Well if you're building it out of stones or other rock probably around 15km since that is around about the tallest we think mountains on earth can be.
this post was submitted on 11 Feb 2025
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Semi relevant xkcd What if we built a 1 billion story skyscraper?
This is a building a pyramid won't sway in the wind etc.
I wonder if we can reach space by combining a pyramid like steel base and then into space elevator
Are there any restrictions on material?
If not, I have stack of dirty nitrogen in my backyard over 100km tall, technically reaching space.
I'm pretty sure anything physical referred to as a pyramid would have to keep its shape, and therefore must be a solid.
How tall a pyramid would you have to build before the base is too wide to reach the ground due to the curvature of the earth?
I don't see why the base would have to be flat. It could have a spherical volume carved out the bottom to accommodate the goofy little planet below
You wouldn't even notice seams. Line the width of human hair if you're using similar to Egyptian pyramid blocks
What would you do as the side length of the base approaches the diameter of the Earth
Stop? Somewhere around 1/3 of the diameter for a 45deg sloped pyramid, adding more layers would start projecting off the sides, offering no additional support for the new layer. Drawing a teardrop shape with a perfectly circular head and perfectly tangential tail with be the same as a cross section of this planet/pyramid
0cm
Because anything we build, future generations will say "THE ALIENS DID IT"
Only if africans built it
Depends on the compressive strength of the material. Sooner or later the weight of the pyramid above the base exceeds the base's ability to support it. Considering that a mountain is basically a stone pyramid, Everest has to be in the neighbourhood of how tall you could go -- call it 10-12 kilometers high. Other materials would do better.
I'm not convinced Mt Everest represents the most weight normal earth can sustain but rather the most height gained by regular tectonic motion. However, I stead of asking how much weight can stony earth support before collapsing, it leads me to ask how much weight can the crust support before buckling? Perhaps this project has diminishing returns as more weight above causes the crust to bulge downward and compensate.
Imagining an aerogel pyramid 30 miles high getting blown around the world
This made me think "WHEEEE!" when I imagined riding along, and that made me think of the longest cocktail party from the hitchhiker guide to the galaxy. So thanks I guess.
With the way the bricks are laid, wouldn't it distribute the weight across the entire base?
Yes, but it doesn't matter enough. The square-cube law means that the mass being supported goes up faster than the area of the layer doing the supporting does. So each additional brick on the bottom still ends up carrying more weight as the pyramid gets taller.
That's not really the limiting factor for pyramids. If you were to build a shape of equal height, say a cube, then yes this would be the main issue.
What are the failure modes for a pyramid?
- A 45° pyramid can't tip over since it's center of mass is always sufficiently far enough from the bottom edge. So tipping isn't one.
- I'd say bending through cross winds is also not an issue for a pyramid unless you make it out of jello. So that's also not a failure mode.
- Crumbling of the bottom layers because of the weight of the top layers is definetly one.
- Uneven foundation strength can cause the supporting area to be weaker in some spots more than in others, so that's another failure mode.
I'd say the crumbling and Foundation issues are heavily mitigated by 2 main factors.
1st:
The outer edge is always of height zero. As the pyramid grows in height it also gets wider, but the only point that is at risk of imminent collapse is the very center of the pyramid, since it is the only point that will reach a critical supporting mass first.
Let's say the pyramid reaches a height and the furthes block at the bottom in the center crumbles (let's assume it actually turns into straight up dust). The clumbled block will still support some pressure but will also transfer it laterally into the adjacent blocks (essentialy like a liquid). Now the main question is "How many adjacent blocks does it need to support one crumbled block?". If the answer is ≤1, than you have no problem, because with each new block in height, the pyramid also gets 1 block wider at each side. Similar to water pressure, the lateral force the blocks exhibit will increase linearly with height therefore never outpassing the increase in pyramid width. If it's >1 than you will reach a point where the outer walls of the pyramid will start to collapse from inside pressure, and that will be your limiting factor for height.
2nd:
The blocks can be cemeted together, so whatever forces are being transfered laterally will not only be supported by the adjacent blocks, but also blocks adjacent to them and so on, and so on...
Same thing goes for uneven foundation strength. The local decrease in support will be spread over a wider area because the blocks are merged together. Also Pyramids are usually not build block on block, but with a 50% offset, which will further aid to stabilize the structure.
Usually, If you look at mathematical calculations for things like sky elevators the form to support the structure looks like a symmetric reciprocal function. This function actually requires way less material to support the weight of the center piece of the structure than a pyramid. So not only could a pyramid essentialy support itself until earths centrifugal forces take over, it would also be way too overkill in doing that.
Space is defined as 100 km high.
For the first 10 km or so, with current technology, it's possible to imagine a very light structure in part composed of big impermeable fabric envelope filled with hydrogen that would have a net weight of about zero because of buoyancy in air.
The difficult part is the next 90 kilometers high for which i believe we wouldn't be able to build anything that could sustain its own weight.
On the other hand, if cost and energy was not an issue, with current technology, we could build enormous number of big tanks into which we would pump all the atmosphere, so the height of space would come down to sea level.
... of course we would then have also to put oceans and all bodies of water in tanks, otherwise they would boil out into space.
This design project might interest you, but do notice that it is not currently possible.
That was an incredibly interesting read. Do you know of any other planned mega structures like that?
Oh there are many wild ideas.. I don't know of any other pyramid shaped ones though.
For other shapes, I think The Line in Saudi Arabia is worth a mention, because it's actually being built. Slave labour and other issues aside, it's interesting that they attempt to follow through on such an insane plan.
Basically as tall as tallest mountains - 8km before gravity starts overcoming the materials. Using stronger materials would allow building higher, but not too much
Probably 5