The present article reviews some of our present understanding of the electromagnetic zero-point (ZP) fields, in particular regarding concepts in thermodynamics related to energy and heat extraction. Topics that will be touched on are (1) the relationship between the ZP fields and the nonzero temperature thermodynamic equilibrium situations, (2) the more general nonequilibrium case, (3) energy and heat extraction, (4) reversible and irreversible thermodynamic operations, (5) the connection of all of these ideas to conventional ideas on thermodynamics, (6) “restraints†on extracting heat and energy from electromagnetic ZP radiation, (7) a brief summary of our present understanding of many of the key properties of electromagnetic ZP fields, and (8) an outlook on making use of the ZP fields for energy extraction. The aim here will be to be fairly qualitative, as a number of articles exist that explain more of the details of these topics.
All of these topics will be treated from the viewpoint that the electromagnetic ZP fields are real. Certainly there are other viewpoints, including Schwinger's source theoretical viewpoint, but these viewpoints are all connected and are presently generally thought to be consistent (Milonni, 1994). Moreover, there are1 “... many observable
consequences of the vacuum field, including spontaneous emission, the Lamb shift, the anomalous magnetic moment, van der Waals forces, and the fundamental laser linewidth, all of which may be attributed at least in part to the vacuum field.†The viewpoint that the ZP fields are real certainly makes the thermodynamic discussion much easier and more natural and so shall be followed here.
Why the interest here? Well, if one does a rough estimate of the energy density associated with electromagnetic ZP energy, it is easy to show that, even with a very conservative estimate, the energy density must be incredibly large, namely, equal to or greater than nuclear energy densities (Feynman, 1973), (Misner, 1973). Can useful work be extracted from this apparent huge source? We will quickly see that the answer here is certainly, “Yes.†Moreover, heat can be extracted, even if the initial temperature could be, in principle, at the temperature of absolute zero, T = 0 . At first thought this statement must appear quite contradictory, since how can one obtain heat from a system initially held at T = 0 ? The example discussed in Sec. III should clarify the answer considerably.
Other questions that then naturally come to mind are, “If heat and useful work can be ‘extracted’ from the electromagnetic fields, exactly how much can be obtained?†After all, perhaps, for some reason, the allowed extracted magnitudes of energy are extremely small, despite the large energy density that exists. Perhaps some thermodynamic principle is violated if this energy was able to be accessed. As we will see, there are indeed some “restraints,†for lack of a better word, on extracting energy from ZP energy. Nevertheless, these restraints are not an absolute barrier, by any means, to extracting heat and useful work, but rather they are simply restricting conditions.
Moreover, I am unaware of any hard analysis that provides limits on the fraction or the total amount of energy that may be extracted from ZP energy in order to perform work, nor does the present article address this point.
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