How Far Radio Signals Traveled From Earth

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While it’s interesting to imagine how far our radio signals have traveled into space, it’s extremely unlikely that an alien civilization will be able to catch the latest episode of our sitcoms. This is thanks to the inverse square law. It’s a form of signal degradation.

As radio signals leave earth, they propagate out in a wave form like dropping a stone in a lake, the waves diffuse or “spread out” over distance thanks to the exponentially larger area they must encompass. The area can be calculated by multiplying length times width which is why we measure it in square units – square centimeters, square miles, etc. This means that the further away from the source, the more square units of area a signal has to ‘illuminate’ inverse square law.

Because of this inverse square law, all of our terrestrial radio signals become indistinguishable from background noise at around a few light-years from earth. For a civilization only a couple hundred light-years away, trying to listen to our broadcasts would be like trying to detect the small ripple from a pebble dropped in the pacific ocean off the coast of California – from Japan.
https://zidbits.com/2011/07/how-far-have-radio-signals-traveled-from-earth/