Geometrodynamics, and Quantum Nondemolition Techniques for LIGO

GEOMETRODYNAMICS:  The nonlinear dynamics of curved spacetime (the “spacetime storm”) created by the black-hole collisions that LIGO has observed.  This dynamics entails physical structures called “tidal tendices” and “frame-drag vortices” that (i) are made from curved spacetime, (ii) are attached to the colliding black holes, and (iii)  interact in remarkable ways, giving rise to the gravitational waves that LIGO detects and monitors. 

QUANTUM NONDEMOLITION (QND) TECHNIQUES:  The set of techniques to  be used in LIGO,  to circumvent the Heisenberg uncertainty principle as applied to LIGO’s 40 kg mirrors.  The uncertainty principle dictates that, when monitoring the separations of the mirrors’ centers of mass, the LIGO instrumentation creates unpredictable quantum fluctuations of the mirrors’ relative momenta,  fluctuations large enough to hide the subsequent influence of gravitational waves.  QND techniques will prevent  these quantum fluctuations from “demolishing” the gravitational-wave signal.  Late this year, the first step toward QND will be installed in LIGO: a capability to inject squeezed vacuum into the output ports of LIGO’s interferometers.  In the 2020s, QND will be a major aspect of LIGO’s instrumentation.