There could be a fourth option: An advanced civilization has control over our region of the galaxy. Perhaps the reason why we don't detect other civilizations i

There could be a fourth option: An advanced civilization has control over our region of the galaxy. Perhaps the reason why we don't detect other civilizations is because the dominant civilization neutralizes others when they get too advanced? If they have a billion years head start, it's hard for other civilizations to put up much of a fight. The reason why we haven't detected the dominant civilization is because they don't want to be detected :) As an alternative, there could also be one or more civilizations out there that studies us and shields us from outside signals.