Physics
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History
-
Main article:
History of physics
- Further information: Famous
physicists, Nobel Prize in physics
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 which were wrong. These
theories were largely couched in philosophical
terms, and never verified by systematic experimental testing as is
popular today. The works of Ptolemy
and Aristotle however, were also not
always found to match everyday observations. There were exceptions and
there are anachronisms: for example, Indian philosophers and
astronomers
gave many
correct descriptions in atomism and astronomy,
and the Greek thinker Archimedes
derived many correct quantitative descriptions of mechanics
and hydrostatics.
The willingness to question previously
held truths and
search for
new answers eventually resulted in a period of major scientific
advancements, now known as the Scientific Revolution of the late 17th
century. The precursors to the scientific revolution can be traced
back to the important developments made in India and Persia,
including the elliptical model of the planets based on the heliocentric
solar
system of gravitation
developed by Indian mathematician-astronomer Aryabhata;
the basic ideas of atomic theory developed by Hindu and Jaina
philosophers; the theory of light being equivalent to energy particles
developed by the Indian Buddhist scholars Dignāga
and Dharmakirti; the optical theory of light
developed by Persian scientist Alhazen;
the Astrolabe
invented by the Persian Mohammad al-Fazari; and the significant
flaws in the Ptolemaic system pointed out by Persian
scientist Nasir al-Din al-Tusi.
As the influence of the Islamic
Caliphate
expanded to Europe, the works of Aristotle preserved by the Arabs, and
the works of the Indians and Persians, became known in Europe by the
12th
and 13th centuries. This eventually lead to the
scientific revolution which culminated with the publication of the Philosophiae
Naturalis Principia Mathematica in 1687 by the
mathematician, physicist, alchemist and inventor Sir Isaac
Newton (1643-1727).
The Scientific Revolution is held by
most historians
(e.g., Howard Margolis) to have begun in 1543, when
the first printed copy of Nicolaus Copernicus's De Revolutionibus
(most of which had been written years prior but whose publication had
been delayed) was brought to the influential Polish astronomer from
Nuremberg.
Further significant advances were made
over the
following century by Galileo Galilei, Christiaan Huygens, Johannes
Kepler, and Blaise
Pascal. During the early 17th
century, Galileo pioneered the use of
experimentation to validate physical theories, which is the key idea in
modern scientific method. Galileo formulated
and successfully tested several results in dynamics, in particular the
Law of Inertia.
From the late 17th
century onwards, 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.
Nature and nature's laws lay hid
in night. God
said: Let Newton be! And all was Light! — Alexander
Pope
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. 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.
After Newton defined classical
mechanics, the next great
field of inquiry within physics was the nature of electricity.
Observations in the 17th and 18th
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.
In 1821, the
English physicist and chemist Michael Faraday integrated the study of
magnetism
with the study of electricity. This was done by demonstrating that a
moving magnet
induced an electric current in a conductor. Faraday also formulated a
physical conception of electromagnetic fields. James Clerk Maxwell
built upon this
conception, in 1864,
with an interlinked set of 20 equations that explained the interactions
between electric and magnetic fields. These 20 equations were
later reduced, using vector calculus, to a set of four equations by
Oliver Heaviside.
In addition to other electromagnetic
phenomena,
Maxwell's equations also can be used to describe light.
Confirmation of this observation was made with the 1888
discovery of radio
by Heinrich Hertz and in 1895 when Wilhelm Roentgen detected X rays.
In 1895, Röntgen discovered
X-rays,
which turned out to be high-frequency electromagnetic radiation.
Radioactivity
was discovered in 1896 by Henri Becquerel, and further studied by Marie
Curie, Pierre
Curie, and others. This initiated the field of nuclear physics.
In 1897, Joseph
J. Thomson discovered the electron,
the elementary particle which carries electrical current in circuits.
In 1900, Max
Planck published his explanation of blackbody radiation. This equation
assumed that radiators are quantized
in nature.
In 1904, J. J.
Thomspn proposed the first model of the atom, known
as the plum pudding model. (The existence of
the atom had been proposed in 1808 by John
Dalton.)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.
But not for long! Let Einstein
be; the devil said!
And it was dark; the light had fled! — George Gamow
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. Einstein
built further on the special theory by including gravity into his
calculations, and published his theory of general relativity in 1915.
One part of the theory of general
relativity is Einstein's field equation. This
describes how the stress-energy tensor creates the 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 and tried (and failed) to fix his equation to
allow for this. However, by 1929 Edwin
Hubble's astronomical observations suggested that the universe is
expanding.
Ludwig Boltzmann, in the 19th century,
is
responsible for the modern form of statistical mechanics.
In 1911, Ernest 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. 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, 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 at Trinity
site, near Alamogordo, New
Mexico.
Beginning in 1900, Planck,
Einstein, Niels Bohr, and others developed quantum
theories to explain various anomalous experimental results by
introducing discrete energy levels. In 1925, Heisenberg and 1926,
Schrödinger and Paul
Dirac formulated quantum mechanics,
which explained the preceding heuristic 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.
During the 1920s Erwin Schrödinger, Werner Heisenberg, and Max
Born
were able to formulate a consistent picture of the chemical behavior of
matter, a complete theory of the electronic structure of the atom, as a
byproduct of the quantum theory.
Quantum field theory was formulated
in order to extend quantum mechanics to be consistent with special
relativity. It was devised in the late 1940s with
work by Richard Feynman, Julian Schwinger, Sin-Itiro Tomonaga, and
Freeman
Dyson. They formulated the theory of quantum electrodynamics, which
describes the electromagnetic interaction, and successfully explained
the Lamb shift. Quantum field theory provided the
framework for modern particle physics, which studies fundamental forces
and elementary
particles.
Chen Ning Yang and Tsung-Dao
Lee, in the 1950s, discovered an unexpected asymmetry
in the decay of a subatomic particle. In 1954, Yang
and Robert Mills then developed a
class of gauge theories which provided the framework
for understanding the nuclear forces. The theory for the strong nuclear
force was first
proposed by Murray Gell-Mann. The electroweak force, the unification of
the weak nuclear force with
electromagnetism, was proposed by Sheldon Lee Glashow, Abdus
Salam and Steven Weinberg. This led to the so-called Standard Model of
particle physics in the 1970s,
which successfully describes all the elementary particles observed to
date. In 1964, CP
violation was discovered by James Watson Cronin and Val
Fitch.
Quantum mechanics also provided the
theoretical tools
for condensed matter physics, whose
largest branch is solid state physics. It 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. The
transistor was developed by physicists John
Bardeen, Walter Houser Brattain and William Bradford Shockley in 1947
at Bell
Telephone Laboratories.
The two themes of the 20th
century, general relativity and quantum mechanics, appear
inconsistent with each other. General relativity describes the universe
on the scale of planets and solar
systems while quantum mechanics operates on sub-atomic scales. This
challenge is being attacked by string
theory, which treats spacetime
as composed, not of points, but of one-dimensional objects, strings.
Strings have properties like a common string (e.g., tension and
vibration).
The theories yield promising, but not yet testable results. The search
for experimental verification of string theory is in progress.
The United Nations declared the year
2005, the
centenary of Einstein's annus mirabilis, as the World Year of Physics.
[edit]
Future directions
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Main article:
Unsolved problems in physics
Research in physics is progressing
constantly on a large
number of fronts, and is likely to do so for the foreseeable future.
In condensed matter physics, the
biggest unsolved
theoretical problem is the explanation for high-temperature
superconductivity. Strong efforts, largely experimental, are being
put into making workable spintronics
and quantum computers.
In particle physics, the first pieces
of experimental
evidence for physics beyond the Standard Model have begun to appear.
Foremost amongst these are indications that neutrinos
have non-zero mass.
These experimental results appear to have solved the long-standing
solar neutrino problem
in solar physics. The physics of massive neutrinos is currently an area
of active theoretical and experimental research. In the next several
years, particle accelerators will begin
probing energy scales in the TeV range, in which experimentalists are
hoping to
find evidence for the Higgs
boson and supersymmetric particles.
Theoretical attempts to unify quantum
mechanics and general relativity into a single theory
of quantum gravity, a program ongoing for
over half a century, have not yet borne fruit. The current leading
candidates are M-theory, superstring theory and loop quantum gravity.
Many astronomical
and cosmological phenomena have yet to be
satisfactorily explained, including the existence of ultra-high
energy cosmic rays, the baryon asymmetry, the acceleration of the
universe and the anomalous rotation rates of galaxies.
Although much progress has been made
in high-energy, quantum,
and astronomical physics, many everyday phenomena, involving
complexity,
chaos, or turbulence
are still poorly understood. Complex problems that seem like they could
be solved by a clever application of dynamics and mechanics, such as
the formation of sandpiles, nodes in trickling water, the
shape of water droplets, mechanisms of surface tension catastrophes,
or self-sorting in shaken heterogeneous collections are unsolved. These
complex phenomena have received growing attention since the 1970s for
several reasons, not least of which has been the availability of modern
mathematical
methods and computers
which enabled complex systems to be modeled in new ways.
The interdisciplinary relevance
of complex physics has also increased, as exemplified by the study of
turbulence
in aerodynamics or the observation
of pattern formation
in biological
systems. In 1932, Horace Lamb correctly prophesized:
I am an old man now, and when I
die and go to
heaven there are
two matters on which I hope for enlightenment. One is quantum
electrodynamics, and the other is the turbulent motion of fluids. And
about the former I am rather optimistic.
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