In classical physics, sound waves are mechanical waves that require a medium to propagate through. The medium can be a solid, liquid, or gas, such as air, water, or steel. When an object vibrates, it disturbs the particles of the medium, causing them to interact with neighboring particles and pass on the energy in the form of a wave. When the sound wave reaches our ears, it causes our eardrums to vibrate, and these vibrations are then converted into electrical signals that our brain interprets as sound.
However, in a vacuum, there is no medium for sound waves to travel through, and hence, sound waves as we know them cannot be heard. This is why sound cannot be transmitted in outer space, which is mostly a vacuum.
In the absence of a medium, other types of waves can still propagate, such as electromagnetic waves (like light), which do not require a medium to travel through. Electromagnetic waves can travel through the vacuum of space and do not need any particles to propagate. But these waves are not perceived as sound by our ears; they are detected by other types of instruments, such as telescopes and cameras.