Theory Einstein's Relativity

German physicist Albert Einstein (1879-1955) is a major actor in the history of physics as by the early 20th century, he set new foundations for the explanation of Nature, which succeded to the Newtonian views

Physics Before Einstein

After that the Greeks, mostly, in the Antiquity, had endeavoured to a global explanation of Nature and somehow keeping science intermingled with philosophy in most cases, Aristotelism as mixed to Christian scholasticism, as far as Europe is concerned, became a foundation for the explanation of the natural world during the Middle Ages, with such concepts of innate or essential nature of objects, perfection, or a defiance to experimentation. That representation of Nature was firmly attacked since the Renaissance with the iconic figure Italien scientist Galileo Galilei (1564–1642). He fathered 'classical mechanics' by mathematically and experimentally studying motion of objects through rolling balls on an inclined plane and with the help too of the new solar system concept by Polish astronomer Nicolaus Copernicus or observational data collected by Danish Kepler. The development of the scientific revolution thereafter, during the Modern Times eventually brought Newton's physics. A Englishman, he theorized like a whole forces, momentum, and gravity, with predictions possible. All such a move already had physicists to theorize basic concepts. The concept of frame of reference is one of those, the frame, set of data, and with a observer by which the position, momentum, etc. of a given object of study are defined. The reflexion even reached to more, like a inertial frame is a steady one, in which a object appear at rest or in a uniform motion depending on whether or not some identifiable forces act upon, and a non-inertial, moving frame is a frame moving relative to a inertial frame, where forces acting upon the object results from that motion only. As soon as by those times, they also began to think about the relativity between frames of reference, as any relation between two reference frames, for example, with a relative velocity between them may be defined through a series of maths formulas known as Galilean transformation where some forces are constant, like the acceleration or force and some not, like the velocity. Galileo Galilei had also well understood that any science stance necessarily is interspersed with philosophical -religious that is- implications. He had seen, for example, that some celestial motions came in contradiction to the yet accepted explanations of Nature by scholasticism. That was to give since any science research a philosophical tone and, in the worst of cases, a anti-Christian one. That came to be surpassed by French philosopher René Descartes or Newton whose intended move was to to elaborate a global explanation of Nature to replace the scholastic Aristotelician tradition where quantitative was to be strongly mixed into qualitative. Despite a attempt by German philosopher Leibniz to maintain a presence of methaphysics in science (as he also stressed the used of infinitesimal calculus), scientists by the 18th century all came to accept the Newtonian physics like forgoing any ontological consideration in the domain of motion hence of science. Classical mechanics thus had become the rationale by which Nature was explained and used as that scientific revolution of the Modern Times further came in accordance with political changes which occurred in Europe at the time, mostly the development of miscellaneous political liberalisms and industrial revolutions. That scientific move kept into the 19th century with some new domains of investigation, with theories, added as complicated concepts based upon fluids maintained the idea among scientists of a global unity of how Nature works. By the second halve of the century two domains however came to emerge like intractable difficulties in relation with Newtonian physics. Some were related to electromagnetism which had been theorized, with light part of it, by Maxwell in the 1870's. According to Maxwell's equations indeed, the speed of light in a vacuum had become a universal constant, dependent only on the electrical permittivity and magnetic permeability of free space which violated the 'Galilean invariance.' He tried to reconcile both theories by assuming the existence of a 'ether", some substance permeating space and allowing light to propagate. Some difficulties were pertaining, as far as they were concerned, to thermodynamics the theory of which had stated the interchangeability of mechanical, chemical, thermal, and electrical forms of work. Entropy, or the fate of any thermodynamic system however was reluctant like a well-defined quantity with classical mechanics failing to reach to the diminutive scales implied. Despite such shortcuts or contradictions, both thermodynamics and electromagnetism had came in any case to add to Newtonian theory to underpin current experiments in physics. Chemistry, by that same time had eventually reached the view of atoms, those ultimate pieces of matter, like a nucleus and electrons. Things thus could have staid alike with some theoretical inaccuracies and the lack of any renewed general theory of Nature

Einstein's Relativity

Three major actors in physics however by the early 20th century, Planck, Bohr and Einstein, revolutionarized the theory of physics as they proposed totally renewed views of how the classical mechanics was failing to a clear explanation of entropy, light and even atom. By 1900, German physicist Max Planck brought a solution to the question of entropy. He demonstrated how energy, in thermodynamics, is radiated and absorbed in discrete 'quanta' only, or that the energy of waves can be described as consisting of small packets, or that hot objects emit electromagnetic radiation in such discrete quanta. Danish Niels Bohr in 1913 came with a better model still of the atom. Einstein, as far as he is concerned, found the solution to the hurdle of light and the ether in electromagnetism. Special Relativity, or the Special Theory of Relativity was exposed in 1905 by him as he was then a clerk at the Swiss Bureau of Patents, in Bern, Switzerland in the seminal paper 'On the Electrodynamics of Moving Bodies.' In 1887, a optical interferometer had allowed to disprove the existence of a luminiferous aether. American physicist Albert Michelson and chemist Edward Morley in 1887 had conducted an experiment to detect a substance, called the aether, which was postulated as a medium that permitted light waves to travel through space. Einstein had went a step further however as he also had inserted into his dissertation some reflexion about reference frames. Special Relativity specifically thus both is a solution to the question of how light journeys, and also a general theory in physics, the one of measurement in inertial frames of reference. According to Galileo, a principle of relativity states that any uniform motion is relative, and that there is no absolute and well-defined state of rest, or no privileged reference frame, which is equivalent. In terms of theory, Special Relativity states that speed of light is the same for any inertial observer regardless of the state of motion of the source. That opposed to the concept of frames of reference according to Galileo, with a principle of relativity stating that any uniform motion is relative, and that there is no absolute and well-defined state of rest, or no privileged reference frame, which is equivalent. The notion that light traveling in a vacuum sets a cosmic speed limit that cannot be exceeded by any matter or information is part of what is called the 'Lorentz invariance.' In terms of electrodynamics specifically and the question of how light moves, Einstein states that the speed of light is a constant in all inertial reference frames, and that electromagnetic laws should remain valid independent of reference frame—assertions. That, thus, rendered the ether “superfluous” to the question as that equaled replacing classical kinematics with a new theory of it that is compatible with classical electromagnetism. In another paper published the same year, Einstein also asserted that electromagnetic radiation, or light is transmitted in discrete quantities or 'quanta' which had just been defined by Planck. For Einstein, light also could exist in discrete particle-like quantities. Einstein demonstrated in his paper that the photoelectric effect is that when a light beam hitting a metal plate liberates electrons it does only on the basis that light acts through small packets of energy, called photons. He thus had also found that a wave like light could be described like a particle! Later in a letter however, Albert Einstein admitted that even after contemplating the quantum nature of light for 50 years, he still could not understand it, writing that 'Nowadays any fool thinks he knows the answer but he deceives himself.'

What had begun like endeavours to push thermodynamics and electromagnetism further eventually proved a scientific revolution which transformed the well established Newtonian views of Nature! The gradual acceptance of all those new views by Planck, Bohr and Einstein finally come to a full-scale effort to reestablish physics on new fundamental principles. Einstein's theoretical advance represents a new universal formal principle to establish a exact validity of any theory about Nature. His views expanded further into the General Relativity in 1916, with General Relativity or the General Theory of Relativity the geometric theory of gravitation or a generalization of Special Relativy incorporating Newton's gravity, or a relativistic theory of gravity and presented to the Prussian Academy of Science like the equations that the geometry of space and time is influenced by any matter present. As most of such concepts first were at the basis of applied physics by the years leading to Word War II like electronics or the atomic weapons, or to a renewed vision of the Universe with space-time or Hubble's expanding galaxies in the 1920's and 1930's, they eventually culminated into the Big Bang theory and the Standard Model of Physics which came to be completed in the 1960's and 1970's respectively. The one was the new, accepted theory of the Universe or physical world for large scales, and the other, the one for the diminutive world of particles. Then again, on a other hand, politics had interfered with science as England, one of the major actor of the Industrial Revolution had now been challenged by other industrial concepts and models as Relativity or the quanta revolution mostly linked to the American model of economics and society

The Special and General Relativity Detailed

Both the theories of Einstein has mostly to be considered under their most theoretical aspect of views which dramatically cut with classical -or Newtonian or Galilean- physics through the theory of the frame of reference. The Special Theory of Relativity came to be termed 'special' as the principle of relativity was applied to inertial reference frames only, or frames of reference in uniform relative motion with respect to each other. The Theory of General Relativity extends the principle in the more general case of any frame so as to handle general coordinate transformations, and to include the effects of gravity. Noneuclidean geometry of Einstein General Relativity brings to that gravity is no other than the curvature of spacetime. Special Relativity is restricted to flat spacetime as curvature is neglectable on small scales. The Lorentz Invariance, core to Einstein's special Relativity is the concept according to which the laws of physics are the same throughout the Universe

Main advance with Special Relativity resides into a renewed view of Galilean relativity, with 'the laws by which the states of physical systems undergo change are not affected, whether these changes of state be referred to the one or the other of two systems in uniform translatory motion relative to each other.' And in the assertion that light 'is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body.' That indeed was a far cry as those two fundamental propositions were said extant regardless of the exact validity of the known laws of electromagnetism at the time. Special Relativity eventually relied upon Galilean transformation as far as one or more reference frames were concerned, as later improved by French Henri Poincaré and German Lorentz as laws of physics are invariant with respect to such transition from one inertial system to another. Transformations between inertial frames are either Euclidean, Galilean, or Lorentzian as, in the Lorentzian case, one can then obtain relativistic interval conservation and a certain finite limiting speed, which mostly is the speed of light. The Lorentz invariance principle states that the laws of physics are independent of the speed and orientation of the experimenter’s frame of reference, and serves as the mathematical foundation for Albert Einstein’s special theory of relativity. The principle of relativity, generally, stating there is no preferred inertial reference frame was Galileo invention, which was then included in Newtonian physics. Evolution of electromagnetism and reflexion about light like a wave had come to the concept of ether, or a absolute reference frame, or state of rest. Einstein thus reinvigorated Galileo principle under a new form that no any reference frame may be considered with pecular characteristics and each reference frame moving with uniform motion will observe the same laws of physics. In particular, the speed of light in a vacuum is always measured to be c, even when measured by multiple systems that are moving at different, but constant velocities (Special relativity has c is not just the velocity of the propagation of electromagnetic radiation or light but rather a fundamental feature of the way space and time are unified as spacetime). Also derived from his Special Relativity, Einstein came to the equivalence of mass and energy, with the famed formula E = Mc2. Energy and momentum are separated in classical physics as Einstein considered energy like the time component. A object at rest is characterized through a four-vector description, like E (which is also t), 0, 0, 0. In a given, x, direction, with a velocity v, which amounts to a Lorentz transformation of frames, four vectors thus become like E, Ev/c2, 0, 0 with momentum equal to energy multiplied by velocity divided by c2. As Newtonian physics holds at some, slow velocities, the conservation law for energy and momentum remains true as mass keeps the ratio of the momentum to the velocity, or E/c2. More generally, Einstein had seen that, generally, emission of light was the result of any work achieved on a given object with mass. This also translates into that, in the world of particles, any decrease of mass must be accompanied by a increase of velocity and conversely that a particle taking in kinetic energy has its mass increased. Specific consequences of the theory appear with the Lorentz transformation of reference frame reaching velocities comparable to the speed of light. Such examples are the famed twin paradox (time lapse albeit not invariant from one observer to another, is dependent on the relative speeds of the observers' reference frames with one twin having voyaged in space at light speed having aged less), length contraction with a objet traveling near speed light to shorten or the upper limit of speed light leading to that speeds do not simply add. Also as a object closing the speed of light its mass appears to increase, making it more and more difficult to accelerate it from within the observer's frame of reference. In Special Relativity, 'reference frame' specifically means a observational perspective in space at rest or in uniform motion, from which a position can be measured along 3 spatial axes. In addition, a reference frame has the ability to determine measurements of the time of events using any reference device with uniform periodicity or 'clock.' Special Relativity yields thus a maze of considerations in physics, like the spatial location of the same for all observers as only our perspective changes and not the underlying reality, or the modification of time or momentum perception. Special Relativity also brought that spatial and temporal separations are interconvertible. In a moving frame, lengths and times are different from their counterparts in a stationary reference frame as some properties remain intrinsic to a object observed. Such implications mostly are at work and taken in consideration in the physics of particles. When Einsteinian physics came to be widely accepted, Newtonian mechanics became considered as a special relativity of slow moving bodies. Theory of Special Relativy has been proved through varied experiments as particle accelerator would simply not work if they were not engineered according to relativistic principles. At the difference of General Relativity, Special Relativity can be merged with quantum physics to a unified theory of quantum gravitation, or the Dirac equation with application in the spin of particles or antimatter. Such a theory also is of use to quantized fields, where particles can be created and destroyed, in quantum electrodynamics or quantum chromodynamics, or also the fine structure constant which eventually brought to the Standard Model which indeed is the 'standard theory of relativistic quantized fields, unifying the principles of special relativity and of quantum physics.' Einstein's Special Relativity also theoretically allows for time travel into the future or past as time between two events is slower for objects which are moving faster. Wormholes or 'cosmic strings' which are part of speculations of travel into the past, still have to be found

General Relativity or the General Theory of Relativity is a geometric theory of gravitation and the current description of gravitation in physics. After a eight-year search Einstein succeded into elaborating the so-called Einstein field equations in 1916, which are showing how the geometry of space and time is not of the Euclidian sort but influenced instead by whatever matter and radiation is present. Gravity now came to be defined like geometric property of space and time, or spacetime and specially its curvature as determined by the four-vector (mass, energy, momentum, etc.) of whatever matter and radiation are present. Universality of free fall may be seen like it means equivalence between gravity and inertial force going with, for example, a acceleration move. Einstein made of the equivalence principle gravity-acceleration the basis to his General Relativity. The equivalence on Earth was measured true to the 13th, then 14th decimal. Theoretically, General Relativity started like a reflexion about free fall motion as the equations of 1916 are the mathematic, relativistic solution to that. In the standard reference frames of Newtonian physics, objects in free motion move along straight lines at constant speed. Such that inertial motion can conversely be used to define the geometry of space, as well as a time coordinate constituting the frame of that motion, except when gravity comes in play. Universality of free fall indeed, or the 'weak equivalence principle' makes that there is no observable distinction between inertial motion and motion under the influence of the gravitational force. If considered a new class of inertial motion however -free fall under the influence of gravity- that motion also defines geometrical space and time data, Einstein reasoned. With Special Relativity mostly suitable in the absence of gravity, bringing gravity into play in the case of free fall, the Special Relativity concept that there is no global inertial frames can be extended and take the form of approximate inertial frames moving alongside the free falling body. Einstein proved that the Lorentz transformations in free fall coincide with that of the reference frames for Special Relativity and that the motion and speed of light is the same. That the laws of Special Relativity hold good for free falling reference frames is known as the 'Einstein equivalence principle.' As in Special Relativity mass is inserted into with energy or momentum, it brings to the famed idea of the curvature of spacetime as the straight time-like lines that define a usual gravity-free inertial frame are deformed by such a interaction. In the case of a free fall inertial frame, that bring to lines that are curved relative to each other or to a curved space and time, or spacetime. That equals to a relation between the geometry of that new, free falling, four-dimensional type of reference frame, or space and time, and the mass-energy-momentum, etc. of any object contained in there. What in classical mechanics results from the Newtonian force of gravity is now the result of inertial motion within a curved geometry of spacetime. The gravitational force is not a external force deflecting objets' path anymore but the changes in the properties of space and time caused by the characteristics of the object self and which modify that path. General Relativity thus does not contain any invariant geometric background structures, in accordance with Special Relativity that the laws of physics are the same for all observers. For weak gravitational fields and slow speed Newton's law of gravitation keeps valid. That is what Einstein field equations mathematically demonstrated. General Relativity mostly is maths, or that set of equations which, when solved or detailed, come to hint, prove or describe some specific physical features or objects of the Universe. General Relativity has important astrophysical implications like black holes, gravitational lensing, gravitational waves, or more generally the basis for the most widely accepted cosmological model of our Universe as Einstein himself and its first commentators soon turned General Relativity to cosmology. Astrophysicist Karl Schwarzschild found the first exact solution to Einstein equations, the so-called Schwarzschild metric, laying ground for the description of what was to be known under the name of black holes. He did so while serving as an artillery officer with the German army on the Russian front during WWI. The Reissner-Nordström solution generalized Schwarzschild's solution to electrically charged objects. Or Einstein in 1917 assumed a static Universe through the cosmological constant added to his field equations as Hubble, then Friedman or Lemaître, in the 1920's described a expanding Universe or the earliest version of the Big Bang, eventually termed into the Friedmann-Lemaître-Robertson-Walker (FLRW)solutions. Experiments swiftly proved also the accuracy of the extended theory, with the anomalous perihelion advance of Mercury consistent (by 1859, French astronomer Urbain Le Verrier had pointed out that Mercury was precessing slightly more than purely Newtonian gravity predicted. Miscellaneous explanations, of which a inner planet called Vulcan, could not withstand scrutiny) and the 1919 British astronomer Eddington expedition observing the predicted deflection of starlight by the Sun during a total solar eclipse on the island of Principe. On a other hand, as far as gravitational waves are concerned, Einstein submitted a paper about the non-existence of those in 1936 to a science review as the latter submitted it to a peer review. As he had not been accustomed to such a procedure in Germany, Einstein withdrew his paper but he however retained a flaw pointed out by the referee and titled his work 'On Gravitational Waves,' which, that time, came to the opposite conclusion that gravitational waves were possible

->The Gravitational Waves Officially Discovered!
The U.S. National Science Foundation (NSF) has announced by early November 2016 the detection of gravitational waves by the Laser Interferometer Gravitational-Wave Observatory (LIGO), a pair of ground-based observatories in Hanford, Washington, and Livingston, Louisiana, issued by a merger between two black holes 1.3 billion light-years ago. That constitutes a major discovery in astronomy! Scientists had been attempting to detect gravitational waves for 50 years. Einstein pictured these waves as ripples in the fabric of space-time produced by massive, accelerating bodies, such as black holes orbiting each other, or supernovas or galaxies merging. Like for the anti-gravitational force which accelerated the Universe's expansion since 7 billion years after the Big Bang, Einstein first had negated the existence of gravitational waves in a paper by 1936 but he took in account what the reader in charge of reviewing had posited and he supported the theory. Scientists are interested in observing and characterizing these waves to learn more about the sources producing them and about gravity itself. Many scientists herald that, as until now, our knowledge of the Universe came from light in all its wavelengths -of which the visible- the study of gravitational waves opens a new window and key information complementing the previous. The discovery of gravitational waves paradoxically is comforting, on the one hand, Einstein's theory of Relativity as, on the other hand, gravitational waves, generally, could suggest that the Universe did indeed expand many times faster than the speed of light in the first few instants after the Big Bang, giving a helping hand to the inflation theory. Scientists had already discovered primordial B-modes by late 2014 as a fraction of the Cosmic Microwave Background (CMB), that light which emerged about 400,000 years after the Big Bang, is a light polarized and B-mode polarization, which comes with gravitational waves might be imprinted with clues about how our Universe was born as B-mode polarization is also of importance for a better mapping how matter, both normal and dark, is distributed throughout the Universe. European ESA's LISA mission, launched late 2015, possessing a level of stability never attained, is a mission to demonstrate technologies that could be used for a future space-based gravitational wave observatory about 2034. Located in space, that observatory will allow for the detection of lower-frequency gravitational waves. More recent studies after that, which might have discovered 'echoes' about the merging black holes, are bringing a question that General Relativity theory could break down in extreme scenarios, such as at the centre of black holes, like already known, and even at the black hole’s edge. The black hole's event horizon then should be replaced by a firewall, a ring of high-energy particles that would burn any matter that passes through and contradicting General relativity. The studies also hypothethize that a black hole is surrounded by mirrored walls rather than just a conventional event horizon, which matched the echoes observed

General Relativity nevertheless became mainstream theory in physics and astrophysics only in the 1960's and 1970's when the Big Bang model of the Universe came to be widely accepted and that more detailed observation of relativistic celestial objects became possible, or more precise tests in the solar system. Derived or demonstrated through the 1916 equations are that time close to a massive body runs more slowly when compared with farther away, or the gravitational time dilation, path of light is bent in a gravitational field, or gravitational lensing, light take longer to move through a gravitational field than it would in the absence of that field. The overall precession of planetary orbits, orbital decay of a binary system due to gravitational waves, the precession of apsides, frame-dragging effects as objects close to a mass get dragged around. 'Singularities' also are a generic feature of General Relativity, or spacetime boundaries where the path of light and falling particles come to an abrupt end, and geometry becomes ill-defined. Best known application of that feature is the singularity which presided to the start of the Big Bang. As Special Relativity may be united with quantum physics, with the quantum field theory of gravity, no consistent theory of quantum gravity, or the merger with General Relativity currently has been found. Some recent speculative theories are questioning Einstein theories as the latter always passed numerous varied scientific tests those last decades. A side effect of Einstein's Relativity is that the closer you get to the celestial objects which bend their surroundings in terms of space and time, the stronger the pull of gravity and the slower time elapses! Experiments have proved that with clocks taken in orbit, or to Mars, and seen accelerating when getting distant from Earth's gravity, and amounting to some one second every 70 years. That was verified most significantly in 1976 when a hydrogen maser atomic clock on NASA's Gravity Probe A was launched 10,000 km into space, confirming the prediction to within 140 parts in a million. Even GPS satellites have to compensate for the effect. Most recent experiments with accurate atom clocks have shown even a difference of a hundred billionths of a second for each foot of height over 100 years, or, at 2.077 feet of altitude for example, time is elapsing 4 billionth of a second faster per day compared to ground level. Einstein’s theory of General Relativity brings to the idea of a Big Bang, or a 'singularity' to have occurred at a point in the past where it is clear that classical concepts of physics no longer hold, which is the beginnings of the Universe. In turn, such a singularity suggests the necessity of a approach in terms of quantum mechanics to gravity, or quantum gravity. There are two main approaches to quantum gravity, Loop Quantum Gravity and String Theory. Loop Quantum Gravity treats gravity as an independent force from other interactions as String Theory attempts to unify all physical interactions and needs one-dimensional objects called 'strings' which are more fundamental ones than particles. Some other theories exist, like Discrete Quantum Gravity, a technical tool to treat spacetime like a discrete object, or a interpretation of quantum gravity that considers spacetime discrete because of the Plank's length

In a letter to philosopher Eric Gutkind in 1954, Einstein stated some views about religion and the Jewish people, or the so-called 'God's letter,' written in German. check for the complete letter's text. 'The word God is for me nothing but the expression and product of human weaknesses, the Bible a collection of venerable but still rather primitive legends which are nevertheless pretty childish,' he wrote. A Ashkenazi Jew, Einstein added that 'the unadulterated Jewish religion is, like all other religions, an incarnation of primitive superstition,' or that 'the Jewish people to whom [he] gladly belongs, and in whose mentality I feel profoundly anchored, still for me does not have any different kind of dignity from all other peoples. As far as my experience goes, they are in fact no better than other human groups, even if they are protected from the worst excesses by a lack of power. Otherwise I cannot perceive anything 'chosen' about them.' That letter supports the argument that the physicist held complex, agnostic views on religion. He rejected organized faith but often spoke of a spiritual force at work in the Universe. When Nazis took power in Germany in the 1930's, they dismissed Einstein's groundbreaking work, including his Relativity, as 'Jewish Physics'