[sorwin]

I don't quite understand the idea or fascination behind the Dyson spheres. Isn't it much more complex to acquire the materials, build, and maintain the structure than to simply build localized nuclear power generators where they need them? Surely it's a lot easier to capture more power of a controlled fusion reaction than build a huge megastructure in space where objects can collide at immense speeds and cause devastating damage.

[thesimp]

Dyson spheres are a nice way to look at what humans are capable of in the future. That is why they probably capture the imagination.

I actually do not see them as much more than beefed up solar panels. 50 Years ago a solar panel was something that most people saw on a novelty pocket calculator. 30 years ago people started thinking about solar panels to actually power a house off-grid. 20 years ago people started things about solar farms that could give useful power to the grid. And now solar panels are ubiquitous and just about anyone can put them on a roof of a house and the world makes them in such large numbers that it is hard to imagine the number of panels made per second.

Maybe in 20 years time we will find out that a solar panel in space is much better because the sunlight does not have to travel through the atmosphere. So why not put large panels in space. Then in 40 years time we understand that we need to position them closely around the sun to get the maximum power output. Of-course the power cord is a bit long to earth so you then also put your factories on those panels. Which is no problem because launching large reusable rockets in space is a problem that is being solved right now. And breaking factories down in container sized chunks to transport them was already invented 60 years ago with containers and container ships.

[TheLoafOfBread]

> Maybe in 20 years time we will find out that a solar panel in space is much better because the sunlight does not have to travel through the atmosphere

It is basically guaranteed that microwave or laser beam from there is going to have a dual use purpose. As a source of energy and as a directed energy weapon. And it is a quite high chance that it will get banned by power which did not build it. Be it China, Russia, EU or USA.

[TheLoafOfBread]

You are correct, it is an absurd and nonsensical idea. Especially from the material perspective. People will tell you that you need only XY amount of weight, which is just few percent of all the mass in solar system... but last time I checked, we are not grabbing random soil from Earth and putting it into a form of a satellite like a sandcastle. We need very specific materials put together in very specific way, where some of them are in very short supply to be wasted on Dyson swarm.

Of course, somebody will chime in and tell that advanced civilization could transmute any matter into any other matter. But if that would be possible, then it is completely negating any motivation to build Dyson swarm at a first place, because you can just transmute your toxic waste from local your local dump into antimatter and you have virtually endless amount of energy at your disposal.

[Veserv]

You are thinking about the wrong order of magnitude.

The sun emits ~3e26 J/s [1].

The internet claims hydrogen fusion generates between ~5-6.5e14 J/kg [2][3].

The internet claims there are ~5 trillion tons of known Hydrogen reserves [4] which is ~5e15 kg. So, if we perfectly fused all known Hydrogen reserves, that would be ~3e30 J, or ~1,000 seconds (~16 minutes) of total Sun output.

The internet claims the Earth is ~260 ppm (~1/4000) Hydrogen by mass [4]. The Earth is ~6e24 kg. So, that is ~1.5e21 kg. So, if we perfectly fused all Hydrogen inside of Earth, that would be ~1e36 J or ~3e9 seconds (~100 years) of total Sun output.

Portable fusion, if possible, would be great for localized power. But if a civilization wants long term power at total solar output scales, then only known source is total solar output. Nothing else known has enough fuel to support that level of usage, let alone the challenge of actually fusing that much material.

[1] https://www.sws.bom.gov.au/Educational/2/1/12

[2] https://www.quora.com/How-much-energy-is-produced-by-the-fus...

[3] https://www.phys.ksu.edu/personal/wysin/astro/review9/p4.htm...

[4] https://en.m.wikipedia.org/wiki/Abundance_of_the_chemical_el...