Ignazio Ciufolini on the First Accurate Test and Direct Measurement of Gravitomagnetism
Fast Moving Front Commentary, January 2011
Article: A confirmation of the general relativistic prediction of the Lense-Thirring effect
Authors: Ciufolini, I;Pavlis, EC
Ignazio Ciufolini talks with ScienceWatch.com and answers a few questions about this month's Fast Moving Fronts paper in the Multidisciplinary field.
Why do you think your paper is highly cited?
Einstein's gravitational theory of General Relativity is a key ingredient for understanding the universe that we observe. During the past century General Relativity gave rise to an experimental triumph.
However, despite all the observational tests passed by General Relativity and its applications to space navigation, we have recently discovered supernovae that appear to accelerate away from us. This may be explained by dark energy that is accelerating the expansion of the Universe, and may imply a non-zero value to Einstein's cosmological constant, or an exotic new form of energy, known as quintessence, or perhaps a modification of Einstein's gravitational theory.
"The LARES (LAser RElativity Satellite) satellite..."
"...Earth gravity field model..."
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Furthermore, General Relativity predicts the occurrence of spacetime singularities, events in which every known physical theory ceases to be valid and, even though a breakdown of General Relativity should occur at the quantum level, some viable modifications of Einstein's gravitational theory already give different predictions at the classical, non quantum, level. Therefore, every aspect of Einstein's gravitational theory should be directly tested and the accuracy of its present tests should be further improved.
Today one of the main challenges in experimental gravitation, together with the direct detection of gravitational waves, is the accurate measurement of gravitomagnetism generated by mass-energy currents, e.g., by the angular momentum of a body. In General Relativity, gravitomagnetism is produced by mass-currents in the same way as, in electrodynamics, magnetism is generated by electric-currents.
Does it describe a new discovery, methodology, or synthesis of knowledge?
This paper, by Ignazio Ciufolini and Erricos Pavlis, describes the first accurate test and direct measurement of gravitomagnetism. Prior to this test, obtained using the laser-ranged satellites LAGEOS and LAGEOS 2 and the GRACE gravity field models, in spite of the many tests that have been proposed and implemented, there was not an accurate direct test of gravitomagnetism. There were only some less accurate observations of gravitomagnetism that we published (Science 1998) using laser-ranged satellites and some astrophysical evidence for it from the accretion disk of black holes and from the orbit of the Moon.
Would you summarize the significance of your paper in layman's terms?
General Relativity is the theory of Albert Einstein that describes the gravitational interaction between celestial bodies. Its role is fundamental to explain our observations of the dynamics of the expanding universe and to study some fascinating and exotic bodies as black holes. However, there are some astrophysical observations that we are not able to explain on the basis of our present knowledge of physics. This is why General Relativity and all its predictions need to be tested.
In particular, Einstein's gravitational theory predicts that the motion of an object around another more massive body, such as the motion of a satellite around Earth, would be influenced not only by the mass of the body but also by its rotation. This is of course not true in Newtonian gravitational theory where only the mass gravitationally affects the motion of other bodies. In our paper we reported the direct measurement of the tiny displacement of the orbits of two laser-ranged satellites—LAGEOS and LAGEOS 2—due to the rotation of Earth.
How did you become involved in this research, and how would you describe the particular challenges, setbacks, and successes that you've encountered along the way?
"...despite all the observational tests passed by General Relativity and its applications to space navigation, we have recently discovered supernovae that appear to accelerate away from us."
I became involved in this research in 1984 when one the great theoretical physicists of the 20th century, John Archibald Wheeler, a former collaborator of Niels Bohr, Enrico Fermi, and Albert Einstein, showed me a paper on the LAGEOS satellite. At that time I was working in Wheeler's group at the University of Texas at Austin. At the beginning, it was not easy to have the relativity community to accept the idea (I.C., Ph.D. dissertation 1984, and I.C., Phys. Rev. Lett. 1986) that we could perform an accurate measurement of gravitomagnetism using two satellites of LAGEOS type. However, 20 years later our Nature paper with the measurement of gravitomagnetism using LAGEOS and LAGEOS 2 was finally published.
Where do you see your research leading in the future?
In 2011 the orbiting around Earth of the new satellite LARES (LAser RElativity Satellite) is planned by the Italian Space Agency. The LARES satellite is now ready for launch and together with the LAGEOS and LAGEOS 2 satellites and with the Earth gravity field models obtained by the GRACE space mission, will provide a measurement of gravitomagnetism with an accuracy of about one percent, i.e., with an improvement of about an order of magnitude with respect to the measurement described in this 2004 paper of ours that used LAGEOS, LAGEOS 2, and the older GRACE gravity models only. LARES will be used for determinations of space geodesy and geodynamics too.
Do you foresee any social or political implications for your research?
Today Einstein's gravitational theory of General Relativity is relevant not only for the study of the universe but it is also useful for everyday applications such as finding a good restaurant. But how?
General Relativity is an important ingredient of space research and space navigation. The best example is the Global Positioning Satellite (GPS) system, if we would not use General and Special Relativity corrections to the motion of the GPS satellites, we would make a substantial error in predicting their orbits.
In addition, satellites such as LAGEOS, LAGEOS 2, and the forthcoming LARES are and will be extremely useful for measurements and studies of space geodesy, geodynamics, and tectonic plate motion. The movements of the Earth's crust are and will be very accurately measured using these satellites. This is useful for studies of prediction of earthquakes too. For example, the movement of the well-known San Andreas Fault in California was initially very accurately measured by LAGEOS and satellite laser ranging in the late '70s.
Prof. Ignazio Ciufolini
University of Salento
KEYWORDS: LAGEOS; SATELLITE; DRAG.
Figure 1: The LARES (LAser RElativity Satellite) satellite for testing Einstein's theory of General Relativity under construction. It is planned for launch in 2011.
Photo courtesy of the Italian Space Agency (ASI).
Figure 2: An artistic view showing an Earth gravity field model obtained by the GRACE spacecraft, the two LAGEOS satellites (the two spheres covered with retro-reflectors below in the figure) and the GRACE spacecraft (the two polar spacecraft above in the figure). This image gives also an artistic view of the gravitomagnetic spacetime distortion due to the Earth rotation predicted by General Relativity (the red twisted curves) and measured using the two LAGEOS satellites.
Ignazio Ciufolini (from introduction):
Ignazio Ciufolini receiving the Occhialini medal and prize 2010 by the Institute of Physics (IOP) in London “For providing further experimental confirmation of Einstein’s theory of General Relativity through the use of laser-ranged satellites to study and measure frame-dragging”. This prize was mainly based on the 2004 Nature paper.