more feasible. also with lifetimes in trillions of years, should keep humans alive till the heat death of the universe.

Edited September 18, 2015 by Nuke

[cantab]

You aren't going to be building a solid passive structure much larger than Earth, if that big. There comes a point when no theoretical material can hold up its own weight and the structure will collapse.

To go larger it can be a network of some sort, not a single structure. The largest things we have already built are networks - the global telecoms network, the internet, the road network, and so on. The original concept of a Dyson sphere was a network of solar power satellites that would relay power presumably by microwaves, the "solid ball" idea is an invention of science fiction writers.

The other way to go larger is with an active structure. The "space fountain" is one such concept, with a powerful particle beam going up and down it, the reaction force to turning the beam at the top holds the tower up. A ringworld might counter its own weight by spinning, though it would still need station-keeping to avoid hitting its star or planet.

[andrewas]

Which is why sensible aliens will build things closer to Halo than Ringworld.

[YNM]

If you consider length on surface and not height, then the Interstate Highway System could be the answer, or China's new expressway project (it's actually gonna be longer than the IHS). On total, the largest structure humanity have build are road networks, or rail networks - we do connect worlds physically. Safe to say, at a point, having a few round-the-world road network doesn't sound that far off...

[Pixel of Life]

So, a building 5x5x5 km is enough to let one billion people live as in usual city.

That is not true. With a standard ceiling height of 2.4 meters, the 5x5x5 km cube would have 5000 m / 2.4 m = ~2083 floors and a total floor area of 2083 * 5 km * 5 km = ~52000 km^2. Even with the population density of Tokyo (~6000 people per square km) it would only have enough room for a bit over 300 million people.

And remember, this is assuming 100% of the station's floor area can be used for habitation. In reality, that is not possible because a significant fraction of the available space is taken up by station systems, transportation, medical facilities, stores, parks, schools, you name it.

E: Well, it would be possible, but considering the above you'd probably need a population density 4, 5 or even 6 times that of Tokyo in order to fit a billion people in there, and it certainly wouldn't be comfortable.

Edited September 18, 2015 by CaptainKorhonen

[problemecium]

My prior readings on the Dyson Sphere have told me this:

- Basically everything acts like a gas on a large enough scale: things like gravity end up becoming more powerful over the length of the object than the bonds between its atoms. No known material is anywhere close to strong enough to build a rigid hollow sphere big enough to enclose the Sun.

- If you did build a giant sphere around the Sun, due to some interesting mathematics, it wouldn't be affected by the Sun's gravity and would thus drift freely as it orbited the galactic core. Given enough time, the Sun would reach the edge of the sphere and burn through the wall. At this point the sphere would be once again subject to its gravity, but... it's kinda ruined now.

- A non-rigid sphere could be built around the Sun: either a cloud of satellites orbiting at different angles or a formation of satellites hovering using radiation pressure. At these scales, radiation pressure is enormous and can support an incredible mass, but the necessary density has a maximum threshold, in terms of mass per unit surface area. Even a piece of tissue paper is much too heavy to do this, so we'd have to invent some kind of ultra-thin, ultra-light solar array.

- If all of the energy emitted by the Sun is trapped within the Dyson sphere, all of the space within will inevitably reach the temperature of the Sun. Kinda bad for people on Earth.

- The Dyson Sphere needn't enclose the entire Solar system. More commonly, plans involve a radius of 1 AU or even smaller. Nevertheless, this is big enough for all of the above concerns to be valid.

[PB666]

My prior readings on the Dyson Sphere have told me this:

- Basically everything acts like a gas on a large enough scale: things like gravity end up becoming more powerful over the length of the object than the bonds between its atoms. No known material is anywhere close to strong enough to build a rigid hollow sphere big enough to enclose the sphere

yeah im not sure why people are brimging up the massive scale thing. You could build essentially a circle around the sun, and you could build up and down in the normal a little bit and you could actively maintain its orbit given n-body problem. The base problem is that if you attempt to make a sphere it would collapse in the normal.

- If you did build a giant sphere around the Sun, due to some interesting mathematics, it wouldn't be affected by the Sun's gravity and would thus drift freely as it orbited the galactic core. Given enough time, the Sun would reach the edge of the sphere and burn through the wall. At this point the sphere would be once again subject to its gravity, but... it's kinda ruined now.

Of course it would have to be in orbit. It would have to be light enough outwise the sun would start falling apart.

- A non-rigid sphere could be built around the Sun: either a cloud of satellites orbiting at different angles or a formation of satellites hovering using radiation pressure. At these scales, radiation pressure is enormous and can support an incredible mass, but the necessary density has a maximum threshold, in terms of mass per unit surface area. Even a piece of tissue paper is much too heavy to do this, so we'd have to invent some kind of ultra-thin, ultra-light solar array.

radiatin pressue is not suuficient enough even to support a solar pressure. The radiation itself can be radiated, gas at the pressure of the outeratmospher of the sun would taken generations to build up. in theory if you had an uktralightstrong material you coukd use solar wind and solar pwer to accelerate the circle launch vehicles. The problem is that the anti

- inertial force applied by the structure is built in the orbital vector and the radial force that comes from the radial. A carbon carbon bond can stretch a few percent and so the orbit would swell. lets asuume the dyson wheel is in orbit, The down forces comes from translations in theta, so for instance the downward force of a motif 1.5A long in the orbital is sine(1.5E-10/150,000,000,000) * breaking force of structure along the 'thread' = 1E-20 stretch strength. The breaking energy per unit is 348kJ/mole and a mole is 6.0229E23 atoms. but two of the angles are at 120 degress to a single orbital sp2-sp2 orbital. It comes out to about 2E-20, but at best we can get half 1E-20. That is a strength of 2E-41 per bond in the radial direction when curved into a circle of earths radius. The strength is carrying a particle of mass 12 daltons or ~2E-24 kg.

Corrections if any welcome will finish later.

Edited September 18, 2015 by PB666

[0111narwhalz]

I've heard of some kind of "Dyson Rail" which uses massive weights orbiting the star, and running on mag-lev tracks. They would tend to keep the shell centered, while requiring only (relatively) small energy input.

[Armchair Rocket Scientist]

Population density of a city, say, 3000 humans/km².

Binocular vision range - several meters, so a ceiling of a large atrium (say, of a large cathedral) is on "visual infinity" and doesn't "press" you visually from above, as also the sky doesn't.

So, we can slice a city into layers each 100 m height with virtual "sky with clouds" and city people won't see much difference.

In this layered city we have 100·1000 / 3000 = 33 m³/human.

The biological studies of 60s gave a result: a spaceship would provide 27 m³ per human to let this human feel enough comfortable in long flight.

This number is close to what we have gotten above.

So, let it be 50 m³/human to feel more or less happy.

One billion people = 50 bln m³ = 50 km³

50^1/3 = 3.7 km.

So, a building 5x5x5 km is enough to let one billion people live as in usual city.

How many people anybody can imagine to use those Dyson spheres and other megalomania?

Hang on... are these "27 cubic meters per person" figures based on astronauts or the general population? Because a spacecraft crew is automatically be made of individuals with a very high tolerance for close quarters and no privacy.

27 cubic meters is a 3m x 3m x 3m box, or with 8 ft ceilings a room less than 11 by 11 feet on a side. That's an average bedroom in America. Probably most prisons have FAR more space per person once you count all the "public" spaces, structure, etc... and they're far from a "comfortable" environment.

You're also forgetting that a city with a high population density will already be built up vertically, so there's more "habitable volume" than you'd think. And actually a habitable volume study is only relevant for spaceships: on Earth you need to think about habitable area: spaces will usually be a mixture of heights, from 2.5 m (comfortable personal/family quarters, offices, etc) to 10 meters and above (large public spaces).

The city you are proposing would most likely have concentration-camp-like conditions.

EDIT: There's something very wrong with your math. A city with 3000 people per square km has 333 m^2 of area per person. Not all of this is habitable, but buildings have multiple stories. For any "sky-like" ceiling height that works out to thousands, or even tens of thousand of cubic meters per person.

Edited September 20, 2015 by Armchair Rocket Scientist