The assumption behind SETI is that intelligent life should be easier to detect than regular, non-intelligent life, because intelligent creatures are capable of really making their presence known. If they’ve invented radio, then they can crank up the FM, creating a bubble of detectability racing away from their home system at the speed of light. If they are capable of harnessing a decent fraction of the energy coming from their star, they can transform their entire solar system. If they’ve cracked interstellar travel, then they can spread like (intelligent) weeds throughout the galaxy.

But something in this argument is going wrong. Either intelligent life isn’t as common as we might have hoped, or it’s not as detectable as we might have hoped. Either way, it doesn’t look like SETI will bear fruit anytime soon.

So perhaps we should just search for extraterrestrial life, rather than focusing on advanced alien civilizations. That means any kind of life: single-celled organisms floating in oceans, moss clinging to rocks or the first hints of complex creatures moving around their environments.

Sure, these kinds of life-forms may not be as loud as intelligent life, but that doesn’t make them invisible. Indeed, one of the key features of any kind of life is the ability to throw a planet out of equilibrium.