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Aether Behavior compiled by Erik Max Francis

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                             version 1.0
                     compiled by Erik Max Francis
          Please send all comments, additions, corrections,
               and suggestions to

Ampere's law (A.M. Ampere)
    The line integral of the magnetic flux around a closed curve is
    proportional to the algebraic sum of electric currents flowing
    through that closed curve.
        This was later modified to add a second term when it was
    incorporated into Maxwell's equations.
anthropic principle
    Weak anthropic principle.  The conditions necessary for the
        development of intelligent life will be met only in certain
        regions that are limited in space and time.  That is, the
        region of the Universe in which we live is not necessarily
        representative of a purely random set of initial conditions;
        only those favorable to intelligent life would actually
        develop creatures who wonder what the initial conditions of
        the Universe were.
    Strong anthropic principle.  A more forceful argument that the
        weak principle:  It states, rather straightforwardly, that if
        the laws of the Universe were not conducive to the development
        of intelligent creatures to ask about the initial conditions
        of the Universe, intelligent life would never have evolved to
        ask the question in the first place.  In other words, the laws
        of the Universe are the way they are because if they weren't,
        you would not be able to ask such a question.
Arago spot
    A bright spot that appears in the shadow of a uniform disc being
    backlit by monochromatic light emanating from a point source.
Archimedes' principle
    A body that is submerged in a fluid is buoyed up by a force equal
    in magnitude to the weight of the fluid that is displaced, and
    directed upward along a line through the center of gravity of the 
    displaced fluid.
Atwood's machine
    A weight-and-pulley system devised to measure the acceleration due 
    to gravity at Earth's surface by measuring the net acceleration of 
    a set of weights of known mass around a frictionless pulley.
Avogadro constant; L; N_A (Count A. Avogadro; 1811)
    The number of atoms or molecules in a sample of an idea gas which 
    is at standard temperature and pressure.  It is equal to about 
    6.022 52 x 10^23 mol^-1.
Avogadro's hypothesis (Count A. Avogadro; 1811)
    Equal volumes of all gases at the same temperature and pressure 
    contain equal numbers of molecules.  It is, in fact, only true for 
    ideal gases.
Balmer series (J. Balmer; 1885)
    An equation which describes the emission spectrum of hydrogen when 
    an electron is jumping to the second orbital; four of the lines 
    are in the visible spectrum, and the remainder are in the 
baryon decay
    The theory, predicted by several grand-unified theories, that a
    class of subatomic particles called baryons (of which the nucleons
    -- protons and neutrons -- are members) are not ultimately stable
    but indeed decay.  Present theory and experimentation demonstrate
    that if protons are indeed unstable, they decay with a halflife of
    at least 10^34 y.
Bernoulli's equation
    An equation which states that an irrotational 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
BCS theory (J. Bardeen, L.N. Cooper, J.R. Schrieffer; 1957)
    A theory put forth to explain both superconductivity and
    superfluidity.  It suggests that in the superconducting (or
    superfluid) state electrons form Cooper pairs, where two electrons
    act as a single unit.  It takes a nonzero amount of energy to
    break such pairs, and the imperfections in the superconducting
    solid (which would normally lead to resistance) are incapable of
    breaking the pairs, so no dissipation occurs and there is no
Biot-Savart law (J.B. Biot, F. Savart)
    A law which describes the contributions to a magnetic field by an 
    electric current.  It is analogous to Coulomb's law for 
blackbody radiation
    The radiation -- the radiance at particular frequencies all across 
    the spectrum -- produced by a blackbody -- that is, a perfect 
    radiator (and absorber) of heat.  Physicists had difficulty 
    explaining it until Planck introduced his quantum of action.
Bode's law
    A mathematical formula which generates, with a fair amount of 
    accuracy, the semimajor axes of the planets in order out from the 
    Sun.  Write down the sequence 0, 3, 6, 12, 24, . . . and then add 
    4 to each term.  Then divide each term by 10.  This is intended to 
    give you the positions of the planets measured in astronomical 
        Bode's law had no theoretical justification when it was first 
    introduced; it did, however, agree with the soon-to-be-discovered 
    planet Uranus' orbit (19.2 au actual; 19.7 au predicted).  
    Similarly, it predicted a missing planet betwen Mars and Jupiter,
    and shortly thereafter the asteroids were found in very similar
    orbits (2.8 au actual for Ceres; 2.8 au predicted).  However, the
    series seems to skip over Neptune's orbit.
Bohr's 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.
Bohr magneton (N. Bohr)
    The quantum of magnetic moment.
Bohr radius (N. Bohr)
    The distance corresponding the mean distance of an electron from
    the nucleus in the ground state.
Boltzmann constant; k (L. Boltzmann)
    A constant which describes the relationship between temperature
    and kinetic energy for molecules in an ideal gas.  It is equal to
    1.380 622 x 10^-23 J/K.
Boyle's law (R. Boyle; 1662); Mariotte's law (E. Mariotte; 1676)
    The product of the pressure and the volume of an ideal gas at
    constant temperature is a constant.
Brackett series (Brackett)
    The series which describes the emission spectrum of hydrogen when
    the electron is jumping to the fourth orbital.  All of the lines
    are in the infrared portion of the spectrum.
Bragg's law (Sir W.L. Bragg; 1912)
    When a beam of x-rays strikes a crystal surface in which the
    layers of atoms or ions are regularly separated, the maximum
    intensity of the reflected ray occurs when the sin of the
    compliment of the angle of incidence is equal to an integer
    multiplied by the wavelength of x-rays divided by twice the
    distance between layers of atoms or ions.
Brewster's law (D. Brewster)
    The extent of the polarization of light reflected from a
    transparent surface is a maximum when the reflected ray is at
    right angles to the refracted ray.
Brownian motion (R. Brown; 1827)
    The continuous random motion of solid microscopic particles when
    suspended in a fluid medium due to the consequence of continuous
    bombardment by atoms and molecules.
Carnot's theorem (S. Carnot)
    The theorem which states that no engine operating between two 
    temperatures can be more efficient than a reversible engine.
centrifugal pseudoforce
    A pseudoforce -- a fictitious force resulting from being in a non- 
    inertial frame of reference -- that occurs when one is moving in 
    uniform circular motion.  One feels a "force" 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 1.2 solar masses.  
    Anything more massive must inevitably collapse into a neutron 
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 radiation (Cherenkov)
    Radiation emitted by a massive 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.
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.
Coriolis pseudoforce (G. de Coriolis; 1835)
    A pseudoforce -- a fictitious force, like the centrifugal "force"
    -- which arises because the rotation of the Earth varies at
    different latitutdes (maximum at the equator, zero at the poles).
correspondence principle
    The principle that when a new, more specialized theory is put
    forth, it must reduce to the more general (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.
cosmic background radiation (primal glow)
    The background of radiation mostly in the frequency range 3 x 
    10^11 to 3 x 10^8 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/m^3.
cosmological redshift
    An effect where light emitted from a distant source appears 
    redshifted because of the expansion of space itself.  Compare with 
    the Doppler effect.
Coulomb's law
    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.
Curie-Weiss law (P. Curie, P.-E. Weiss)
    A more general form of Curie's law, which states that the
    susceptibility of a paramagnetic substance is inversely
    proportional to the thermodynamic temperature of the substance
    less the Weiss constant, a characteristic of that substance.
Curie's law (P. Curie)
    The susceptibility of a paramagnetic substance is inversely
    proportional to the thermodynamic temperature of the substance.
    The constant of proportionality is called the Curie constant.
Dalton's law of partial pressures (J. Dalton)
    The total pressure of a mixture of ideal gases is equal to the sum
    of the partial pressures of its components; that is, the sum of
    the pressures that each component would exert if it were present
    alone and occuped the same volume as the mixture.
Davisson-Germer experiment (C.J. Davisson, L.H. Germer; 1927)
    An experiment that conclusively confirmed the wave nature of
    electrons; diffraction patterns were observed by an electron beam
    penetrating into a nickel target.
de Broglie wavelength (L. de Broglie; 1924)
    The prediction that particles also have wave characteristics,
    where the effective wavelength of a particle would be inversely 
    proportional to its momentum, where the constant of 
    proportionality is the Planck constant.
Doppler effect (C.J. Doppler)
    Waves emitted by a moving observer will be blueshifted 
    (compressed) if approaching, redshifted (elongated) if receding.  
    It occurs both in sound as well as electromagnetic phenomena, 
    although it takes on different forms in each.
Dulong-Petit law (P. Dulong, A.T. Petit; 1819)
    The molar heat capacity is approximately equal to the three times 
    the gas constant.
Einstein-Podolsky-Rosen effect
    Consider the following quantum mechanical thought-experiment:  
    Take a particle which is at rest and has spin zero.  It 
    spontaneously decays into two fermions (spin 1/2 particles), which 
    stream away in opposite directions at high speed.  Due to the law 
    of conservation of spin, we know that one is a spin +1/2 and the 
    other is spin -1/2.  Which one is which?  According to quantum 
    mechanics, neither takes on a definite state until it is observed 
    (the wavefunction is collapsed).
        The EPR effect demonstrates that if one of the particles is
    detected, and its spin is then measured, then the other particle
    -- no matter where it is in the Universe -- instantaneously is
    forced to choose as well and take on the role of the other
    particle.  This illustrates that certain kinds of quantum
    information travel instantaneously; not everything is limited by
    the speed of light.
        However, it can be easily demonstrated that this effect does
    not make faster-than-light communication possible.
equivalence principle
    The basic postulate of A. Einstein's general theory of relativity,
    which posits that an acceleration is fundamentally
    indistinguishable from a gravitational field.  In other words, if
    you are in an elevator which is utterly sealed and protected from
    the outside, so that you cannot "peek outside," then if you feel a
    force (weight), it is fundamentally impossible for you to say
    whether the elevator is present in a gravitational field, or
    whether the elevator has rockets attached to it and is
    accelerating "upward."
        The equivalence principle predicts interesting general
    relativistic effects because not only are the two
    indistinguishable to human observers, but also to the Universe as
    well, in a way -- any effect that takes place when an observer is
    accelerating should also take place in a gravitational field, and
    vice versa.
    The region around a rotating black hole, between the event horizon
    and the static limit, where rotational energy can be extracted
    from the black hole.
event horizon
    The radius of surrounding a black hole at which a particle would
    need an escape velocity of lightspeed to escape; that is, the
    point of no return for a black hole.
Faraday constant; F (M. Faraday)
    The electric charge carried by one mole of electrons (or singly-
    ionized ions).  It is equal to the product of the Avogadro
    constant and the (absolute value of the) charge on an electron; it
    is 9.648 670 x 10^4 C/mol.
Faraday's law (M. Faraday)
    The line integral of the electric flux around a closed curve is
    proportional to the instantaneous time rate of change of the 
    magnetic flux through a surface bounded by that closed curve.
Faraday's laws of electrolysis (M. Faraday)
    1.  The amount of chemical change during electrolysis is 
        proportional to the charge passed.
    2.  The charge required to deposit or liberate a mass is 
        proportional to the charge of the ion, the mass, and 
        inversely proprtional to the relative ionic mass.  The 
        constant of proportionality is the Faraday constant.
Faraday's laws of electromagnetic induction (M. Faraday)
    1.  An electromotive force is induced in a conductor when the 
        magnetic field surrounding it changes.
    2.  The magnitude of the electromotive force is proportional to 
        the rate of change of the field.
    3.  The sense of the induced electromotive force depends on the 
        direction of the rate of the change of the field.
Fermat's principle; principle of least time (P. de Fermat)
    The principle, put forth by P. de Fermat, states that the path 
    taken by a ray of light between any two points in a system is 
    always the path that takes the least time.
Gauss' law (K.F. Gauss)
    The electric flux through a closed surface is proportional to the
    algebraic sum of electric charges contained within that closed
Gauss' law for magnetic fields (K.F. Gauss)
    The magnetic flux through a closed surface is zero; no magnetic
    charges exist.
grandfather paradox
    A paradox proposed to discount time travel and show why it
    violates causality.  Say that your grandfather builds a time
    machine.  In the present, you use his time machine to go back in
    time a few decades to a point before he married his wife (your
    grandmother).  You meet him to talk about things, and an argument
    ensues (presumably he doesn't believe that you're his
    grandson/granddaughter), and you accidentally kill him.
        If he died before he met your grandmother and never had
    children, then your parents could certainly never have met (one of
    them didn't exist!) and could never have given birth to you.  In
    addition, if he didn't live to build his time machine, what are
    you doing here in the past alive and with a time machine, if you
    were never born and it was never built?
Hall effect
    When charged particles flow through a tube which has both an 
    electric field and a magnetic field (perpendicular to the electric 
    field) present in it, only certain velocities of the charged 
    particles are preferred, and will make it undeviated through the 
    tube; the rest will be deflected into the sides.  This effect is 
    exploited in such devices as the mass spectrometer and in the 
    Thompson experiment.  This is called the Hall effect.
Hawking radiation (S.W. Hawking; 1973)
    The theory that black holes emit radiation like any other hot 
    body.  Virtual particle-antiparticle pairs are constantly being 
    created in supposedly empty space.  Every once in a while, one 
    will be created in the vicinity of a black hole's event horizon.  
    One of these particles might be catpured by the black hole, 
    forever trapped, while the other might escape the black hole's 
    gravity.  The trapped particle, which would have negative energy 
    (by definition), would reduce the mass of the black hole, and the 
    particle which escaped would have positive energy.  Thus, from a 
    distant, one would see the black hole's mass decrease and a 
    particle escape the vicinity; it would appear as if the black hole
    were emitting radiation.  The rate of emission has a negative
    relationship with the mass of the black hole; massive black holes
    emit radiation relatively slowly, while smaller black holes emit
    radiation -- and thus decrease their mass -- more rapidly.
Heisenberg uncertainty principle (W. Heisenberg; 1927)
    A principle, central to quantum mechanics, which states that the
    momentum (mass times velocity) and the position of a particle
    cannot both be known to infinite accuracy; the more you know about
    one, the lest you know about the other.
        It can be illustrated in a fairly clear way as follows:  To
    see something (let's say an electron), we have to fire photons at
    it, so they bounce off and come back to us, so we can "see" it.
    If you choose low-frequency photons, with a low energy, they do
    not impart much momentum to the electron, but they give you a very
    fuzzy picture, so you have a higher uncertainty in position so
    that you can have a higher certainty in momentum.  On the other
    hand, if you were to fire very high-energy photons (x-rays or
    gammas) at the electron, they would give you a very clear picture
    of where the electron is (high certainty in position), but would
    impart a great deal of momentum to the electron (higher 
    uncertainty in momentum).
        In a more generalized sense, the uncertainty principle tells 
    us that the act of observing changes the observed in fundamental 
Hooke's law (R. Hooke)
    The stress applied to any solid is proportional to the strain it 
    produces within the elastic limit for that solid.  The constant of 
    that proportionality is the Young modulus of elasticity for that 
Hubble constant; H` (E.P. Hubble; 1925)
    The constant which determines the relationship between the 
    distance to a galaxy and its velocity of recession due to the 
    expansion of the Universe.  It is not known to great accuracy, but 
    is believed to lie between 49 and 95 km/s/Mpc.
Hubble's law (E.P. Hubble; 1925)
    A relationship discovered between distance and radial velocity.  
    The further away a galaxy is away from is, the faster it is 
    receding away from us.  The cause is interpreted as the expansion 
    of space itself.
Huygens' construction; Huygens' principle (C. Huygens)
    The mechanics propagation of a wave of light is equivalent to
    assuming that every point on the wavefront acts as point source of
    wave emission.
ideal gas constant; universal molar gas constant; R
    The constant that appears in the ideal gas equation.  It is equal
    to 8.314 34 J/K/mol.
ideal gas equation
    An equation which sums up the ideal gas laws in one simple
    equation.  It states that the product of the pressure and the
    volume of a sample of ideal gas is equal to the product of the
    amount of gas present, the temperature of the sample, and the
    ideal gas constant.
ideal gas laws
    Boyle's law.  The pressure of an ideal gas is inversely
        proportional to the volume of the gas at constant temperature.
    Charles' law.  The volume of an ideal gas is directly proportional
        to the thermodynamic temperature at constant pressure.
    The pressure law.  The pressure of an ideal gas is directly
        proportional to the thermodynamic temperature at constant
Joule-Thomson effect; Joule-Kelvin effect (J. Joule, W. Thomson)
    The change in temperature that occurs when a gas expands into a
    region of lower pressure.
Joule's laws
    Joule's first law.  The heat produced when an electric current
        flows through a resistance for a specified time is equal to
        the square of the current multiplied by the resistivity
        multiplied by the time.
    Joule's second law.  The internal energy of an ideal gas is
        independent of its volume and pressure, depending only on its
Josephson effects (B.D. Josephson; 1962)
    Electrical effects observed when two superconducting materials are
    separated by a thin layer of insulating material.
Kepler's laws (J. Kepler)
    Kepler's first law.  A planet orbits the Sun in an ellipse with
        the Sun at one focus.
    Kepler's second law.  A ray directed from the Sun to a planet
        sweeps out equal areas in equal times.
    Kepler's third law.  The square of the period of a planet's orbit 
        is proportional to the cube of that planet's semimajor axis; 
        the constant of proportionality is the same for all planets.
Kerr effect (J. Kerr; 1875)
    The ability of certain substances to differently refract light 
    waves whose vibrations are in different directions when the 
    substance is placed in an electric field.
Kirchhoff's law of radiation (G.R. Kirchhoff)
    The emissivity of a body is equal to its absorptance at the same 
Kirchhoff's rules (G.R. Kirchhoff)
    The loop rule.  The sum of the potential differences encountered 
        in a round trip around any closed loop in a circuit is zero.
    The point rule.  The sum of the currents toward a branch point is 
        equal to the sum of the currents away from the same branch 
Kohlrausch's law (F. Kohlrausch)
    If a salt is dissolved in water, the conductivity of the solution 
    is the sum of two values -- one depending on the positive ions and 
    the other on the negative ions.
Lambert's laws (J.H. Lambert)
    Lambert's first law.  The illuminance on a surface illuminated by
        light falling on it perpendicularly from a point source is
        proportional to the inverse square of the distance between the
        surface and the source.
    Lambert's second law.  If the rays meet the surface at an angle,
        then the illuminance is also proportional to the cosine of the
        angle with the normal.
    Lambert's third law.  The luminous intensity of light decreases
        exponentially with the distance that it travels through an
        absorbing medium.
Landauer's principle
    A principle which states that it doesn't explicitly take energy to
    compute data, but rather it takes energy to _erase_ any data,
    since erasure is an important step in computation.
Laplace's equation (P. Laplace)
    For steady-state heat conduction in one dimension, the temperature
    distrubtion is the solution to Laplace's equation, which states
    that the second derivative of temperature with respect to
    displacement is zero.
Laue pattern (M. von Laue)
    The pattern produced on a photographic film when high-frequency 
    electromagnetic waves (such as x-rays) are fired at a crystalline 
laws of conservation
    A law which states that, in a closed system, the total quantity of 
    something will not increase or decrease, but remain exactly the 
    same.  For physical quantities, it states that something can 
    neither be created nor destroyed.
        The most commonly seen are the laws of conservation of mass- 
    energy (formerly two conservation laws before A. Einstein), of 
    electric charge, of linear momentum, and of angular momentum.  
    There are several others that deal more with particle physics, 
    such as conservation of baryon number, of strangeness, etc., which 
    are conserved in some fundamental interactions but not others.
law of reflection
    For a wavefront intersecting a reflecting surface, the angle of 
    incidence is equal to the angle of reflection.
laws of black hole dynamics
    First law of black hole dynamics.  For interactions between black 
        holes and normal matter, the conservation laws of total
        energy, total momentum, angular momentum, and electric charge,
    Second law of black hole dynamics.  With black hole interactions,
        or interactions between black holes and normal matter, the sum
        of the surface areas of all black holes involved can never
laws of thermodynamics
    First law of thermodynamics.  The change in internal energy of a
        system is the sum of the heat transferred to or from the
        system and the work done on or by the system.
    Second law of thermodynamics.  The entropy -- a measure of the
        unavailability of a system's energy to do useful work -- of a
        closed system tends to increase with time.
    Third law of thermodynamics.  For changes involving only perfect
        crystalline solids at absolute zero, the change of the total
        entropy is zero.
    Zeroth law of thermodynamics.  If two bodies are each in thermal
        equilibrium with a third body, then all three bodies are in
        thermal equilibrium with each other.
Lawson criterion (J.D. Lawson)
    A condition for the release of energy from a thermonuclear 
    reactor.  It is usually stated as the minimum value for the 
    product of the density of the fuel particles and the containment 
    time for energy breakeven.  For a half-and-half mixture of 
    deuterium and tritium at ignition temperature, n_G tau is between 
    10^14 and 10^15 s/cm^3.
Le Chatelier's principle (H. Le Chatelier; 1888)
    If a system is in equilibrium, then any change imposed on the 
    system tends to shift the equilibrium to reduce the effect of that 
    applied change.
Lenz's law (H.F. Lenz; 1835)
    An induced electric current always flows in such a direction that 
    it opposes the change producing it.
Loschmidt constant; Loschmidt number; N_L
    The number of particles per unit volume of an ideal gas at 
    standard temperature and pressure.  It has the value 2.687 19 x 
    10^25 m^-3.
lumeniferous aether
    A substance, which filled all the empty spaces between matter, 
    which was used to explain what medium light was "waving" in.  Now
    it has been discredited, as Maxwell's equations imply that
    electromagnetic radiation can propagate in a vacuum, since they
    are disturbances in the electromagnetic field rather than
    traditional waves in some substance, such as water waves.
Lyman series
    The series which describes the emission spectrum of hydrogen when
    electrons are jumping to the ground state.  All of the lines are
    in the ultraviolet.
Mach's principle (E. Mach; 1870s)
    The inertia of any particular particle or particles of matter is
    attributable to the interaction between that piece of matter and
    the rest of the Universe.  Thus, a body in isolation would have no
Magnus effect
    A rotating cylinder in a moving fluid drags some of the fluid
    around with it, in its direction of rotation.  This increases the
    speed in that region, and thus the pressure is lower.
    Consequently, there is a net force on the cylinder in that
    direction, perpendicular to the flow of the fluid.  This is called
    the Magnus effect.
Malus's law (E.L. Malus)
    The light intensity travelling through a polarizer is proportional
    to the initial intensity of the light and the square of the cosine
    of the angle between the polarization of the light ray and the
    polarization axis of the polarizer.
Maxwell's demon (J.C. Maxwell)
    A thought experiment illustrating the concepts of entropy.  We
    have a container of gas which is partitioned into two equal sides;
    each side is in thermal equilibrium with the other.  The walls
    (and the partition) of the container are a perfect insulator.
        Now imagine there is a very small demon who is waiting at the
    partition next to a small trap door.  He can open and close the
    door with negligible work.  Let's say he opens the door to allow a
    fast-moving molecule to travel from the left side to the right, or
    for a slow-moving molecule to travel from the right side to the
    left, and keeps it closed for all other molecules.  The next
    effect would be a flow of heat -- from the left side to the right
    -- even though the container was in thermal equilibrium.  This is
    clearly a violation of the second law of thermodynamics.
        So where did we go wrong?  It turns out that information has 
    to do with entropy as well.  In order to sort out the molecules 
    according to speeds, the demon would be having to keep a memory of 
    them -- and it turns out that increase in entropy of the simple 
    maintenance of this simple memory would more than make up for the 
    decrease in entropy due to the heat flow.
Maxwell's equations (J.C. Maxwell; 1864)
    Four elegant equations which describe classical electromagnetism 
    in all its splendor.  They are:
        Gauss' law.  The electric flux through a closed surface is 
            proportional to the algebraic sum of electric charges 
            contained within that closed surface.
        Gauss' law for magnetic fields.  The magnetic flux through a 
            closed surface is zero; no magnetic charges exist.
        Faraday's law.  The line integral of the electric flux around 
            a closed curve is proportional to the instantaneous time 
            rate of change of the magnetic flux through a surface 
            bounded by that closed curve.
        Ampere's law, modified form.  The line integral of the 
            magnetic flux around a closed curve is proportional to the 
            sum of two terms:  first, the algebraic sum of electric
            currents flowing through that closed curve; and second,
            the instantaneous time rate of change of the electric flux
            through a surface bounded by that closed curve.
    In addition to describing electromagnetism, his equations also
    predict that waves can propagate through the electromagnetic
    field, and would always propagate at the same speed -- these are
    electromagnetic waves.
Meissner effect (W. Meissner; 1933)
    The decrease of the magnetic flux within a superconducting metal
    when it is cooled below the critical temperature.  That is,
    superconducting materials reflect magnetic fields.
Michelson-Morley experiment (A.A. Michelson, E.W. Morley; 1887)
    Possibly the most famous null-experiment of all time, designed to
    verify the existence of the proposed "lumeniferous aether" through
    which light waves were thought to propagate.  Since the Earth
    moves through this aether, a lightbeam fired in the Earth's
    direction of motion would lag behind one fired sideways, where no
    aether effect would be present.  This difference could be detected
    with the use of an interferometer.
        The experiment showed absolutely no aether shift whatsoever, 
    where one should have been quite detectable.  Thus the aether 
    concept was discredited as was the constancy of the speed of 
Millikan oil drop experiment (R.A. Millikan)
    A famous experiment designed to measure the electronic charge.  
    Drops of oil were carried past a uniform electric field between 
    charged plates.  After charging the drop with x-rays, he adjusted 
    the electric field between the plates so that the oil drop was 
    exactly balanced against the force of gravity.  Then the charge on 
    the drop would be known.  Millikan did this repeatedly and found 
    that all the charges he measured came in integer multiples only of 
    a certain smallest value, which is the charge on the electron.
Newton's law of universal gravitation (Sir I. Newton)
    Two bodies attract each other with equal and opposite forces; the 
    magnitude of this force is proportional to the product of the two 
    masses and is also proportional to the inverse square of the 
    distance between the centers of mass of the two bodies.
Newton's laws of motion (Sir I. Newton)
    Newton's first law of motion.  A body continues in its state of 
        rest or of uniform motion unless it is acted upon by an
        external force.
    Newton's second law of motion.  For an unbalanced force acting on
        a body, the acceleration produces is proportional to the force
        impressed; the constant of proportionality is the inertial
        mass of the body.
    Newton's third law of motion.  In a system where no external
        forces are present, every action is always opposed by an equal
        and opposite reaction.
Ohm's law (G. Ohm; 1827)
    The ratio of the potential difference between the ends of a
    conductor to the current flowing through it is constant; the
    constant of proportionality is called the resistance, and is
    different for different materials.
Olbers' paradox (H. Olbers; 1826)
    If the Universe is infinite, uniform, and unchanging then the
    entire sky at night would be bright -- about as bright as the Sun.
    The further you looked out into space, the more stars there would
    be, and thus in any direction in which you looked your line-of-
    sight would eventually impinge upon a star.  The paradox is
    resolved by the Big Bang theory, which puts forth that the 
    Universe is not infinite, non-uniform, and changing.
Pascal's principle
    Pressure applied to an enclosed imcompressible static fluid is 
    transmitted undiminished to all parts of the fluid.
Paschen series
    The series which describes the emission spectrum of hydrogen when 
    the electron is jumping to the third orbital.  All of the lines 
    are in the infrared portion of the spectrum.
Pauli exclusion principle (W. Pauli; 1925)
    No two identical fermions in a system, such as electrons in an 
    atom, can have an identical set of quantum numbers.
Peltier effect (J.C.A. Peltier; 1834)
    The change in temperature produced at a junction between two 
    dissimilar metals or semiconductors when an electric current 
    passes through the junction.
permeability of free space; magnetic constant; mu_0
    The ratio of the magnetic flux density in a substance to the 
    external field strength for vacuum.  It is equal to 4 pi x 10^-7 
permittivity of free space; electric constant; epsilon_0
    The ratio of the electric displacement to the intensity of the
    electric field producing it in vacuum.  It is equal to 8.854 x
    10^-12 F/m.
Pfund series
    The series which describes the emission spectrum of hydrogen when
    the electron is jumping to the fifth orbital.  All of the lines
    are in the infrared portion of the spectrum.
photoelectric effect
    An effect explained by A. Einstein that demonstrate that light
    seems to be made up of particles, or photons.  Light can excite
    electrons (called photoelectrons) to be ejected from a metal.
    Light with a frequency below a certain threshold, at any
    intensity, will not cause any photoelectrons to be emitted from
    the metal.  Above that frequency, photoelectrons are emitted in
    proportion to the intensity of incident light.
        The reason is that a photon has energy in proportion to its
    wavelength, and the constant of proportionality is Planck's
    constant.  Below a certain frequency -- and thus below a certain
    energy -- the incident photons do not have enough energy to knock
    the photoelectrons out of the metal.  Above that threshold energy,
    called the workfunction, photons will knock the photoelectrons out
    of the metal, in proportion to the number of photons (the
    intensity of the light).  At higher frequencies and energies, the
    photoelectrons ejected obtain a kinetic energy corresponding to
    the difference between the photon's energy and the workfunction.
Planck constant; h
    The fundamental constant equal to the ratio of the energy of a
    quantum of energy to its frequency.  It is the quantum of action.
    It has the value 6.626 196 x 10^-34 J s.
Planck's radiation law
    A law which more accurately described blackbody radiation because
    it assumed that electromagnetic radiation is quantized.
principle of causality
    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.
        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.
principle of determinism
    The principle that if one knows the state to an infinite accuracy 
    of a system at one point in time, one would be able to predict the 
    state of that system with infinite accuracy at any other time, 
    past or future.  For example, if one were to know all of the 
    positions and velocities of all the particles in a closed system, 
    then determinism would imply that one could then predict the 
    positions and velocities of those particles at any other time.  
    This principle has been disfavored due to the advent of quantum 
    mechanics, where probabilities take an important part in the 
    actions of the subatomic world, and the Heisenberg uncertainty
    principle implies that one cannot know both the position and
    velocity of a particle to arbitrary precision.
Rayleigh criterion; resolving power
    A criterion for the how finely a set of optics may be able to
    distinguish.  It begins with the assumption that central ring of
    one image should fall on the first dark ring of the other.
    relativity principle; principle of relativity
Rydberg formula
    A formula which describes all of the characteristics of hydrogen's
    spectrum, including the Balmer, Lyman, Paschen, Brackett, and
    Pfund series.
Schroedinger's cat (E. Schroedinger; 1935)
    A thought experiment designed to illustrate the counterintuitive
    and strange notions of reality that come along with quantum
        A cat is sealed inside a closed box; the cat has ample air,
    food, and water to survive an extended period.  This box is
    designed so that no information (i.e., sight, sound, etc.) can
    pass into or out of the box -- the cat is totally cut off from
    your observations.  Also inside the box with the poor kitty 
    (apparently Schroedinger was not too fond of felines) is a phial 
    of a gaseous poison, and an automatic hammer to break it, flooding 
    the box and killing the cat.  The hammer is hooked up to a Geiger 
    counter; this counter is monitoring a radioactive sample and is 
    designed to trigger the hammer -- killing the cat -- should a 
    radioactive decay be detected.  The sample is chosen so that 
    after, say, one hour, there stands a fifty-fifty chance of a decay 
        The question is, what is the state of the cat after that one 
    hour has elapsed?  The intuitive answer is that the cat is either 
    alive or dead, but you don't know which until you look.  But it 
    _is_ one of them.  Quantum mechanics, on the other hands, says 
    that the wavefunction describing the cat is in a superposition of 
    states:  the cat is, in fact, fifty per cent alive and fifty per 
    cent dead; it is both.  Not until one looks and "collapses the 
    wavefunction" is the Universe forced to choose either a live cat 
    or a dead cat and not something in between.
        This indicates that observation also seems to be an important 
    part of the scientific process -- quite a departure from the 
    absolutely objective, deterministic way things used to be with
Schwarzchild radius
    The radius that a spherical mass must be compressed to in order to
    transform it into a black hole; that is, the radius of compression
    where the escape velocity at the surface would reach lightspeed.
Snell's law; law of refraction
    A relation which relates the change in incidence angle of a
    wavefront due to refraction between two different media.
speed of light _in vacuo_; c
    One of the postulates of A. Einstein's special theory of
    relativity, which puts forth that the speed of light in vacuum --
    often written c, and which has the value 299 792 458 m/s -- 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 (photons, gravitons, and possibly neutrinos, should they 
    indeed prove to be massless) travel at lightspeed, and all other 
    particles must travel at slower speeds.
spin-orbit effect
    An effect that causes atomic energy levels to be split because 
    electrons have intrinsic angular momentum (spin) in addition to 
    their extrinsic orbital angular momentum.
static limit
    The distance from a rotating black hole where no observer can 
    possibly remain at rest (with respect to the distant stars) 
    because of inertial frame dragging.
Stefan-Boltzmann constant; sigma (Stefan, L. Boltzmann)
    The constant of proportionality present in the Stefan-Boltzmann 
    law.  It is equal to 5.6697 x 10^-8 W/m^2/K^4.
Stefan-Boltzmann law (Stefan, L. Boltzmann)
    The radiated power (rate of emission of electromagnetic energy) of 
    a hot body is proportional to the emissivity, an efficiency 
    rating, the radiating surface area, and the fourth power of the 
    thermodynamic temperature.  The constant of proportionality is the 
    Stefan-Boltzmann constant.
Stern-Gerlach experiment (O. Stern, W. Gerlach; 1922)
    An experiment that demonstrates the features of spin (intrinsic
    angular momentum) as a distinct entity apart from orbital angular
    The phenomena by which, at sufficiently low temperatures, a
    conductor can conduct charge with zero resistance.
    The phenomena by which, at sufficiently low temperatures, a fluid
    can flow with zero viscosity.
superposition principle of forces
    The net force on a body is equal to the sum of the forces
    impressed upon it.
superposition principle of states
    The resultant quantum mechnaical wavefunction due to two or more
    individual wavefunctions is the sum of the individual
superposition principle of waves
    The resultant wave function due to two or more individual wave
    functions is the sum of the individual wave functions.
Thomson experiment; Kelvin effect (Sir W. Thomson [later Lord Kelvin])
    When an electric current flows through a conductor whose ends are
    maintained at different temperatures, heat is released at a rate
    approximately proportional to the product of the current and the
    temperature gradient.
twin paradox
    One of the most famous "paradoxes" in history, predicted by A.
    Einstein's special theory of relativity.  Take two twins, born on
    the same date on Earth.  One, Albert, leaves home for a trip
    around the Universe at very high speeds (very close to that of
    light), while the other, Henrik, stays at home at rests.  Special
    relativity predicts that when Albert returns, he will find himself
    much younger than Albert.
        That is actually not the paradox.  The paradox stems from
    attempting to naively analyze the situation to figure out why.
    From Henrik's point of view (and from everyone else on Earth),
    Albert seems to speed off for a long time, linger around, and then
    return.  Thus he should be the younger one, which is what we see.
    But from Albert's point of view, it's Henrik (and the whole of the
    Earth) that are travelling, not he.  According to special 
    relativity, if Henrik is moving relative to Albert, then Albert 
    should measure his clock as ticking slower -- and thus Henrik is 
    the one who should be younger.  But this is not what happens.
        So what's wrong with our analysis?  The key point here is that 
    the symmetry was broken.  Albert did something that Henrik did 
    not -- Albert accelerated in turning around.  Henrik did no 
    accelerating, as he and all the other people on the Earth can 
    attest to (neglecting gravity).  So Albert broke the symmetry, and 
    when he returns, _he_ is the younger one.
ultraviolet catastrophe
    A shortcoming of the Rayleigh-Jeans formula, which attempted to 
    describe the radiancy of a blackbody at various frequencies of the 
    electromagnetic spectrum.  It was clearly wrong because as the 
    frequency increased, the radiancy increased without bound; 
    something quite not observed; this was dubbed the "ultraviolet 
    catastrophe."  It was later reconciled and explained by the 
    introduction of Planck's radiation law.
universal constant of gravitation; G
    The constant of proportionality in Newton's law of universal 
    gravitation and which plays an analogous role in A. Einstein's
    general relativity.  It is equal to 6.664 x 10^-11 N m^2/kg^2.
van der Waals force (J.D. van der Waals)
    Forces responsible for the non-ideal behavior of gases, and for
    the lattice energy of molecular crystals.  There are three causes:
    dipole-dipole interaction; dipole-induced dipole moments; and
    dispersion forces arising because of small instantaneous dipoles
    in atoms.
wave-particle duality
    The principle of quantum mechanics which implies that light (and,
    indeed, all other subatomic particles) sometimes act like a wave,
    and sometime act like a particle, depending on the experiment you
    are performing.  For instance, low frequency electromagnetic
    radiation tends to act more like a wave than a particle; high
    frequency electromagnetic radiation tends to act more like a
    particle than a wave.
Widenmann-Franz law
    The ratio of the thermal conductivity of any pure metal to its
    electrical conductivity is approximately constant for any given
    temperature.  This law holds fairly well except at low
Wien's displacement law
    For a blackbody, the product of the wavelength corresponding to 
    the maximum radiancy and the thermodynamic temperature is a 
    constant.  As a result, as the temperature rises, the maximum of 
    the radiant energy shifts toward the shorter wavelength (higher 
    frequency and energy) end of the spectrum.
Woodward-Hoffmann rules
    Rules governing the formation of products during certain types of 
    organic reactions.
Young's experiment; double-slit experiment (T. Young; 1801)
    A famous experiment which shows the wave nature of light (and 
    indeed of other particles).  Light is passed from a small source 
    onto an opaque screen with two thin slits.  The light is refracted 
    through these slits and develops an interference pattern on the 
    other side of the screen.
Zeeman effect; Zeeman line splitting (P. Zeeman; 1896)
    The splitting of the lines in a spectrum when the source is 
    exposed to a magnetic field.
maximum radiancy and the thermodynamic temperature is a 
    constant.  As a result, as the temperature rises, the maximum of 
    the radiant energy shifts toward the shorter wavelength (higher 
    frequency and energy) end of the spectrum.
Woodward-Hoffmann rules
    Rules governing the formation of products during certain types of 
    organic reactions.
Young's experiment; double-slit experiment (T. Young; 1801)
    A famous experiment which shows the wave nature of light (and 
    indeed of other particles).  Light is passed from a small source 
    onto an opaque screen with two thin slits.  The light is refracted 
    through these slits and develops an interference pattern on the 
    other side of the screen.
Zeeman effect; Zeeman line splitting (P. Zeeman; 1896)
    The splitting of the lines in a spectrum when the source is 
    exposed to a magnetic field.