Hans Christian Öttinger

The concept of freely falling frames suggests that gravity exhibits a local Lorentz gauge symmetry and requires a background Minkowski reference frame. The gauge vector fields of a Yang–Mills-type theory can be constructed from the transformations to these local freely falling frames, thereby leading to a composite theory of gravity. We propose coordinate conditions under which an exact black-hole solution can be obtained. Our analysis of planar gravitational waves reveals that, despite the large symmetry group, composite gravity possesses the proper number of physical degrees of freedom. We elaborate a Hamiltonian formulation of composite gravity, derive the full set of constraints for the nonlinear theory, and outline the pathway toward its quantization.

Research aimed at elucidating the foundations of quantum theory can have a direct impact on quantum technology. Two examples illustrate this potential: (1) the coupling of quantum systems to arbitrary classical environments that can be described by irreversible thermodynamics. In the spirit of Dirac’s replacement of classical Poisson brackets by commutators, a thermodynamically consistent coupling of quantum and classical systems can be obtained by quantization of the geometric structure of classical irreversible thermodynamics. (2) The stochastic bra-ket interpretation of quantum mechanics, which is obtained by unraveling density matrices in terms of bra-ket pairs of stochastic jump processes in Hilbert space. It offers an alternative realization of entanglement and avoids paradoxes by imposing severe but natural restrictions on the types of systems to which quantum mechanics can be applied.

The stochastic nature of quantum mechanics is more naturally reflected in a bilinear two-process representation of density matrices rather than in squared wave functions. This proposition comes with a remarkable change of the entanglement mechanism: entanglement effects do not originate from superpositions of wave functions, but they result from the bilinear structure of density matrices. Quantum interference appears as a multiplicative phenomenon rather than an additive superposition mechanism. We propose two general requirements such that the bilinear representation of density matrices is given in terms of two uniquely defined, identically distributed, Markovian stochastic jump processes. These general ideas are illustrated for the Einstein-Podolsky-Rosen and double-slit experiments. The expression of the stochastic nature of quantum mechanics in terms of random variables rather than their probability distributions facilitates an ontological viewpoint and leads us to a bra-ket interpretation of quantum mechanics.

Traditionally, stress fluctuations in flowing and deformed materials are overlooked, with an obvious focus on average stresses in a continuum mechanical approximation. However, these fluctuations, often dismissed as “noise,” hold the potential to provide direct insights into the material structure and its structure-stress coupling, uncovering detailed aspects of fluid transport and relaxation behaviors. Despite advancements in experimental techniques allowing for the visualization of these fluctuations, their significance remains largely untapped as modeling efforts continue to target Newtonian fluids within the confines of Gaussian noise assumptions. In the present work, a comparative analysis of stress fluctuations in two distinct microstructural models is carried out: the temporary network model and the hydrodynamic dumbbell model. Despite both models conforming to the upper convected Maxwell model at a macroscopic level, the temporary network model predicts non-Gaussian fluctuations. We find that stress fluctuations within the temporary network model exhibit more pronounced abruptness at the local scale, with only an enlargement of the control volume leading to a gradual Gaussian-like noise, diminishing the differences between the two models. These findings underscore the heightened sensitivity of fluctuating rheology to microstructural details and the microstructure–flow coupling, beyond what is captured by macroscopically averaged stresses.

The stochastic nature of quantum mechanics is more naturally reflected in a bilinear two-process representation of density matrices rather than in squared wave functions. This proposition comes with a remarkable change of the entanglement mechanism: entanglement effects do not originate from superpositions of wave functions, but result from the bilinear structure of density matrices. Quantum interference appears as a multiplicative phenomenon rather than an additive superposition mechanism. We propose two general requirements such that the bilinear representation of density matrices is given in terms of two uniquely defined, identically distributed, Markovian stochastic jump processes. These general ideas are illustrated for the Einstein-Podolsky-Rosen and double-slit experiments. The expression of the stochastic nature of quantum mechanics in terms of random variables rather than their probability distributions facilitates an ontological viewpoint and leads us to a bra-ket interpretation of quantum mechanics.

We present an ontological argument why elementary particles with nonzero spin must be massless. This argument implies that, from an ontological perspective, the massive quarks and leptons of the standard model cannot be elementary particles. This conclusion is less disquieting than it might seem at first sight because the Higgs mechanism entails that not only the masses of the W and Z bosons but also the masses of quarks and leptons arise from the interaction of massless elementary particles with the vacuum expectation value of the Higgs field, which is a result of symmetry breaking.

While it is often assumed that liquid-vapor interfaces in nonequilibrium processes are in states of local thermodynamic equilibrium, this might not be the case for strong deviations from equilibrium. Clausius-Clapeyron equations for bulk properties yield a consistently defined temperature of the interface that is close to the liquid bulk temperature. The alternative interface temperature defined through the surface tension will be different for stronger nonequilibrium processes. Structural variables are introduced to extend the thermodynamic description of interfaces to a wider range of processes. Interfacial resistivities will depend on interface temperature as well as mass and heat flux through the interface.

Due to a calculation error several equations in our paper1 must be corrected. The corrections only concern the entry M 44 relax in the relaxation matrix, which

Even for large nonequilibrium systems, local equilibrium subsystems in the presence of strong inhomogeneities may be very small. Such situations typically arise either in the presence of large gradients of temperature, velocity or pressure, or in transition zones between different phases. For small thermodynamic systems, the Euler equation of macroscopic thermodynamics does not hold. One less equation implies one additional degree of freedom, which is the hallmark of small thermodynamic systems. I would like to offer some remarks on the description and role of small local equilibrium subsystems in nonequilibrium thermodynamics.

For the Yang-Mills–type gauge-field theory with Lorentz symmetry group, we propose and verify an explicit expression for the conserved currents in terms of the energy-momentum tensor. A crucial ingredient is the assumption that the gauge symmetry arises from the decomposition of a metric in terms of tetrad variables. The currents exist under the weak condition that the energy-momentum tensor and the Ricci tensor commute. We show how the conserved currents can be used to obtain a composite theory of gravity and discuss the static isotropic field around a point mass at rest.