Vacuum energy is the product of the uncertainty principle though - the Casimir force is the result of the fact that in any given volume of free space there's a certain number of standing electromagnetic waves which could fit, and thanks to quantum mechanics these are in fact quite real.
Put a pair of parallel conducting plates between a given bounded volume though, and interesting thing happens: while shorter, higher energy standing waves can still fit between them, the longer, lower energy ones cannot.
As a result, there is now no longer an unbounded number of virtual photons between the inside plates and the outside ones, and this manifests as a very slight force on the plates because you now have a higher energy on the outside then on the inside. But it's a lossy process: the plates can only exclude longer, lower energy wavelengths, so there's a very finite upper bound on how much energy any given arrangement of this system can produce since as you move the plates closer together the remaining energy inside grows much faster then the energy outside (shorter virtual wavelengths).
If you're wondering how this affects you: it's all around you. Vacuum energy - the Casimir force - is believed to account for most of the force known to be due to van der Waal's forces in chemistry - i.e. the basic force which sticks non-ionic, non-covalent things together. The difficulty of removing dust for example, is being driven by that.
EDIT: "Dark Energy" - which is what's being discussed here, is very different.
Put a pair of parallel conducting plates between a given bounded volume though, and interesting thing happens: while shorter, higher energy standing waves can still fit between them, the longer, lower energy ones cannot.
As a result, there is now no longer an unbounded number of virtual photons between the inside plates and the outside ones, and this manifests as a very slight force on the plates because you now have a higher energy on the outside then on the inside. But it's a lossy process: the plates can only exclude longer, lower energy wavelengths, so there's a very finite upper bound on how much energy any given arrangement of this system can produce since as you move the plates closer together the remaining energy inside grows much faster then the energy outside (shorter virtual wavelengths).
If you're wondering how this affects you: it's all around you. Vacuum energy - the Casimir force - is believed to account for most of the force known to be due to van der Waal's forces in chemistry - i.e. the basic force which sticks non-ionic, non-covalent things together. The difficulty of removing dust for example, is being driven by that.
EDIT: "Dark Energy" - which is what's being discussed here, is very different.