Sonic boom the ground. For example, the speed of sound at is about , but an aircraft must travel at least (Mach 1.12, where Mach 1 equals the speed of sound) for a boom to be heard on the ground. The composition of the atmosphere is also a factor. Temperature variations, humidity, atmospheric pollution, and winds can all have an effect on how a sonic boom is perceived on the ground. Even the ground itself can influence the sound of a sonic boom. Hard surfaces such as concrete, pavement, and large buildings can cause reflections which may amplify the sound of a
Faster-than-light oscillator ticking too fast. In special relativity, it is impossible to accelerate an object the speed of light, or for a massive object to move the speed of light. However, it might be possible for an object to exist which moves faster than light. The hypothetical elementary particles with this property are called tachyonic particles. Attempts to quantize them failed to produce faster-than-light particles, and instead illustrated that their presence leads to an instability. Various theorists have suggested that the neutrino might have a tachyonic nature, while others have disputed the possibility. Mechanical equations to describe hypothetical exotic matter which