&gt; Another is that they would need that much energy.<p>Even <i>if</i> they needed that much energy, the best way to do that [that we know of] is to build a Dyson sphere. With every star shrouded by a Dyson sphere you no longer need to shroud the galaxy.<p>A more critical assumption is that a type III civilization even <i>cares</i> about masking its presence. If they were even worried about being attacked, the speed of light would mask their progress for a great deal of time and, because of the distances involved, even seeing them once the light reaches you would be a massive accomplishment - most likely you&#x27;d have to search for individual stars in <i>another</i> galaxy which are disappearing in unusual ways.<p>A type II civilization could possibly build a telescope with a large enough aperture but I assume that type II civilizations would be long past their ignorant warring ways.