Transmission rate of grey goo across the universe

[Drakkith]

Again, why? It's a guarantee. Submit or die, even if you defeat us, our weapons will still obliterate you. Humans did the same thing. Communists over there, capitalists over there, either side flinches and we'll wipe out the entire planet. We developed nuclear and biological weapons that could cause our own extinction and render our planet barely habitable for hundreds of years, and rigged them to go off if they thought their side was gone. And after millions or billions of years, they would be arrogant and believe that they were invincible, even to their own creations.

Parallels to modern history aside, we're talking about a weapon that literally devours all non-stellar matter it can get its grubby, robotic hands on. If let loose there wouldn't be any planets in the galaxy left to colonize. That may not be an issue considering this race has the technology to destroy and create matter at will, but in such a case I have to question what possible motivation this race has to create this weapon in the first place. Matter-energy conversion technology would allow the creation of an unimaginably vast number of 'conventional' weapons and would itself be potentially one of the most powerful weapons imaginable depending on the details of its operation and deployment.

That being said, there's no need to go into these kinds of details if you just want a weapon like you've described and don't care to get into all the moral/technical implications and all that.

 

[newjerseyrunner]

They aren't colonists, this is a K2 almost K1 civilization, they don't care about planets, they only care about stars. They consider non K2 level civilizations to be like insect colonies. A human civilization on a planet isn't an enemy, or a potential trade partner, it's an infestation. When dealing with a civilization that's had no resistance for millions of years, it wouldn't even be fair to classify this as a weapon of war, more like an extermination and cleanup tool. A war implies some sort of fighting, they wage "war" on undeveloped species the way you wage "war" on termites. Humans and Earth to a civilization like this would simply be in the way, or a potential threat in the future that they might as well get rid of now.