I'm sure you all recall the premise to the Star Trek series: The Galactic Federation is watching all those millions of busy little planets out there. As soon as one develops Warp Drive, it gets invited into the GF.

You might not be so familiar with the Fermi Paradox which roughly states: Given there are so many planets out there, where the heck is everyone?

I think Gene Roddenberry (or whoever wrote that series) got it wrong. There are plenty of aliens out there, they are watching all the busy little planets. Any species stupid enough to detonate a nuclear device is instantly quarantined (and immediately annihilated if they ever do invent a Warp Drive).

The other explanation might come in the form of the big bang that occurs when they do actually get CERN's Large Hadron Collider to work, i.e. every civilization capable of communicating across the vastness of space, can't 'cause they annihilate themselves first.