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Experiment Generates Particles from the Vacuum

Black Hole Physics of Particle Creation Mimicked in Table-top experiment with Graphene: Experiment Verifies Long-standing Prediction of Using the Electric Field to Generate Particles from the Quantum Vacuum
By: William Brown, scientist at the Resonance Science Foundation

The Quantum Vacuum—Ubiquitous Mass-energy of Space

There is a hypothetical state of space referred to in physics as the vacuum. The idea of the vacuum is a completely empty space devoid of any matter, energy, or forces. This state is hypothetical because it does not exist anywhere in nature. The reason for this is that the very fabric of the universe, space, is a substantive medium, a sea of energy. In fact, the preeminent physicist Paul Dirac— known for the Dirac equation, an extension of the Schrodinger equation that is consistent with special relativity— posited that the vacuum must be filled with an infinite sea of negative energy electrons (see also his fascinating work on the large number hypothesis).

This is known as the Dirac sea, and is a result of the negative energy solutions of the Dirac equation and his prediction that relativistic electrons must continuously emit energy (as photons) causing them to drop to lower energy values: this should be able to continue without limit, such that electrons would descend past “zero energy” into negative energy values, of which there is no bottom value. Dirac hypothesized that the only reason we do not observe this occurring is that all negative energy values are already filled, and because of the Pauli Exclusion principle positive energy electrons cannot occupy these already filled states. Interestingly, this led to the prediction of the positron—the antimatter counterpart of the electron— as Dirac predicted that a hole, or unoccupied level in the Dirac Sea would appear to cause the immediate “annihilation” of an electron as it quickly emitted all positive energy to occupy the hole (it has not annihilated but rather gone into the Dirac Sea where it is not directly observable).

A photon transfers energy to an electron with negative energy in the Dirac Sea giving it a positive energy value E > 0, leaving a hole with the same mass as the electron but with a positive charge. In 1930 Carl Anderson located this particle called a positron in an experiment.

The Dirac Sea has been supplanted by quantum field theory in which the vacuum is filled with a much more encompassing sea of particles, such that every conceivable particle-antiparticle pair is constantly fluctuating between creation and annihilation in a never-ending dance occupying an infinite range of modes of their respective quantum fields. In quantum field theory particles are not little objects in space, they are seemingly point-like manifestations of extended spatial distributions of excitations of quantum fields—little vortices of quantum harmonic resonators that continuously energetically oscillate through all space.

This non-zero energy of space— where it otherwise should be  at the “zero-point” energy value if there was such a thing as “nothing”— is not trivial, vacuum energy fluctuations have significant physical effects that are observed in a variety of phenomena such as:

  • the Lamb shift (the harbinger of modern quantum electrodynamics developed by Julian Schwinger, Richard Feynman, and Freeman Dyson)
  • zitterbewegung, from the Dirac equation for relativistic electrons in free space there is known to be an interference between positive and negative energy states that produces what appears to be a fluctuation (up to the speed of light) of the position of an electron
  • fluctuating gluons account for how hadrons get 98% of the mass that is not attributed to the so-called Higgs mechanism (in Quantum Chromodynamics the nucleon is a volume of billions of fluctuating quark anti-quark particle pairs that all cancel out, except for three of them, and these interact with the Higgs field to give 2% of the baryon mass)
  • and of course, can be directly observed in the Casimir effect (see my article controlling the vacuum with functional Casimir Devices). In fact, in the Dynamical Casimir effect photons are directly emitted from the quantum vacuum.

Why is it then that we are not more aware of this infinite sea of energy and the substantive nature of space? One reason is that the quantum vacuum in free space is in a state of equilibrium: if you think about this in terms of matter it has an infinite number of particles and their antiparticles so that at a macroscopic scale that we observe they completely “cancel out”, and there is no net effect. Similarly for forces, space is infinitely positively curved and infinitely negatively curved so that at macroscopic scales it appears flat. It is only in conditions were there is a gradient in the structure of the vacuum that particles, energy, or forces are observed. For instance, spin induces a gradient in the structure of space, so if you picture space as comprised of infinite little polarizable units, then vortices in this quantum vacuum plasma will appear as substantive, having mass, charge, and binding forces like strong gravity and electromagnetism (see Nassim Haramein and Dr. Olivier Alirol’s upcoming paper Scale Invariant Unification of Forces, Fields & Particles in a Quantum Vacuum Plasma).  

Another way to describe the formation of a gradient in space is Vacuum polarization, and indeed it has long been predicted that with sufficient vacuum polarization the particles that abound in the vacuum will be emitted: this is the case with the Hawking-Unruh effect, where strong gravitational curvature is the source of gradient in the vacuum that causes emission of particles, and in the focus of our discussion here the Schwinger effect: where an extremely strong electrical field causes vacuum polarization and results in the emission of particles from the quantum vacuum.

The Schwinger Effect

In the quantum field extension of the idea of the Dirac Sea, one of the energetic modes of the quantum vacuum are electron–positron particle pairs: no electrostatic field is measured at a macroscopic scale of the vacuum in free space because the negative charge of the electron is balanced by the positive charge of the positron (as are their mass, spin, momentum, and other properties). However, if we were to generate an extremely strong electrical field, then instead of continuously cycling between creation and annihilation, the different charges would cause the particle pairs to accelerate in different directions in the electric field. Under such a condition, the particles would appear to emerge from the quantum vacuum, and you would have observable electrons and positrons generated in the extremely strong electrical field. This is known as the Schwinger effect and was first hypothesized by Julian Schwinger over 70 years ago [1]. In the Schwinger effect matter is created from a strong electric field, vacuum polarization causes emission of electron–positron particle pairs causing decay of the electric field—essentially the electric field can only become so strong before the energy goes to generating electrons and positrons from the quantum vacuum.

In the presence of a strong, constant electric field, electrons, e, and positrons, e+, will be spontaneously created.

Note that when particles are produced in this way they are necessarily quantum entangled with each other, since they are  formed from a singlet state (the vacuum), so this effect is also the realization of the Wheeler wormhole, which describes electron-positron pairs as a quantum wormhole in the vacuum structure—this is known as the holographic Schwinger effect [2]. The Schwinger effect is analogous to Unruh-Hawking radiation where instead of an electrical field it is the extremely strong gravitational field of a black hole that causes separation of the vacuum particle-pairs, in both instances a gradient is being generated in the vacuum energy density that causes mass-energy to be extracted from the vacuum. This is a key consideration in developing technologies that can tap the quantum vacuum energy—a key is to generate a gradient in the vacuum structure.

Indeed, the field strengths involved for both effects are so strong that it is thought to only occur in extremely compact massively high-energy astronomical objects, like black holes and neutron stars (especially extremely strong versions of neutron stars called magnetars). This property of black holes to generate particles and energy from the quantum vacuum is one reason why us researchers at the Resonance Science Foundation consider black holes as engines of mass-energy creation (read more about this in our article Galactic Engines). In fact, such astronomical objects are the natural laboratories for testing these theories of matter-creation in quantum field theory and the substantive nature of the vacuum. Neutron Stars are some of the most exciting stellar objects known to astronomers: they have the most extreme magnetic fields, with values up to 1015 G, and, with the exception of stellar-mass black holes, they are the most-dense stars, with densities of ≈ 1014 g cm−3 (basically macroscopic-sized atomic nuclei).

In 2018 observations of polarized light emitted by a neutron star showed that it experienced vacuum birefringence [3]. Birefringence is an optical effect that is normally observed in crystals, and is utilized to separate light into separate beams, it occurs because electromagnetic waves with different polarizations interact differentially with the electronic structure of atoms in the crystal lattice depending on the relation of their orientation. The extremely strong electrical and magnetic fields of a neutron star cause spatial symmetry breaking in the vacuum structure, giving it a crystalline phase, and causing light to undergo birefringence as it is emitted from the neutron star. This was a clear observation of the substantive nature of the medium of space, the quantum vacuum plasma.

First Direct Observation of the Schwinger Effect

It was thought that the field strengths necessary to produce these vacuum polarization effects would only be able to occur around neutron stars and black holes, making any Earth-bound laboratory experimental test of predictions like the Schwinger effect impossible… until now. In an experiment reported in the journal Science, led by The University of Manchester, an international team of researchers have utilized a phenomenal property of graphene to observe the Schwinger effect for the first time [4]. Graphene has become a focus of material scientist’s research as it has remarkable structural and electronic properties, for example it can carry huge current densities—about 108 A/cm2, roughly two orders of magnitude greater than copper, and even though it occurs in single planar honeycomb configurations or “sheets”, it is remarkably strong (if rolled into a carbon nanotube it is stronger than steel). Researchers have purported to observe superconducting properties in graphene, something that is normally only observed in supercooled metals or metal alloys.

In graphene a vacuum exists at the point (in momentum space) where the material’s conduction and valence electron bands meet and no intrinsic charge carriers are present. Working with colleagues in Spain, the US, Japan and elsewhere in the UK, the Manchester team led by Andre Geim identified a signature of the Schwinger effect at this Dirac point, observing pairs of electrons and holes (the solid-state equivalent of positrons) created out of the vacuum.

Graphene in real-space and momentum-space representations. (a) Each carbon atom in graphene’s honeycomb lattice forms strong covalent bonds with its neighbors, with one unbound electron left over to wander across the two-dimensional crystal. (b) A band-structure picture of the crystal describes the energy dependence of that electronic motion. A semimetal, graphene has valence and conduction bands that just touch at discrete points in the Brillouin zone. The energy-momentum dispersion relation becomes linear in the vicinity of those points, with the dispersion described by the relativistic energy equation E = |ℏ k|v F, where v F is the Fermi velocity and ℏ k its momentum. Consequently, an electron has an effective mass of zero and behaves more like a photon than a conventional massive particle whose energy—momentum dispersion is parabolic. Image and image description from [5].

The team achieved this by constructing devices from what are known as graphene superlattices, where essentially each planar crystalline lattice of carbon atoms are stacked but slightly misaligned, enabling non-linear electronic interactions between atoms in the lattice. In these graphene superlattices, graphene’s unit cell—the simple repetition of carbon atoms in its crystal structure— significantly expands such that the crystal is stretched by a factor of 100 in all directions. This stretching dramatically changes the material’s properties, enabling the researchers to produce electric field strengths of ~1018 V/m, what is known as the Schwinger limit, above which the electromagnetic field becomes nonlinear (and starts generating  electron–positron pairs).

As the research team reports key signatures that they observed indicating realization of the Schwinger effect were current-voltage characteristics that resemble those of superconductors, sharp peaks in differential resistance, sign reversal of the Hall effect, and a marked anomaly caused by the Schwinger-like production of hot electron-hole plasma. By applying strong electrical currents to the graphene-superlattice-based devices, with current densities up to 0.1 mA mm−1, the team was able to identify current-voltage characteristics that only occur with the production of electrons and holes (positrons).

Surprisingly the team observed another unusual high-energy process that has, as yet, no analogue in particle physics or astrophysics. When the researchers filled the vacuum in graphene with electrons and accelerated them to the maximum possible velocity allowed in the material (around 1/300 the speed of light), the electrons appeared to become Superluminous! Under such a condition, the electrons provided an electric current much greater than that allowed by theory, which the researchers further attributed to the spontaneous generation of additional production of hot electron-hole plasma in the vacuum. The increased conduction resembles that of superconductivity to such a high degree that the researchers suggest that some previous reports of superconductivity in some special configurations of graphene could have been observations of Schwinger-like production of electron-hole plasma, rather than evidence for superconductivity.

RSF in Perspective-

One of the central aspects of the unified physics of physicist Nassim Haramein and the Resonance Science Foundation is that space is not empty, it is substantive, absolutely saturated with mass-energy just as quantum field theory says it should be (predicting an infinite energy density vacuum expectation value in the non-renormalized regime). Interestingly, although this is a central aspect of physics and quantum theory many scientists still seem to consider space as empty, indeed many layman reports of this very study described here reported that scientists had “created something from nothing”. The key to overcoming this misunderstanding is to stop describing the vacuum as “nothing”— as the moniker implies, nothing does not exist, a true vacuum exists only in the imagination of scientists. When it is understood that space is substantive and full of fluctuating energy it does not seem confounding that particles are generated from it, that it is the source of mass, forces, and fields, and even further that we can utilize natural processes to access this limitless reservoir of energy for technological applications. 

References

[1] J. Schwinger, “On Gauge Invariance and Vacuum Polarization,” Phys. Rev., vol. 82, no. 5, pp. 664–679, Jun. 1951, doi: 10.1103/PhysRev.82.664

[2] J. Sonner, “Holographic Schwinger Effect and the Geometry of Entanglement,” Phys. Rev. Lett., vol. 111, no. 21, p. 211603, Nov. 2013, doi: 10.1103/PhysRevLett.111.211603

[3] R. P. Mignani et al., “Evidence of vacuum birefringence from the polarisation of the optical emission from an Isolated Neutron Star.” arXiv, Feb. 14, 2018. Accessed: Oct. 18, 2022. [Online]. Available: http://arxiv.org/abs/1710.08709

[4] A. I. Berdyugin et al., “Out-of-equilibrium criticalities in graphene superlattices,” Science, vol. 375, no. 6579, pp. 430–433, Jan. 2022, doi: 10.1126/science.abi8627. (ArXiv Preprint https://arxiv.org/abs/2106.12609)

[5] M. Wilson, “Electrons in atomically thin carbon sheets behave like massless particles,” Physics Today, vol. 59, no. 1, pp. 21–23, Jan. 2006, doi: 10.1063/1.2180163

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