What's the easiest way for your stereotypical aliens to destroy civilization from orbit? I'm taking "destroy civilization" to mean the destruction of all large-scale forms of governance, but bonus points for extinction.

Criteria: Either cheapest or least energy consumption. The aliens have access to anything that's roughly possible for a Kardashev II civilization. The aliens use a magic-plot-teleporty device to get here, but everything else should be as hard-science as possible.

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    $\begingroup$ If aliens have the technology to travel through the vastness of space and achieve a planetary orbit, causing severe damage to that planetary system should be trivial. Given that inter-stellar travel would require technology way beyond current human understanding, we must infer that equally advanced weapons would also exist. Since you've tagged the question with hard-science we must be bound by these inferences. What is not clear is why the aliens would go to the effort. Some sort of anti-matter weapon targeting stars within the system would destroy all solar dependent life. $\endgroup$ – Jodrell Aug 13 '15 at 7:36
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    $\begingroup$ "Imagine that our entire Solar System were the size of a quarter. The Sun is now a microscopic speck of dust, as are its nine planets, whose orbits are represented by the flat disc of the coin. How far away is the nearest star to our sun? In our model, Proxima Centauri (and any planets that might be around it) would be another quarter, two soccer fields away. This is the typical separation of stars in our part of the galaxy." nasa.gov/audience/foreducators/5-8/features/… $\endgroup$ – Jodrell Aug 13 '15 at 8:35
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    $\begingroup$ To clarify your question, please define the context for "efficient" and "easy." Do you mean costs the least in alien resources, takes the least time, has the highest human death per alien resource ratio etc? $\endgroup$ – ryanyuyu Aug 13 '15 at 13:35
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    $\begingroup$ Nuke it from orbit, it's the only way to be sure. $\endgroup$ – Zikato Aug 14 '15 at 6:17
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    $\begingroup$ Does the planet need to survive? $\endgroup$ – Mast Aug 15 '15 at 10:06

31 Answers 31


Okay energy efficient on the scale of a K-II civilisation how about a Nicoll-Dyson Beam, a single system K-II civilisation has access to this weapon by definition, and they don't even have to come here to use it but it will take some time from decision to death of the world in question since light-speed is an issue.

  • $\begingroup$ Why are you answering this question? It already has an accepted answer and has not had activity in roughly two years. There is no reason to bump this thread. $\endgroup$ – Braydon Sep 3 '17 at 18:55
  • $\begingroup$ Why not, and every answer I read had missed the implications of a K-II civilisation in answering the question. $\endgroup$ – Ash Sep 3 '17 at 18:58
  • $\begingroup$ Well why not is that it has been resolved, and I doubt the user who asked even still has a use for answers to this. (He has likely finished whatever he was doing and moved on.) $\endgroup$ – Braydon Sep 3 '17 at 19:03
  • $\begingroup$ And? The OP is far from the only person who may have a use for this. $\endgroup$ – Ash Sep 3 '17 at 19:05

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