[justa-hairyape]

There is yet another possibility. They don't want us to see them. We are quarantined. Surrounded by a filter. Entire solar system. Possible for a civilization 1 million years advanced.

[NorthMountain]

There is yet another possibility. WE'RE the most advanced species in the universe. We don't see any radio from the rest of the universe's denizens, because they're still using stone knives and wearing bear skins.

[SunkenCiv]

For ground based comm they would probably be using something like a fiber network; for planet-to-craft, something like Ursula K. Le Guin's ansible.