The most convincing answer to Fermi's paradox is that since the galaxy is not saturated with Bracewell - von Neumann self-replicating slow interstellar probes,

The most convincing answer to Fermi's paradox is that since the galaxy is not saturated with Bracewell - von Neumann self-replicating slow interstellar probes, no civilization has yet launched one, and thus there has not yet been a civilization in our galaxy capable of launching one. The launch of a working BvN probe is basically a permanent phase change for a galaxy.