The York Research Database

We extend previous work on quantum stress tensor operators which have been averaged over finite time intervals to include averaging
over finite regions of space as well. The space and time averaging can be viewed as describing a measurement process for a stress
tensor component, such as the energy density of a quantized field in its vacuum state. Although spatial averaging reduces the probability
of large vacuum fluctuations compared to time averaging alone, we find that the probability distribution decreases more slowly than exponentially
as the magnitude of the measured energy density increases. This implies that vacuum fluctuations can sometimes dominate over thermal
fluctuations and potentially have observable effects.