In a simple spatial interference effect we start out with a source of particles (lets say very heavy molecules) that are emitted in a spontaneous manner with a position distribution that is determined by the state description in position representation. This also indicates the momentum/energy of the system. The system is then "split up" into multiple possible paths (lest say with a double slit aperture) which will still have a state description that is a single particle pure state accept it has an expanded path basis. (note: pure states apparently have zero entropy) The system is then prepared to be recombined which would have the multiple paths converge to a single spatial outcome. At the point of recombination/overlap the position of the system is measured (with a screen) and when it is measured there is the presence of fringes in the detection probability. There is interference. My claim is that the system has went from a state of spontaneous emission to an ordered state of fringes. If we had measured the system after emission then we would measure a position distribution that is determined by the uncertainties, a virtual "blob", a gaussian. But the interference measurement has an ordered position distribution, and an increase in order is a decrease in entropy. Although, many would argue that the state is always pure, therefore no change in entropy. And if there was a decrease in entropy there would be an increase in energy, so where is the increase in energy? The increase in energy is like this, consider the interference effect and its preparation to be the only things in the universe. By going from the state of emission, where the position distribution is a blob, to a state of interference, where the position distribution is ordered in fringes, we have an increased state of total gravitational potential of the system. We all know that a state of "lumped up" mass is a state of greater total gravitational potential energy as long as its being compared to a state of more evenly distributed mass evaluated over the same volume (in our case the system is spread over the total uncertainty in position which does not change). Therefore the state of interference fringes is a state of increased gravitational potential energy. Ergo, interference creates energy! (even though it is an extremely small amount of energy) Consider the case of charged particle interference effects, the energy created is not gravitational potential energy but it is electromagnetic potential energy.