You are correct; you cannot hear a sound wave if there is no medium for it to travel through. Sound waves are mechanical waves that require a physical medium to propagate. The medium can be a solid, liquid, or gas, but it must have particles that can interact with one another to transmit the wave energy.
When you hear a sound, what is actually happening is as follows:
Sound Source: There is a vibrating object or source (like a speaker diaphragm or vocal cords) that sets the surrounding particles of a medium into motion.
Propagation: These vibrating particles then transmit the mechanical disturbances or waves through the medium by passing their energy to adjacent particles.
Ear Reception: When these waves reach your ears, they cause the eardrum to vibrate, which, in turn, is detected and interpreted by your auditory system, allowing you to perceive the sound.
If there is no medium present, like in a vacuum (where there are no particles), sound cannot travel, and you won't be able to hear anything. This is why space, which is a near-vacuum, is famously known as silent.
On the other hand, electromagnetic waves, such as visible light, radio waves, and infrared waves, do not require a medium to propagate. They can travel through a vacuum because they are a different type of wave – electromagnetic waves consist of oscillating electric and magnetic fields and do not rely on the motion of particles in a medium for their transmission. However, unlike sound waves, electromagnetic waves are not detected by the human auditory system. We perceive them through our eyes (as light) or by using specialized devices that can detect and convert them into other forms of signals (like radio waves being detected by a radio receiver).