[Ultra-Tech] Conservative hard SF... but not implausibly conservative

[Anthony]

Originally Posted by AlexanderHowl

If each colony of the Dyson Swarm requires 300 square kilometers of solar panels, there will be 150 trillion SM+16 colonies. With a mass of 1e7 per colony

That mass estimate seems extremely high.

For a statite swarm, the total power output of the sun is 3.8e+26 watts, which means its total light pressure is about 1.3e+18N. Solar gravity at 1 AU (we could do it closer, but we sort of don't want to) is 6e-4N/kg, which gives us a total potential mass of statites of 2e+21 kg; at 0.4 AU that's reduced to 3e+20 kg.

A 1 AU sphere has a surface area of 2.8e+17 km^2, implying a mass of around 7 tons per square kilometer; the areal density at 0.4 AU is the same. An orbiting solution could be heavier but would still tend to be mostly lightweight mirrors.

[sir_pudding]

Originally Posted by AlexanderHowl

It comes down to the basic assumption of a Dyson Swarm, that it is a swarm of habitats that in totality absorb over 99% of the emissions of a star.

This isn't a requirement. All it needs to do is collect enough that it would be detectable in the IR spectra of the star, which depending on the sensitivity of your telescopes, is significantly less than 99%.

It also doesn't include the habitats, just the collectors.

[Fred Brackin]

Originally Posted by sir_pudding

Yeah what you want is carbon, mostly, probably.

Which you could get by disassembling gas giants and then fusing the hydrogen to helium and the helium to carbon. Small but otherwise useless rocky bodies you use for synthetic granite counter-tops in your many many habitats.

Why yes, there is quite a bit of energy released as a by-product of your carbon-building. That's probably discarded as you only want solar energy.

One reason these sorts of aliens don't fix Fermi's Paradox might be that older alien species spot them early and treat them like metastatizing cancer.

[Flyndaran]

All of these speculations still assume very human psychologies. That may be plausible, likely, or even inevitable, but I'm not so sure.
Especially once you reach the technology capable of changing your nature, who knows how societies are likely to develop? We haven't reached it and we have little to no clue how we'll change.
It seems like only have one species of pond scum and trying to speculate how all of its descendants will behave over the next billion years.

[Michael Thayne]

Originally Posted by Anthony

It's not guaranteed that a fusion rocket is feasible at all, and getting usable power density may be an issue, but if it's possible at all, probably a few percent of c.

Why is this? Exhaust velocity equal to a few percent of c is what Atomic Rockets indicates as the theoretical maximum, but as I've been researching this, I'm seeing a lot of estimates of ~10^7 m/s, maximum.

[Ulzgoroth]

Originally Posted by Fred Brackin

One reason these sorts of aliens don't fix Fermi's Paradox might be that older alien species spot them early and treat them like metastatizing cancer.

You, uh, probably mean something other than 'desperately attempt broad-spectrum poisoning of the entire region, and anticipate a poor prognosis'...

[whswhs]

Originally Posted by Ulzgoroth

You, uh, probably mean something other than 'desperately attempt broad-spectrum poisoning of the entire region, and anticipate a poor prognosis'...

I think Fred may have been thinking "surgery" rather than "chemo."

[Ulzgoroth]

Originally Posted by whswhs

I think Fred may have been thinking "surgery" rather than "chemo."

Metastasis means surgery isn't really going to fix your problem anymore because the cancer has gone free range.

[Fred Brackin]

Originally Posted by whswhs

I think Fred may have been thinking "surgery" rather than "chemo."

"Radiation" might be the appropriate metaphor. "Imminent danger of metastasis" might be the technical description.

[Ulzgoroth]

Originally Posted by Fred Brackin

"Imminent danger of metastasis" might be the technical description.

That's your key thing, there. Metastasizing and looking likely to metastasize soon are profoundly different in implications...