March 2024: Universcience and Le Palais de la Découverte produced a series of movies on analogue black holes. The first issue deals with analogue hydraulic black holes and can been seen on the Blob extra media.
January 2024: We were invited to give a recorded talk at the prestigious Zakharov Seminar on Nonlinear Waves of Moscow on Analogue Gravity and the effect of non-linearity on Hawking radiation.
January 2024: The CNRS Delegation DR8 organized with our laboratory an immersion in the World of Research for around 40 Physics teachers within the Year of Physics celebration. We presented our work on Analogue Gravity and gave a talk on the battle of Actium.
December 2023: The journalist David Larousserie graciously made a nice critic of our last book l’Histoire du Rémora with Isabelle Jouteur (FoReLLis, Poitiers) and Johan Fourdrinoy (EDF, Chatou) in the French top-tier journal Le Monde.
December 2023: With Severine Atis, newly appointed CNRS researcher at Pprime Institute in the Curiosity team, we participated to the 24 vulga event organized by the Collectif Conscience, a 2h live on Twitch with the following program, an event labeled by the Year of Physics. We presented our work on Analogue Gravity and Instabilities in Interfacial Hydrodynamics with an artistic approach.
November 2023: With Scott Robertson, newly appointed CNRS chair at Pprime Institute in the Curiosity team and Maxime Jacquet from LKB laboratory, we organized the first meeting of one of the Transverse Task Forces on Analogue Gravity and Analogue Cosmology of the National Research Group on Physical Cosmology (GDR COPHY). The presentations are available on the website of the meeting. We discussed the analogies between cosmology and classical mechanics or hydrodynamics.
October 2023: Our research on the dead-water effect was presented during the launching of the Year of Physics thanks to the drawing of Morgane Parisi of Studio Brou in the workshop on the Synergy between Research and Higher Education.
October 2023: Our research on analogue gravity is discussed in a Perspective paper published by Nature Review Physics in its October Issue. It is time for Quantum Gravity experts to discuss with the plumbers !
August 2023: We are pleased to announce the release of a new book written jointly by Isabelle Jouteur, Johan Froudrinoy and Germain Rousseaux on the History of the Remora that resumes a decade of interdisciplinary research on the reasons of the defeat of Mark-Anthony and Cleopatra at the battle of Actium. Editions Classiques Garnier are publishing our work.
June 2023: Our research on the battle of Actium and the dead-water effect was discussed by Johan Fourdrinoy during the National Days « Cartoon and Higher Education » thanks to the drawings of PEB with the support of the ministries of Culture and Research & Higher Education.
June 2023: Our research on Analogue Gravity and Pattern Formation in Humid Zones was discussed during the National Days « Cartoons and Higher Education » thanks to the drawings of Morgane Parisi of Studio Brou with the support of the Foundation of the Poitiers University and the Biodiversity Chair of the Poitiers University.
May 2023: We were interviewed by Jon Cartwright for New Scientist on the implications of analogue gravity for space-time physics.
May 2023: We were interviewed by Science & Vie journal to comment on the observation of particles pair production during inflation in an analogue cosmology experiment.
February 2023: We were invited by the LFML of Lille for a webinar on Analogue Gravity. The video can be seen on the Youtube Channel of the laboratory.
January 2023: We participated to the kick-off meeting of the research group on Physical Cosmology by giving a talk on Analogue Gravity and Cosmology.
of Edgar Allan Poe
January 2023: Véronique Fortuné and Germain Rousseaux are the new team leaders of Curiosity, our interdisciplinary cocktail group in Pprime.
December 2022: With Morgane Parisi from Studio Brou, we created a comic « Le Père Mottureaux » on pedological patterns observed in the salty marshes of Western France. This research is funded by the Foundation of the Poitiers University, the Biodiversity chair of the Poitiers University and the Mission for Transversal and Interdisciplinary Initiatives (MITI) of CNRS. The comic is only available in print from the authors.
November 2022: The XVIII Hydrodynamics Days has taken place in our lab with a presentation of Alexis Bossard, a new PhD student in our group, on the Black Hole Laser effect configurations in Hydrodynamics.
May 2022: The HYDROPHY Chair aims at strengthening the high-range expertise of CNRS in hydrodynamics in an interdisciplinary context, and to increase the fundamental knowledge of phenomena in interaction, in order to tackle major challenges related to environmental transitions.
May 2022: Johan Fourdrinoy and Yann Devaux participated to the Pint of Science Festival on the 11th of May by discussing our research on Physical Hydrodynamics and their connexion to History.
April 2022: Our paper on doubly transcritical flows in Analogue Gravity is published in Physical Review D.
Press Release: Slow fluctuations of analogue white-hole flows.
We have realized, in a narrow water channel, a series of doubly transcritical flows in which the flow speed is first accelerated to become supercritical (faster than the speed of surface waves), and then returns to subcritical. In the Analogue Gravity context, such flows engender an effective metric containing a black-hole horizon followed by a white-hole horizon (its time reverse), both of which are of interest in the study of analogue Hawking radiation. However, the white-hole horizon is associated with the emission of short-wavelength waves characterized by the dispersive properties of the system, and this leads to dramatically different observational consequences compared to its black-hole counterpart: the Hawking effect engenders a « checkerboard » pattern in the two-point correlation function [1], while the background tends to develop a standing wave (or « undulation ») [2]. In this work, we observe the appearance of an undulation that it is associated with a noticeable degree of time-dependence in the flow profile. In flows with a free condition at the downstream end, the free surface fluctuations thus generated can lead to a checkerboard-like pattern reminiscent of that associated with the Hawking effect, though this pattern can be suppressed by an explicit separation of timescales in the data analysis (this appears to be similar in origin to the undulatory pattern observed in an early experiment of J. Steinhauer [3-5].) On the other hand, in flows regulated by a gate at the downstream end, the slow fluctuations do not significantly contribute to the correlation pattern, which is unaffected by the separation of timescales and is likely a true representation of the scattering processes taking place (including the analogue Hawking effect).
[1] C. Mayoral et al., New J. Phys. 13, 025007 (2011).[2] A. Coutant and R. Parentani, Physics of Fluids 26, 044106 (2014).[3] J. Steinhauer, Nat. Phys. 10, 864 (2014).[4] Y.-H. Wang et al., SciPost Phys. 3, 022 (2017).[5] V. I. Kolobov et al., Nat. Phys. 17, 362 (2021).
April 2022: The Foundation of the Poitiers University is funding our research on self-organization in collaboration with the Biodiversity chair of the Poitiers University.
March 2022: We participated to the Research Spring at Poitiers University where we demonstrated the dead water effect which slows down boats in stratified fluid layers of different salinities.
March 2022: The manuscript of the PhD thesis of Johan Fourdrinoy on the scientific viewpoint about the battle of Actium is now available.
March 2022: We participated to the French science popularization television program « C’est toujours pas sorcier » on black holes.
February 2022: Our research on Self-Organization is funded for a second year by the Mission for Transversal and Interdisciplinary Initiatives (MITI) of CNRS.
January 2022: Congratulations to the team of high school students working on the circular jump as an analogue white hole who got a first prize at the French Physics Olympiad.
December 2021: Our work on the defeat of Anthony and Cleopatra at Actium is discussed in the French maritime journal Le Chasse-marée.
September 2021: Our PhD collaborator Johan Fourdrinoy explains the subject of his thesis with cartoons of Peb & Fox for the Science Fair (« Sciences en Bulles« ).
September 2021: We were invited to give a review on Underwater Orbital Sand Ripples in the Laboratory at the Euromech 609 Colloquium on Granular Patterns in Oscillatory Flows.
June 2021: We were invited to the Trimester New Horizons In Dispersive Hydrodynamics of the Isaac Newton Institute for Mathematical Sciences where we gave a recorded talk « Analog Tidal Bores in the Laboratory ».
June 2021: Our PhD collaborator Johan Fourdrinoy gave a recorded talk on Internal Breaking Waves at the online workshop B'(reaking)Waves 2021 organized by Henrik Kalisch, University of Bergen (Norway) and Mario Ricchiuto, Inria (France).
March 2021: We were invited to the yearly meeting of the Relativistic Quantum Information Society RQI-Online 2020/2021 conference organized by the Perimeter Institute, Waterloo (Canada) where we gave a recorded talk on Analogue Gravity « When Unruh meets Vasarely ».
March 2021: We are laureate of the call on Self-Organization by the Mission for Transversal and Interdisciplinary Initiatives (MITI) of CNRS which supports risk-taking, disruption and emergence for the year 2021.
January 2021: We are part of a new team created in January to foster interdisciplinary and curiosity driven research at Pprime Institute. The name is Curiosity.
« The next scientific revolution will be driven by scientists who have: – A multidisciplinary view of science, – The opportunity to take risks, – The infrastructure to work, – And the freedom to think. » Daniel Zajfman, Colloquium at Collège de France « Recherche et innovation : quel avenir ? » (Oct. 2019).
January 2021: As in 2017 for the interstellar travel, the readership of Pour La Science selected the article presenting our work on the dead water effect(s) in the top ten of the year 2020.
October 2020: When seven researchers of the Poitiers University working on Time meet an artist.
October 2020: We were invited to the LMA Colloquium for a webinar on the life of the polar explorer Fridtjof Nansen and his encounter with the dead-water phenomenon.
July 2020: Our review on Classical Hydrodynamics for Analogue Spacetimes is published in the July special issue of PTRSA with other great contributions following the Royal Society Meeting (listen to the audio presentations) of December 2019: these papers constitute the state of the art on Analogue Gravity for the next generation of scientists working on this subject. With Hamid Kellay from Bordeaux University (France), we introduced a new system for Analogue Gravity namely soap films with their mechanical waves.
Press Release: Flowing soap films as an effective metric.
As part of a review article following a conference organized at the Royal Society of London in December 2019, researchers from the Pprime Institute in Poitiers and LOMA in Bordeaux proposed a new system for analogue gravity in classical hydrodynamics which mimics the propagation of light in a curved space-time like that of a black hole, a white fountain (the time reversal of a black hole) or a wormhole (the bridge between a black hole and a white fountain). This analogue consists of the flow of a film of soap at variable speed by the modification of the section of the hydrodynamic tunnel controlled by the distance between two fishing wires AND of the mechanical waves which propagate on the film of soap. Three types of waves are allowed: elastic waves, and two types of hydrodynamic waves controlled by surface tension. In this work, the analogue of astrophysical horizons corresponds to the equality between the speed of the film flow and the speed of the so-called sinuous hydrodynamic waves whose interfaces deform in phase unlike varicose waves which deform in opposition to phase according to the pioneering work of the great English fluid mechanician G.I. Taylor [0]. Supersonic flows generated by the constriction and expansion of the hydrodynamic tunnel are tested by observation of Mach cones. The shape of the wakes (geometry and characteristics) is explained by the theory of waves in the presence of the medium motion generating a spatially inhomogeneous speed. The thickness of the soap film is deduced from the flow rate imposed by a pump and from the average speed in the film which is obtained by measuring the speed profile in the channel by Doppler Laser Velocimetry. From the measurement of the angle alpha of the Mach cone and that of the speed of the flow v, the researchers deduced the speed of the waves c by the relation of Mach sin (alpha) = c / v = 1 / Ma (where Ma = v / c is the Mach number greater than 1 in supersonic flows). This new system will probably allow the observation of analogue Hawking radiation [1, 2, 3, 4] but also analogue interstellar travel [5], analogue Laser effects [6] in the cavity formed by the black and white horizons or even to test the co-existence of several types of waves in an effective metric system. The properties of sinuous capillary thickness waves in soap films are very similar to those of acoustic waves in condensates of cold atoms [4] where the thickness of the soap film plays the role of the so-called healing length of the condensate (characterizing the way in which the quantum wave function is disturbed in the vicinity of an obstacle) with an immediate transposition of previous works on condensates to soap films and this for a low cost!
[0] G.I. Taylor, Proc. R. Soc. Lond. Ser. A, 253, 296-312 (1959).
[1] S. Weinfurtner et al., Phys. Rev. Lett., 106 2 (2011).
[2] L.-P. Euvé et al., Phys. Rev. Lett., 117, 12 (2016).
[3] J. Drori et al., Phys. Rev. Lett., 122 (1) 010404 (2019).
[4] J.R.M. de Nova et al., Nature, 569 (7758) 688 (2019).
[5] L.-P. Euvé and G. Rousseaux, Phys. Rev. D, 96 (6) 064042 (2017).
[6] C. Peloquin et al., Phys. Rev. D, 93(8) 084032 (2016).
July 2020: Our paper on the dead-water effect(s) is published in the Proceedings of the National Academy of Sciences of the United States of America (PNAS).
Official Press Release by CNRS and University of Poitiers.
June 2020: We gave a talk at the Zoom conference New Horizons in Analogue Gravity chaired by Yaron Kedem (Stockholm University, Sweden), Jaakko Nissinen (Aalto University, Finland) and Justin H. Wilson (Rutgers University, NJ, USA). The following video is also available on the Youtube channel of the conference.
May 2020: With Stefan Mancas from Embry-Riddle Aeronautical University (USA), we have shown that the Friedman-Lemaître set of equations at the theoretical roots of the description of the Universe Expansion can be written in a mathematical form akin to the Rayleigh-Plesset equation which rules the dynamics of a bubble in a liquid. The paper is published in General Relativity and Gravitation.
Press Release: Is our Universe a visco-elastic bubble?
Scientists Germain Rousseaux from Institut Pprime, Poitiers (France) and Stefan C. Mancas from Embry-Riddle Aeronautical University, Daytona Beach (USA) have shown, in a recent paper published in General Relativity and Gravitation, that the Friedman-Lemaître set of equations at the theoretical roots describing the expansion of the Universe can be written in a mathematical form akin to the Rayleigh-Plesset equation which rules the dynamics of a bubble in a liquid. About 150 years ago, a British mathematician, W. H. Besant studied the dynamics of a spherical bubble in an infinite fluid body of incompressible flow, such as a bubble filled with gas in a body of water. Neglecting surface tension and viscosity he derived an equation that he presented in his 1859 book. It took about 60 years when Lord Rayleigh in 1917 realized that the assumption of constant pressure inside the cavity would become wrong as the radius decreases the pressure near the boundary of the cavity would become greater than the ambient pressure. After about 30 more years Milton S. Plesset first applied the equation to traveling cavitation bubbles by including effects of surface tension. On the other hand, the set of three equations of cosmic dynamics based on Einstein’s field equations of General Relativity assuming an isotropic and homogeneous universe were first derived by Friedman in 1922, and rediscovered by Lemaître in 1927 to include the elusive cosmological constant term which is an equivalent to the vacuum energy, which might be one of the reasons why the universe is expanding, as de Sitter predicted with an inflated balloon analogy. For the first time, the two scientists were able to combine these equations into a master equation for the evolution of the scale factor a(t) which is a measure of the time evolution of the Universe and which contains different density terms and viscous effects of shear type. Surprisingly, this newly written universal equation is analogous to the one describing the radial dynamics of a bubble immersed in a vast liquid. In addition to the core terms which are function of either acceleration or speed, the curvature term in astrophysics is similar to the pressure drop across the bubble interface in continuum mechanics, which implies that for open universes, when curvature is negative the inner pressure of the bubble is larger than outer pressure, as if the bubble is expanding, while closed universes are similar to collapsing bubbles. Similarly, the contribution of dust density, with zero pressure is translated into the effect of surface tension whereas the contribution of radiation density mimics the effect an elastic shell. Both fluid mechanics and cosmic equations feature dissipative terms whose influence remains to be compared as well as the infamous cosmological constant who does not have yet an obvious interpretation in fluid mechanics or elasticity. Let us hope that both systems will be analyzed even more deeply such that physicists and mathematicians will take mutual inspirations from their own approaches to elude the mysteries of the Universe.
April 2020: Our paper on the plunge into an analogue black hole in classical hydrodynamics is published in Physical Review Letters.
Press Release: Plunge into an analogue black hole flow.
We have realized a water flow that mimics a black hole and, for the first time, probed the scattering of surface waves on such a flow. More precisely, the flow increases such that, at some point, it reaches and then starts to exceed the speed of long-wavelength waves on the water’s surface. This point behaves like the horizon of a black hole, since beyond it all waves are dragged downstream and cannot “escape” back upstream (i.e., outside the black hole). We probe the system with long incident waves, a scenario analogous to light falling into a black hole (previous experiments in this context [1-3] were performed on subcritical decelerating flows with no horizon for long wavelengths). The subsequent scattering of these ingoing waves is found to be well described by the theoretical tools of field theory in curved spacetime, thus justifying the correspondence between the realized flow and an effective black-hole spacetime. This result opens up the possibility of observing the analogue of the Hawking effect from a black hole horizon in such a system, whereby waves are amplified to an extent that mimics thermal emission, the associated temperature being given by the rate of change of the flow at the horizon. Such an observation would complement Jeff Steinhauer’s experiments in Bose-Einstein condensates [4].
[1] G. Rousseaux et al., New J. Phys 10, 053015 (2008)
[2] S. Weinfurtner et al., Phys. Rev. Lett. 106, 021302 (2011)
[3] L.-P. Euvé et al., Phys. Rev. Lett. 117, 121301 (2016)
[4] J. R. M. de Nova et al., Nature 569, 688 (2019)
February 2020: We are laureate of the CNRS 80ans initiative with the LMA team on PDE. The OFHyS (Optimisation de formes en hydrodynamique à surface libre) project co-lead by Julien Dambrine (University of Poitiers, LMA, Poitiers) and Germain Rousseaux (CNRS, Institut Pprime, Poitiers) has been funded for a second year (2020).
January 2020: We are laureate of the internal funding scheme of the Pprime laboratory with the LMA team on PDE. The GrAnHysMice (Gravitation Analogue en Hydrodynamique Physique avec les Films Minces) project co-lead by Nicolas James (University of Poitiers, LMA, Poitiers) and Germain Rousseaux (CNRS, Institut Pprime, Poitiers) has been funded for two years 2020-2021.
germain.rousseaux (at) cnrs.fr