The
Annus Mirabilis papers (from
LatinLatin is an Italic language originally spoken in Latium and Ancient Rome. Through the Roman conquest, Latin spread throughout the Mediterranean and a large part of Europe...
annus mīrābilisAnnus mirabilis is a Latin phrase meaning "wonderful year" or "year of wonders" . It was used originally to refer to the year 1666, but is today also used to refer to different years with events of major importance such as 1905 when Albert Einstein published his breakthrough four articles on Physics...
, 'extraordinary year') are the papers of
Albert EinsteinAlbert Einstein was a theoretical physicist. His many contributions to physics include the special and general theories of relativity, the founding of relativistic cosmology, the first post-Newtonian expansion, explaining the perihelion advance of Mercury, prediction of the deflection of...
published in the
Annalen der PhysikAnnalen der Physik is one of the best-known and oldest physics journals worldwide.The journal publishes original papers in the areas of experimental, theoretical, applied and mathematical physics and related areas...
scientific journalIn academic publishing, a scientific journal is a periodical publication intended to further the progress of science, usually by reporting new research. There are thousands of scientific journals in publication, and many more have been published at various points in the past...
in 1905. These four articles contributed substantially to the foundation of modern physics and changed views on
spaceSpace is the boundless, three-dimensional extent in which objects and events occur and have relative position and direction. Physical space is often conceived in three linear dimensions, although modern physicists usually consider it, with time, to be part of the boundless four-dimensional...
,
timeTime is a component of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify the motions of objects...
, and
matterThe term matter traditionally refers to the substance that all objects are made of. One common way to identify this "substance" is through its physical properties; a common definition of matter is anything that has mass and occupies a volume...
. The
Annus Mirabilis is often called the "Miracle Year" in
EnglishEnglish is a West Germanic language that developed in England during the Anglo-Saxon era. As a result of the military, economic, scientific, political, and cultural influence of the British Empire during the 18th, 19th, and early 20th centuries, and of the United States since the mid 20th century,...
or in
GermanGerman is a West Germanic language, thus related to and classified alongside English and Dutch. It is one of the world's major languages and the most widely spoken first language in the European Union. Around the world, German is spoken by approximately 105 million native speakers and also by...
, the
"Wunderjahr".
Background
At the time the papers were written, Einstein did not have easy access to a complete set of scientific reference materials, although he did regularly read and contribute reviews to
Annalen der Physik. Additionally, scientific colleagues available to discuss his
theoriesThe term theory has two broad sets of meanings, one used in the empirical sciences and the other used in philosophy, mathematics, logic, and across other fields in the humanities. There is considerable difference and even dispute across academic disciplines as to the proper usages of the term...
were few. He worked as an examiner at the
Patent OfficeA patent office is a governmental or intergovernmental organization which controls the issue of patents. In other words, "patent offices are government bodies that may grant a patent or reject the patent application based on whether or not the application fulfils the requirements for...
in Bern,
SwitzerlandSwitzerland , officially the Swiss Confederation , is a federal republic consisting of 26 states named cantons, with Bern as the seat of the federal authorities...
, and he later said of a co-worker there,
Michele BessoMichele Angelo Besso was a Swiss/Italian engineer of Jewish Italian descent and a close friend of Albert Einstein during his years at the Federal Polytechnic Institute in Zurich, today the ETH Zurich, and then at the patent office in Bern...
, that he "could not have found a better sounding board for his ideas in all of Europe". In addition to co-workers and the other members of the self-styled "Olympian Academy" (Solovine and Habicht), his wife,
Mileva MarićMileva Marić was one of the first women to study mathematics and physics in Europe...
, may have had some influence on Einstein's work but how much is unclear. Through these papers, Einstein tackles some of the era's most important physics questions and problems. In 1900, a lecture titled "Nineteenth-Century Clouds over the Dynamical Theory of Heat and Light", by Lord Kelvin, suggested that physics had no satisfactory explanations for the results of the
Michelson-Morley experimentThe Michelson–Morley experiment was performed in 1887 by Albert Michelson and Edward Morley at what is now Case Western Reserve University. It is generally considered to be the first strong evidence against the theory of a luminiferous aether...
and for
black bodyIn physics, a black body is an idealized object that absorbs all electromagnetic radiation that falls on it. No electromagnetic radiation passes through it and none is reflected. Because no light is reflected or transmitted, the object appears black when it is cold. However, a black body emits a...
radiation. As introduced, special relativity provided an account for the results of the Michelson-Morley experiments. Einstein's theories for the photoelectric effect extended the
quantum theoryQuantum theory may mean:In science:*Quantum mechanics, an umbrella term for describing all quantum physics*Old quantum theory under the Bohr model* Quantum field theory, a generic type of relativistic quantum theory, which includes:...
which
Max PlanckMax Planck was a German physicist. He is considered to be the founder of the quantum theory, and thus one of the most important physicists of the twentieth century. Planck was awarded the Nobel Prize in Physics in 1918.-Biography:Planck came from a traditional, intellectual family...
had developed in his successful explanation of black body radiation.
Despite the greater fame achieved by his other works, such as that on
special relativitySpecial relativity is the physical theory of measurement in inertial frames of reference proposed in 1905 by Albert Einstein in the paper "On the Electrodynamics of Moving Bodies"...
, it was his work on the
photoelectric effectThe photoelectric effect is a phenomenon in which electrons are emitted from matter as a consequence of their absorption of energy from electromagnetic radiation of very short wavelength, such as visible or ultraviolet light. Electrons emitted in this manner may be referred to as "photoelectrons"...
which won him his
Nobel PrizeThe Nobel Prize is a Sweden-based international monetary prize. The award was established by the 1895 will and estate of Swedish chemist and inventor Alfred Nobel. It was first awarded in Physics, Chemistry, Physiology or Medicine, Literature, and Peace in 1901...
in 1921: "For services to theoretical physics and especially for the discovery of the law of the photoelectric effect." The Nobel committee had waited patiently for experimental confirmation of special relativity; however none was forthcoming until the
time dilationTime dilation is a phenomenon described by the theory of relativity. It can be illustrated by supposing that two observers are in motion relative to each other, and/or differently situated with regard to nearby gravitational masses. They each carry a clock of identically similar construction and...
experiments of Ives and Stilwell (1938), (1941) and Rossi and Hall (1941).
Photoelectric effect
The paper, "On a
HeuristicHeuristic is an adjective for experience-based techniques that help in problem solving, learning and discovery. A heuristic method is particularly used to rapidly come to a solution that is hoped to be close to the best possible answer, or 'optimal solution'...
Viewpoint Concerning the Production and Transformation of
LightLight is electromagnetic radiation, particularly radiation of a wavelength that is visible to the human eye ....
", proposed the idea of
energy quanta. This idea, motivated by
Max PlanckMax Planck was a German physicist. He is considered to be the founder of the quantum theory, and thus one of the most important physicists of the twentieth century. Planck was awarded the Nobel Prize in Physics in 1918.-Biography:Planck came from a traditional, intellectual family...
's earlier derivation of the law of
black bodyIn physics, a black body is an idealized object that absorbs all electromagnetic radiation that falls on it. No electromagnetic radiation passes through it and none is reflected. Because no light is reflected or transmitted, the object appears black when it is cold. However, a black body emits a...
radiationElectromagnetic radiation is a ubiquitous phenomenon that takes the form of self-propagating waves in a vacuum or in matter. It consists of electric and magnetic field components which oscillate in phase perpendicular to each other and perpendicular to the direction of energy propagation...
, assumes that
luminous energyIn photometry, luminous energy is the perceived energy of light. This is sometimes also called the quantity of light.Luminous energy is not the same as the radiant energy, the corresponding objective physical quantity. This is because the human eye can only see light in the visible spectrum and has...
can be absorbed or emitted only in discrete amounts, called
quantaIn physics, a quantum is the minimum unit of any physical entity involved in an interaction. An example of an entity that is quantized is the energy transfer of elementary particles of matter and of photons and other bosons...
. Einstein states,
- Energy, during the propagation of a ray of light
Light is electromagnetic radiation, particularly radiation of a wavelength that is visible to the human eye ....
, is not continuously distributed over steadily increasing spaces, but it consists of a finite number of energy quantaIn physics, a photon is an elementary particle, the quantum of the electromagnetic field and the basic "unit" of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
localised at points in spaceIn geometry, topology and related branches of mathematics a spatial point describes a specific object within a given space that consists of neither volume, area, length, nor any other higher dimensional analogue. Thus, a point is a 0-dimensional object...
, moving without dividing and capable of being absorbed or generated only as entitiesAn entity is something that has a distinct, separate existence, though it need not be a material existence. In particular, abstractions and legal fictions are usually regarded as entities. In general, there is also no presumption that an entity is animate...
.
In explaining the
photoelectric effectThe photoelectric effect is a phenomenon in which electrons are emitted from matter as a consequence of their absorption of energy from electromagnetic radiation of very short wavelength, such as visible or ultraviolet light. Electrons emitted in this manner may be referred to as "photoelectrons"...
, the hypothesis that
energyIn physics, energy is a scalar physical quantity that describes the amount of work that can be performed by a force, an attribute of objects and systems that is subject to a conservation law...
consists of
discrete packets, as Einstein illustrates, can be directly applied to
black bodiesIn physics, a black body is an idealized object that absorbs all electromagnetic radiation that falls on it. No electromagnetic radiation passes through it and none is reflected. Because no light is reflected or transmitted, the object appears black when it is cold. However, a black body emits a...
, as well.
The idea of light quanta contradicts the wave theory of light that follows naturally from
James Clerk MaxwellJames Clerk Maxwell was a Scottish theoretical physicist and mathematician. His most significant achievement was the development of the classical electromagnetic theory, synthesizing all previous unrelated observations, experiments and equations of electricity, magnetism and even optics into a...
's equations for
electromagneticElectromagnetism is the physics of the electromagnetic field, a field that exerts a force on particles with the property of electric charge and is reciprocally affected by the presence and motion of such particles....
behavior and, more generally, the assumption of
infinite divisibilityThe concept of infinite divisibility arises in different ways in philosophy, physics, economics, order theory , and probability theory...
of energy in physical systems.
- A profound formal difference exists between the theoretical concepts that physicists have formed about gases and other ponderable bodies, and Maxwell's theory of electromagnetic processes in so-called empty space. While we consider the state of a body to be completely determined by the positions and velocities of an indeed very large yet finite number of atoms and electrons, we make use of continuous spatial functions to determine the electromagnetic state of a volume of space, so that a finite number of quantities cannot be considered as sufficient for the complete determination of the electromagnetic state of space.
- [... this] leads to contradictions when applied to the phenomena of emission and transformation of light.
- According to the view that the incident light consists of energy quanta [...], the production of cathode rays by light can be conceived in the following way. The body's surface layer is penetrated by energy quanta whose energy is converted at least partially into kinetic energy of the electrons. The simplest conception is that a light quantum transfers its entire energy to a single electron [...]
Einstein noted that the photoelectric effect depended on the wavelength, and hence the frequency of the light. At too low a frequency, even intense light produced no electrons. However, once a certain frequency was reached, even low intensity light produced electrons. He compared this to Planck's hypothesis that light could be emitted only in packets of energy given by
hf, where
h is Planck's constant and
f is the frequency. He then postulated that light travels in packets whose energy depends on the frequency, and therefore only light above a certain frequency would bring sufficient energy to liberate an electron.
Even after experiments confirmed that Einstein's equations for the
photoelectric effectThe photoelectric effect is a phenomenon in which electrons are emitted from matter as a consequence of their absorption of energy from electromagnetic radiation of very short wavelength, such as visible or ultraviolet light. Electrons emitted in this manner may be referred to as "photoelectrons"...
were accurate, his explanation was not universally accepted.
Niels BohrNiels Henrik David Bohr was a Danish physicist who made fundamental contributions to understanding atomic structure and quantum mechanics, for which he received the Nobel Prize in Physics in 1922. Bohr mentored and collaborated with many of the top physicists of the century at his institute in...
, in his 1922 Nobel address, stated, "The hypothesis of light-quanta is not able to throw light on the nature of radiation."
By 1921, when Einstein was awarded the Nobel Prize and his work on photoelectricity was mentioned by name in the award citation, some physicists accepted that the equation was correct and light quanta were possible. In 1923,
Arthur ComptonArthur Holly Compton was an American physicist and Nobel laureate in physics for his discovery of the Compton effect. He served as Chancellor of Washington University in St. Louis from 1945 to 1953.-Early years:...
's
X-ray scattering experimentIn physics, Compton scattering or the Compton effect is the decrease in energy of an X-ray or gamma ray photon, when it interacts with matter. Because of the change in photon energy, it is an inelastic scattering process. Inverse Compton scattering also exists, where the photon gains energy upon...
helped more of the scientific community to accept this formula. The theory of light quanta was a strong indicator of wave-particle duality, a fundamental principle of
quantum mechanicsQuantum mechanics is a set of principles describing the physical reality at the atomic level of matter and the subatomic . These descriptions include the simultaneous wave-like and particle-like behavior of both matter and radiation...
. A complete picture of the theory of photoelectricity was realized after the maturity of quantum mechanics.
Brownian motion
The article "Über die von der molekularkinetischen Theorie der Wärme geforderte Bewegung von in ruhenden Flüssigkeiten suspendierten Teilchen" ("On the Motion of Small Particles Suspended in a Stationary Liquid, as Required by the Molecular Kinetic Theory of Heat") delineated a
stochasticStochastic means random.A stochastic process is one whose behavior is non-deterministic in that a system's subsequent state is determined both by the process's predictable actions and by a random element....
model of
Brownian motionBrownian motion is the seemingly random movement of particles suspended in a fluid or the mathematical model used to describe such random movements, often called a particle theory....
.
- In this paper it will be shown that, according to the molecular kinetic theory of heat, bodies of a microscopically visible size suspended in liquids must, as a result of thermal molecular motions, perform motions of such magnitudes that they can be easily observed with a microscope. It is possible that the motions to be discussed here are identical with so-called Brownian molecular motion; however, the data available to me on the latter are so imprecise that I could not form a judgment on the question ...
Brownian motion generates expressions for the
root mean squareIn mathematics, the root mean square , also known as the quadratic mean, is a statistical measure of the magnitude of a varying quantity. It is especially useful when variates are positive and negative, e.g., sinusoids....
displacementIn physics, displacement is the vector that specifies the change in position of a point or a particle in reference to a previous position. When the previous point is the origin, this is better referred to as a position....
of particles. Using the kinetic theory of fluids, which at the time was controversial, the article established the phenomenon, which was lacking a satisfactory explanation even decades after the first observation, provided empirical evidence for the reality of the
atomThe atom is a basic unit of matter consisting of a dense, central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...
. It also lent credence to
statistical mechanicsStatistical mechanics is the application of probability theory, which includes mathematical tools for dealing with large populations, to the field of mechanics, which is concerned with the motion of particles or objects when subjected to a force...
, which had been controversial at that time, as well. Before this paper, atoms were recognized as a useful concept, but physicists and chemists 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 OstwaldFriedrich Wilhelm Ostwald was a Baltic German chemist. He received the Nobel Prize in Chemistry in 1909 for his work on catalysis, chemical equilibria and reaction velocities...
, one of the leaders of the anti-atom school, later told
Arnold SommerfeldArnold Johannes Wilhelm Sommerfeld was a German theoretical physicist who pioneered developments in atomic and quantum physics, and also educated and groomed a large number of students for the new era of theoretical physics...
that he had been convinced of the existence of atoms by Einstein's complete explanation of Brownian motion.
Special relativity
Einstein's "On the Electrodynamics of Moving Bodies", his third paper that year, was published on June 30. It reconciles
Maxwell's equationsMaxwell's equations are a set of four partial differential equations that relate the electric and magnetic fields to their sources, charge density and current density. These equations can be combined to show that light is an electromagnetic wave...
for electricity and magnetism with the laws of mechanics, by introducing major changes to mechanics close to the
speed of lightIn physics, the speed of light is a physical constant, the speed at which electromagnetic radiation, such as light, travels in free space . Its value is 299,792,458 metres per second...
. This later became known as Einstein's special theory of relativity.
The paper mentions the name of only five other scientists,
Isaac NewtonSir Isaac Newton FRS was an English physicist, mathematician, astronomer, natural philosopher, alchemist, and theologian who is perceived and considered by a substantial number of scholars and the general public as one of the most influential men in history...
,
James Clerk MaxwellJames Clerk Maxwell was a Scottish theoretical physicist and mathematician. His most significant achievement was the development of the classical electromagnetic theory, synthesizing all previous unrelated observations, experiments and equations of electricity, magnetism and even optics into a...
, Heinrich Hertz,
Christian DopplerChristian Andreas Doppler was an Austrian mathematician and physicist. He is most famous for what is now called the Doppler effect, which is the apparent change in frequency and wavelength of a wave as perceived by an observer moving relative to the wave's source.- Life and work :Christian...
, and
Hendrik LorentzHendrik Antoon Lorentz was a Dutch physicist who shared the 1902 Nobel Prize in Physics with Pieter Zeeman for the discovery and theoretical explanation of the Zeeman effect...
. It does not have any references to any other publications. Many of the ideas had already been published by others, as detailed in
History of special relativityThe history of special relativity consists of many theoretical results and empirical findings obtained by Albert Michelson, Hendrik Lorentz, Henri Poincaré and others...
. However, Einstein's paper introduces a radical new theory of time, distance, mass, and energy that was consistent with
electromagnetismElectromagnetism is the physics of the electromagnetic field, a field that exerts a force on particles with the property of electric charge and is reciprocally affected by the presence and motion of such particles....
, but omitted the force of gravity.
At the time, it was known that Maxwell's equations, when applied to moving bodies, led to asymmetries, and that it had not been possible to discover any motion of the Earth relative to the 'light medium'. Einstein puts forward two postulates to explain these observations. First, he applies the classic principle of relativity, which states that the laws of physics remain the same for any non-accelerating
frame of referenceA frame of reference in physics, may refer to a coordinate system or set of axes within which to measure the position, orientation, and other properties of objects in it, or it may refer to an observational reference frame tied to the state of motion of an observer.It may also refer to both an...
(called an inertial reference frame), to the laws of electrodynamics and
opticsOptics is the branch of physics which studies the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light...
as well as mechanics. In the second postulate, Einstein proposes that the speed of light has the same value in all inertial frames of reference, independent of the state of motion of the emitting body.
Special relativity is thus consistent with the result of the
Michelson-Morley experimentThe Michelson–Morley experiment was performed in 1887 by Albert Michelson and Edward Morley at what is now Case Western Reserve University. It is generally considered to be the first strong evidence against the theory of a luminiferous aether...
, which had not detected a
mediumA transmission medium is a material substance which can propagate energy waves. For example, the transmission medium for sound received by the ears is usually air, but solids and liquids may also act as transmission media for sound.The absence of a material medium can also be thought of as a...
of conductance (or
aetherIn the late 19th century, "luminiferous aether" , meaning light-bearing aether, was the term used to describe a medium for the propagation of light. The word aether stems via Latin from the Greek αιθήρ, from a root meaning to kindle, burn, or shine...
) for light waves unlike other known
waveA wave is a disturbance that propagates through space and time, usually with transference of energy. A mechanical wave is a wave that propagates or travels through a medium due to the restoring forces it produces upon deformation. There also exist waves capable of traveling through a vacuum,...
s that require a medium (such as
waterWater is an ubiquitous chemical substance that is composed of hydrogen and oxygen and is essential for all known forms of life.In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71%...
or air). Einstein states,
- … the unsuccessful attempts to discover any motion of the earth relatively to the "light medium
In the late 19th century, "luminiferous aether" , meaning light-bearing aether, was the term used to describe a medium for the propagation of light. The word aether stems via Latin from the Greek αιθήρ, from a root meaning to kindle, burn, or shine...
," suggest that the phenomena of electrodynamics as well as of mechanicsMechanics is the branch of physics concerned with the behaviour of physical bodies when subjected to forces or displacements, and the subsequent effect of the bodies on their environment....
possess no properties corresponding to the idea of absolute restRest in physics refers to an object being stationary relative to a particular frame of reference or another object. According to the theory of relativity it is said that an object is: at rest relative to another. For example, a train decelerates on approach to a station and eventually stops...
.
The speed of light is fixed, and thus
not relative to the movement of the observer. This was impossible under
NewtonianSir Isaac Newton FRS was an English physicist, mathematician, astronomer, natural philosopher, alchemist, and theologian who is perceived and considered by a substantial number of scholars and the general public as one of the most influential men in history...
classical mechanicsIn the fields of physics, classical mechanics is one of the two major sub-fields of study in the science of mechanics, which is concerned with the set of physical laws governing and mathematically describing the motions of bodies and aggregates of bodies geometrically distributed within a certain...
. Einstein argues,
- … the same laws of electrodynamics and optic
Optic may mean:* optic, a British term for a device for dispensing fixed amounts of alcoholic spirits* Optics, the study of the behavior and properties of light...
s will be valid for all frames of reference for which the equationAn equation is a mathematical statement, in symbols, that two things are exactly the same . Equations are written with an equal sign, as in...
s of mechanics hold good. We will raise this conjectureA conjecture is a proposition which is presumed to be real, true, or genuine, mostly based on inconclusive grounds. Karl Popper pioneered the use of the term "conjecture" in scientific philosophy. Conjecture is contrasted by hypothesis , which is a testable statement based on accepted grounds...
(the purport of which will hereafter be called the "Principle of Relativity") to the status of a postulate, and also introduce another postulate, which is only apparently irreconcilable with the former, namely, that light is always propagated in empty space with a definite velocityIn physics, velocity is the rate of change of position. It is a vector physical quantity; both speed and direction are required to define it. In the SI system, it is measured in meters per second: or ms-1. The scalar absolute value of velocity is speed...
c which is independentThe terms "dependent variable" and "independent variable" are used in similar but subtly different ways in mathematics and statistics as part of the standard terminology in those subjects...
of the state of motion of the emittingAn emitter may be:-In general:*A device used to exude any signal, beacon, light, odor, liquid, fragrance, or any other type of signal....-In electronics and instrument physics:...
body. These two postulates suffice for the attainment of a simple and consistent theory of the electrodynamics of moving bodies based on Maxwell's theory for stationary bodies. The introduction of a "luminiferous etherIn the late 19th century, "luminiferous aether" , meaning light-bearing aether, was the term used to describe a medium for the propagation of light. The word aether stems via Latin from the Greek αιθήρ, from a root meaning to kindle, burn, or shine...
" will prove to be superfluous in as much as the view here to be developed will not require an "absolutely stationary space" provided with special properties, nor assign a velocity-vector to a point of the empty space in which electromagnetic processes take place.
- The theory […] is based—like all electrodynamics—on the kinematics
Kinematics is the branch of classical mechanics that describes the motion of objects without consideration of the causes leading to the motion....
of the rigid bodyIn physics, a rigid body is an idealization of a solid body of finite size in which deformation is neglected. In other words, the distance between any two given points of a rigid body remains constant in time regardless of external forces exerted on it...
, since the assertions of any such theory have to do with the relationships between rigid bodies (systems of co-ordinate- Configuration space in physics :In classical mechanics, the configuration space is the space of possible positions that a physical system may attain, possibly subject to external constraints...
s), clockA clock is an instrument used to indicate, measure, keep, and co-ordinate time. The word clock is derived ultimately from the Celtic words clagan and clocca meaning "bell"...
s, and electromagnetic processesElectromagnetism is the physics of the electromagnetic field, a field that exerts a force on particles with the property of electric charge and is reciprocally affected by the presence and motion of such particles....
. Insufficient consideration of this circumstance lies at the root of the difficulties which the electrodynamics of moving bodies at present encounters.
It had previously been conjectured, by
George FitzGeraldGeorge Francis FitzGerald was an Irish professor of "natural and experimental philosophy" at Trinity College, Dublin, in the late 19th century....
in 1894 and by Lorentz 1895, independent of each other, that the Michelson-Morley result could be accounted for if moving bodies were contracted in the direction of their motion. Some of the paper's core equations, the
Lorentz transformsIn physics, the Lorentz transformation describes how, according to the theory of special relativity, two observers' varying measurements of space and time can be converted into each other's frame of reference. It reflects the surprising fact that observers moving at different velocities report...
, had been published by
Joseph LarmorSir Joseph Larmor , a physicist and mathematician who made innovations in the understanding of electricity, dynamics, thermodynamics, and the electron theory of matter...
(1897, 1900),
Hendrik LorentzHendrik Antoon Lorentz was a Dutch physicist who shared the 1902 Nobel Prize in Physics with Pieter Zeeman for the discovery and theoretical explanation of the Zeeman effect...
(1899, 1903, 1904) and
Henri PoincaréJules Henri Poincaré was a French mathematician and theoretical physicist, and a philosopher of science...
(1905), in a development of Lorentz's 1904 paper. Einstein revealed the underlying causes for this geometrical oddity, which differed from the explanations given by FitzGerald, Larmor, and Lorentz, but were similar in many respects to the reasons given by Poincaré (1905).
His explanation arises from two axioms. First,
Galileo'sGalileo Galilei was an Italian physicist, mathematician, astronomer, and philosopher who played a major role in the Scientific Revolution. His achievements include improvements to the telescope and consequent astronomical observations, and support for Copernicanism...
idea that the laws of nature should be the same for all observers that move with constant speed relative to each other. Einstein writes,
- The laws by which the states of physical systems undergo change are not affected, whether these changes of state be referred to the one or the other of two systems of co-ordinates in uniform translatory motion.
The second is the rule that the
speed of lightIn physics, the speed of light is a physical constant, the speed at which electromagnetic radiation, such as light, travels in free space . Its value is 299,792,458 metres per second...
is the same for every observer.
- Any ray of light moves in the "stationary" system of co-ordinates with the determined velocity c, whether the ray be emitted by a stationary or by a moving body.
The theory, now called the
special theory of relativitySpecial relativity is the physical theory of measurement in inertial frames of reference proposed in 1905 by Albert Einstein in the paper "On the Electrodynamics of Moving Bodies"...
, distinguishes it from his later
general theory of relativityGeneral relativity or the general theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the current description of gravitation in modern physics. It unifies special relativity and Newton's law of universal gravitation, and describes gravity as a...
, which considers all observers to be equivalent. Special relativity gained widespread acceptance remarkably quickly, confirming Einstein's comment that it had been "ripe for discovery" in 1905. Acknowledging the role of Max Planck in the early dissemination of his ideas, Einstein wrote in 1913 "The attention that this theory so quickly received from colleagues is surely to be ascribed in large part to the resoluteness and warmth with which he [Planck] intervened for this theory". In addition, the improved mathematical formulation of the theory by
Hermann MinkowskiHermann Minkowski was a German mathematician of Polish Jewish descent, who created and developed the geometry of numbers and who used geometrical methods to solve difficult problems in number theory, mathematical physics, and the theory of relativity.- Life and work :Hermann Minkowski was born in...
in 1907 was influential in gaining acceptance for the theory. Also, and most importantly, the theory was supported by an ever-increasing body of confirmatory experimental evidence.
Matter and energy equivalence
On September 27
Annalen der Physik published a fourth paper, "Does the Inertia of a Body Depend Upon Its Energy Content?", in which Einstein developed an argument for arguably the most famous equation in the field of physics:
E = mc²In physics, mass–energy equivalence is the concept that the mass of a body is a measure of its energy content. The mass of a body as measured on a scale is always equal to the total energy inside, multiplied by a constant c
2 that changes the units appropriately:where E is energy, m is...
. Einstein considered the equivalency equation to be of paramount importance because it showed that a massive particle possesses an energy, the "rest energy", distinct from its classical
kineticThe kinetic energy of an object is the extra energy which it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its current velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its...
and
potential energiesPotential energy is energy stored within a physical system as a result of the position or configuration of the different parts of that system. It is called potential energy because it has the potential to be converted into other forms of energy, such as kinetic energy, and to do work in the process...
.
The paper is based on
James Clerk MaxwellJames Clerk Maxwell was a Scottish theoretical physicist and mathematician. His most significant achievement was the development of the classical electromagnetic theory, synthesizing all previous unrelated observations, experiments and equations of electricity, magnetism and even optics into a...
's and
Heinrich Rudolf HertzHeinrich Rudolf Hertz was a German physicist who clarified and expanded the electromagnetic theory of light that had been put forth by Maxwell...
's investigations and, in addition, the
axiomIn traditional logic, an axiom or postulate is a proposition that is not proved or demonstrated but considered to be either self-evident, or subject to necessary decision...
s of relativity, as Einstein states,
- The results of the previous investigation lead to a very interesting conclusion, which is here to be deduced.
- The previous investigation was based "on the Maxwell-Hertz equations
Maxwell's equations are a set of four partial differential equations that relate the electric and magnetic fields to their sources, charge density and current density. These equations can be combined to show that light is an electromagnetic wave...
for empty space, together with the Maxwellian expression for the electromagnetic energy of space ..."
- The laws by which the states of physical systems alter are independent of the alternative, to which of two systems of coordinates, in uniform motion of parallel translation relatively to each other, these alterations of state are referred (principle of relativity).
The equation sets forth that
energyIn physics, energy is a scalar physical quantity that describes the amount of work that can be performed by a force, an attribute of objects and systems that is subject to a conservation law...
of a body at rest (
E) equals its mass (
m) times the speed of light (
c) squared, or
E = mc².
- If a body gives off the energy L in the form of radiation, its mass diminishes by L/c². The fact that the energy withdrawn from the body becomes energy of radiation evidently makes no difference, so that we are led to the more general conclusion that
- The mass of a body is a measure of its energy-content; if the energy changes by L, the mass changes in the same sense by L/9 × 1020, the energy being measured in ergs, and the mass in grammes.
- [...]
- If the theory corresponds to the facts, radiation conveys inertia between the emitting
An emitter may be:-In general:*A device used to exude any signal, beacon, light, odor, liquid, fragrance, or any other type of signal....-In electronics and instrument physics:...
and absorbing bodiesIn high energy physics experiments, an absorber is a block of material used to absorb some of the energy of an incident particle. Absorbers can be made of a variety of materials, depending on the purpose; lead and liquid hydrogen are common choices....
.
The
mass-energy relationIn physics, mass–energy equivalence is the concept that the mass of a body is a measure of its energy content. The mass of a body as measured on a scale is always equal to the total energy inside, multiplied by a constant c
2 that changes the units appropriately:where E is energy, m is...
can be used to predict how much energy will be released or consumed by nuclear reactions; one simply measures the mass of all constituents and products and multiplies the difference by
c2. The result shows how much energy will be released or consumed, usually in the form of
lightElectromagnetic radiation is a ubiquitous phenomenon that takes the form of self-propagating waves in a vacuum or in matter. It consists of electric and magnetic field components which oscillate in phase perpendicular to each other and perpendicular to the direction of energy propagation...
or
heatIn physics and thermodynamics, heat is the process of energy transfer from one body or system due to thermal contact, which in turn is defined as an energy transfer to a body in any other way than due to work performed on the body....
. When applied to certain nuclear reactions, the equation shows that an extraordinarily large amount of energy will be released, much larger than in the combustion of chemical explosives, where the mass difference is hardly measurable at all. This explains why nuclear weapons produce such phenomenal amounts of energy, as they release
binding energyBinding energy is the mechanical energy required to disassemble a whole into separate parts. A bound system has typically a lower potential energy than its constituent parts; this is what keeps the system together...
during
nuclear fissionIn nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts, often producing free neutrons and lighter nuclei, which may eventually produce photons...
and
nuclear fusionIn nuclear physics and nuclear chemistry, nuclear fusion is the process by which multiple like-charged atomic nuclei join together to form a heavier nucleus...
, and also convert a much larger portion of subatomic mass to energy.
Commemoration
The International Union of Pure and Applied Physics (IUPAP) resolved to commemorate the 100th year of the publication of Einstein's extensive work in 1905 as the '
World Year of Physics 2005The year 2005 has been named the World Year of Physics in recognition of the 100th anniversary of Albert Einstein's "Miracle Year," in which he published four landmark papers, and the subsequent advances in the field of physics.-History:...
'. This was subsequently endorsed by both the
United NationsThe United Nations is an international organization whose stated aims are facilitating cooperation in international law, international security, economic development, social progress, human rights, and the achieving of world peace...
and the
United States CongressThe United States Congress is the bicameral legislature of the federal government of the United States of America, consisting of two houses, the Senate and the House of Representatives. Both senators and representatives are chosen through direct election....
.
Further reading
- Stachel, John, et al., Einstein's Miraculous Year. Princeton University Press, 1998. ISBN 0-691-05938-1
- Renn, Jürgen, and Dieter Hoffmann, "1905 — a miraculous year". 2005 J. Phys. B: At. Mol. Opt. Phys. 38 S437-S448 (Max Planck Institute for the History of Science) [Issue 9 (14 May 2005)]
External links
- Einstein's Annus Mirabilis 1905 - collection at Johns Hopkins University
The Johns Hopkins University, commonly referred to as Johns Hopkins, JHU, or simply Hopkins, is a private research university located in Baltimore, Maryland, United States. Johns Hopkins also maintains full-time campuses elsewhere in Maryland, Washington, D.C., Italy, China, and Singapore...