Hacker News Reader

Comment by ardit33 | Hacker News Reader

Dyson spheres are just inane.... sorry but they don't make sense.

Any advanced form of civilization that can build one, probably figured how to do fusion efficiently locally and doesn't have to build these insanely inefficient energy harversters.

Keep in mind that the sun is very inefficient at energy release.

Dyson sphere prediction is like predictions in the 1800s how we would have coal and steam powered airships to travel around.

The reality is that steam via coal fire is too inefficient. Coal is just too heavy. Jet fuel is much more efficient/energy dense and not need to build giant airships.

Same with any advanced civilization. Dyson spheres just don't make sense, but they sure make good sci-fi movies/stories for the gullible.

View on HN

"do fusion efficiently locally" - with what? The vast majority of available fuel is in the stars. Dyson spheres are different than planet size civilization. For planet size civilization, with population in the order of billions/trillions ppl, local fusion is probably good enough. But for populations a billion times bigger, so billions of billions of ppl, you need dyson spheres, or alternatively, a way to destroy stars and get the raw hydrogen - probably harder to do.

Hint: Jupiter is made mostly out of hydrogen. Saturn too. Uranus and Neptune, if those get used up. Also plenty of helium, maybe even more useful.

Also: the Pacific, Atlantic, Indian, and Arctic oceans are made of water, which has hydrogen in it. Also all of the Antarctic and Greenland ice, the Great Lakes, Caspian Sea, Lake Baikal, and Lake Victoria.

Jupiter is much smaller than the Sun, so it isn't really relevant what it's made of.

It is right there, completely unused, and not too hot to get close to.

Most likely you would use up Neptune first, and save Jupiter for later.

Why wouldn't they do fusion locally but also build a Dyson sphere? Doing only the former produces less energy than doing both the former and the latter.

The view that they wouldn't do both is premised on the assumption that they won't need or want that much energy, combined with the assumption that the problem of disposing of the waste heat makes the extra energy not worthwhile.

Because building out a Dyson sphere is a hell of a lot of trouble to go to for something you manifestly don't need.

"Why buy the loaf when you get free slices?"

The word "need" is misplaced. It's not about need. It's about whether the upside of the additional energy is bigger than the downside of having to build the thing out. You're making an assumption that that upside is too small relative to that downside.

You assume that energy would still be considered a limiting resource. When you have overabundant energy, your choices are driven by other concerns. With plentiful energy, materials are cheap, dismantling moons and minor planets. The actually valuable commodity becomes cold, because high-energy processes produce waste heat that must be radiated away, so you move out to the Kuiper belt.

It's worth noting "Dyson Sphere" is a product of sci-fi literature. Freeman Dyson himself only described an "artificial biosphere" in some paper he published, sci-fi authors mistook him literally (or were just being creative). He wasn't even describing anything resembling a physical sphere surrounding a star.

He speaks to the subject in this excellent interview playlist, link is to the specific Dyson Sphere part:

https://www.youtube.com/watch?v=GPB775_BZlw&list=PLVV0r6CmEs...

The ingredients for fusion reactors (deuterium, tritium and helium-3) are rare, not fully reacted intermediate byproducts of the proton-proton cycle that powers the sun.

The likeliest case for a Dyson Sphere civilization would be some sort of solar powered Gray Goo von Neumann replicator.

In theory you can fuse up to Iron.... the last stage of stars. You are not limited to just Hydrogen.

I assume that some of fusions done by the star are net energy consumption (i.e. not usable for energy production)

You assume wrong. Anything beyond iron is made in a supernova, i.e. in the last moments before it is not really a star at all, anymore.

takes a star's worth of gravitational force to push atoms like those together in the core to produce fusion.

To reproduce such heavier elements in fusion reactors on earth would require, likely, a much higher energy than the output.

The ingredients for the most primitive, low-tech, hayseed fusion reactors are sort of rare. But anybody with any sophistication at all has no need for such primitive processes. They fuse plentiful regular hydrogen, helium, and, not to be wasteful, whatever they get from fusing those, too.

It is not very meaningful to talk about the efficiency of something that is already running and needs no more fuel for the next billion years.

Wouldn’t the theoretical maximum output of a Dyson sphere (the entire output of a star) dwarf that of doing fusion yourself locally?

If you were using that much energy you would have the much bigger problem of disposing of all the waste heat afterward. You could not do that close to a star.

Not necessarily as some stars are wasteful (use energy to fuse bigger atoms) or have material in the core it can't fuse. If you are just concerned with energy output per mass you can do better artificially in theory

> the sun is very inefficient at energy release

I'm not clear what is meant by "inefficient at energy release". Does that mean that the in the process of energy release, some of the energy is converted into heat? I.e., more energy?

Presumably if your super-advanced civilization needed more energy than could be fused from all the matter in a planet, you would have to get it from a star.

Or use a bigger planet.

Presumably if you are a super-advanced civilation, you would get power from what would appear to us mere primates as essentially thin air, in a fashion we can't even fathom.

"Any sufficiently advanced technology is indistinguishable from magic."

So a Dyson Sphere is inane, but energy from nothing isn't? Got it.

I'm right here with you, love the haters too that downvote you. The real takeaway is simply this: we don't (and can't) KNOW what type of energy advanced civilizations will have (and we might not even be able to understand it if we saw it!), and collective scientific time is much better spent on things that we DO know, like searching for bio markers similar to earth.

Reply on news.ycombinator.com