AERO 721 Gravity - Essay Example

AERO 721 Gravity Introduction: What goes up must come down! Yes, that’s gravity for you summed up in a single word. In this fast paced world of Science and Technology, great research is being carried on in all areas of study. One such area of study that is continuously under research is the area of gravitation. In lieu of this, a unique approach is used by the author to emphasize the field theoretic aspects of gravitation and the deep analogies shared between gravitation and other different areas in physics. This theory-centered text which is both clear and concise, includes the simplest experimental facts, which later goes on to explain about the corresponding differential equations, theoretical constructs such as energy, momentum and stress and several other applications. This unique textbook which is both clear and concise is a combination of a novel approach together with a simple down-to-earth treatment of electromagnetism andIt focuses mainly on basic principles rather than on applications while avoiding any abstractions. A physical theory, the classical field theory describes in detail how one or more physical fields correspondingly interacts with matter. Any physical quantity, in a given point of space and time represents a physical field. A good example of this would be measuring the velocity1 of wind over a region by assigning vectors at certain points. This is very useful for depicting weather forecasts in different regions. The term “classical” is used to differentiate it from other field theories using quantum2 mechanics. The “classical field theory” is essentially reserved for the physical theories involving gravitation and electromagnetism. Classical field theories are categorized both as relativistic and non – relativistic. In the Non- relativistic category, the vector force fields are considered to be the simplest physical fields. Faraday’s lines of force describing an electric field were the first time that these fields were taken seriously. The same method was used to describe the fields of gravitation. According to Newtonian gravitation, the classical field theory described the force of gravitation “as a mutual interaction between two masses.” However, it was found that the Newtonian Gravitation was inconsistent with regard to special relativity and hence a new theory of gravitation which was named general relativity was put together by Albert Einstein. According to Einstein’s theory, gravitation is treated as a geometric phenomena (curved space time) that are caused by masses. The gravitational field that occurs is mathematically represented by a metric tensor to depict a tensor field. The equations of the Einstein field accurately describe how this curvature is produced. In the Relativistic field category, we have the Covariant Classical Field Theory. The Lorentz Covariance is presently accepted and recognized as one of the fundamental aspects of nature, which is required in the field of modern formulations for the classical field theories. These theories are expressed mathematically making use of Lagrangians. After being subjected to an action principle, the function brings forth field equations and a law of conservation for the theory. Classical Field Theory - Electromagnetism and Gravitation Speaking on special cases of general geometry, the author Shahverdiyev, 2005) states that, “We find relations between quantities defining geometry and quantities defining the length of a curve in geometries underlying Electromagnetism and unified model of electromagnetism and Gravitation.” The theory-centered text deals with a new geometry, called General geometry, the special case of which is, geometry underlying Electromagnetism. To determine this, in the first case, the quantities defining geometry F__ and the length of a curve Aμ were noted. In the second case, relations between quantities defining geometry F__, 􀀀_μ_ and the length of a curve gμ_, Aμ were also noted. Both the above were proved to be true, provided the length of the vector did not change. In another special case of Riemannian geometry, since the vector length does not change, it is understood to be an underlying geometry for Gravitation. Action for electromagnetic field and Maxwell equations are derived from curvature function of geometry underlying Electromagnetism. It is shown that equation of motion for a particle interacting with electromagnetic field coincides exactly with equation for geodesics of geometry underlying Electromagnetism. It is also shown that Electromagnetism can not be geometrized in the framework of Riemannian geometry. Using General Geometry we propose a unified model of electromagnetism and gravitation which reproduces Electromagnetism and Gravitation and predicts that electromagnetic field is a source for gravitational field. This theory is formulated in a four dimensional space-time and does not contain additional fields. In his journal on the Gravitational Spacecraft Fran De Aquino (1998) says that “There is a electromagnetic factor of correlation between gravitational mass and inertial mass, which in specific electromagnetic conditions, can be reduced, nullified, negated, and increased.” This means that electro – magnetic fields have the capacity to reduce, nullify, invert or intensify gravitational forces. Therefore many practical applications may be utilized by controlling various gravitational interactions. A good example of this would be the concept of the spacecraft and also aerospace flight. In the 19th century, the first attempt was established by Faraday that a correlation existed between gravitation and electromagnetism. It was supported by Einstein who was also convinced of this correlation and thus the unified field theory was the outcome of his convictions. Newton carried out many experiments in order to find a correlation between gravitational mass mg and inertial mass mi. Only recently however, it was found that, “a particle’s gravitational mass decreases with the increase in temperature and that only in absolute zero (T=0o K) are gravitational mass and inertial mass equivalent.” (Donoghue, J.F, Holstein, B.R (1987) The topic of Gravitational Radiation is an area of intense experimental and theoretical research, even though there is no direct evidence of its existence. According to many theories, radiation may be utilized for propulsion. In Modern space propulsion, high technology is applied to ancient concepts. Though propulsion through reaction is a highly established technology, yet it is not very suitable for interstellar space travel for the very reason that the huge amount of propellant required is highly unfeasible. In addition to this, the related speed limitations would make missions last for decades and maybe even centuries. Over the years there have been quite a number of new techniques trying to improve the space propulsion system, but they had their own limitations. But in 1994, Miguel Alcubierre came out with a theoretical approach which appeared to be a form of propellantless propulsion capable of reaching the highest speeds. (Alcubierre, 1994) Nevertheless, the analysis of Alcubierre too fell short of expectations because neither did it address the problem of energy that was required, nor was the precise nature of the propulsor explained. However, in 1993, Taylor and Hulse were recognized for their work by being honored with the Nobel Prize in Physics. (Hulse, 1994), (Taylor, 1994) They had discovered “the signature of emission of gravitational radiation in the emitted radio pulses, and verified the validity of general relativity.” According to an article that appeared in the New Scientist, titled “Take a Leap into hyperspace” it stated that the American Institute of Aeronautics and Astronautics awarded prizes for the best paper every year. In last year’s nuclear and future flight category, the award was given to a paper asking for experimental tests with an amazing new kind of engine. According to them, the “hyper-drive motor would propel a craft through another dimension at enormous speeds. It could leave Earth at lunchtime and get to the moon in time for dinner.”(Haiko Lietz, New Scientist, 2006) However, the catch here is that the idea depends largely on an unrecognized kind of physics. The US military has shown a lot of interest in the hyper-drive concept and Sandia National Laboratories, a space propulsion researcher of the US Department of Energy showed keen interest of putting the idea to the test. An aerospace engineer Pavlos Mikellides who reviewed the winning paper had this to say, “the device would put travel to the stars within reach for the first time.” Dreamers - Pass Out The Tin Foil Hats Anti-Gravitational means of travel, is it Possible? Dreams of deep space exploration have been to a great degree just that – dreams. Barring development of a propulsion source capable of interstellar travel, our exploration will be limited to current achievements. Where do the lines of theory and reality cross? Men have long since dreamt of gaining control over gravity and they continue to dream as centuries pass us by. The value of such a dream seems immeasurable and just as indispensable, but surely within reach. What is it then that keeps eluding us having a major breakthrough? The answer to this is nothing but “Antigravity! The question arises whether antigravity is a myth or reality. In this section of the paper we are going to discuss certain key factors that would lead us to getting the right answer. Our Government is taking giant strides in brining us closer to reality – the reality of anti-gravitation. It has set up around 46 research projects around the country dealing with various angles of gravity control. Thirty three of these projects are under the control of the Air Force, with the rest of the projects being distributed among five other agencies. Two of the 46 Government projects are at Air Force Laboratories of Flight Dynamics and General Physics Research. In addition to these other research projects are being undertaken at the Manchester (England), Fitchburg, Massachusetts; Israel Institute of Technology; the Universities of California, Stockholm (Sweden), Denver, Harvard, Indiana, Maryland, Michigan, Minnesota, Ohio, Purdue, Syracuse, Barkley and Dexter Laboratories, and two New York schools - Queens College and Yeshiva Graduate School of Science, and at Texas, Besides these there are research agencies that are run secretly by the government which are neither registered publicly nor advertised without necessary permission. In addition to these, private agencies have shown great interest in this area of research and some of the giants of the industry like Boeing, Bell Aerospace, Douglas and General Electric, Hughes Aircraft, and quite a few others have taken the issue of gravity very seriously and have set up various research projects. Therefore, in other words, the total number of projects undertaken by both government and private agencies are approximately around 65 to 70 projects, so this means that there are a good number of brains, both scientific and engineering working on the problem of gravity. A second school of thought is of the opinion that what goes up, does not necessarily have to come down. Major Keyhoe who has been observing and writing about Unidentified Flying Objects (UFO's) for the last 15 years, [written in 1967.Vangard] insists that flying saucers are not only real but also interplanetary. According to him, the only sane explanation that could be given for such an astounding fact is that the saucers have complete control over gravity which helps them make amazing maneuvers and that too with lightening speed and unimaginable altitudes. Many of the top- notch authorities such as scientists, researchers and astronomers do agree with Major Keyhoe’s current chapter titled "The Great Flying Saucer Story", but many other physicists dismiss his theory as “fundamentally erroneous”. In the face of this debated issue, Major Keyhoe maintains that, “Not known fields of force' allow saucers to behave peculiarly: To hover motionlessly, turn on a dime, and accelerate at fantastic speeds. And only a crash `G' program on our part can counteract it.” (Maj. Donald E. Keyhoe, 1967) One such fantastic encounter took place right over the North Pacific on a night last February 15th. Taking a group of military people from the U.S into Japan, the Flying Tiger plane seemed about 4 hours out of anchorage. The radar in the cockpit picked up signals of three objects whizzing past at incredible speed. What the captain and his astonished crew saw made their adrenalin rush through their body- They saw three gigantic oval- shaped ships that glowed red in the night sky. One of the passengers on board the aircraft was an Air Force captain who was requested to come forward to testify what he had observed. The National Investigations Committee houses his signed report on the spectacular aerial phenomena. According to the report presented by the captain, the unknown machines had slowed down its speed which was almost the same as the aircraft and flew together in a close formation for about thirty minutes along with the plane. Soon after that, they suddenly swiftly accelerated at approximately 1,200 knots and vanished from sight in a matter of seconds. Since such a maneuver was next to impossible from any ship made on Earth, it became evident that it had been giant Unidentified Flying Objects which possessed an unknown type of propulsion and what made this stance even more believable was that there were no jet exhausts visible. Without a doubt the nagging question arises – what made it possible for the UFO’s? Then, if UFO’s could do it, why not we? The only possible answer to every query of scientists, researchers and engineers is only “ANTIGRAVITY”. Gaining control over gravity by creating artificial gravity fields would help us gain ground in the right direction. Dr. Hermann Oberth, a leading scientist and a highly recognized authority who was the co – designer for the rocket named V2, stated that ordinary propulsion would prove dangerous to the airship as the force would crush the creatures aboard it. In a statement he made, Doctor Oberth said that, “….with an artificial gravity field the force applies simultaneously to the passengers and the spaceship. Even in swift changes of speed and direction, the ship is not strained and the passengers feel nothing." (Dr. Hermann Oberth, 1961) Furthermore, Doctor Oberth gives his candid opinion saying "that energy, inertia and gravitational fields are only aspects of one and the same thing" (Dr. Hermann Oberth, 1961) William P. Lear, Sr. who is not only a multimillionaire inventor, pilot, designer of air and space equipment and also a builder of jet aircrafts is also a noted authority on the subject of gravity. He too was one of the lucky few to have spotted a UFO while flying his executive plane and predicted that in the near future the air vehicles in the U.S would also be using artificial gravity. According to Lear, … "The people on board would probably not feel any more effect," Lear says, "than they do from the tremendous speed of the Earth as it rotates and orbits the sun." Predicting on this subject was G.S Trimble, the vice – president of Glenn Martin who said that by the year 1985 almost all the airliners would be making use of artificial gravity and flying at mind- boggling speeds. Dr. Walter Dornberger, who is presently Bell Aerospace’s President, pictured the speed of future airliners to be around 10,000 mph. Seconding Trimble but with greater force, consultant and pioneer air craft builder of the Air Force Grover Loening stated that, "I firmly believe that before long man will acquire the ability to build an electromagnetic contra- gravity mechanism that works," Anti-Gravity - Myth or Reality? Anti-gravity seems to be that elusive word that is most talked about in the circles of research. While many critics believe that UFO’s belong to the species called Dreamers, whereas others swear that UFO’s are nothing less than the truth. Based on the many eyewitness identification samples given above, one cannot but believe in its authenticity. Therefore the question arises if this myth or reality is conceivable or not. Debilitating on this burning issue, Jesse V. Honeycutt, a top official of Bethlehem Steel stated that if Loening reported rightly we could expect some spectacular results in the very near future. He made a statement saying that, "Serious research is being concentrated on in an attempt to solve the mystery of gravity and bring about a control of its power.... It would bring about a greater revolution in power, transportation and many other fields than the discovery of atomic power," .... It would bring about a greater revolution in power, transportation and many other fields than the discovery of atomic power," (Jesse V. Honeycutt, 1967) The primary and the only possible explanation that could be presented for the breathtaking performance of the UFO’s is anti-gravity. Therefore, research centers all over the world – both governmental and private are beating their heads against the wall to find a seedy solution to this perennial problem of conquering gravity and creating spacecrafts that would move like the elusive UFO. Since the stakes are extremely high, it is not possible to leave any stone unturned. The Technical Intelligence of the Air Force are going all out to comb the area thoroughly for any leads that have been overlooked. Hundreds of verified reports on the UFO are being thoroughly checked to find out about the operating of these strange vehicles. Casting a little more light on the working of these objects and eyewitness says how he observed a rounded metallic spacecraft that had a diameter of approximately 125 feet, landed in a field near Staunton, Virginia, just 4 days before Christmas. On closer examination by two Du Pont scientists using Geiger counters, it was found to be extremely hot from radioactivity. A second incident took place in Puerto Rico on December 26th 1964. Two large discs were picked up by the Ramey Air Force Base radar at dusk. When an attempt was made by the A4D jets to pursue them, the discs made instant right – angle turns and vanished into the night sky at an alarming speed over the Atlantic. Captain Yoshiaki Inada was yet another eyewitness to the UFO when he flew Toa Airlines Convair on a domestic Japanese flight, on March 21st in 1965. He reported that he had been chased by a “"mysterious, elliptical luminous object." And after blanking out his radio, the object "violently interfered" with his automatic direction finding equipment. In another puzzling incident that occurred on July 1st, 1954, the pilot of an AF F- 94 relates how the cockpit of his plane filled with unbearable heat when he tried to close in on the UFO quite near Walesville in New York. The peculiar phenomena of strange electrical interference, extreme heat and high radiation were thought to be the side effects of the devices of gravity control. Though in many areas gravity could be much of a problem yet we seldom give a thought about the builders of rockets and Aircraft who need to construct heavy engines and massive weights of fuel in order to offset gravity. Gravity therefore is an indispensable part of our lives and we cannot do without it. Just imagine, if we did not have gravity on the Earth we would all be flying around in space eternally! The very thought of this is not only boring but also frightening. Gravity helps us in more than a million ways in our lives. Firstly and most importantly it keeps our feet close to the ground and secondly though it does cost us in billions we need gravity for the construction of our buildings, bridges, for growing our food, for transport and communication and yes, for flying our aircrafts! Looking at gravity from a different point of view such as gaining control over it, could help us to bring to a close many problems that face us in everyday life. Though some skeptics look at conquering gravity as a far away dream, there are enthusiasts who are sure that we are on the threshold of a major breakthrough. When this happens, our space programs would take a giant leap ahead in matching the speeds and maneuvers of the UFO’s. As Alexander de Seversky rightly stated that, "with abundant energy available, we will move in space with constant acceleration or deceleration. Accelerating halfway to our goal and decelerating the rest of the way at one G or 32.2 feet per second, the moon will be reached in three and a half hours, Venus in 36 hours, Mars in two days, Jupiter in six." (Alexander de Seversky, 1967) According to many scientists conquering gravity would enable us to explore various star or planet systems and the possibility of different military operations becomes a rather hair –raising issue. One such documented case was that of Navy scientists who had tracked a UFO whizzing at a speed of 18,000mph at the White Sands Proving Ground. This sort of unimaginable speeds could replace bombers in the place of missiles. Another phenomenal change due to gravity control would be in the area of air travel. Several researchers have remarked that when flying we would not need seat belts because even at such incredible speeds, though one would feel weightless, one would not experience any motion. In addition to this, the aircraft could make arches and circles, but yet one would not feel any bumps or roughness. The aircraft would be able to skim over roof tops and descend vertically and land and in case traffic is quite heavy, it would be able to hover in mid- air till the traffic eases and then make a landing. Inspite of all odds, one would be much safer. In trying to solve the much debated riddle of gravity, project scientists keep on trying out different approaches. In lieu of this, a team from the University of Detroit built a specially wired rotor that weighed around 4,000 pounds and spun at 100,000rpm. Making use of this unique device scientists are trying their best to find a possible key leading to G control through testing the relevant gravitational radiation theories. A special network of gravity stations are set up around the world making it convenient for Air Force teams to travel between the poles and around the equator to measure the Earth’s gravitational pull. Based on all these findings, two very clear facts have been established – Gravity and electro- magnetic fields have a definite connection. The G field of the Earth is significantly weaker when compared to the gravitational pull between the sun and the planets. According to Igor Sikorsky, if it were not for gravity, the Earth would need an 8,000 mile thick steel cable to keep the Earth from moving out of its orbit. Efforts are also being made to capture one of the UFO’s s that it would give us a shortcut to success in our research on gravity control saving us precious time and money in our scientific endeavors. There have been numerous UFO chases but just as they near the spot, the UFO spins rapidly out of sight. Therefore, the search is still on and would continue till the flag of success is raised. “For this is one race we dare not lose!” Non-Conventional Propulsion Experience is a good teacher they say, but yet Rome was not built in a day! Especially in the world of scientific research, the going is hard and tedious, but good results are always anticipated. The same was the case for inventions such as the radar, nuclear power plants, inter -continental missiles, high speed trains (TGV), computers, television, transistor, antibiotics, the genome, organ transplants and many others. There is no doubt that the last few centuries have been a witness to a technological revolution which has essentially made life much easier for us – in fact I should say quite comfortable. But yet there are many areas that seem to be a mystery or should I say out of a book of fiction. It is these areas that have made the ingenuity of man dance according to its own tune for the past thirty odd years. This includes inter planetary space travel, man’s trip to the moon, and the use of robotics. Yet even currently we make use of the same highly expensive techniques that do not permit repeated accomplishments because of this. The invincible enemy that seems to block our progress is “weight”. Three centuries after the phenomenon of Newton’s manifestation of gravitation, our goal seems far out of reach but yet getting closer each day. As referred to earlier, there exists an electromagnetic factor of correlation between the gravitational mass and the inertial mass, which in certain specific electromagnetic settings can be either reduced, nullified, inverted and intensified by the creation of electromagnetic fields. These theoretical consequences are based on Newton’s new law for inertia (2nd law of motion) and the deduction involving differential equation for entropy (2nd law of Thermodynamics) in addition to the unification resulting from the gravitational and electromagnetic interactions. In trying to arrive at a reasonable solution, NASA had come forward to support the “Breakthrough Propulsion Physics Project” which took place between the years 1996 through 2002. The project consisted of three great challenges- To discover propulsion that did not need a propellant. To discover new methods to procure hyper- fast travel. To discover significant breakthrough methods that would power spacecraft. Since the above challenges seem quite far fetched, emphasis has been laid on selecting research methods that are affordable and incremental. About 1/3 of the sixteen incremental projects were not found to be viable. By Propulsion Breakthrough we mean the type of breakthrough which could make interstellar exploration reasonably practical. This kind of breakthrough speaks of faster – than – light travel and spaces drives without propellant. Research and investigations are being carried out on a regular basis but no such breakthroughs are imminently visible. One such project was conducted by NASA during the period 1996 – 2002 to find a suitable breakthrough in spaceflight making use of physics. The assessments of three of its facets reported the following – (1) predicting benefits, (2) selecting research, and (3) recent technical progress. It is rather challenging to predict its benefits since they are still in the conceptual stage. However, energy was considered as the basis of comparison. Making an assessment of a particular research is both dicey and challenging because though the taste of success is profound and sweet, yet most times the goals are out of reach since they may go beyond our knowledge of physics. In order to mitigate or lay to rest such challenges, a process of selection I considered, such as – 1. Research tasks are restricted to addressing only the immediate unknowns. 2. The outcomes or implications are not as important as the reliability of assertions. 3. Credibility is given more credence than feasibility by those who review them. The results of the recent findings show that out of the 14 tasks that were reviewed, 6 of them arrived at null and void conclusions, while four of them remained unresolved. The last four had significant opportunities for further sequels. The quantum vacuum, inertial frames and properties regarding space were the themes that dominated the research in the sequels. So the search is on and will never stop till it is conquered. Practical Applications The application of Newton’s law has given us a fairly conventional understanding of flight in aerospace. It has enabled man to design components that provide propulsive and lifting forces. A lot of advancement in the field had taken place since then in this century, but before this achievement could be reached there had been a lot of fantasizing and speculation. Recent studies have resulted in the emergence of three professional programs which are directed towards discovering brand new ways of propulsion. The first one is the NASA Breakthrough Propulsion Physics program, the second is the BAE SYSTEMS Project Greenglow and the third is the work at ESA. Many of the evolving scientific and technical progress involving competitive advantages of all its products are closely monitored by BAE SYSTEMS. In the specialized field of advanced propulsion, many of these speculations are considered and rightly described as breakthroughs. All the matter that has been published goes under their scanner and they probe deep to find out the truths and falsehoods on the issue. The primary goal of BAE SYSTEMS is to design new and innovative aeronautical systems based on the new physical principles. The strategy followed by this paper is as follows – • To account for previous patents, claims, and investigations and assess their validity. • To conduct scientific experiments involving new phenomena and generate theories. • To propose radically new and innovative ways (engines) of providing aeronautical forces. • To assess whether any of these imaginary engines could possibly improve performance in aerospace. The aim of Project Greenglow is to link new physics with innovative engines and the performance of global transport by using the techniques in the most creative way. According to German physicist Burkhard Heim Oberth, and many other scientists, space ships would be able to reach far greater speeds than those that exist today provided we conquer gravity. The advanced machines that would be invented would help us explore the various star systems more than a century ahead of our current time. Another far fetched application that is being considered is creating a gravity shield when we conquer gravity. This gravity shield would shield us against light, heat and sound waves. Scientists are of the opinion that UFO’s make use of a gravity field which enables them to travel at such supersonic speeds and make twists and turns which are definitely not possible by any machine made today. Conclusion: However, every effort is being made by the governmental and private sectors to find a solution to the mystery of anti-gravity. Many scientists have criticized Einstein’s well known theory of “relativity” saying that it may turn out to be totally fallacious. Even Newton’s law has come in for irrational attacks. Capturing a UFO and finding out the specifics of how it is made and how it travels with such speed has caused a few sleepless nights to many a researcher and scientist. Maybe if they do get one, our problems of gravity would come to a close and who knows, the next thing we know we might be taking a trip to the moon for a picnic! That’s easier said than done! Our scientists and researchers have taken on the challenge discovering new scientific laws that may out date the old ones and one thing is sure the chase s on without a doubt. The achievement in this century was preceded by a whole horde of tantalizing speculation, fanciful fantasies including many brave and practical attempts of how to conquer gravity and thereby usher in a century of innovative manned flight. We are therefore on the very threshold of accomplishing our long awaited aeronautical ambitions thereby realizing our dreams with stars in our eyes. Bibliography Alcubierre Miguel, “The Warp Drive: Hyper-Fast Travel within General Relativity”, Class. Quantum Grav. Classical Field Theory http://www.en.wikipedia.org/wiki/Classical_field_theory De Aquino, F. (1992) Gravitational-Electromagnetic Field Theory, V. Press, N.Y, p 27. Donoghue, J.F, Holstein, B.R (1987) European J. of Physics, 8,105. Published in Electric Spacecraft Journal, issue 27,Dec.,1998 , pp.6-13. http://www.arxiv.org/html/physics/9904018v1 Hulse Russel A., “The Discovery of the Binary Pulsar”, Reviews of Modern Physics, 66, No. 3, July 1994, pp. 699-710. Maj. Donald E. Keyhoe, 1967, Saucers Secret: Antigravity 1967 Issue of Flying Saucer. Submitted by: Ronald Barker Vangard Sciences Marc G. Mills, NASA, John H. Glenn Research Center at Lewis Field, Cleveland, Ohio, USA http://www.annalsonline.org/cgi/content/abstract/1065/1/441 Shervgi Shahverdiyev, Proceedings of the workshop in “Fizika” N12, 2004. arXiv:physics/0507034v1 [physics.gen-ph] p. 1 – 5. Shervgi Shahverdiyev, On Special Cases of General Geometry: geometries with changing length of vectors. 2006. Taylor Joseph H., Jr, “Binary pulsar and relativistic gravity”, Reviews of Modern Physics, 66, No. 3, July 1994, pp. 711-719. Read More