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"A universal speed limit for spreading of coherence" (2025) https://www.nature.com/articles/s41586-025-09735-z https://www.nature.com/articles/s41586-025-09735-
by westurner 1y ago
"A universal speed limit for spreading of coherence" (2025) https://www.nature.com/articles/s41586-025-09735-z https://www.nature.com/articles/s41586-025-09735-z :
> Abstract: Discoveries of fundamental limits for the rates of physical processes, from the speed of light to the Lieb–Robinson bound for information propagation [1,2], often lead to breakthroughs in the understanding of the underlying physics. Here we observe such a limit for a paradigmatic many-body phenomenon, the spreading of coherence during the formation of a weakly interacting Bose–Einstein condensate [...]. We study condensate formation in an isolated homogeneous atomic gas [...] that is initially far from equilibrium, in an incoherent low-energy state, and condenses as it relaxes towards equilibrium. Tuning the interatomic interactions that drive condensation, we show that the spreading of coherence through the system is initially slower for weaker interactions and faster for stronger ones, but always eventually reaches the same limit, at which the square of the coherence length grows at a universal rate given by the ratio of Planck’s constant and the particle mass, or, equivalently, by the quantum of velocity circulation associated with a quantum vortex. These observations are robust to changes in the initial state, the gas density, and the system size. Our results provide benchmarks for theories of universality far from equilibrium [...], are relevant for quantum technologies that rely on large-scale coherence, and invite similar measurements in other systems.
- westurner 1y agoThe space changes, so GR and the speed of light are preserved. "Slow and fast light in plasma using optical wave mixing" (2021) https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.126.205001 https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.12... .. https://scholar.google.com/scholar?cluster=9479750199684683164&hl=en&as_sdt=5,43&sciodt=0,43 https://scholar.google.com/scholar?cluster=94797501996846831... : > We show the first experimental demonstration of slow and fast light in a plasma, measuring group velocities between 0.12c and −0.34c . Also, photons can be FTL (relative to an outside observer) in dielectrics; > LightSlinger antennae are FTL within the dielectric, but the EMR is not FTL; from https://news.ycombinator.com/item?id=37342016 https://news.ycombinator.com/item?id=37342016 Also, do these findings apply to this post-Fourier model of thermal spreading limits at material interfaces given phase ? From https://news.ycombinator.com/item?id=45921309 https://news.ycombinator.com/item?id=45921309 : > ScholarlyArticle: "Time-domain theory of transient heat conduction in the local limit" (2025) https://journals.aps.org/prb/abstract/10.1103/p8wg-p1j3 https://journals.aps.org/prb/abstract/10.1103/p8wg-p1j3 > NewsArticle: "From engines to nanochips: Physicists redefine how heat really moves" (2025-10) https://phys.org/news/2025-10-nanochips-physicists-redefine.html https://phys.org/news/2025-10-nanochips-physicists-redefine....
- westurner 1y agoBut specifically on velocity in superfluids or superfluids aka BEC Bose-Einstein Condensates, This model predicts the multi body gravitational motions of the planets including the perihelion of Mercury and also vortices in superfluids: "Physical vacuum as a dilatant fluid yields exact solutions to Pioneer anomaly and Mercury’s perihelion precession" (2019) https://cdnsciencepub.com/doi/10.1139/cjp-2018-0744 https://cdnsciencepub.com/doi/10.1139/cjp-2018-0744 .. https://news.ycombinator.com/item?id=45220585 https://news.ycombinator.com/item?id=45220585 This model derives gravity from the Standard Model of particle physics: "Perihelion precession of planetary orbits solved from quantum field theory" (2025) https://arxiv.org/abs/2506.14447 https://arxiv.org/abs/2506.14447 .. https://news.ycombinator.com/item?id=45220460 https://news.ycombinator.com/item?id=45220460 And this model describes all in terms of consistency maximization > "The Self-Consistent Coherence-Maximizing Universe: Complete Derivation of the Standard Model and General Relativity from Mathematical Self-Consistency" (2025) https://www.academia.edu/144466150/The_Self_Consistent_Coherence_Maximizing_Universe_Complete_Derivation_of_the_Standard_Model_and_General_Relativity_from_Mathematical_Self_Consistency https://www.academia.edu/144466150/The_Self_Consistent_Coher... : > Abstract: We derive the complete structure of fundamental physics from a single principle: Quantum coherence maximization under self-consistency constraints. [...] And this model describes all terms in terms of Consistency Functional K; https://news.ycombinator.com/item?id=45909513 https://news.ycombinator.com/item?id=45909513 : "The Consistency Functional K: Variational Unification of Quantum Mechanics, Thermodynamics, and General Relativity" (2025) https://doi.org/10.5281/zenodo.17405041 https://doi.org/10.5281/zenodo.17405041 \delta\mathcal{K}(\rho, g) = 0 And Wolfram has a unified theory, too What are the limits to model unification?