QED vacuum

The QED vacuum or quantum electrodynamic vacuum is the field-theoretic vacuum of quantum electrodynamics. It is the lowest energy state (i.e., the ground state) of the electromagnetic field when the fields are quantized.^[1] When the Planck constant is hypothetically allowed to approach zero, QED vacuum is converted to classical vacuum; that is, the vacuum of classical electromagnetism.^[2]^[3]

Another field-theoretic vacuum is the QCD vacuum of the Standard Model.

Fluctuations

The QED vacuum is subject to fluctuations about a dormant zero average-field condition:^[4]

Video of an experiment showing vacuum fluctuations (red ring) amplified by spontaneous parametric down-conversion.

A description of the quantum vacuum is given by Joseph Silk in On the Shores of the Unknown (pg. 62):^[5]

The quantum theory asserts that a vacuum, even the most perfect vacuum devoid of any matter, is not really empty. Rather the quantum vacuum can be depicted as a sea of continuously appearing and disappearing [pairs of] particles that manifest themselves in the apparent jostling of particles that is quite distinct from their thermal motions. These particles are ‘virtual’, as opposed to real, particles. ...At any given instant, the vacuum is full of such virtual pairs, which leave their signature behind, by affecting the energy levels of atoms.

Virtual particles

An intuitive picture of virtual particles can be attempted based upon the Heisenberg energy-time uncertainty principle $\Delta E\Delta t\geq {\frac {\hbar }{2}},$ where $Δ E$ and $Δ t$ are the uncertainties in energy and time, respectively, with $ħ$ the Planck constant divided by 2 $π$ . Using this starting point, it could be argued that the short lifetime of virtual particles allows the "borrowing" of large energies from the vacuum, thus permitting particle generation over short time intervals.^[6]

This interpretation of the energy-time uncertainty relation is not universally accepted, however.^[7]^[8] One issue is the use of an uncertainty relation limiting measurement accuracy as though a time uncertainty $Δ t$ determines a "budget" for borrowing energy $Δ E$ . Another issue is the meaning of "time" in this relation, because energy and time (unlike position $q$ and momentum $p$ , for example) do not satisfy a canonical commutation relation (such as $[q, p] = iħ$ ).^[9] Various schemes have been advanced to construct an observable that has some kind of time interpretation while also satisfying a canonical commutation relation with energy.^[10]^[11] The many approaches to the energy-time uncertainty principle are a continuing subject of study.^[11]

Quantization of the fields

The Heisenberg uncertainty principle does not allow a particle to exist in a state in which the particle is simultaneously at a fixed location and has also zero momentum. Instead, the particle has a range of momenta, the distribution of which is attributable to quantum fluctuations; if confined, it has a zero-point energy.^[12]

An uncertainty principle applies to all quantum mechanical operators that do not commute.^[13] In particular, it applies also to the electromagnetic field; in order to understand this, it is necessary to elucidate the role of commutators for this field.^[14]

The standard approach to the quantization of the electromagnetic field begins by introducing a vector potential $A$ and a scalar potential $V$ to represent the electric field $E$ and magnetic field $B$ using the relations^[14] ${\begin{aligned}\mathbf {B} &=\mathbf {\nabla \times A} ;\\\mathbf {E} &=-{\frac {\partial }{\partial t}}\mathbf {A} -\mathbf {\nabla } V.\end{aligned}}$ The vector potential is not completely determined by these relations, leaving open a so-called gauge freedom. Resolving this ambiguity using the Coulomb gauge leads to a description of the electromagnetic fields in the absence of charges in terms of the vector potential and the momentum field $Π$ , given by $\mathbf {\Pi } =\varepsilon _{0}{\frac {\partial }{\partial t}}\mathbf {A} ,$ where $ε 0$ is the electric constant in SI units. Quantization is achieved by insisting that the momentum field and the vector potential do not commute. That is, the equal-time commutator is^[15] ${\bigl [}\Pi _{i}(\mathbf {r} ,t),\ A_{j}(\mathbf {r} ',t){\bigr ]}=-i\hbar \delta _{ij}\delta (\mathbf {r} -\mathbf {r} '),$ where $r$ , $r'$ are spatial locations, $ħ$ is the reduced Planck constant, $δ ij$ is the Kronecker delta, and $δ (r - r')$ is the Dirac delta function. The notation $[ , ]$ represents the commutator.

Quantization can be achieved without introducing the vector potential in terms of the underlying fields themselves:^[16] $\left[{\hat {E}}_{k}({\boldsymbol {r}}),{\hat {B}}_{k'}({\boldsymbol {r}}')\right]=-\varepsilon _{kk'm}{\frac {i\hbar }{\varepsilon _{0}}}{\frac {\partial }{\partial x_{m}}}\delta ({\boldsymbol {r-r'}}),$ where the circumflex denotes a Schrödinger time-independent field operator, and $ε ijk$ is the antisymmetric Levi-Civita tensor.

Because of the non-commutation of field variables, the variances of the fields cannot be zero, although their averages are zero.^[17] So, the electromagnetic field has a zero-point energy, and therefore a lowest quantum state. The interaction of an excited atom with this lowest quantum state of the electromagnetic field is what leads to spontaneous emission: The transition of an excited atom to a state of lower energy by emission of a photon even when no external perturbation of the atom is present.^[18]

Electromagnetic properties

As a result of quantization, the quantum electrodynamic vacuum can be considered a material medium.^[20] It is capable of vacuum polarization.^[21]^[22] In particular, the force law between charged particles is affected.^[23]^[24] The electrical permittivity of the quantum electrodynamic vacuum can be calculated, and it differs slightly from the simple $ε 0$ of the classical vacuum. (Likewise, its permeability can also be calculated and differs slightly from $μ 0$ .) This medium is a dielectric with relative dielectric constant greater than 1, and is diamagnetic, with relative magnetic permeability less than 1.^[25]^[26] In extreme conditions in which the field exceeds the Schwinger limit (e.g., in the exterior regions of pulsars^[27]), the quantum electrodynamic vacuum is thought to exhibit nonlinearity in the fields.^[28] Calculations also indicate birefringence and dichroism in the presence of strong fields.^[29] Many electromagnetic effects of the vacuum are difficult to detect, and only recently have experiments been designed to enable the observation of nonlinear effects.^[30] To this end, PVLAS and other teams are working towards the needed sensitivity to detect quantum electrodynamic nonlinearity.

Attainability

A perfect vacuum is itself only attainable in principle.^[31]^[32] It is an idealization, similar to absolute zero for temperature, that can be approached, but never actually realized. This idea is summarized by Luciano Boi in Creating the physical world ex nihilo? (pg. 55):^[31]

One reason [a vacuum is not empty] is that the walls of a vacuum chamber emit light in the form of black-body radiation...If this soup of photons is in thermodynamic equilibrium with the walls, it can be said to have a particular temperature, as well as a pressure. Another reason that perfect vacuum is impossible is the Heisenberg uncertainty principle which states that no particles can ever have an exact position ...Each atom exists as a probability function of space, which has a certain nonzero value everywhere in a given volume. ...More fundamentally, quantum mechanics predicts ...a correction to the energy called the zero-point energy [that] consists of energies of virtual particles that have a brief existence. This is called vacuum fluctuation.

Virtual particles make a perfect vacuum unrealizable, but leave open the question of attainability of a quantum electrodynamic vacuum, or QED vacuum. Predictions of QED vacuum such as spontaneous emission, the Casimir effect, and the Lamb shift have been experimentally verified, suggesting QED vacuum is a good model for a near-perfect realizable vacuum. There are competing theoretical models for vacuum, however. For example, quantum chromodynamic vacuum includes many virtual particles not treated in quantum electrodynamics. The vacuum of quantum gravity treats gravitational effects not included in the Standard Model.^[33] It remains an open question whether further refinements in experimental technique will ultimately support another model for a realizable vacuum.

References

^ Cao, Tian Yu, ed. (2004). Conceptual Foundations of Quantum Field Theory. Cambridge University Press. p. 179. ISBN 978-0-521-60272-3. For each stationary classical background field there is a ground state of the associated quantized field. This is the vacuum for that background.
^ Mackay, Tom G.; Lakhtakia, Akhlesh (2010). Electromagnetic Anisotropy and Bianisotropy: A Field Guide. World Scientific. p. 201. ISBN 978-981-4289-61-0.
^ Classical vacuum is not a material medium, but a reference state used to define the SI units. Its permittivity is the electric constant and its permeability is the magnetic constant, both of which are exactly known by definition, and are not measured properties. See Mackay & Lakhtakia, p. 20, footnote 6.
^ Shankar, Ramamurti (1994). Principles of Quantum Mechanics (2nd ed.). Springer. p. 507. ISBN 978-0-306-44790-7.
^ Silk, Joseph (2005). On the Shores of the Unknown: A Short History of the Universe. Cambridge University Press. p. 62. ISBN 978-0-521-83627-2.
^ For an example, see Davies, P. C. W. (1982). The Accidental Universe. Cambridge University Press. p. 106. ISBN 978-0-521-28692-3.
^ A vaguer description is provided by Allday, Jonathan (2002). Quarks, Leptons and the Big Bang (2nd ed.). CRC Press. p. 224. ISBN 978-0-7503-0806-9. The interaction will last for a certain duration $Δ t$ . This implies that the amplitude for the total energy involved in the interaction is spread over a range of energies $Δ E$ .
^ This "borrowing" idea has led to proposals for using the zero-point energy of vacuum as an infinite reservoir and a variety of "camps" about this interpretation. See, for example, King, Moray B. (2001). Quest for Zero Point Energy: Engineering Principles for 'Free Energy' Inventions. Adventures Unlimited Press. p. 124ff. ISBN 978-0-932813-94-7.
^ Quantities satisfying a canonical commutation rule are said to be noncompatible observables, by which is meant that they can both be measured simultaneously only with limited precision. See Itô, Kiyosi, ed. (1993). "§ 351 (XX.23) C: Canonical commutation relations". Encyclopedic Dictionary of Mathematics (2nd ed.). MIT Press. p. 1303. ISBN 978-0-262-59020-4.
^ Busch, Paul; Grabowski, Marian; Lahti, Pekka J. (1995). "§III.4: Energy and time". Operational Quantum Physics. Springer. p. 77. ISBN 978-3-540-59358-4.
^ ^a ^b For a review, see Paul Busch (2008). "Chapter 3: The Time–Energy Uncertainty Relation". In Muga, J. G.; Sala Mayato, R.; Egusquiza, Í. L. (eds.). Time in Quantum Mechanics (2nd ed.). Springer. p. 73ff. arXiv:quant-ph/0105049. Bibcode:2002tqm..conf...69B. doi:10.1007/978-3-540-73473-4_3. ISBN 978-3-540-73472-7. S2CID 14119708.
^ Schwabl, Franz (2007). "§ 3.1.3: The zero-point energy". Quantum Mechanics (4th ed.). Springer. p. 54. ISBN 978-3-540-71932-8.
^ Lambropoulos, Peter; Petrosyan, David (2007). Fundamentals of Quantum Optics and Quantum Information. Springer. p. 30. Bibcode:2007fqoq.book.....L. ISBN 978-3-540-34571-8.
^ ^a ^b Vogel, Werner; Welsch, Dirk-Gunnar (2006). "Chapter 2: Elements of quantum electrodynamics". Quantum Optics (3rd ed.). Wiley-VCH. p. 18. ISBN 978-3-527-40507-7.
^ This commutation relation is oversimplified, and a correct version replaces the $δ$ product on the right by the transverse $δ$ -tensor:
$\delta _{\perp \ ij}(\mathbf {x} )={\frac {1}{8\pi ^{3}}}\int d^{3}\mathbf {k} \left(\delta _{ij}-{\hat {u}}_{i}{\hat {u}}_{j}\right)e^{i\mathbf {k\cdot x} }\ ,$
where $û$ is the unit vector of $k$ , $û = .mw-parser-output .sfrac{white-space:nowrap}.mw-parser-output .sfrac.tion,.mw-parser-output .sfrac .tion{display:inline-block;vertical-align:-0.5em;font-size:85%;text-align:center}.mw-parser-output .sfrac .num{display:block;line-height:1em;margin:0.0em 0.1em;border-bottom:1px solid}.mw-parser-output .sfrac .den{display:block;line-height:1em;margin:0.1em 0.1em}.mw-parser-output .sr-only{border:0;clip:rect(0,0,0,0);clip-path:polygon(0px 0px,0px 0px,0px 0px);height:1px;margin:-1px;overflow:hidden;padding:0;position:absolute;width:1px}⁠k/k⁠$ . For a discussion see, Compagno, G.; Passante, R.; Persico, F. (2005). "§2.1 Canonical quantization in the Coulomb gauge". Atom-Field Interactions and Dressed Atoms. Cambridge Studies in Modern Optics, vol. 17. Cambridge University Press. p. 31. ISBN 978-0-521-01972-9.
^ Vogel, Werner; Welsch, Dirk-Gunnar (2006). "§2.2.1 Canonical quantization: Eq. (2.50)". Quantum Optics (3rd ed.). Wiley-VCH. p. 21. ISBN 978-3-527-40507-7.
^ Grynberg, Gilbert; Aspect, Alain; Fabre, Claude (2010). "§5.2.2 Vacuum fluctuations and their physical consequences". Introduction to Quantum Optics: From the Semi-Classical Approach to Quantized Light. Cambridge University Press. p. 351. ISBN 978-0-521-55112-0.
^ Parker, Ian (2003). Biophotonics, Volume 360, Part 1. Academic Press. p. 516. ISBN 978-0-12-182263-7.
^ "First Signs of Weird Quantum Property of Empty Space? – VLT observations of neutron star may confirm 80-year-old prediction about the vacuum". www.eso.org. Retrieved 5 December 2016.
^ Bregant, M.; et al. (2003). "Particle laser production at PVLAS: Recent developments". In Curwen Spooner, Neil John; Kudryavtsev, Vitaly (eds.). Proceedings of the Fourth International Workshop on the Identification of Dark Matter: York, UK, 2-6 September 2002. World Scientific. ISBN 9789812791313.
^ Gottfried, Kurt; Weisskopf, Victor Frederick (1986). Concepts of Particle Physics, Volume 2. Oxford University Press. p. 259. ISBN 978-0195033939.
^ Zeidler, Eberhard (2011). "§19.1.9 Vacuum polarization in quantum electrodynamics". Quantum Field Theory, Volume III: Gauge Theory: A Bridge Between Mathematicians and Physicists. Springer. p. 952. ISBN 978-3-642-22420-1.
^ Peskin, Michael Edward; Schroeder, Daniel V. (1995). "§7.5 Renormalization of the electric charge". An Introduction to Quantum Field Theory. Westview Press. p. 244. ISBN 978-0-201-50397-5.
^ Schweber, Silvan S. (2003). "Elementary particles". In Heilbron, J. L. (ed.). The Oxford Companion to the History of Modern Science. Oxford University Press. pp. 246–247. ISBN 978-0-19-511229-0. Thus in QED the presence of an electric charge $e o$ polarizes the "vacuum" and the charge that is observed at a large distance differs from $e o$ and is given by $e = ⁠ e o / ε ⁠$ with $ε$ the dielectric constant of the vacuum.
^ Donoghue, John F.; Golowich, Eugene; Holstein, Barry R. (1994). Dynamics of the Standard Model. Cambridge University Press. p. 47. ISBN 978-0-521-47652-2.
^ QCD vacuum is paramagnetic, while QED vacuum is diamagnetic. See Bertulani, Carlos A. (2007). Nuclear Physics in a Nutshell. Princeton University Press. p. 26. Bibcode:2007npn..book.....B. ISBN 978-0-691-12505-3.
^ Mészáros, Peter (1992). "§2.6 Quantum electrodynamics in strong fields". High-Energy Radiation from Magnetized Neutron Stars. University of Chicago Press. p. 56. ISBN 978-0-226-52094-0.
^ Hartemann, Frederic V. (2002). High-Field Electrodynamics. CRC Press. p. 428. ISBN 978-0-8493-2378-2.
^ Heyl, Jeremy S.; Hernquist, Lars (1997). "Birefringence and Dichroism of the QED Vacuum". J. Phys. A30 (18): 6485–6492. arXiv:hep-ph/9705367. Bibcode:1997JPhA...30.6485H. doi:10.1088/0305-4470/30/18/022. S2CID 32306183.
^ Mendonça, José Tito; Eliezer, Shalom (2008). "Nuclear and particle physics with ultraintense lasers". In Eliezer, Shalom; Mima, Kunioki (eds.). Applications of Laser-Plasma Interactions. CRC Press. p. 145. ISBN 978-0-8493-7604-7.
^ ^a ^b Luciano Boi (2009). "Creating the physical world ex nihilo? On the quantum vacuum and its fluctuations". In Carafoli, Ernesto; Danieli, Gian Antonio; Longo, Giuseppe O. (eds.). The Two Cultures: Shared Problems. Springer. p. 55. ISBN 978-88-470-0868-7.
^ Dirac, P. A. M. (2001). Jong-Ping Hsu; Yuanzhong Zhang (eds.). Lorentz and Poincaré Invariance: 100 Years of Relativity. World Scientific. p. 440. ISBN 978-981-02-4721-8.
^ For example, see Gambini, Rodolfo; Pullin, Jorge (2010). "Chapter 1: Why quantize gravity?". A First Course in Loop Quantum Gravity. Oxford University Press. p. 1. ISBN 978-0-19-959075-9. and Rovelli, Carlo (2004). "§5.4.2 Much ado about nothing: the vacuum". Quantum Gravity. Cambridge University Press. p. 202ff. ISBN 978-0-521-83733-0. We use three distinct notions of vacuum in quantum gravity

This article incorporates material from the Citizendium article "Vacuum (quantum electrodynamic)", which is licensed under the Creative Commons Attribution-ShareAlike 3.0 Unported License but not under the GFDL.

[Cao-1] Cao, Tian Yu, ed. (2004). Conceptual Foundations of Quantum Field Theory. Cambridge University Press. p. 179. ISBN 978-0-521-60272-3. For each stationary classical background field there is a ground state of the associated quantized field. This is the vacuum for that background.

[Mackay-2] Mackay, Tom G.; Lakhtakia, Akhlesh (2010). Electromagnetic Anisotropy and Bianisotropy: A Field Guide. World Scientific. p. 201. ISBN 978-981-4289-61-0.

[classical-3] Classical vacuum is not a material medium, but a reference state used to define the SI units. Its permittivity is the electric constant and its permeability is the magnetic constant, both of which are exactly known by definition, and are not measured properties. See Mackay & Lakhtakia, p. 20, footnote 6.

[Shankar-4] Shankar, Ramamurti (1994). Principles of Quantum Mechanics (2nd ed.). Springer. p. 507. ISBN 978-0-306-44790-7.

[Silk-5] Silk, Joseph (2005). On the Shores of the Unknown: A Short History of the Universe. Cambridge University Press. p. 62. ISBN 978-0-521-83627-2.

[Davies-6] For an example, see Davies, P. C. W. (1982). The Accidental Universe. Cambridge University Press. p. 106. ISBN 978-0-521-28692-3.

[Allday-7] A vaguer description is provided by Allday, Jonathan (2002). Quarks, Leptons and the Big Bang (2nd ed.). CRC Press. p. 224. ISBN 978-0-7503-0806-9. The interaction will last for a certain duration $Δ t$ . This implies that the amplitude for the total energy involved in the interaction is spread over a range of energies $Δ E$ .

[King-8] This "borrowing" idea has led to proposals for using the zero-point energy of vacuum as an infinite reservoir and a variety of "camps" about this interpretation. See, for example, King, Moray B. (2001). Quest for Zero Point Energy: Engineering Principles for 'Free Energy' Inventions. Adventures Unlimited Press. p. 124ff. ISBN 978-0-932813-94-7.

[commutation-9] Quantities satisfying a canonical commutation rule are said to be noncompatible observables, by which is meant that they can both be measured simultaneously only with limited precision. See Itô, Kiyosi, ed. (1993). "§ 351 (XX.23) C: Canonical commutation relations". Encyclopedic Dictionary of Mathematics (2nd ed.). MIT Press. p. 1303. ISBN 978-0-262-59020-4.

[Busch0-10] Busch, Paul; Grabowski, Marian; Lahti, Pekka J. (1995). "§III.4: Energy and time". Operational Quantum Physics. Springer. p. 77. ISBN 978-3-540-59358-4.

[Busch-11] For a review, see Paul Busch (2008). "Chapter 3: The Time–Energy Uncertainty Relation". In Muga, J. G.; Sala Mayato, R.; Egusquiza, Í. L. (eds.). Time in Quantum Mechanics (2nd ed.). Springer. p. 73ff. arXiv:quant-ph/0105049. Bibcode:2002tqm..conf...69B. doi:10.1007/978-3-540-73473-4_3. ISBN 978-3-540-73472-7. S2CID 14119708.

[Schwabl-12] Schwabl, Franz (2007). "§ 3.1.3: The zero-point energy". Quantum Mechanics (4th ed.). Springer. p. 54. ISBN 978-3-540-71932-8.

[Petrosyan-13] Lambropoulos, Peter; Petrosyan, David (2007). Fundamentals of Quantum Optics and Quantum Information. Springer. p. 30. Bibcode:2007fqoq.book.....L. ISBN 978-3-540-34571-8.

[Vogel2-14] Vogel, Werner; Welsch, Dirk-Gunnar (2006). "Chapter 2: Elements of quantum electrodynamics". Quantum Optics (3rd ed.). Wiley-VCH. p. 18. ISBN 978-3-527-40507-7.

[Compagno-15] This commutation relation is oversimplified, and a correct version replaces the $δ$ product on the right by the transverse $δ$ -tensor:
$\delta _{\perp \ ij}(\mathbf {x} )={\frac {1}{8\pi ^{3}}}\int d^{3}\mathbf {k} \left(\delta _{ij}-{\hat {u}}_{i}{\hat {u}}_{j}\right)e^{i\mathbf {k\cdot x} }\ ,$
where $û$ is the unit vector of $k$ , $û = .mw-parser-output .sfrac{white-space:nowrap}.mw-parser-output .sfrac.tion,.mw-parser-output .sfrac .tion{display:inline-block;vertical-align:-0.5em;font-size:85%;text-align:center}.mw-parser-output .sfrac .num{display:block;line-height:1em;margin:0.0em 0.1em;border-bottom:1px solid}.mw-parser-output .sfrac .den{display:block;line-height:1em;margin:0.1em 0.1em}.mw-parser-output .sr-only{border:0;clip:rect(0,0,0,0);clip-path:polygon(0px 0px,0px 0px,0px 0px);height:1px;margin:-1px;overflow:hidden;padding:0;position:absolute;width:1px}⁠k/k⁠$ . For a discussion see, Compagno, G.; Passante, R.; Persico, F. (2005). "§2.1 Canonical quantization in the Coulomb gauge". Atom-Field Interactions and Dressed Atoms. Cambridge Studies in Modern Optics, vol. 17. Cambridge University Press. p. 31. ISBN 978-0-521-01972-9.

[Vogel-16] Vogel, Werner; Welsch, Dirk-Gunnar (2006). "§2.2.1 Canonical quantization: Eq. (2.50)". Quantum Optics (3rd ed.). Wiley-VCH. p. 21. ISBN 978-3-527-40507-7.

[Grynberg-17] Grynberg, Gilbert; Aspect, Alain; Fabre, Claude (2010). "§5.2.2 Vacuum fluctuations and their physical consequences". Introduction to Quantum Optics: From the Semi-Classical Approach to Quantized Light. Cambridge University Press. p. 351. ISBN 978-0-521-55112-0.

[Parker-18] Parker, Ian (2003). Biophotonics, Volume 360, Part 1. Academic Press. p. 516. ISBN 978-0-12-182263-7.

[19] "First Signs of Weird Quantum Property of Empty Space? – VLT observations of neutron star may confirm 80-year-old prediction about the vacuum". www.eso.org. Retrieved 5 December 2016.

[medium-20] Bregant, M.; et al. (2003). "Particle laser production at PVLAS: Recent developments". In Curwen Spooner, Neil John; Kudryavtsev, Vitaly (eds.). Proceedings of the Fourth International Workshop on the Identification of Dark Matter: York, UK, 2-6 September 2002. World Scientific. ISBN 9789812791313.

[Weisskopf-21] Gottfried, Kurt; Weisskopf, Victor Frederick (1986). Concepts of Particle Physics, Volume 2. Oxford University Press. p. 259. ISBN 978-0195033939.

[Zeidler-22] Zeidler, Eberhard (2011). "§19.1.9 Vacuum polarization in quantum electrodynamics". Quantum Field Theory, Volume III: Gauge Theory: A Bridge Between Mathematicians and Physicists. Springer. p. 952. ISBN 978-3-642-22420-1.

[Schroeder-23] Peskin, Michael Edward; Schroeder, Daniel V. (1995). "§7.5 Renormalization of the electric charge". An Introduction to Quantum Field Theory. Westview Press. p. 244. ISBN 978-0-201-50397-5.

[Schweber-24] Schweber, Silvan S. (2003). "Elementary particles". In Heilbron, J. L. (ed.). The Oxford Companion to the History of Modern Science. Oxford University Press. pp. 246–247. ISBN 978-0-19-511229-0. Thus in QED the presence of an electric charge $e o$ polarizes the "vacuum" and the charge that is observed at a large distance differs from $e o$ and is given by $e = ⁠ e o / ε ⁠$ with $ε$ the dielectric constant of the vacuum.

[Donoghue-25] Donoghue, John F.; Golowich, Eugene; Holstein, Barry R. (1994). Dynamics of the Standard Model. Cambridge University Press. p. 47. ISBN 978-0-521-47652-2.

[Bertulani-26] QCD vacuum is paramagnetic, while QED vacuum is diamagnetic. See Bertulani, Carlos A. (2007). Nuclear Physics in a Nutshell. Princeton University Press. p. 26. Bibcode:2007npn..book.....B. ISBN 978-0-691-12505-3.

[Meszaros-27] Mészáros, Peter (1992). "§2.6 Quantum electrodynamics in strong fields". High-Energy Radiation from Magnetized Neutron Stars. University of Chicago Press. p. 56. ISBN 978-0-226-52094-0.

[Hartemann-28] Hartemann, Frederic V. (2002). High-Field Electrodynamics. CRC Press. p. 428. ISBN 978-0-8493-2378-2.

[Heyl-29] Heyl, Jeremy S.; Hernquist, Lars (1997). "Birefringence and Dichroism of the QED Vacuum". J. Phys. A30 (18): 6485–6492. arXiv:hep-ph/9705367. Bibcode:1997JPhA...30.6485H. doi:10.1088/0305-4470/30/18/022. S2CID 32306183.

[nonlinear-30] Mendonça, José Tito; Eliezer, Shalom (2008). "Nuclear and particle physics with ultraintense lasers". In Eliezer, Shalom; Mima, Kunioki (eds.). Applications of Laser-Plasma Interactions. CRC Press. p. 145. ISBN 978-0-8493-7604-7.

[Longo-31] Luciano Boi (2009). "Creating the physical world ex nihilo? On the quantum vacuum and its fluctuations". In Carafoli, Ernesto; Danieli, Gian Antonio; Longo, Giuseppe O. (eds.). The Two Cultures: Shared Problems. Springer. p. 55. ISBN 978-88-470-0868-7.

[Dirac-32] Dirac, P. A. M. (2001). Jong-Ping Hsu; Yuanzhong Zhang (eds.). Lorentz and Poincaré Invariance: 100 Years of Relativity. World Scientific. p. 440. ISBN 978-981-02-4721-8.

[gravity-33] For example, see Gambini, Rodolfo; Pullin, Jorge (2010). "Chapter 1: Why quantize gravity?". A First Course in Loop Quantum Gravity. Oxford University Press. p. 1. ISBN 978-0-19-959075-9. and Rovelli, Carlo (2004). "§5.4.2 Much ado about nothing: the vacuum". Quantum Gravity. Cambridge University Press. p. 202ff. ISBN 978-0-521-83733-0. We use three distinct notions of vacuum in quantum gravity

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[2]

[3]

[4]

[5]

[6]

[7]

[8]

[9]

[10]

[11]

[12]

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[14]

[15]

[16]

[17]

[18]

[19]

[20]

[21]

[22]

[23]

[24]

[25]

[26]

[27]

[28]

[29]

[30]

[31]

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v t e Quantum electrodynamics
Formalism	Euler–Heisenberg Lagrangian Feynman diagram Gupta–Bleuler formalism Path integral formulation
Particles	Dual photon Electron Faddeev–Popov ghost Photon Positron Positronium Virtual particles
Concepts	Anomalous magnetic dipole moment Furry's theorem Klein–Nishina formula Landau pole QED vacuum Self-energy Schwinger limit Uehling potential Vacuum polarization Vertex function Ward–Takahashi identity
Processes	Bhabha scattering Breit–Wheeler process Bremsstrahlung Compton scattering Delbrück scattering Lamb shift Møller scattering Schwinger effect Photon-photon scattering
See also: Template:Quantum mechanics topics

v t e Quantum mechanics
Background	Introduction History Timeline Classical mechanics Old quantum theory Glossary
Fundamentals	Born rule Bra–ket notation Complementarity Density matrix Energy level Ground state Excited state Degenerate levels Zero-point energy Entanglement Hamiltonian Interference Decoherence Measurement Nonlocality Quantum state quantum jump Superposition Tunnelling Scattering theory Symmetry in quantum mechanics Uncertainty Wave function Collapse Wave–particle duality
Formulations	Formulations Heisenberg Interaction Matrix mechanics Schrödinger Path integral formulation Phase space
Equations	Klein–Gordon Dirac Weyl Majorana Rarita–Schwinger Pauli Rydberg Schrödinger
Interpretations	Bayesian Consciousness causes collapse Consistent histories Copenhagen de Broglie–Bohm Ensemble Hidden-variable Local Superdeterminism Many-worlds Objective collapse Quantum logic Relational Transactional
Experiments	Bell test Davisson–Germer Delayed-choice quantum eraser Double-slit Franck–Hertz Mach–Zehnder interferometer Elitzur–Vaidman Popper Quantum eraser Stern–Gerlach Wheeler's delayed choice
Science	Quantum biology Quantum chemistry Quantum chaos Quantum cosmology Quantum differential calculus Quantum dynamics Quantum geometry Quantum measurement problem Quantum mind Quantum stochastic calculus Quantum spacetime
Technology	Quantum algorithms Quantum amplifier Quantum bus Quantum cellular automata Quantum finite automata Quantum channel Quantum circuit Quantum complexity theory Quantum computing Timeline Quantum cryptography Quantum electronics Quantum error correction Quantum imaging Quantum image processing Quantum information Quantum key distribution Quantum logic Quantum logic gates Quantum machine Quantum machine learning Quantum metamaterial Quantum metrology Quantum network Quantum neural network Quantum optics Quantum programming Quantum sensing Quantum simulator Quantum teleportation
Extensions	Quantum fluctuation Casimir effect Quantum statistical mechanics Quantum field theory History Quantum gravity Relativistic quantum mechanics
Related	Schrödinger's cat in popular culture Wigner's friend EPR paradox Quantum mysticism
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Classical Electrodynamic Vacuum

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