SETI (the Search for ExtraTerrestrial Intelligence) continues to listen for signals from space, but has to guess at what kind of signal to listen for. Since 2001, radio astronomers have been picking up signals with no known natural source, that seem mathematically linked, and are anywhere from nearby to billions of light years away. Scientists are necessarily curious. Now that they’ve exhausted most of the natural possibilities, the possibility of an intelligent source is being addressed. Such a discovery would affect almost every human societal debate. For now, they are a set of undecipherable signals, either because we don’t know how to translate the message or because there is none.