| ▲ | rolph 7 days ago | |
The existence of radio waves was first proven by German physicist Heinrich Hertz on 11 November 1886. The first commercial radio broadcast was transmitted on 2 November 1920 that means intentional radio signal was underway about 100 years ago. so suppose that signal despite the "low" power is heard by someone that listens very closely. they tease it out of the noise, and right away know what it is, and try to send back. at most, they are about 50 radio-years away, if thier signal reaches us now. beyond that, no signal from earth has propagated that far. https://en.wikipedia.org/wiki/List_of_nearest_stars https://en.wikipedia.org/wiki/List_of_star_systems_within_45... | ||