If space is empty, how do the signals transmitted by us reach their target (human or machine)?

Answer

Dear Willy

This depends on what signals you have in mind. Sound will not reach its target because it needs atoms as medium to move. In a vacuum the latter are absent so no signal will be able to pass. However, if we use electromagnetic waves (such as light or radio waves), it will work, since they do not need atoms as medium to be able to move.

Since a vacuum is only distinguished by the lack of atoms, any kind of signals it does not need to move will simply move through that vacuum. That’s why we can see stars from very far away. In fact, with the latter, the presence of atoms and dust obscures our view because these particles capture the light and may or may not re-emit it in a random direction.

Regards,

Danny