08-17-2017, 07:31 PM
That's right. A laser message, or any kind of collimated(focused) beam, would be just about invisible to anyone not at the intended target. There are two possible reasons that we could pick up a signal - firstly, if the aliens deliberately try to target us with a message; they might periodically send messages to a list of target stars. Alternately we might be lucky and get in the beam of a message not intended for us. The most likely reason for this could be that they are targeting a ship which is already in our system, or a monitoring station that has been here since time immemorial.