When an aircraft passes through the air it creates a series of pressure waves in front of it and behind it, similar to the bow and stern waves created by a boat. These waves travel at the speed of sound, and as the speed of the object increases, the waves are forced together, or compressed, because they cannot get out of the way of each other. Eventually they merge into a single shock wave, which travels at the speed of sound, a critical speed known as Mach 1, and is approximately 1,225 km/h (761 mph) at sea level and 20 °C (68 °F).
In smooth flight, the shock wave starts at the nose of the aircraft and ends at the tail. Because the different radial directions around the aircraft’s direction of travel are equivalent (given the “smooth flight” condition), the shock wave forms a Mach cone, similar to a vapour cone, with the aircraft at its tip.
Some studies claim to show that sonic booms from U.S. Navy testing in Vieques, Puerto Rico, increased the incidence of vibroacoustic disease, a thickening of heart tissue. However, other scientists dispute the claims.