I've been reading some of the excellent answers on this question about galactic empires and it led me to imagine a reasonably realistic multi-system 'empire' might keep most or all of its population within a single system and have a presence around other stars only for the purpose of harvesting their energy.

The most naive conception of such a scenario would be to have a dyson swarm of some description around each exploited star (built by self-replicating robots) and use lasers or microwaves to beam the energy back to the Sol system. This energy could conceivably also be used by a sufficiently advanced society to produce matter in a kind of long-distance stellar lifting - my back of the envelope maths puts the energy output of a Sol-like star as sufficient for ~4.3 billion kg per second before (likely considerable) efficiency losses.

My crude calculations (based on this data) suggest that even with only 1% overall efficiency a single star could supply raw material equal to almost eighty times the total mining output of humanity in 2017, though I have no idea how optimistic (or otherwise) that 1% figure is or what proportion of human resource consumption is represented by mining.

The biggest question for this proposal is whether or not it's actually feasible to send energy on this scale across interstellar distances reasonably safely and without it dispersing so much as to be infeasible to collect at the other end. If it is, what's the best way to do so and what would that look like?

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    $\begingroup$ I think this question is very interesting and I look forward to seeing an answer, however I think your title is not what you are asking at all in the text. As such you might reconsider the title to something more appropriate. My suggestion would be along the lines of "Realistic interstellar energy transfer" $\endgroup$ – BMS21 Jul 31 '19 at 13:18
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    $\begingroup$ The problem that makes this opinion based (IMO) is that whether it's feasible or safe to send energy across interstellar distances in some distant future cannot be said. What tech is available to such a civilization is beyond any reasonable estimate. $\endgroup$ – StephenG Jul 31 '19 at 13:36
  • $\begingroup$ Certainly nothing available today has any hope of interstellar transfer of energy at anything remotely approaching 1%. Judging by the laser reflecting-corner things left on the moon by the Apollo missions. You need to be pretty technically good to detect the beam at all when it returns. Also, if you have a Dyson swarm around your home star, you should find it a lot easier to harvest energy at home. $\endgroup$ – puppetsock Jul 31 '19 at 13:45
  • $\begingroup$ Some perspective on just Sol's power output is worth having The Sun's power output. Hard to see a use for power from another star added to that. $\endgroup$ – StephenG Jul 31 '19 at 14:08
  • $\begingroup$ @puppetsock: I am assuming in this scenario that either Sol already has a swarm and its power output is insufficient or the civilization in question is unwilling to harvest the matter necessary for one from the local system and would rather preserve it as-is. $\endgroup$ – 666lumberjack Jul 31 '19 at 14:13
  1. Capture radiant energy in a form easier to transport. A good way to harvest and transport energy is to convert it into a form that is easier to transport and from which is it easy to reclaim energy on demand. Capturing the suns energy as biomass, harvesting the stable biomass, and later burning the biomass. Slightly edgier is capturing hydroelectric energy by refining aluminum oxide to the stable metal, then later oxidizing the metal and reclaiming the energy.

Your energy operation will not send energy as electromagnetic radiation, but convert the output of that star to a different form that is more efficient to transport.

  1. Your energy capture operation is intrinsically dangerous, and so is kept out of the neighborhood. An example would be creation of antimatter. The antimatter is kept out of the home system because it is so dangerous. Perhaps this outside system is not the first one used for this endeavor, as prior implementations have damaged the systems they were in beyond use.

Antimatter is the regular thing people think of - maximal energy density, goes boom, someone tried to blow up the Vatican with it, OK. But I think to keep it edgy you need to take it up a notch. Have them capturing energy and storing it with Casimir forces or Z point energy, or maybe something to do with string theory. When that system goes kablooey you mess with space/time and dimensional boundaries and things get spooky in a hurry. Definitely something to be done in someone else's backyard. The fact that things have gone kablooey in the past will foreshadow a visit to one of those kablooey systems by your characters, so they can learn what flavor of spooky that kind of disaster brings.

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    $\begingroup$ Did you blow up another solar system, Rodney? $\endgroup$ – Joe Bloggs Jul 31 '19 at 15:01
  • $\begingroup$ @JoeBloggs - wow, that episode is pretty much exactly what I proposed. Z point energy is lifted right from SG Atlantis but I missed that solar system destroying episode. $\endgroup$ – Willk Jul 31 '19 at 15:23

TL;DR: why? a mere kardashev level of 2 not good enough for you? Not enough mass in the sun for you to harvest? Shipping stuff across interstellar distances is very hard, and there doesn't seem to be a good reason for it.

The obvious answer, for energy at least, is a Nicoll-Dyson beam (also youtube) which is where you build a dyson swarm and turn it into one giant phased-array laser. You could certainly hit a planet-sized target a few tens of lightyears away (too lazy to work out practical focussing distances right now, though).

The biggest problem you'll have is receiving the power. You'll need a pretty big dyson swarm of solar receivers, and you're going to start hitting the limits of available mass in the solar system. Then you'll have problems of efficiency... you're already going to be sucking up as much power from the sun as possible, and inefficiencies are going to make your swarm pretty hot. Suddenly, you're not only doubling the amount of power you're absorbing (and hence doubling the amount of waste heat you'll be producing) but you're also pointing gigantic lasers at the bits of your dyson swarm most suited for radiating heat away.

Harvesting mass from stars via some starlifting mechanism is possible, but getting it back to your home system in the absense of FTL, wormholes or some sort of very fast sublight mechanism probably involving reactionless drives is going to be very, very, very time consuming. Making giant solar sails and propelling them with your dyson lasers would work. Not sure how best to slow down at the other end... you've probably stopped any chance at using magnetic breaking (your dyson swarm is going to interfere with the solar wind, and you won't want to waste all that energy anyway) so you'll need to beam right back at them... but that means you can't have more mass in flight that you could boost with a single dyson beam at a time (because otherwise you'll be bombarding your home dyson swarm with hypervelocity giant solar sails continuously, and that sounds bad to me).

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