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If the vacuum energy is extracted, then what will happen to the cosmological constant? Will it remain the same? .

Abhimanyu Pallavi Sudhir
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Andrea Scaglioni
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If the vacuum energy is extracted, then what will happen to the cosmological constant? Will it remain the same?

A cosmological constant is one possible description of how dark energy behaves. We don't know the equation of state of dark energy for sure, but current data do seem to be consistent with the hypothesis that it behaves as a cosmological constant, which is also the simplest hypothesis mathematically.

A cosmological constant is constant, and therefore it can't be extracted in the sense of lowering the amount of dark energy in a given cubic meter of space and transforming it into some other, useful form of energy. There are various kooks who claim to have promising ideas about how to do this, the most prominent probably being Myron Evans. They are kooks.

Regardless of the equation of state, general relativity has local conservation of mass-energy (technically expressed by the fact that GR is not self-consistent unless the divergence of the stress-energy tensor is zero). This implies that you can't just locally increase some form of energy (e.g., by doing mechanical work) without decreasing some other form of energy (e.g., dark energy).

On a cosmological scale, it is certainly true in some sense that dark energy causes other forms of energy to appear. It drives the accelerating expansion of the universe, which can be thought of as involving large amounts of kinetic energy. The reason for the qualifiers like "in some sense" and "can be thought of as" is that general relativity doesn't have a global law of conservation of energy that applies to cosmological spacetimes. In fact, there is not even any satisfactory way of defining the total energy of a region of the universe that spans cosmological distances. (The technical statement is that we don't have a measure of mass-energy that is conserved and transforms as a tensor.)

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    Just to head it off at the pass: "There are various kooks who claim to have promising ideas about how to do this" These guys invariably bring up the Casimir effect, but a proper understanding of the Casimir effect shows that the force is due to currents in the conducting materials. The fact that the leading order term is independent of the material (a sort of universality) lets you loosely describe it as a vacuum effect, but insulators don't feel a Casimir force. So it is closely analogous to the dispersion forces, and no more mysterious. – Michael Aug 28 '13 at 14:56
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    @MichaelBrown : Are you reffering to this paper ? – Trimok Aug 28 '13 at 15:07
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    @Trimok Yes, that's a good one. Thanks. Another one that may interest the OP is 1205.3365, which discusses the cosmological constant problem pedagogically at great length, and explicitly shows that e.g. the Casimir stress energy is very different from the vacuum stress energy. – Michael Aug 29 '13 at 04:42
  • @MichaelBrown see this one http://www.google.com/patents/US7379286. It's almost certainly a sophisticated deliberate fraud and I make this comment grounded not on the paper's contents (which are more sophisticated than the wonted unlimited energy claims) but on a draught of the patent I saw several years ago that made me fall off my chair laughing some years ago. There was actually a photo (very seldom in patents) of "the device" and it showed a plain aluminium box with a power cord leading to a fluorescent light bulb. Needless to say, the latter was glowing brightly. The patent was .... – Selene Routley Feb 25 '14 at 04:06
  • ... granted, but I suspect one of the examiners ordered the removal of the photo. The fact that one would try to include that bespeaks outright fraud. The company's name "Jovion" is I think a play on "Jovial" and has the same kind of spirit for the names of trusts and entities that Enron used to transfer their debts too: on the balance sheets the names looked reasonable, but on permuting the letters something else was revealed: for example, an "investor" named "M. Yass" in Yemen: swap the space and the "y" and you get "My Ass". This was one of the milder examples I recall. – Selene Routley Feb 25 '14 at 04:10