Zero-point energy
Part of a series of articles about |
Quantum mechanics |
---|
Zero-point energy (ZPE) is the lowest possible
The notion of a zero-point energy is also important for
Etymology and terminology
The term zero-point energy (ZPE) is a translation from the German Nullpunktsenergie.[8] Sometimes used interchangeably with it are the terms zero-point radiation and ground state energy. The term zero-point field (ZPF) can be used when referring to a specific vacuum field, for instance the QED vacuum which specifically deals with quantum electrodynamics (e.g., electromagnetic interactions between photons, electrons and the vacuum) or the QCD vacuum which deals with quantum chromodynamics (e.g., color charge interactions between quarks, gluons and the vacuum). A vacuum can be viewed not as empty space but as the combination of all zero-point fields. In quantum field theory this combination of fields is called the vacuum state, its associated zero-point energy is called the vacuum energy and the average energy value is called the vacuum expectation value (VEV) also called its condensate.
Overview
In classical mechanics all particles can be thought of as having some energy made up of their potential energy and kinetic energy. Temperature, for example, arises from the intensity of random particle motion caused by kinetic energy (known as Brownian motion). As temperature is reduced to absolute zero, it might be thought that all motion ceases and particles come completely to rest. In fact, however, kinetic energy is retained by particles even at the lowest possible temperature. The random motion corresponding to this zero-point energy never vanishes; it is a consequence of the uncertainty principle of quantum mechanics.
The uncertainty principle states that no object can ever have precise values of position and velocity simultaneously. The total energy of a quantum mechanical object (potential and kinetic) is described by its
Given the equivalence of mass and energy expressed by
The idea that "empty" space can have an intrinsic energy associated with it, and that there is no such thing as a "true vacuum" is seemingly unintuitive. It is often argued that the entire universe is completely bathed in the zero-point radiation, and as such it can add only some constant amount to calculations. Physical measurements will therefore reveal only deviations from this value.
Many physical effects attributed to zero-point energy have been experimentally verified, such as
History
Early aether theories
Zero-point energy evolved from historical ideas about the
Late in the 19th century, however, it became apparent that the evacuated region still contained
To those who maintained the existence of a plenum as a philosophical principle, nature's abhorrence of a vacuum was a sufficient reason for imagining an all-surrounding aether ... Aethers were invented for the planets to swim in, to constitute electric atmospheres and magnetic effluvia, to convey sensations from one part of our bodies to another, and so on, till a space had been filled three or four times with aethers.[23]
However, the results of the Michelson–Morley experiment in 1887 were the first strong evidence that the then-prevalent aether theories were seriously flawed, and initiated a line of research that eventually led to special relativity, which ruled out the idea of a stationary aether altogether. To scientists of the period, it seemed that a true vacuum in space might be created by cooling and thus eliminating all radiation or energy. From this idea evolved the second concept of achieving a real vacuum: cool a region of space down to absolute zero temperature after evacuation. Absolute zero was technically impossible to achieve in the 19th century, so the debate remained unsolved.
Second quantum theory
In 1900, Max Planck derived the average energy ε of a single energy radiator, e.g., a vibrating atomic unit, as a function of absolute temperature:[24]
where h is
The concept of zero-point energy was developed by Max Planck in Germany in 1911 as a corrective term added to a zero-grounded formula developed in his original quantum theory in 1900.[26]
In 1912, Max Planck published the first journal article to describe the discontinuous emission of radiation, based on the discrete quanta of energy.[27] In Planck's "second quantum theory" resonators absorbed energy continuously, but emitted energy in discrete energy quanta only when they reached the boundaries of finite cells in phase space, where their energies became integer multiples of hν. This theory led Planck to his new radiation law, but in this version energy resonators possessed a zero-point energy, the smallest average energy a resonator could take on. Planck's radiation equation contained a residual energy factor, one hν/2, as an additional term dependent on the frequency ν, which was greater than zero (where h is Planck's constant). It is therefore widely agreed that "Planck's equation marked the birth of the concept of zero-point energy."[28] In a series of papers from 1911 to 1913,[29] Planck found the average energy of an oscillator to be:[26][30]
Soon, the idea of zero-point energy attracted the attention of Albert Einstein and his assistant
There is a weighty argument to be adduced in favour of the aether hypothesis. To deny the aether is ultimately to assume that empty space has no physical qualities whatever. The fundamental facts of mechanics do not harmonize with this view ... according to the general theory of relativity space is endowed with physical qualities; in this sense, therefore, there exists an aether. According to the general theory of relativity space without aether is unthinkable; for in such space there not only would be no propagation of light, but also no possibility of existence for standards of space and time (measuring-rods and clocks), nor therefore any space-time intervals in the physical sense. But this aether may not be thought of as endowed with the quality characteristic of ponderable media, as consisting of parts which may be tracked through time. The idea of motion may not be applied to it.[35][36]
In 1913
Quantum field theory and beyond
In 1926 Pascual Jordan[49] published the first attempt to quantize the electromagnetic field. In a joint paper with Max Born and Werner Heisenberg he considered the field inside a cavity as a superposition of quantum harmonic oscillators. In his calculation he found that in addition to the "thermal energy" of the oscillators there also had to exist an infinite zero-point energy term. He was able to obtain the same fluctuation formula that Einstein had obtained in 1909.[50] However, Jordan did not think that his infinite zero-point energy term was "real", writing to Einstein that "it is just a quantity of the calculation having no direct physical meaning".[51] Jordan found a way to get rid of the infinite term, publishing a joint work with Pauli in 1928,[52] performing what has been called "the first infinite subtraction, or renormalisation, in quantum field theory".[53]
Building on the work of Heisenberg and others, Paul Dirac's theory of emission and absorption (1927)[54] was the first application of the quantum theory of radiation. Dirac's work was seen as crucially important to the emerging field of quantum mechanics; it dealt directly with the process in which "particles" are actually created: spontaneous emission.[55] Dirac described the quantization of the electromagnetic field as an ensemble of harmonic oscillators with the introduction of the concept of creation and annihilation operators of particles. The theory showed that spontaneous emission depends upon the zero-point energy fluctuations of the electromagnetic field in order to get started.[56][57] In a process in which a photon is annihilated (absorbed), the photon can be thought of as making a transition into the vacuum state. Similarly, when a photon is created (emitted), it is occasionally useful to imagine that the photon has made a transition out of the vacuum state. In the words of Dirac:[54]
The light-quantum has the peculiarity that it apparently ceases to exist when it is in one of its stationary states, namely, the zero state, in which its momentum and therefore also its energy, are zero. When a light-quantum is absorbed it can be considered to jump into this zero state, and when one is emitted it can be considered to jump from the zero state to one in which it is physically in evidence, so that it appears to have been created. Since there is no limit to the number of light-quanta that may be created in this way, we must suppose that there are an infinite number of light quanta in the zero state ...
Contemporary physicists, when asked to give a physical explanation for spontaneous emission, generally invoke the zero-point energy of the electromagnetic field. This view was popularized by Victor Weisskopf who in 1935 wrote:[58]
From quantum theory there follows the existence of so called zero-point oscillations; for example each oscillator in its lowest state is not completely at rest but always is moving about its equilibrium position. Therefore electromagnetic oscillations also can never cease completely. Thus the quantum nature of the electromagnetic field has as its consequence zero point oscillations of the field strength in the lowest energy state, in which there are no light quanta in space ... The zero point oscillations act on an electron in the same way as ordinary electrical oscillations do. They can change the eigenstate of the electron, but only in a transition to a state with the lowest energy, since empty space can only take away energy, and not give it up. In this way spontaneous radiation arises as a consequence of the existence of these unique field strengths corresponding to zero point oscillations. Thus spontaneous radiation is induced radiation of light quanta produced by zero point oscillations of empty space
This view was also later supported by
Throughout the 1940s improvements in
In 1948
In 1951
In 1963 the
The uncertainty principle
Zero-point energy is fundamentally related to the Heisenberg uncertainty principle.[91] Roughly speaking, the uncertainty principle states that complementary variables (such as a particle's position and momentum, or a field's value and derivative at a point in space) cannot simultaneously be specified precisely by any given quantum state. In particular, there cannot exist a state in which the system simply sits motionless at the bottom of its potential well, for then its position and momentum would both be completely determined to arbitrarily great precision. Therefore, the lowest-energy state (the ground state) of the system must have a distribution in position and momentum that satisfies the uncertainty principle, which implies its energy must be greater than the minimum of the potential well.
Near the bottom of a potential well, the Hamiltonian of a general system (the quantum-mechanical operator giving its energy) can be approximated as a quantum harmonic oscillator,
The uncertainty principle tells us that
making the expectation values of the kinetic and potential terms above satisfy
The expectation value of the energy must therefore be at least
where ω = √k/m is the angular frequency at which the system oscillates.
A more thorough treatment, showing that the energy of the ground state actually saturates this bound and is exactly E0 = V0 + ħω/2, requires solving for the ground state of the system.
Atomic physics
The idea of a quantum harmonic oscillator and its associated energy can apply to either an atom or a subatomic particle. In ordinary atomic physics, the zero-point energy is the energy associated with the
If more than one ground state exists, they are said to be
According to the
The wave function of the ground state of a particle in a one-dimensional well is a half-period sine wave which goes to zero at the two edges of the well. The energy of the particle is given by:
where h is the Planck constant, m is the mass of the particle, n is the energy state (n = 1 corresponds to the ground-state energy), and L is the width of the well.
Quantum field theory
Quantum field theory |
---|
History |
In quantum field theory (QFT), the fabric of "empty" space is visualized as consisting of fields, with the field at every point in space and time being a quantum harmonic oscillator, with neighboring oscillators interacting with each other. According to QFT the universe is made up of matter fields whose quanta are fermions (e.g. electrons and quarks), force fields whose quanta are bosons (i.e. photons and gluons) and a Higgs field whose quantum is the Higgs boson. The matter and force fields have zero-point energy.[2] A related term is zero-point field (ZPF), which is the lowest energy state of a particular field.[92] The vacuum can be viewed not as empty space, but as the combination of all zero-point fields.
In QFT the zero-point energy of the vacuum state is called the vacuum energy and the average expectation value of the Hamiltonian is called the vacuum expectation value (also called condensate or simply VEV). The QED vacuum is a part of the vacuum state which specifically deals with quantum electrodynamics (e.g. electromagnetic interactions between photons, electrons and the vacuum) and the QCD vacuum deals with
Each point in space makes a contribution of E = ħω/2, resulting in a calculation of infinite zero-point energy in any finite volume; this is one reason renormalization is needed to make sense of quantum field theories. In cosmology, the vacuum energy is one possible explanation for the cosmological constant[18] and the source of dark energy.[19][20]
Scientists are not in agreement about how much energy is contained in the vacuum. Quantum mechanics requires the energy to be large as
In quantum
The quantum electrodynamic vacuum
The oldest and best known quantized force field is the
Redefining the zero of energy
In the quantum theory of the electromagnetic field, classical wave amplitudes α and α* are replaced by operators a and a† that satisfy:
The classical quantity |α|2 appearing in the classical expression for the energy of a field mode is replaced in quantum theory by the photon number operator a†a. The fact that:
implies that quantum theory does not allow states of the radiation field for which the photon number and a field amplitude can be precisely defined, i.e., we cannot have simultaneous eigenstates for a†a and a. The reconciliation of wave and particle attributes of the field is accomplished via the association of a probability amplitude with a classical mode pattern. The calculation of field modes is entirely classical problem, while the quantum properties of the field are carried by the mode "amplitudes" a† and a associated with these classical modes.
The zero-point energy of the field arises formally from the non-commutativity of a and a†. This is true for any harmonic oscillator: the zero-point energy ħω/2 appears when we write the Hamiltonian:
It is often argued that the entire universe is completely bathed in the zero-point electromagnetic field, and as such it can add only some constant amount to expectation values. Physical measurements will therefore reveal only deviations from the vacuum state. Thus the zero-point energy can be dropped from the Hamiltonian by redefining the zero of energy, or by arguing that it is a constant and therefore has no effect on Heisenberg equations of motion. Thus we can choose to declare by fiat that the ground state has zero energy and a field Hamiltonian, for example, can be replaced by:[10]
without affecting any physical predictions of the theory. The new Hamiltonian is said to be normally ordered (or Wick ordered) and is denoted by a double-dot symbol. The normally ordered Hamiltonian is denoted :HF, i.e.:
In other words, within the normal ordering symbol we can commute a and a†. Since zero-point energy is intimately connected to the non-commutativity of a and a†, the normal ordering procedure eliminates any contribution from the zero-point field. This is especially reasonable in the case of the field Hamiltonian, since the zero-point term merely adds a constant energy which can be eliminated by a simple redefinition for the zero of energy. Moreover, this constant energy in the Hamiltonian obviously commutes with a and a† and so cannot have any effect on the quantum dynamics described by the Heisenberg equations of motion.
However, things are not quite that simple. The zero-point energy cannot be eliminated by dropping its energy from the Hamiltonian: When we do this and solve the Heisenberg equation for a field operator, we must include the vacuum field, which is the homogeneous part of the solution for the field operator. In fact we can show that the vacuum field is essential for the preservation of the commutators and the formal consistency of QED. When we calculate the field energy we obtain not only a contribution from particles and forces that may be present but also a contribution from the vacuum field itself i.e. the zero-point field energy. In other words, the zero-point energy reappears even though we may have deleted it from the Hamiltonian.[94]
The electromagnetic field in free space
From Maxwell's equations, the electromagnetic energy of a "free" field i.e. one with no sources, is described by:
We introduce the "mode function" A0(r) that satisfies the Helmholtz equation:
where k = ω/c and assume it is normalized such that:
We wish to "quantize" the electromagnetic energy of free space for a multimode field. The field intensity of free space should be independent of position such that |A0(r)|2 should be independent of r for each mode of the field. The mode function satisfying these conditions is:
where k · ek = 0 in order to have the transversality condition ∇ · A(r,t) satisfied for the Coulomb gauge[dubious ] in which we are working.
To achieve the desired normalization we pretend space is divided into cubes of volume V = L3 and impose on the field the periodic boundary condition:
or equivalently
where n can assume any integer value. This allows us to consider the field in any one of the imaginary cubes and to define the mode function:
which satisfies the Helmholtz equation, transversality, and the "box normalization":
where ek is chosen to be a unit vector which specifies the polarization of the field mode. The condition k · ek = 0 means that there are two independent choices of ek, which we call ek1 and ek2 where ek1 · ek2 = 0 and e2
k1 = e2
k2 = 1. Thus we define the mode functions:
in terms of which the vector potential becomes[clarification needed]:
or:
where ωk = kc and akλ, a†
kλ are photon annihilation and creation operators for the mode with wave vector k and polarization λ. This gives the vector potential for a plane wave mode of the field. The condition for (kx, ky, kz) shows that there are infinitely many such modes. The linearity of Maxwell's equations allows us to write:
for the total vector potential in free space. Using the fact that:
we find the field Hamiltonian is:
This is the Hamiltonian for an infinite number of uncoupled harmonic oscillators. Thus different modes of the field are independent and satisfy the commutation relations:
Clearly the least eigenvalue for HF is:
This state describes the zero-point energy of the vacuum. It appears that this sum is divergent – in fact highly divergent, as putting in the density factor
shows. The summation becomes approximately the integral:
for high values of v. It diverges proportional to v4 for large v.
There are two separate questions to consider. First, is the divergence a real one such that the zero-point energy really is infinite? If we consider the volume V is contained by perfectly conducting walls, very high frequencies can only be contained by taking more and more perfect conduction. No actual method of containing the high frequencies is possible. Such modes will not be stationary in our box and thus not countable in the stationary energy content. So from this physical point of view the above sum should only extend to those frequencies which are countable; a cut-off energy is thus eminently reasonable. However, on the scale of a "universe" questions of general relativity must be included. Suppose even the boxes could be reproduced, fit together and closed nicely by curving spacetime. Then exact conditions for running waves may be possible. However the very high frequency quanta will still not be contained. As per John Wheeler's "geons"[95] these will leak out of the system. So again a cut-off is permissible, almost necessary. The question here becomes one of consistency since the very high energy quanta will act as a mass source and start curving the geometry.
This leads to the second question. Divergent or not, finite or infinite, is the zero-point energy of any physical significance? The ignoring of the whole zero-point energy is often encouraged for all practical calculations. The reason for this is that energies are not typically defined by an arbitrary data point, but rather changes in data points, so adding or subtracting a constant (even if infinite) should be allowed. However this is not the whole story, in reality energy is not so arbitrarily defined: in general relativity the seat of the curvature of spacetime is the energy content and there the absolute amount of energy has real physical meaning. There is no such thing as an arbitrary additive constant with density of field energy. Energy density curves space, and an increase in energy density produces an increase of curvature. Furthermore, the zero-point energy density has other physical consequences e.g. the Casimir effect, contribution to the Lamb shift, or anomalous magnetic moment of the electron, it is clear it is not just a mathematical constant or artifact that can be cancelled out.[96]
Necessity of the vacuum field in QED
The vacuum state of the "free" electromagnetic field (that with no sources) is defined as the ground state in which nkλ = 0 for all modes (k, λ). The vacuum state, like all stationary states of the field, is an eigenstate of the Hamiltonian but not the electric and magnetic field operators. In the vacuum state, therefore, the electric and magnetic fields do not have definite values. We can imagine them to be fluctuating about their mean value of zero.
In a process in which a photon is annihilated (absorbed), we can think of the photon as making a transition into the vacuum state. Similarly, when a photon is created (emitted), it is occasionally useful to imagine that the photon has made a transition out of the vacuum state.[54] An atom, for instance, can be considered to be "dressed" by emission and reabsorption of "virtual photons" from the vacuum. The vacuum state energy described by Σkλ ħωk/2 is infinite. We can make the replacement:
the zero-point energy density is:
or in other words the spectral energy density of the vacuum field:
The zero-point energy density in the frequency range from ω1 to ω2 is therefore:
This can be large even in relatively narrow "low frequency" regions of the spectrum. In the optical region from 400 to 700 nm, for instance, the above equation yields around 220 erg/cm3.
We showed in the above section that the zero-point energy can be eliminated from the Hamiltonian by the normal ordering prescription. However, this elimination does not mean that the vacuum field has been rendered unimportant or without physical consequences. To illustrate this point we consider a linear dipole oscillator in the vacuum. The Hamiltonian for the oscillator plus the field with which it interacts is:
This has the same form as the corresponding classical Hamiltonian and the Heisenberg equations of motion for the oscillator and the field are formally the same as their classical counterparts. For instance the Heisenberg equations for the coordinate x and the canonical momentum p = mẋ +eA/c of the oscillator are:
or:
since the rate of change of the vector potential in the frame of the moving charge is given by the convective derivative
For nonrelativistic motion we may neglect the magnetic force and replace the expression for mẍ by:
Above we have made the electric dipole approximation in which the spatial dependence of the field is neglected. The Heisenberg equation for akλ is found similarly from the Hamiltonian to be:
In the electric dipole approximation.
In deriving these equations for x, p, and akλ we have used the fact that equal-time particle and field operators commute. This follows from the assumption that particle and field operators commute at some time (say, t = 0) when the matter-field interpretation is presumed to begin, together with the fact that a Heisenberg-picture operator A(t) evolves in time as A(t) = U†(t)A(0)U(t), where U(t) is the time evolution operator satisfying
Alternatively, we can argue that these operators must commute if we are to obtain the correct equations of motion from the Hamiltonian, just as the corresponding Poisson brackets in classical theory must vanish in order to generate the correct Hamilton equations. The formal solution of the field equation is:
and therefore the equation for ȧkλ may be written:
where:
and:
It can be shown that in the radiation reaction field, if the mass m is regarded as the "observed" mass then we can take:
The total field acting on the dipole has two parts, E0(t) and ERR(t). E0(t) is the free or zero-point field acting on the dipole. It is the homogeneous solution of the Maxwell equation for the field acting on the dipole, i.e., the solution, at the position of the dipole, of the wave equation
satisfied by the field in the (source free) vacuum. For this reason E0(t) is often referred to as the "vacuum field", although it is of course a Heisenberg-picture operator acting on whatever state of the field happens to be appropriate at t = 0. ERR(t) is the source field, the field generated by the dipole and acting on the dipole.
Using the above equation for ERR(t) we obtain an equation for the Heisenberg-picture operator that is formally the same as the classical equation for a linear dipole oscillator:
where τ = 2e2/3mc3. in this instance we have considered a dipole in the vacuum, without any "external" field acting on it. the role of the external field in the above equation is played by the vacuum electric field acting on the dipole.
Classically, a dipole in the vacuum is not acted upon by any "external" field: if there are no sources other than the dipole itself, then the only field acting on the dipole is its own radiation reaction field. In quantum theory however there is always an "external" field, namely the source-free or vacuum field E0(t).
According to our earlier equation for akλ(t) the free field is the only field in existence at t = 0 as the time at which the interaction between the dipole and the field is "switched on". The state vector of the dipole-field system at t = 0 is therefore of the form
where |vac⟩ is the vacuum state of the field and |ψD⟩ is the initial state of the dipole oscillator. The expectation value of the free field is therefore at all times equal to zero:
since akλ(0)|vac⟩ = 0. however, the energy density associated with the free field is infinite:
The important point of this is that the zero-point field energy HF does not affect the Heisenberg equation for akλ since it is a c-number or constant (i.e. an ordinary number rather than an operator) and commutes with akλ. We can therefore drop the zero-point field energy from the Hamiltonian, as is usually done. But the zero-point field re-emerges as the homogeneous solution for the field equation. A charged particle in the vacuum will therefore always see a zero-point field of infinite density. This is the origin of one of the infinities of quantum electrodynamics, and it cannot be eliminated by the trivial expedient dropping of the term Σkλ ħωk/2 in the field Hamiltonian.
The free field is in fact necessary for the formal consistency of the theory. In particular, it is necessary for the preservation of the commutation relations, which is required by the unitary of time evolution in quantum theory:
We can calculate [z(t),pz(t)] from the formal solution of the operator equation of motion
Using the fact that
and that equal-time particle and field operators commute, we obtain:
For the dipole oscillator under consideration it can be assumed that the radiative damping rate is small compared with the natural oscillation frequency, i.e., τω0 ≪ 1. Then the integrand above is sharply peaked at ω = ω0 and:
the necessity of the vacuum field can also be appreciated by making the small damping approximation in
and
Without the free field E0(t) in this equation the operator x(t) would be exponentially dampened, and commutators like [z(t),pz(t)] would approach zero for t ≫ 1/τω2
0. With the vacuum field included, however, the commutator is iħ at all times, as required by unitarity, and as we have just shown. A similar result is easily worked out for the case of a free particle instead of a dipole oscillator.[97]
What we have here is an example of a "fluctuation-dissipation elation". Generally speaking if a system is coupled to a bath that can take energy from the system in an effectively irreversible way, then the bath must also cause fluctuations. The fluctuations and the dissipation go hand in hand we cannot have one without the other. In the current example the coupling of a dipole oscillator to the electromagnetic field has a dissipative component, in the form of the zero-point (vacuum) field; given the existence of radiation reaction, the vacuum field must also exist in order to preserve the canonical commutation rule and all it entails.
The spectral density of the vacuum field is fixed by the form of the radiation reaction field, or vice versa: because the radiation reaction field varies with the third derivative of x, the spectral energy density of the vacuum field must be proportional to the third power of ω in order for [z(t),pz(t)] to hold. In the case of a dissipative force proportional to ẋ, by contrast, the fluctuation force must be proportional to in order to maintain the canonical commutation relation.[97] This relation between the form of the dissipation and the spectral density of the fluctuation is the essence of the fluctuation-dissipation theorem.[76]
The fact that the canonical commutation relation for a harmonic oscillator coupled to the vacuum field is preserved implies that the zero-point energy of the oscillator is preserved. it is easy to show that after a few damping times the zero-point motion of the oscillator is in fact sustained by the driving zero-point field.[98]
The quantum chromodynamic vacuum
The QCD vacuum is the vacuum state of quantum chromodynamics (QCD). It is an example of a
The Higgs field
The Standard Model hypothesises a field called the Higgs field (symbol: ϕ), which has the unusual property of a non-zero amplitude in its ground state (zero-point) energy after renormalization; i.e., a non-zero vacuum expectation value. It can have this effect because of its unusual "Mexican hat" shaped potential whose lowest "point" is not at its "centre". Below a certain extremely high energy level the existence of this non-zero vacuum expectation
The Higgs mechanism is a type of superconductivity which occurs in the vacuum. It occurs when all of space is filled with a sea of particles which are charged and thus the field has a nonzero vacuum expectation value. Interaction with the vacuum energy filling the space prevents certain forces from propagating over long distances (as it does in a superconducting medium; e.g., in the Ginzburg–Landau theory).
Experimental observations
Zero-point energy has many observed physical consequences.[11] It is important to note that zero-point energy is not merely an artifact of mathematical formalism that can, for instance, be dropped from a Hamiltonian by redefining the zero of energy, or by arguing that it is a constant and therefore has no effect on Heisenberg equations of motion without latter consequence.[100] Indeed, such treatment could create a problem at a deeper, as of yet undiscovered, theory.[101] For instance, in general relativity the zero of energy (i.e. the energy density of the vacuum) contributes to a cosmological constant of the type introduced by Einstein in order to obtain static solutions to his field equations.[102] The zero-point energy density of the vacuum, due to all quantum fields, is extremely large, even when we cut off the largest allowable frequencies based on plausible physical arguments. It implies a cosmological constant larger than the limits imposed by observation by about 120 orders of magnitude. This "cosmological constant problem" remains one of the greatest unsolved mysteries of physics.[103]
Casimir effect
A phenomenon that is commonly presented as evidence for the existence of zero-point energy in vacuum is the Casimir effect, proposed in 1948 by Dutch physicist Hendrik Casimir, who considered the quantized electromagnetic field between a pair of grounded, neutral metal plates. The vacuum energy contains contributions from all wavelengths, except those excluded by the spacing between plates. As the plates draw together, more wavelengths are excluded and the vacuum energy decreases. The decrease in energy means there must be a force doing work on the plates as they move.
Early experimental tests from the 1950s onwards gave positive results showing the force was real, but other external factors could not be ruled out as the primary cause, with the range of experimental error sometimes being nearly 100%.[104][105][106][107][108] That changed in 1997 with Lamoreaux[109] conclusively showing that the Casimir force was real. Results have been repeatedly replicated since then.[110][111][112][113]
In 2009, Munday et al.[114] published experimental proof that (as predicted in 1961[115]) the Casimir force could also be repulsive as well as being attractive. Repulsive Casimir forces could allow quantum levitation of objects in a fluid and lead to a new class of switchable nanoscale devices with ultra-low static friction.[116]
An interesting hypothetical side effect of the Casimir effect is the Scharnhorst effect, a hypothetical phenomenon in which light signals travel slightly faster than c between two closely spaced conducting plates.[117]
Lamb shift
The quantum fluctuations of the electromagnetic field have important physical consequences. In addition to the Casimir effect, they also lead to a splitting between the two energy levels 2S1/2 and 2P1/2 (in term symbol notation) of the hydrogen atom which was not predicted by the Dirac equation, according to which these states should have the same energy. Charged particles can interact with the fluctuations of the quantized vacuum field, leading to slight shifts in energy;[118] this effect is called the Lamb shift.[119] The shift of about 4.38×10−6 eV is roughly 10−7 of the difference between the energies of the 1s and 2s levels, and amounts to 1,058 MHz in frequency units. A small part of this shift (27 MHz ≈ 3%) arises not from fluctuations of the electromagnetic field, but from fluctuations of the electron–positron field. The creation of (virtual) electron–positron pairs has the effect of screening the Coulomb field and acts as a vacuum dielectric constant. This effect is much more important in muonic atoms.[120]
Fine-structure constant
Taking ħ (
The fine-structure constant is the coupling constant of quantum electrodynamics (QED) determining the strength of the interaction between electrons and photons. It turns out that the fine-structure constant is not really a constant at all owing to the zero-point energy fluctuations of the electron-positron field.[121] The quantum fluctuations caused by zero-point energy have the effect of screening electric charges: owing to (virtual) electron-positron pair production, the charge of the particle measured far from the particle is far smaller than the charge measured when close to it.
The Heisenberg inequality where ħ = h/2π, and Δx, Δp are the standard deviations of position and momentum states that:
It means that a short distance implies large momentum and therefore high energy i.e. particles of high energy must be used to explore short distances. QED concludes that the fine-structure constant is an increasing function of energy. It has been shown that at energies of the order of the
rather than the low-energy α ≈ 1/137.[122][123] The renormalization procedure of eliminating zero-point energy infinities allows the choice of an arbitrary energy (or distance) scale for defining α. All in all, α depends on the energy scale characteristic of the process under study, and also on details of the renormalization procedure. The energy dependence of α has been observed for several years now in precision experiment in high-energy physics.
Vacuum birefringence
In the presence of strong electrostatic fields it is predicted that virtual particles become separated from the vacuum state and form real matter.[citation needed] The fact that electromagnetic radiation can be transformed into matter and vice versa leads to fundamentally new features in quantum electrodynamics. One of the most important consequences is that, even in the vacuum, the Maxwell equations have to be exchanged by more complicated formulas. In general, it will be not possible to separate processes in the vacuum from the processes involving matter since electromagnetic fields can create matter if the field fluctuations are strong enough. This leads to highly complex nonlinear interaction - gravity will have an effect on the light at the same time the light has an effect on gravity. These effects were first predicted by Werner Heisenberg and Hans Heinrich Euler in 1936[124] and independently the same year by Victor Weisskopf who stated: "The physical properties of the vacuum originate in the "zero-point energy" of matter, which also depends on absent particles through the external field strengths and therefore contributes an additional term to the purely Maxwellian field energy".[125][126] Thus strong magnetic fields vary the energy contained in the vacuum. The scale above which the electromagnetic field is expected to become nonlinear is known as the Schwinger limit. At this point the vacuum has all the properties of a birefringent medium, thus in principle a rotation of the polarization frame (the Faraday effect) can be observed in empty space.[127][128]
Both Einstein's theory of special and general relativity state that light should pass freely through a vacuum without being altered, a principle known as
Roberto Mignani at the
Speculated involvement in other phenomena
Dark energy
Why does the large zero-point energy of the vacuum not cause a large cosmological constant? What cancels it out?[18][103][135]
In the late 1990s it was discovered that very distant supernovae were dimmer than expected suggesting that the universe's expansion was accelerating rather than slowing down.[136][137] This revived discussion that Einstein's cosmological constant, long disregarded by physicists as being equal to zero, was in fact some small positive value. This would indicate empty space exerted some form of negative pressure or energy.
There is no natural candidate for what might cause what has been called dark energy but the current best guess is that it is the zero-point energy of the vacuum.[138] One difficulty with this assumption is that the zero-point energy of the vacuum is absurdly large compared to the observed cosmological constant. This issue, called the cosmological constant problem, is one of the greatest unsolved mysteries in physics.
The
Cosmic inflation
Why does the observable universe have more matter than antimatter?
The mechanism for inflation is unclear, it is similar in effect to dark energy but is a far more energetic and short lived process. As with dark energy the best explanation is some form of vacuum energy arising from quantum fluctuations. It may be that inflation caused baryogenesis, the hypothetical physical processes that produced an asymmetry (imbalance) between baryons and antibaryons produced in the very early universe, but this is far from certain.
Cosmology
Paul S. Wesson examined the cosmological implications of assuming that zero-point energy is real.[142] Among numerous difficulties, general relativity requires that such energy not gravitate, so it cannot be similar to electromagnetic radiation.
Alternative theories
There has been a long debate[143] over the question of whether zero-point fluctuations of quantized vacuum fields are "real" i.e. do they have physical effects that cannot be interpreted by an equally valid alternative theory? Schwinger, in particular, attempted to formulate QED without reference to zero-point fluctuations via his "source theory".[144] From such an approach it is possible to derive the Casimir Effect without reference to a fluctuating field. Such a derivation was first given by Schwinger (1975)[145] for a scalar field, and then generalized to the electromagnetic case by Schwinger, DeRaad, and Milton (1978).[146] in which they state "the vacuum is regarded as truly a state with all physical properties equal to zero". More recently Jaffe (2005)[147] has highlighted a similar approach in deriving the Casimir effect stating "the concept of zero-point fluctuations is a heuristic and calculational aid in the description of the Casimir effect, but not a necessity in QED."
Nevertheless, as Jaffe himself notes in his paper, "no one has shown that source theory or another S-matrix based approach can provide a complete description of QED to all orders." Furthermore,
Chaotic and emergent phenomena
Beyond the Standard Model |
---|
Standard Model |
The mathematical models used in
What are called Maxwell's equations today, are in fact a simplified version of the original equations reformulated by Heaviside, FitzGerald, Lodge and Hertz. The original equations used Hamilton's more expressive quaternion notation,[165] a kind of Clifford algebra, which fully subsumes the standard Maxwell vectorial equations largely used today.[166] In the late 1880s there was a debate over the relative merits of vector analysis and quaternions. According to Heaviside the electromagnetic potential field was purely metaphysical, an arbitrary mathematical fiction, that needed to be "murdered".[167] It was concluded that there was no need for the greater physical insights provided by the quaternions if the theory was purely local in nature. Local vector analysis has become the dominant way of using Maxwell's equations ever since. However, this strictly vectorial approach has led to a restrictive topological understanding in some areas of electromagnetism, for example, a full understanding of the energy transfer dynamics in Tesla's oscillator-shuttle-circuit can only be achieved in quaternionic algebra or higher SU(2) symmetries.[168] It has often been argued that quaternions are not compatible with special relativity,[169] but multiple papers have shown ways of incorporating relativity.[170][171][172][173]
A good example of nonlinear electromagnetics is in high energy dense plasmas, where
One may query what this has to do with zero-point energy. Given the complex and adaptive behaviour that arises from nonlinear systems considerable attention in recent years has gone into studying a new class of
has shown that the hydrodynamic equations of compressible fluids, together with the London equations, lead to a macroscopic parameter ( = electric charge density / mass density), without involving either quantum phase factors or Planck's constant. In essence, it has been asserted that Beltrami plasma vortex structures are able to at least simulate the morphology of Type I and Type II superconductors. This occurs because the "organised" dissipative energy of the vortex configuration comprising the ions and electrons far exceeds the "disorganised" dissipative random thermal energy. The transition from disorganised fluctuations to organised helical structures is a phase transition involving a change in the condensate's energy (i.e. the ground state or zero-point energy) but without any associated rise in temperature.[192] This is an example of zero-point energy having multiple stable states (see Quantum phase transition, Quantum critical point, Topological degeneracy, Topological order[193]) and where the overall system structure is independent of a reductionist or deterministic view, that "classical" macroscopic order can also causally affect quantum phenomena. Furthermore, the pair production of Beltrami vortices has been compared to the morphology of pair production of virtual particles in the vacuum.The idea that the vacuum energy can have multiple stable energy states is a leading hypothesis for the cause of
Purported applications
Physicists overwhelmingly reject any possibility that the zero-point energy field can be exploited to obtain useful energy (
Nevertheless, the allure of free energy has motivated such research, usually falling in the category of
Casimir batteries and engines
A common assumption is that the Casimir force is of little practical use; the argument is made that the only way to actually gain energy from the two plates is to allow them to come together (getting them apart again would then require more energy), and therefore it is a one-use-only tiny force in nature.[197] In 1984 Robert Forward published work showing how a "vacuum-fluctuation battery" could be constructed; the battery can be recharged by making the electrical forces slightly stronger than the Casimir force to reexpand the plates.[200]
In 1999, Pinto, a former scientist at NASA's Jet Propulsion Laboratory at Caltech in Pasadena, published in Physical Review his thought experiment (Gedankenexperiment) for a "Casimir engine". The paper showed that continuous positive net exchange of energy from the Casimir effect was possible, even stating in the abstract "In the event of no other alternative explanations, one should conclude that major technological advances in the area of endless, by-product free-energy production could be achieved."[201]
Garret Moddel at University of Colorado has highlighted that he believes such devices hinge on the assumption that the Casimir force is a nonconservative force, he argues that there is sufficient evidence (e.g. analysis by Scandurra (2001)[202]) to say that the Casimir effect is a conservative force and therefore even though such an engine can exploit the Casimir force for useful work it cannot produce more output energy than has been input into the system.[203]
In 2008, DARPA solicited research proposals in the area of Casimir Effect Enhancement (CEE). The goal of the program is to develop new methods to control and manipulate attractive and repulsive forces at surfaces based on engineering of the Casimir force.[204]
A 2008 patent by Haisch and Moddel[205] details a device that is able to extract power from zero-point fluctuations using a gas that circulates through a Casimir cavity. A published test of this concept by Moddel[206] was performed in 2012 and seemed to give excess energy that could not be attributed to another source. However it has not been conclusively shown to be from zero-point energy and the theory requires further investigation.[207]
Single heat baths
In 1951
There have been a growing number of papers showing that in some instances the classical laws of thermodynamics, such as limits on the Carnot efficiency, can be violated by exploiting negative entropy of quantum fluctuations.[82][214][215][216][217][218][219][220][221][222]
Despite efforts to reconcile quantum mechanics and thermodynamics over the years, their compatibility is still an open fundamental problem. The full extent that quantum properties can alter classical thermodynamic bounds is unknown[223]
Space travel and gravitational shielding
The use of zero-point energy for space travel is speculative and does not form part of the mainstream scientific consensus. A complete
In 1963
From 1971 to 1974 Henry William Wallace, a scientist at GE Aerospace was issued with three patents.[235][236][237] Wallace used Dewitt's theory to develop an experimental apparatus for generating and detecting a secondary gravitational field, which he named the kinemassic field (now better known as the gravitomagnetic field). In his three patents, Wallace describes three different methods used for detection of the gravitomagnetic field – change in the motion of a body on a pivot, detection of a transverse voltage in a semiconductor crystal, and a change in the specific heat of a crystal material having spin-aligned nuclei. There are no publicly available independent tests verifying Wallace's devices. Such an effect if any would be small.[238][239][240][241][242][243] Referring to Wallace's patents, a New Scientist article in 1980 stated "Although the Wallace patents were initially ignored as cranky, observers believe that his invention is now under serious but secret investigation by the military authorities in the USA. The military may now regret that the patents have already been granted and so are available for anyone to read."[244] A further reference to Wallace's patents occur in an electric propulsion study prepared for the Astronautics Laboratory at Edwards Air Force Base which states: "The patents are written in a very believable style which include part numbers, sources for some components, and diagrams of data. Attempts were made to contact Wallace using patent addresses and other sources but he was not located nor is there a trace of what became of his work. The concept can be somewhat justified on general relativistic grounds since rotating frames of time varying fields are expected to emit gravitational waves."[245]
In 1986 the
In 1988
In 1992
In 2002
Froning and Roach (2002)[266] put forward a paper that builds on the work of Puthoff, Haisch and Alcubierre. They used fluid dynamic simulations to model the interaction of a vehicle (like that proposed by Alcubierre) with the zero-point field. Vacuum field perturbations are simulated by fluid field perturbations and the aerodynamic resistance of viscous drag exerted on the interior of the vehicle is compared to the Lorentz force exerted by the zero-point field (a Casimir-like force is exerted on the exterior by unbalanced zero-point radiation pressures). They find that the optimized negative energy required for an Alcubierre drive is where it is a saucer-shaped vehicle with toroidal electromagnetic fields. The EM fields distort the vacuum field perturbations surrounding the craft sufficiently to affect the permeability and permittivity of space.
In 2009 Giorgio Fontana and Bernd Binder presented a new method to potentially extract the Zero-point energy of the electromagnetic field and nuclear forces in the form of gravitational waves.[267] In the spheron model of the nucleus,[268] proposed by the two times Nobel laureate Linus Pauling, dineutrons are among the components of this structure. Similarly to a dumbbell put in a suitable rotational state, but with nuclear mass density, dineutrons are nearly ideal sources of gravitational waves at X-ray and gamma-ray frequencies. The dynamical interplay, mediated by nuclear forces, between the electrically neutral dineutrons and the electrically charged core nucleus is the fundamental mechanism by which nuclear vibrations can be converted to a rotational state of dineutrons with emission of gravitational waves. Gravity and gravitational waves are well described by General Relativity, that is not a quantum theory, this implies that there is no Zero-point energy for gravity in this theory, therefore dineutrons will emit gravitational waves like any other known source of gravitational waves. In Fontana and Binder paper, nuclear species with dynamical instabilites, related to the Zero-point energy of the electromagnetic field and nuclear forces, and possessing dineutrons, will emit gravitational waves. In experimental physics this approach is still unexplored.
In 2014
See also
References
Notes
- ^ a b c Sciama (1991), p. 137.
- ^ a b c Milonni (1994), p. 35.
- ^ Davies (2011).
- ^ See Weinberg (1989) and Peebles & Ratra (2003) for review articles and Shiga (2005), Siegel (2016) for press comment
- ^ a b Weinberg (2015), p. 376.
- ^ a b Sciama (1991), p. 138.
- ^ a b Davies (1985), p. 104.
- ^ Einstein (1995), pp. 270–285.
- ^ a b Battersby (2008).
- ^ a b Itzykson & Zuber (1980), p. 111.
- ^ a b c Milonni (1994), p. 111.
- ^ Greiner, Müller & Rafelski (2012), p. 12.
- ^ Bordag et al. (2009), p. 4.
- ^ Cho (2015).
- ^ Choi (2013).
- ^ a b See Haisch, Rueda & Puthoff (1994) for proposal and Matthews (1994, 1995), Powell (1994) and Davies (1994) for comment.
- ^ See Urban et al. (2013), Leuchs & Sánchez-Soto (2013) and O'Carroll (2013) for comment.
- ^ a b c Rugh & Zinkernagel (2002).
- ^ a b "Dark Energy May Be Vacuum" (Press release). Niels Bohr Institute. 19 January 2007. Archived from the original on 31 May 2017.
- ^ a b Wall (2014).
- ^ Saunders & Brown (1991), p. 1.
- ^ Conlon (2011), p. 225.
- ^ Kragh & Overduin (2014), p. 7.
- ^ Planck (1900).
- ^ Loudon (2000), p. 9.
- ^ a b Kragh (2012), p. 7.
- ^ Planck (1912a).
- ^ Milonni (1994), p. 10.
- ^ See (Planck 1911, 1912a, 1912b, 1913) and Planck (1958) for reprints
- ^ Kuhn (1978), p. 235.
- .
- ^ Einstein (1993), pp. 563–565.
- .
- ^ Nernst, Walther (1916). "Über einen Versuch, von quantentheoretischen Betrachtungen zur Annahme stetiger Energieänderungen zurückzukehren" [On an attempt to return from quantum-theoretical considerations to the assumption of constant energy changes]. Verhandlungen der Deutschen Physikalischen (in German). 18: 83–116.
- ^ Einstein, Albert (1920). Äther und Relativitäts-Theorie [Aether and relativity theory] (in German). Berlin: Springer.
- ^ Einstein, Albert (1922). Jeffery, G. B.; Perrett, W. (eds.). Sidelights on Relativity: Ether and the Theory of Relativity. New York: Methuen & Co. pp. 1–24.
- S2CID 121049183.
- S2CID 4130047.
- S2CID 98061516.
- S2CID 4121118.
- OCLC 7331244990.
- ^ Kragh (2002), p. 162.
- .
- .
- .
- ^ Jeans, James Hopwood (1915). The mathematical theory of electricity and magnetism (3rd ed.). Cambridge: Cambridge University Press. p. 168.
- .
- OCLC 638472161.
- S2CID 186237037.
- Bibcode:1909PhyZ...10..185E.
- OCLC 722601833.
- S2CID 120536476.
- OCLC 439849774.
- ^ a b c Dirac (1927).
- JSTOR 20024506.
- ^
Yokoyama, H.; Ujihara, K. (1995). Spontaneous emission and laser oscillation in microcavities. Boca Raton: CRC Press. p. 6. OCLC 832589969.
- ^ Scully & Zubairy (1997), §1.5.2 pp. 22–23.
- S2CID 6780937.
- .
- ^ .
- ^ .
- OCLC 1015092892.
- ^ Weisskopf (1936), p. 6.
- S2CID 120434909.
- ^ Power (1964), p. 35.
- ^ Pauli, Wolfgang (1946). "Exclusion principle and quantum mechanics" (PDF). nobelprize.org. Royal Swedish Academy of Sciences. Retrieved 20 October 2016.
- .
- ^ Casimir, Hendrik Brugt Gerhard (1948). "On the attraction between two perfectly conducting plates" (PDF). Proceedings of the Royal Netherlands Academy of Arts and Sciences. 51: 793–795. Retrieved 19 October 2016.
- S2CID 125644826.
- S2CID 123122363.
- ISSN 0953-8585. Retrieved 24 October 2016.
- ^ Lifshitz, E. M. (1954). "The Theory of Molecular Attractive Forces between Solids". Journal of Experimental Theoretical Physics USSR. 29: 94–110.
- ^ Lifshitz, E. M. (1956). "The theory of molecular Attractive Forces between Solids". Soviet Physics. 2 (1): 73–83.
- .
- OCLC 925046024.
- ^ .
- ^ .
- ^ .
- ^ a b Milonni (1994), p. 54.
- ^ S2CID 119728862.
- ^ S2CID 32579381.
- ^ a b Scully et al. (2003).
- .
- ^ Drexhage (1970).
- ^ Drexhage (1974), p. [page needed].
- PMID 10032058.
- PMID 10034639.
- .
- ^ Goy et al. (1983).
- ^ Milonni (1983).
- S2CID 122763326.
- ^
Gribbin, J. R. (1998). Gribbin, M. (ed.). Q is for Quantum: An Encyclopedia of Particle Physics. OCLC 869069919.
- ^ Peskin & Schroeder (1995), pp. 786–791.
- ^ Milonni (1994), pp. 73–74.
- .
- ^ Power (1964), pp. 31–33.
- ^ a b Milonni (1981).
- .
- ^ "Higgs bosons: theory and searches" (PDF). PDGLive. Particle Data Group. 12 July 2012. Retrieved 15 August 2012.
- ^ Milonni (1994), pp. 42–43.
- ^ Peskin & Schroeder (1995), p. 22.
- ^ Milonni (2009), p. 865.
- ^ .
- .
- .
- S2CID 4258508.
- .
- .
- .
- S2CID 56132451.
- ^ Chan et al. (2001).
- ^ Bressi et al. (2002).
- ^ Decca et al. (2003).
- PMID 19129843.
- .
- ^ Capasso et al. (2007).
- ^ a b See Barton & Scharnhorst (1993) and Chown (1990)
- ^ Itzykson & Zuber (1980), p. 80.
- ^
Hawton, M. (1993). "Self-consistent frequencies of the electron–photon system". PMID 9909797.
- ^ Le Bellac (2006), p. 381.
- ^ Le Bellac (2006), p. 33.
- ISBN 9781466512993.
- ISBN 9789814545143.
- ^ Heisenberg & Euler (1936).
- ^ Weisskopf (1936), p. 3.
- ^ Greiner, Müller & Rafelski (2012), p. 278.
- ^ Greiner, Müller & Rafelski (2012), p. 291.
- ^ See Dunne (2012) for a historical review of the subject.
- ^ Heyl & Shaviv (2000), p. 1.
- ^ See Carroll & Field (1997) and Kostelecký and Mewes (2009, 2013) for an overview of this area.
- ^ See Mignani et al. (2017) for experiment and Cho (2016), Crane (2016) and Bennett (2016) for comment.
- ^ Rees (2012), p. 528.
- ^ Crane (2016).
- ^ Cho (2016).
- ^ Battersby (2016).
- ^ Riess et al. (1998).
- ^ Perlmutter et al. (1998).
- ^ Clark, Stuart (2016). "The Universe is Flat as a Pancake". New Scientist. Vol. 232, no. 3097. p. 35.
- ^ Miller, Katrina (1 July 2023). "The Dark Universe Is Waiting. What Will the Euclid Telescope Reveal?". The New York Times. Retrieved 23 August 2023.
- S2CID 14539052.
- ^ Tyson, Neil deGrasse and Donald Goldsmith (2004), Origins: Fourteen Billion Years of Cosmic Evolution, W. W. Norton & Co., pp. 84–85.
- ^ Wesson, Paul S. "Cosmological constraints on the zero-point electromagnetic field." Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 378, Sept. 10, 1991, p. 466-470. Research supported by NSERC. 378 (1991): 466-470.
- S2CID 118779716.
- ^ See Schwinger (1998a, 1998b, 1998c)
- S2CID 126297065.
- .
- S2CID 13171179.
- ^ Milonni (1994), p. 48.
- ^ Greiner, Müller & Rafelski (2012), p. 20.
- ISBN 9789812779977.
- ^ Greiner, Müller & Rafelski (2012), p. 23.
- ^ Ehrenberg, W; Siday, RE (1949). "The Refractive Index in Electron Optics and the Principles of Dynamics". .
- ^
Aharonov, Y; Bohm, D (1959). "Significance of electromagnetic potentials in quantum theory". S2CID 121421318.
- Bibcode:1981JETPL..33...94A. Archived from the original(PDF) on 4 November 2016. Retrieved 3 November 2016.
- S2CID 46623507.
- PMID 10034484.
- S2CID 118184376.
- PMID 10034203.
- .
- .
- ^ K. v. Klitzing; G. Dorda; M. Pepper (1980). "New method for high-accuracy determination of the fine-structure constant based on quantized Hall resistance". Physical Review Letters. 45 (6): 494–497. .
- ^ De Haas, W. J.; Van Alphen, P. M. (1930). "The dependance of the susceptibility of diamagnetic metals upon the field". Proc. Netherlands R. Acad. Sci. 33: 1106.
- ^ Penrose (2004), pp. 453–454.
- ISBN 978-981-02-2095-2.
- ISBN 9780801482342.
- .
- ISBN 9780801482342.
- ISSN 0182-4295. Archived from the original(PDF) on 13 September 2016. Retrieved 3 November 2016.
- ^ Penrose (2004), p. 201.
- .
- S2CID 123315936.
- ^ Kauffmann, T.; Sun, Wen IyJ (1993). "Quaternion mechanics and electromagnetism". Annales de la Fondation Louis de Broglie. 18 (2): 213–219.
- ^ Lambek, Joachim. "QUATERNIONS AND THREE TEMPORAL DIMENSIONS" (PDF).
- ^ Bostick et al. (1966).
- ^ Ferraro, V .; Plumpton, C. (1961). An Introduction to Magneto-Fluid Mechanics. Oxford: Oxford University Press.
- ISBN 978-0918388049.
- ^ Noether, E. (1918). "Invariante Variationsprobleme". Nachr. D. König. Gesellsch. D. Wiss. Zu Göttingen, Math-phys. Klasse. 1918: 235–257.
- ^ Scott (2006), p. 163.
- ISBN 9783540304319.
- ^ The Nobel Foundation (1977). "The Nobel Prize in Chemistry 1977". nobelprize.org. Royal Swedish Academy of Sciences. Retrieved 3 November 2016.
- ISBN 978-0471024019.
- ISBN 978-0-00-654115-8.
- ISBN 9780749386061.
- ISBN 978-0674009875.
- ISBN 978-1-84816-724-7.
- ^ "Classical Physics Makes a Comeback". The Times. London. 14 January 1982.
- ^ Bostick, W. (1985). "On the Controversy over Whether Classical Systems Like Plasmas Can Behave Like Superconductors (Which Have Heretofore Been Supposed to Be Strictly Quantum Mechanically Dominated)" (PDF). International Journal of Fusion Energy. 3 (2): 47–51. Archived (PDF) from the original on 3 April 2016. Retrieved 22 May 2020.
- ^ Bostick, W. (1985). "The Morphology of the Electron" (PDF). International Journal of Fusion Energy. 3 (1): 9–52. Archived (PDF) from the original on 3 April 2016. Retrieved 22 May 2020.
- ^ Bostick, W. (1985). "Recent Experimental Results of The Plasma-Focus Group at Darmstadt, West Germany: A Review and Critique" (PDF). International Journal of Fusion Energy. 3 (1): 68. Archived (PDF) from the original on 3 April 2016. Retrieved 22 May 2020.
- .
- .
- ^ Reed (1995), p. 226.
- S2CID 14593420.
- ISBN 978-3-540-22495-2.
- ISBN 978-0674009875.
- ^ Peterson, I (1997). "Peeking inside an electron's screen". Science News. 151: 89. Retrieved 24 October 2016.
- ^ U.S. Army National Ground Intelligence Center.
Forays into "free energy" inventions and perpetual-motion machines using ZPE are considered by the broader scientific community to be pseudoscience.
- ^ "Zero-point energy, on season 8 , episode 2". Scientific American Frontiers. Chedd-Angier Production Company. 1997–1998. PBS. Archived from the original on 1 January 2006.
- ^ a b Scott (2004).
- .
- ^ Pinto (1999).
- arXiv:hep-th/0104127.
- S2CID 17095906.
- ^ "Research in a Vacuum: DARPA Tries to Tap Elusive Casimir Effect for Breakthrough Technology". www.scientificamerican.com. Scientific American. 2008. Retrieved 22 February 2024.
- ^ U.S. patent 7,379,286
- doi:10.1016/j.phpro.2012.08.007. Archived from the original(PDF) on 7 May 2021. Retrieved 1 November 2016.
- .
- .
- .
- .
- ISBN 9780444869920.
- .
- ^ Abbott et al. (1996).
- ^ Scully (2001).
- .
- S2CID 119262651.
- PMID 23214736.
- .
- ^ Roßnagel et al. (2014).
- ^ Correa et al. (2014).
- S2CID 118468331.
- PMID 27003686.
- ISBN 978-3-540-70510-9.
- .
- S2CID 15382105.
- arXiv:physics/0108005.
- ^ Matthews, Robert (21 September 1996). "Antigravity machine weighed down by controversy". New Scientist. Retrieved 26 October 2016.
- arXiv:hep-th/9603077.
- .
- S2CID 51650940.
- ].
- ^ "Physicist Predicts Gravitational Analogue Of Electrical Transformers". MIT Technology Review. 6 July 2010. Retrieved 28 October 2016.
- .
- .
- ^ U.S. patent 3,626,606
- ^ U.S. patent 3,626,605
- ^ U.S. patent 3,823,570
- S2CID 121728055.
- .
- .
- .
- S2CID 35509153.
- PMID 10054182.
- ^ "Antigravity Not So Crazy After All". Patents Review. New Scientist. Vol. 85, no. 1194. 14 February 1980. p. 485.
- ^ Cravens, D. L. (1990). "Electric Propulsion Study: Final Report" (PDF). Contract F04611-88-C-0014, Astronautics Laboratory (AFSC), Air Force Space Technology Center, Space Systems Division, Air Force Systems Command, Edwards AFB, CA. Archived from the original (PDF) on 12 August 2011. Retrieved 26 October 2016.
- S2CID 110771631.
- PMID 10038800.
- ISBN 978-0521857147.
- S2CID 4797900.
- .
- Bibcode:1997physics...5043R.
- ^ Woods et al. (2001).
- arXiv:gr-qc/0603033v1.
- ^ Robertson, Glen A. (1999). "On the Mechanism for a Gravity Effect using Type II Superconductors" (PDF). NASA Technical Reports Server. Retrieved 26 October 2016.
- PMID 10013404.
- PMID 10004334.
- S2CID 122075917.
- ^ Kowitt (1994).
- S2CID 115204136.
- ^ Woods (2005).
- S2CID 24997124.
- .
- ^ Lucentini (2000).
- ^ "Annual Report on Cooperative Agreements and Other Transactions Entered into During FY2001 Under 10 USC 2371". DOD. p. 66. Archived from the original on 1 August 2021. Retrieved 6 March 2014.
- ^ Cook (2002).
- ISBN 978-1-62410-115-1.
- ISSN 0094-243X.
- PMID 16578621.
- ^ White, March, Williams et al. (2011).
- ^ Maxey, Kyle (11 December 2012). "Propulsion on an Interstellar Scale – the Quantum Vacuum Plasma Thruster". engineering.com. Retrieved 24 October 2016.
- ^ Hambling, David (31 July 2014). "Nasa validates 'impossible' space drive". Wired UK. Retrieved 24 October 2016.
- ^ White, March, Lawrence et al. (2016).
- ^ Drake, Nadia; Greshko, Michael (21 November 2016). "NASA Team Claims 'Impossible' Space Engine Works—Get the Facts". National Geographic. Archived from the original on 22 November 2016. Retrieved 22 November 2016.
Articles in the press
- Battersby, S. (20 November 2008). "It's Confirmed: Matter is Merely Vacuum Fluctuations". New Scientist. Archived from the original on 27 May 2017.
- Bennett, J. (30 November 2016). "Scientists Catch "Virtual Particles" Hopping In and Out of Existence". Popular Mechanics. Archived from the original on 29 May 2017.
- Cho, A. (1 October 2015). "Physicists Observe Weird Quantum Fluctuations Of Empty Space—Maybe". Science. from the original on 27 May 2017.
- Cho, A. (30 November 2016). "Astronomers Spot Signs of Weird Quantum Distortion in Space". Science. from the original on 29 May 2017.
- Choi, C. Q. (12 February 2013). "Something from Nothing? A Vacuum Can Yield Flashes of Light". Scientific American. Archived from the original on 30 May 2017.
- Chown, M. (7 April 1990). "Science: Can Photons Travel 'Faster Than Light'?". New Scientist. Archived from the original on 30 May 2017.
- Cook, N. (29 July 2002). "Anti-Gravity Propulsion Comes "Out of the Closet"". Jane's Defence Weekly. London. Archived from the original on 2 August 2002.
- Crane, L. (30 November 2016). "Quantum Particles Seen Distorting Light From a Neutron Star". New Scientist. Archived from the original on 29 May 2017.
- Davies, P. C. W. (22 September 1994). "Inertia Theory: Magic Roundabout. Paul Davies on the Meaning of Mach's Principle". The Guardian. Archived from the original on 17 January 1999.
- .
- Lucentini, J. (28 September 2000). "Weighty Implications: NASA Funds Controversial Gravity Shield". SPACE.com. Archived from the original on 9 November 2000.
- Matthews, R. (25 February 1995). "Nothing Like a Vacuum". New Scientist. Vol. 145, no. 1966. pp. 30–33. Archived from the original on 13 April 2016. Via Calphysics Institute.
- O'Carroll, E. (25 March 2013). "Scientists Examine Nothing, Find Something". Christian Science Monitor. Archived from the original on 31 March 2013.
- Pilkington, M. (17 July 2003). "Zero Point Energy". The Guardian. Archived from the original on 7 February 2017.
- Powell, C. S. (1994). "Unbearable Lightness: A New Theory May Explain Why Objects Tend to Stay Put". Scientific American. 270 (5): 30–31. .
- Scott, W. B. (March 2004). "To the Stars" (PDF). Aviation Week & Space Technology. pp. 50–53. Archived from the original (PDF) on 26 February 2017. Retrieved 25 October 2016.
- Siegel, E. (22 September 2016). "What Is The Physics Of Nothing?". Forbes. Archived from the original on 27 May 2017.
- Shiga, D. (28 September 2005). "Vacuum Energy: Something For Nothing?". New Scientist. Archived from the original on 27 May 2017.
- Wall, M. (27 March 2014). "Does Dark Energy Spring From the 'Quantum Vacuum?'". SPACE.com. Archived from the original on 29 March 2014.
Bibliography
- Abbott, D.; Davis, B. R.; Phillips, N. J.; Eshraghian, K. (1996). "Simple derivation of the thermal noise formula using window-limited Fourier transforms and other conundrums". IEEE Transactions on Education. 39 (1): 1–13. .
- Barton, G.; Scharnhorst, K. (1993). "QED Between Parallel Mirrors: Light Signals Faster Than c, or Amplified by the Vacuum". Journal of Physics A: Mathematical and General. 26 (8): 2037–2046. ISSN 0305-4470.
- Battersby, Stephen (2016). "Dark energy: Staring into darkness". Nature. 537 (7622): 201–204. S2CID 4398296.
- Bordag, M; Klimchitskaya, G. L.; Mohideen, U.; Mostepanenko, V. M. (2009). Advances in the Casimir Effect. Oxford: Oxford University Press. OCLC 319209483.
- Bostick, W. H.; Prior, W.; Grunberger, L.; Emmert, G. (1966). "Pair Production of Plasma Vortices". Physics of Fluids. 9 (10): 2078. .
- Bressi, G.; Carugno, G.; Onofrio, R.; Ruoso, G. (2002). "Measurement of the Casimir Force between Parallel Metallic Surfaces". Physical Review Letters. 88 (4): 041804. S2CID 43354557.
- Capasso, F.; Munday, J. N.; Iannuzzi, D.; Chan, H. B. (2007). "Casimir Forces and Quantum Electrodynamical Torques: Physics and Nanomechanics" (PDF). IEEE Journal of Selected Topics in Quantum Electronics. 13 (2): 400–414. S2CID 32996610.
- S2CID 13943605.
- Chan, H. B.; Aksyuk, V. A.; Kleiman, R. N.; Bishop, D. J.; Capasso, F. (2001). "Quantum Mechanical Actuation of Microelectromechanical Systems by the Casimir Force" (PDF). Science. 291 (5510): 1941–1944. S2CID 17072357.
- Conlon, T. E. (2011). Thinking About Nothing : Otto Von Guericke and The Magdeburg Experiments on the Vacuum. San Francisco: Saint Austin Press. OCLC 840927124.
- Correa, L. A.; Palao, J. P.; Alonso, D.; Adesso, G. (2014). "Quantum-enhanced absorption refrigerators". Scientific Reports. 4 (3949): 3949. PMID 24492860.
- OCLC 12397205.
- Decca, R. S.; López, D.; Fischbach, E.; Krause, D. E. (2003). "Measurement of the Casimir Force between Dissimilar Metals". Physical Review Letters. 91 (5): 050402. S2CID 20243276.
- Dirac, Paul A. M. (1927). "The Quantum Theory of the Emission and Absorption of Radiation" (PDF). Proc. R. Soc. A. 114 (767): 243–265. doi:10.1098/rspa.1927.0039. Archived from the original(PDF) on 25 October 2016. Retrieved 17 October 2016.
- Drexhage, K. H. (1970). "Monomolecular Layers and Light". Scientific American. 222 (3): 108–119. .
- Drexhage, K. H. (1974). "IV Interaction of Light with Monomolecular Dye Layers". In Wolf, E. (ed.). Progress in Optics. Vol. 12. pp. 163–232. ISBN 978-0-444-10571-4.
- Dunne, G. V. (2012). "The Heisenberg-Euler Effective Action: 75 years on". International Journal of Modern Physics A. 27 (15): 1260004. S2CID 119258601.
- Einstein, A. (1995). Klein, Martin J.; Kox, A. J.; Renn, Jürgen; Schulmann, Robert (eds.). The Collected Papers of Albert Einstein Vol. 4 The Swiss Years: Writings, 1912–1914. Princeton: Princeton University Press. OCLC 929349643.
- Einstein, A. (1993). Klein, Martin J.; Kox, A. J.; Schulmann, Robert (eds.). The Collected Papers of Albert Einstein Vol. 5 The Swiss Years: Correspondence, 1902–1914. Princeton: Princeton University Press. OCLC 921496342.
- Goy, P.; Raimond, J. M.; Gross, M.; Haroche, S. (1983). "Observation of Cavity-Enhanced Single-Atom Spontaneous Emission". Physical Review Letters. 50 (24): 1903–1906. .
- Greiner, W.; Müller, B.; Rafelski, J. (2012). Quantum Electrodynamics of Strong Fields: With an Introduction into Modern Relativistic Quantum Mechanics. Springer. OCLC 317097176.
- Haisch, B.; Rueda, A.; Puthoff, H. E. (1994). "Inertia as a Zero-Point-Field Lorentz Force" (PDF). Physical Review A. 49 (2): 678–694. PMID 9910287. Archived from the original(PDF) on 31 July 2018. Retrieved 17 October 2016.
- Heisenberg, W.; Euler, H. (1936). "Folgerungen aus der Diracschen Theorie des Positrons". Zeitschrift für Physik. 98 (11–12): 714–732. S2CID 120354480.
- Heyl, J. S.; Shaviv, N. J. (2000). "Polarization evolution in strong magnetic fields". Monthly Notices of the Royal Astronomical Society. 311 (3): 555–564. S2CID 11717019.
- Itzykson, C.; Zuber, J.-B. (1980). Quantum Field Theory (2005 ed.). Mineola, New York: Dover Publications. OCLC 61200849.
- Kostelecký, V. Alan; Mewes, M. (2009). "Electrodynamics with Lorentz-violating operators of arbitrary dimension". Physical Review D. 80 (1): 015020. S2CID 119241509.
- Kostelecký, V. Alan; Mewes, M. (2013). "Constraints on Relativity Violations from Gamma-Ray Bursts". Physical Review Letters. 110 (20): 201601. S2CID 8579347.
- Kowitt, Mark (1994). "Gravitomagnetism and magnetic permeability in superconductors". Physical Review B. 49 (1): 704–708. PMID 10009347.
- Kragh, H. (2002). Quantum Generations: A History of Physics in the Twentieth Century. Princeton University Press. OCLC 248763258.
- Kragh, H. (2012). "Preludes to Dark Energy: Zero-Point Energy and Vacuum Speculations". Archive for History of Exact Sciences. 66 (3): 199–240. S2CID 118593162.
- Kragh, H. S.; Overduin, J. M. (2014). The Weight of the Vacuum : A Scientific History of Dark Energy. New York: Springer. OCLC 884863929.
- OCLC 803538583.
- Le Bellac, M. (2006). Quantum Physics (2012 ed.). Cambridge University Press. OCLC 957316740.
- Leuchs, G.; Sánchez-Soto, L. L. (2013). "A Sum Rule For Charged Elementary Particles". The European Physical Journal D. 67 (3): 57. S2CID 118643015.
- OCLC 44602993.
- Matthews, R. (1994). "Inertia: Does Empty Space Put Up the Resistance?". Science. 263 (5147): 612–613. PMID 17747645– via Calphysics Institute.
- Mignani, R. P.; Testa, V.; González Caniulef, D.; Taverna, R.; Turolla, R.; Zane, S.; Wu, K. (2017). "Evidence for vacuum birefringence from the first optical-polarimetry measurement of the isolated neutron star RX J1856.5−3754" (PDF). Monthly Notices of the Royal Astronomical Society. 465 (1): 492–500. S2CID 38736536.
- .
- S2CID 119991060.
- OCLC 422797902.
- OCLC 297803628.
- S2CID 118961123.
- Penrose, Roger (2004). The Road to Reality (8th ed.). New York: Alfred A. Knopf. OCLC 474890537.
- S2CID 118910636.
- Peskin, M. E.; Schroeder, D. V. (1995). An Introduction To Quantum Field Theory. Addison-Wesley. OCLC 635667163.
- Pinto, F. (1999). "Engine cycle of an optically controlled vacuum energy transducer". Physical Review B. 60 (21): 14740. .
- Planck, M. (1900). "Zur Theorie des Gesetzes der Energieverteilung im Normalspektrum". Verhandlungen der Deutschen Physikalischen Gesellschaft. 2: 237–245.
- Planck, M. (1911). "Eine neue Strahlungshypothese". Verhandlungen der Deutschen Physikalischen Gesellschaft. 13: 138–148.
- .
- OCLC 5894537227.
- OCLC 924400975.
- OCLC 603096370.
- OCLC 490279969.
- Reed, D. (1995). "Foundational Electrodynamics and Beltrami Vector Fields". In Barrett, Terence William; Grimes, Dale M. (eds.). Advanced Electromagnetism: Foundations, Theory and Applications. Singapore: World Scientific. pp. 217–249. ISBN 978-981-02-2095-2.
- OCLC 851193468.
- Riek, C.; Seletskiy, D. V.; Moskalenko, A. S.; Schmidt, J. F.; Krauspe, P.; Eckart, S.; Eggert, S.; Burkard, G.; Leitenstorfer, A. (2015). "Direct Sampling of Electric-Field Vacuum Fluctuations" (PDF). Science. 350 (6259): 420–423. S2CID 40368170.
- S2CID 15640044.
- Roßnagel, J.; Abah, O.; Schmidt-Kaler, F.; Singer, K.; Lutz, E. (2014). "Nanoscale Heat Engine Beyond the Carnot Limit". Physical Review Letters. 112 (3): 030602. S2CID 1826585.
- Rugh, S. E.; Zinkernagel, H. (2002). "The Quantum Vacuum and the Cosmological Constant Problem". Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics. 33 (4): 663–705. S2CID 9007190.
- OCLC 774073198.
- OCLC 40544377.
- OCLC 40544377.
- OCLC 40544377.
- OCLC 774073198.
- Scott, Alwyn (2006). Encyclopedia of Nonlinear Science. Routledge. OCLC 937249213.
- Scully, M. O.; Zubairy, M. S. (1997). Quantum optics. Cambridge UK: Cambridge University Press. OCLC 444869786.
- Scully, M. O. (2001). "Extracting Work from a Single Thermal Bath via Quantum Negentropy". Physical Review Letters. 87 (22). 220601. PMID 11736390.
- Scully, M. O.; Zubairy, M. S.; Agarwal, G. S.; Walther, H. (2003). "Extracting Work from a Single Heat Bath via Vanishing Quantum Coherence". Science. 299 (5608): 862–863. S2CID 120884236.
- Urban, M.; Couchot, F.; Sarazin, X.; Djannati-Atai, A. (2013). "The Quantum Vacuum as the Origin of the Speed of Light". The European Physical Journal D. 67 (3): 58. S2CID 15753833.
- S2CID 122259372.
- OCLC 910664598.
- Weisskopf, V. (1936). "Über die Elektrodynamik des Vakuums auf Grund des Quantentheorie des Elektrons" [On the Elecrodynamics of the Vacuum on the Basis of the Quantum Theory of the Electron] (PDF). Kongelige Danske Videnskabernes Selskab, Mathematisk-fysiske Meddelelse. 24 (6): 3–39.
- White, H.; March, P.; Lawrence, J.; Vera, J.; Sylvester, A.; Brady, D.; Bailey, P. (2016). "Measurement of Impulsive Thrust from a Closed Radio-Frequency Cavity in Vacuum". Journal of Propulsion and Power. 33 (4): 830–841. S2CID 126303009.
- White, H.; March, P.; Williams, N.; O'Neill, W. (5 December 2011). Eagleworks Laboratories: Advanced Propulsion Physics Research (PDF). JANNAF Joint Propulsion Meeting; 5–9 December 2011; Huntsville, AL. Retrieved 24 October 2016.
- Wilson, C. M.; Johansson, G.; Pourkabirian, A.; Simoen, M.; Johansson, J. R.; Duty, T.; Nori, F.; Delsing, P. (2011). "Observation of the Dynamical Casimir Effect in a Superconducting Circuit". Nature. 479 (7373): 376–379. S2CID 219735.
- Woods, R. C. (2005). "Manipulation of gravitational waves for communications applications using superconductors". Physica C: Superconductivity. 433 (1–2): 101–107. .
- Woods, R. C.; Cooke, S. G.; Helme, J.; Caldwell, C. H. (2001). "Gravity modification by high-temperature superconductors". AIAA 37th Joint Propulsion Conference and Exhibit. .
Further reading
Press articles
- Brumfiel, G. (3 June 2011). "Moving Mirrors Make Light From Nothing". Nature. .
- Brooks, M. (16 November 2011). "Light Pulled Out of Empty Space". New Scientist. Archived from the original on 30 May 2017.
- Cartlidge, E. (17 November 2011). "How to Turn Darkness into Light". Physics World. Institute of Physics. Archived from the original on 30 May 2017.
- Marcus, A. (12 October 2009). "Research in a Vacuum: DARPA Tries to Tap Elusive Casimir Effect for Breakthrough Technology". Scientific American. Archived from the original on 2 March 2015.
- Matthews, R.; Sample, I. (1 September 1996). "'Anti-Gravity' Device Gives Science a Lift". The Sunday Telegraph. Archived from the original on 6 March 2003.
- Sciama, D. W. (2 February 1978). "The Ether Transmogrified". New Scientist. Vol. 77, no. 1088. pp. 298–300 – via Google Books.
- Yirka, B. (2 October 2015). "Research Team Claims to Have Directly Sampled Electric-Field Vacuum Fluctuations". Phys.org. Archived from the original on 27 May 2017.
Journal articles
- Boyer, T. H. (1970). "Quantum Zero-Point Energy and Long-Range Forces". Annals of Physics. 56 (2): 474–503. ISSN 0003-4916.
- Bulsara, A. R.; Gammaitoni, L. (1996). "Tuning in to Noise" (PDF). Physics Today. 49 (3): 39–45. ISSN 0031-9228. Archived from the original(PDF) on 12 July 2018. Retrieved 31 May 2017.
- Lahteenmaki, P.; Paraoanu, G. S.; Hassel, J.; Hakonen, P. J. (2013). "Dynamical Casimir Effect in a Josephson Metamaterial". Proceedings of the National Academy of Sciences. 110 (11): 4234–4238. S2CID 10972781.
Books
- Beiser, A. (2003). Concepts of Modern Physics (6th ed.). Boston: McGraw-Hill. OCLC 48965418.
- OCLC 924845769.
- OCLC 946050522.