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Equivalence Principle

Equivalence principle

In relativity, the equivalence principle is applied to several related concepts dealing with gravitation and the uniformity of physical measurements in different frames of reference. They are related to the Copernican idea that the laws of physics should be the same everywhere in the universe, to the equivalance of gravitational and inertial mass, and also to Albert Einstein's assertion that the gravitational "force" as experienced locally while standing on a massive body (such as the Earth) is actually the same as the pseudo-force experienced by an observer in a non-inertial (accelerated) frame of reference.

History

The origins of the equivalence principle begin with Galileo demonstrating in the late 16th century that all objects are accelerated towards the center of the Earth at the same rate. This was codified by Newton with his gravitational theory in which it was postulated that inertial and gravitational masses are one and the same. The equivalence principle proper was introduced by Albert Einstein in 1907. At that time, he made the observation that the acceleration of bodies towards the center of the Earth with acceleration 1g (g=9.81 m/s2 is the acceleration of gravity at the Earth's surface) is equivalent to the acceleration of inertially moving bodies that one would observe if one was on a rocket in free space being accelerated at a rate of 1g. Einstein stated it thus: :we [...] assume the complete physical equivalence of a gravitational field and a corresponding acceleration of the reference system. (Einstein, 1907) That is, remaining at rest in a uniform gravitational field is physically equivalent to experiencing an acceleration (e.g. being at rest with respect to the Earth, while under the influence of its gravitational field, is an accelerated state of motion). From this principle, Einstein deduced that free-fall is actually inertial motion. By contrast, in Newtonian mechanics, gravity is assumed to be a force. This force draws objects towards the center of a massive body. At the Earth's surface, the force of gravity is counter-balanced by the mechanical resistance of the Earth's surface. So in Newtonian physics, a person at rest on the surface of a (non-rotating) massive object is in an inertial frame of reference. While this picture works very well for most calculations, it was a mystery why the inertial mass in Newton's second law, F=ma, is equal to the gravitational mass in Newton's law of universal gravitation. Under the equivalence principle, this mystery is solved by virtue of gravity being an acceleration from inertial motion caused by the mechanical resistance of the Earth's surface. So a corollary of the equivalence principle is that :Whenever an observer detects the local presence of a force that acts on all objects in direct proportion to the inertial mass of each object, that observer is in an accelerated frame of reference. This equivalence principle was precisely formulated by Einstein in 1911, referring to two reference frames K and K'. The frame K is in a uniform gravitational field, whereas K' has no gravitational field but is uniformly accelerated such that objects in two frames experience identical forces: :We arrive at a very satisfactory interpretation of this law of experience, if we assume that the systems K and K' are physically exactly equivalent, that is, if we assume that we may just as well regard the system K as being in a space free from gravitational fields, if we then regard K as uniformly accelerated. This assumption of exact physical equivalence makes it impossible for us to speak of the absolute acceleration of the system of reference, just as the usual theory of relativity forbids us to talk of the absolute velocity of a system; and it makes the equal falling of all bodies in a gravitational field seem a matter of course. (Einstein, 1911) This observation was the start of a process that led to the development of general relativity. Einstein suggested that it should be elevated to the status of a general principle when constructing his theory of relativity: :As long as we restrict ourselves to purely mechanical processes in the realm where Newton's mechanics holds sway, we are certain of the equivalence of the systems K and K'. But this view of ours will not have any deeper significance unless the systems K and K' are equivalent with respect to all physical processes, that is, unless the laws of nature with respect to K are in entire agreement with those with respect to K'. By assuming this to be so, we arrive at a principle which, if it is really true, has great heuristic importance. For by theoretical consideration of processes which take place relatively to a system of reference with uniform acceleration, we obtain information as to the career of processes in a homogeneous gravitational field. (Einstein, 1911) He used this principle, together with special relativity, to predict that clocks run at different rates in a gravitational potential and the bending of light-rays in a gravitational field, even before he developed the concept of curved spacetime. So the original equivalence principle, as described by Einstein, was one of the physical equivalence of free fall and inertial motion. Although the equivalence principle helped to guide the development of general relativity, it is not a founding principle, but rather is a simple consequence of the geometrical nature of the theory. In general relativity, objects follow geodesics of spacetime, and what we perceive as the force of gravity is instead a result of our being being unable to follow those geodesics of spacetime due to the mechanical resistance of matter keeping us from doing so. Interest in the modern extensions of the equivalence principle was catalyzed in 1937 when Paul Dirac formulated his large numbers hypothesis which asserts that large, dimensionless numbers should not arise as fundamental quantities in physics: there should only be one fundamental energy scale in physics. He supported this by pointing out a coincidence: the dimensionless ratio of electric to gravitational forces in a hydrogen atom is about the same as the age of the universe, measured by the time it takes light to cross the hydrogen atom. Both are about 1040. To explain this surprising coincidence, Dirac postulated that Newton's constant varied as the inverse of the age of the universe, and the feebleness of gravity was due to the great age of the universe. While he turned out to be wrong, he led people to consider that the laws of physics may be different at different points in space and time, and the values of the physical constants, rather than being fundamental, may be set dynamically. These ideas, together with Mach's principle – roughly, the idea that inertia of a mass should be induced by the other masses in the universe – led physicists to develop scalar-tensor theories, in particular Brans-Dicke theory, in which the value of the gravitational constant is determined dynamically.

Modern usage

A number of different forms of the equivalence principle are used in research today.

The weak equivalence principle

The weak equivalence principle, also known as the universality of free fall: :The trajectory of a falling test body depends only on its initial position and velocity, and is independent of its composition. The principle does not apply to large bodies, which might experience tidal forces, or heavy bodies, whose presence will substantially change the gravitational field around them. This form of the equivalence principle is closest to Einstein's original statement: in fact, his statements imply this one. Since Einstein developed general relativity, there was a need to develop a framework to test the theory against other possible theories of gravity compatible with special relativity. This was developed by Robert Dicke as part of his program to test general relativity. Two new principles were suggested, the so-called Einstein equivalence principle and the strong equivalence principle, each of which assumes the weak equivalence principle as a starting point. They only differ in whether or not they apply to gravitational experiments. The Einstein equivalence principle states that the result of a local non-gravitational experiment in an inertial frame of reference is independent of the velocity or location in the universe of the experiment. This is a kind of Copernican extension of Einstein's original formulation, which requires that suitable frames of reference all over the universe behave identically. It is an extension of the postulates of special relativity in that it requires that dimensionless physical values such as the fine-structure constant and electron-to-proton mass ratio be constant. Many physicists believe that any Lorentz invariant theory that satisfies the weak equivalence principle also satisfies the Einstein equivalence principle. The strong equivalence principle states that the results of any local experiment, gravitational or not, in an inertial frame of reference are independent of where and when in the universe it is conducted. This is the only form of the equivalence principle that applies to self-gravitating objects (such as stars), which have substantial internal gravitational interactions. It requires that the gravitational constant be the same everywhere in the universe and is incompatible with a fifth force. It is much more restrictive than the Einstein equivalence principle. General relativity is the only known theory of gravity compatible with this form of the equivalence principle.

Tests of the weak equivalence principle

Tests of the weak equivalence principle are those that verify the equivalence of gravitational mass and inertial mass. These experiments demonstrate that all objects fall at the same rate when the effect of air resistance is either eliminated or negligible. The simplest way to test the weak equivalence principle is to drop two objects of different masses or compositions in a vacuum, and see if they hit the ground at the same time. More sophisticated tests use a torsion balance of a type invented by Roland Eötvös. Experiments are still being performed at the University of Washington which have placed limits on the differential acceleration of objects towards the Earth, the sun and towards dark matter in the galactic center. Future satellite experiments – STEP (Satellite Test of the Equivalence Principle), Galileo Galilei, and MICROSCOPE (MICROSatellite pour l'Observation de Principe d'Equivalence) – will test the weak equivalence principle in space, to much higher accuracy. The need to continue testing Einstein's theory of gravity may seem superfluous, as it is by far the most elegant theory of gravity known, and is compatible with almost all observations to date (except for instance the Pioneer anomaly). However, no quantum theory of gravity is known, and most suggestions violate one of the equivalence principles at some level. String theory, supergravity and even quintessence, for example, seem to violate the weak equivalence principle because they contain many light scalar fields with long Compton wavelengths. These fields should generate fifth forces and variation of the fundamental constants. There are a number of mechanisms that have been suggested by physicists to reduce these violations of the equivalence principle to below observable levels.

The Einstein equivalence principle

The Einstein equivalence principle states that the weak equivalence principle holds, and that : The outcome of any local non-gravitational experiment in a laboratory moving in an inertial frame of reference is independent of the velocity of the laboratory, or its location in spacetime. Here local has a very special meaning: not only must the experiment not look outside the laboratory, but it must also be small compared to variations in the gravitational field, tidal forces, so that the entire laboratory is moving inertially. The principle of relativity implies that the outcome of local experiments must be independent of the velocity of the apparatus, so the most important consequence of this principle is the Copernican idea that any of the fundamental physical parameters – other than masses and Newton's gravitational constant – must not depend on where in space or time we measure them. In practice, these are dimensionless numbers, such as the ratio of two masses, or coupling constants such as the fine-structure constant. Schiff's conjecture suggests that the weak equivalence principle actually implies the Einstein equivalence principle, but it has not been proven. Nonetheless, the two principles are tested with very different kinds of experiments. The Einstein equivalence principle has been criticized as imprecise, because there is no universally accepted way to distinguish gravitational from non-gravitational experiments (see for instance Hadley [http://arxiv.org/abs/quant-ph/9706018] and Durand [http://stacks.iop.org/ob/4/S351]). A further drawback is that assuming fundamental constants do not depend on time or location would appear to rule out deducing their value from first principles in some theory of everything to be discovered.

Tests of the Einstein equivalence principle

In addition to the tests of the weak equivalence principle, the Einstein equivalence principle can be tested by searching for variation of dimensionless constants and mass ratios. The present best limits on the variation of the fundamental constants have mainly been set by studying the naturally occurring Oklo fission reactor, where nuclear reactions similar to ones we observe today have been shown to have occurred underground approximately two billion years ago. These reactions are extremely sensitive to the values of the fundamental constants. There have been a number of controversial attempts to constrain the variation of the strong interaction constant. There have been several suggestions that "constants" do vary on cosmological scales. The best known is the reported detection of variation (at the 10-5 level) of the fine-structure constant from measurements of distant quasars (see Webb et al [http://arxiv.org/abs/astro-ph/0012539]. Other researchers dispute these findings. Other tests of the Einstein equivalence principle are gravitational redshift experiments, such as the Pound-Rebka experiment which test the position independence of experiments.

The strong equivalence principle

The strong equivalence principle suggests the laws of gravitation are independent of velocity and location. In particular, :The gravitational motion of a small test body depends only on its initial position in spacetime and velocity, and not on its constitution. and : The outcome of any local experiment, whether gravitational or not, in a laboratory moving in an inertial frame of reference is independent of the velocity of the laboratory, or its location in spacetime. The first part is a version of the weak equivalence principle that applies to objects that exert a gravitational force on themselves, such as stars, planets, black holes or Cavendish experiments. The second part is the Einstein equivalence principle, restated to allow gravitational experiments and self-gravitating bodies. The freely-falling object or laboratory, however, must still be small, so that tidal forces may be neglected. This idealized requirement has been misunderstood. This form of the equivalence principle does not imply that the effects of a gravitational field cannot be measured by observers in free-fall. For example, an observer in free-fall into a black hole will experience strong tidal forces: he will notice a more powerful force on his feet than his head. The strong equivalence principle suggests that gravity is entirely geometrical by nature (that is, the metric alone determines the effect of gravity) and does not have any extra fields associated with it. If an observer measures a patch of space to be flat, then the strong equivalence principle suggests that it is absolutely equivalent to any other patch of flat space elsewhere in the universe. Einstein's theory of general relativity (including the cosmological constant) is thought to be the only theory of gravity that satisfies the strong equivalence principle. A number of alternative theories, such as Brans-Dicke theory, satisfy only the Einstein equivalence principle.

Tests of the strong equivalence principle

The strong equivalence principle can be tested by searching for a variation of Newton's gravitational constant G over the life of the universe, or equivalently, variation in the masses of the fundamental particles. A number of independent constraints, from orbits in the solar system and studies of big bang nucleosynthesis have shown that G cannot have varied by more than 10%. Thus, the strong equivalence principle can be tested by searching for fifth forces (deviations from the gravitational force-law predicted by general relativity). These experiments typically look for failures of the inverse-square law (specifically Yukawa forces or failures of Birkhoff's theorem) behavior of gravity in the laboratory. The most accurate tests over short distances have been performed by the Eöt-Wash group. A future satellite experiment, SEE (Satellite Energy Exchange), will search for fifth forces in space and should be able to further constrain violations of the strong equivalence principle. Other limits, looking for much longer-range forces, have been placed by searching for the Nordtvedt effect, a "polarization" of solar system orbits that would be caused by gravitational self-energy accelerating at a different rate from normal matter. This effect has been sensitively tested by the Lunar Laser Ranging Experiment. Other tests include studying the deflection of radiation from distant radio sources by the sun, which can be accurately measured by very long baseline interferometry. Another sensitive test comes from measurements of the frequency shift of signals to and from the Cassini spacecraft. Together, these measurements have put tight limits on Brans-Dicke theory and other alternative theories of gravity.

References


- R. H. Dicke, "New Research on Old Gravitation," Science 129, 3349 (1959). This paper is the first to make the distinction between the strong and weak equivalence principles.
- R. H. Dicke, "Mach's Principle and Equivalence," in Evidence for gravitational theories: proceedings of course 20 of the International School of Physics "Enrico Fermi", ed C. Møller (Academic Press, New York, 1962). This article outlines the approach to precisely testing general relativity advocated by Dicke and pursued from 1959 onwards.
- Albert Einstein, "Über das Relativitätsprinzip und die aus demselben gezogene Folgerungen," Jahrbuch der Radioaktivitaet und Elektronik 4 (1907); translated "On the relativity principle and the conclusions drawn from it," in The collected papers of Albert Einstein. Vol. 2 : The Swiss years: writings, 1900–1909 (Princeton University Press, Princeton, NJ, 1989), Anna Beck translator. This is Einstein's first statement of the equivalence principle.
- Albert Einstein, "Über den Einfluß der Schwerkraft auf die Ausbreitung des Lichtes," Annalen der Physik 35 (1911); translated "On the Influence of Gravitation on the Propagation of Light" in The collected papers of Albert Einstein. Vol. 3 : The Swiss years: writings, 1909–1911 (Princeton University Press, Princeton, NJ, 1994), Anna Beck translator, and in The Principle of Relativity, (Dover, 1924), pp 99–108, W. Perrett and G. B. Jeffery translators, ISBN 0-486-60081-5. The two Einstein papers are discussed online at [http://www1.kcn.ne.jp/~h-uchii/gen.GR.html The Genesis of General Relativity].
- C. Brans, "The roots of scalar-tensor theory: an approximate history", [http://www.arxiv.org/gr-qc/0506063 arXiv:gr-qc/0506063]. Discusses the history of attempts to construct gravity theories with a scalar field and the relation to the equivalence principle and Mach's principle.
- C. W. Misner, K. S. Thorne and J. A. Wheeler, Gravitation, W. H. Freeman and Company, New York (1973), Chapter 16 discusses the equivalence principle.
- Hans Ohanian and Remo Ruffini Gravitation and Spacetime 2nd edition, Norton, New York (1994). ISBN 0-393-96501-5 Chapter 1 discusses the equivalence principle, but incorrectly, according to modern usage, states that the strong equivalence principle is wrong.
- J. P. Uzan, "The fundamental constants and their variation: Observational status and theoretical motivations," Rev. Mod. Phys. 75, 403 (2003). [http://www.arxiv.org/abs/hep-ph/0205340] This technical article reviews the best constraints on the variation of the fundamental constants.
- C. M. Will, Theory and experiment in gravitational physics, Cambridge University Press, Cambridge (1993). This is the standard technical reference for tests of general relativity.
- C. M. Will, Was Einstein Right?: Putting General Relativity to the Test, Basic Books (1993). This is a popular account of tests of general relativity.
- C. M. Will, [http://relativity.livingreviews.org/Articles/lrr-2001-4/index.html The Confrontation between General Relativity and Experiment,] Living Reviews in Relativity (2001). An online, technical review, covering much of the material in Theory and experiment in gravitational physics. The Einstein and strong variants of the equivalence principles are discussed in sections [http://relativity.livingreviews.org/Articles/lrr-2001-4/node3.html 2.1] and [http://relativity.livingreviews.org/Articles/lrr-2001-4/node7.html 3.1], respectively.

Experiments


- University of Washington [http://www.npl.washington.edu/eotwash/ Eöt-Wash group]
- Lunar Laser Ranging [http://funphysics.jpl.nasa.gov/technical/grp/lunar-laser.html]
- Galileo-Galilei satellite experiment [http://eotvos.dm.unipi.it/nobili/]
- Satellite Test of the Equivalence Principle (STEP) [http://einstein.stanford.edu/STEP/]
- MICROSCOPE [http://smsc.cnes.fr/MICROSCOPE/index.htm]
- Satellite Energy Exchange (SEE) [http://www.phys.utk.edu/see/]
- [http://physicsweb.org/articles/news/8/11/8/1 16 November 2004, physicsweb: Equivalence principle passes atomic test] Quote: "...Physicists in Germany have used an atomic interferometer to perform the most accurate ever test of the equivalence principle at the level of atoms..." Category:General relativity Category:Albert Einstein ko:등가 원리

Relativity

In physics, the term relativity is used in several, related contexts:
- Galileo first developed the principle of relativity, which is the postulate that the laws of physics are the same for all observers.
- Einstein's theory of relativity consists of special relativity and general relativity, which are built on the principle of relativity and the local constancy of the speed of light. In these theories space and time became unified as spacetime. In general relativity, the concept that this spacetime could be curved was introduced. This curved spacetime replaced Newton's force of gravity and the source of gravitation. The term "relativity" should not be confused with relativism. Much work has been done on the theory of relativity. It qualifies as objective science with very concrete, testable consequences, while the purpose of relativism is very different, namely to question all universal truths.

Other meanings


- Relativity is also the title of a Star Trek: Voyager Episode.
- Relativity was also a television series that aired on ABC from 1996 to 1997.

Copernican principle

The Copernican principle is the philosophical statement that no "special" observers should be proposed. The term originated in the paradigm shift from the Ptolemaic model of the heavens, which placed Earth at the center of the Solar system because it appears that everything revolved around Earth. Nicolaus Copernicus demonstrated that the motion of the heavens can be explained without the Earth being in the geometric center of the system, so the assumption that we are observing from a special position can be dispensed with.

See also


- Anthropic principle
- Cosmological principle
- Doomsday argument
- Mediocrity principle
- Scientific revolution Category:Cosmology Category:Philosophical terminology

Albert Einstein

Albert Einstein (March 14, 1879–April 18, 1955) was a German-born Jewish theoretical physicist, who is widely regarded as the greatest scientist of the 20th century. He proposed the theory of relativity and also made major contributions to the development of quantum mechanics, statistical mechanics, and cosmology. He was awarded the 1921 Nobel Prize for Physics for his explanation of the photoelectric effect in 1905 (his "miracle year") and "for his services to Theoretical Physics." After his general theory of relativity was formulated in November 1915, Einstein became world-famous, an unusual achievement for a scientist. In his later years, his fame exceeded that of any other scientist in history. In popular culture, his name has become synonymous with great intelligence and even genius. Einstein himself was deeply concerned with the social impact of scientific discoveries. His reverence for all creation, his belief in the grandeur, beauty, and sublimity of the universe (the primary source of inspiration in science), his awe for the scheme that is manifested in the material universe—all of these show through in his work and philosophy.

Biography

genius.]]

Youth and college

Einstein was born on March 14, 1879 at Ulm in Baden-Württemberg, Germany, about 100 km east of Stuttgart. His parents were Hermann Einstein, a featherbed salesman who later ran an electrochemical works, and Pauline, whose maiden name was Koch. They were married in Stuttgart-Bad Cannstatt. The family was Jewish (non-observant); Albert attended a Catholic elementary school and, at the insistence of his mother, was given violin lessons. When Albert was five, his father showed him a pocket compass, and Einstein realized that something in "empty" space acted upon the needle; he would later describe the experience as one of the most revelatory of his life. Though he built models and mechanical devices for fun, he was considered a slow learner, possibly due to dyslexia, simple shyness, or the significantly rare and unusual structure of his brain (examined after his death). He later credited his development of the theory of relativity to this slowness, saying that by pondering space and time later than most children, he was able to apply a more developed intellect. Another, more recent, theory about his mental development is that he had Asperger's syndrome, a condition related to autism. See People speculated to have been autistic. Einstein attended the Luitpold Gymnasium where he received a relatively progressive education. He began to learn mathematics around age twelve. There is a recurring rumor that he failed mathematics later in his education, but this is untrue; a change in the way grades were assigned caused confusion years later. Two of his uncles fostered his intellectual interests during his late childhood and early adolescence by suggesting and providing books on science, mathematics and philosophy. In 1894, following the failure of Hermann's electrochemical business, the Einsteins moved from Munich to Pavia, Italy (near Milan). During this year, Einstein's first scientific work was written (called "The Investigation of the State of Aether in Magnetic Fields"). Albert remained behind in Munich lodgings to finish school, completing only one term before leaving the gymnasium in spring 1895 to rejoin his family in Pavia. He quit without telling his parents and a year and a half prior to final examinations, Einstein convinced the school to let him go with a medical note from a friendly doctor, but this meant he had no secondary-school certificate. Despite excelling in the mathematics and science portion, his failure of the liberal arts portion of the Eidgenössische Technische Hochschule (ETH, Swiss Federal Institute of Technology, in Zurich) entrance exam the following year was a setback; his family sent him to Aarau, Switzerland, to finish secondary school, where he received his diploma in September 1896. During this time he lodged with Professor Jost Winteler's family and became enamoured with Marie, their daughter, his first sweetheart. Albert's sister Maja was to later marry their son Paul, and his friend Michele Besso married their other daughter Anna. Einstein subsequently enrolled at the Eidgenössische Technische Hochschule in October and moved to Zurich, while Marie moved to Olsberg for a teaching post. The same year, he renounced his Württemberg citizenship and became stateless. In the spring of 1896, the Serbian Mileva Marić started initially as a medical student at the University of Zurich, but after a term switched to the same section as Einstein as the only woman that year to study for the same diploma. Einstein's relationship with Mileva developed into romance over the next few years. In 1900, he was granted a teaching diploma by the Eidgenössische Technische Hochschule (ETH Zurich) and was accepted as a Swiss citizen in 1901. He kept his Swiss passport for his whole life. During this time Einstein discussed his scientific interests with a group of close friends, including Mileva. He and Mileva had an illegitimate daughter Lieserl, born in January 1902.

Work and doctorate

1902"]] Upon graduation, Einstein could not find a teaching post, mostly because his brashness as a young man had apparently irritated most of his professors. The father of a classmate helped him obtain employment as a technical assistant examiner at the Swiss Patent Office in 1902. There, Einstein judged the worth of inventors' patent applications for devices that required a knowledge of physics to understand. He also learned how to discern the essence of applications despite sometimes poor descriptions, and was taught by the director how "to express [him]self correctly". He occasionally rectified their design errors while evaluating the practicality of their work. Einstein married Mileva Marić on January 6, 1903. Einstein's marriage to Marić, who was a mathematician, was both a personal and intellectual partnership: Einstein referred to Mileva as "a creature who is my equal and who is as strong and independent as I am". Ronald W. Clark, a biographer of Einstein, claimed that Einstein depended on the distance that existed in his and Mileva's marriage in order to have the solitude necessary to accomplish his work; he required intellectual isolation. Abram Joffe, a Soviet physicist who knew Einstein, in an obituary of Einstein, wrote, "The author of [the papers of 1905] was ... a bureaucrat at the Patent Office in Bern, Einstein-Marić" and this has recently been taken as evidence of a collaborative relationship. However, according to Alberto A. Martínez of the Center for Einstein Studies at Boston University, Joffe only ascribed authorship to Einstein, as he believed that it was a Swiss custom at the time to append the spouse's last name to the husband's name. Whatever the truth, the extent of her influence on Einstein's work is a highly controversial and debated question. On May 14, 1904, the couple's first son, Hans Albert Einstein, was born. In 1904, Einstein's position at the Swiss Patent Office was made permanent. He obtained his doctorate after submitting his thesis "A new determination of molecular dimensions" ("Eine neue Bestimmung der Moleküldimensionen") in 1905. That same year, he wrote four articles (possibly with Mileva's help) that provided the foundation of modern physics, without much scientific literature to which he could refer or many scientific colleagues with whom he could discuss the theories. Most physicists agree that three of those papers (on Brownian motion, the photoelectric effect, and special relativity) deserved Nobel Prizes. Only the paper on the photoelectric effect would win one. This is ironic, not only because Einstein is far better-known for relativity, but also because the photoelectric effect is a quantum phenomenon, and Einstein became somewhat disenchanted with the path quantum theory would take. What makes these papers remarkable is that, in each case, Einstein boldly took an idea from theoretical physics to its logical consequences and managed to explain experimental results that had baffled scientists for decades. quantum theory

Annus Mirabilis Papers

Einstein submitted the series of papers to the "Annalen der Physik". They are commonly referred to as the "Annus Mirabilis Papers" (from Annus mirabilis, Latin for 'year of wonders'). The International Union of Pure and Applied Physics (IUPAP) is commemorating the 100th year of the publication of Einstein's extensive work in 1905 as the 'World Year of Physics 2005'. The first paper, named "On a Heuristic Viewpoint Concerning the Production and Transformation of Light", ("Über einen die Erzeugung und Verwandlung des Lichtes betreffenden heuristischen Gesichtspunkt") proposed that "energy quanta" (which are essentially what we now call photons) were real, and showed how they could be used to explain such phenomena as the photoelectric effect. This paper was specifically cited for his Nobel Prize. Max Planck had made the formal assumption that energy was quantized in deriving his black-body radiation law, published in 1901, but had considered this to be a no more than a mathematical trick. His second article in 1905, named "On the Motion—Required by the Molecular Kinetic Theory of Heat—of Small Particles Suspended in a Stationary Liquid", ("Über die von der molekularkinetischen Theorie der Wärme geforderte Bewegung von in ruhenden Flüssigkeiten suspendierten Teilchen") covered his study of Brownian motion, and provided empirical evidence for the existence of atoms. Before this paper, atoms were recognized as a useful concept, but physicists and chemists hotly debated whether atoms were real entities. Einstein's statistical discussion of atomic behavior gave experimentalists a way to count atoms by looking through an ordinary microscope. Wilhelm Ostwald, one of the leaders of the anti-atom school, later told Arnold Sommerfeld that he had been converted to a belief in atoms by Einstein's complete explanation of Brownian motion. Einstein's third paper that year, "On the Electrodynamics of Moving Bodies" ("Zur Elektrodynamik bewegter Körper"), was published in September 1905. While developing this paper, Einstein wrote to Mileva about "our work on relative motion", and this has led some to ask whether Mileva played a part in its development. This paper introduced the special theory of relativity, a theory of time, distance, mass and energy which was consistent with electromagnetism, but omitted the force of gravity. A fourth paper, "Does the Inertia of a Body Depend Upon Its Energy Content?", ("Ist die Trägheit eines Körpers von seinem Energieinhalt abhängig?") published late in 1905, showed one further deduction from relativity's axioms, the famous equation that the energy of a body at rest (E) equals its mass (m) times the speed of light (c) squared: E = mc2 .

Middle years

E = mc2.]] In 1906, Einstein was promoted to technical examiner second class. In 1908, Einstein was licensed in Bern, Switzerland, as a Privatdozent (unsalaried teacher at a university). Einstein's second son, Eduard, was born on July 28, 1910. In 1911, Einstein became first associate professor at the University of Zurich, and shortly afterwards full professor at the (German) University of Prague, only to return the following year to Zurich in order to become full professor at the ETH Zurich. At that time, he worked closely with the mathematician Marcel Grossmann. In 1912, Einstein started to refer to time as the fourth dimension (although H.G. Wells had done this earlier, in The Time Machine). In 1914, just before the start of World War I, Einstein settled in Berlin as professor at the local university and became a member of the Prussian Academy of Sciences. He took German citizenship. His pacifism and Jewish origins irritated German nationalists. After he became world-famous, nationalistic hatred of him grew and for the first time he was the subject of an organized campaign to discredit his theories. From 1914 to 1933, he served as director of the Kaiser Wilhelm Institute for Physics in Berlin, and it was during this time that he was awarded his Nobel Prize and made his most groundbreaking discoveries. He was also an extraordinary professor at the Leiden University from 1920 till officially 1946, where he regularly gave guest lectures. Einstein divorced Mileva on February 14, 1919, and married his cousin Elsa Löwenthal (born Einstein: Löwenthal was the surname of her first husband, Max) on June 2, 1919. Elsa was Albert's first cousin (maternally) and his second cousin (paternally). She was three years older than Albert, and had nursed him to health after he had suffered a partial nervous breakdown combined with a severe stomach ailment; there were no children from this marriage. The fate of Albert and Mileva's first child, Lieserl, is unknown. Some believe she died in infancy, while others believe she was given out for adoption. They later had two sons: Eduard and Hans Albert. Eduard intended to practice as a Freudian analyst but was institutionalized for schizophrenia and died in an asylum. Hans Albert, his older brother, became a professor of hydraulic engineering at the University of California, Berkeley, having little interaction with his father. University of California, Berkeley

General relativity

In November 1915, Einstein presented a series of lectures before the Prussian Academy of Sciences in which he described his theory of general relativity. The final lecture climaxed with his introduction of an equation that replaced Newton's law of gravity. This theory considered all observers to be equivalent, not only those moving at a uniform speed. In general relativity, gravity is no longer a force (as it is in Newton's law of gravity) but is a consequence of the curvature of space-time. The theory provided the foundation for the study of cosmology and gave scientists the tools for understanding many features of the universe that were discovered well after Einstein's death. A truly revolutionary theory, general relativity has so far passed every test posed to it and has become a powerful tool used in the analysis of many subjects in physics. Initially, scientists were skeptical because the theory was derived by mathematical reasoning and rational analysis, not by experiment or observation. But in 1919, predictions made using the theory were confirmed by Arthur Eddington's measurements (during a solar eclipse), of how much the light emanating from a star was bent by the Sun's gravity when it passed close to the Sun, an effect called gravitational lensing. The observations were carried out on May 29, 1919, at two locations, one in Sobral, Ceará, Brazil, and another in the island of Principe, in the west coast of Africa. On November 7, The Times reported the confirmation, cementing Einstein's fame. Many scientists were still unconvinced for various reasons ranging from disagreement with Einstein's interpretation of the experiments, to not being able to tolerate the absence of an absolute frame of reference. In Einstein's view, many of them simply could not understand the mathematics involved. Einstein's public fame which followed the 1919 article created resentment among these scientists some of which lasted well into the 1930s. In the early 1920s Einstein was the lead figure in a famous weekly physics colloquium at the University of Berlin. On March 30, 1921, Einstein went to New York to give a lecture on his new Theory of Relativity, the same year he was awarded the Nobel Prize. Though he is now most famous for his work on relativity, it was for his earlier work on the photoelectric effect that he was given the Prize, as his work on general relativity was still disputed. The Nobel committee decided that citing his less-contested theory in the Prize would gain more acceptance from the scientific community.

The "Copenhagen" interpretation

Einstein's relationship with quantum physics was quite remarkable. He was the first to say that quantum theory was revolutionary. His postulation that light can be described not only as a wave with no kinetic energy, but also as massless discrete packets of energy called quanta with measurable kinetic energy (now known as photons) marked a landmark break with the classical physics. In 1909 Einstein presented his first paper on the quantification of light to a gathering of physicists and told them that they must find some way to understand waves and particles together. In the mid-1920s, as the original quantum theory was replaced with a new theory of quantum mechanics, Einstein balked at the Copenhagen interpretation of the new equations because it settled for a probabilistic, non-visualizable account of physical behaviour. Einstein agreed that the theory was the best available, but he looked for a more "complete" explanation, i.e., more deterministic. He could not abandon the belief that physics described the laws that govern "real things", the belief which had led to his successes with atoms, photons, and gravity. In a 1926 letter to Max Born, Einstein made a remark that is now famous: : Quantum mechanics is certainly imposing. But an inner voice tells me it is not yet the real thing. The theory says a lot, but does not really bring us any closer to the secret of the Old One. I, at any rate, am convinced that He does not throw dice. To this, Bohr, who sparred with Einstein on quantum theory, retorted, "Stop telling God what He must do!" The Bohr-Einstein debates on foundational aspects of quantum mechanics happened during the Solvay conferences. Einstein was not rejecting probabilistic theories per se. Einstein himself was a great statistician, using statistical analysis in his works on Brownian motion and photoelectricity and in papers published before the miraculous year 1905; Einstein had even discovered Gibbs ensembles. He believed, however, that at the core reality behaved deterministically. Many physicists argue that experimental evidence contradicting this belief was found much later with the discovery of Bell's Theorem and Bell's inequality. Nonetheless, there is still space for lively discussions about the interpretation of quantum mechanics. For example, Shahriar Afshar conducted the Afshar experiment in 2004, which he claims disproves Bohr's notion of wave-particle duality as embodied in his Principle of Complementarity, apparently vindicating Einstein's objections to the Principle.

Bose-Einstein statistics

In 1924, Einstein received a short paper from a young Indian physicist named Satyendra Nath Bose describing light as a gas of photons and asking for Einstein's assistance in publication. Einstein realized that the same statistics could be applied to atoms, and published an article in German (then the lingua franca of physics) which described Bose's model and explained its implications. Bose-Einstein statistics now describe any assembly of these indistinguishable particles known as bosons. The Bose-Einstein condensate phenomenon was predicted in the 1920s by Bose and Einstein, based on Bose's work on the statistical mechanics of photons, which was then formalized and generalized by Einstein. The first such condensate was produced by Eric Cornell and Carl Wieman in 1995 at the University of Colorado at Boulder. Einstein's original sketches on this theory were recovered in August 2005 in the library of Leiden University (see website with original manuscript: ). Einstein also assisted Erwin Schrödinger in the development of the quantum Boltzmann distribution, a mixed classical and quantum mechanical gas model although he realized that this was less significant than the Bose-Einstein model and declined to have his name included on the paper.

The Einstein refrigerator

quantum Boltzmann distribution Einstein and former student Leó Szilárd co-invented a unique type of refrigerator (usually called the Einstein refrigerator) in 1926. On November 11, 1930, was awarded to Albert Einstein and Leó Szilárd. The patent covered a thermodynamic refrigeration cycle providing cooling with no moving parts, at a constant pressure, with only heat as an input. The refrigeration cycle used ammonia, butane, and water.

World War II

After Adolf Hitler came to power in 1933, expressions of hatred for Einstein reached new levels. He was accused by the National Socialist regime of creating "Jewish physics" in contrast with Deutsche Physik—"German" or "Aryan physics". Nazi physicists (notably including the Nobel laureates Johannes Stark and Philipp Lenard) continued the attempts to discredit his theories and to blacklist politically those German physicists who taught them (such as Werner Heisenberg). Einstein renounced his German citizenship and fled to the United States, where he was given permanent residency. He accepted a position at the newly founded Institute for Advanced Study in Princeton Township, New Jersey. He became an American citizen in 1940, though he still retained Swiss citizenship. In 1939, under the encouragement of Szilárd, Einstein sent a letter to President Franklin Delano Roosevelt urging the study of nuclear fission for military purposes, under fears that the Nazi government would be first to develop atomic weapons. Roosevelt started a small investigation into the matter which eventually became the massive Manhattan Project. ed. For more information, see the section below on Einstein's political views.

Institute for Advanced Study

His work at the Institute for Advanced Study focused on the unification of the laws of physics, which he referred to as the Unified Field Theory. He attempted to construct a model which would describe all of the fundamental forces as different manifestations of a single force. His attempt was hindered because the strong and weak nuclear forces were not understood independently until around 1970, fifteen years after Einstein's death. Einstein's goal of unifying the laws of physics under a single model survives in the current drive for unification of the forces, embodied most notably by string theory.

Generalized theory

Einstein began to form a generalized theory of gravitation with the Universal Law of Gravitation and the electromagnetic force in his first attempt to demonstrate the unification and simplification of the fundamental forces. In 1950 he described his work in a Scientific American article. Einstein was guided by a belief in a single statistical measure of variance for the entire set of physical laws. Einstein's Generalized Theory of Gravitation is a universal mathematical approach to field theory. He investigated reducing the different phenomena by the process of logic to something already known or evident. Einstein tried to unify gravity and electromagnetism in a way that also led to a new subtle understanding of quantum mechanics. Einstein postulated a four-dimensional space-time continuum expressed in axioms represented by five component vectors. Particles appear in his research as a limited region in space in which the field strength or the energy density are particularly high. Einstein treated subatomic particles as objects embedded in the unified field, influencing it and existing as an essential constituent of the unified field but not of it. Einstein also investigated a natural generalization of symmetrical tensor fields, treating the combination of two parts of the field as being a natural procedure of the total field and not the symmetrical and antisymmetrical parts separately. He researched a way to delineate the equations and systems to be derived from a variational principle. Einstein became increasingly isolated in his research on a generalised theory of gravitation and was ultimately unsuccessful in his attempts. variational principle (112 Mercer Street).]]

Final years

In 1948, Einstein served on the original committee which resulted in the founding of Brandeis University. A portrait of Einstein was taken by Yousuf Karsh on February 11 of that same year. In 1952, the Israeli government proposed to Einstein that he take the post of second president. He declined the offer, and remains the only United States citizen ever to be offered a position as a foreign head of state. On March 30, 1953, Einstein released a revised unified field theory. He died at 1:15 AM[http://faculty.washington.edu/chudler/ein.html] in Princeton hospital[http://www.princetonhistory.org/museum_alberteinstein.cfm] in Princeton, New Jersey, on April 18, 1955, leaving the Generalized Theory of Gravitation unsolved. The only person present at his deathbed, a hospital nurse, said that just before his death he mumbled several words in German that she did not understand. He was cremated without ceremony on the same day he died at Trenton, New Jersey, in accordance with his wishes. His ashes were scattered at an undisclosed location. His brain was preserved by Dr. Thomas Stoltz Harvey, the pathologist who performed the autopsy on Einstein. Harvey found nothing unusual with his brain, but in 1999 further analysis by a team at McMaster University revealed that his parietal operculum region was missing and, to compensate, his inferior parietal lobe was 15% wider than normal . The inferior parietal region is responsible for mathematical thought, visuospatial cognition, and imagery of movement. Einstein's brain also contained 73% more glial cells than the average brain.

Personality

Albert Einstein was much respected for his kind and friendly demeanor rooted in his pacifism. He was modest about his abilities, and had distinctive attitudes and fashions—for example, he minimized his wardrobe so that he would not need to waste time in deciding on what to wear. He occasionally had a playful sense of humor, and enjoyed sailing and playing the violin. He was also the stereotypical "absent-minded professor"; he was often forgetful of everyday items, such as keys, and would focus so intently on solving physics problems that he would often become oblivious to his surroundings. In his later years, his appearance inadvertently created (or reflected) another stereotype of scientist in the process: the researcher with unruly white hair.

Religious views

Although he was raised Jewish, he was not a believer in the religious aspect of Judaism, though he still considered himself a Jew. He simply admired the beauty of nature and the universe. From a letter written in English, dated March 24, 1954, Einstein wrote, "It was, of course, a lie what you read about my religious convictions, a lie which is being systematically repeated. I do not believe in a personal God and I have never denied this but have expressed it clearly. If something is in me which can be called religious then it is the unbounded admiration for the structure of the world so far as our science can reveal it." He also said (in an essay reprinted in Living Philosophies, vol. 13 (1931)): "A knowledge of the existence of something we cannot penetrate, our perceptions of the profoundest reason and the most radiant beauty, which only in their most primitive forms are accessible to our minds—it is this knowledge and this emotion that constitute true religiosity; in this sense, and this [sense] alone, I am a deeply religious man." The following is a response made to Rabbi Herbert Goldstein of the International Synagogue in New York which read, "I believe in Spinoza's God who reveals himself in the orderly harmony of what exists, not in a God who concerns himself with the fates and actions of human beings." After being pressed on his religious views by Martin Buber, Einstein exclaimed, "What we [physicists] strive for is just to draw His lines after Him." Summarizing his religious beliefs, he once said: "My religion consists of a humble admiration of the illimitable superior spirit who reveals himself in the slight details we are able to perceive with our frail and feeble mind." Einstein was an Honorary Associate of the Rationalist Press Association beginning in 1934.

Political views

Rationalist Press Association Solomon Mikhoels, 1943]] Einstein considered himself a pacifist and humanitarian , and in later years, a committed democratic socialist. He once said, "I believe Gandhi's views were the most enlightened of all the political men of our time. We should strive to do things in his spirit: not to use violence for fighting for our cause, but by non-participation of anything you believe is evil." Einstein's views on other issues, including socialism, McCarthyism and racism, were controversial (see Einstein on socialism). In a 1949 article, Albert Einstein described the "predatory phase of human development", exemplified by a chaotic capitalist society, as a source of evil to be overcome. He disapproved of the totalitarian regimes in the Soviet Union and elsewhere, and argued in favor of a democratic socialist system which would combine a planned economy with a deep respect for human rights. Einstein was a co-founder of the liberal German Democratic Party. Einstein was very much involved in the Civil Rights movement. He was a close friend of Paul Robeson for over 20 years. Einstein was a member of several civil rights groups (including the Princeton chapter of the NAACP) many of which were headed by Paul Robeson. He served as co-chair with Paul Robeson of the American Crusade to end lynching. W.E.B. DuBois was charged frivously as a communist spy during the McCarthy era while he was in his 80s, and Einstein volunteered as a character witness in the case. The case was dismissed shortly after it was annouced he was to appear in that capacity. Einstein was quoted as saying that "racism is America's greatest disease". The U.S. FBI kept a 1,427 page file on his activities and recommended that he be barred from immigrating to the United States under the Alien Exclusion Act, alleging that Einstein "believes in, advises, advocates, or teaches a doctrine which, in a legal sense, as held by the courts in other cases, 'would allow anarchy to stalk in unmolested' and result in 'government in name only'", among other charges. They also alleged that Einstein "was a member, sponsor, or affiliated with thirty-four communist fronts between 1937-1954" and "also served as honorary chairman for three communist organizations." It should be noted that many of the documents in the file were submitted to the FBI, mainly by civilian political groups, and not actually written by FBI officials. 1954 arguing that the United States should start funding research into the development of nuclear weapons.]] Einstein opposed tyrannical forms of government, and for this reason (and his Jewish background), opposed the Nazi regime and fled Germany shortly after it came to power. At the same time, Einstein's anarchist nephew Carl Einstein, who shared many of his views was fighting the fascists in the Spanish Civil War. Einstein initially favored construction of the atomic bomb, in order to ensure that Hitler did not do so first, and even sent a letter to President Roosevelt (dated August 2, 1939, before World War II broke out, and probably written by Leó Szilárd) encouraging him to initiate a program to create a nuclear weapon. Roosevelt responded to this by setting up a committee for the investigation of using uranium as a weapon, which in a few years was superseded by the Manhattan Project. After the war, though, Einstein lobbied for nuclear disarmament and a world government: "I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones." Einstein was a supporter of Zionism. He supported Jewish settlement of the ancient seat of Judaism and was active in the establishment of the Hebrew University in Jerusalem, which published (1930) a volume titled About Zionism: Speeches and Lectures by Professor Albert Einstein, and to which Einstein bequeathed his papers. However, he opposed nationalism and expressed skepticism about whether a Jewish nation-state was the best solution. He may have imagined Jews and Arabs living peacefully in the same land. In later life, in 1952, he was offered the post of second president of the newly created state of Israel, but declined the offer, claiming that he lacked the necessary people skills. Einstein was disturbed by the violence taking place in the Palestine after the Second World War and expressed that he was disappointed with the Jewish Ultra-Nationalist Organization (Irgun and Stern Gang). Nonetheless, Einstein remained deeply committed to the welfare of Israel and the Jewish people for the rest of his life. Einstein, along with Albert Schweitzer and Bertrand Russell, fought against nuclear tests and bombs. As his last public act, and just days before his death, he signed the Russell-Einstein Manifesto, which led to the Pugwash Conferences on Science and World Affairs. His letter to Russell read: :Dear Bertrand Russell, ::Thank you for your letter of April 5. I am gladly willing to sign your excellent statement. I also agree with your choice of the prospective signers. :With kind regards, A. Einstein

Popularity and cultural impact

Einstein's popularity has led to widespread use of Einstein in advertising and merchandising, including the registration of "Albert Einstein" as a trademark. trademark, 1951, UPI]]

Entertainment

Albert Einstein has become the subject of a number of novels, films and plays, including Nicolas Roeg's film Insignificance, Fred Schepisi's film I.Q., Alan Lightman's novel Einstein's Dreams, and Steve Martin's comedic play "Picasso at the Lapin Agile". He was the subject of Philip Glass's groundbreaking 1976 opera Einstein on the Beach. Since 1978, Einstein's humorous side has been the subject of a live stage presentation Albert Einstein: The Practical Bohemian, a one man show performed by actor Ed Metzger. He is often used as a model for depictions of eccentric scientists in works of fiction; his own character and distinctive hairstyle suggest eccentricity, or even lunacy and are widely copied or exaggerated. TIME magazine writer Frederic Golden referred to Einstein as "a cartoonist's dream come true." On Einstein's 72nd birthday in 1951, the UPI photographer Arthur Sasse was trying to coax him into smiling for the camera. Having done this for the photographer many times that day, Einstein stuck out his tongue instead . The image has become an icon in pop culture for its contrast of the genius scientist displaying a moment of levity. Yahoo Serious, an Australian film maker, used the photo as an inspiration for the intentionally anachronistic movie Young Einstein.

Licensing

Einstein bequeathed his estate, as well as the use of his image (see personality rights), to the Hebrew University of Jerusalem. Einstein actively supported the university during his life and this support continues with the royalties received from licensing activities. The Roger Richman Agency licences the commercial use of the name "Albert Einstein" and associated imagery and likenesses of Einstein, as agent for the Hebrew University of Jerusalem. As head licensee the agency can control commercial usage of Einstein's name which does not comply with certain standards (e.g., when Einstein's name is used as a trademark, the ™ symbol must be used ). As of May, 2005, the Roger Richman Agency was acquired by Corbis.

Honors

Corbis Einstein has received a number of posthumous honors. For example:
- In 1992, he was ranked #10 on Michael H. Hart's list of the most influential figures in history.
- In 1999, he was named Person of the Century by TIME magazine.
- The year 2005 was designated as the "World Year of Physics" by UNESCO for its coinciding with the centennial of the "Annus Mirabilis" papers, celebrated at the Einstein Symposium. Among Einstein's many namesakes are:
- a unit used in photochemistry, the einstein.
- the chemical element 99, einsteinium.
- the asteroid 2001 Einstein.
- the Albert Einstein Peace Prize.
- the Albert Einstein College of Medicine of Yeshiva Universitywas named after Einstein upon his death in 1955.
- the Albert Einstein Medical Centerin Philadelphia, PA.

References


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- Sandra Ionno Butcher (March 2005) [http://www.pugwash.org/publication/phs/phslist.htm The Origins of the Russell-Einstein Manifesto].
- — Discusses the final disposition of Einstein's brain, hair, and eyes as well as the importance of Einstein and his work in the shaping of science and culture. Philadelphia in Washington, DC]] # # # # # # # # # # # # # # # #

Works by Albert Einstein


- [http://www.worldscibooks.com/phy_etextbook/4454/4454_chap1.pdf The Investigation of the State of Aether in Magnetic Fields]. (PDF)
- Ideas & Opinions ISBN 0517003937
- The World As I See It ISBN 080650711X (translation of "Mein Weltbild") Washington, DC]
- Relativity: The Special and General Theory. ISBN 0517884410 ([http://www.gutenberg.net/browse/BIBREC/BR5001.HTM Project Gutenberg E-text])
- "[http://www.fourmilab.ch/etexts/einstein/specrel/www/ On the Electrodynamics of Moving Bodies]" Annalen der Physik. June 30, 1905
- "[http://www.fourmilab.ch/etexts/einstein/E_mc2/www/ Does the Inertia of a Body Depend Upon Its Energy Content?]" Annalen der Physik. September 27, 1905.
- "[http://alberteinstein.info/gallery/pdf/CP6Doc3_English_pp16-18.pdf Inaugural Lecture to the Prussian Academy of Sciences]." 1914. [PDF]
- "[http://hem.bredband.net/b153434/Works/Einstein.htm The Foundation of the General Theory of Relativity ]." Annalen der Physik, 49. 1916.
- "Fundamental ideas and problems of the theory of relativity." 1921 Nobel Lecture in Physics. Nordic Assembly of Naturalists at Gothenburg, 11 July 1923.
- Einstein A., Lorenz H. A., Weyl H. and Minkowski H. The Principle of Relativity. Trans. W. Perrett and G. B. Jeffery. New York: Dover Publications, 1923.
- "[http://www.monthlyreview.org/598einst.htm Why Socialism?]" Monthly Review. May 1949.
- [http://www.alberteinstein.info/db/ViewImage.do?DocumentID=34170&Page=1 On the Generalized Theory of Gravitation]. April, 1950.

External links


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- Nobel Prize in Physics: [http://www.nobel.se/physics/laureates/1921/press.html The Nobel Prize in Physics 1921]—[http://www.nobel.se/physics/laureates/1921/index.html Albert Einstein]
- Annalen der Physik: [http://gallica.bnf.fr/Catalogue/noticesInd/FRBNF34462944.htm#listeUC Works by Einstein] digitalized at The University of Applied Sciences in Jena (Fachhochschule Jena)
- S. Morgan Friedman, "[http://www.westegg.com/einstein/ Albert Einstein Online]"—Comprehensive listing of online resources about Einstein.
- TIME magazine 100: [http://www.time.com/time/time100/scientist/profile/einstein.html Albert Einstein]
- Audio excerpts of famous speeches: [http://www.time.com/time/time100/poc/audio/einstein1.ram E=mc2 and relativity], [http://www.time.com/time/time100/poc/audio/einstein2.ram Impossibility of atomic energy], [http://www.time.com/time/time100/poc/audio/einstein3.ram arms race] (From Time magazine archives)
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- Leiden University: [http://www.lorentz.leidenuniv.nl/history/Einstein_archive/ Einstein Archive]
- PBS: [http://www.pbs.org/wgbh/amex/truman/psources/ps_einstein.html Einstein's letter to Roosevelt]
- PBS [http://www.pbs.org/wgbh/nova/einstein/ NOVA—Einstein]
- PBS [http://www.pbs.org/opb/einsteinswife/ Einstein's wife]: Mileva Maric
- FBI: [http://foia.fbi.gov/foiaindex/einstein.htm FBI files]—investigation regarding affiliation with the Communist Party
- University of Frankfurt: [http://www.th.physik.uni-frankfurt.de/~jr/physpiceinfam.html Einstein family pictures]
- Salon.com: [http://dir.salon.com/people/feature/2000/07/06/einstein/index.html Did Einstein cheat?]
- [http://www.germanheritage.com/biographies/atol/einstein.html Albert Einstein Biography from "German-American corner: History and Heritage"]
- [http://www.alberteinstein.info/ Official Einstein Archives Online]
- [http://www.alberteinstein.info/manuscripts/index.html Einstein's Manuscripts]
- [http://www.albert-einstein.org/ Albert Einstein Archive]
- [http://www.einstein.caltech.edu/ Einstein Papers Project]
- Max Planck Institute: [http://living-einstein.mpiwg-berlin.mpg.de/living_einstein Living Einstein]
- American Institute of Physics: [http://www.aip.org/history/einstein/index.html Albert Einstein] includes his life and work, audio files and full site available as a downloadable PDF for classroom use
- American Museum of Natural History: [http://www.amnh.org/exhibitions/einstein/index.php Albert Einstein]
- [http://www.aeinstein.org The Albert Einstein Institution]
- The Economist: [http://www.economist.com/displaystory.cfm?story_id=3518580 "100 years of Einstein"]
- Einstein@Home:[http://www.physics2005.org/events/einsteinathome/index.html Distributed computing project searching for gravitational waves predicted by Einstein's theories]
- World Year of Physics 2005 [http://www.physics2005.o

Inertial frame of reference

An inertial frame is a coordinate system defined by the non-accelerated motion of objects with a common direction and speed.

Introduction

In physics, an object has inertial motion if no external forces are being applied to it, famously stated as Newton's first law of motion. When such an object’s state of motion is extrapolated over a region of space to take in all other possible objects in the region with the same state of motion, and these are used to define a common coordinate system, this system is referred to as a frame.

Use of inertial frames

Inertial frames of reference are relevant to Newtonian relativity and Einstein's special theory of relativity.
- Under Newtonian mechanics, all inertial states of motion are considered to be equivalent: if two inertial observers, A and B have a relative velocity, then the laws of physics should be the same regardless of whether we take A as our “stationary” reference and say that B is moving, or if we take B as our fixed reference and say that A is moving. Included in these rules of physics is the explicit assumption that time progresses at the same rate for all observers, meaning that clocks calibrated in one inertial coordinate system will not become uncalibrated due to one of them being moved into another inertial frame of reference.
- Under special relativity, this equivalence of different inertial states of motion still applies. However, the assumption of constant progression of proper time in all frames of reference is replaced by the assumption that the speed of light is constant, and that this is equally true for every inertial observer. This required the use of a set of protocols created by Einstein (Einstein synchronisation) that allows observers to define apparent distances and times according to the assumption of fixed light speed in their own frame, and then build an extended coordinate system for labeling the times and distances of distant events. Observers using different reference frames will derive different nominal distance and time separations between the same two events. The formulas for converting, or "transforming" values between different frames of reference allow each observer to calculate how the physics taking place appears for another observer. As seen from different points of view the nominal distance and time separation between two events differs, but the combined spacetime interval is unchanged: it is "frame-independent", or "invariant".

Transformations

The way that nominal distances and times are converted from one coordinate system to another is referred to as a transformation. In classical mechanics the kinetic energy of a system depends on the inertial frame of reference. It is lowest with respect to the center of mass, i.e., in a frame of reference in which the center of mass is stationary. In another frame of reference the additional kinetic energy is that corresponding to the total mass and the speed of the center of mass. Einstein argued that if we only assume that light propagates at c in a single preferred frame (i.e., if we assume an absolute fixed aether, classical theory), transformation of space and time coordinates is performed using Galilean transformations, whereas with special relativity we obtain Lorentz transformations, which only coincide with the earlier results for relative velocities that are reasonably small in comparison with the speed of light.

Einstein’s general theory of relativity

Einstein’s general theory modifies the distinction between nominally "inertial" and "noninertial" effects, by replacing special relativity's "flat", Euclidean geometry with a curved non-Euclidean metric. In general relativity, the principle of inertia is replaced with the principle of geodesic motion, whereby objects move in a way dictated by the curvature of spacetime. As a consequence of this curvature, it is not a given in general relativity that inertial objects moving at a given rate with respect to each other will continue to do so. This phenomenon of geodesic deviation means that inertial frames of reference do not exist globally as they do in Newtonian mechanics and special relativity. However, the general theory reduces to the special theory over sufficiently small regions of spacetime, where curvature effects become less important and the earlier inertial frame arguments can come back into play. Consequently, modern SR is now sometimes described as only a “local theory”. (However, this refers to the theory’s application rather than to its derivation.)

External links


- [http://plato.stanford.edu/entries/spacetime-iframes/ Stanford Encyclopedia of Philosophy entry]

References


- Edwin F. Taylor and John Archibald Wheeler, Spacetime Physics 2nd ed. (Freeman, NY, 1992)
- Albert Einstein, Relativity, the special and the general theories, 15th ed. (1954) Category:Astrodynamics Category:Classical mechanics Category:Relativity Category:Frames of reference

Galileo

Galileo Galilei (Pisa, February 15 1564 – Arcetri, January 8 1642), was an Italian physicist, astronomer, and philosopher who is closely associated with the scientific revolution. His achievements include improvements to the telescope, a variety of astronomical observations, the first law of motion and the second law of motion, and effective support for Copernicanism. He has been referred to as the "father of modern astronomy," as the "father of modern physics," and as "father of science." His experimental work is widely considered complementary to the writings of Francis Bacon in establishing the modern scientific method. Galileo's career coincided with that of Johannes Kepler. The work of Galileo is considered to be a significant break from that of Aristotle. In addition, his conflict with the Roman Catholic Church is taken as a major early example of the conflict of authority and freedom of thought, particularly with science, in Western society.

Galileo's Family & Early Careers

Galileo was born in Pisa, in the Tuscan region of Italy, the son of Vincenzo Galilei, a mathematician and musician born in Florence in 1520, and Giulia Ammannati, born in Pescia and married in 1563. Galileo was their first child. Although a devout Catholic, Galileo fathered three children out of wedlock. All were the children of Galileo and Marina Gamba. Because of their illegitimate birth, both girls were sent to the convent of San Matteo in Arcetri at early ages.
- Virginia (b. 1600) who took the name Maria Celeste upon entering a convent. Galileo's eldest child, the most beloved, and inherited her father's sharp mind. She died in 1634 on April second. She is buried with Galileo at the Basilica di Santa Croce di Firenze.
- Livia (b. 1601) took the name Suor Arcangela. Was sickly for most of her life at the convent.
- Vincenzio (b. 1606) was later legitimized and married Sestilia Bocchineri He was home schooled at a very young age. After that he attended the University of Pisa, but was forced to cease his study there for financial reasons. However, he was offered a position on its faculty in 1589 and taught mathematics. Soon after, he moved to the University of Padua, and served on its faculty teaching geometry, mechanics, and astronomy until 1610. During this time he explored science and made many landmark discoveries.

Experimental science

In the pantheon of the scientific revolution, Galileo takes a high position because of his pioneering use of quantitative experiments with results analyzed mathematically. There was no tradition of such methods in European thought at that time; the great experimentalist who immediately preceded Galileo, William Gilbert, did not use a quantitative approach. However, Galileo's father, Vincenzo Galilei, had performed experiments in which he discovered what may be the oldest known non-linear relation in physics, between the tension and the pitch of a stretched string. Galileo also contributed to the rejection of blind allegiance to authority (like the Church) or other thinkers (such as Aristotle) in matters of science and to the separation of science from philosophy or religion. These are the primary justifications for his description as the "father of science." In the 20th century some authorities challenged the reality of Galileo's experiments, in particular the distinguished French historian of science Alexandre Koyré. The experiments reported in Two New Sciences to determine the law of acceleration of falling bodies, for instance, required accurate measurements of time, which appeared to be impossible with the technology of the 1600s. According to Koyré, the law was arrived at deductively, and the experiments were merely illustrative thought experiments. Later research, however, has validated the experiments. The experiments on falling bodies (actually rolling balls) were replicated using the methods described by Galileo (Settle, 1961), and the precision of the results was consistent with Galileo's report. Later research into Galileo's unpublished working papers from as early as 1604 clearly showed the reality of the experiments and even indicated the particular results that led to the time-squared law (Drake, 1973).

Astronomy

Contributions

Although the popular idea of Galileo inventing the telescope is inaccurate, he was one of the first people to use the telescope to observe the sky, and for a time was one of very few people able to make a good enough telescope for the purpose. Based on sketchy descriptions of telescopes invented in the Netherlands in 1608, Galileo made one with about 8x magnification, and then made improved models up to about 20x. On August 25, 1609, he demonstrated his first telescope to Venetian lawmakers. His work on the device also made for a profitable sideline with merchants who found it useful for their shipping businesses. He published his initial telescopic astronomical observations in March 1610 in a short treatise entitled Sidereus Nuncius (Sidereal Messenger). Sidereus Nuncius. This observation upset the notion that all celestial bodies must revolve around the Earth. Galileo published a full description in Sidereus Nuncius in March 1610.]] On January 7, 1610 Galileo discovered three of Jupiter's four largest satellites (moons): Io, Europa, and Callisto. Ganymede he discovered four nights later. He determined that these moons were orbiting the planet since they would appear and disappear; something he attributed to their movement behind Jupiter. He made additional observations of them in 1620. Later astronomers overruled Galileo's naming of these objects, changing his Medicean stars to Galilean satellites. The demonstration that a planet had smaller planets orbiting it was problematic for the orderly, comprehensive picture of the geocentric model of the universe, in which everything circled around the Earth. Galileo noted that Venus exhibited a full set of phases like the Moon. The heliocentric model of the solar system developed by Copernicus predicted that all phases would be visible since the orbit of Venus around the Sun would cause its illuminated hemisphere to face the Earth when it was on the opposite side of the Sun and to face away from the Earth when it was on the Earth-side of the Sun. By contrast, the geocentric model of Ptolemy predicted that only crescent and new phases would be seen, since Venus was thought to remain between the Sun and Earth during its orbit around the Earth. Galileo's observation of the phases of Venus proved that Venus orbited the Sun and lent support to (but did not prove) the heliocentric model. Galileo was one of the first Europeans to observe sunspots, although there is evidence that Chinese astronomers had done so before. The very existence of sunspots showed another difficulty with the unchanging perfection of the heavens as assumed in the older philosophy. And the annual variations in their motions, first noticed by Francesco Sizzi, presented great difficulties for either the geocentric system or that of Tycho Brahe. A dispute over priority in the discovery of sunspots led to a long and bitter feud with Christoph Scheiner; in fact, there can be little doubt that both of them were beaten by David Fabricius and his son Johannes. He was the first to report lunar mountains and craters, whose existence he deduced from the patterns of light and shadow on the Moon's surface. He even estimated the mountains' heights from these observations. This led him to the conclusion that the Moon was "rough and uneven, and just like the surface of the Earth itself", and not a perfect sphere as Aristotle had claimed. Galileo observed the Milky Way, previously believed to be nebulous, and found it to be a multitude of stars, packed so densely that they appeared to be clouds from Earth. He also located many other stars too distant to be visible with the naked eye. Galileo observed the planet Neptune in 1612, but did not realize that it was a planet and took no particular notice of it. It appears in his notebooks as one of many unremarkable dim stars.

Modern claims of scientific errors and misconduct

Although Galileo is generally considered one of the first modern scientists, as evidenced by his position in the sunspot controversy, he is often said to have arrogantly considered himself to be the sole-propietor of the discoveries in astronomy. Furthermore, he never accepted Kepler's elliptical orbits for the planets, holding to the circular orbits of Copernicus, which still employed epicycles to account for irregularities in planetary motions. Concerning his theory on tides, Galileo attributed them to momentum despite his great knowledge of the ideas of relative motion and Kepler's better theories using the Moon as the cause. (Neither of these great scientists, however, had a workable physical theory of tides; this had to wait for the work of Newton) Galileo stated in his Dialogue that, if the Earth spins on its axis and is traveling at a certain speed around the Sun, parts of the Earth must travel "faster" at night and "slower" during the day. This, of course, is true in the Sun's frame of reference; but it is by no means adequate to explain the tides. Many commentators consider that Galileo developed this position simply to justify his own opinion because the theory was not based on any real scientific observations because if his theory was correct, there would be only one high tide per day and it would happen at noon. The fact that there are two daily high tides at Venice instead of one, and that they travel around the clock, Galileo and his contemporaries knew, but he dismissed as due to several secondary causes, such as the shape of the sea, its depth, and other things. Against the imputation that Galileo was guilty of some kind of deceit in making these arguments one may take the position of Albert Einstein, as one who had done original work in physics, that Galileo developed his "fascinating arguments" and accepted them too uncritically out of a desire for a physical proof of the motion of the Earth (Einstein, 1952)

Physics

Galileo's theoretical and experimental work on the motions of bodies, along with the largely independent work of Kepler and René Descartes, was a precursor of the Classical mechanics developed by Sir Isaac Newton. He was a pioneer, at least in the European tradition, in performing rigorous experiments and insisting on a mathematical description of the laws of nature. One of the most famous stories about Galileo is that he dropped balls of different masses from the Leaning Tower of Pisa to demonstrate that their time of descent was independent of their mass (excluding the limited effect of air resistance). This was contrary to what Aristotle had taught: that heavy objects fall faster than lighter ones, in direct proportion to weight. Though the story of the tower first appeared in a biography by Galileo's pupil Vincenzo Viviani, it is not now generally accepted as true. However, Galileo did perform experiments involving rolling balls down inclined planes, which proved the same thing: falling or rolling objects (rolling is a slower version of falling, as long as the distribution of mass in the objects is the same) are accelerated independently of their mass. He determined the correct mathematical law for acceleration: the total distance covered, starting from rest, is proportional to the square of the time (This law is regarded as a predecessor to the many later scientific laws expressed in mathematical form.). He also concluded that objects retain their velocity unless a force -- often friction -- acts upon them, refuting the accepted Aristotelian hypothesis that objects "naturally" slow down and stop unless a force acts upon them. Galileo's Principle of Inertia stated: "A body moving on a level surface will continue in the same direction at constant speed unless disturbed." This principle was incorporated into Newton's laws of motion (1st law). Newton's laws of motion Galileo also noted that a pendulum's swings always take the same amount of time, independently of the amplitude. The story goes that he came to this conclusion by watching the swings of the bronze chandelier in the cathedral of Pisa, using his pulse to time it. While Galileo believed this equality of period to be exact, it is only an approximation appropriate to small amplitudes. It is good enough to regulate a clock, however, as Galileo may have been the first to realize. (See Technology below) In the early 1600s, Galileo and an assistant tried to measure the speed of light. They stood on different hilltops, each holding a shuttered lantern. Galileo would open his shutter, and, as soon as his assistant saw the flash, he would open his shutter. At a distance of less than a mile, Galileo could detect no delay in the round-trip time greater than when he and the assistant were only a few yards apart. While he could reach no conclusion on whether light propagated instantaneously, he recognized that the distance between the hilltops was perhaps too small for a good measurement. Galileo is lesser known for, yet still credited with being one of the first to understand sound frequency. After scraping a chisel at different speeds, he linked the pitch of sound to the spacing of the chisel's skips (frequency). In his 1632 Dialogue Galileo presented a physical theory to account for tides, based on the motion of the Earth. If correct, this would have been a strong argument for the reality of the Earth's motion. (The original title for the book, in fact, described it as a dialogue on the tides; the reference to tides was removed by order of the Inquisition.) His theory gave the first insight into the importance of the shapes of ocean basins in the size and timing of tides; he correctly accounted, for instance, for the negligible tides halfway along the Adriatic Sea compared to those at the ends. As a general account of the cause of tides, however, his theory was a failure. Kepler and others correctly associated the Moon with an influence over the tides, based on empirical data; a proper physical theory of the tides, however, was not available until Newton. Galileo also put forward the basic principle of relativity, that the laws of physics are the same in any system that is moving at a constant speed in a straight line, regardless of its particular speed or direction. Hence, there is no absolute motion or absolute rest. This principle provided the basic framework for Newton's laws of motion and Einstein's theory of relativity.

Mathematics

While Galileo's application of mathematics to experimental physics was innovative, his mathematical methods were the standard ones of the day. The analyses and proofs relied heavily on the Eudoxian theory of proportion, as set forth in the fifth book of Euclid's Elements. This theory had become available only a century before, thanks to accurate translations by Tartaglia and others; but by the end of Galileo's life it was being superseded by the algebraic methods of Descartes, which a modern finds incomparably easier to follow. Galileo produced one piece of original and even prophetic work in mathematics: