Defense Intelligence Reference Document High-Frequency Gravitational Wave Communications

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1.0 Introduction
1.1 INTRODUCTION
Of the applications of high-frequency gravitational waves (HFGWs), communication
appears to be the most important and most immediate. Gravitational waves have a
very low cross section for absorption by normal matter, so high-frequency waves could,
in principle, carry significant information content with effectively no absorption unlike
electromagnetic (EM) waves. Multi-channel HFGW communications can be both point-
to-point (for example, to deeply submerged submarines) and point-to-multipoint, like
cell phones. HFGWs pass through all ordinary material things without attenuation and
represent the ultimate wireless system. One could communicate directly through the
Earth from Moscow in Russia to Caracas in Venezuela-without the need for fiber optic
cables, microwave relays, or satellite transponders. Antennas, cables, and phone lines
would be things of the past. A timing standard alone, provided by HFGW stations
around the globe, could result in a multi-billion dollar savings in conventional telecom
systems over ten years, according to the recent analysis of Harper and Stephenson
(2007). The communication and navigation needs of future magneto hydrodynamic
(MHD) aerospace vehicles, such as the MHD aerodyne (www.mhdprospects.com), which
is high in electromagnetic interference, similar to plasma interference seen at reentry,
would be another possible applications area for HFGW communications.
1.2 DEFINITION OF HIGH-FREQUENCY GRAVITATIONAL WAVES
Visualize the luffing of a sail as a sailboat comes about or tacks. The waves in the sail's
fabric are similar in many ways to gravitational waves (GWs), but instead of sailcloth
fabric, gravitational waves move through a "fabric" of space. Einstein called this fabric
the "space-time continuum" in his 1915 work known as General Relativity (GR).
Although his theory is very sophisticated, the concept is relatively simple. This fabric is
four-dimensional: it has the three usual dimensions of space-east-west, north-south,
and up-down-plus the fourth dimension of time. Here is an example: we define a
location on this "fabric" (Einstein, 1916) as 5th Street and Third Avenue on the fourth
floor at 9 AM. No one can see this "fabric," just as no one can see wind, sound, or
gravity. Nevertheless, those elements are real, and so is this "fabric." If one could
generate ripples in this space-time fabric, many applications would become available.
Much like radio waves can be used to transmit information through space, gravitational
waves could be used to perform analogous functions. Gravitational waves are the
subject of extensive current research, which so far has focused on low frequencies.
High-frequency gravitational waves, as defined by physicists Douglass and Braginsky
(1979), are gravitational waves having frequencies higher than 100 kHz. Low-frequency
gravitational waves (LFGWs), such as those detectable by interferometric GW detectors
(for example, the Laser Interferometer Gravitational Observatory, or UGO) are not
applicable to communications due to their very long wavelengths, often thousands of
kilometers in length and, even more importantly, the inability to generate them
effectively in the laboratory. Furthermore LFGW detectors cannot detect HFGWs
(Shawhan, P. 5., 2004).
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