High frequency background gravitational waves from spontaneous emission of gravitons by hydrogen and helium

A direct consequence of quantization of gravity would be the existence of gravitons. Therefore, spontaneous transition of an atom from an excited state to a lower-lying energy state accompanied with the emission of a graviton is expected. In this paper, we take the gravitons emitted by hydrogen and helium in the Universe after recombination as a possible source of high frequency background gravitational waves, and calculate the energy density spectrum. Explicit calculations show that the most prominent contribution comes from the $$3d-1s$$ 3 d - 1 s transition of singly ionized helium $$\mathrm {He}^{+}$$ He + , which gives a peak in frequency at $$\sim 10^{13}$$ ∼ 10 13 Hz. Although the corresponding energy density is too small to be detected even with state-of-the-art technology today, we believe that the spontaneous emission of $$\mathrm {He}^{+}$$ He + is a natural source of high frequency gravitational waves, since it is a direct consequence if we accept that the basic quantum principles we are already familiar with apply as well to a quantum theory of gravity.

KINETICS OF THE SPONTANEOUS DECAY IN COLD ATOMIC SYSTEMS

We discuss the spontaneous decay in a system of cold identical two-level atoms when, due to the strong dipole-dipole interaction, the collision-induced spontaneous decay plays the leading role in the process. We show that the time profile of the spontaneous transition is essentially non-exponential. Also, we argue that at a low initial temperature of the atomic system the spontaneous decay is accompanied by a strong heating caused by the inelastic atom-atom collisions. We show that the spontaneous emission spectrum is asymmetric. In addition, the width of the emission spectrum is a function of time. While atoms decay the emission spectrum becomes broader. The spectrum’s asymmetry and the atomic system’s heating have the same physical origin coming from the peculiarities of the atoms distribution function.

Spontaneous transition rates near the focus of a parabolic mirror with identification of the vectorial modes involved

Each natural mode of the electromagnetic field within a parabolic mirror exhibits spatial localization and polarization properties that can be exploited for the quantum control of its interaction with atomic systems. The region of localization is not restricted to the focus of the mirror leading to a selective response of atomic systems trapped on its vicinity. We report calculations of the spontaneous emission rates for an atom trapped inside the mirror accounting for all atomic polarizations and diverse trapping regions. It is shown that electric dipole transitions can be enhanced near the focus of a deep parabolic mirror with a clear identification of the few vectorial modes involved. Out of the focus the enhancement vanishes gradually, but the number of relevant modes remains small. Ultimately this represents a quantum electrodynamic system where internal and external degrees of freedom cooperate to maximize a selective exchange and detection of single excitations.

A Contextual Foundation for Mechanics, Thermodynamics, and Evolution

The prevailing interpretations of physics are based on deeply entrenched assumptions, rooted in classical mechanics. Logical implications include: the denial of entropy and irreversible change as fundamental properties of state; the inability to explain random quantum measurements and nonlocality without unjustifiable assumptions and untestable metaphysical implications; and the inability to explain or even define the evolution of complexity. The dissipative conceptual model (DCM) is based on empirically justified assumptions. It generalizes mechanics’ definition of state by acknowledging the contextual relationship between a physical system and its positive-temperature ambient background, and it defines the DCM entropy as a fundamental contextual property of physical states. The irreversible production of entropy establishes the thermodynamic arrow of time and a system’s process of dissipation as fundamental. The DCM defines a system’s utilization by the measurable rate of internal work on its components and as an objective measure of stability for a dissipative process. The spontaneous transition of dissipative processes to higher utilization and stability defines two evolutionary paths. The evolution of life proceeded by both competition for resources and cooperation to evolve and sustain higher functional complexity. The DCM accommodates classical and quantum mechanics and thermodynamics as idealized non-contextual special cases.

Distinct conformational states of SARS-CoV-2 spike protein

Intervention strategies are urgently needed to control the SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) pandemic. The trimeric viral spike (S) protein catalyzes fusion between viral and target cell membranes to initiate infection. Here we report two cryo-EM structures, derived from a preparation of the full-length S protein, representing its prefusion (2.9Å resolution) and postfusion (3.0Å resolution) conformations, respectively. The spontaneous transition to the postfusion state is independent of target cells. The prefusion trimer has three receptor-binding domains clamped down by a segment adjacent to the fusion peptide. The postfusion structure is strategically decorated by N-linked glycans, suggesting possible protective roles against host immune responses and harsh external conditions. These findings advance our understanding of SARS-CoV-2 entry and may guide development of vaccines and therapeutics.

A Contextual Foundation for Mechanics, Thermodynamics, and Evolution

The prevailing interpretations of physics are based on deeply entrenched assumptions, rooted in classical mechanics. Logical implications include: the denial of entropy and irreversible change as fundamental properties of state; the inability to explain random quantum measurements and nonlocality without implausible and empirically unjustified metaphysical implications; and the inability to explain or even define the evolution of complexity. The dissipative conceptual model (DCM) is based on empirically justified assumptions. It generalizes mechanics’ definition of state by acknowledging the contextual relationship between a physical system and its positive-temperature ambient background, and it defines the DCM entropy as a fundamental contextual property of physical states. The irreversible production of entropy establishes the thermodynamic arrow of time and a system’s process of dissipation as fundamental. The DCM defines a system’s utilization by the measurable rate of internal work on its components and as an objective measure of stability for a dissipative process. The spontaneous transition to dissipative processes of higher utilization and stability defines two evolutionary paths. The evolution of life proceeded by both competition for resources and cooperation to evolve and sustain higher functional complexity. The DCM accommodates classical and quantum mechanics and thermodynamics as idealized non-contextual special cases.

Disordered interfaces in soft fluids with suspended colloids

Computer simulations of bi-continuous two-phase fluids with interspersed dumbbells show that, unlike rigid colloids, soft dumbbells do not lead to arrested coarsening. However, they significantly alter the curvature dynamics of the fluid–fluid interface, whose probability density distributions are shown to exhibit (i) a universal spontaneous transition (observed even in the absence of colloids) from an initial broad-shape distribution towards a highly localized one and (ii) super-diffusive dynamics with long-range effects. Both features may prove useful for the design of novel families of soft porous materials.