Universal language - 2,3,5,7,11...
As we wander among the stars we will have to carry with us a universal language, one based on physics and/or mathematics. How should we construct the fundamentals of such communication? (Remember the "gold record" carried by Voyager? Or SETI beaming prime numbers into space?)
For instance, we could present water to an alien salt-monster, but it might mistake our gesture as a threat with that fundamental solvent. An extraterrestrial who corresponds with gamma radiation may be perceived as dangerous to us.
How can we extend a mathematical linguistic to a more practical, yet general one of physics?