As i child i was an eavesdropper. Whenever i wasn't supposed to hear something i would always try and hear it anyways. I tried everything from pressing a glass to the door as well as (when i was desperate) just sticking my ear against the door to hear the latest gossip. Sound is transported by a collision of molecules. On earth we have the medium of air which allows the molecules to collide and form waves. this helps so that we can hear what is going on around us. The difference between space and earth is just that: you cannot hear in space. The reasoning is this: there are no mediums in space. This means that there is nothing for the waves to bounce off of or travel through. A medium can be a solid, liquid, gas or simply just made of matter. In order to hear there myst be something to let the waves travel through. in space, molecules don't collide regularly because they are stretched far apart and are unable to collide to form sound waves. Therefore there is no eavesdropping in space; let alone talking unless there is a medium.