|  Energy | 
In General > s.a. technology.
  * Idea: A conserved quantity
    for a system, associated with invariance under time translation.
  * History: Energy conservation
    was introduced by Galileo [@ Galilei 1638],
    but the concept was fully developed around 1850.
  @ General references:
    Pielou 01 [I];
    issue SA(06)sep [future];
    Lam PhSc(11) [need for a background structure];
    > s.a. physics teaching.
  @ History of the concept: Crease pw(02)jul;
    Frontali PhysEd(14).
  > Specific theories: see electromagnetism;
    gravitational energy; newtonian gravity.
In Classical Physics
  > s.a. conservation laws; energy-momentum
  tensor [for a field]; Work-Energy Theorem.
  * Energy theory: The computation
    of a sufficient condition for stability of the laminar flow of a fluid.
  * For a wave: Of the form E(t)
    = ∫ [A f 2 + B
    (df/dt)2] dx (with A = 0
    for some granular systems, and B = 0 for electromagnetic waves).
  @ General references: Schrödinger NC(58);
    Arminjon AMP(16)-a1510-conf [conservation, for particles and fields, and the energy-momentum tensor].
  @ Kinetic energy: Madhu Rao AJP(00)apr [and invariance];
    Prentis AJP(05)aug [derivation];
    Riggs TPT(16) [Newtonian vs relativistic dynamics].
  > Related topics: see Equipartition
    of Energy; physics teaching; tunneling [particles
    with complex energy]; Virial Theorem.
In Relativistic Physics
  > s.a. energy conditions; relativistic particle.
  * Relativistic particle: If a particle's
    4-momentum with respect to an observer ξa
    is pa, its energy with respect to that
    observer is E = −pa
    ξa = m (1 −
    v2)−1/2;
    This represents the "inertial" energy of the particle (rest mass and kinetic energy);
    The "total" energy is generally not a well-defined concept, but if there is a timelike
    ("stationary") Killing vector field Ka,
    then the conserved quantity pa
    Ka can be considered the particle's
    energy in the gravitational field.
  @ General references:
    Sonego & Pin EJP(05),
    Adkins AJP(08)nov [in special relativity];
    Carini et al IJGMP(07) [covariant, non-inertial frames];
    Serafin & Głazek AJP(17)apr-a1705 [extended physical systems in special relativity];
    Grib & Pavlov Symm(20)-a2004 [particles with negative energies].
  @ And gravity:
    Bruschi a1701 [not all energy is a source of gravity];
    Dewar & Weatherall FP(18)-a1707-conf [in Newtonian gravitation];
    > s.a. matter near black holes [energy extraction].
  @ Self-energy:
    Arnowitt et al PR(60) [coupled to gravity];
    Cheon IJTP(79) [in modified quantum electrodynamics];
    de Souza ht/95,
    ht/96,
    JPA(97)ht/96 [electron self-field without renormalization];
    van Holten NPB(98)ht/97;
    Hirayama & Hara PTP(00)gq/99 [in curved spacetime];
    Hod PRD(02) [black-hole background];
    Barceló & Jaramillo a1112 [localization];
    > s.a. non-linear electrodynamics; self-force.
In Quantum Physics
  > s.a. measurement; quantum field theory effects [negative
  energy density]; quantum information; Virial Theorem.
  * For a particle in quantum mechanics:
    For a photon, E = hν = \(\hbar\)ω.
  @ General references:
    Frank QIP(05)qp/04 [as rate of information processing];
    Tejero & Vitolo IJGMP(14) [geometry of the energy operator].
  @ Conservation: Prentis & Fedak AJP(04)may [and the work-energy theorem];
    Sołtan a1907 [and the measurement context].
  @ Reated topics: Boukas a0812 [minimal operating time for energy supply];
    El Dahab & Tawfik CJP(14)-a1401 [maximal measurable energy].
For Curves or Loops
  $ Def: For γ:
→M, relative to γ(u), the invariant
E(γ):= ∫ E(γ, γ(u)) |\(\dot\gamma\)(u)| du, where E(γ, γ(u)):= ∫ {|γ(v) − γ(u)|−2 − [D(γ(v), γ(u))]2} |\(\dot\gamma\)(v)| dv ,
    and D(γ(v), γ(u))
    is the distance along γ.
  @ References:
    Freedman et al AM(94);
    Strzelecki & von der Mosel PRP(13) [Menger curvature as a knot energy].
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