I am thinking about the industrial capacity of the Culture. Setting aside the physical complexities of whether the thing would be structurally sound, could one be made?

Background: I was reading about the Ringworld by Larry Nevin, and came across a quote to the effect of "the Ringworld is an intermediary step between a planet and a dyson sphere." Which got me to thinking how big is the Ringworld, and how does it compare to an orbital?

Turns out, the Ringworld is 18,700 times bigger (by surface area) than a standard Culture Orbital. But the Culture has built "millions" of Orbitals, so the Ringworld itself is within the Culture's production capacity, though it seems like it would be a project for thousands of GSVs over hundreds of years. Let's say 10,000 GSVs over 200 years, for future discussion.

So then scaling up, a Dyson sphere at with Ringworld parameters (same "orbit, mainly). The Ringworld is 1 million miles across, for reference.

1 AU of radius means that the total surface area of an equivalently sized Dyson sphere is a mindbogglingly 7.031*10¹⁰ Ringworlds.

So, it seems like the answer is no? That's an increase in size that's truly hard to fathom.

I guess there's a different direction to take which is, "how long would it take to build a fleet big enough to build the sphere?"

From Excession, we know that GSVs can replicate themselves in 30 years. So if we take our Ringworld-building fleet and instead double it, what we're really doing is taking that 7.031*10¹⁰ number and dividing by 2^n, where n is the number of doublings, each taking 30 years.

Interestingly, 7.031 * 10¹⁰ is 102% of 2^36. So, if the Culture spent 1000 years doing nothing but functionally being a hegemonizing swarm in order to build a fleet big enough, they could theoretically pull it off. This does result in a kind of mind numbing 687 trillion GSVs. Let's assume instead that they're willing to take longer, say 1000 more years, and we only need 10000 * 10³¹ GSVs. Which is still 21 trillion, so I dunno how much better that is.

Then I guess I want to think about material. A Culture orbital takes 4x10²¹ kilograms of material to build. A Ringworld is 18,700X an Orbital (again, using surface area, which doesn't scale perfectly with mass, but I'm not sure how much of a distinction it really makes). And the dyson sphere is 7.031*10¹⁰ Ringworlds.

Run all those numbers together, and you get 4x10²¹ * 18,700 * 7.031 * 10^10. Result, 5.259 * 10³⁶ kilograms. Or more relevantly, 2.644 * 10⁶ solar masses. That seems like an insurmountable problem. There are 100 billion stars in the milky way, we won't miss 2.6 million of them. But I don't believe the Culture have any where near the logistical or engineering capacity to move suns with any kind of expediency. I don't think any amount of ship doubling fixes that.

I guess the final thought is energy-to-matter conversion via energy grid, so as to not need to move the suns around, but I don't know where to get any numbers on the throughput of a ship's ability to convert it to matter. Interestingly, and only ever so slightly related, 1 kg of mass is roughly equal to 25 exawatt-hours of energy. Total energy required to create the dyson sphere is 4.726*10^53. If someone knows how much energy per second we can get from the grid we can do that math I suppose!