DOW-UAP-D132, AAWSAP DIRD, Advanced Space Propulsion Based on Vacuum (Spacetime Metric) Engineering, March 2010

This document is a Defense Intelligence Reference Document (DIRD), a technical reference format used by the Defense Intelligence Agency (DIA) to capture baseline knowledge on a specific topic for later analytic use. DIRDs are best understood as reference and synthesis products rather than as original research. It is one of 38 DIRDs produced under the Advanced Aerospace Weapon System Applications Program (AAWSAP) between 2009 and 2011. Because AAWSAP’s scope permitted a broad range of supporting topics, not every DIRD in the series directly concerns aerospace systems or future threat assessment. The following summary reflects the DIRD’s scope and framing at the time of writing and should not be read as implying current validation of the concepts discussed. This DIRD examines the idea of vacuum or spacetime-metric engineering: the possibility that an unspecified future technology might alter the structure of spacetime in ways useful for propulsion, power generation, or extremely rapid long-distance travel. Using general relativity as a model-independent framework, it explores the physical effects that would theoretically follow if such metric changes could be artificially induced, including altered time rates, changes in effective mass, modified light propagation, gravity-like effects, and warp-drive propulsion. The document does not propose any mechanism for generating these effects and treats these physical consequences as an assumed result of spacetime manipulation rather than as the outcome of a practical engineering pathway. It also emphasizes that the energy requirements predicted by current theory to create such effects are far beyond existing technological capability.

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Defense
Intelligence
Reference
Document
Acquisition Threat Support
29 March 2010
ICOD: 1 December 2009
DIA-08-1003-015
Advanced Space Propulsion
Based on Vacuum (Spacetime
Metric) Engineering
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Advanced Space Propulsion based on Vacuum (Spacetime
Metric) Engineering
Prepared by:
Acquisition Support Division (DW0-3)
Defense Warning Office
Directorate for Analysis
Defense Intelligence Agency
Author:
AAP Person 57
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This product is one in a series of advanced technology reports produced in FY 2009
under the Defense Intelligence Agency, Defense Warning Office's Advanced Aerospace
Weapon System Applications (AAWSA) Program. Comments or questions pertaining to
!,
this document should be addressed tolAAP Person 1 AAWSA Program
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Contents
Advanced Space Propulsion Based on Vacuum (Spacetime Metric} Engineering ....iii
Preface and Introduction .......................................................................................iii
I. Spacetime Modification - Metric Tensor Approach .............................................. 1
II. Physical Effects as a Function of Metric Tensor Coefficients .............................. 2
Time Interval, Frequency, Energy ...................................................................... 3
Spatial Interval ................................................ .................................................................................. 4
Velocity of Light in Spacetime-Altered Regions .............................................. 4
Refractive Index Modeling .......................................................................................... 5
Effective Mass in Spacetime-Altered Regions ................................................. 6
Gravity/Antigravity "Forces" ......................................................................... 6
III. Significance of Physical Effects Applicable to Advanced Aerospace Craft
Technologies as a Function of Metric Tensor Coefficients....................................... 6
Time Alteration .................................................................................................. 6
Spatial Alteration ............................................................................................... 8
Velocity of Light/Craft in Spacetime-Altered Regions ........................................ 8
Refractive Index Effects ..................................................................................... 9
Effective Mass in Spacetime-Altered Regions ..................................................... 9
Gravity/Antigravity/Propulsion Effects............................................................ 10
IV. Discussion ...................................................................................................... 11
Figures
Figure 1. Blueshifting of Infrared Heat Power Spectrum ........................................ 7
Figure 2. Light-Bending in a Spacetime-Altered Reigon ......................................... 9
Figure 3. Alcubierre Warp Drive Metric Structure ................................................. 11
Tables
Table 1. Metric Effects on Physical Processes in an Altered Spacetime as
Interpreted by a Remote (Unaltered Spacetime) Observer ....................... 4
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Advanced Space Propulsion Based on Vacuum (Spacetime
Metric) Engineering
Preface and Introduction
A theme that has come to the fore in advanced planning for long-range space
exploration in the future is the concept that empty space itself (the quantum
vacuum, or spacetime metric) might be engineered to provide energy/thrust
for future space vehicles. Although far reaching, such a proposal is solidly
grounded in modern physical theory, and therefore the possibility that
matter/vacuum interactions might be engineered for spaceflight applications
is not a priori ruled out (Reference 1). Given the current development of
mainstream theoretical physics on such topics as warp drives and traversable
wormholes that provides for such vacuum engineering possibilities
(References 2-6), provided in this paper is a broad perspective of the physics
and consequences of the engineering of the spacetime metric.
The concept of "engineering the vacuum" found its first expression in the
mainstream physics literature when it was introduced by Nobelist T. D. Lee in
his textbook Particle Physics and Introduction to Field Theory (Reference 7).
There he stated, "The experimental method to alter the properties of the
vacuum may be called vacuum engineering.... If indeed we are able to alter
the vacuum, then we may encounter new phenomena, totally unexpected."
This legitimization of the vacuum engineering concept was based on the
recognition that the vacuum is characterized by parameters and structure that
leave no doubt that it constitutes an energetic and structured medium in its
own right. Foremost among these are that (1) within the context of quantum
theory, the vacuum is the seat of energetic particle and field fluctuations and
(2) within the context of general relativity, the vacuum is the seat of a
spacetime structure (metric) that encodes the distribution of matter and
energy. Indeed, on the flyleaf of a book of essays by Einstein and others on
the properties of the vacuum, there is the statement, "The vacuum is fast
emerging as the central structure of modern physics" (Reference 8). Perhaps
the most definitive statement acknowledging the central role of the vacuum in
modern physics is provided by 2004 Nobelist Frank Wilczek in his book The
Lightness of Being: Mass, Ether and the Unification of Forces (Reference 9):
"What is space? An empty stage where the physical world of matter acts
out its drama? An equal participant that both provides background and
has a life of its own? Or the primary reality of which matter is a
secondary manifestation? Views on this question have evolved, and
several times have changed radically, over the history of science. Today
the third view is triumphant."
Given the known characteristics of the vacuum, one might reasonably inquire
why it is not immediately obvious how to catalyze robust interactions of the
type sought for spaceflight applications. For starters, in the case of quantum
vacuum processes, uncertainties regarding global thermodynamic and energy
constraints remain to be clarified. Furthermore, it is likely that energetic
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components of potential utility involve very-small-wavelength, high-frequency
field structures and thus resist facile engineering solutions. With regard to
perturbation of the spacetime metric, the required energy densities predicted
by present theory exceed by many orders of magnitude values achievable with
existing engineering techniques. Nonetheless, one can examine the
possibilities and implications under the expectation that as science and its
attendant derivative technologies mature, felicitous means may yet be found
that permit the exploitation of the enormous, as-yet-untapped potential of
engineering so-called "empty space," the vacuum.
This paper introduces the underlying mathematical platform for investigating
spacetime structure, the metric tensor approach. It then outlines the
attendant physical effects that derive from alterations in the spacetime
structure. Finally, the paper examines these effects as they would be exhibited
in the presence of advanced aerospace craft technologies based on spacetime
modification.
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I. Spacetime Modification - Metric Tensor Approach
Despite the daunting energy requirements to restructure the spacetime metric to a
significant degree, one can investigate the forms that such restructuring would take to
be useful for spaceflight applications and determine their corollary attributes and
consequences. Thus we embark on a "Blue Sky," general-relativity-for-engineers
approach, as it were.
As a mathematical evaluation tool, the metric tensor that describes the measurement of
spacetime intervals is used . Such an approach, well known from studies in general
relativity (GR), has the advantage of being model independent-that is, it does not
depend on knowledge of the specific mechanisms or dynamics that result in spacetime
alterations but rather only assumes that a technology exists that can control and
manipulate (that is, engineer) the spacetime metric to advantage. Before discussing the
predicted characteristics of such engineered spacetimes, beginning in Section III, a
brief mathematical digression for those interested in the mathematical structure behind
the discussion to follow is introduced.
As a brief introduction, the expression for the four-dimensional line element ds2 in
terms of the metric tensor gµ., is given by
=
ds2 g µvd x"dx" {l)
where summation over repeated indices is assumed unless otherwise indicated. In
ordinary Minkowski flat spacetime, a (four-dimensional) infinitesimal interval ds is given
by the expression (in Cartesian coordinates)
c/s2 =c2dt2 - (dx2 +dy2 +dx2
)
(2)
where the identification dx0 = cdt , dx' = dx, dx2 =dy , dx3 =dz is made, with metric
tensor coefficients g 00 =1, g II = g 22 = g 33 =- 1, gµ v =0 for µ --t= v.
For spherical coordinates in ordinary Minkowski flat spacetime
=
ds2 c2dt 2 -dr2 - r2d02 - r 2 sin 2 0dql (3)
= =
where dx0 = cc/t , dx' = dr, dx 2 = d0, dx3 d(f), with metric tensor coefficients g 1,
00
g 11 =-1, g 22 = -r2 , g 33 = -r2sin20, gµv= O for µ -t; v.
As an example of spacetime alteration, in a spacetime altered by the presence of a
spherical mass distribution mat the origin (Schwarzschild-type solution), the above can
be transformed into (Reference 10)
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with the metric tensor coefficients modifying the Minkowski flat-spacetime intervals
gµv
dt, dr, and so forth, accordingly.
As another example of spacetime alteration, in a spacetime altered by the presence of a
charged spherical mass distribution (Q,m)at the origin (Reissner-Nordstrom-type
solution), the above can be transformed into (Reference 11)
with the metric tensor coefficients again changed accordingly. Note that the effect
gµv
on the metric due to charge Qdiffers in sign from that due to mass m, leading to what
in the literature has been referred to as electrogravitic repulsion (Reference 12).
Similar relatively simple solutions exist for a spinning mass (Kerr solution) and for a
spinning electrically charged mass (Kerr-Newman solution). In the general case,
appropriate solutions for the metric tensor can be generated for arbitrarily engineered
spacetimes, characterized by an appropriate set of spacetime variables d.x:11 and metric
tensor coefficients Of significance now is to identify the associated physical effects
g µ 11 •
and to develop a table of such effects for quick reference.
We begin by simply cataloging metric effects-that is, physical effects associated with
alteration of spacetime variables-saving for Section IV the significance of such effects
within the context of advanced aerospace craft technologies.
II. Physical Effects as a Function of Metric Tensor
Coefficients
In undistorted spacetime, measurements with physical rods and clocks yield spatial
intervals and time intervals dt, defined in a flat Minkowski spacetime, the spacetime
dxµ
of common experience. In spacetime-altered regions, dx;i and dt are still chosen as
natural coordinate intervals to represent a coordinate map, but now local
measurements with physical rods and clocks yield spatial intervals ✓-8µ v dxµ and time
intervals .j'i;dt , so-called proper coordinate intervals. From these relationships a table
of associated physical effects to be expected in spacetime regions altered by either
natural or advanced technological means can be generated. Given that, as seen from
an unaltered region, alteration of spatial and temporal intervals in a spacetime-altered
region result in an altered velocity of light, from an engineering viewpoint such
alterations can in essence be understood in terms of a variable refractive index of the
vacuum (see Section III below) that affects all measurement.
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TIMEINTERVAL, FREQUENCY, ENERGY
Begin by considering the case where ~ < 1, typical for an altered spacetime metric in
the vicinity of, say, a stellar mass, as expressed by the leading term in Equation (4).
Local measurements with physical clocks within the altered spacetime yield a time
interval ..[i";;dt < dt; thus an interval of time dt between two events in an undistorted
spacetime remote1 from the mass-say, 10 seconds-would be judged by local (proper)
measurement from within the altered spacetime to occur in a lesser time interval,
.[i";;;dt <dt-say, 5 seconds. From this one can rightly infer that, relatively speaking,
clocks (atomic processes and so forth) within the altered spacetime run slower. Given
this result, a physical process (for example, interval between clock ticks, atomic
M/.ji;,
emissions) that takes a time !:::.t in unaltered spacetime slows to !).t ➔ when
occurring within the altered spacetime. Conversely, under conditions (for example,
metric engineering) for which Ji;; > 1, processes within the spacetime-altered region
are sped up. Thus the first entry for a table of physical effects (see Table 1) is made.
Given that frequency measurements are the reciprocal of time duration measurements,
m m.Jg;; ,
the associated expression for frequency w is given by ➔ our second entry in
Table 1. This accounts, for example, for the redshifting of atomic emissions from dense
masses where ..[i";; < 1. Conversely, under conditions for which Ji;; > 1, blueshifting of
emissions would occur. In addition, given that quanta of energy are given by E = hm,
Jg;; ,
energy scales with as does frequency, E ➔ E.jg;,, our third entry in the table.
Depending on the value of .Ji:in the spacetime-altered region, energy states may be
raised or lowered relative to an unaltered spacetime region.
1 An observer at "infinity."
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Table 1. Metric Effects on Physical Processes in an Altered Spacetime as
Interpreted by a Remote (Unaltered Spacetime) Observer
Variable Typical Stellar Mass Spacetime-Engineered
Metric
(goo < 1, lg11 I>1)
(g(X) > 1, lg11 I < 1)
Processes (for example, Processes (for example,
. M ➔ tit/ ji:i
Time