Everything about History Of Physics totally explained
Since antiquity, human beings have sought to understand the workings of nature: why unsupported objects drop to the ground, why different
materials have different properties, the character of the
universe such as the form of the
Earth and the behavior of celestial objects such as the
Sun and the
Moon, and so forth. Typically the behavior and nature of the world was explained by invoking the actions of
gods. Eventually explanations were proposed based on
philosophical speculation. Rarely verified by systematic
experimental testing, many of them were wrong, but this is part of the
dialectical nature of scientific inquiry, and even modern theories of
quantum mechanics and
relativity are merely considered "theories that have not been broken yet".
The growth of
physics has brought not only fundamental changes in ideas about the
material world,
mathematics and
philosophy, but also, through
technology, a transformation of
society. Physics is considered both a body of knowledge and the practice that makes and transmits it. The
Scientific Revolution, beginning about year
1543, is a convenient boundary between ancient thought and classical physics. The emergence of physics as a science distinct from
natural philosophy began with the
scientific revolution of the 16th and 17th centuries, and continued through the dawn of modern physics in the early 20th century. The year
1900 marks the beginnings of a more modern physics. Today, the
science shows no sign of completion, as more issues are raised, with questions rising from the
age of the universe, to the nature of the
vacuum, to the ultimate nature of the properties of
subatomic particles.
Partial theories are currently the best that physics has to offer, at the present time. The list of
unsolved problems in physics is large.
Early cultures
Inquiry into natural phenomenon can be traced back to earliest of human cultures. The first written records come from the Babylonian, which made detailed observations in astronomy. The first evidence of recognition that astronomical phenomena are periodic and of the application of mathematics to their prediction is Babylonian. Tablets dating back to the
Old Babylonian period document the application of mathematics to the variation in the length of daylight over a solar year. Centuries of Babylonian observations of celestial phenomena are recorded in the series of
cuneiform tablets known as the
Enūma Anu Enlil..
Babylonian astronomy was the basis for much of what was done in Greece, in India, in Sassanian Iran, in Byzantium, in Syria, in Islam, in Central Asia, and in Western Europe.
Further investigations into early ideas in physics began with eminent
Greek pre-Socratic philosophers such as
Thales,
Anaximander, possibly
Pythagoras,
Heraclitus,
Anaxagoras,
Empedocles and
Philolaus, many of whom were involved in various schools. For example, Anaximander and Thales belonged to the
Milesian school.
Plato, briefly and
Aristotle at length, continued these studies of nature in their works, the earliest surviving complete treatises dealing with
natural philosophy.
Democritus, a contemporary, was of the school of
Atomists who attempted to characterize the nature of matter. Similar atomic philosophy would develop in ancient india. Due to the absence of advanced experimental equipment such as
telescopes and accurate time-keeping devices, experimental testing of physical hypotheses was impossible or impractical. There were exceptions and there are
anachronisms. Greek thinkers like Archimedes proposed calculating the volume of objects like
spheres and
cones by dividing them into very thin disks and adding up the volume of each disk, using methods resembling
integral calculus. It was also
Archimedes who derived many correct quantitative descriptions of mechanics and also hydrostatics when, so the story goes, he noticed that his own body displaced a volume of water while he was getting into a bath one day. In doing so
Archimedes would be the first to uncover a
law of nature. Another remarkable example was that of
Eratosthenes, who deduced that the
Earth was a sphere, and accurately calculated its circumference using the shadows of vertical sticks to measure the angle between two widely separated points on the Earth's surface.
Modern knowledge of many early ideas in physics, and the extent to which they were experimentally tested, is unknown. Almost all direct record of these ideas was lost when the
Library of Alexandria was destroyed, around
400 AD. Perhaps the most remarkable idea we know of from this era was the deduction by
Aristarchus of Samos that the Earth was a planet that traveled around the Sun once a year, and rotated on its axis once a day (accounting for the seasons and the cycle of day and night), and that the stars were other, very distant suns which also had their own accompanying planets (and possibly, lifeforms upon those planets).
The discovery of the
Antikythera mechanism, which is considered to be the earliest
analog computer, points to a detailed understanding of movements of these astronomical objects, as well as a use of
gear-trains that pre-dates any other known civilization's use of gears, except that of
ancient China.
An early version of the steam engine,
Hero's aeolipile was only a curiosity which didn't solve the problem of transforming its rotational energy into a more usable form, not even by gears. The
Archimedes screw is still in use today, to lift water from rivers onto irrigated farmland. The simple machines were unremarked, with the exception (at least) of Archimedes' elegant proof of the law of the
lever. Ramps were in use several millennia before Archimedes, to build the Pyramids.
A particularly important ancient contribution that would allow physics to develop into a science came from Indian. It was the introduction of the
Hindu-Arabic numerals. Modern physics can hardly be imagined without a system of arithmetic in which simple calculation is easy enough to make large calculations even possible. The modern
positional numeral system (the
Hindu-Arabic numeral system) and the number
zero were first developed in India.
Physics in the Middle Ages
Islamic world
Like the later
Scientific revolution in the
West, Islamic science was built on a foundation laid in antiquity, in this case, the intellectual patrimony of the
Byzantines,
Persians and
Indians they conquered. The Arab and Persian scholars of the
Islamic Golden Age made advances by building on previous work in astronomy, mathematics, and physics while developing new fields like
alchemy.
The most important scientific development during the
Middle Ages was the pioneering development of the
experimental
scientific method by
Ibn al-Haytham (commonly Latinized
Alhazen,
ca. 965–1040), as recorded in his
Book of Optics. Alhazen, who is regarded as the father of
optics and the pioneer of the
scientific method, developed a broad theory that explained vision, using
geometry and
anatomy, which stated that each point on an illuminated area or object radiates light rays in every direction, but that only one ray from each point, which strikes the eye perpendicularly, can be seen. The other rays strike at different angles and are not seen. He built a
camera obscura and used the example of the
pinhole camera, which produces an inverted image, to support his argument. This contradicted
Ptolemy's
emission theory of vision that objects are seen by rays of light emanating from the eyes. Alhazen held light rays to be streams of minute particles that travelled at a finite speed. He improved Ptolemy's theory of the
refraction of light, and went on to discover the
law of refraction. He also carried out the first experiments on the dispersion of light into its constituent colors. His major work
Book of Optics was translated into
Latin in the
Middle Ages, as well as his book dealing with the colors of sunset. He dealt at length with the theory of various physical phenomena like shadows, eclipses, and the rainbow. He also attempted to explain binocular vision and the
moon illusion. Through these extensive researches on optics, he's considered the father of modern
optics. Alhazen also correctly argued that we see objects because the sun's rays of light, which he believed to be streams of tiny particles traveling in straight lines, are reflected from objects into our eyes. He understood that light must travel at a large but finite velocity, and that refraction is caused by the velocity being different in different substances. He also studied spherical and parabolic mirrors, and understood how refraction by a lens will allow images to be focused and magnification to take place. He understood mathematically why a spherical mirror produces aberration.
In the
mechanics field of
physics, the eldest
Banū Mūsā brother,
Muhammad ibn Musa, in his
Astral Motion and
The Force of Attraction, hypothesized that there was a
force of
attraction between heavenly bodies in the 9th century,
In the early 11th century,
Ibn al-Haytham discussed the theory of
attraction between
masses, and it seems that he was aware of the
magnitude of
acceleration due to
gravity. Ibn al-Haytham's contemporary,
Avicenna, discovered the concept of
momentum, when he referred to
impetus as being proportional to
weight times
velocity, a precursor to the concept of momentum in
Newton's second law of motion. He is thus considered the father of the fundamental concept of
momentum in
physics. Avempace's contemporary,
Hibat Allah Abu'l-Barakat al-Baghdaadi, was the first to negate
Aristotle's idea that a constant
force produces uniform
motion, and he instead argued that a force applied continuously produces
acceleration, an important concept in
classical mechanics. He described acceleration as the rate of change of
velocity. In 1121,
al-Khazini, in his treatise
The Book of the Balance of Wisdom, further elaborated an idea first proposed by the
Greeks that all bodies are attracted towards the
center of the earth.
Al-Khazini was also one of the first to clearly differentiate between
force,
mass, and
weight.
Medieval Europe
Following the collapse of the
Western Roman Empire, the knowledge of
classical antiquity was preserved in its monasteries, in the
Byzantine Empire, and in the
Islamic world. Works lost in Western Christendom but preserved in the Islamic world led
clerical scholars such as
Michael the Scot to learn Arabic in order to study them. Their
translations made available to medieval Europe not only the works of the ancients, but also contemporary work. Works both ancient and contemporary also became known in medieval Europe through such points of contact as the
Republic of Venice,
al-Andalus, and returning
Crusaders. By providing a locus for the exchange of ideas and scholarly collaboration, the birth of the
medieval university was key to the intellectual revitalization of Europe.
By the
13th century, precursors of the modern
scientific method can be seen on
Robert Grosseteste's emphasis on
mathematics as a way to understand nature and on the
empirical approach admired by
Roger Bacon.
Bacon conducted experiments into optics, although much of it was similar to what had been done and was being done at the time by Arab scholars. He did make a major contribution to the development of science in medieval Europe by writing to the
Pope to encourage the study of natural science in university courses and compiling several volumes recording the state of scientific knowledge in many fields at the time. He described the possible construction of a
telescope, but there's no strong evidence of his having made one. He recorded the manner in which he conducted his experiments in precise detail so that others could reproduce and independently test his results - a cornerstone of the
scientific method, and a continuation of the work of researchers like
Al Battani.
In the
14th century, some scholars, such as
Jean Buridan and
Nicole Oresme, started to question the received wisdom of
Aristotle's mechanics. In particular, Buridan developed the theory of
impetus which was the first step towards the modern concept of
inertia.
In his turn, Oresme showed that the reasons proposed by the physics of Aristotle against the movement of the earth were not valid and adduced the argument of simplicity for the theory that the earth moves, and
not the heavens. In the whole of his argument in favor of the earth's motion Oresme is both more explicit and much clearer than that given two centuries later by
Copernicus. He was also the first to assume that color and light are of the same nature and the discoverer of the curvature of light through
atmospheric refraction; even though, up to now, the credit for this latter achievement has been given to
Hooke.
In the 14th century Europe was rocked by the
Black Death which led to much social upheaval. In spite of this pause, the
15th century saw the artistic flourishing of the
Renaissance. The rediscovery of ancient texts was improved when many
Byzantine scholars had to seek refuge in the West after the
fall of Constantinople in
1453. Meanwhile, the invention of
printing was to make learning more accessible and allow a faster propagation of new ideas. All that paved the way to the
Scientific Revolution, which may also be understood as a resumption of the process of scientific change halted around the middle of the 14th century.
Early modern physics
The
early modern period is seen as a flowering of the
Renaissance, in what is often known as the "
Scientific Revolution", viewed as a foundation of
modern science. Historians like Howard Margolis hold that the Scientific Revolution began in
1543, when
Nicolaus Copernicus received the first copy of his
De Revolutionibus, printed in
Nuremberg (Nürnberg) by
Johannes Petreius. Most of its contents had been written years prior, but the publication had been delayed. Copernicus died soon after receiving the copy.
Further significant advances were made over the following century by
Galileo Galilei,
Christiaan Huygens,
Johannes Kepler, and
Blaise Pascal. During the early
seventeenth century, Galileo made extensive use of experimentation to validate physical theories, which is the key idea in the modern
scientific method. Galileo formulated and successfully tested several results in
dynamics, in particular the Law of
Inertia. In Galileo's
Two New Sciences, a dialogue between the characters Simplicio and Salviati discuss the motion of a ship (as a moving frame) and how that ship's cargo is indifferent to its motion. Huygens used the motion of a boat along a Dutch canal to illustrate an early form of the conservation of momentum.
The scientific revolution is considered to have culminated with the publication of the
Philosophiae Naturalis Principia Mathematica in
1687 by the mathematician, physicist, alchemist and inventor Sir
Isaac Newton (
1643-
1727). In
1687,
Newton published the
Principia, detailing two comprehensive and successful physical theories:
Newton's laws of motion, from which arise
classical mechanics; and
Newton's Law of Gravitation, which describes the
fundamental force of
gravity. Both theories agreed well with experiment. The Principia also included several theories in
fluid dynamics.
From the late
seventeenth century onward,
thermodynamics was developed by physicist and chemist
Boyle,
Young, and many others. In
1733,
Bernoulli used statistical arguments with classical mechanics to derive thermodynamic results, initiating the field of
statistical mechanics. In
1798,
Thompson demonstrated the conversion of mechanical work into heat, and in
1847 Joule stated the law of conservation of
energy, in the form of heat as well as mechanical energy.
Ludwig Boltzmann, in the nineteenth century, is responsible for the modern form of statistical mechanics.
Classical mechanics was re-formulated and extended by
Leonhard Euler, French mathematician
Joseph-Louis Comte de Lagrange, Irish mathematical physicist
William Rowan Hamilton, and others, who produced new results in mathematical physics. The law of universal gravitation initiated the field of
astrophysics, which describes
astronomical phenomena using physical theories. Newton's Law of gravitation also helped put
celestial mechanics on proper scientific and mathematical footing.
After Newton defined
classical mechanics, the next great field of inquiry within physics was the nature of
electricity. Observations in the
seventeenth and
eighteenth century by scientists such as
Robert Boyle,
Stephen Gray, and
Benjamin Franklin created a foundation for later work. These observations also established our basic understanding of electrical charge and
current.
By
1808 John Dalton had discovered that atoms of different elements have different weights and proposed the modern
theory of the atom.
It was
Hans Christian Ørsted who first proposed the connection between electricity and magnetism after observing the deflection of a compass needle by a nearby electric current. By the early 1830s
Michael Faraday had demonstrated that magnetic fields and electricity could generate each other. In
1864 James Clerk Maxwell presented to the
Royal Society a set of equations that described this relationship between electricity and magnetism.
Maxwell's equations also predicted correctly that
light is an
electromagnetic wave.
The Scientific Revolution began in the late 16th century with only a few researchers, and evolved into an enterprise which continues to the present day. Starting with astronomy, the principles of
natural philosophy] crystallized into fundamental
laws of physics which were enunciated and improved in the succeeding centuries. By the 19th century, the sciences had segmented into multiple fields with specialized researchers and the field of physics, although logically pre-eminent, no longer could claim sole ownership of the entire field of scientific research.
16th century
In the
16th century Nicolaus Copernicus revived
Aristarchus' heliocentric model of the
solar system in Europe (which survived primarily in a passing mention in
The Sand Reckoner of
Archimedes). When this model was published at the end of his life, it was with a preface by
Andreas Osiander that piously represented it as only a mathematical convenience for calculating the positions of planets, and not an account of the true nature of the planetary orbits.
In England
William Gilbert (1544-1603) studied
magnetism and
electricity, and published a seminal work,
De Magnete (1600), in which he thoroughly presented his numerous experimental results.
Gilbert who designed the
versorium: a device that detected the presence of statically charged objects.
17th century
In the early 17th century, the invention of the
telescope and
microscope, which is claimed to have been invented by three individuals (
Hans Lippershey,
Jacob Metius, and
Zacharias Jansen) would have profound implications on the history of
science, in particular
astronomy and
physics. In the early
17th century Johannes Kepler formulated a model of the solar system based upon the five
Platonic solids, in an attempt to explain why the orbits of the planets had the relative sizes they did. His access to extremely accurate astronomical observations by
Tycho Brahe enabled him to determine that his model was inconsistent with the observed orbits. After a heroic seven-year effort to more accurately model the motion
of the planet
Mars (during which he laid the foundations of modern
integral calculus) he concluded that the planets follow not circular orbits, but
elliptical orbits with the Sun at one focus of the ellipse. This breakthrough overturned a millennium of dogma based on
Ptolemy's idea of "perfect" circular orbits for the "perfect" heavenly bodies. Kepler then went on to formulate his
three laws of planetary motion. He also proposed the first known model of planetary motion in which a force emanating from the Sun deflects the planets from their "natural" motion, causing them to follow curved orbits.
In 1643,
Evangelista Torricelli invented the
barometer, which arose from solving an important practical problem. Torricelli discovered
Torricelli's Law, regarding the speed of a fluid flowing out of an opening, which was later shown to be a particular case of
Bernoulli's principle. Torecielli also devised an equation sometimes called
Torricelli's equation, which is used in the study of
kinematics.
In 1660,
Robert Hooke, an English scientist, formulated
Hooke's law of
elasticity, which describes the linear variation of
tension with extension in an elastic spring.
An important device, the
vernier, which allows the accurate mechanical measurement of angles and distances was invented by a Frenchman,
Pierre Vernier in
1631. It is in widespread use in scientific laboratories and machine shops to this day.
Otto von Guericke constructed the first air pump in
1650 and demonstrated the physics of the vacuum and atmospheric pressure using the
Magdeburg hemispheres. Later, he turned his interests to
static electricity, and he invented a mechanical device consisting of a sphere of sulfur that could be turned on a crank and repeatedly charged and discharged to produce electric sparks.
In
1656 the Dutch physicist and astronomer,
Christian Huygens invented a
mechanical clock using a
pendulum that swung through an elliptical arc, powered by a falling counterweight, to usher in the era of accurate timekeeping. Huygens also formulated Newton's second law of motion, but in quadratic form. Huygens greatest contribution comes from his early theory that light travels in waves (
Wave–particle duality), and for his development of
Huygens–Fresnel principle, along with French physicist
Augustin-Jean Fresnel. This mathematical principle provided a method of analysis that could be applied to problems of wave propagation, and it would have applications in the later development of
quantum mechanics.
The first quantitative estimate of the
speed of light was made in
1676 by
Ole Rømer, by timing the motions of Jupiter's satellite
Io with a telescope.
During the early
17th century,
Galileo Galilei made extensive use of experimentation to validate physical theories, which is the key idea in the
scientific method. Galileo's use of experiment, and the insistence of Galileo and Kepler that observational results must always take precedence over theoretical results (in which they followed the precepts of
Aristotle if not his practice), brushed away the acceptance of dogma, and gave birth to an era where scientific ideas were openly discussed and rigorously tested. Galileo formulated and successfully tested several results in
dynamics, including the correct law of accelerated motion, the parabolic trajectory, the relativity of unaccelerated motion, and an early form of the Law of
Inertia.
A French mathematician and scientist
Blaise Pascal invented the
hydraulic press, and an early
calculator. Pascal also formulated Pascal's law, which states that for all points at the same absolute height in a connected body of an incompressible fluid at rest, the fluid pressure is the same, even if additional pressure is applied on the fluid at some place. Pascal also wrote many important papers on the
scientific method.
René Descartes, French mathematician, philosopher, and natural scientist, invented analytic geometry, and discovered the law of conservation of momentum. He outlined his views on the universe in his
Principles of Philosophy.
In
1687,
Isaac Newton published the
Philosophiae Naturalis Principia Mathematica, detailing two comprehensive and successful physical theories:
Newton's laws of motion, from which arise
classical mechanics; and
Newton's Law of Gravitation, which describes the
fundamental force of
gravity. Newton's theory of gravity would be so successful that it would be used by
William Herschel a century later to discover a new planet in the
solar system,
Uranus. Both theories agreed well with experiment. The Law of Gravitation initiated the field of
astrophysics and
celestial mechanics, which describes
astronomical phenomena using physical theories. In the Principia Mathematica Newton also enunciated the principles of
conservation of momentum and the conservation of
angular momentum. Later on in life Newton would move on to formulate the
law of cooling and developed a theory of light based on his experiments with decomposing light through a
prism. Newton would also invent a
reflecting telescope and along with
Gottfried Leibniz would move on to independently of one another invent
calculus, which has many important applications in physics.
The 17th century would also witness the beginning of the
metric system, which would result in the formation of set of standards for weight and measurements. Early work in developing the metric system were pioneered by
John Wilkins,
Gabriel Mouton, and
Antoine Lavoisier among others.
18th century
From the
18th century onwards,
thermodynamic concepts were developed by
Robert Boyle,
Thomas Young, and many others, concurrently with the development of the steam engine, onward into the next century. In
1733,
Daniel Bernoulli used statistical arguments with classical mechanics to derive thermodynamic results, initiating the field of
statistical mechanics.
Bernoulli would also lay the foundation of
kinetic molecular theory in 1738, with the publication of
Hydrodynamica. In
Hydrodynamica,
Bernoulli would state that all gases consist of
molecules that are constantly in motion, moving in all directions, and impacting on surfaces. It was these movements and impacts that resulted in
pressure, and that
heat is the
kinetic energy of these moving molecules. Another pioneer of kinetic molecular theory during the 18th century was
Mikhail Lomonosov. Kinetic molecular theory would have wide ranging applications in physics, in particular
thermodynamics, and
chemistry.
Bernoulli would also move on to develop what become known as
Bernoulli's principle. It states that when an
ideal fluid that has no work acting on it, an increase in velocity will result in a simultaneous decrease in
pressure or a change in the fluids
gravitational potential energy. The principle plays a central role in
fluid dynamics and would have considerable impact on the development of
aerodynamics in the 19th and 20th century. During the beginning of the 18th century methods were slowly taking shape in order to provide a standard set of measures to determine
temperature. One set of measure was put forward by
Anders Celsius in
1742. A peculiarity of
Celsius scale was that melting point of an object was set at 0 degrees Celsius and wasn't until a famous
botanist,
Carl Linnaeus, would have the scale inverted to read
boiling point being at 100 degrees Celsius. Another method for determining
temperature was put forward by
Gabriel Fahrenheit, in
1724. Both methods are named after their respective originators and both are used interchangeably by scientists all over the world to the present date.
In
1746 an important step in the development of electricity was taken in the invention of the
Leyden jar, a capacitor, that could store and discharge electrical charge in a controlled way. In the 18th century many of the fundamental concepts about the nature of electricity were discovered. In 1733,
C. F. du Fay, discovered the existence of two types of electricity and named them "vitreous" and "resinous" (later known as positive and negative charge respectively).
William Watson, in 1747 discovered that a discharge of static electricity was equivalent to an electric current.
Charles Augustin de Coulomb formulated
Coulomb law, which gives the definition of the electrostatic force of attraction and repulsion. Nearing the 18th century
André-Marie Ampère discovered the relationship that relates the circulating magnetic field in a closed loop to the electric current passing through the loop.
Carl Friedrich Gauss would develop
Gauss's law which is used in the electrostatic application of the generalized
Gauss's theorem giving the equivalence relation between any flux, for example of liquids, electric or gravitational, flowing out of any closed surface and the result of inner sources and sinks, such as electric charges or masses enclosed within the closed surface. Nearing the end of the century the relationship that exists between magnetism and electricity continued to described which resulted in the formulation of the fundamental equation of the
Biot-Savart Law, which is an equation in electromagnetism that describes the magnetic field vector B in terms of the magnitude and direction of the source electric current, the distance from the source electric current, and the magnetic permeability weighting factor. In the mid 18th century
Henry Cavendish made important discoveries concerning
electricity. Among Cavendish's discoveries were the concept of
electric potential, an early unit of
capacitance, a formula for the
capacitance of a plate capacitor, concept of the
dielectric constant of a material, and Laws for the division of current in parallel circuits, now attributed to
Charles Wheatstone. Cavendish also devised a method that allowed for the first time in obtaining a numerical value for gravity. Benjamin Thompson]] demonstrated the conversion of unlimited mechanical work into heat. Other pioneers were
Robert Boyle, who in 1675 stated that electric attraction and repulsion can act across a vacuum;
Stephen Gray, who in 1729 classified materials as conductors and insulators and
Luigi Galvani discovered that muscle and nerve cells produce electricity.
Benjamin Franklin effectively used them (together with von Guericke's generator) in his researches into the nature of
electricity in
1752
In about
1788,
Joseph Louis Lagrange elaborated an important new formulation of mechanics using the
calculus of variations, the
principle of least action and the
Euler-Lagrange equations This led to the development of what is called
Lagrangian mechanics, which fuses classical mechanics with
conservation of momentum and
conservation of energy. The end of the 18th century would also witness a historic change as profound if not more than the
agricultural revolution. It began with the conversion of steam into mechanical energy, which would ultimately lead to the
industrial revolution. Various steam engines were developed from
Thomas Newcomen's to
James Watts steam engines. The
industrial revolution is significant in terms of physics because as various
steam engines were being developed there was a greater need to make them more powerful and
efficient. It was this quest to make
steam engines more efficient that would lead to the development of the branch of physics called
thermodynamics (
History of thermodynamics). It is the subsequent discoveries in thermodynamics that led to technological wonders such as the
internal combustion engine and other forms of
heat engines, which are used to power
airplanes,
automobiles,
locomotives, and all forms of mobile transport. The 18th century would witness an explosive growth of
mathematical physics, which would help formulation of theories that would come about in the 19th and 20th century. The most important work
mathematical physics came from the development of wave equations. These second-order linear
partial differential equation that describes the propagation of a variety of
waves, such as
sound waves,
light waves and
water waves. They are extensively used fields such as
acoustics,
electromagnetics, and
fluid dynamics. These equations were developed and studied by
Jean le Rond d'Alembert,
Leonhard Euler,
Daniel Bernoulli, and
Joseph-Louis Lagrange.
Modern physics
19th century
In a letter to the
Royal Society in
1800,
Alessandro Volta described his invention of the
electric battery, thus providing for the first time the means to generate a constant electric current, and opening up a new field of physics for investigation. In announcing his discovery of the pile, Volta paid tribute to the influences of
William Nicholson,
Tiberius Cavallo and
Abraham Bennet. Volta also studied what we now call capacitance, developing separate means to study both electrical potential V and charge Q, and discovering that for a given object they're proportional. This may be called Volta's Law of
Capacitance, and likely for this work the unit of electrical potential has been named the
volt.
The onset of 1800 also witnessed
William Herschel's discoverey of
infrared radiation by passing
sunlight through a
prism and holding a
thermometer just beyond the
red end of the
visible spectrum. This thermometer was meant to be a control to measure the ambient air temperature in the room. He was
shocked when it showed a higher temperature than the
visible spectrum. Further experimentation led to Herschel's conclusion that there must be an
invisible form of
light beyond the
visible spectrum.
Some of the most important experiments during the on set of the 19th century were performed by
Thomas Young.
Young would demonstrate the wave nature of
light and finally provide evidence to overturn a long held theory put forward by
Isaac Newton that light consisted of particles. With the ripple tank he demonstrated the idea of
interference in the context of water waves. With the two-slit, or double-slit experiment, he demonstrated interference in the context of light as a
wave. In the
two-slit experiment, c. 1801, Young passed a beam of light through two parallel slits in an opaque screen; on the other side was a white screen, where a pattern of alternating light and dark bands formed. This supported Young's contention that light is composed of waves. Young performed and analyzed a number of experiments, including interference of light from reflection off nearby pairs of micrometer grooves, from reflection off thin films of soap and oil, and from Newton's rings. He also performed two important diffraction experiments using fibers and long narrow strips. Within ten years, much of Young's work was reproduced and then extended by
Fresnel. In 1817, Young had proposed a small transverse component to light, while yet retaining a far larger longitudinal component.
Fresnel, by the year 1821, was able to show via mathematical methods that polarization could be explained only if light was entirely transverse, with no longitudinal vibration whatsoever.
By
1808 John Dalton's earlier ideas about the existence of
atoms of different weights and the
law of multiple proportions had led him to the modern
theory of the atom and many other theories used today in modern physics. The convergence of various estimates of
Avogadro's number lent decisive evidence for atomic theory.
In 1807
Thomas Young described the characterization of
elasticity that came to be known as
Young's modulus, denoted as E, in 1807, and further described it in his subsequent works such as his 1845 Course of Lectures on
Natural Philosophy and the Mechanical Arts, which is used to determine the stiffness of a material. In 1804 Young founded the theory of capillary phenomena on the principle of surface
tension. He also observed the constancy of the angle of contact of a liquid surface with a solid, and showed how from these two principles to deduce the phenomena of capillary action.
In 1822,
Claude-Louis Navier and
George Gabriel Stokes would publish a series of papers on equations that are central to
fluid dynamics and would later be called
navier-stokes equations. These set of equations describe the motion of fluid substances such as
liquids and gasses. The genius of these set of equations comes from their versatility in several varying branches of
science. They can be used to model
weather,
ocean currents, water flow in pipes, blood flow, flow around an
airfoil, motion of
stars inside a
galaxy, and when combined with
Maxwell's equations can be used to model
Magnetohydrodynamics. Therefore;
navier-stokes equations play a central role design of
aircraft,
cars,
power stations, and used in the analysis of the effects of
pollution. Claude-Louis Navier would move onto to form the general
theory of elasticity in 1821, and would eventually develop the
elastic modulus in 1826. It is for his work on the elastic modulus that Navier is often referred to as the founder of
structural analysis.
The
Coriolis effect was discovered by
Gaspard-Gustave Coriolis, in 1835.
Coriolis effect is an apparent deflection of moving objects from a straight path when they're viewed from a
rotating frame of reference. The mathematics used by
Coriolis to describe this phenomenon appeared in the
tidal equations of
Pierre-Simon Laplace in 1778. The effect has a wide varitey of applications in physics but play a particularly important role in
meteorology.
Although early investigations into a branch of physics called
thermodynamics were done by
Boyle,
Hooke, and
Guericke among others, the science didn't come into its own until the work of a young French physicist and military engineer called
Sadi Carnot. In 1824
Carnot published the
Reflections on the Motive Power of Fire, which is considered the founding paper in
thermodynamics. In this paper Carnot established a general theory of
heat engines. Carnot outlined the principles of what would later become known as the
Carnot cycle, the
Carnot heat engine,
Carnot theorem, and
thermodynamic efficiency, to name a few. This monumental work laid the foundations for the
first law of thermodynamics and the
second law of thermodynamics.
The behavior of
electricity and
magnetism was studied by
Michael Faraday,
Georg Ohm,
Hans Christian Ørsted, and others. Faraday, who began his career in chemistry working under
Humphry Davy at the Royal Institution, demonstrated that
electrostatic phenomena, the action of the newly discovered electric pile or
battery, electrochemical phenomena, and
lightning were all different manifestations of electrical phenomena.. Faraday further discovered in 1821 that electricity can cause rotational mechanical motion, and in 1831 discovered the principle of
electromagnetic induction, by which means a moving
magnet induces an
electrical current in a
conductor. Thus it was Faraday who laid the foundations for both the
electric motor and the
electric generator
James Clerk Maxwell built upon
Michael Faraday's physical conception of
electromagnetic fields with an interlinked set of twenty equations that explained the interactions between
electric and
magnetic fields and unified the two phenomena into a single theory of
electromagnetism.
Maxwell's equations were presented to the
Royal Society in
1864. These twenty equations were later reduced, using
vector calculus, to a set of four equations by
Oliver Heaviside. A prediction of
Maxwell's equations was that
light is an
electromagnetic wave. Confirmation of Maxwell's insight into electromagnetism was made with the observation, in
1888, and the discovery of
radio by
Heinrich Hertz and in
1895 when
Wilhelm Roentgen detected
X-rays. Aside from Maxwell's work in the electromagnetism, he'd also make important contributions to thermodynamics through a set of equations called
Maxwell Relations, which provide an experimental way in which to measure
entropy. Maxwell along with
Ludwig Boltzmann would establish
Maxwell–Boltzmann, which is a
probability distribution for molecular speeds in a gas.
In 1842, an
Austrian scientist by the name of
Christian Doppler would publish a paper on what would become known as the
Doppler effect. The summation of his work was an equation which described a change in
frequency and
wavelength of a
wave as perceived by an observer moving relative to the source of the waves. In 1848,
John Scott Russell conducted a series of experiments to verify some of the conclusions of the
Doppler effect. The equation has applications has applications in
astronomy, temperature measurement,
radar,
medical imaging, flow measurement, and underwater
acoustics.
Building upon the work of physicists before him a young German physicist by the name of
Gustav Kirchhoff, while still a student in 1845, would formulate
Kirchhoff's circuit laws, which are now used in all of
electrical engineering. In 1859 Kirchoff would proceed to explain what became known as
Kirchoff's law of thermal radiation, which provided a general statement about
emission and
absorption in heated objects. Later on in his career Kirchoff would work with
Robert Bunsen to establish the field of
spectroscopy, specifically through their formulation of Kirchoff's three laws of spectroscopy.
In
1847 James Prescott Joule stated the law of conservation of
energy, in the form of heat as well as mechanical energy. However, the principle of conservation of energy had been suggested in various forms by perhaps a dozen German, French, British and other scientists during the first half of the 19th century. About the same time,
entropy and the second law of thermodynamics were first clearly described in the work of
Rudolf Clausius. In 1875
Ludwig Boltzmann made the important connection between the number of possible states that a system could occupy and its entropy. With two installments in 1876 and 1878,
Josiah Willard Gibbs developed much of the theoretical formalism for
thermodynamics, and a decade later firmly laid the foundation for
statistical mechanics — much of which
Ludwig Boltzmann had independently invented. In
1881 Gibbs also was very influential in moving much of the notation of physics from Hamilton's
quaternions to
vectors. From 1873-76 Gibbs would help to apply thermodynamics to chemical processes, thus laying the foundations of
chemical thermodynamics. Gibbs would publish 3 papers, the most famous being titled
On the Equilibrium of Heterogeneous Substances in which he demonstrated that thermodynamic processes could be graphically analyzed, by studying the
energy,
entropy,
volume,
temperature and
pressure of the thermodynamic system, in such a manner to determine if a process would occur spontaneously. The first and second laws of thermodynamics emerged in the 1850s, primarily out of the works of
William Rankine,
Rudolf Clausius, and
William Thomson. The
third law of thermodynamics, which was established by
Ludwig Boltzmann, states that the
entropy of a pure substance approaches zero as the absolute temperature approaches zero.
The discovery of the
Hall effect in
1879 gave the first direct evidence that the carrier of electricity was negatively charged. In 1879,
Sir William Crookes would discover a new form of matter which he called "radiant matter". What Crookes has discovered was what became known as
plasma, the most abundant state of matter in the universe. Crookes was able to make his discovery of plasma by inventing the
Crookes tube. The discovery of
plasma is important because it constitutes the first time since a new state of matter had been discovered, aside from common knowledge of solids, liquids, and gases. Secondly, further research into plasma demonstrated its importance not only to science but also many technological applications such as
plasma displays,
fusion energy research, and production of
integrated circuits to name a few.
Dimensional analysis was used for the first time in 1878 by
Lord Rayleigh who was trying to understand why the
sky is blue.
In
1887 the
Michelson-Morley experiment was conducted and it was interpreted as counter to the generally held theory of the day, that the
Earth was moving through a "
luminiferous aether".
Albert Abraham Michelson and
Edward Morley were not fully convinced of the non-existence of the aether. Morley conducted further experiments with
Dayton Miller with improved interferometers, again giving null results.
In
1887,
Nikola Tesla investigated
X-rays using his own devices as well as Crookes tubes. In
1895,
Wilhelm Conrad Röntgen observed and analysed X-rays, which turned out to be high-frequency
electromagnetic radiation.
Radioactivity was discovered in
1896 by
Henri Becquerel, and further studied by
Pierre and
Marie Curie and others. This initiated the field of
nuclear physics.
In the late 19th century
Johannes Diderik van der Waals would postulate the existence of forces which act between molecules, but are weak compared to those in
chemical bonds. These forces would later be named
Van der Waals forces. A German physict by the name of
Fritz London would also discover similar forces which Waals had first proposed.
Van der Waals forces occupy an important role in
thermodynamics and
chemistry.
In
1897,
J. J. Thomson deduced that
cathode rays were composed of negatively charged particles, which he called "
corpuscles", later realized to be
electrons.
Philipp Lenard showed that the particles ejected in the
photoelectric effect were the same as those in cathode rays, and that their energy was independent of the intensity of the light, but was greater for short wavelengths of the incident light.
These discoveries revealed that the assumption of many physicists, that atoms were the basic unit of
matter, was flawed, and prompted further study into the structure of
atoms, such as
Ernest Rutherford's in 1911.
20th century
The turn of the
20th century brought the start of a
revolution in physics. This revolution centered around the advent on
quantum mechanics and special and
general relativity, the two concepts that mark the advent of
modern physics. Both of these theories would offer fundamental insights into the universe and the laws the govern it.
Quantum mechanics would describe the microscopic nature of matter, while relativity would describe
space and
time.
In
thermodynamics,
zeroth law of thermodynamics, which is a generalized statement about bodies in contact at thermal equilibrium and is the basis for the concept of temperature was formalized, although the principles behind the law were well known in the 19th century, wasn't until the 20th century that the law finally incorporated into thermodynamics. In 1929,
Lars Onsager, would establish
Onsager reciprocal relations-sometimes referred to as the fourth law of thermodynamics.
The
Lorentz transformations, the fundamental equations of special relativity, were published in 1897 and 1900 and also by
Joseph Larmor and by
Hendrik Lorentz in 1899 and 1904. They both showed that Maxwell's equations were invariant under the transformations. The ability to describe light in electromagnetic terms helped serve as a springboard for
Albert Einstein's publication of the theory of
special relativity in 1905. This theory combined classical mechanics with Maxwell's equations. The theory of
special relativity unifies space and time into a single entity,
spacetime. Relativity prescribes a different transformation between
reference frames than classical mechanics; this necessitated the development of relativistic mechanics as a replacement for classical mechanics. In the regime of low (relative) velocities, the two theories agree.
In
1900,
Max Planck published his explanation of
blackbody radiation. This equation assumed that radiators are
quantized, which proved to be the opening argument in the edifice that would become
quantum mechanics. By introducing discrete energy levels, Planck, Einstein,
Niels Bohr, and others developed
quantum theories to explain other anomalous experimental results like the
photoelectric effect. The discovery of
quantum mechanics in the early 20th century revolutionized physics, and quantum mechanics is fundamental to most areas of current research.
In
1904,
J. J. Thomson proposed the first model of the
atom, known as the
plum pudding model. In
1911,
Ernest Rutherford deduced from
scattering experiments the existence of a compact
atomic nucleus, with positively charged constituents dubbed
protons. The first quantum mechanical model of the atom, the
Bohr model, was published in 1913 by
Niels Bohr. Sir
W. H. Bragg and his son Sir
William Lawrence Bragg, also in 1913, began to unravel the arrangement of atoms in crystalline matter by the use of
x-ray diffraction.
Neutrons, the neutral nuclear constituents, were discovered in
1932 by
James Chadwick.
One of the most important concepts in modern physics and one which would help usher in
quantum mechanics was proposed by
Louis de Broglie.
Broglie's 1922 doctoral thesis,
Recherches sur la théorie des quanta (Research on Quantum Theory), introduced his theory of electron waves. This included the
wave-particle duality theory of matter, based on the work of
Albert Einstein and
Planck. This research culminated in the
de Broglie hypothesis stating that
any moving particle or object had an associated wave. De Broglie thus created a new field in physics, the
mécanique ondulatoire, or wave mechanics, uniting the physics of light and matter. Among the applications of this work has been the development of
electron microscopes to get much better image resolution than optical ones, because of shorter wavelengths of electrons compared with
photon.
In
1911,
Ernest Rutherford deduced from
scattering experiments the existence of a compact atomic nucleus, with positively charged constituents dubbed
protons. Rutheford along with
Frederick Soddy would also achieve the first case of
Nuclear transmutation, a phenomenon, which had been speculated since the time of the Greeks. Rutheford and Soddy noticed they has achieved this when during their experiments in 1901 radioactive
thorium was converting itself into radium.
Neutrons, the neutral nuclear constituents, were discovered in
1932 by
Chadwick. The equivalence of mass and energy (Einstein, 1905) was spectacularly demonstrated during
World War II, as research was conducted by each side into
nuclear physics, for the purpose of creating a
nuclear bomb. The German effort, led by Heisenberg, didn't succeed, but the Allied
Manhattan Project reached its goal. In America, a team led by
Fermi achieved the first man-made
nuclear chain reaction in
1942, and in
1945 the world's first
nuclear explosive was detonated at
Trinity site, near
Alamogordo,
New Mexico.
In
1915, Einstein extended special relativity to describe gravity with the
general theory of relativity. One principal result of general relativity is the
gravitational collapse into
black holes, which was anticipated two centuries earlier, but elucidated by
Robert Oppenheimer. Important exact solutions of
Einstein's field equation were found by
Karl Schwarzschild in 1915 and
Roy Kerr only in 1963. One part of the theory of general relativity is
Einstein's field equation. This describes how the
stress-energy tensor creates curvature of
spacetime and forms the basis of general relativity. Further work on Einstein's field equation produced results which predicted the
Big Bang,
black holes, and the
expanding universe. Einstein believed in a static universe. He tried, and failed, to fix his equation to allow for this. In
1929, however,
Edwin Hubble published his discovery that that the universe is expanding at a possibly exponential rate. This is the basis for understanding that the
universe is expanding. Thus, the universe must have been smaller and therefore hotter in the past. In
1933 Karl Jansky at Bell Labs discovered the radio emission from the
Milky Way, and thereby initiated the science of
radio astronomy. By the
1940s, researchers like
George Gamow proposed the
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