Historical research guide · 0438 · 2005
Applications of High-Frequency Gravitational Waves (HFGWs)
Robert M. L. Baker, Jr.
In one minute
Robert Baker has spent decades on a single question — what would you do with gravitational waves you made yourself — and this STAIF-2005 paper is his catalogue of answers. High-frequency gravitational waves, which he defines as anything above 100 kilohertz, pass through ordinary matter almost unabsorbed: through rock, through seawater, through a submarine hull. So his first application is communication with no infrastructure at all, point to multipoint straight through the Earth, no cable, no relay, no satellite. His second is propulsion, resting on Landau and Lifshitz’s statement that a gravitational wave carries energy and therefore sources a gravitational field of its own, an effect strengthened at high frequency: beam that energy and you raise hills and valleys in spacetime that a craft falls toward, carrying no propellant. Then imaging through ground and ocean, a telescope for the patterned relic high-frequency background that would give navigation fixes without GPS, and focused beams intense enough to reach nuclei. An appendix derives the jerk form of Einstein’s quadrupole power equation that the whole programme rests on.
Connection
This is the applications half of chapter 4’s argument — a wave in the metric is something you can generate, aim and focus — and it supplies chapter 10 with its cleanest case of a signal that goes through matter instead of around it, and chapter 11 with a concrete job for high-temperature superconductors as gravitational lenses and mirrors.
From the source
High-frequency gravitational waves are defined as those with frequencies above 100 kilohertz, and the case for making them on a bench rather than waiting for the sky is a force ratio: electromagnetic forces are more than ten to the thirty-fifth times larger than gravitational ones, and Einstein’s own formulation does not require the driving force to be gravitational. Baker’s conclusion is that non-gravitational forces are the right tool for laboratory generation.Introduction, first paragraph; The Quadrupole Approximation, point (3)
Baker recasts Einstein’s 1916 quadrupole power approximation into a jerk formulation — the radiated power goes as the square of twice the radius of gyration times the rate of change of force — so that generator design becomes a question of how fast you can change a force on an asymmetrically arranged energizable element. He states this equation as central to every laboratory generator concept then on the table.The Quadrupole Approximation, Equations 1 and 2; Appendix
Because gravitational waves have a very low cross-section for absorption by normal matter, a high-frequency gravitational wave link would reach deeply submerged submarines or pass directly through the Earth, giving point-to-multipoint communication with no fibre, no transponders and no microwave relays. Baker quotes Thomas Prince, then chief scientist at NASA JPL, that of all the applications communication would seem to be the most important. Whether a transmitter can also serve as a receiver is flagged as needing experimental validation.Applications — Communication
For propulsion Baker leans on Landau and Lifshitz page 349: a gravitational wave has definite energy and is therefore itself the source of an additional gravitational field, a second-order effect that is significantly strengthened for high-frequency waves. Energy beamed from off board would then create hills and valleys in the spacetime continuum that a craft falls toward — propellantless propulsion — and the same lever would let you perturb the motion of distant objects or coalesce a cloud of hazardous vapour by changing the gravitational field around it.Applications — Propulsion
Shorter gravitational wavelengths mean sharper images, by the ordinary diffraction limit of 1.22 wavelengths divided by aperture diameter, so a high-frequency gravitational wave telescope becomes conceivable if a high-temperature superconductor really does refract or reflect gravitational waves, as Ning Li and David Torr argued in 1992. Baker marks those optical properties as speculative and requiring further study, and notes the payoff if they hold: the patterned relic high-frequency background could be read for navigational fixes anywhere in or under the Earth, with no reliance on GPS satellites.Applications — Astronomy, Equation 3
Focusing a high-intensity beam with superconducting lenses or mirrors down to a few microns could, on Baker’s numbers, put fluxes above ten to the nineteenth watts per square metre into a small volume and drive nuclear phenomena there. He closes by naming the one result the whole catalogue waits on: the successful generation and detection of high-frequency gravitational waves in the laboratory, after which, he expects, applications nobody has thought of will follow — as microwave ovens and radar followed Marconi’s spark gap.Applications — Physics; Conclusions
The way in
https://doi.org/10.1063/1.1867259How to cite it
Robert M. L. Baker, Jr. (2005) Applications of High-Frequency Gravitational Waves (HFGWs) doi:10.1063/1.1867259