Why do radio waves travel at the speed of light and not sound?

Radio waves are a form of electromagnetic radiation – the same phenomenon as light, X-rays and various other types of radiation, but with much longer wavelengths. As such, they travel at the speed of light (ie 300,000 kilometres/186,000 miles per second) – a lot faster than the 340 metres (1,125 feet) per second that sound itself moves through the air. It’s easy to be fooled by the fact that when you hear the word ‘radio’, you usually think of voices or music, but radio waves aren’t sounds themselves – just the medium used to broadcast an electronic signal from the studio to your hi-fi, which the speaker then turns back into the vibrations in the air which we hear.

Answered by Giles Sparrow.