It might not be very christmassy, but I think this is worth a watch. The latest video from the PBS Spacetime series considers whether an alien civilisation could by now have detected any radio communications from earth. After all, we have been broadcasting them for over a century, so it is possible that a distant civilisation could have picked them up by now. It also considers why we haven’t picked up any signals from space yet, and goes into quite a lot of detail about why this may be. For me, this is one of the most important and fascinating questions facing humanity today: is anyone out there, and are they watching us? I also can’t help but wonder, as the video itself does, whether there are aliens up there right now watching old episodes of Star Trek.