Type III Societies (Apparently) Do Not Exist

Re:Type III Societies (Apparently) Do Not Exist by DennisP on Friday April 29, 2016 @10:03AM (#11595754)

Stars use different fuel than reactors. To fuse simple hydrogen, four nuclei have to collide at once. This is so unlikely that it requires a very large mass of fuel to sustain a reaction: at least the size of the Earth, according to one article I saw.

It's entirely possible to burn deuterium in small reactors but there's only about 1/2500 as much deuterium as hydrogen.

(Perhaps some unthinkably advanced civilization could figure out how to get energy from hydrogen fusion in a small reactor, but you did specify "our current understanding of physics.")

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Re:Type III Societies (Apparently) Do Not Exist by Retric on Friday April 29, 2016 @10:15AM (#11595831)

That's not accurate, stars have several fuel cycles for pure hydrogen. At 1.3 solar masses you sun mostly get: https://en.wikipedia.org/wiki/CNO_cycle

As to size, on galactic scales all our current fusion designs are tiny. Scale it up to even just 20 miles on a side and proton proton fusion is doable. For a type III civilization capable of destroying starts that's also tiny. Remember your suggesting dysons spheres as the 'reasonable' option.

PS: The proton proton chain also produces deuterium as an intermediary. https://en.wikipedia.org/wiki/Proton%E2%80%93proton_chain_re...

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