Humans cannot hear sound in space because sound requires a medium to travel through, and there is no air in space. Sound waves are vibrations that travel through the air, air molecules create vibrations, which are then detected by our ears and converted into the sensation of sound. In a vacuum, such as outer space, there are no air molecules to create and transmit vibrations, so sound cannot travel.

Therefore, astronauts communicate in space through various other means, such as radios or special communication systems that transmit signals that can be received and understood even in the absence of air. These systems utilize electromagnetic waves, which do not require a medium to propagate and can transmit information over vast distances in space.