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Published entries: 206
Matching entries: 206. Showing 176–200 of 206.
Paper · 2023
The Princeton Field-Reversed Configuration for Compact Nuclear Fusion Power Plants
- Christopher Galea(Author)
- Stephanie Thomas(Author)
- Michael Paluszek(Author)
- Samuel Cohen(Author)
Christopher Galea, Stephanie Thomas, Michael Paluszek and Samuel Cohen review the Princeton Field-Reversed Configuration, a fusion concept that prioritises low neutron output and small size. Plasma inside a cylinder of coils is confined and heated by external radio-frequency antennas driving a rotating magnetic field. The PFRC-1 and PFRC-2 experiments heated electrons well above 100 eV and sustained plasmas for 300 ms, over 10^4 times the predicted tilt instability growth time. Deuterium and helium-3 fuel could suit the high-beta configuration, and the small size would let tritium ash be exhausted quickly. The planned 1–10 MW reactors would suit uses from submarines and cities to space propulsion.
Paper · 2003
The quantum inequalities do not forbid spacetime shortcuts
- S. Krasnikov(Author)
S. Krasnikov studies spacetime shortcuts, a class including the Alcubierre bubble, the Krasnikov tube and certain wormholes, that permit superluminal travel in a strictly defined sense. Such shortcuts had been suspected impossible, because quantum inequality calculations suggested Planck-scale energy densities and huge total negative energy. He argues these spacetimes may be entirely physical. With explicit examples he proves that the relevant quantum inequality does not always force large energy densities, that large densities need not give large total negative energy, and that such totals can be physically meaningless and need not exclude shortcuts.
Paper · 1999
The Quantum Interest Conjecture
- L. H. Ford(Author)
- Thomas A. Roman(Author)
L. H. Ford and Thomas Roman study the limits quantum field theory places on negative energy, which it allows locally but restricts in size and extent. Quantum inequalities require a negative energy pulse to be followed by a compensating positive pulse, with a separation inversely proportional to their amplitude. Their quantum interest conjecture adds that the positive pulse must overcompensate by an amount that grows with the separation. They prove it for massless scalar fields in two- and four-dimensional flat spacetime and show it follows from the quantum inequalities. In short, a negative energy loan must be repaid with interest that grows with its size or duration, illustrated by pulses from a moving mirror.
Article · 2022
The Quest for Fusion Energy
- Daniel Jassby(Author)
Daniel Jassby examines the conventional hot-fusion programme and argues that, despite relentlessly optimistic announcements, practical fusion electricity from it remains a distant prospect. He compares the 2021 deuterium-tritium campaigns at JET, a magnetic confinement tokamak, and NIF, a laser-driven inertial confinement facility. Taken together, he argues, these results matter more to the field than anything since the T-3 tokamak results of 1968. JET reported a record 59 megajoules per shot, and NIF reached 1.3 MJ, eight times its previous best. On his reading, inertial confinement has taken a clear lead over magnetic confinement in reaching reactor-relevant conditions. He also describes the practical burden of tritium handling in magnetic devices.
Paper · 2022
The Return of the Singularities: Applications of the Smeared Null Energy Condition
- Ben Freivogel(Author)
- Eleni-Alexandra Kontou(Author)
- Dimitrios Krommydas(Author)
Freivogel, Kontou and Krommydas note that the classic singularity theorems of general relativity rest on energy conditions that semiclassical gravity can violate. They motivate the smeared null energy condition, a bound on the weighted average of null energy along a finite stretch of a null geodesic. Its field theory version addresses the Fewster-Roman counterexample and reduces to the averaged null energy condition over long segments. Using it as an assumption, they prove a singularity theorem that extends Penrose's theorem to semiclassical gravity. Applied to evaporating black holes and the Maldacena-Milekhin-Popov traversable wormhole, the bound is not saturated by the wormhole in four dimensions, though a reduced two-dimensional version is.
talk · 2026
The Trajectory of Recent Solid State Fusion Results
- Lawrence P Forsley(Author)
Forsley sets two solid-state fusion efforts side by side, noting that both NASA and Google have explored and funded low energy nuclear reactions. NASA has funded efforts since 1989, and Google Research began in 2014. Google and the researchers it funded published in Nature, Nature Communications and the Journal of Applied Physics, while the Physical Review C papers led to a commercialized neutron generator built by Astral Systems in the UK. Those separate efforts, unknown to the researchers at the time, provided the impetus for the ARPA-E programme and then a DARPA programme. He highlights a reported finite yield floor in the deuterium fusion yield below about 2 keV in metallic hydrides, observed reproducibly in both palladium and titanium hosts.
Paper · 2008
The vacuum fluctuation theorem: Exact Schroedinger equation via nonequilibrium thermodynamics
- Gerhard Grössing(Author)
Gerhard Grössing asks where the basic quantum rule that a particle's energy equals Planck's constant times a frequency actually comes from. Rather than accept these quantum oscillations as an axiom, he treats them as the result of known physical laws, since oscillations generally arise from dissipative processes. He models a particle as a dissipative system held in a nonequilibrium steady state by a constant flow of energy. That energy throughput is likely tied to the vacuum, with the zero-point energy as a leading candidate. From this he obtains the shortest derivation of the Schrödinger equation from modern classical physics in the literature, and the only exact one, leading to a vacuum fluctuation theorem aimed at understanding quantum nonlocality.
Paper · 1994
The warp drive: hyper-fast travel within general relativity
- Miguel Alcubierre(Author)
Alcubierre’s 1994 paper specifies a mathematical geometry in which space expands behind a moving region and contracts ahead of it. A spacecraft at its center follows a freely falling path, remaining below the local speed of light even when distant observers assign it faster-than-light motion. In the prescribed geometry, its clock runs at the same rate as distant clocks during this central trajectory. Tidal forces near the spacecraft can be small for suitable size and shape parameters, while forces near the boundary can be large. Calculating the required matter and energy reveals negative energy density and violations of classical energy conditions. The paper invokes quantum examples such as the Casimir effect but supplies no method for producing the required distribution.
Paper · 2015
Theory of a Mach Effect Thruster I
- Heidi Fearn(Author)
- Adam Zachar(Author)
- Keith Wanser(Author)
- James Woodward(Author)
Fearn, Zachar, Wanser and Woodward explain the Mach Effect Thruster, a propellantless drive that uses Mach's principle to produce thrust in an accelerating material whose mass-energy fluctuates. The programme tests Mach's principle directly: make an object's mass fluctuate in the laboratory, turn that into steady thrust, and match theory to experiment. The devices run on 100 to 200 watts and currently produce thrusts of a few micronewtons. The theory uses gravitation and advanced waves, so momentum is conserved between the device and the rest of the universe. After reviewing absorber theory from Dirac, Wheeler and Feynman, and Hoyle and Narlikar, they derive Woodward's mass fluctuation formula from first principles in the fully Machian Hoyle-Narlikar theory.
Paper · 2015
Theory of dark matter superfluidity
- Lasha Berezhiani(Author)
- Justin Khoury(Author)
Lasha Berezhiani and Justin Khoury propose dark matter superfluidity, which matches the cosmological successes of the standard ΛCDM model while reproducing MOND behaviour in galaxies. Dark matter is made of strongly self-interacting axion-like particles of about an electronvolt, forming a superfluid core in galaxies. Superfluid phonons follow a MOND-like effective action and mediate MOND-like acceleration between ordinary matter particles. It separates galaxies, where MOND works, from clusters, where hotter dark matter is partly or fully in the normal phase. Testable signatures include vortices in galaxies, merger dynamics set by infall speed versus phonon sound speed, and separate mass peaks in bullet-like cluster mergers.
Paper · 2017
Thermal effect in the Casimir force for graphene and graphene-coated substrates
- G. Bimonte(Author)
- G. L. Klimchitskaya(Author)
- V. M. Mostepanenko(Author)
Bimonte, Klimchitskaya and Mostepanenko use the finite-temperature polarisation tensor of quantum electrodynamics to study how graphene's mass gap and chemical potential affect the Casimir force and its thermal correction. They treat a gold sphere facing a real graphene sheet or graphene-coated dielectric substrates. A larger mass gap weakens the force while a larger chemical potential strengthens it, so the two act in opposite directions. Graphene-coated substrates give a much stronger force than free-standing graphene, but a smaller thermal correction and fractional thermal share. A proposed differential experiment to observe graphene's giant thermal Casimir effect remains feasible once the mass gap and chemical potential of real samples are included.
Paper · 2025
Thermal Effects in the Casimir Torque between Birefringent Plates
- Benjamin Spreng(Author)
- Jeremy N. Munday(Author)
The Casimir effect, driven by quantum and thermal fluctuations, is well known for creating forces between closely spaced surfaces. Benjamin Spreng and Jeremy Munday study the related Casimir torque, which rotates optically anisotropic surfaces relative to each other. They examine, for the first time, how thermal fluctuations affect the torque between birefringent plates. Thermal modes reduce the torque substantially, by up to 2 orders of magnitude for strongly birefringent materials. Temperature also bends the torque's angular dependence away from the usual sinusoidal form, especially beyond the thermal wavelength. Pairs of dissimilar plates whose torque reverses with distance allow temperature to control both its size and direction, a design handle for nanoscale sensors.
Paper · 2024
Thermal noise-limited beam balance as prototype of the Archimedes vacuum weight experiment
- Annalisa Allocca(Author)
- Saverio Avino(Author)
- Enrico Calloni(Author)
- Sergio Caprara(Author)
- Massimo Carpinelli(Author)
- Andrea Contu(Author)
- Luca D’Onofrio(Author)
- Domenico D’Urso(Author)
- Rosario De Rosa(Author)
- L. Errico(Author)
- Marina Esposito(Author)
- Gianluca Gagliardi(Author)
- Marco Grilli(Author)
- Valentina Mangano(Author)
- Maria Marsella(Author)
- Luca Naticchioni(Author)
- Antonio Pasqualetti(Author)
- Gianpiero Pepe(Author)
- Maurizio Perciballi(Author)
- Paola Puppo(Author)
- Piero Rapagnani(Author)
- Fulvio Ricci(Author)
- Luigi Rosa(Author)
- Carlo Rovelli(Author)
- Davide Rozza(Author)
- Paolo Ruggi(Author)
- Naurang L. Saini(Author)
- Valeria Sequino(Author)
- Valeria Sipala(Author)
- Daniela Stornaiuolo(Author)
- Francesco Tafuri(Author)
- Lucia Trozzo(Author)
Allocca and colleagues describe a room-temperature beam balance that prototypes the cryogenic balance of the Archimedes experiment, which aims to measure how electromagnetic vacuum fluctuations interact with gravity. It has a 50 cm aluminium arm carrying a 0.2 kg aluminium sample and a lead counterweight, with interferometric closed-loop readout in the low-seismic-noise SAR-GRAV laboratory in Sardinia. Torque sensitivity reaches about 7 × 10^-13 N m per root hertz at tens of millihertz. Matching the thermal noise estimate, this confirms the optical and mechanical design and clears the way to the final balance. Because weight and counterweight are different materials, the balance also senses B-L dark photons, and a first short run gave encouraging constraints.
Paper · 1995
Thermodynamics of Spacetime: The Einstein Equation of State
- Ted Jacobson(Author)
Ted Jacobson derives the Einstein equation from two ingredients: entropy proportional to horizon area, and the thermodynamic relation δQ = T dS linking heat, entropy and temperature. The relation is required to hold for every local Rindler horizon through each point of spacetime, with heat read as energy flux and temperature as the Unruh temperature seen by an accelerated observer. For that to work, matter must bend the causal structure of spacetime in exactly the way the Einstein equation describes. Seen this way, the Einstein equation is an equation of state. Jacobson suggests it may be no more appropriate to quantize it canonically than to quantize the wave equation for sound in air.
Paper · 2018
Tolman-like temperature gradients in stationary spacetimes
- Jessica Santiago(Author)
- Matt Visser(Author)
Jessica Santiago and Matt Visser start from the point that a heat bath is specified by both a temperature and a four-velocity, which fixes its rest frame. In static spacetimes the natural and unique choice is the normalised timelike Killing vector. In stationary but non-static spacetimes several different natural four-velocity fields can each define the bath's rest frame, which makes the problem much more subtle. Buchdahl's 1949 analysis of the Tolman temperature gradient is therefore only part of the story. For Hawking radiation from a rotating black hole, the best-suited heat bath follows a gradient flow normal to spacelike hypersurfaces rather than Killing vectors.
Paper · 2025
Total Calorimetry ('From the Wall') in a Brillouin Reactor
- Francis Tanzella(Author)
- Robert Godes(Author)
- Jin Liu(Author)
- Robert George(Author)
Tanzella, Godes, Liu and George report calorimetry on Brillouin Energy's catalyst tubes, ceramic tubes coated with metal, ceramic and copper layers, run in hydrogen with nanosecond pulses across the coatings. The Energy Research Center has verified this calorimetry for over 5 years, across more than 2000 runs on more than 300 catalyst tubes. A new reactor system uses only mass flow calorimetry, making it easier to see when output exceeds input. Running in hydrogen between 200 and 600 °C, several runs gave total output power above the electrical input power. The outer nickel layer's temperature is estimated from its resistance, and plans for even better calorimeters are laid out.
Paper · 2017
Traversable Wormholes via a Double Trace Deformation
- Ping Gao(Author)
- Daniel Louis Jafferis(Author)
- Aron C. Wall(Author)
Ping Gao, Daniel Jafferis and Aron Wall address a central obstacle to traversable wormholes: they need matter that violates the null energy condition, which reasonable classical theories obey. Coupling the two boundaries of an eternal BTZ black hole produces a quantum matter stress tensor with negative average null energy. Its gravitational backreaction makes the Einstein-Rosen bridge traversable. The bridge becomes slightly traversable, opening by an amount proportional to the strength of the two-boundary coupling. In the ER=EPR picture the wormhole may relate to quantum teleportation, while still respecting causality. They expect a similar effect in higher dimensions and discuss implications for energy and holographic entropy in the dual conformal field theory.
Paper · 2006
Ultra low momentum neutron catalyzed nuclear reactions on metallic hydride surfaces
- A. Widom(Author)
- L. Larsen(Author)
A. Widom and L. Larsen propose that nuclear reactions on metallic hydride surfaces are catalysed by neutrons of ultra low momentum. The process starts with the weak interaction: protons capture heavy electrons and become neutrons, releasing neutrinos. The electrons become heavy because collective oscillations of surface hydride protons create local electromagnetic fields that raise their effective mass. Condensed matter quantum electrodynamics can shift the density of final states, giving appreciable numbers of extremely slow neutrons that nearby nuclei absorb efficiently. No Coulomb barrier stands in the way of this neutron production or the reactions it catalyses.
Paper · 2024
Universal Casimir attraction between filaments at the cell scale
- Benjamin Spreng(Author)
- Hélène Berthoumieux(Author)
- Astrid Lambrecht(Author)
- Anne-Florence Bitbol(Author)
- Paulo Maia Neto(Author)
- Serge Reynaud(Author)
Spreng and colleagues start from the fact that the Casimir interaction between dielectric objects in salty water contains a universal part the solvent does not screen, so it reaches over long distances. That non-screened universal force has already been measured experimentally, on a microsphere held by optical tweezers next to a larger fixed sphere. They derive the Casimir free energy for two parallel dielectric cylinders with the scattering method. Its magnitude far exceeds the thermal energy scale over a wide range, including the sizes of actin filaments and microtubules in cells. At every distance of biological interest the free energy depends only on geometry, not on the cylinders' dielectric response. This universal attraction should help hold bundles of parallel filaments together.
Paper · 2022
Universal Casimir interactions in the sphere–sphere geometry
- Tanja Schoger(Author)
- Benjamin Spreng(Author)
- Gert-Ludwig Ingold(Author)
- Astrid Lambrecht(Author)
- Paulo A. Maia Neto(Author)
- Serge Reynaud(Author)
Schoger, Spreng, Ingold, Lambrecht, Maia Neto and Reynaud study universal Casimir interactions between spheres in two configurations that turn out to be dual. One has Drude-model metal spheres in vacuum, the other dielectric spheres in salt water beyond the Debye screening length. In both, the long-distance or high-temperature limit is dominated by low-frequency transverse magnetic thermal fluctuations. The results do not depend on material details, because metals and salt water both have finite conductivity and so an infinite static dielectric constant. Their dependence on geometry is also universal, linked to an approximate conformal invariance of the reduced free energy.
Paper · 2011
Vacuum Cherenkov effect in logarithmic nonlinear quantum theory
- Konstantin G. Zloshchastiev(Author)
Konstantin Zloshchastiev works within a candidate effective quantum gravity theory built on logarithmic nonlinear quantum mechanics, motivated by astrophysical hints of deviations from classical relativity. He describes radiation that can occur in the physical vacuum itself, such as Cherenkov-type shock waves. He computes their cone angle, flash duration, radiation yield and spectral distribution. Because this vacuum is dispersive, the cone angle differs from one wavelength to another. The radiation yield scales with the square of the vacuum's own energy scale, which is also its instability threshold and natural ultraviolet cutoff. Some results should hold for any Lorentz-violating theory that treats the vacuum as a continuous medium at long wavelengths.
Paper · 2023
Visualization and analysis of the curvature invariants in the Alcubierre warp-drive spacetime
- José Rodal(Author)
José Rodal computes and visualises the scalar curvature invariants of the Alcubierre warp drive spacetime, from the Weyl and Ricci tensors. Writing the Ricci invariants through the Einstein tensor lets them be read directly in terms of the energy-momentum tensor. Detailed plots show that creating the warp bubble requires four distinct layers of anisotropic stress-energy. He also examines how the Kretschmann quadratic invariant decomposes. He finds that plots in earlier work by Mattingly and colleagues understated the curvature invariants by 8 to 16 orders of magnitude. He compares the drive's curvature with that of a black hole of Saturn's mass and confirms the Alcubierre spacetime is Petrov type I.
Paper · 1996
Vortex formation in neutron-irradiated superfluid 3He as an analogue of cosmological defect formation
- V. M. H. Ruutu(Author)
- V. B. Eltsov(Author)
- A. J. Gill(Author)
- T. W. B. Kibble(Author)
- M. Krusius(Author)
- Yu. G. Makhlin(Author)
- B. Plaçais(Author)
- G. E. Volovik(Author)
- Wen Xu(Author)
Ruutu, Eltsov, Gill, Kibble, Krusius, Makhlin and colleagues observe vortices forming when a thermal neutron is absorbed in a rotating container of superfluid helium-3 B phase. The reaction releases 0.76 MeV and heats a cigar-shaped region into the normal phase. As it cools back through the superfluid transition, quantised vortices nucleate. Large enough rings grow under the Magnus force and are detected one by one with nuclear magnetic resonance, and varying the superflow velocity reveals the shape of the initial defect network. They propose this rapid cool-down mirrors defect formation during cosmological phase transitions in the early universe.
Paper · 2022
Warp Drive Aerodynamics
- Carlos Barceló(Author)
- Valentin Boyanov(Author)
- Luis J. Garay(Author)
- Eduardo Martín-Martínez(Author)
- Jose M. Sánchez Velázquez(Author)
Barceló, Boyanov, Garay, Martín-Martínez and Sánchez Velázquez analyse whether quantum matter can destabilise a warp drive spacetime. They search for points of infinite blueshift, which resemble a black hole's inner horizon with its semiclassical instability, and classify them by how nearby geodesics behave. Warp bubbles in 2+1 dimensions or more turn out likely to be stable: they contain only isolated divergent points, so the destabilising energy that accumulates stays finite. The causal structure found in the 1+1 case carries over to higher dimensions, at least along one axis. Any remaining instability from energy-density build-up can be reduced further with more aerodynamic bubble shapes and trajectories.
Paper · 2017
Warp drive basics
- Miguel Alcubierre(Author)
- Francisco S. N. Lobo(Author)
In this 2017 chapter, Alcubierre and Lobo examine warp geometries as mathematical ways to shorten distant journeys without the ship outrunning light in its immediate surroundings. For the Alcubierre geometry, they calculate negative energy density in the bubble walls, even at low speeds. Their analysis with a finite-mass ship relates the energy requirement to bubble speed, size and wall thickness. At faster-than-light bubble speeds, onboard signals cannot reach the outer front edge, so the crew cannot simply create or control the entire bubble on demand. They discuss Krasnikov’s alternative: modify the route during an initial outward journey to enable a shortened round trip. Suitably combined routes can form paths returning to an earlier time, although the original single Alcubierre geometry does not itself contain such loops.