““What is important here is that for every given curvature there are precisely fixed masses. And since we recall that the virtual mass that fluctuates in the vacuum is not constant in time, we infer that the curvature of space follows this pattern: It must fluctuate. Along with this fluctuating curvature, the distances between two points in space and time must fluctuate. This inference has caused far reaching speculations. We have no idea around which value the curvature of space in fact fluctuates; but from the observational fact that we can look along straight lines deeply into space, we can deduce that any actual curvature must be very small. It is only when we deal with very small distances in both space and time that the fluctuations of their fields lead to wide uncertainties in the energy and mass of the local vacuum. It is thinkable that at extremely small distances the space-time structure becomes mushy, a kind of foam.””
