The laws list
candela to Curie-Weiss law.

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candela; cd
The fundamental SI unit of luminous intensity defined as the luminous intensity in a given direction of a source that emits monochromatic photons of frequency 540 x 1012 Hz and has a radiant intensity in that direction of 1/683 W/sr.
Carnot's theorem (S. Carnot)
The theorem which states that no engine operating between two temperatures can be more efficient than a reversible engine.
Casimir effect (Casimir)
A quantum mechanical effect, where two very large plates placed close to each other will experience an attractive force, in the absence of other forces. The cause is virtual particle-antiparticle pair creation in the vicinity of the plates. Also, the speed of light will be increased in the region between the two plates, in the direction perpendicular to them.
causality principle
The principle that cause must always preceed effect. More formally, if an event A ("the cause") somehow influences an event B ("the effect") which occurs later in time, then event B cannot in turn have an influence on event A. That is, event B must occur at a later time t than event A, and further, all frames must agree upon this ordering.

The principle is best illustrated with an example. Say that event A constitutes a murderer making the decision to kill his victim, and that event B is the murderer actually committing the act. The principle of causality puts forth that the act of murder cannot have an influence on the murderer's decision to commit it. If the murderer were to somehow see himself committing the act and change his mind, then a murder would have been committed in the future without a prior cause (he changed his mind). This represents a causality violation. Both time travel and faster-than-light travel both imply violations of causality, which is why most physicists think they are impossible, or at least impossible in the general sense.

centrifugal pseudoforce
A pseudoforce that occurs when one is moving in uniform circular motion. One feels a "force" directed outward from the center of motion.
Chandrasekhar limit (S. Chandrasekhar; 1930)
A limit which mandates that no white dwarf (a collapsed, degenerate star) can be more massive than about 1.4 masses solar. Any degenerate mass more massive must inevitably collapse into a neutron star.
Charles' law (J.A.C. Charles; c. 1787)
The volume of an ideal gas at constant pressure is proportional to the thermodynamic temperature of that gas.
Cherenkov [Cerenkov] radiation (P.A. Cherenkov)
Radiation emitted by a charged particle which is moving faster than light in the medium through which it is travelling. No particle can travel faster than light in vacuum, but the speed of light in other media, such as water, glass, etc., are considerably lower. Cherenkov radiation is the electromagnetic analogue of the sonic boom, though Cherenkov radiation is a shockwave set up in the electromagnetic field.
chronology protection conjecture (S.W. Hawking)
The concept that the formation of any closed timelike curve will automatically be destroyed by quantum fluctuations as soon as it is formed. In other words, quantum fluctuations prevent time machines from being created.
Coanda effect
The effect that indicates that a fluid tends to flow along a surface, rather than flow through free space.
complementarity principle (N. Bohr)
The principle that a given system cannot exhibit both wave-like behavior and particle-like behavior at the same time. That is, certain experiments will reveal the wave-like nature of a system, and certain experiments will reveal the particle-like nature of a system, but no experiment will reveal both simultaneously.
Compton effect (A.H. Compton; 1923)
An effect that demonstrates that photons (the quantum of electromagnetic radiation) have momentum. A photon fired at a stationary particle, such as an electron, will impart momentum to the electron and, since its energy has been decreased, will experience a corresponding decrease in frequency.
conservation laws
A law which states that, in a closed system, the total quantity of something will not increase or decrease, but remain exactly the same; that is, its rate of change is zero. For physical quantities, it states that something can neither be created nor destroyed. Mathematically, if a scalar X is the quantity considered, then
dX/dt = 0,
or, equivalently,
X = constant.
For a vector field F, the conservation law is written as
div F = 0;
that is, the vector field F is divergence-free everywhere (i.e., has no sources or sinks).

Some specific examples of conservation laws are:

conservation of mass-energy
The total mass-energy of a closed system remains constant.
conservation of electric charge
The total electric charge of a closed system remains constant.
conservation of linear momentum
The total linear momentum of a closed system remains constant.
conservation of angular momentum
The total angular momentum of a closed system remains constant.

There are several other laws that deal with particle physics, such as conservation of baryon number, of strangeness, etc., which are conserved in some fundamental interactions (such as the electromagnetic interaction) but not others (such as the weak interaction).

constancy principle (A. Einstein)
One of the postulates of A. Einstein's special theory of relativity, which puts forth that the speed of light in vacuum is measured as the same speed to all observers, regardless of their relative motion. That is, if I'm travelling at 0.9 c away from you, and fire a beam of light in that direction, both you and I will independently measure the speed of that beam as c.

One of the results of this postulate (one of the predictions of special relativity) is that no massive particle can be accelerated to (or beyond) lightspeed, and thus the speed of light also represents the ultimate cosmic speed limit. Only massless particles (collectively called luxons, including photons, gravitons, and possibly neutrinos, should they prove to indeed be massless) travel at lightspeed, and all other particles must travel at slower speeds.

See tachyons, causality principle.

equation of continuity
An equation which states that a fluid flowing through a pipe flows at a rate which is inversely proportional to the cross-sectional area of the pipe. That is, if the pipe constricts, the fluid flows faster; if it widens, the fluid flows slower. It is in essence a restatement of the consevation of mass during constant flow.
Cooper pairs (L.N. Cooper; 1957)
See BCS theory.
Copernican principle (N. Copernicus)
The idea, suggested by Copernicus, that the Sun, not the Earth, is at the center of the Universe. We now know that neither idea is correct (the Sun is not even located at the center of our Galaxy, much less the Universe), but it set into effect a long chain of demotions of Earth's and our place in the Universe, to where it is now: On an unimpressive planet orbiting a mediocre star in a corner of a typical galaxy, lost in the Universe.
Coriolis pseudoforce (G. de Coriolis; 1835)
A pseudoforce which arises because of motion relative to a frame which is itself rotating relative to second, inertial frame. The magnitude of the Coriolis "force" is dependent on the speed of the object relative to the noninertial frame, and the direction of the "force" is orthogonal to the object's velocity.
correspondence limit (N. Bohr)
The limit at which a more general theory reduces to a more specialized theory when the conditions that the specialized theory requires are taken away.

See correspondence principle.

correspondence principle (N. Bohr)
The principle that when a new, more general theory is put forth, it must reduce to the more specialized (and usually simpler) theory under normal circumstances. There are correspondence principles for general relativity to special relativity and special relativity to Newtonian mechanics, but the most widely known correspondence principle (and generally what is meant when one says "correspondence principle") is that of quantum mechanics to classical mechanics.

See correspondence limit.

cosmic background radiation; primal glow
The background of radiation mostly in the frequency range 3 x 1011 to 3 x 108 Hz discovered in space in 1965. It is believed to be the cosmologically redshifted radiation released by the big bang itself. Presently it has an energy density in empty space of about 4 x 10-14 J/m3.
cosmic censorship conjecture (R. Penrose, 1979)
The conjecture, so far totally undemonstrated within the context of general relativity, that all singularities (with the possible exception of the big bang singularity) are accompanied by event horizons which completely surround them at all points in time. That is, problematic issues with the singularity are rendered irrelevant, since no information can ever escape from a black hole's event horizon.
cosmological constant; Lambda
The constant introduced to the Einstein field equation, intended to admit static cosmological solutions. At the time the current philosophical view was the steady-state model of the Universe, where the Universe has been around for infinite time. Early analysis of the field equation indicated that general relativity allowed dynamic cosmological models only (ones that are either contracting or expanding), but no static models. Einstein introduced the most natural abberation to the field equation that he could think of: the addition of a term proportional to the spacetime metric tensor, g, with the constant of proportionality being the cosmological constant:
G + Lambda g = 8 pi T.

Hubble's later discovery of the expansion of the Universe indicated that the introduction of the cosmological constant was unnecessary; had Einstein believed what his field equation was telling him, he could have claimed the expansion of the Universe as perhaps the greatest and most convincing prediction of general relativity; he called this the "greatest blunder of my life."

cosmological redshift
An effect where light emitted from a distant source appears redshifted because of the expansion of spacetime itself.

Compare Doppler effect.

coulomb; C (after C. de Coulomb, 1736-1806)
The derived SI unit of electric charge, defined as the amount of charge transferred by a current of 1 A in a period of 1 s; it thus has units of A s.
Coulomb's law (C. de Coulomb)
The primary law for electrostatics, analogous to Newton's law of universal gravitation. It states that the force between two point charges is proportional to the algebraic product of their respective charges as well as proportional to the inverse square of the distance between them; mathematically,
F = 1/(4 pi epsilon0) (q Q/r2) e,
where q and Q are the strengths of the two charges, r is the distance between the two, and e is a unit vector directed from the test charge to the second.
Curie constant; C (P. Curie)
A characteristic constant, dependent on the material in question, which indicates the proportionality between its susceptibility and its thermodynamic temperature.
Curie's law (P. Curie)
The susceptibility, khi, of an isotropic paramagnetic substance is related to its thermodynamic temperature T by the equation
khi = C/T

See Curie-Weiss law.

Curie-Weiss law (P. Curie, P.-E. Weiss)
A more general form of Curie's law, which states that the susceptibility, khi, of an paramagnetic substance is related to its thermodynamic temperature T by the equation
khi = C/T - W
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