Cosmic cats and nuclear blasts: the strange history of interstellar messages
Any solution to the problem of interstellar communication comes laden with assumptions about the nature of extraterrestrial intelligence and inevitably reflects the technological sophistication of the era.
The problem, briefly stated, is how to design a message that can be understood by an extraterrestrial intelligence about which you can know nothing with absolute certainty.
This turns the design of interstellar messages into an exercise in identifying universals that can be presumed to be recognised by any entity endowed with higher intelligence. It is, in other words, the search for what may be called a language of the universe.
See the full story here; https://www.theguardian.com/science/2019/nov/06/cosmic-cats-nuclear-interstellar-messages-extraterrestrial-intelligence