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History of physics
This article has changed substantially from its original
form as the "Ridiculously Brief History of Physics" on the main
Physics page. However, further work is needed to fill in some obvious gaps,
and to include more detail about the development of physics (and, concurrently,
astromomy and mathematics) in non-European cultures. It is intended that this
article should grow to be a brief but comprehensive history of physics. The
history on the Physics page should remain as a summary only.
This article is a work in progress: please add more
material here
Since antiquity, people have tried to understand the behavior
of matter: why unsupported objects drop to the ground, why different materials
have different properties, and so forth. Also a mystery was 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.
Several theories were proposed, most of them were wrong, but this is part of the
nature of the scientific enterprise, and even modern theories of
quantum mechanics and
relativity are considered merely as "theories that haven't broken yet".
Physical theories in antiquity were largely couched in
philosophical terms, and rarely verified by systematic experimental testing.
Typically the behaviour and nature of the world were
explained by invoking the actions of gods.
Around 200 BC, many
Greek philosophers began to propose that the world could be understood as
the result of natural processes. Many also challenged traditional ideas
presented in mythology, such as the origin of the human species (anticipating
the ideas of
Charles Darwin), although this falls into the history of
biology, not physics.
Due to the absence of advanced experimental equipment such as
telescopes and accurate time-keeping devices, experimental testing of many
such ideas was impossible or impractical. There were exceptions and there are
anachronisms: for example, the
Greek thinker
Archimedes 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. 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. Greek mathematicians also 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 -
anticipating the invention of
integral calculus by almost two millennia.
Modern knowledge of these early ideas in physics, and the
extent to which they were experimentally tested, is sketchy. 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 travelled 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 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.
Regrettably, this period of inquiry into the nature of the
world was eventually stifled by a tendency to accept the ideas of eminent
philosophers, rather than to question and test those ideas. New discoveries,
such as
Pythagoras's deduction of the existence of
irrational numbers, were suppressed, and technical knowledge was turned
increasingly to the development of advanced weapons, rather than experimental
investigations of nature. For one thousand years following the destruction of
the
Library of Alexandria,
Ptolemy's (not to be confused with the
Egyptian Ptolemies) model of an Earth-centred universe with planets moving
in perfect circular orbits was accepted as absolute truth.
-
We should mention physics and astronomy outside Europe
at this stage, especially Mesoamerican, Babylonian, Arabic and Chinese
astronomy. The Japanese were also very big on mathematical puzzles - it's not
exactly physics but it might be a worthwhile aside, to make this history more
balanced. We also need to include a lot about middle-eastern physics, here's a
start...(The section Middle Ages)
When the power of Greek civilization was eclipsed by the
Roman Empire, many Greek doctors began to practice medicine for the Roman
elite, but sadly the physical sciences were not so well supported. Following the
collapse of the
Roman Empire, Europe entered the so-called
Dark Ages, and almost all scientific research ground to a halt. The rise of
Christianity saw the suppression and destruction of most classical Greek
philosophy (along with Greek and Roman art, literature and religious
iconography) as heretical and pagan. In the Middle East, however, many Greek
natural philosophers were able to find support in the newly created Arab
Caliphate (Empire), and the Islamic scholars built upon previous work in
medicine, astronomy and mathematics while developing such new fields as alchemy
(chemistry). For example, the scholar Muhammad ibn Musa
al-Khwarizmi gave his name to what we now call an
algorithm, and the word
algebra is derived from al-jabr, the beginning of the name of one
of his publications in which he developed a system of solving quadratic
equations, thus beginning Al-gebra.
It is sometime assumed that the Islamic civilization simply
preserved the older learning without any innovation. In astronomy, chemistry,
and mathematics, at least, this is certainly not true.
Could someone write about what Arabs, Persians and others
actually did in physics? Arab
Alchemy inspired both
Roger Bacon and
Isaac Newton.
The monk
Roger 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 is 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. The relation of this to earlier Islamic experimental
work ought to be explored here.
The withdrawal of the Islamic empire from Mediterranean
Europe (especially Spain) in the 15th century coincided with the dawn of the
Renaissance. This "rebirth" of European culture was in part brought about by
the re-discovery of those elements of ancient Greek, Indian, Chinese and Islamic
culture preserved and further developed by Islam from the 8th to the 15th
centuries, and translated by Christian Monks into Latin.
In the
16th century
Nicholas Copernicus revived the
heliocentric model of the
solar system devised by
Aristarchus (which survives 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
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 published a seminal work, De Magnete (1600), in which
he thoroughly presented his numerous experimental results.
In the early
17th century
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.
During the early
17th century,
Galileo pioneered the use of experiment 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.
In
1687,
Isaac Newton published the
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. Both theories agreed well with experiment. Classical mechanics
would be exhaustively extended by
Lagrange,
Hamilton, and others, who produced new formulations, principles, and
results. The Law of Gravitation initiated the field of
astrophysics, which describes
astronomical phenomena using physical theories.
-
We should include something here about Huygens'
observations of Saturn's rings, and his debates with Newton about whether
light was a wave or a particle.
From the
18th century onwards,
thermodynamics was developed by
Boyle,
Young, and many others. In
1733,
Daniel 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.
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
1847
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 or enunciated in various
forms by perhaps a dozen German, French, British and other scientists during the
first half of the 19th Century.
The behavior of
electricity and
magnetism was studied by
Faraday,
Ohm, and others. Faraday, who began his career in chemistry working under
Humphrey 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 mechanical motion is converted into
electricity. Thus it was Faraday who laid the foundations for both the electric
motor and the electric generator.
In
1855,
Maxwell unified the two phenomena into a single theory of
electromagnetism, described by
Maxwell's equations. A prediction of this theory was that
light is an
electromagnetic wave. A more subtle part of Maxwell's deduction was that the
observed speed of light does not depend on the speed of the observer, a
premonition of the development of
special relativity by
Einstein.
In
1887
the
Michelson-Morley experiment is conducted and it is interpertated as counter
to the general held theory of the day, that the
Earth was moving through a "luminiferous
aether". The development of what later became
Einstein's
Special Theory of Relativity provided a complete explanation which did not
require an aether, and was consistent with the results of the experiment.
Michelson and Morely are not convinced of the non-existence of the aether.
Morely goes on to conduct experiments with
Miller.
In
1887,
Tesla investigates
X-rays using his own devices as well as Crookes tubes. In 1895,
Röntgen observes and analysies X-rays, which turned out to be high-frequency
electromagnetic radiation.
Radioactivity was discovered in
1896
by
Henri Becquerel, and further studied by the
Pierre Curie and
Marie Curie and others. This initiated the field of
nuclear physics.
In
1897,
Thomson studies the
electron, the elementary particle which carries electrical current in
circuits. He deduces that
cathode rays existed and were negatively charged "particles", which
he called "corpuscles".
The beginning of the 20th century brought the start of a
revolution in physics. The long-held theories of
Newton were shown not to be correct in all circumstances. Not only did
quantum mechanics show that the laws of motion didn't hold on small scales,
but even more disturbingly,
general relativity showed that the fixed background of
spacetime, on which both
Newtonian mechanics and
special relativity depended, could not exist.
In
1904,
Thomson proposed the first model of the
atom,
known as the
plum pudding model. (The existence of the atom had been proposed in
1808
by
Dalton.)
In
1905,
Einstein formulated the theory of
special relativity, unifying space and time into a single entity,
spacetime. Relativity prescribes a different transformation between
reference frames than classical mechanics, necessitating the development of
relativistic mechanics as a replacement for classical mechanics. In the regime
of low (relative) velocities, the two theories agree. In
1915,
Einstein extended special relativity to explain gravity with the
general theory of relativity, which replaces Newton's law of gravitation. In
the regime of low masses and energies, the two theories agree.
In
1911,
Rutherford deduced from
scattering experiments the existence of a compact atomic nucleus, with
positively charged constituents dubbed
protons.
Neutrons, the neutral nuclear constituents, were discovered in
1932
by
Chadwick.
Beginning in
1900,
Planck,
Einstein,
Bohr, and others developed
quantum theories to explain various anomalous experimental results by
introducing discrete energy levels. In
1925,
Heisenberg and
Schrödinger formulated
quantum mechanics, which explained the preceding quantum theories. In
quantum mechanics, the outcomes of physical measurements are inherently
probabilistic. The theory describes the calculation of these probabilities.
It successfully describes the behavior of matter at small distance scales.
Quantum mechanics also provided the theoretical tools for
condensed matter physics, which studies the physical behavior of solids and
liquids, including phenomena such as
crystal structures,
semiconductivity, and
superconductivity. The pioneers of condensed matter physics include
Bloch, who created a quantum mechanical description of the behavior of
electrons in crystal structures in
1928.
In
1929,
Edwin Hubble published his discovery that the speed at which galaxies recede
positively correlates with their distance. This is the basis for understanding
that the
universe is expanding.
In
1937,
Tesla challenges
Einstein's
theory of relativity, announcing a
dynamic theory of gravity and argue that a field of force was a better
concept and did away with the
curvature of space. Unfortunately the theory was never published, but Tesla
may have been developing a theory about gravity waves.
During
World War II, research was conducted by each side into
nuclear physics, for the purpose of creating a
nuclear bomb. The German effort, led by Heisenberg, did not 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 in
Alamagordo,
New Mexico.
Quantum field theory was formulated in order to extend quantum mechanics to
be consistent with special relativity. It achieved its modern form in the late
1940s with work by
Feynman,
Schwinger,
Tomonaga, and
Dyson. They formulated the theory of
quantum electrodynamics, which describes the electromagnetic interaction.
Quantum field theory provided the framework for modern
particle physics, which studies
fundamental forces and elementary particles. In
1954,
Yang and
Mills developed a class of
gauge theories, which provided the framework for the
Standard Model. The Standard Model, which was completed in the
1970s, successfully describes almost all elementary particles observed to
date.
Attempts to unify
quantum mechanics and
general relativity made signficant progress during the 1990s. At the close
of the century, a
Theory of everything was still not in hand, but some of its characteristics
were taking shape.
Loop quantum gravity,
string theory, and
black hole thermodynamics all predicted
quantized
spacetime on the
Planck scale.
-
please add to this
Gravity was
shown to propagate at the
speed of light, confirming one prediction of
loop quantum gravity.
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