[rbanffy]

> I wonder if the gamma bursts from nuclear testing are discernible from the solar noise? It would reduce the distance to about about 60 light years.

Maybe. It's a given a civilization more advanced than ours would be able to observe the Solar System with better resolution than we currently can observe our neighbors, but that's a very narrow time window to watch. We no longer do test blasts. Any alien species would have to be incredibly lucky to be watching us at the precise decades we would be visible. While any seriously alien-life seeking advanced civilization would have tons of telescopes all over the spectrum looking at everything interesting they have the resources watch, as well as a couple probes on their way to promising targets, there are literally billions of places to examine.

[jacquesm]

It would also serve as a warning that we're only 'mostly harmless' so if a house-call is in order (or a preventive visit) then better come packing heat.

Of course that assumes a whole raft of things such as the ability of ET to show up in person but since we don't know anything about the technological state of the rest of the universe mostly because we don't know anything about them at all that's not too far out.

[rbanffy]

To any civilization capable of showing up face to face, we are completely harmless. They don't even need to bring the guns: just pointing the engine our way while braking would do the trick.