In quantum field theory the vacuum expectation value (also called condensate or simply VEV) of an operator is its average or expectation value in the vacuum.
This concept is important for working with correlation functions in quantum field theory.
Similarly a tensor field, Gμν, can only have a scalar expectation value such as
In some vacua of string theory, however, non-scalar condensates are found.[which?]
If these describe our universe, then Lorentz symmetry violation may be observable.