[seanc]

And radio! We use lots of radio as well.

I wonder what the longest information carrying electric wire is? They used to cross oceans, but not anymore. There are loads of DSL twisted pairs and co-ax cables in the "last mile" that maybe go 5km max. In rural areas maybe up to 50km with repeaters?

Is there something in between? Some old buried copper trunk cable between two university campuses or something like that?

[ThrowawayTestr]

Depending on your definition of wire, probably the earth. The first telegraph systems used the earth (or sea water can't remember) as the return path.