35 years of testing relativistic gravity: where do we go from here?
This paper addresses the motivation, technology and recent results in the tests of the general theory of relativity in the solar system.
lunar lidar ranging, gravity↗
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Highly Structured Plasma Density and Associated Electric and Magnetic Field Irregularities at Sub-Auroral, Middle, and Low Latitudes in the Topside Ionosphere Observed with the DEMETER and DMSP Satellites
Detailed observations of the plasma structure and irregularities that characterize the topside ionosphere at sub-auroral, middle, and low-latitudes are gathered with probes on the DEMETER and DMSP satellites. In particular, we present DEMETER observations near 700 km altitude that reveal: (1) the electric field irregularities and density depletions at mid-latitudes are remarkably similar to those associated with equatorial spread-F at low latitudes; (2) the mid-latitude density structures contain both depletions and enhancements with scale lengths along the spacecraft trajectory that typically vary from 10's to 100's of km; (3) in some cases, ELF magnetic field irregularities are observed in association with the electric field irregularities on the walls of the plasma density structures and appear to be related to finely-structured spatial currents and/or Alfven waves; (4) during severe geomagnetic storms, broad regions of nightside plasma density structures are typically present, in some instances extending from the equator to the subauroral regions; and (5) intense, broadband electric and magnetic field irregularities are observed at sub-auroral latitudes during geomagnetic storm periods that are typically associated with the trough region. Data from successive DEMETER orbits during storm periods in both the daytime and nighttime illustrate how enhancements of both the ambient plasma density, as well as sub-auroral and mid-latitude density structures, correlate and evolve with changes in the Dst. The DEMETER data are compared with near simultaneous observations gathered by the DMSP satellites near 840 km. The observations are related to theories of sub-auroral and mid-latitude plasma density structuring during geomagnetic storms and penetration electric fields and are highly germane to understanding space weather effects regarding disruption of communication and navigation signals in the near-space environment.
Pfaff, Robert F.↗
Using Game Theory to Qualitatively Analyze Global Relations
As the world becomes smaller, the importance of global education increases. Technological advancements have made news instantaneous. The advent of the Internet has made contact with another part of the world just a click away. Such achievements have put pressure on educational institutions to prepare students for the global community in which they already live. !~ey must not only ~e taug~~ about the world and the interactions among countries, but also, how the decIsions are made which facillta~e. these interactions and what factors might contribute to the chain reactions which might erupt from such declsl?n~. It is critical that students learn the skills of decision-making and analysis in order to be able to operate Within a world where threats and crises abound. As tomorrow's leaders, today's students must be exposed to the global world and its mechanisms and learn the tools to navigate within it.
Tacosa, Corliss A.↗
Gravitational-Wave Astronomy
Einstein's General Theory of Relativity is our best classical description of gravity, and informs modern astronomy and astrophysics at all scales: stellar, galactic, and cosmological. Among its surprising predictions is the existence of gravitational waves -- ripples in space-time that carry energy and momentum away from strongly interacting gravitating sources. In my talk, I will give an overview of the properties of this radiation, recent breakthroughs in computational physics allowing us to calculate the waveforms from galactic mergers, and the prospect of direct observation with interferometric detectors such as LIGO and LISA.
Kelly, Bernard J.↗
LiAISON-Supplemented Navigation for Geosynchronous and Lunar L1 Orbiter
A high-fidelity simulation is developed to test the theory that relative range and range-rate measurements between a satellite in a geosynchronous orbit and a satellite in orbit about the Earth-Moon L1 point may be used to improve the navigation accuracy of both satellites, compared with ground-only tracking. Recent research has determined that satellite-to-satellite range measurements between these two orbits are su cient to perform absolute state estimation as well as relative state estimation of both satellites - a technology known as LiAISON (Linked Autonomous Interplanetary Satellite Orbit Navigation). This study quanties the improvement in accuracy when LiAISON is used to supplement ground tracking of one or both satellites in a very realistic simulation. Orbit determination techniques show that the inclusion of LiAISON measurements with ground tracking observations can greatly improve absolute position and velocity estimates for both satellites in geosynchronous orbit and about the Earth-Moon L1 point.
satellite-to-satellite tracking (SST)↗
Physics of the Cosmos: Program Annual Technology Report
From ancient times, humans have looked up at the night sky and wondered: Are we alone? How did the universe come to be? How does the universe work? PCOS focuses on that last question. Scientists investigating this broad theme use the universe itself as their laboratory, investigating its fundamental laws and properties. They test Einstein's General Theory of Relativity to see if our current understanding of space-time is borne out by observations. They examine the behavior of the most extreme environments - supermassive black holes, active galactic nuclei, and others - and the farthest reaches of the universe, to expand our understanding. With instruments sensitive across the spectrum, from radio, through infrared (IR), visible light, ultraviolet (UV), to X rays and gamma rays, as well as gravitational waves (GWs), they peer across billions of light-years, observing echoes of events that occurred instants after the Big Bang. The Laser Interferometer Gravitational-Wave Observatory (LIGO) recently recorded the first direct measurement of long-theorized GWs. Another surprising recent discovery is that the universe is expanding at an ever-accelerating rate, the first hint of so-called "dark energy," estimated to account for 75% of mass-energy in the universe. Dark matter, so called because we can only observe its effects on regular matter, accounts for another 20%, leaving only 5% for regular matter and energy. Scientists now also search for special polarization in the cosmic microwave background to support the notion that in the split-second after the Big Bang, the universe inflated faster than the speed of light! The most exciting aspect of this grand enterprise today is that we can finally develop the tools needed for such discoveries.
COR↗
Program Annual Technology Report: Physics of the Cosmos Program Office
From ancient times, humans have looked up at the night sky and wondered: Are we alone? How did the universe come to be? How does the universe work? PCOS focuses on that last question. Scientists investigating this broad theme use the universe as their laboratory, investigating its fundamental laws and properties. They test Einstein’s General Theory of Relativity to see if our current understanding of space-time is borne out by observations. They examine the behavior of the most extreme environments – supermassive black holes, active galactic nuclei, and others – and the farthest reaches of the universe, to expand our understanding. With instruments sensitive across the spectrum, from radio, through infrared (IR), visible light, ultraviolet (UV), to X rays and gamma rays, as well as gravitational waves (GWs), they peer across billions of light-years, observing echoes of events that occurred instants after the Big Bang. Last year, the LISA Pathfinder (LPF) mission exceeded expectations in proving the maturity of technologies needed for the Laser Interferometer Space Antenna (LISA) mission, and the Laser Interferometer Gravitational-Wave Observatory (LIGO) recorded the first direct measurements of long-theorized GWs. Another surprising recent discovery is that the universe is expanding at an ever-accelerating rate, the first hint of so-called “dark energy,” estimated to account for 75% of mass-energy in the universe. Dark matter, so called because we can only observe its effects on regular matter, is thought to account for another20%, leaving only 5% for regular matter and energy. Scientists now also search for special polarization in the cosmic microwave background to support the notion that in the split-second after the Big Bang, the universe inflated faster than the speed of light! The most exciting aspect of this grand enterprise today is the extraordinary rate at which we can harness technologies to enable these key discoveries.
COR↗
A Telescope at the Solar Gravitational Lens: Problems and Solutions
By Einstein's general theory of relativity, gravity of a massive body deflects light, and thus the sun can be used as a lens. The focus of the sun's gravitational lens is about 550 AU (Astronomical Units). (The sun continues to act as a lens beyond this minimum; at longer distances, the focused light passes increasingly far from the solar limb.) A mission to the gravitational focus of the sun, beyond the edge of the solar system, but far closer than the nearest stars, could be a target for an interstellar precursor. Proposed methods of reaching the focal distance include electric propulsion or laser- or solar sails. An objective for such a mission is to use the gravitational lens to image and map an extrasolar planet.
Landis, Geoffrey A.↗
A Lorentz-invariant look at quantum clock synchronization protocols based on distributed entanglement
We discuss possible directions of research in quantum information theory which may lead to a complete, working quantum clock synchronization clock protocol.
quantum↗
LiAISON-supplemented navigation for geosynchronous and Lunar L1 orbiters
A high-fidelity simulation is developed to test the theory that relative range and range-rate measurements between a satellite in a geosynchronous orbit and a satellite in orbit about the Earth-Moon L₁ point may be used to improve the navigation accuracy of both satellites, compared with ground-only tracking. Recent research has determined that satellite-to-satellite range measurements between these two orbits are sufficient to perform absolute state estimation as well as relative state estimation of both satellites–a technology known as LiAISON(Linked Autonomous Interplanetary Satellite Orbit Navigation). This study quantifies the improvement in accuracy when LiAISON is used to supplement ground tracking of one or both satellites in a very realistic simulation. Orbit determination techniques show that the inclusion of LiAISON measurements with ground tracking observations can greatly improve absolute position and velocity estimates for both satellites in geosynchronous orbit and about the Earth-Moon L₁ point.
Anderson, Rodney L.↗
GW190412: Observation of a binary-black-hole coalescence with asymmetric masses
We report the observation of gravitational waves from a binary-black-hole coalescence during the first two weeks of LIGO’s and Virgo’s third observing run. The signal was recorded on April 12, 2019 at05∶30∶44 UTC with a network signal-to-noise ratio of 19. The binary is different from observations during the first two observing runs most notably due to its asymmetric masses: a∼30M⊙black hole merged with a ∼8M⊙black hole companion. The more massive black hole rotated with a dimensionless spin magnitude between 0.22 and 0.60 (90% probability). Asymmetric systems are predicted to emit gravitational waves with stronger contributions from higher multipoles, and indeed we find strong evidence for gravitational radiation beyond the leading quadrupolar order in the observed signal. A suite of tests performed onGW190412 indicates consistency with Einstein’s general theory of relativity. While the mass ratio of this system differs from all previous detections, we show that it is consistent with the population model of stellar binary black holes inferred from the first two observing runs.
R. Abbott↗
Blood electrolytes and exercise in relation to temperature regulation in man
Current knowledge and theories about the relation of blood electrolytes and exercise to thermoregulation in man are reviewed. It is shown that the elevation of body temperature during physical exercise is a regulated process and is not due to a failure of the heat dissipating mechanisms. Core and skin temperatures do not provide sufficient information to account for the control of sweating during exercise. Evidence is presented that suggests an association between equilibrium levels of rectal temperature and the osmotic concentration of the blood with essentially no influence of variations in plasma volume.
Greenleaf, J. E.↗
Application of spacecraft tracking data to experimental general relativity
Gravitational relativistic theory tests using tracking data from interplanetary spacecraft, orbiters and landers
Anderson, J. D.↗
A preliminary in-duct measurement of spinning modes in the inlet of a rotating vehicle
Suppression of noise radiated from a jet engine duct is an important environmental problem. Results are presented for a study aimed at developing and evaluating an experimental method for measuring the complex acoustic pressure field at a plane in the inlet of a fan duct. The theory of modal propagation is outlined and related to the theory of measuring spinning modes in the duct. A spinning mode measurement apparatus is described, and preliminary test results of the modal measurement for several operating speeds are presented. The measurement of spinning modes is successfully carried out in the inlet of a rotating vehicle under conditions representative of an actual jet engine. Data repeatability and problems encountered in the measurement are examined. In particular, it is important to calibrate the probe systems for phase and level. Recommendations for future improvements in the method are made.
Kraft, R. E.↗
The geomagnetic main field and the geodynamo
Information available on the geomagnetic main field and the geodynamo is presented. Attention is given to the process of mapping the magnetic field, the last version of International Geomagnetic Reference Field Model, and maps of the magnetic field at the core-mantle boundary and their interpretation. Particular consideration is given to the existing geodynamo theories, with special relation given to the Braginsky and Meytlis theory of core turbulence in which the turbulence differs fundamentally from classical turbulence of Kolmogorov type.
Bloxham, Jeremy↗
Using the HHT to Search for Gravitational Waves
Gravitational waves are a consequence of Einstein's theory of general relativity applied to the motion of very dense and massive objects such as black holes and neutron stars. Their detection will reveal a wealth of information about these mysterious objects that cannot be obtained with electromagnetic probes. Two projects are underway to attempt the detection of gravitational waves: NASA's Laser Interferometer Space Antenna (LISA), a space based mission being designed to search for waves from supermassive black holes at the centers of galaxies, and the NSF's Laser Interferometer Gravitational Wave Observatory (LIGO), a ground based facility that is now searching for waves from supernovae. pulsars, and the coalescence of black hole and neutron star systems. Because general relativity is an inherently non-linear theory, many of the predicted source waveforms show strong frequency modulation. In addition, the LIGO and LISA detectors are highly sensitive devices that produce a variety of non-linear transient noise features. Thus the unique capabilities of the HHT. the extraction of intrawave modulation and the characterization of non-linear and non-stationary signals, have a natural application to both signal detection and experimental characterization of the detectors. In this talk I will give an overview of the status of the field. including some of the expected sources of gravitational waves, and I will also describe the LISA and LIGO detectors. Then I will describe some applications of the HHT to waveform detection and detector noise characterization.
Camp, Jordan↗
Periodic Forcing of a Turbulent Axisymmetric Wake
Effects of variable-frequency forcing. Relation to linear theory. Effects of three-dimensional forcing. Relation between instability mechanisms. Future work includes open-loop control and feedback control.
Qubain, Ala↗
(abstract) Spacecraft Doppler Tracking with the Deep Space Network in the Search for Gravitational Waves
The Deep Space Network generates accurate radio science data observables for investigators who use radio links between spacecraft and the Earth to examine small changes in the phase and/or amplitude of the signal to study a wide variety of structures and phenomena in space. Several such studies are directed at aspects of the theory of general relativity such as gravitational redshift and gravitational waves. A gravitational wave is a propagating, polarized gravitational field, a ripple in the curvature of space-time. In Einstein's theory of general relativity, the waves are propagating solutions of the Einstein field equations. Their amplitudes are dimensionless strain amplitudes that change the fractional difference in distance between test masses and the rates at which separated clocks keep time. Predicted by all relativistic theories of gravity, they are extremely weak (the ratio of gravitational forces to electrical forces is about 10(sup -40)) and are generated at detectable levels only by astrophysical sources - very massive sources under violent dynamical conditions. The waves have never been detected but searches in the low-frequency band using Doppler tracking of many spacecraft have been conducted and others are being planned. Upper limits have been placed on the gravitational wave strength with the best sensitivities to date are for periodic waves being 7 x 10(sup -15).
gravitational waves theory of general relativity D↗