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This Defense Intelligence Reference Document (DIA-08-1003-018), dated 30 March 2010, was produced by the Defense Intelligence Agency as part of its FY 2009 Advanced Aerospace Weapon System Applications (AAWSA) Program. It reviews theoretical approaches to antigravity for aerospace propulsion, drawing on Newtonian physics, general relativity, cosmological dark energy and quantum vacuum effects. The report notes that no current technology can actively control gravity and that many concepts are far from practicable engineering.
UNCLASSIFIED/ ,'f811. lilffllil,t.k l.llilii g•11 X whereby this term now behaves like the stress-energy tensor of the vacuum, "(:;, which acts as a gravitational source: (15) (16) One should note that the absence of a preferred frame in special relativity means that '(:;· must be the same (that is, isotropic or invariant) for all observers. There is only one isotropic tensor of rank 2 that meets this requirement: 17f'" (the Minkowski flat spacetime metric tensor in locally inertial frames). So in order for T,~:- to remain invariant under Lorentz transformations, the only requirement is that it must be proportional to 11μ". But this generalizes in a straightforward way from inertial coordinates to arbitrary coordinates by replacing rf'' with ir"·, thus justifying the curved spacetime metric tensor in Equation (16). By comparing Equation (16) with the perfect- fluid stress-energy tensor in Equation (12), one finds that the vacuum looks like a perfect fluid with an isotropic pressure /Jv,w opposite in sign to the energy density pv,\c• Therefore, the vacuum must possess a negative-pressure equation of state (according to the first law of thermodynamics): (17) The vacuum energy density should be constant throughout spacetime, since a gradient would not be Lorentz invariant. So by substituting Equation (17) into PE+ 3p, the following is produced (18) <0. The vacuum equation of state is therefore manifestly negative. Last, when incorporating pvac into the Einstein field equation as a gravitational source term, and comparing its corresponding (Lorentz invariant) stress-energy tensor p,.,cR'"' with Equation (16), then the usual identification (or definition) is made that: Ac 4 f\,,c = SrrG Thus the terms "cosmological constant" and "vacuum energy" are essentially interchangeable in this perspective and mean the same thing (whereupon p,,.c = p.,), which is seen in the present-day cosmological literature. 14 UNCLASSIFIED//F81it 8FFIIIAI!: 1!181! &••LY (19)
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