1.
Alfred North Whitehead
–
Alfred North Whitehead OM FRS was an English mathematician and philosopher. In his early career Whitehead wrote primarily on mathematics, logic and his most notable work in these fields is the three-volume Principia Mathematica, which he wrote with former student Bertrand Russell. Beginning in the late 1910s and early 1920s, Whitehead gradually turned his attention from mathematics to philosophy of science and he developed a comprehensive metaphysical system which radically departed from most of western philosophy. Today Whiteheads philosophical works – particularly Process and Reality – are regarded as the texts of process philosophy. For this reason, one of the most promising applications of Whiteheads thought in recent years has been in the area of ecological civilization, cobb, Jr. Alfred North Whitehead was born in Ramsgate, Kent, England, in 1861. His father, Alfred Whitehead, was a minister and schoolmaster of Chatham House Academy, Whitehead himself recalled both of them as being very successful schoolmasters, but that his grandfather was the more extraordinary man. Whiteheads mother was Maria Sarah Whitehead, formerly Maria Sarah Buckmaster, Whitehead was apparently not particularly close with his mother, as he never mentioned her in any of his writings, and there is evidence that Whiteheads wife, Evelyn, had a low opinion of her. Whitehead was educated at Sherborne School, Dorset, then considered one of the best public schools in the country and his childhood was described as over-protected, but when at school he excelled in sports and mathematics and was head prefect of his class. In 1880, Whitehead began attending Trinity College, Cambridge, and his academic advisor was Edward John Routh. He earned his BA from Trinity in 1884, and graduated as fourth wrangler, in 1890, Whitehead married Evelyn Wade, an Irish woman raised in France, they had a daughter, Jessie Whitehead, and two sons, Thomas North Whitehead and Eric Whitehead. Eric Whitehead died in action serving in the Royal Flying Corps during World War I at the age of 19. In 1910, Whitehead resigned his Senior Lectureship in Mathematics at Trinity, toward the end of his time in England, Whitehead turned his attention to philosophy. Though he had no advanced training in philosophy, his work soon became highly regarded. After publishing The Concept of Nature in 1920, he served as president of the Aristotelian Society from 1922 to 1923, in 1924, Henry Osborn Taylor invited the 63-year-old Whitehead to join the faculty at Harvard University as a professor of philosophy. During his time at Harvard, Whitehead produced his most important philosophical contributions, in 1925, he wrote Science and the Modern World, which was immediately hailed as an alternative to the Cartesian dualism that plagued popular science. A few years later, he published his seminal work Process and Reality, the Whiteheads spent the rest of their lives in the United States. Alfred North retired from Harvard in 1937 and remained in Cambridge, the two volume biography of Whitehead by Victor Lowe is the most definitive presentation of the life of Whitehead. However, many details of Whiteheads life remain obscure because he left no Nachlass, additionally, Whitehead was known for his almost fanatical belief in the right to privacy, and for writing very few personal letters of the kind that would help to gain insight on his life
2.
Gravity
–
Gravity, or gravitation, is a natural phenomenon by which all things with mass are brought toward one another, including planets, stars and galaxies. Since energy and mass are equivalent, all forms of energy, including light, on Earth, gravity gives weight to physical objects and causes the ocean tides. Gravity has a range, although its effects become increasingly weaker on farther objects. The most extreme example of this curvature of spacetime is a hole, from which nothing can escape once past its event horizon. More gravity results in time dilation, where time lapses more slowly at a lower gravitational potential. Gravity is the weakest of the four fundamental interactions of nature, the gravitational attraction is approximately 1038 times weaker than the strong force,1036 times weaker than the electromagnetic force and 1029 times weaker than the weak force. As a consequence, gravity has an influence on the behavior of subatomic particles. On the other hand, gravity is the dominant interaction at the macroscopic scale, for this reason, in part, pursuit of a theory of everything, the merging of the general theory of relativity and quantum mechanics into quantum gravity, has become an area of research. While the modern European thinkers are credited with development of gravitational theory, some of the earliest descriptions came from early mathematician-astronomers, such as Aryabhata, who had identified the force of gravity to explain why objects do not fall out when the Earth rotates. Later, the works of Brahmagupta referred to the presence of force, described it as an attractive force. Modern work on gravitational theory began with the work of Galileo Galilei in the late 16th and this was a major departure from Aristotles belief that heavier objects have a higher gravitational acceleration. Galileo postulated air resistance as the reason that objects with less mass may fall slower in an atmosphere, galileos work set the stage for the formulation of Newtons theory of gravity. In 1687, English mathematician Sir Isaac Newton published Principia, which hypothesizes the inverse-square law of universal gravitation. Newtons theory enjoyed its greatest success when it was used to predict the existence of Neptune based on motions of Uranus that could not be accounted for by the actions of the other planets. Calculations by both John Couch Adams and Urbain Le Verrier predicted the position of the planet. A discrepancy in Mercurys orbit pointed out flaws in Newtons theory, the issue was resolved in 1915 by Albert Einsteins new theory of general relativity, which accounted for the small discrepancy in Mercurys orbit. The simplest way to test the equivalence principle is to drop two objects of different masses or compositions in a vacuum and see whether they hit the ground at the same time. Such experiments demonstrate that all objects fall at the rate when other forces are negligible
3.
General relativity
–
General relativity is the geometric theory of gravitation published by Albert Einstein in 1915 and the current description of gravitation in modern physics. General relativity generalizes special relativity and Newtons law of gravitation, providing a unified description of gravity as a geometric property of space and time. In particular, the curvature of spacetime is directly related to the energy and momentum of whatever matter, the relation is specified by the Einstein field equations, a system of partial differential equations. Examples of such differences include gravitational time dilation, gravitational lensing, the redshift of light. The predictions of relativity have been confirmed in all observations. Although general relativity is not the only theory of gravity. Einsteins theory has important astrophysical implications, for example, it implies the existence of black holes—regions of space in which space and time are distorted in such a way that nothing, not even light, can escape—as an end-state for massive stars. The bending of light by gravity can lead to the phenomenon of gravitational lensing, General relativity also predicts the existence of gravitational waves, which have since been observed directly by physics collaboration LIGO. In addition, general relativity is the basis of current cosmological models of an expanding universe. Soon after publishing the special theory of relativity in 1905, Einstein started thinking about how to incorporate gravity into his new relativistic framework. In 1907, beginning with a thought experiment involving an observer in free fall. After numerous detours and false starts, his work culminated in the presentation to the Prussian Academy of Science in November 1915 of what are now known as the Einstein field equations. These equations specify how the geometry of space and time is influenced by whatever matter and radiation are present, the Einstein field equations are nonlinear and very difficult to solve. Einstein used approximation methods in working out initial predictions of the theory, but as early as 1916, the astrophysicist Karl Schwarzschild found the first non-trivial exact solution to the Einstein field equations, the Schwarzschild metric. This solution laid the groundwork for the description of the stages of gravitational collapse. In 1917, Einstein applied his theory to the universe as a whole, in line with contemporary thinking, he assumed a static universe, adding a new parameter to his original field equations—the cosmological constant—to match that observational presumption. By 1929, however, the work of Hubble and others had shown that our universe is expanding and this is readily described by the expanding cosmological solutions found by Friedmann in 1922, which do not require a cosmological constant. Lemaître used these solutions to formulate the earliest version of the Big Bang models, in which our universe has evolved from an extremely hot, Einstein later declared the cosmological constant the biggest blunder of his life
4.
Aristotle
–
Aristotle was an ancient Greek philosopher and scientist born in the city of Stagira, Chalkidice, on the northern periphery of Classical Greece. His father, Nicomachus, died when Aristotle was a child, at seventeen or eighteen years of age, he joined Platos Academy in Athens and remained there until the age of thirty-seven. Shortly after Plato died, Aristotle left Athens and, at the request of Philip II of Macedon, teaching Alexander the Great gave Aristotle many opportunities and an abundance of supplies. He established a library in the Lyceum which aided in the production of many of his hundreds of books and he believed all peoples concepts and all of their knowledge was ultimately based on perception. Aristotles views on natural sciences represent the groundwork underlying many of his works, Aristotles views on physical science profoundly shaped medieval scholarship. Their influence extended from Late Antiquity and the Early Middle Ages into the Renaissance, some of Aristotles zoological observations, such as on the hectocotyl arm of the octopus, were not confirmed or refuted until the 19th century. His works contain the earliest known study of logic, which was incorporated in the late 19th century into modern formal logic. Aristotle was well known among medieval Muslim intellectuals and revered as The First Teacher and his ethics, though always influential, gained renewed interest with the modern advent of virtue ethics. All aspects of Aristotles philosophy continue to be the object of academic study today. Though Aristotle wrote many elegant treatises and dialogues – Cicero described his style as a river of gold – it is thought that only around a third of his original output has survived. Aristotle, whose means the best purpose, was born in 384 BC in Stagira, Chalcidice. His father Nicomachus was the physician to King Amyntas of Macedon. Aristotle was orphaned at a young age, although there is little information on Aristotles childhood, he probably spent some time within the Macedonian palace, making his first connections with the Macedonian monarchy. At the age of seventeen or eighteen, Aristotle moved to Athens to continue his education at Platos Academy and he remained there for nearly twenty years before leaving Athens in 348/47 BC. Aristotle then accompanied Xenocrates to the court of his friend Hermias of Atarneus in Asia Minor, there, he traveled with Theophrastus to the island of Lesbos, where together they researched the botany and zoology of the island. Aristotle married Pythias, either Hermiass adoptive daughter or niece and she bore him a daughter, whom they also named Pythias. Soon after Hermias death, Aristotle was invited by Philip II of Macedon to become the tutor to his son Alexander in 343 BC, Aristotle was appointed as the head of the royal academy of Macedon. During that time he gave not only to Alexander
5.
Gottfried Wilhelm Leibniz
–
Leibnizs notation has been widely used ever since it was published. It was only in the 20th century that his Law of Continuity and he became one of the most prolific inventors in the field of mechanical calculators. He also refined the number system, which is the foundation of virtually all digital computers. Leibniz, along with René Descartes and Baruch Spinoza, was one of the three great 17th-century advocates of rationalism and he wrote works on philosophy, politics, law, ethics, theology, history, and philology. Leibnizs contributions to this vast array of subjects were scattered in various learned journals, in tens of thousands of letters and he wrote in several languages, but primarily in Latin, French, and German. There is no complete gathering of the writings of Leibniz in English, Gottfried Leibniz was born on July 1,1646, toward the end of the Thirty Years War, in Leipzig, Saxony, to Friedrich Leibniz and Catharina Schmuck. Friedrich noted in his journal,21. Juny am Sontag 1646 Ist mein Sohn Gottfried Wilhelm, post sextam vespertinam 1/4 uff 7 uhr abents zur welt gebohren, in English, On Sunday 21 June 1646, my son Gottfried Wilhelm is born into the world a quarter after six in the evening, in Aquarius. Leibniz was baptized on July 3 of that year at St. Nicholas Church, Leipzig and his father died when he was six and a half years old, and from that point on he was raised by his mother. Her teachings influenced Leibnizs philosophical thoughts in his later life, Leibnizs father had been a Professor of Moral Philosophy at the University of Leipzig, and the boy later inherited his fathers personal library. He was given access to it from the age of seven. Access to his fathers library, largely written in Latin, also led to his proficiency in the Latin language and he also composed 300 hexameters of Latin verse, in a single morning, for a special event at school at the age of 13. In April 1661 he enrolled in his fathers former university at age 15 and he defended his Disputatio Metaphysica de Principio Individui, which addressed the principle of individuation, on June 9,1663. Leibniz earned his masters degree in Philosophy on February 7,1664, after one year of legal studies, he was awarded his bachelors degree in Law on September 28,1665. His dissertation was titled De conditionibus, in early 1666, at age 19, Leibniz wrote his first book, De Arte Combinatoria, the first part of which was also his habilitation thesis in Philosophy, which he defended in March 1666. His next goal was to earn his license and Doctorate in Law, in 1666, the University of Leipzig turned down Leibnizs doctoral application and refused to grant him a Doctorate in Law, most likely due to his relative youth. Leibniz then enrolled in the University of Altdorf and quickly submitted a thesis, the title of his thesis was Disputatio Inauguralis de Casibus Perplexis in Jure. Leibniz earned his license to practice law and his Doctorate in Law in November 1666 and he next declined the offer of an academic appointment at Altdorf, saying that my thoughts were turned in an entirely different direction
6.
Qualia
–
In philosophy and certain models of psychology, qualia are individual instances of subjective, conscious experience. Examples of qualia include the pain of a headache, the taste of wine, as qualitative characters of sensation, qualia stand in contrast to propositional attitudes. Much of the debate over their importance hinges on the definition of the term, There are many definitions of qualia, which have changed over time. One of the simpler, broader definitions is, The what it is character of mental states. There are recognizable qualitative characters of the given, which may be repeated in different experiences, but although such qualia are universals, in the sense of being recognized from one to another experience, they must be distinguished from the properties of objects. Confusion of these two is characteristic of many historical conceptions, as well as of current essence-theories, the quale is directly intuited, given, and is not the subject of any possible error because it is purely subjective. Frank Jackson later defined qualia as. certain features of the bodily sensations especially, but also of certain perceptual experiences, Daniel Dennett identifies four properties that are commonly ascribed to qualia. According to these, qualia are, ineffable, that is, they cannot be communicated, intrinsic, that is, they are non-relational properties, which do not change depending on the experiences relation to other things. Private, that is, all comparisons of qualia are systematically impossible. Directly or immediately apprehensible in consciousness, that is, to experience a quale is to know one experiences a quale, another way of defining qualia is as raw feels. A raw feel is a perception in and of itself, considered entirely in isolation from any effect it might have on behavior, in contrast, a cooked feel is that perception seen as existing in terms of its effects. For example, the perception of the taste of wine is an ineffable, raw feel, a cooked feel is not qualia. While very few ever claim that such an entity, called a zombie, actually exists. Since it is by definition impossible to convey qualia verbally, it is impossible to demonstrate them directly in an argument. Arguments for qualia generally come in the form of thought experiments designed to lead one to the conclusion that qualia exist, although it does not actually mention the word qualia, Thomas Nagels paper What Is it Like to Be a Bat. is often cited in debates over qualia. Nagel argues that consciousness has a subjective character, a what-it-is-like aspect. He states that an organism has conscious mental states if and only if there is something that it is like to be that organism—something it is like for the organism. Nagel also suggests that the aspect of the mind may not ever be sufficiently accounted for by the objective methods of reductionistic science
7.
Galen
–
Aelius Galenus or Claudius Galenus, often Anglicized as Galen and better known as Galen of Pergamon, was a prominent Greek physician, surgeon and philosopher in the Roman Empire. The son of Aelius Nicon, an architect with scholarly interests, Galen received a comprehensive education that prepared him for a successful career as a physician. Galens understanding of anatomy and medicine was influenced by the then-current theory of humorism. His theories dominated and influenced Western medical science for more than 1,300 years, Medical students continued to study Galens writings until well into the 19th century. Galen saw himself as both a physician and a philosopher, as he wrote in his treatise entitled That the Best Physician is Also a Philosopher. Many of his works have been preserved and/or translated from the original Greek, although many were destroyed, although there is some debate over the date of his death, he was no younger than seventy when he died. In medieval Europe, Galens writings on anatomy became the mainstay of the medieval university curriculum. Some of Galens ideas were incorrect, he did not dissect a human body, Galens original Greek texts gained renewed prominence during the early modern period. In the 1530s, Belgian anatomist and physician Andreas Vesalius took on a project to many of Galens Greek texts into Latin. Vesaliuss most famous work, De humani corporis fabrica, was influenced by Galenic writing. Galens name Γαληνός, Galēnos comes from the adjective γαληνός, calm, Galen describes his early life in On the affections of the mind. Galen describes his father as an amiable, just, good. His studies also took in each of the philosophical systems of the time. His father had planned a career for Galen in philosophy or politics and took care to expose him to literary. However, Galen states that in around AD145 his father had a dream in which the god Asclepius appeared and commanded Nicon to send his son to study medicine, there he came under the influence of men like Aeschrion of Pergamon, Stratonicus and Satyrus. Asclepiea functioned as spas or sanitoria to which the sick would come to seek the ministrations of the priesthood, romans frequented the temple at Pergamon in search of medical relief from illness and disease. It was also the haunt of notable people such as Claudius Charax the historian, Aelius Aristides the orator, Polemo the sophist, in 148, when he was 19, his father died, leaving him independently wealthy. In 157, aged 28, he returned to Pergamon as physician to the gladiators of the High Priest of Asia, one of the most influential and wealthy men in Asia
8.
Spacetime
–
In physics, spacetime is any mathematical model that combines space and time into a single interwoven continuum. Until the turn of the 20th century, the assumption had been that the 3D geometry of the universe was distinct from time, Einsteins theory was framed in terms of kinematics, and showed how measurements of space and time varied for observers in different reference frames. His theory was an advance over Lorentzs 1904 theory of electromagnetic phenomena. A key feature of this interpretation is the definition of an interval that combines distance. Although measurements of distance and time between events differ among observers, the interval is independent of the inertial frame of reference in which they are recorded. The resultant spacetime came to be known as Minkowski space, non-relativistic classical mechanics treats time as a universal quantity of measurement which is uniform throughout space and which is separate from space. Classical mechanics assumes that time has a constant rate of passage that is independent of the state of motion of an observer, furthermore, it assumes that space is Euclidean, which is to say, it assumes that space follows the geometry of common sense. General relativity, in addition, provides an explanation of how gravitational fields can slow the passage of time for an object as seen by an observer outside the field. Mathematically, spacetime is a manifold, which is to say, by analogy, at small enough scales, a globe appears flat. An extremely large scale factor, c relates distances measured in space with distances measured in time, waves implied the existence of a medium which waved, but attempts to measure the properties of the hypothetical luminiferous aether implied by these experiments provided contradictory results. For example, the Fizeau experiment of 1851 demonstrated that the speed of light in flowing water was less than the speed of light in air plus the speed of the flowing water, the partial aether-dragging implied by this result was in conflict with measurements of stellar aberration. By 1904, Lorentz had expanded his theory such that he had arrived at equations formally identical with those that Einstein were to derive later, but with a fundamentally different interpretation. As a theory of dynamics, his theory assumed actual physical deformations of the constituents of matter. For example, most physicists believed that Lorentz contraction would be detectable by such experiments as the Trouton–Noble experiment or the Experiments of Rayleigh and Brace. However, these negative results, and in his 1904 theory of the electron. Einstein performed his analyses in terms of kinematics rather than dynamics and it would appear that he did not at first think geometrically about spacetime. It was Einsteins former mathematics professor, Hermann Minkowski, who was to provide an interpretation of special relativity. Einstein was initially dismissive of the interpretation of special relativity
9.
Bertrand Russell
–
Bertrand Arthur William Russell, 3rd Earl Russell, OM, FRS was a British philosopher, logician, mathematician, historian, writer, social critic, political activist and Nobel laureate. At various points in his life he considered himself a liberal, a socialist, and a pacifist and he was born in Monmouthshire into one of the most prominent aristocratic families in the United Kingdom. In the early 20th century, Russell led the British revolt against idealism and he is considered one of the founders of analytic philosophy along with his predecessor Gottlob Frege, colleague G. E. Moore, and protégé Ludwig Wittgenstein. He is widely held to be one of the 20th centurys premier logicians, with A. N. Whitehead he wrote Principia Mathematica, an attempt to create a logical basis for mathematics. His philosophical essay On Denoting has been considered a paradigm of philosophy, Russell mostly was a prominent anti-war activist, he championed anti-imperialism. Occasionally, he advocated preventive nuclear war, before the opportunity provided by the monopoly is gone. He went to prison for his pacifism during World War I, in 1950 Russell was awarded the Nobel Prize in Literature in recognition of his varied and significant writings in which he champions humanitarian ideals and freedom of thought. Bertrand Russell was born on 18 May 1872 at Ravenscroft, Trellech, Monmouthshire and his parents, Viscount and Viscountess Amberley, were radical for their times. Lord Amberley consented to his wifes affair with their childrens tutor, both were early advocates of birth control at a time when this was considered scandalous. Lord Amberley was an atheist and his atheism was evident when he asked the philosopher John Stuart Mill to act as Russells secular godfather, Mill died the year after Russells birth, but his writings had a great effect on Russells life. His paternal grandfather, the Earl Russell, had asked twice by Queen Victoria to form a government. The Russells had been prominent in England for several centuries before this, coming to power, Lady Amberley was the daughter of Lord and Lady Stanley of Alderley. Russell often feared the ridicule of his grandmother, one of the campaigners for education of women. Russell had two siblings, brother Frank, and sister Rachel, in June 1874 Russells mother died of diphtheria, followed shortly by Rachels death. In January 1876, his father died of bronchitis following a period of depression. Frank and Bertrand were placed in the care of their staunchly Victorian paternal grandparents and his grandfather, former Prime Minister Earl Russell, died in 1878, and was remembered by Russell as a kindly old man in a wheelchair. His grandmother, the Countess Russell, was the dominant family figure for the rest of Russells childhood, the countess was from a Scottish Presbyterian family, and successfully petitioned the Court of Chancery to set aside a provision in Amberleys will requiring the children to be raised as agnostics. Her favourite Bible verse, Thou shalt not follow a multitude to do evil, the atmosphere at Pembroke Lodge was one of frequent prayer, emotional repression, and formality, Frank reacted to this with open rebellion, but the young Bertrand learned to hide his feelings
10.
Consciousness
–
Consciousness is the state or quality of awareness, or, of being aware of an external object or something within oneself. Despite the difficulty in definition, many believe that there is a broadly shared underlying intuition about what consciousness is. Western philosophers, since the time of Descartes and Locke, have struggled to comprehend the nature of consciousness, the majority of experimental studies assess consciousness in humans by asking subjects for a verbal report of their experiences. The origin of the concept of consciousness is often attributed to John Lockes Essay Concerning Human Understanding. Locke defined consciousness as the perception of what passes in a mans own mind and his essay influenced the 18th-century view of consciousness, and his definition appeared in Samuel Johnsons celebrated Dictionary. Consciousness is also defined in the 1753 volume of Diderot and dAlemberts Encyclopédie, the earliest English language uses of conscious and consciousness date back, however, to the 1500s. This phrase had the meaning of knowing that one knows. In its earliest uses in the 1500s, the English word conscious retained the meaning of the Latin conscius. For example, Thomas Hobbes in Leviathan wrote, Where two, or more men, know of one and the fact, they are said to be Conscious of it one to another. The Latin phrase conscius sibi, whose meaning was more related to the current concept of consciousness, was rendered in English as conscious to oneself or conscious unto oneself. For example, Archbishop Ussher wrote in 1613 of being so conscious unto myself of my great weakness, Lockes definition from 1690 illustrates that a gradual shift in meaning had taken place. A related word was conscientia, which primarily means moral conscience, in the literal sense, conscientia means knowledge-with, that is, shared knowledge. The word first appears in Latin juridical texts by such as Cicero. Here, conscientia is the knowledge that a witness has of the deed of someone else, rené Descartes is generally taken to be the first philosopher to use conscientia in a way that does not fit this traditional meaning. Descartes used conscientia the way modern speakers would use conscience, in Search after Truth he says conscience or internal testimony. The dictionary meaning of the word consciousness extends through several centuries, B. inward awareness of an external object, state, or fact. The philosophy of mind has given rise to many stances regarding consciousness, something within ones mind is introspectively conscious just in case one introspects it. Introspection is often thought to deliver ones primary knowledge of ones mental life, an experience or other mental entity is phenomenally conscious just in case there is something it is like for one to have it
11.
Special relativity
–
In physics, special relativity is the generally accepted and experimentally well-confirmed physical theory regarding the relationship between space and time. In Albert Einsteins original pedagogical treatment, it is based on two postulates, The laws of physics are invariant in all inertial systems, the speed of light in a vacuum is the same for all observers, regardless of the motion of the light source. It was originally proposed in 1905 by Albert Einstein in the paper On the Electrodynamics of Moving Bodies, as of today, special relativity is the most accurate model of motion at any speed. Even so, the Newtonian mechanics model is useful as an approximation at small velocities relative to the speed of light. Not until Einstein developed general relativity, to incorporate general frames of reference, a translation that has often been used is restricted relativity, special really means special case. It has replaced the notion of an absolute universal time with the notion of a time that is dependent on reference frame. Rather than an invariant time interval between two events, there is an invariant spacetime interval, a defining feature of special relativity is the replacement of the Galilean transformations of Newtonian mechanics with the Lorentz transformations. Time and space cannot be defined separately from each other, rather space and time are interwoven into a single continuum known as spacetime. Events that occur at the time for one observer can occur at different times for another. The theory is special in that it applies in the special case where the curvature of spacetime due to gravity is negligible. In order to include gravity, Einstein formulated general relativity in 1915, Special relativity, contrary to some outdated descriptions, is capable of handling accelerations as well as accelerated frames of reference. e. At a sufficiently small scale and in conditions of free fall, a locally Lorentz-invariant frame that abides by special relativity can be defined at sufficiently small scales, even in curved spacetime. Galileo Galilei had already postulated that there is no absolute and well-defined state of rest, Einstein extended this principle so that it accounted for the constant speed of light, a phenomenon that had been recently observed in the Michelson–Morley experiment. He also postulated that it holds for all the laws of physics, Einstein discerned two fundamental propositions that seemed to be the most assured, regardless of the exact validity of the known laws of either mechanics or electrodynamics. These propositions were the constancy of the speed of light and the independence of physical laws from the choice of inertial system, the Principle of Invariant Light Speed –. 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 is, light in vacuum propagates with the c in at least one system of inertial coordinates. Following Einsteins original presentation of special relativity in 1905, many different sets of postulates have been proposed in various alternative derivations, however, the most common set of postulates remains those employed by Einstein in his original paper
