Normal text size Very large text size You are here in the universe: on a rock with clouds and oceans and fire in its gut, orbiting a star in the outer suburbs of the Milky Way galaxy. As far as we know, nothing else beyond this rock is alive and chances are you haven’t left it. But our radio waves have. Since humanity’s very first broadcasts hit the air one hundred-odd years ago, they have travelled more than one hundred light years (or roughly 900 trillion kilometres). They’ve reached other planets and other stars. Those within sixty light years of Earth would already know we have a space program. That is, if anything is out there listening.