
#REDIRECT Physics
Physics (from the Greek language, φυσικός (''phusikos''), "natural", and φύσις (''phusis''), "nature") is the science of Nature in the broadest sense. Physicists study the behavior and properties of matter in a wide variety of contexts, ranging from the sub-nuclear particles from which all ordinary matter is made (particle physics) to the behavior of the material Universe as a whole (cosmology). Some of the properties studied in physics are common to ''all'' material systems, such as the conservation of energy. Such properties are often referred to as law of physics. Physics is sometimes said to be the "fundamental science", because each of the other natural sciences (biology, chemistry, geology, etc.) deals with particular types of material systems that obey the laws of physics. For example, chemistry is the science of molecules and the chemical compounds that they form in the bulk. The properties of a chemical are determined by the properties of the underlying molecules, which are accurately described by areas of physics such as quantum mechanics, thermodynamics, and electromagnetism. Physics is also closely related to mathematics. Physical theory are almost invariably expressed using mathematical relations, and the mathematics involved is generally more complicated than in the other sciences. The difference between physics and mathematics is that physics is ultimately concerned with descriptions of the material world, whereas mathematics is concerned with abstract patterns that need not have any bearing on it. However, the distinction is not always clear-cut. There is a large area of research intermediate between physics and mathematics, known as mathematical physics, devoted to developing the mathematical structure of physical theories. == Overview of physics research == === Theoretical and experimental physics === The culture of physics research differs from the other sciences in the separation of theory and experiment. Since the 20th century, most individual physicists have specialized in either theoretical physics or experimental physics, and in the twentieth century, very few physicists have been successful in both forms of research #fn_1. In contrast, almost all the successful theorists in biology and chemistry have also been experimentalists. Roughly speaking, theorists seek to develop theories that can describe and interpret existing experimental results and successfully predict future results, while experimentalists devise and perform experiments to explore new phenomena and test theoretical predictions. Although theory and experiment are developed separately, they are strongly dependent on each other. Progress in physics frequently comes about when experimentalists make a discovery that existing theories cannot account for, necessitating the formulation of new theories. Likewise, ideas arising from theory often inspire new experiments. In the absence of experiment, theoretical research can go in the wrong direction; this is one of the criticisms that have been levelled against M-theory, a popular theory in high-energy physics for which no practical experimental test has ever been devised. === Central theories === While physics deals with a wide variety of systems, there are certain theories that are used by all physicists. Each of these theories is believed to be basically correct, within a certain domain of validity. For instance, the theory of classical mechanics accurately describes the motion of objects, provided they are much larger than atoms and moving at much less than the speed of light. These theories continue to be areas of active research; for instance, a remarkable aspect of classical mechanics known as chaos theory was discovered in the 20th century, three centuries after the original formulation of classical mechanics by Isaac Newton. These "central theories" are important tools for research into more specialized topics, and any student of physics, regardless of his or her specialization, is expected to be well-versed in them. {| !Theory || Major subtopics || Concepts |- | Classical mechanics | Newton's laws of motion, Lagrangian mechanics, Hamiltonian mechanics, Chaos theory, Fluid dynamics, Continuum mechanics | Dimension, Space, Time, Motion, Length, Velocity, Mass, Momentum, Force (physics), Energy, Angular momentum, Torque, Conservation law, Harmonic oscillator, Wave, Mechanical work, Power (physics), |- | Electromagnetism | Electrostatics, Electricity, Magnetism, Maxwell's equations | Electric charge, Current (electricity), Electric field, Magnetic field, Electromagnetic field, Electromagnetic radiation, Magnetic monopole |- | Thermodynamics and Statistical mechanics | Heat engine, Kinetic theory | Boltzmann's constant, Entropy, Free energy, Heat, Partition function (statistical mechanics), Temperature |- | Quantum mechanics | Path integral formulation, Schrödinger equation, Quantum field theory | Hamiltonian (quantum mechanics), Identical particles, Planck's constant, Quantum entanglement, Quantum harmonic oscillator, Wavefunction, Zero-point energy |- | Theory of relativity | Special relativity, General relativity | Equivalence principle, Four-momentum, Reference frame, Spacetime, Speed of light |} === Major fields of physics === Contemporary research in physics is divided into several distinct fields that study different aspects of the material world. Condensed matter physics, by most estimates the largest single field of physics, is concerned with how the properties of bulk matter, such as the ordinary solids and liquids we encounter in everyday life, arise from the properties and mutual interactions of the constituent atoms. The field of atomic, molecular, and optical physics deals with the behavior of individual atoms and molecules, and in particular the ways in which they absorb and emit light. The field of particle physics, also known as "high-energy physics", is concerned with the properties of submicroscopic particles much smaller than atoms, including the elementary particles from which all other units of matter are constructed. Finally, the field of astrophysics applies the laws of physics to explain astronomy phenomena, ranging from the Sun and the other objects in the solar system to the universe as a whole. {| !Field ||Subfields || Major theories || Concepts |- | Astrophysics | Physical cosmology, Planetary science, Plasma physics | Big Bang, Cosmic inflation, General relativity, Law of universal gravitation | Black hole, Cosmic background radiation, Galaxy, Gravity, Gravitational radiation, Planet, Solar system, Star |- | Atomic, molecular, and optical physics | Atomic physics, Molecular physics, Optics, Photonics | Quantum optics | Atom, Diffraction, Electromagnetic radiation, Laser, Polarization, Spectral line |- | Particle physics | Accelerator physics, Nuclear physics | Standard Model, Grand unification theory, M-theory | Fundamental force (gravity, electromagnetism, weak interaction, strong interaction), Elementary particle, Antimatter, Spin (physics), Spontaneous symmetry breaking, Theory of everything Vacuum energy |- | Condensed matter physics | Solid state physics, Materials physics, Polymer physics | BCS theory, Bloch wave, Fermi gas, Fermi liquid, Many-body theory | Phase (matter) (gas, liquid, solid, Bose-Einstein condensate, superconductivity, superfluid), Electrical conduction, Magnetism, Self-organization, Spin (physics), Spontaneous symmetry breaking |} === Related fields === There are many areas of research that mix physics with other disciplines. For example, the wide-ranging field of biophysics is devoted to the role that physical principles play in biological systems, and the field of quantum chemistry studies how the theory of quantum mechanics gives rise to the chemical behavior of atoms and molecules. Some of these are listed below. Acoustics - Astronomy - Biophysics - Computational physics - Electronics - Engineering - Geophysics - Materials science - Mathematical physics - Medical physics - Physical chemistry - Physics of computation - Quantum chemistry - Quantum information science - Vehicle dynamics === Fringe theories === Cold fusion - Dynamic theory of gravity - Luminiferous aether - Steady state theory - Wave Structure Matter ==History== ''Main article: History of physics. See also Famous physicists and 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 science 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 philosophy terms, and never verified by systematic experimental testing as is popular today. There were exceptions and there are anachronisms: for example, the Hellenic civilization thinker Archimedes derived many correct quantitative descriptions of mechanics and hydrostatics. The works of Ptolemy (Astronomy) and Aristotle (Physics) were also found to not always match everyday observations. An example of this is an arrow flying through the air after leaving a bow contradicts with Aristotle's assertion that the natural state of all objects is at rest. [[Image:GodfreyKneller-IsaacNewton-1689.jpg|thumb|left|Isaac Newton]] The willingness to question previously held truths and search for new answers resulted in a period of major scientific advancements, now known as the Scientific Revolution. Its origins can be found in the European re-discovery of Aristotle in the twelfth and thirteenth centuries. This period culminated with the publication of the Philosophiae Naturalis Principia Mathematica in 1687 by Isaac Newton (dates disputed). The Scientific Revolution is held by most historians (e.g., Howard Margolis) to have begun in 1543, when there was brought to the Polish astronomer Nicolaus Copernicus the first printed copy of the book ''De Revolutionibus Orbium Coelestium '' he had written about a dozen years earlier. The thesis of this book is that the Earth moves around the Sun. Other significant scientific advances were made during this time by Galileo Galilei, Christiaan Huygens, Johannes Kepler, and Blaise Pascal. During the early 17th century, Galileo Galilei pioneered the use of experimentation to validate physical theories, which is the key idea in the scientific method. Galileo formulated and successfully tested several results in dynamics (mechanics), in particular the Law of Inertia. 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 gravity, 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 extended by Leonhard Euler, Joseph-Louis de Lagrange, William Rowan Hamilton, and others, who produced new results and new formulations of the theory. The law of universal gravitation initiated the field of astrophysics, which describes astronomy 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 century 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 electric current. [[Image:James Clerk Maxwell.jpg|thumb|left|140px|James Clerk Maxwell]] In 1821, 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 field and magnetic field. These 20 equations were later reduced, using vector calculus, to a set of Maxwell's equations by Oliver Heaviside. [[Image:Einstein patentoffice.jpg|thumb|right|140px|Albert Einstein in 1905]] 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. The ability to describe light in electromagnetic terms helped serve as a springboard for Albert Einstein's publication of his theory of special relativity. 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 inertial frame of reference 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 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 argued that astronomical observations demonstrate that the universe is expanding. From the 18th century onwards, thermodynamics was developed by Robert Boyle, Thomas Young (scientist), 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, Benjamin Thompson demonstrated the conversion of mechanical work into heat, and in 1847 James Joule stated the law of conservation of energy, in the form of heat as well as mechanical energy. Ludwig Boltzmann, in the 19th century, is responsible for the modern form of statistical mechanics. In 1895, Wilhelm 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 Maria Sklodowska-Curie, Pierre Curie, and others. This initiated the field of nuclear physics. In 1897, J.J. Thomson discovered the electron, the elementary particle which carries electrical current in electrical circuit. In 1904, he proposed the first model of the atom, known as the atom/plum pudding. (The existence of the atom had been proposed in 1808 by John Dalton.) Henri Becquerel accidentally discovered radioactivity in 1896. The next year J.J. Thomson discovered the electron. 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. In 1911, Ernest Rutherford deduced from rutherford scattering the existence of a compact atomic nucleus, with positively charged constituents dubbed protons. neutron, the neutral nuclear constituents, were discovered in 1932 by James 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 weapon. The German effort, led by Heisenberg, did not succeed, but the Allied Manhattan Project reached its goal. In America, a team led by Enrico Fermi achieved the first man-made nuclear chain reaction in 1942, and in 1945 the world's first nuclear weapon was detonated at Trinity site, near Alamogordo, New Mexico. In 1900, Max Planck published his explanation of blackbody radiation. This equation assumed that radiators are quantum in nature, which proved to be the opening argument in the edifice that would become quantum mechanics. Beginning in 1900, Max Planck, Einstein, Niels Bohr, and others developed quantum theories to explain various anomalous experimental results by introducing discrete energy levels. In 1925, Werner Heisenberg and 1926, Erwin Schrödinger and Paul Dirac formulated quantum mechanics, which explained the preceding heuristic quantum theories. In quantum mechanics, the outcomes of physical measurements are inherently probability; 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. [[Image:Richard feynman.jpg|thumb|left|140px|Richard Feynman]] 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 theory, 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 and confirmed in 1964 by James Watson Cronin and Val Fitch. This led to the so-called Standard Model of particle physics in the 1970s, which successfully describes all the elementary particles observed to date. 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, semiconductor, and superconductor. The pioneers of condensed matter physics include Felix 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 have declared the year 2005, the centenary of Einstein's annus mirabilis, as the World Year of Physics. == Future directions == ''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 supersymmetry. 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 astronomy and cosmology phenomena have yet to be satisfactorily explained, including the existence of GZK paradox, the baryon asymmetry, the accelerating universe and the galaxy rotation problem. Although much progress has been made in high-energy, quantum, and astronomical physics, many everyday phenomena, involving complex systems, chaos, or turbulence are still poorly understood. Complex problems that seem like they could be solved by a clever application of dynamics and mechanics, like the formation of sandpiles, nodes in trickling water, the shape of water droplet, mechanisms of surface tension catastrophe theory, 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 mathematics methods and computers which enabled complex systems to be modelled 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 biology systems. In 1932, Horace Lamb correctly prophesized:
''Please post new comments down the bottom. If you are adding a new topic, you can click the plus sign next to edit.'' ==Definition== ''[...]'' As for a definition, may I suggest: Physics is the study of nature in the broadest sense. Physicists attempt to find the most general rules that govern all of nature. Physics generally breaks down in to the study of the properties of matter, fields, space, time, and energy and how they interact. To describe these phenomena, physicists generally us the most precise language available to them, mathematics. Or something of that general sort. Perhaps even a mention that physics really is the study of everything in nature (i.e., mention that chemistry is a subset of physics that is governed by the molecular-atomic description of matter, and that biology is a subset of chemistry). Just musing. --BlackGriffen :Ok, I like your definition ''[...]'' :I'm not sure all biologist would agree with your reductionist view of biology as a subset of chemistry as a subset of physics, so I don't want to go there. Biologists pose and answer questions that are different from questions of physics. For instance, even if you knew all laws of physics, you still wouldn't know why we have our eyes in the head and not on our asses. --AxelBoldt ::''[...]'' I suggest to move :Quantum electrodynamics and :Statistical Mechanics to central theories. --:css ::I think something should be included on ancient greek physics. Not all was :Aristotle. From the top of my head :Archimedes found out interesting things that are still applied. :If I may return to the proposed definition ... I think it's a huge improvement. The current physics and chemistry definitions seem as if they were contrived solely to appear complementary. The distinction between physics and chemistry isn't that one emphasizes energy and the other matter, but rather that chemistry tends to focus on the interactions of chemical elements and compounds, whereas physics has a much broader (but more fundamental) scope ranging from quanta to cosmology. --Scrutchfield ::And what do "quanta" and "cosmology" have in common? Energy. To simply categorize physics as "the study of everything" is imperceptive. When modeling sand falling into a pile (or nuts sorting in a jar) a physicist doesn't really care about the identity of the particles at hand, just certain "bulk" properties that relate to its energetics. The chemist tries to understand how the material composition in turn generates those energetic qualities, but then usually isn't capable of formulating the dynamic description of what happens when it's shaken (or spilled). A physicst usually could care less about why niobium is better for a collider than copper, just that it is. And chemists don't just care about chemical elements and compounds, there is a whole field of chemistry dedicated to monitoring interactions of nuclei with nucleons (nuclear chemistry) -- still matter. As a point of culture, chemists tend to focus on the diversity of matter and how that affects interactions with energy-- and physicists focus on the unity of energy, and how that affects matter. Physical chemists very nicely bridge this -- they put quite a bit of energetics while still caring deeply about the identity of that which is being studied. While the duality may sound a bit contrived, there is definitely some truth to the statements, and while not perfect, it's more meaningful than what's there now. :::''And what do "quanta" and "cosmology" have in common? Momentum. To simply categorize physics as "the study of everything" is imperceptive. When modeling sand falling into a pile (or nuts sorting in a jar) a physicist doesn't really care about the identity of the particles at hand, just certain "bulk" properties that relate to its momenta.'' (Or replace momentum by mass, spin, or any of the other fundamental properties of objects, and you start to see the problem. There is nothing special about energy.) -- User:CYD :::: Momentum is intimately related to energy, anyways -- it's the velocity-integral of energy. Maybe here is something which will help out the distinction (as a simplified) example of the difference of cultures: One thing which astrophysicists study is the color of stars. This has everything to do with the blackbody radiation, which has to do with the temperature of the star, and really has not much to do with the composition of the stars. There are scientists who study the spectral lines which emanate from stars. This property depends very intimately on the matter composition of those stars. These scientists are known as astrochemists (Tak Oka@chicago is an example). Maybe I phrased that first sentence wrongly, but to distill physics to the "study of everything" can be seen as rendering it meaningless or maybe is a sign of arrogance on the part of physicists. The point is this: physicists care deeply about energy and the identity of the matter is usually irrelevant (insert "assume cow is a sphere" joke here). Chemists care deeply about the identity of the matter, and energetics are used only as a tool to descriptively understand what makes matter tick. :::: Maybe I should say it this way: momentum, spin, or any of the 'fundamental properties of objects' are manifestations of energy (or vice versa). Mass, in our current model, is the only one that you suggested that really isn't (I guess it's "sort of a mystery" as to why gravitational and inertial mass are the same). Energy is a convenient label because it's sort of 'in opposition' to matter. There is something special about matter which makes it diverse and interesting to chemists, an attitude which the canoncial physicist doesn't share (and of course there are people in between like physical chemists). When you say that physics is 'the study of everything', that implies that the biologist is a physicist and a chemist is a physicist, but I doubt either of them would agree, nor would a physicist feel that a biologist or a chemist is one of them. I'm not trying to drive a wedge between the disciplines, because there is still room for people who approach their subject of study in a hybrid way, but there are significant cultural differences which need to be addressed in the definition. I personally find it interesting that "conservation of mass" which frequently gets attributed as a "law of physics", when historically speaking, a chemist (Antoine Lavoisier) came up with it first. :::Actually, there are plenty of people who identify themselves as astrophysicists, that spend most of their time poring over spectral lines; that's how you find a star's redshift, among other things. As for signs of arrogance, making a blanket statement that physicists don't care about the identity of the matter they are looking at sure sounds like a great example of it. Incidentally, about two centuries passed after the formulation of mechanics before people started paying attention to the quantity we now call "energy"; I hope you're not trying to imply that Isaac Newton wasn't doing physics. There are countless other examples of physics research in which "energy" plays a minimal or zero role (for instance, cosmologists hardly ever talk about energy, because it is not "globally" well defined in general relativity.) But maybe you think of them as "hybrid" physicists? :::As for "''momentum, spin, or any of the 'fundamental properties of objects' are manifestations of energy (or vice versa)''", the less said the better. :::You'll probably reply that what you mean isn't really ''energy'' in the technical sense, but something else that makes a thing interesting to a physicist (call it "oompf" or whatever.) But then your thesis degenerates into a kind of hand-wavy philosophizing that may be an interesting topic of discussion of sci.physics, but doesn't belong on Wikipedia. -- User:CYD ::::Fair enough. However, there is something distinctly different about the cultures of chemistry and physics. When physicists deal with matter, they tend to deal with its bulk properties (elasticity, conductance, granularity, charge density, ionization potential, et cetera). You describe astrophysicists poring over spectral lines -- but, in your own words, the emphasis is on finding the redshift. There's nothing arrogant about noting the differences between cultures, there's no judgement involved there. Chemists use physicist's tools and physicists use chemist's tools. Nowhere am I implying that Newton wasn't doing physics -- in fact, he is the quintessential physicist -- Newton described the motion of planets and the effects of gravity in the most general and bulk of terms -- to him it didn't matter if it was a cow or a cannonball. ::::Maybe the problem is this: At one point, physics was "the study of everything" (and before that it was actually what we would call "medicine") -- this definition is rather outdated and imprecise. It needs to be revised. All life is physiology, all physiology is biology, all biology is chemistry, all chemistry is physics, and all physics is math..... User:Gelsamel 03:17, 1 Dec 2004 (UTC) ---- Hmm, I see that the history section in Physics has been copied pretty much wholesale into that article. That's fine, but I think we should also keep the section in Physics, because in addition to giving a history it also describes the subtopics of physics which I think is important for the article. As for History of Physics, if it is supposed to justify its own article, more historical material should be added to distinguish it, e.g. precise dates and a greater level of detail. Then at the end of Physics we add a line like "for a more detailed history of physics, see History of Physics" (currently pointless, as there isn't more detail yet.) --user:CYD ---- How about renaming "proposed theories" to, say, "current research topics"? Then we can include current experimental efforts as well. I don't think a new section should be added to the end of the article just for this, putting it with the other lists should be fine. -- user:CYD Then we'd have to get rid of Grand Unified Theory and Theory of Everything. There's no correspondence between the two categories so it wouldn't be a renaming but a replacing. :I'm not sure about that. GUTs and TOEs are part of current research efforts, aren't they? Alternatively, we could add descriptions of current research efforts to the end of the article, after the History of Physics section (actual descriptions, not just a list bullet points.) Or, we could have another article, say Current research topics in physics and link to it. --user:CYD What does TOE mean? Principally, it means M-theory. F-theory is related to M. Loop quantum gravity was never meant to be and never will be a TOE (and I agree with the opinion that it's not even scientific). Friedman(?) is looking at something that may or may not even be interesting. So basically TOE = M. I got the impression that research in GUTs is dead. Especially after '95 or so when everyone joined M-theory, or should I say, when the strings community absorbed the supergravity community. I'm sure that people are doing various calculations with GUTs and hoping for evidence one way or another but nobody seems to look for, nor expects, any conceptual breakthroughs. We can have anything you like, I'm not picky. But when the topic of hot research was introduced I came up with a big blank, which led me to think "hmmm, good question!" It took me quite a bit of brain raking to come up with 'search for SUSY' and 'search for Higgs boson'. I'd add dark matter (maybe!), gravitational waves and gamma ray bursts to the list, but I really don't know that much. -- ark Explaning high Tc superconductivity; explaining sonoluminescence; search for WIMPs; search for axions; explaining neutrino oscillations (and thus the solar neutrino problem); explaining the muon g-2 factor; explaining energetic cosmic rays; the large extra dimensions hypothesis; etc. Baez has a longer list at http://math.ucr.edu/home/baez/physics/General/open_questions.html -- user:CYD Large extra dimensions hypothesis? I've never heard of that! What is it? :An alternative to SUSY that's being seriously considered. You can find plenty of related sites with a Google search, but the original paper is here: http://arxiv.org/abs/hep-ph/9803315 -- user:CYD ::How about "Proposed theories and research directions"? And then we add Supersymmetry, Higgs boson etc. user:AxelBoldt, Monday, June 3, 2002 ---- I just replaced the translation of "phusis" as "matter" back to "nature", given the following two sites: http://www.studylight.org/lex/grk/view.cgi?number=5449 and http://www.dictionary.com/search?q=physics . user:AxelBoldt, Wednesday, May 29, 2002 ---- When a current is run through a wire, this current creates a magnetic field. (Please note that current is flows from the positive to the negative, while electrons actually flow from the negative to the positive. Although this makes current imaginary and backwards, it is still used here.) If this current carrying wire is placed in another magnetic field, the two fields will interact, and there will be a force on the wire. This force is perpendicular both to the flow of the current and the direction of the other magnetic field. In order to make this relationship between current direction, magnetic field direction, and force on current easier to understand, our high school physics teacher taught us a hand symbol affectionately known as the physics gang sign. First of all, this sign is always done with the RIGHT HAND. If done with the left, the directions will be incorrect. To make the gang sign: 1. Extend the right hand and stick up the thumb. 2. Point the index finger straight ahead, as if pointing the kid's version of a gun at someone. 3. Extend the middle finger to the left, so it is perpendicular to the index finger. The result is that each finger is perpendicular to the other two. If this is the case, you have made the sign correctly. If not, repeat steps 1-3. Middle finger represents Magnetic Field, the Index finger represents current (represented by I.), and the thumb therefore represents the force. Armed with this knowledge, you will be equipped to answer questions about electricity and magnetism interaction, and when you see your fellow physics students in the halls, you can flash the physics gang sign confident in the knowledge that you are the only ones who know how to use it. == Physics Exercises == I just created a new Wikibook here: http://wikibooks.org/wiki/Physics:_Exercises_with_Solutions. If anybody is good at or enjoys making up physics problems in any branch that would be a big help. What's there seems good. Perhaps the solutions could be more thorough? User:Brianjd 05:56, 2004 Jun 16 (UTC) == Theories == There are two theories on the physics page that are not on the theoretical physics page: Time Cube and Variable Speed of Light. I have not read much on physics so I dunno how accurate the lists are in general. But they seem to be inconsistent enough to warrant changing. User:Brianjd 05:59, 2004 Jun 16 (UTC) == Another category is experimental physics == Well, as an experimental physicist, I protest :-) The page mentiones 2 categories, theoretical and applied phyisics. I think they are apples and pears. The correct division is theoretical vs experimental, and fundamental vs applied. There are 4 combinations, so 4 categories. I am an experimental fundamentalist :-) (particle physics). I think I'll correct the page soon. User:Hidaspal 01:04, 10 Jul 2004 (UTC) :Thank you. I was wary about my division and nomenclature. User:Rmalloy 16:55, 11 Jul 2004 (UTC) == Proposed better definition for physics == As it appears "the study of energy and its interactions with matter" (symmetric to the definition of chemistry -- "the study of matter and its interactions with energy"). This is, generally, speaking, what physicists do: Celestial Mechanics (doesn't matter what planets and moons are made of, it still works). Quantum physics (doesn't matter what the particle is, it obeys these rules) Thermodynamics Fluid Dynamics Electrodynamics The only exception is possibly Nuclear Physics, which concerns itself deeply with the identity of the nucleons involved (but then some people would consider that to be Nuclear Chemistry) and the categorization of Elementary particles... Can someone remove the rambling portion about how Physicists think they are fundamental. I don't think that it really adds anything, or, at least, maybe, be moved to a section on the "culture" of physics. == Went ahead and streamlined this page. == There were some really rambling sections, which had very little to do with physics and more to do with rivalries between physicists and other scientists, or vague philosophical supposition of how physics is more important than the other sciences. I removed those and summed it up in a 'hinting' fashion in the introductory paragaph. I hope these aggressive changes aren't too unpalatable. :I think that you got rid of too much important information. Providing different points of view is extremely important, and there's nothing wrong with too much information, as long as it's right. Perhaps a vote on keeping it the way it is now or reverting it? --User:SonicAD 13:26, 17 Aug 2004 (UTC) :: Not true. Too much information can drown the reader in information, bore them, or just generally turn them away from the page. This is the "Physics" page, it should be very general, and in particular, it needs to be well organized. Look at how the Chemistry and Biology pages look (if you want, before I made some minor changes to them) and check out the history of the Physics page, and see how much of a sorry state it was in, in comparison. Instead of rambling on about it, provide links to other wiki pages which present alternative viewpoints, as well as 'generally accepted' viewpoints. :::It's true that streamlining was necessary. But you deleted a whole bunch of useful information. Quoting from the page on Wikipedia's Wikipedia:Editing policy: ::::"With large proposed deletions or replacements, it may be best to suggest changes in a discussion, lest the original author is discouraged from posting again. One person's improvement is another's desecration, and nobody likes to see their work destroyed without warning." :::The best idea would probably have been to have discussed the changes here first before making them. Doesn't quite matter right now, though. (Just remember that for the future) Best option right now, of course, is to allow for discussion. I, myself, do think that, especially in the first section, streamlining was needed, but not a few whole paragraphs worth of deletion --User:SonicAD 23:27, 17 Aug 2004 (UTC) ::::Fair enough. As a compromise measure i will replace some of the paragraphs and stick them elsewhere in the article. At the very least, they didn't belong at the top. == Calculus based VS. Algebra-based Physics == What exactly is the difference between calculus-based and algebra-based physics? Are they two different ways of approaching the same field, or is there a deeper meaning? I'm interested in taking an undergraduate degree in physics; therefore, before I take classes I'd like to familiarize myself with it on a general level. Thank you. --User:Cormac Canales 22:09, 26 Sep 2004 (UTC) :Well, IMO, the difference is that you can do derivations from more fundamental physical principles and solve more complex problems with knowledge from Calculus-based Physics courses, whereas with Algebra-based physics it's going to be more like "Here's the equation you use to get the solution." In any case, Algebra-based Physics courses will not go far beyond classical mechanics, very simple thermodynamics problems, a little special relativity, very simple electromagnetism, and some modern physics (probably a little more I'm missing...) There is absolutely no fundamental distinction aside from the fact that any treatment of Physics without Calculus will be extremely elementary. It's the difference between Little League and Major League.--User:Conwiktion 06:38, 2 Oct 2004 (UTC) :I've only taken a physics course where calculus was not applied (basic high school level physics), but I knew a little calculus at the time and it made some things much simpler. Now that I know calculus and have done some more physics in my spare time it seems frankly silly to approach physics without calculus. Using calculus makes the physics seem more unified, and less - like Conwiktion points out - like a bunch of equations. --User:Tothebarricades.tk 09:07, Jun 16, 2005 (UTC) == Ok... Time Cube link == Ok, I just wanted to call people's attentions to the fact that someone added link to the Time Cube article. Given that it is not a purely "physical" theory (in that it is not in the tradition of physics, and is based in a great part on pure metaphysics), I personally think that it should be removed. However, I would be greatly interested in what others thought on this (that's primarily the reason why I'm saying this ;) ).--User:Conwiktion 02:31, 6 Oct 2004 (UTC) :I vote to remove it, but I can't claim this is an unbiased opinion; I think the Time Cube theory was written by a Kook. --User:Mtruch 22:36, 10 Oct 2004 (UTC) == Theories, Truth, Proof, and the Scientific Method == I don't like the phrase "Experimental physicists perform experiments designed to be able to decide which of the proposed theories is true." as it implies that theories can be proven correct. Experiments only prove a theory false; positive results merely add support or strength to a theory, but never proof. Eventually a theory may become so well supported people think of it as proven, but that is dogma, not real proof. User:Mtruch 22:17, 10 Oct 2004 (UTC) :I agree with you. Would it be better to say something along the lines "Experimental physicists perform experiments designed to find evidence for or against a theoretical model" or "Experimental physicists perform experiments designed to test the predictions of a theoretical model"? Neither of these statements really have the same meaning of your correction, but they at least are not misleading like the article is currently, and they are easy to grasp by a lay audience. We don't want to give people like a 5th grader doing a school project the impression that (all) experimentalists are out to squash the careers of theorists by trying deliberately to disprove their theories :P--User:Conwiktion 04:49, 12 Oct 2004 (UTC) ::This is a ridiculously idealized picture of what experimentalists do. Experimentalists often work to find out how something works, in the absence of any theory. In fact it's often been the case that theory follows experiment! -- User:CYD :::Right, and the text in the article reflects this as well- I typed in a couple sentences that state that new theories are most often born of experimental results that contradict current theory. Should we re-arrange the text to make it clearer? I think that the idea that new theories are motivated by experimental results is implied in the (still highly idealized) idea that experimentalists perform experiments to test the predictions of a theory. If the theory does not have prediction power, then another theory must take its place. Aside from which, this article should be directed towards a lay audience- a proffesional or quasi-proffesional audience should have a clear enough picture of the roles that theorists and experimentalists play anyways. :::(Also, it appears that a pro-experimentalist has editted this section of the article, making it perilously close to being NPOV, in my opinion. Shall we correct this, or is the text as it stands OK?)--User:Conwiktion 14:25, 12 Oct 2004 (UTC) ::::Both points are important. As an experimentalist, I know that often theory follows experiment, and many experiments probe where no theories exist. The interaction between theorist and experimentalist is complex, with either side playing 'leader' whenever they see fit to head in that direction. That does not contradict with the fact that as a science, physics' theories cannot be ''proven''. Too many lay people I talk to talk about proven physics theories, or dismiss theories because they heard it was not (or has not yet) been proven. Theories get stronger with more supporting evidence (especially if they made a new prediction that experiments later support), or weaker (or fail) when experiments provide contradicting evidence, but never proven. ::::You can argue that I'm being pedantic, but the power of physics (actually, of the scientific method) comes from the inability to prove something; that a theory is only as good as the scientific experiments that support it, and long after people ''believe'' it's true, it can be squashed by a single experiment. (Of course, many theories that have been found false are still very accurate in certain regiemes, and therefore still have their place, i.e. classical mechanics). User:Mtruch 15:20, 12 Oct 2004 (UTC) :::::Yes, you are being pedantic. There is a distinction between Scientific Proof and Mathematical Proof. Scientific proof involves the concept of Occam's Razor. Sure you can really never prove anything right or wrong 100%, in science. You always have a model that is "good enough, for now" or "as good as we can seem to get it". The notion of "proof" does it imply that it must be 100% -- otherwise we would never need the phrase "proving beyond the shadow of a doubt". == Why aren't women good at physics? == You can call it stereotyping, you can call it sexist, you can call it whatever but physics history has shown that men has alway been better than women at this subject due to the extreme amount of dorkism men possess. Harvard/MIT has roughly 100 students annually graduating with a degree in physics and about less than 10 of those are women. It simply can't be coincidence. I continue to ask why in this present day and age, where both sexes are essentially equal, women can't do physics? Has there been any scientific research on this topic? Any links would be appreciated. :You answer yourself there. It is stereotyping, sexism and many more things. I direct you to read a bit of history of the human race. You will find that women were, are and most likely will be for sometime discriminated in education and in all other areas of society. Fact. --User:LexCorp 20:21, 19 Feb 2005 (UTC) :Incidentally, there's an article in a recent Scientific American issue about just this topic, and it's very interesting. It's a very touchy issue, but if we can accept that there are some fundamental differences in the brains of males and females, as research suggests, certain things can follow. [http://www.sciam.com/article.cfm?articleID=000363E3-1806-1264-980683414B7F0000 Here is the article.] --User:Tothebarricades.tk 09:01, Jun 16, 2005 (UTC) == How much force could an egg withstand? == Does anyone know how much force (in Newtons) a raw egg could withstand? User:Green789 15:32, 19 Feb 2005 (UTC) :At least 600N. User:Lecture Demonstration 14:28, 9 Mar 2005 (UTC) ::This would definately depend on how the force is applied. Squashing an egg vertically and horizontally is bound to be different. Also you could wind a string around the egg and increase the tension. If you really want to know you'll have to do some experiments.User:MarSch 14:55, 18 Mar 2005 (UTC) ==Energy conservation== is a consequence of time translation symmetry. I believe there are some models of GR that don't have this. Thus energy can simply disappear.User:MarSch 14:55, 18 Mar 2005 (UTC) == Learning Physics == I think there should be something on the main Physics page about Learning Physics, both as advice to the reader and to remind us all to attempt pedagogical coherence. Here's a draft: We "learn" a topic in Physics many times, in many ways. There are many aspects of Mechanics that our bodies understand perfectly, long before we learn names for things like angular momentum; for these, it is just a matter of learning a language -- a set of names for things and conventions for discussing their relationships. Electricity and Magnetism are quite different; we have almost no instinctive understanding of the subject and have to learn the words and their referents at the same time. This is often the "watershed" at which those comfortable with abstractions go on in Physics and those who rely on physical Common Sense balk at the strangeness of Physics. In primary and secondary school, most people get the impression that Physics is an exercise in algebra: all you need to do is pick the right formula, plug the right numbers in and "turn the crank". These unlucky souls are usually shocked when they meet up with University Physics for the first time and discover that the formulas are merely "shorthand" for something they are meant to ''understand''. The aspiring Physicist learns and re-learns each topic in Physics over and over, each time discovering the shallowness and inadequacy of her previous understanding. This is a delightful and rewarding experience that even those who do not aspire to become Physicists can enjoy. To accomodate this experience, it is important to identify the "level" at which any particular treatment is presented. There is no point in ''introducing'' Electricity and Magnetism using vector calculus for readers who have not yet studied calculus of any kind, even though it is a beautiful and elegant way to describe the subject. And there is no point in talking about "''F'' = ''m'' ''a''" to someone who has just completed a course in Lagrangian Mechanics. The reader needs to have a way of estimating whether the material is at his level, or mistaken impressions will result. OK, this is a little rambly; your turn. -- Jess :I think as an encyclopedia Electricity and Magnetism should be very general like "there exists something called charge and like charges attract etc..", but should then refer the reader to the different theories about electromagnetism, like "special relativity explains the necessity of magnetism in the presence of electrism(?)..". I will now take a look and see whether this is the caseUser:MarSch 16:39, 25 Mar 2005 (UTC) == Orgones and Times cubes == Dear all, As my first edit (I'm not even registered yet) I took out some references to "orgone theory" and "timecube theory" in the Fringe Theories section. Since there are many physicists, such as myself, contributing to this page (and I have little time) I won't even try to explain why these theories do not qualify as science. Just wanted to warn everyone that these links have been re-added (they are in the main article right now) by IP 136.186.1.117, with no reason stated. I will not revert the changes, since I consider myself an outsider. But someone with a little more time should take care of this. Cheers (Just took 5 minutes more checking the other contributions of IP 136.186.1.117. Seems that the Greenwich Mean Time article was also heavily edited... with timecube theory.) 14.55, 26th of April 2005 (GMT) :Very good obvservation. These are not physics theories at all. They aren't even scientific. Time cube is even up for deletion. Will remove these links. -User:MarSch 13:15, 27 Apr 2005 (UTC) == History == I thought the history section was a mess. A lot of physicists were never mentioned by their full name, some were mentioned twice for the same reason (Schwinger, Tomonoga and Feynman) and there was no clear order to the discussion of the 20th century. I've tried to spend a few minutes improving it. One thing I find frustrating about it is that there is a lot of emphasis given to theoretical particle physics at the expense of the experimental side and other branches of physics. It would be great if someone could make it a little more balanced. --User:Joke137 16:28, 7 May 2005 (UTC)
[[Image:Galileo2.png|thumb|130px|Galileo Galilei, :Category:physicists of the Scientific Revolution]] Physics (from Greek language from φυσικός (''physikos''): ''natural'', from φύσις (''physis''): Nature) is the study of energy and its interaction with matter (see chemistry, biology). Because of the primacy of energy in terms of the history of the universe, because all matter must interact with energy to express its properties and engage in transformations, and because energy is the key player when matter is decomposed into its most basic parts, physics is often considered to be the ''fundamental'' science. See also: Category talk:Physics Science Academic disciplines br:Category:Fizik lv:Category:Fizika ms:Category:Fizik nds:Category:Physik ta:Category:இயற்பியல் th:Category:ฟิสิกส์ vi:Category:Vật lý học zh-cn:Category:物理学 Add physics subcategory here
Ah - there is a cut-off occurring because you can only have 200 links on a page. So the quantum mechanics category and page aren't linked from here! Serious need to categorise some pages, here. User:Charles Matthews 19:43, 19 Feb 2005 (UTC) I agree. I came looking for a link to Particle Physics, but it seems to be cut off. This page needs to be cleaned up, particularly the individual articles in the category. User:StuTheSheep 20:29, Mar 17, 2005 (UTC) :Category talk:Physics#How to add categories to the physics articles: :You are free to restore the notice if you believe the issue is not yet properly addressed. I merely commented out the notice. User:Ancheta Wis 08:56, 23 Mar 2005 (UTC) ---- == How to add categories to the physics articles == You can add relevant categories to help populate the subcategory lists. To do this, at the foot of a Physics article (see section below for Physics subcategory), add the text
Add physics subcategory here
By saving your edit, you will produce a link to the physics subcategory. To test out the view, you can hit the Preview button to check whether your chosen subcategory is working. A colon (":") before the "category tag", e.g., :Category:Add physics subcategory here , will allow you to include the link to a physics subcategory in an article, without placing the article in that physics subcategory. By convention, the category tags are placed before the interwiki links, which are usually the very last tags on the article.
Note: To navigate the category lists, you can use the Category TOC links. Just click on the letter corresponding to the first letter of the article or subcategory which you seek. Alternatively, click on the ''next 200'' or ''previous 200'' links on the category page.
For more information, see also: Wikipedia:Category -- See the source text (click ''Edit this page'' above) for an example of the ''pipe trick'', which forces an alphabetization in the category sequence for an item.
==How to assign physics subcategories to the physics category==
To add subcategories to the :category:physics, first view that physics subcategory page via a link from some pertinent physics article in the subcategory. When viewing that physics subcategory page, click ''Edit this page'', and place the text
physics
at the foot of the physics subcategory page, above the interwiki links. (The category software currently allocates 200 links per category page, whether they are subcategory or article links.) ==Cleanup still needed==
See other meanings of words starting from letter:
Words begining with Physics:
PhysIcs
Physics
Physics
Physics
Physics
Physics-footer
Physics-footer
Physics-Mathematics_School_146
Physics-stub
Physics/Gravity
Physics86
Physicsforums.com
PhysicsWeb
Physics_(Aristotle)
Physics_(Aristotle)
Physics_(band)
Physics_Analysis_Workstation
Physics_and_Astronomy_Classification_Scheme
Physics_and_Astronomy_Students'_Union
Physics_and_Star_Trek
Physics_and_Star_Trek
Physics_and_Star_Trek/Miscellaneous_where_they_got_it_wrong
Physics_and_Star_Trek/Miscellaneous_where_they_got_it_wrong
Physics_and_Star_Trek/The_phaser
Physics_and_Star_Wars
Physics_and_Star_Wars
Physics_basic_topics
Physics_basic_topics
Physics_basic_topics
Physics_education
Physics_engine
Physics_Engineering
Physics_experiments
Physics_First
Physics_First
Physics_first
Physics_instrumentation
Physics_in_fiction
Physics_journals
Physics_lists
Physics_of_Computation
Physics_of_computation
Physics_of_firearms
Physics_of_mighty_beans
Physics_of_music
Physics_of_music
Physics_of_skiing
Physics_of_skiing
Physics_organizations
Physics_package
Physics_portal/?
Physics_portal/Categories
Physics_portal/Did_you_know
Physics_portal/Experimental_physics
Physics_portal/Exploring_physics
Physics_portal/Featured_article
Physics_portal/Featured_picture
Physics_portal/Intro
Physics_portal/Physics_news
Physics_portal/Related_fields
Physics_portal/Theoretical_physics
Physics_portal/Things_you_can_do
Physics_portal/Where_to_start
Physics_portal/Wikibooks
Physics_portal/Wikiprojects
Physics_practicals
Physics_Processing_Unit
Physics_professors
Physics_software
Physics_stubs
Physics_stubs
Physics_theory
Physics_theory
Physics_World
PhysIcs
#REDIRECT Physics
Physics
Physics (from the Greek language, φυσικός (''phusikos''), "natural", and φύσις (''phusis''), "nature") is the science of Nature in the broadest sense. Physicists study the behavior and properties of matter in a wide variety of contexts, ranging from the sub-nuclear particles from which all ordinary matter is made (particle physics) to the behavior of the material Universe as a whole (cosmology). Some of the properties studied in physics are common to ''all'' material systems, such as the conservation of energy. Such properties are often referred to as law of physics. Physics is sometimes said to be the "fundamental science", because each of the other natural sciences (biology, chemistry, geology, etc.) deals with particular types of material systems that obey the laws of physics. For example, chemistry is the science of molecules and the chemical compounds that they form in the bulk. The properties of a chemical are determined by the properties of the underlying molecules, which are accurately described by areas of physics such as quantum mechanics, thermodynamics, and electromagnetism. Physics is also closely related to mathematics. Physical theory are almost invariably expressed using mathematical relations, and the mathematics involved is generally more complicated than in the other sciences. The difference between physics and mathematics is that physics is ultimately concerned with descriptions of the material world, whereas mathematics is concerned with abstract patterns that need not have any bearing on it. However, the distinction is not always clear-cut. There is a large area of research intermediate between physics and mathematics, known as mathematical physics, devoted to developing the mathematical structure of physical theories. == Overview of physics research == === Theoretical and experimental physics === The culture of physics research differs from the other sciences in the separation of theory and experiment. Since the 20th century, most individual physicists have specialized in either theoretical physics or experimental physics, and in the twentieth century, very few physicists have been successful in both forms of research #fn_1. In contrast, almost all the successful theorists in biology and chemistry have also been experimentalists. Roughly speaking, theorists seek to develop theories that can describe and interpret existing experimental results and successfully predict future results, while experimentalists devise and perform experiments to explore new phenomena and test theoretical predictions. Although theory and experiment are developed separately, they are strongly dependent on each other. Progress in physics frequently comes about when experimentalists make a discovery that existing theories cannot account for, necessitating the formulation of new theories. Likewise, ideas arising from theory often inspire new experiments. In the absence of experiment, theoretical research can go in the wrong direction; this is one of the criticisms that have been levelled against M-theory, a popular theory in high-energy physics for which no practical experimental test has ever been devised. === Central theories === While physics deals with a wide variety of systems, there are certain theories that are used by all physicists. Each of these theories is believed to be basically correct, within a certain domain of validity. For instance, the theory of classical mechanics accurately describes the motion of objects, provided they are much larger than atoms and moving at much less than the speed of light. These theories continue to be areas of active research; for instance, a remarkable aspect of classical mechanics known as chaos theory was discovered in the 20th century, three centuries after the original formulation of classical mechanics by Isaac Newton. These "central theories" are important tools for research into more specialized topics, and any student of physics, regardless of his or her specialization, is expected to be well-versed in them. {| !Theory || Major subtopics || Concepts |- | Classical mechanics | Newton's laws of motion, Lagrangian mechanics, Hamiltonian mechanics, Chaos theory, Fluid dynamics, Continuum mechanics | Dimension, Space, Time, Motion, Length, Velocity, Mass, Momentum, Force (physics), Energy, Angular momentum, Torque, Conservation law, Harmonic oscillator, Wave, Mechanical work, Power (physics), |- | Electromagnetism | Electrostatics, Electricity, Magnetism, Maxwell's equations | Electric charge, Current (electricity), Electric field, Magnetic field, Electromagnetic field, Electromagnetic radiation, Magnetic monopole |- | Thermodynamics and Statistical mechanics | Heat engine, Kinetic theory | Boltzmann's constant, Entropy, Free energy, Heat, Partition function (statistical mechanics), Temperature |- | Quantum mechanics | Path integral formulation, Schrödinger equation, Quantum field theory | Hamiltonian (quantum mechanics), Identical particles, Planck's constant, Quantum entanglement, Quantum harmonic oscillator, Wavefunction, Zero-point energy |- | Theory of relativity | Special relativity, General relativity | Equivalence principle, Four-momentum, Reference frame, Spacetime, Speed of light |} === Major fields of physics === Contemporary research in physics is divided into several distinct fields that study different aspects of the material world. Condensed matter physics, by most estimates the largest single field of physics, is concerned with how the properties of bulk matter, such as the ordinary solids and liquids we encounter in everyday life, arise from the properties and mutual interactions of the constituent atoms. The field of atomic, molecular, and optical physics deals with the behavior of individual atoms and molecules, and in particular the ways in which they absorb and emit light. The field of particle physics, also known as "high-energy physics", is concerned with the properties of submicroscopic particles much smaller than atoms, including the elementary particles from which all other units of matter are constructed. Finally, the field of astrophysics applies the laws of physics to explain astronomy phenomena, ranging from the Sun and the other objects in the solar system to the universe as a whole. {| !Field ||Subfields || Major theories || Concepts |- | Astrophysics | Physical cosmology, Planetary science, Plasma physics | Big Bang, Cosmic inflation, General relativity, Law of universal gravitation | Black hole, Cosmic background radiation, Galaxy, Gravity, Gravitational radiation, Planet, Solar system, Star |- | Atomic, molecular, and optical physics | Atomic physics, Molecular physics, Optics, Photonics | Quantum optics | Atom, Diffraction, Electromagnetic radiation, Laser, Polarization, Spectral line |- | Particle physics | Accelerator physics, Nuclear physics | Standard Model, Grand unification theory, M-theory | Fundamental force (gravity, electromagnetism, weak interaction, strong interaction), Elementary particle, Antimatter, Spin (physics), Spontaneous symmetry breaking, Theory of everything Vacuum energy |- | Condensed matter physics | Solid state physics, Materials physics, Polymer physics | BCS theory, Bloch wave, Fermi gas, Fermi liquid, Many-body theory | Phase (matter) (gas, liquid, solid, Bose-Einstein condensate, superconductivity, superfluid), Electrical conduction, Magnetism, Self-organization, Spin (physics), Spontaneous symmetry breaking |} === Related fields === There are many areas of research that mix physics with other disciplines. For example, the wide-ranging field of biophysics is devoted to the role that physical principles play in biological systems, and the field of quantum chemistry studies how the theory of quantum mechanics gives rise to the chemical behavior of atoms and molecules. Some of these are listed below. Acoustics - Astronomy - Biophysics - Computational physics - Electronics - Engineering - Geophysics - Materials science - Mathematical physics - Medical physics - Physical chemistry - Physics of computation - Quantum chemistry - Quantum information science - Vehicle dynamics === Fringe theories === Cold fusion - Dynamic theory of gravity - Luminiferous aether - Steady state theory - Wave Structure Matter ==History== ''Main article: History of physics. See also Famous physicists and 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 science 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 philosophy terms, and never verified by systematic experimental testing as is popular today. There were exceptions and there are anachronisms: for example, the Hellenic civilization thinker Archimedes derived many correct quantitative descriptions of mechanics and hydrostatics. The works of Ptolemy (Astronomy) and Aristotle (Physics) were also found to not always match everyday observations. An example of this is an arrow flying through the air after leaving a bow contradicts with Aristotle's assertion that the natural state of all objects is at rest. [[Image:GodfreyKneller-IsaacNewton-1689.jpg|thumb|left|Isaac Newton]] The willingness to question previously held truths and search for new answers resulted in a period of major scientific advancements, now known as the Scientific Revolution. Its origins can be found in the European re-discovery of Aristotle in the twelfth and thirteenth centuries. This period culminated with the publication of the Philosophiae Naturalis Principia Mathematica in 1687 by Isaac Newton (dates disputed). The Scientific Revolution is held by most historians (e.g., Howard Margolis) to have begun in 1543, when there was brought to the Polish astronomer Nicolaus Copernicus the first printed copy of the book ''De Revolutionibus Orbium Coelestium '' he had written about a dozen years earlier. The thesis of this book is that the Earth moves around the Sun. Other significant scientific advances were made during this time by Galileo Galilei, Christiaan Huygens, Johannes Kepler, and Blaise Pascal. During the early 17th century, Galileo Galilei pioneered the use of experimentation to validate physical theories, which is the key idea in the scientific method. Galileo formulated and successfully tested several results in dynamics (mechanics), in particular the Law of Inertia. 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 gravity, 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 extended by Leonhard Euler, Joseph-Louis de Lagrange, William Rowan Hamilton, and others, who produced new results and new formulations of the theory. The law of universal gravitation initiated the field of astrophysics, which describes astronomy 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 century 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 electric current. [[Image:James Clerk Maxwell.jpg|thumb|left|140px|James Clerk Maxwell]] In 1821, 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 field and magnetic field. These 20 equations were later reduced, using vector calculus, to a set of Maxwell's equations by Oliver Heaviside. [[Image:Einstein patentoffice.jpg|thumb|right|140px|Albert Einstein in 1905]] 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. The ability to describe light in electromagnetic terms helped serve as a springboard for Albert Einstein's publication of his theory of special relativity. 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 inertial frame of reference 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 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 argued that astronomical observations demonstrate that the universe is expanding. From the 18th century onwards, thermodynamics was developed by Robert Boyle, Thomas Young (scientist), 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, Benjamin Thompson demonstrated the conversion of mechanical work into heat, and in 1847 James Joule stated the law of conservation of energy, in the form of heat as well as mechanical energy. Ludwig Boltzmann, in the 19th century, is responsible for the modern form of statistical mechanics. In 1895, Wilhelm 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 Maria Sklodowska-Curie, Pierre Curie, and others. This initiated the field of nuclear physics. In 1897, J.J. Thomson discovered the electron, the elementary particle which carries electrical current in electrical circuit. In 1904, he proposed the first model of the atom, known as the atom/plum pudding. (The existence of the atom had been proposed in 1808 by John Dalton.) Henri Becquerel accidentally discovered radioactivity in 1896. The next year J.J. Thomson discovered the electron. 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. In 1911, Ernest Rutherford deduced from rutherford scattering the existence of a compact atomic nucleus, with positively charged constituents dubbed protons. neutron, the neutral nuclear constituents, were discovered in 1932 by James 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 weapon. The German effort, led by Heisenberg, did not succeed, but the Allied Manhattan Project reached its goal. In America, a team led by Enrico Fermi achieved the first man-made nuclear chain reaction in 1942, and in 1945 the world's first nuclear weapon was detonated at Trinity site, near Alamogordo, New Mexico. In 1900, Max Planck published his explanation of blackbody radiation. This equation assumed that radiators are quantum in nature, which proved to be the opening argument in the edifice that would become quantum mechanics. Beginning in 1900, Max Planck, Einstein, Niels Bohr, and others developed quantum theories to explain various anomalous experimental results by introducing discrete energy levels. In 1925, Werner Heisenberg and 1926, Erwin Schrödinger and Paul Dirac formulated quantum mechanics, which explained the preceding heuristic quantum theories. In quantum mechanics, the outcomes of physical measurements are inherently probability; 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. [[Image:Richard feynman.jpg|thumb|left|140px|Richard Feynman]] 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 theory, 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 and confirmed in 1964 by James Watson Cronin and Val Fitch. This led to the so-called Standard Model of particle physics in the 1970s, which successfully describes all the elementary particles observed to date. 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, semiconductor, and superconductor. The pioneers of condensed matter physics include Felix 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 have declared the year 2005, the centenary of Einstein's annus mirabilis, as the World Year of Physics. == Future directions == ''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 supersymmetry. 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 astronomy and cosmology phenomena have yet to be satisfactorily explained, including the existence of GZK paradox, the baryon asymmetry, the accelerating universe and the galaxy rotation problem. Although much progress has been made in high-energy, quantum, and astronomical physics, many everyday phenomena, involving complex systems, chaos, or turbulence are still poorly understood. Complex problems that seem like they could be solved by a clever application of dynamics and mechanics, like the formation of sandpiles, nodes in trickling water, the shape of water droplet, mechanisms of surface tension catastrophe theory, 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 mathematics methods and computers which enabled complex systems to be modelled 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 biology 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.''==Notes== * Enrico Fermi, for example, was notable for his success in both experiment and theory. *Alpher, Herman, and Gamow. ''Nature'' 162,774 (1948). *[http://nobelprize.org/physics/laureates/1978/wilson-lecture.pdf Wilson's 1978 Nobel lecture] *[http://cwp.library.ucla.edu/Phase2/Wu,_Chien_Shiung@841234567.html see also: C.S. Wu's contribution to the overthrow of the conservation of parity ] *Yang, Mills 1954 ''Physical Review'' 95, 631. *Yang, Mills 1954 ''Physical Review'' 96, 191. == Suggested readings == *Richard Feynman, ''The Character of Physical Law'', Random House (Modern Library), 1994, hardcover, 192 pages, ISBN 0679601279 *Richard Feynman, Leighton, Sands, ''The Feynman Lectures on Physics'', Addison-Wesley 1970, 3 volumes, paperback, ISBN 0201021153. Hardcover commemorative edition, 1989, ISBN 0201500647 * Lev Davidovich Landau, ''et. al.'', ''Course of Theoretical Physics'', Butterworth-Heinemann, 1976, 10 volumes, paperback, ISBN 0750628960 * Roger Penrose, ''The Road to Reality: A complete guide to the laws of the universe'', Knopf, 2004, ISBN 0-679-45443-8, LoC QC20.P366 2005 * Jearl Walker, ''The Flying Circus of Physics'', Wiley, 1977, paperback, 312 pages, ISBN 047102984X * Anthony James Leggett, ''The Problems of Physics'', Oxford University Press, 1988, ISBN 0192891863 * Paul A. Tipler & Ralph A. Llewellyn, ''Modern Physics, Fourth edition'', W H Freeman & Co, 2002, hardcover, 700 pages, ISBN 0716743450 == Basic Physics == * Paul Hewitt, ''Conceptual Physics with Practicing Physics Workbook (9th Edition)'', Addison Wesley Publishing Company, 2001, hardcover, 790 pages, ISBN 0321052021. A non-mathematical introduction to physics. * Douglas C. Giancoli, ''Physics: Principles with Applications, 6/E'', Prentice Hall, 2005, 1040 pages, ISBN: 0130606200. This is an algebra-based physics textbook. * Jerry D. Wilson & Anthony J. Buffa, ''College Physics (5th edition)'', Prentice Hall, 2002, 2 volumes, 1040 pages, ISBN 0130676446. This is a calculus-based physics textbook. == See also == * List of physics topics == External links == * [news://sci.physics sci.physics] The Usenet general physics newsgroup. * [http://math.ucr.edu/home/baez/physics/ Usenet Physics FAQ]. An FAQ compiled by sci.physics and other physics newsgroups. * [http://scienceworld.wolfram.com/physics/ World of Physics]. An online encyclopedic dictionary of physics. * [http://hyperphysics.phy-astr.gsu.edu/hbase/hph.html HyperPhysics]. An online "exploration environment" for physics. * [http://www.nobel.se/physics/articles/karlsson/index.html#2 The Nobel Prize in Physics 1901-2000]. Website of the Nobel Prize in Physics. * [http://www.physics.org/ Physics.org]. Web portal run by the [http://www.iop.org/ Institute of Physics]. * [http://www.aip.org/index.html AIP.org] Website of the American Institute of Physics. * [http://spsnational.org] Website of the Society of Physics Students * [http://www.physicstoday.org] [http://www.physicstoday.org Physics Today] - Your daily physics news and research source * [http://www.physics2005.org] Website of the World Year of Physics 2005 * [http://www.aps.org] Website of the American Physical Society * [http://musr.physics.ubc.ca/~jess/hr/skept/] The Skeptic's Guide to Physics Physics for students *[http://www.onlinephysicshelp.com Online Physics Help for Students] Physics Science Natural sciences Academic disciplines School subjects bn:পদার্থবিদ্যা br:Fizik bs:Fizika fa:فیزیک ga:Fisic hi:भौतिकी ka:ფიზიკა la:Physica li:Natuurkónde lv:Fizika ms:Fizik nds:Physik simple:Physics th:ฟิสิกส์ vi:V%E1%BA%ADt l%C3%BD h%E1%BB%8Dc vo:Fsd zh-min-nan:Bu̍t-lí-ha̍k
Physics
''Please post new comments down the bottom. If you are adding a new topic, you can click the plus sign next to edit.'' ==Definition== ''[...]'' As for a definition, may I suggest: Physics is the study of nature in the broadest sense. Physicists attempt to find the most general rules that govern all of nature. Physics generally breaks down in to the study of the properties of matter, fields, space, time, and energy and how they interact. To describe these phenomena, physicists generally us the most precise language available to them, mathematics. Or something of that general sort. Perhaps even a mention that physics really is the study of everything in nature (i.e., mention that chemistry is a subset of physics that is governed by the molecular-atomic description of matter, and that biology is a subset of chemistry). Just musing. --BlackGriffen :Ok, I like your definition ''[...]'' :I'm not sure all biologist would agree with your reductionist view of biology as a subset of chemistry as a subset of physics, so I don't want to go there. Biologists pose and answer questions that are different from questions of physics. For instance, even if you knew all laws of physics, you still wouldn't know why we have our eyes in the head and not on our asses. --AxelBoldt ::''[...]'' I suggest to move :Quantum electrodynamics and :Statistical Mechanics to central theories. --:css ::I think something should be included on ancient greek physics. Not all was :Aristotle. From the top of my head :Archimedes found out interesting things that are still applied. :If I may return to the proposed definition ... I think it's a huge improvement. The current physics and chemistry definitions seem as if they were contrived solely to appear complementary. The distinction between physics and chemistry isn't that one emphasizes energy and the other matter, but rather that chemistry tends to focus on the interactions of chemical elements and compounds, whereas physics has a much broader (but more fundamental) scope ranging from quanta to cosmology. --Scrutchfield ::And what do "quanta" and "cosmology" have in common? Energy. To simply categorize physics as "the study of everything" is imperceptive. When modeling sand falling into a pile (or nuts sorting in a jar) a physicist doesn't really care about the identity of the particles at hand, just certain "bulk" properties that relate to its energetics. The chemist tries to understand how the material composition in turn generates those energetic qualities, but then usually isn't capable of formulating the dynamic description of what happens when it's shaken (or spilled). A physicst usually could care less about why niobium is better for a collider than copper, just that it is. And chemists don't just care about chemical elements and compounds, there is a whole field of chemistry dedicated to monitoring interactions of nuclei with nucleons (nuclear chemistry) -- still matter. As a point of culture, chemists tend to focus on the diversity of matter and how that affects interactions with energy-- and physicists focus on the unity of energy, and how that affects matter. Physical chemists very nicely bridge this -- they put quite a bit of energetics while still caring deeply about the identity of that which is being studied. While the duality may sound a bit contrived, there is definitely some truth to the statements, and while not perfect, it's more meaningful than what's there now. :::''And what do "quanta" and "cosmology" have in common? Momentum. To simply categorize physics as "the study of everything" is imperceptive. When modeling sand falling into a pile (or nuts sorting in a jar) a physicist doesn't really care about the identity of the particles at hand, just certain "bulk" properties that relate to its momenta.'' (Or replace momentum by mass, spin, or any of the other fundamental properties of objects, and you start to see the problem. There is nothing special about energy.) -- User:CYD :::: Momentum is intimately related to energy, anyways -- it's the velocity-integral of energy. Maybe here is something which will help out the distinction (as a simplified) example of the difference of cultures: One thing which astrophysicists study is the color of stars. This has everything to do with the blackbody radiation, which has to do with the temperature of the star, and really has not much to do with the composition of the stars. There are scientists who study the spectral lines which emanate from stars. This property depends very intimately on the matter composition of those stars. These scientists are known as astrochemists (Tak Oka@chicago is an example). Maybe I phrased that first sentence wrongly, but to distill physics to the "study of everything" can be seen as rendering it meaningless or maybe is a sign of arrogance on the part of physicists. The point is this: physicists care deeply about energy and the identity of the matter is usually irrelevant (insert "assume cow is a sphere" joke here). Chemists care deeply about the identity of the matter, and energetics are used only as a tool to descriptively understand what makes matter tick. :::: Maybe I should say it this way: momentum, spin, or any of the 'fundamental properties of objects' are manifestations of energy (or vice versa). Mass, in our current model, is the only one that you suggested that really isn't (I guess it's "sort of a mystery" as to why gravitational and inertial mass are the same). Energy is a convenient label because it's sort of 'in opposition' to matter. There is something special about matter which makes it diverse and interesting to chemists, an attitude which the canoncial physicist doesn't share (and of course there are people in between like physical chemists). When you say that physics is 'the study of everything', that implies that the biologist is a physicist and a chemist is a physicist, but I doubt either of them would agree, nor would a physicist feel that a biologist or a chemist is one of them. I'm not trying to drive a wedge between the disciplines, because there is still room for people who approach their subject of study in a hybrid way, but there are significant cultural differences which need to be addressed in the definition. I personally find it interesting that "conservation of mass" which frequently gets attributed as a "law of physics", when historically speaking, a chemist (Antoine Lavoisier) came up with it first. :::Actually, there are plenty of people who identify themselves as astrophysicists, that spend most of their time poring over spectral lines; that's how you find a star's redshift, among other things. As for signs of arrogance, making a blanket statement that physicists don't care about the identity of the matter they are looking at sure sounds like a great example of it. Incidentally, about two centuries passed after the formulation of mechanics before people started paying attention to the quantity we now call "energy"; I hope you're not trying to imply that Isaac Newton wasn't doing physics. There are countless other examples of physics research in which "energy" plays a minimal or zero role (for instance, cosmologists hardly ever talk about energy, because it is not "globally" well defined in general relativity.) But maybe you think of them as "hybrid" physicists? :::As for "''momentum, spin, or any of the 'fundamental properties of objects' are manifestations of energy (or vice versa)''", the less said the better. :::You'll probably reply that what you mean isn't really ''energy'' in the technical sense, but something else that makes a thing interesting to a physicist (call it "oompf" or whatever.) But then your thesis degenerates into a kind of hand-wavy philosophizing that may be an interesting topic of discussion of sci.physics, but doesn't belong on Wikipedia. -- User:CYD ::::Fair enough. However, there is something distinctly different about the cultures of chemistry and physics. When physicists deal with matter, they tend to deal with its bulk properties (elasticity, conductance, granularity, charge density, ionization potential, et cetera). You describe astrophysicists poring over spectral lines -- but, in your own words, the emphasis is on finding the redshift. There's nothing arrogant about noting the differences between cultures, there's no judgement involved there. Chemists use physicist's tools and physicists use chemist's tools. Nowhere am I implying that Newton wasn't doing physics -- in fact, he is the quintessential physicist -- Newton described the motion of planets and the effects of gravity in the most general and bulk of terms -- to him it didn't matter if it was a cow or a cannonball. ::::Maybe the problem is this: At one point, physics was "the study of everything" (and before that it was actually what we would call "medicine") -- this definition is rather outdated and imprecise. It needs to be revised. All life is physiology, all physiology is biology, all biology is chemistry, all chemistry is physics, and all physics is math..... User:Gelsamel 03:17, 1 Dec 2004 (UTC) ---- Hmm, I see that the history section in Physics has been copied pretty much wholesale into that article. That's fine, but I think we should also keep the section in Physics, because in addition to giving a history it also describes the subtopics of physics which I think is important for the article. As for History of Physics, if it is supposed to justify its own article, more historical material should be added to distinguish it, e.g. precise dates and a greater level of detail. Then at the end of Physics we add a line like "for a more detailed history of physics, see History of Physics" (currently pointless, as there isn't more detail yet.) --user:CYD ---- How about renaming "proposed theories" to, say, "current research topics"? Then we can include current experimental efforts as well. I don't think a new section should be added to the end of the article just for this, putting it with the other lists should be fine. -- user:CYD Then we'd have to get rid of Grand Unified Theory and Theory of Everything. There's no correspondence between the two categories so it wouldn't be a renaming but a replacing. :I'm not sure about that. GUTs and TOEs are part of current research efforts, aren't they? Alternatively, we could add descriptions of current research efforts to the end of the article, after the History of Physics section (actual descriptions, not just a list bullet points.) Or, we could have another article, say Current research topics in physics and link to it. --user:CYD What does TOE mean? Principally, it means M-theory. F-theory is related to M. Loop quantum gravity was never meant to be and never will be a TOE (and I agree with the opinion that it's not even scientific). Friedman(?) is looking at something that may or may not even be interesting. So basically TOE = M. I got the impression that research in GUTs is dead. Especially after '95 or so when everyone joined M-theory, or should I say, when the strings community absorbed the supergravity community. I'm sure that people are doing various calculations with GUTs and hoping for evidence one way or another but nobody seems to look for, nor expects, any conceptual breakthroughs. We can have anything you like, I'm not picky. But when the topic of hot research was introduced I came up with a big blank, which led me to think "hmmm, good question!" It took me quite a bit of brain raking to come up with 'search for SUSY' and 'search for Higgs boson'. I'd add dark matter (maybe!), gravitational waves and gamma ray bursts to the list, but I really don't know that much. -- ark Explaning high Tc superconductivity; explaining sonoluminescence; search for WIMPs; search for axions; explaining neutrino oscillations (and thus the solar neutrino problem); explaining the muon g-2 factor; explaining energetic cosmic rays; the large extra dimensions hypothesis; etc. Baez has a longer list at http://math.ucr.edu/home/baez/physics/General/open_questions.html -- user:CYD Large extra dimensions hypothesis? I've never heard of that! What is it? :An alternative to SUSY that's being seriously considered. You can find plenty of related sites with a Google search, but the original paper is here: http://arxiv.org/abs/hep-ph/9803315 -- user:CYD ::How about "Proposed theories and research directions"? And then we add Supersymmetry, Higgs boson etc. user:AxelBoldt, Monday, June 3, 2002 ---- I just replaced the translation of "phusis" as "matter" back to "nature", given the following two sites: http://www.studylight.org/lex/grk/view.cgi?number=5449 and http://www.dictionary.com/search?q=physics . user:AxelBoldt, Wednesday, May 29, 2002 ---- When a current is run through a wire, this current creates a magnetic field. (Please note that current is flows from the positive to the negative, while electrons actually flow from the negative to the positive. Although this makes current imaginary and backwards, it is still used here.) If this current carrying wire is placed in another magnetic field, the two fields will interact, and there will be a force on the wire. This force is perpendicular both to the flow of the current and the direction of the other magnetic field. In order to make this relationship between current direction, magnetic field direction, and force on current easier to understand, our high school physics teacher taught us a hand symbol affectionately known as the physics gang sign. First of all, this sign is always done with the RIGHT HAND. If done with the left, the directions will be incorrect. To make the gang sign: 1. Extend the right hand and stick up the thumb. 2. Point the index finger straight ahead, as if pointing the kid's version of a gun at someone. 3. Extend the middle finger to the left, so it is perpendicular to the index finger. The result is that each finger is perpendicular to the other two. If this is the case, you have made the sign correctly. If not, repeat steps 1-3. Middle finger represents Magnetic Field, the Index finger represents current (represented by I.), and the thumb therefore represents the force. Armed with this knowledge, you will be equipped to answer questions about electricity and magnetism interaction, and when you see your fellow physics students in the halls, you can flash the physics gang sign confident in the knowledge that you are the only ones who know how to use it. == Physics Exercises == I just created a new Wikibook here: http://wikibooks.org/wiki/Physics:_Exercises_with_Solutions. If anybody is good at or enjoys making up physics problems in any branch that would be a big help. What's there seems good. Perhaps the solutions could be more thorough? User:Brianjd 05:56, 2004 Jun 16 (UTC) == Theories == There are two theories on the physics page that are not on the theoretical physics page: Time Cube and Variable Speed of Light. I have not read much on physics so I dunno how accurate the lists are in general. But they seem to be inconsistent enough to warrant changing. User:Brianjd 05:59, 2004 Jun 16 (UTC) == Another category is experimental physics == Well, as an experimental physicist, I protest :-) The page mentiones 2 categories, theoretical and applied phyisics. I think they are apples and pears. The correct division is theoretical vs experimental, and fundamental vs applied. There are 4 combinations, so 4 categories. I am an experimental fundamentalist :-) (particle physics). I think I'll correct the page soon. User:Hidaspal 01:04, 10 Jul 2004 (UTC) :Thank you. I was wary about my division and nomenclature. User:Rmalloy 16:55, 11 Jul 2004 (UTC) == Proposed better definition for physics == As it appears "the study of energy and its interactions with matter" (symmetric to the definition of chemistry -- "the study of matter and its interactions with energy"). This is, generally, speaking, what physicists do: Celestial Mechanics (doesn't matter what planets and moons are made of, it still works). Quantum physics (doesn't matter what the particle is, it obeys these rules) Thermodynamics Fluid Dynamics Electrodynamics The only exception is possibly Nuclear Physics, which concerns itself deeply with the identity of the nucleons involved (but then some people would consider that to be Nuclear Chemistry) and the categorization of Elementary particles... Can someone remove the rambling portion about how Physicists think they are fundamental. I don't think that it really adds anything, or, at least, maybe, be moved to a section on the "culture" of physics. == Went ahead and streamlined this page. == There were some really rambling sections, which had very little to do with physics and more to do with rivalries between physicists and other scientists, or vague philosophical supposition of how physics is more important than the other sciences. I removed those and summed it up in a 'hinting' fashion in the introductory paragaph. I hope these aggressive changes aren't too unpalatable. :I think that you got rid of too much important information. Providing different points of view is extremely important, and there's nothing wrong with too much information, as long as it's right. Perhaps a vote on keeping it the way it is now or reverting it? --User:SonicAD 13:26, 17 Aug 2004 (UTC) :: Not true. Too much information can drown the reader in information, bore them, or just generally turn them away from the page. This is the "Physics" page, it should be very general, and in particular, it needs to be well organized. Look at how the Chemistry and Biology pages look (if you want, before I made some minor changes to them) and check out the history of the Physics page, and see how much of a sorry state it was in, in comparison. Instead of rambling on about it, provide links to other wiki pages which present alternative viewpoints, as well as 'generally accepted' viewpoints. :::It's true that streamlining was necessary. But you deleted a whole bunch of useful information. Quoting from the page on Wikipedia's Wikipedia:Editing policy: ::::"With large proposed deletions or replacements, it may be best to suggest changes in a discussion, lest the original author is discouraged from posting again. One person's improvement is another's desecration, and nobody likes to see their work destroyed without warning." :::The best idea would probably have been to have discussed the changes here first before making them. Doesn't quite matter right now, though. (Just remember that for the future) Best option right now, of course, is to allow for discussion. I, myself, do think that, especially in the first section, streamlining was needed, but not a few whole paragraphs worth of deletion --User:SonicAD 23:27, 17 Aug 2004 (UTC) ::::Fair enough. As a compromise measure i will replace some of the paragraphs and stick them elsewhere in the article. At the very least, they didn't belong at the top. == Calculus based VS. Algebra-based Physics == What exactly is the difference between calculus-based and algebra-based physics? Are they two different ways of approaching the same field, or is there a deeper meaning? I'm interested in taking an undergraduate degree in physics; therefore, before I take classes I'd like to familiarize myself with it on a general level. Thank you. --User:Cormac Canales 22:09, 26 Sep 2004 (UTC) :Well, IMO, the difference is that you can do derivations from more fundamental physical principles and solve more complex problems with knowledge from Calculus-based Physics courses, whereas with Algebra-based physics it's going to be more like "Here's the equation you use to get the solution." In any case, Algebra-based Physics courses will not go far beyond classical mechanics, very simple thermodynamics problems, a little special relativity, very simple electromagnetism, and some modern physics (probably a little more I'm missing...) There is absolutely no fundamental distinction aside from the fact that any treatment of Physics without Calculus will be extremely elementary. It's the difference between Little League and Major League.--User:Conwiktion 06:38, 2 Oct 2004 (UTC) :I've only taken a physics course where calculus was not applied (basic high school level physics), but I knew a little calculus at the time and it made some things much simpler. Now that I know calculus and have done some more physics in my spare time it seems frankly silly to approach physics without calculus. Using calculus makes the physics seem more unified, and less - like Conwiktion points out - like a bunch of equations. --User:Tothebarricades.tk 09:07, Jun 16, 2005 (UTC) == Ok... Time Cube link == Ok, I just wanted to call people's attentions to the fact that someone added link to the Time Cube article. Given that it is not a purely "physical" theory (in that it is not in the tradition of physics, and is based in a great part on pure metaphysics), I personally think that it should be removed. However, I would be greatly interested in what others thought on this (that's primarily the reason why I'm saying this ;) ).--User:Conwiktion 02:31, 6 Oct 2004 (UTC) :I vote to remove it, but I can't claim this is an unbiased opinion; I think the Time Cube theory was written by a Kook. --User:Mtruch 22:36, 10 Oct 2004 (UTC) == Theories, Truth, Proof, and the Scientific Method == I don't like the phrase "Experimental physicists perform experiments designed to be able to decide which of the proposed theories is true." as it implies that theories can be proven correct. Experiments only prove a theory false; positive results merely add support or strength to a theory, but never proof. Eventually a theory may become so well supported people think of it as proven, but that is dogma, not real proof. User:Mtruch 22:17, 10 Oct 2004 (UTC) :I agree with you. Would it be better to say something along the lines "Experimental physicists perform experiments designed to find evidence for or against a theoretical model" or "Experimental physicists perform experiments designed to test the predictions of a theoretical model"? Neither of these statements really have the same meaning of your correction, but they at least are not misleading like the article is currently, and they are easy to grasp by a lay audience. We don't want to give people like a 5th grader doing a school project the impression that (all) experimentalists are out to squash the careers of theorists by trying deliberately to disprove their theories :P--User:Conwiktion 04:49, 12 Oct 2004 (UTC) ::This is a ridiculously idealized picture of what experimentalists do. Experimentalists often work to find out how something works, in the absence of any theory. In fact it's often been the case that theory follows experiment! -- User:CYD :::Right, and the text in the article reflects this as well- I typed in a couple sentences that state that new theories are most often born of experimental results that contradict current theory. Should we re-arrange the text to make it clearer? I think that the idea that new theories are motivated by experimental results is implied in the (still highly idealized) idea that experimentalists perform experiments to test the predictions of a theory. If the theory does not have prediction power, then another theory must take its place. Aside from which, this article should be directed towards a lay audience- a proffesional or quasi-proffesional audience should have a clear enough picture of the roles that theorists and experimentalists play anyways. :::(Also, it appears that a pro-experimentalist has editted this section of the article, making it perilously close to being NPOV, in my opinion. Shall we correct this, or is the text as it stands OK?)--User:Conwiktion 14:25, 12 Oct 2004 (UTC) ::::Both points are important. As an experimentalist, I know that often theory follows experiment, and many experiments probe where no theories exist. The interaction between theorist and experimentalist is complex, with either side playing 'leader' whenever they see fit to head in that direction. That does not contradict with the fact that as a science, physics' theories cannot be ''proven''. Too many lay people I talk to talk about proven physics theories, or dismiss theories because they heard it was not (or has not yet) been proven. Theories get stronger with more supporting evidence (especially if they made a new prediction that experiments later support), or weaker (or fail) when experiments provide contradicting evidence, but never proven. ::::You can argue that I'm being pedantic, but the power of physics (actually, of the scientific method) comes from the inability to prove something; that a theory is only as good as the scientific experiments that support it, and long after people ''believe'' it's true, it can be squashed by a single experiment. (Of course, many theories that have been found false are still very accurate in certain regiemes, and therefore still have their place, i.e. classical mechanics). User:Mtruch 15:20, 12 Oct 2004 (UTC) :::::Yes, you are being pedantic. There is a distinction between Scientific Proof and Mathematical Proof. Scientific proof involves the concept of Occam's Razor. Sure you can really never prove anything right or wrong 100%, in science. You always have a model that is "good enough, for now" or "as good as we can seem to get it". The notion of "proof" does it imply that it must be 100% -- otherwise we would never need the phrase "proving beyond the shadow of a doubt". == Why aren't women good at physics? == You can call it stereotyping, you can call it sexist, you can call it whatever but physics history has shown that men has alway been better than women at this subject due to the extreme amount of dorkism men possess. Harvard/MIT has roughly 100 students annually graduating with a degree in physics and about less than 10 of those are women. It simply can't be coincidence. I continue to ask why in this present day and age, where both sexes are essentially equal, women can't do physics? Has there been any scientific research on this topic? Any links would be appreciated. :You answer yourself there. It is stereotyping, sexism and many more things. I direct you to read a bit of history of the human race. You will find that women were, are and most likely will be for sometime discriminated in education and in all other areas of society. Fact. --User:LexCorp 20:21, 19 Feb 2005 (UTC) :Incidentally, there's an article in a recent Scientific American issue about just this topic, and it's very interesting. It's a very touchy issue, but if we can accept that there are some fundamental differences in the brains of males and females, as research suggests, certain things can follow. [http://www.sciam.com/article.cfm?articleID=000363E3-1806-1264-980683414B7F0000 Here is the article.] --User:Tothebarricades.tk 09:01, Jun 16, 2005 (UTC) == How much force could an egg withstand? == Does anyone know how much force (in Newtons) a raw egg could withstand? User:Green789 15:32, 19 Feb 2005 (UTC) :At least 600N. User:Lecture Demonstration 14:28, 9 Mar 2005 (UTC) ::This would definately depend on how the force is applied. Squashing an egg vertically and horizontally is bound to be different. Also you could wind a string around the egg and increase the tension. If you really want to know you'll have to do some experiments.User:MarSch 14:55, 18 Mar 2005 (UTC) ==Energy conservation== is a consequence of time translation symmetry. I believe there are some models of GR that don't have this. Thus energy can simply disappear.User:MarSch 14:55, 18 Mar 2005 (UTC) == Learning Physics == I think there should be something on the main Physics page about Learning Physics, both as advice to the reader and to remind us all to attempt pedagogical coherence. Here's a draft: We "learn" a topic in Physics many times, in many ways. There are many aspects of Mechanics that our bodies understand perfectly, long before we learn names for things like angular momentum; for these, it is just a matter of learning a language -- a set of names for things and conventions for discussing their relationships. Electricity and Magnetism are quite different; we have almost no instinctive understanding of the subject and have to learn the words and their referents at the same time. This is often the "watershed" at which those comfortable with abstractions go on in Physics and those who rely on physical Common Sense balk at the strangeness of Physics. In primary and secondary school, most people get the impression that Physics is an exercise in algebra: all you need to do is pick the right formula, plug the right numbers in and "turn the crank". These unlucky souls are usually shocked when they meet up with University Physics for the first time and discover that the formulas are merely "shorthand" for something they are meant to ''understand''. The aspiring Physicist learns and re-learns each topic in Physics over and over, each time discovering the shallowness and inadequacy of her previous understanding. This is a delightful and rewarding experience that even those who do not aspire to become Physicists can enjoy. To accomodate this experience, it is important to identify the "level" at which any particular treatment is presented. There is no point in ''introducing'' Electricity and Magnetism using vector calculus for readers who have not yet studied calculus of any kind, even though it is a beautiful and elegant way to describe the subject. And there is no point in talking about "''F'' = ''m'' ''a''" to someone who has just completed a course in Lagrangian Mechanics. The reader needs to have a way of estimating whether the material is at his level, or mistaken impressions will result. OK, this is a little rambly; your turn. -- Jess :I think as an encyclopedia Electricity and Magnetism should be very general like "there exists something called charge and like charges attract etc..", but should then refer the reader to the different theories about electromagnetism, like "special relativity explains the necessity of magnetism in the presence of electrism(?)..". I will now take a look and see whether this is the caseUser:MarSch 16:39, 25 Mar 2005 (UTC) == Orgones and Times cubes == Dear all, As my first edit (I'm not even registered yet) I took out some references to "orgone theory" and "timecube theory" in the Fringe Theories section. Since there are many physicists, such as myself, contributing to this page (and I have little time) I won't even try to explain why these theories do not qualify as science. Just wanted to warn everyone that these links have been re-added (they are in the main article right now) by IP 136.186.1.117, with no reason stated. I will not revert the changes, since I consider myself an outsider. But someone with a little more time should take care of this. Cheers (Just took 5 minutes more checking the other contributions of IP 136.186.1.117. Seems that the Greenwich Mean Time article was also heavily edited... with timecube theory.) 14.55, 26th of April 2005 (GMT) :Very good obvservation. These are not physics theories at all. They aren't even scientific. Time cube is even up for deletion. Will remove these links. -User:MarSch 13:15, 27 Apr 2005 (UTC) == History == I thought the history section was a mess. A lot of physicists were never mentioned by their full name, some were mentioned twice for the same reason (Schwinger, Tomonoga and Feynman) and there was no clear order to the discussion of the 20th century. I've tried to spend a few minutes improving it. One thing I find frustrating about it is that there is a lot of emphasis given to theoretical particle physics at the expense of the experimental side and other branches of physics. It would be great if someone could make it a little more balanced. --User:Joke137 16:28, 7 May 2005 (UTC)
Physics
[[Image:Galileo2.png|thumb|130px|Galileo Galilei, :Category:physicists of the Scientific Revolution]] Physics (from Greek language from φυσικός (''physikos''): ''natural'', from φύσις (''physis''): Nature) is the study of energy and its interaction with matter (see chemistry, biology). Because of the primacy of energy in terms of the history of the universe, because all matter must interact with energy to express its properties and engage in transformations, and because energy is the key player when matter is decomposed into its most basic parts, physics is often considered to be the ''fundamental'' science. See also: Category talk:Physics Science Academic disciplines br:Category:Fizik lv:Category:Fizika ms:Category:Fizik nds:Category:Physik ta:Category:இயற்பியல் th:Category:ฟิสิกส์ vi:Category:Vật lý học zh-cn:Category:物理学 Add physics subcategory here
Physics
Ah - there is a cut-off occurring because you can only have 200 links on a page. So the quantum mechanics category and page aren't linked from here! Serious need to categorise some pages, here. User:Charles Matthews 19:43, 19 Feb 2005 (UTC) I agree. I came looking for a link to Particle Physics, but it seems to be cut off. This page needs to be cleaned up, particularly the individual articles in the category. User:StuTheSheep 20:29, Mar 17, 2005 (UTC) :Category talk:Physics#How to add categories to the physics articles: :You are free to restore the notice if you believe the issue is not yet properly addressed. I merely commented out the notice. User:Ancheta Wis 08:56, 23 Mar 2005 (UTC) ---- == How to add categories to the physics articles == You can add relevant categories to help populate the subcategory lists. To do this, at the foot of a Physics article (see section below for Physics subcategory), add the text
By saving your edit, you will produce a link to the physics subcategory. To test out the view, you can hit the Preview button to check whether your chosen subcategory is working. A colon (":") before the "category tag", e.g.,
at the foot of the physics subcategory page, above the interwiki links. (The category software currently allocates 200 links per category page, whether they are subcategory or article links.) ==Cleanup still needed==
See other meanings of words starting from letter:
P
PA | PB | PC | PD | PE | PF | PG | PH | PI | PJ | PK | PL | PM | PN | PO | PR | PS | PT | PU | PW | PX | PY | PZ |Words begining with Physics:
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