excitations
Synonyms
Examples
Assuming that sound waves are the most important excitations in helium-4 at low temperatures, he showed that helium-4 flowing past a wall would not spontaneously create excitations if the flow velocity was less than the sound velocity.
Because the group velocity for such a field is superluminal, naively it appears that its excitations propagate faster than light.
By our current understanding, these elementary particles are excitations of the quantum fields that also govern their interactions.
From the momentum and flow velocity of the excitations he could then define a "normal fluid" density, which is zero at zero temperature and increases with temperature.
From the point of view of quantum field theory, particles are identical if and only if they are excitations of the same underlying quantum field.
Inelastic scattering is useful for probing such excitations of matter, but not in determining the distribution of scatterers within the matter, which is the goal of X-ray crystallography.