I Can you extract useful work from vacuum energy?

[Kavorka]

I know that you couldn't extract work from vacuum fluctuations without violating the laws of thermodynamics, but what if there was a gradient in the vacuum energy. If you did work on the vacuum by applying some field you could then extract this work from the gradient, but if the gradient was naturally produced such as by a star, could you theoretically extract energy from that source from the vacuum energy gradient?

 

[vanhees71]

Since there is no vacuum energy you cannot take out anything of it ;-).

 

[Kavorka]

I don't see how that can possibly be true considering the quantization of all fundamental fields at each point in space as determined by quantum field theory as well as spontaneous symmetry breaking

 

[houlahound]

Can you explain how QFT and symmetry breaking led you to your position.

 

[Paul Colby]

I heard of schemes "based" on the Casimir force between 2 conducting plates. A) the force is conservative so once the plates come together you're done. 2) the forces is exceedingly tiny. I think the answer you're looking for is no.

 

[vanhees71]

As has been discussed at length recently in this forum, the Casimir force has nothing to do with "vacuum energy". The issue is completely solved in standard QED as the residual interactions (a la van der Waals forces) due to charge fluctuations of the charges in the plates by Jaffe:

http://arxiv.org/abs/hep-th/0503158

 

[ddd123]

Since there is no vacuum energy you cannot take out anything of it ;-).

The OP didn't specify the context to be QFT before your answer. There may be vacuum energy in future quantum gravity theories: http://math.ucr.edu/home/baez/vacuum.html .

 

[Demystifier]

As has been discussed at length recently in this forum, the Casimir force has nothing to do with "vacuum energy". The issue is completely solved in standard QED as the residual interactions (a la van der Waals forces) due to charge fluctuations of the charges in the plates by Jaffe:
http://arxiv.org/abs/hep-th/0503158

I would add that Casimir effect is not the only effect that is frequently but incorrectly attributed to vacuum energy and vacuum fluctuations. This is also the case with Schwinger effect (electron-positron pair creation in strong EM fields), Unruh effect (creation of thermal excitations by acceleration of the detector) and Hawking radiation (thermal radiation from the black hole). In all cases, it is only an oversimplified semi-classical effective description that suggests that the effect has something to do with the vacuum. A full quantum description (which is poorly understood in the case of black holes) always reveals that those effects have not much to do with the vacuum.

 

[vanhees71]

Well, what's simple to see on hand of all your examples is that never there is the vacuum. In some sense we cannot observe the vacuum, because to observe it we need to introduce matter, i.e., a measurement device to measure something (that's the point of the Unruh effect, which you describe from the point of view of an inertial observer, who uses an accelerated detector). The Schwinger effect is to introduce a very strong electromagnetic field, which leads to spontaneous pair creation (of electrons is most easy, because they are the lightest charged particels we have available). That's not vacuum either, because there is this field to begin with, and to create it you have to use some charged particles too. The Hawking radiation seems to me the worst understood of the examples since we don't have a complete quantum theory of gravity yet.

 

[Demystifier]

Since there is no vacuum energy you cannot take out anything of it ;-).

Well, perhaps the vacuum energy is even infinite, but the reason you cannot take out anything of it is different. To take energy from something, you must have a change in the system which conserves total energy and increases entropy. On the other hand, vacuum has a very low degeneracy (or no degeneracy at all), so you cannot have such a change with the vacuum.