JLowe said:
In my opinion, the most realistic way some far, far future ultra technolohically adcanced civilization would get their power would be fusion. Stripping the gas giants if they had to. Sounds unrealistic, but much more realistic than a Dyson sphere. If they were totally efficient, there's enough raw materials too sustain them for a very long time.
If it turns out fusion can't be mastered, I doubt any civilization would ever be able to exist that long honestly.
Fusion power plants still use the Carnot cycle. In order for the Carnot cycle to work you need a heat sink. There will be radiators. The radiator surfaces give off infra red. That star has a Dyson swarm.
The Sun is a fusion power supply. Why would you not use it?
Lithium and deuterium stocks exists but they are limited. As energy supplies they would be useful in the Kuiper belt, Oort cloud, and in interstellar colonies. Deuterium has uses in transmutation and lithium has numerous technology applications. Accessing deuterium reserves in Jupiter, Saturn, and/or the Sun would require the energy surpluses that become available with Dyson swarms. If you do not have one then taking apart planets will be difficult.
sophiecentaur said:
OK. But it has to be used somewhere for making or doing something. That energy needs to be converted and 'beamed' efficiently and beam dispersion over large distances would nullify any advantage that the DS would give you. ...
This is not standard for descriptions of Dyson Swarms people want to build in the Solar System. Check out Gerard O'Neill island III cylinder. It is not likely to look exactly like that design. Technology like LED lighting make the windows and Sun centered mirror panels unnecessary. The habitats in a Dyson swarm would occupy the habitable zone. Most energy collectors would deliver to a very nearby customer.
sophiecentaur said:
...
My feeling is that the idea is to add more and more orders of magnitude to the model that people just stop being able to give it serious thought. We're into Drake equation figures. Just what sort of civilisation would be that far-seeing to invest so much into the fortunes of individuals, living millennia in the future?
Lets face it, humans are now doing their best to spend their own kids' inheritances and are more than happy to accept that the next generations will have no chance of buying their own homes until they are into their forties and fifties. So, not only are we discussing a technology that's unbelievably advanced, compared with ours but also a totally alien attitude to the future of their species. That's the real SciFi part of the idea, imo.
The idea that economy and energy consumption will grow exponentially is religiously clung to by economists and politicians. Perhaps that wing of the university may be insane while you are perfectly sane. They are in control of civilization though so do not tell them too bluntly. Just suggesting they look for a way to stop exponential growth will get you labeled an anti-natalist neoMalthusian or communist.
The math is straight forward. If energy consumption grows at 3% annual the doubling time is under 24 years. In 240 years a factor of 1000x. Within in a millennium it needs to be 10^12 higher energy consumption. We can plug in other growth rates. At 1% annual the doubling time is 70 years.
Energy return on investment for silicon solar panels is currently estimated at well under 2 years. The solar power available on Luna's surface is much higher than on Earth's surface because there is no atmosphere or clouds and very slow dust accumulation. Getting to the point where you have a lunar surface industry that can make 1 functioning PV panel is a huge hurdle. Let's not minimize the effort that project will take. However, once (if) that hurdle is cleared there is not anything obvious preventing production from expanding exponentially. If half of production is diverted to other things the Lunar semiconductor industry could still be doubling itself annually while sprawling across the far side. After the first square kilometer solar farm is in place it takes only a few decades to cover Luna. Kids in school today
could see it built before they retire even if there is no life extension.
A hundred terrawatt power supply on Luna can power a substantial mass driver. We could eliminate all extraction activity on Earth's surface. Lunar calcium could be used to make Portland cement. That would build houses and also work as a carbon sink.
You and I do not have a reasonable motive for wanting more than a 100 terawatt power supply. But the replicating system of automated robots that did this on Luna will be made of known off the shelf technology. Why not send some missions to the belt and to Mercury? Why stop the replication process after Mercury's arctic is utilized? Is there a reason we would want to insist on radiating visible light out the Sun's north pole instead of infra-red?
I think it is nice to consider civilizations might put a stop to expanding energy consumption. Humanity could increase energy supply by a factor of 1 million and the Sun's infrared excess would still be lower than the current zodiacal light. That is enough power to easily boil the oceans. Interstellar travel might be possible using much less energy. This limited growth in energy allows for the possibility that aliens could be anywhere or almost everywhere (except here) in the Milky Way. Is possible that civilizations will put a stop to most asteroid collisions and will accelerate cleaning up the dust. The colonized stars could have a lower infrared excess. Sexy aliens living all around us is definitely more fun than the drudgery work of expansion the economics department wants to force us to do.
For astronomy the important thing is measuring the infrared excesses. Alpha Centauri has 10 to 100 zodis. Vega like stars have orders of magnitude more infra-red.