Jean-Philippe Uzan

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Jean-Philippe Uzan (born 1969) is a French cosmologist and directeur de recherche employed by the Centre national de la recherche scientifique (CNRS).

Contents

Education and career

In 1987 Uzan graduated from secondary school with the degree Baccalauréat C with honours. From 1987 to 1990 he studied at Lycée Saint-Louis to prepare for competitive scientific examinations. From 1990 to 1993 he studied in the Engineering School of the École des Mines de Paris. There he graduated in 1993 with a civil engineering degree with specialisation in Earth science. From 1993 to 1994 he did his French military service as a cooperant doing research at the Institutet for rymdfysik (IRF, Swedish Institute of Space Physics). At Paris-Sud University (Paris XI), he obtained a Diplôme d'études approfondies (DEA) in theoretical physics and then completed a Ph.D. thesis in theoretical physics in 1998. [1] His thesis was supervised by Nathalie Deruelle, [2] who worked at the (DARC, Department of Relativistic Astrophysics and Cosmology) at the Meudon Observatory. After holding a postdoctoral position under the supervision of Ruth Durrer at the department of theoretical physics of the University of Geneva, he was recruited in 1999 at the CNRS (section 02) and assigned to the physics laboratory theory from the University of Paris-Sud (Paris XI) at Orsay. He was assigned in 2005 to the Institut d'Astrophysique de Paris (IAP) and appointed directeur de recherche in 2009. He received his habilitation degree (Habilitation à diriger des recherches, HDR) in 2007 from Pierre and Marie Curie University (Paris 6). [1]

Uzan specializes in gravitation and relativistic cosmology and is the author or coauthor of more than 130 articles in peer-reviewed journals. [1] He is an editor for the journal Foundations of Physics . [3]

From June 2013 to June 2017 he was the deputy director, with Cédric Villani as director, of the Institut Henri-Poincaré (IHP). Uzan contributed to the expansion of the institute and the creation of the Maison des Mathématiques containing, among other things, a museum of mathematics. [4] [5] He co-authored, with Cédric Villani and Vincent Moncorgé, the book La Maison des Mathématiques (2015) describing the life of the institute. Uzan also directed the collective work Modèles mathématiques (2017), describing the collection of models from the IHP library. In 2015, for the 100th anniversary of the publication of Einstein's theory of general relativity, Uzan co-authored and presented the documentary Einstein et la Relativité Générale, une histoire singulière (Einstein and General Relativity, a unique story). Directed by filmmaker Quentin Lazzarotto, the film features major international researchers such as Jocelyn Bell Burnell, Roger Penrose, Thibault Damour, and Carlo Rovelli. [6]

Uzan was one of the keynote speakers invited for the public session of the 26th meeting of the Conférence générale des poids et mesures (CGPM, General Conference on Weights and Measures) on the day of the vote on the historical revision of the International System of Units on November 16, 2018, in Versailles. [7]

He has collaborated with many artists and is the author or coauthor of nine popular science books. He also works on science outreach. [8]

Research

Jean-Philippe Uzan is a specialist in gravitation and relativistic cosmology. He worked on several aspects related to observational cosmology and the cosmology of the early universe.

He has developed numerous tests of general relativity at astrophysical and cosmological scales. The study of fundamental constants [9] offers a test of the equivalence principle at the heart of Einstein's theory of gravitation. He established several constraints on fundamental constants' possible variations, in particular, from primordial nucleosynthesis, [10] cosmic microwave background, [11] population III stars, [12] and the MICROSCOPE satellite results. [13] He studied tensor-scalar theories (such as tensor–vector–scalar gravity, scalar–tensor–vector gravity and bi-scalar tensor vector gravity), various potential alternatives to general relativity, and their observational signatures in cosmology (primordial nucleosynthesis, cosmic microwave background, and large-scale structure). In 2001, he proposed, with Francis Bernardeau of the Commissariat à l'énergie atomique et aux énergies alternatives (CEA), a test [14] [15] of general relativity at cosmological scales.

In observational cosmology, he has worked on primordial nucleosynthesis, the cosmic microwave background, large-scale structure, the effects of gravitational lensing and the diffuse background of gravitational waves. [16] In particular, he obtained the first prediction of the power spectrum of the stochastic background of gravitational waves of astrophysical origin and the power spectrum's correlations with the distribution of galaxies and the effects of gravitational shear. [17] With Julien Larena and Pierre Fleury, he proposed in 2015 "stochastic lensing", a new approach to the effects of small-scale structures on the effects of gravitational lensing in cosmology [18] and in 2017 a solution to the Ricci-Weyl problem. [19]

He proposed various tests of the assumptions on which the standard model of cosmology is based. See, for an overview, his reviews. [20] [21] [22] He proposed in 2008, with George F. R. Ellis and Chris Clarkson, a test of the Copernican principle [23] and in 2016, with Cyril Pitrou and Thiago Pereira, a test of the isotropy of the expansion of the universe. [24] Uzan with collaborators also proposed several tests of Etherington's cosmic distance duality relation (CDDR). [25] [26] He also studied the topology of the universe and obtained numerous constraints on the size and shape of the universe. [27]

In the cosmology of the early universe, he also obtained results concerning the non-Gaussianity of large structures, whether during inflation [28] or generated by nonlinear dynamics (in particular for their observational signatures on the cosmic microwave background [29] ), as well as on the theory of perturbations in non-isotropic space-times (of the type Bianchi I). [30] [31] [32] With Lev Kofman and Francis Bernardeau, he proposed an extension of inflation leading to a modulation of perturbations during the warming phase. [33]

With Shinji Mukohyama, he published a speculative model in which the physical concept of time is an emergent phenomenon. [34]

Awards and honours

Books

Scientific monographs

Non-technical books

Related Research Articles

<span class="mw-page-title-main">Physical cosmology</span> Branch of cosmology which studies mathematical models of the universe

Physical cosmology is a branch of cosmology concerned with the study of cosmological models. A cosmological model, or simply cosmology, provides a description of the largest-scale structures and dynamics of the universe and allows study of fundamental questions about its origin, structure, evolution, and ultimate fate. Cosmology as a science originated with the Copernican principle, which implies that celestial bodies obey identical physical laws to those on Earth, and Newtonian mechanics, which first allowed those physical laws to be understood.

In physical cosmology, cosmic inflation, cosmological inflation, or just inflation, is a theory of exponential expansion of space in the early universe. The inflationary epoch is believed to have lasted from 10−36 seconds to between 10−33 and 10−32 seconds after the Big Bang. Following the inflationary period, the universe continued to expand, but at a slower rate. The re-acceleration of this slowing expansion due to dark energy began after the universe was already over 7.7 billion years old.

<span class="mw-page-title-main">Copernican principle</span> Principle that humans are not privileged observers of the universe

In physical cosmology, the Copernican principle states that humans, on the Earth or in the Solar System, are not privileged observers of the universe, that observations from the Earth are representative of observations from the average position in the universe. Named for Copernican heliocentrism, it is a working assumption that arises from a modified cosmological extension of Copernicus' argument of a moving Earth.

<span class="mw-page-title-main">Cosmic microwave background</span> Trace radiation from the early universe

The cosmic microwave background is microwave radiation that fills all space in the observable universe. It is a remnant that provides an important source of data on the primordial universe. With a standard optical telescope, the background space between stars and galaxies is almost completely dark. However, a sufficiently sensitive radio telescope detects a faint background glow that is almost uniform and is not associated with any star, galaxy, or other object. This glow is strongest in the microwave region of the radio spectrum. The accidental discovery of the CMB in 1965 by American radio astronomers Arno Penzias and Robert Wilson was the culmination of work initiated in the 1940s.

<span class="mw-page-title-main">General relativity</span> Theory of gravitation as curved spacetime

General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics. General relativity generalizes special relativity and refines Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time or four-dimensional spacetime. In particular, the curvature of spacetime is directly related to the energy and momentum of whatever matter and radiation are present. The relation is specified by the Einstein field equations, a system of second order partial differential equations.

<span class="mw-page-title-main">Quantum gravity</span> Description of gravity using discrete values

Quantum gravity (QG) is a field of theoretical physics that seeks to describe gravity according to the principles of quantum mechanics. It deals with environments in which neither gravitational nor quantum effects can be ignored, such as in the vicinity of black holes or similar compact astrophysical objects, such as neutron stars as well as in the early stages of the universe moments after the Big Bang.

In physics, quintessence is a hypothetical form of dark energy, more precisely a scalar field, postulated as an explanation of the observation of an accelerating rate of expansion of the universe. The first example of this scenario was proposed by Ratra and Peebles (1988) and Wetterich (1988). The concept was expanded to more general types of time-varying dark energy, and the term "quintessence" was first introduced in a 1998 paper by Robert R. Caldwell, Rahul Dave and Paul Steinhardt. It has been proposed by some physicists to be a fifth fundamental force. Quintessence differs from the cosmological constant explanation of dark energy in that it is dynamic; that is, it changes over time, unlike the cosmological constant which, by definition, does not change. Quintessence can be either attractive or repulsive depending on the ratio of its kinetic and potential energy. Those working with this postulate believe that quintessence became repulsive about ten billion years ago, about 3.5 billion years after the Big Bang.

The following is a timeline of gravitational physics and general relativity.

Cosmic strings are hypothetical 1-dimensional topological defects which may have formed during a symmetry-breaking phase transition in the early universe when the topology of the vacuum manifold associated to this symmetry breaking was not simply connected. Their existence was first contemplated by the theoretical physicist Tom Kibble in the 1970s.

The Big Bounce hypothesis is a cosmological model for the origin of the known universe. It was originally suggested as a phase of the cyclic model or oscillatory universe interpretation of the Big Bang, where the first cosmological event was the result of the collapse of a previous universe. It receded from serious consideration in the early 1980s after inflation theory emerged as a solution to the horizon problem, which had arisen from advances in observations revealing the large-scale structure of the universe.

The Sachs–Wolfe effect, named after Rainer K. Sachs and Arthur M. Wolfe, is a property of the cosmic microwave background radiation (CMB), in which photons from the CMB are gravitationally redshifted, causing the CMB spectrum to appear uneven. This effect is the predominant source of fluctuations in the CMB for angular scales larger than about ten degrees.

The Lambda-CDM, Lambda cold dark matter, or ΛCDM model is a mathematical model of the Big Bang theory with three major components:

  1. a cosmological constant denoted by lambda (Λ) associated with dark energy
  2. the postulated cold dark matter
  3. ordinary matter

A variable speed of light (VSL) is a feature of a family of hypotheses stating that the speed of light may in some way not be constant, for example, that it varies in space or time, or depending on frequency. Accepted classical theories of physics, and in particular general relativity, predict a constant speed of light in any local frame of reference and in some situations these predict apparent variations of the speed of light depending on frame of reference, but this article does not refer to this as a variable speed of light. Various alternative theories of gravitation and cosmology, many of them non-mainstream, incorporate variations in the local speed of light.

<span class="mw-page-title-main">Gravitational-wave astronomy</span> Branch of astronomy using gravitational waves

Gravitational-wave astronomy is an emerging field of science, concerning the observations of gravitational waves to collect relatively unique data and make inferences about objects such as neutron stars and black holes, events such as supernovae, and processes including those of the early universe shortly after the Big Bang.

In physical cosmology and astronomy, dark energy is an unknown form of energy that affects the universe on the largest scales. Its primary effect is to drive the accelerating expansion of the universe. Assuming that the lambda-CDM model of cosmology is correct, dark energy is the dominant component of the universe, contributing 68% of the total energy in the present-day observable universe while dark matter and ordinary (baryonic) matter contribute 26% and 5%, respectively, and other components such as neutrinos and photons are nearly negligible. Dark energy's density is very low: 6×10−10 J/m3, much less than the density of ordinary matter or dark matter within galaxies. However, it dominates the universe's mass–energy content because it is uniform across space.

<span class="mw-page-title-main">Primordial black hole</span> Hypothetical black hole formed soon after the Big Bang

In cosmology, primordial black holes (PBHs) are hypothetical black holes that formed soon after the Big Bang. In the inflationary era and early radiation-dominated universe, extremely dense pockets of subatomic matter may have been tightly packed to the point of gravitational collapse, creating primordial black holes without the supernova compression typically needed to make black holes today. Because the creation of primordial black holes would pre-date the first stars, they are not limited to the narrow mass range of stellar black holes.

<span class="mw-page-title-main">Uroš Seljak</span> Slovenian cosmologist

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<span class="mw-page-title-main">Modern searches for Lorentz violation</span> Overview about the modern searches for Lorentz violation

Modern searches for Lorentz violation are scientific studies that look for deviations from Lorentz invariance or symmetry, a set of fundamental frameworks that underpin modern science and fundamental physics in particular. These studies try to determine whether violations or exceptions might exist for well-known physical laws such as special relativity and CPT symmetry, as predicted by some variations of quantum gravity, string theory, and some alternatives to general relativity.

The Etherington's distance-duality equation is the relationship between the luminosity distance of standard candles and the angular diameter distance. The equation is as follows: , where is the redshift, is the luminosity distance and the angular-diameter distance.

Ruth Durrer is a professor of Cosmology at the University of Geneva. She works on the cosmic microwave background, brane cosmology and massive gravity.

References

  1. 1 2 3 "Jean-Philippe Uzan (CNRS)". Institut d'Astrophysique de Paris.
  2. ↑ Uzan, Jean-Philippe (1998). Défauts topologiques et conditions aux limites en cosmologie primordiale. Thèse de doctorat (These de doctorat) (in French). Paris 11.
  3. ↑ "Editors". Foundations of Physics. Springer.
  4. ↑ "La Maison des mathématiques 2020, Chapitre 1". YouTube. Institut Henri Poincaré. June 14, 2017.
  5. ↑ "La Maison des mathématiques 2020, Chapitre 2". YouTube. Institut Henri Poincaré. December 22, 2017.
  6. ↑ "Einstein et la Relativité Générale". Nébuleuse Productions (in French).
  7. ↑ "Jean-Philippe Uzan - "The role of the Planck constant in physics" 26th CGPM". YouTube. The BIPM. November 16, 2018.
  8. ↑ "Jean-Philippe Uzan". Villa Albertine.
  9. ↑ Uzan, Jean-Philippe (2003-04-07). "The fundamental constants and their variation: observational and theoretical status". Reviews of Modern Physics. 75 (2). American Physical Society (APS): 403–455. arXiv: hep-ph/0205340 . Bibcode:2003RvMP...75..403U. doi:10.1103/revmodphys.75.403. ISSN   0034-6861. S2CID   118684485.
  10. ↑ Coc, Alain; Nunes, Nelson J.; Olive, Keith A.; Uzan, Jean-Philippe; Vangioni, Elisabeth (July 2007). "Coupled variations of fundamental couplings and primordial nucleosynthesis". Physical Review D. 76 (2): 023511–023522. arXiv: astro-ph/0610733 . Bibcode:2007PhRvD..76b3511C. doi:10.1103/PhysRevD.76.023511. S2CID   30230380.
  11. ↑ Ade, P. A. R.; et al. (2015-07-22). "Planck intermediate results. XXIV. Constraints on variation of fundamental constants". Astronomy & Astrophysics. 580. EDP Sciences: A22. arXiv: 1406.7482 . Bibcode:2015A&A...580A..22P. doi:10.1051/0004-6361/201424496. ISSN   0004-6361. S2CID   33250997. arXiv preprint
  12. ↑ Coc, A.; Ekström, S.; Descouvemont, P.; Meynet, G.; Uzan, J.-Ph.; Vangioni, E.; Tanihara, Isao; Ong, Hooi Jin; Tamii, Atsushi; Kishimoto, Tadafumi; Kajino, Toshitaka; Kubono, Shigeru; Shima, Tatsushi (2010). Effects of the variation of fundamental constants on Pop III stellar evolution. AIP Conference Proceedings. AIP. pp. 21–26. arXiv: 0911.2420 . doi:10.1063/1.3485139. ISSN   0094-243X. arXiv preprint
  13. ↑ Bergé, Joel; Brax, Philippe; Métris, Gilles; Pernot-Borràs, Martin; Touboul, Pierre; Uzan, Jean-Philippe (2018). "MICROSCOPE Mission: First Constraints on the Violation of the Weak Equivalence Principle by a Light Scalar Dilaton" (PDF). Physical Review Letters. 120 (14): 141101. arXiv: 1712.00483 . Bibcode:2018PhRvL.120n1101B. doi:10.1103/PhysRevLett.120.141101. PMID   29694146. S2CID   206309271.
  14. ↑ Uzan, Jean-Philippe; Bernardeau, Francis (2001). "Lensing at cosmological scales: A test of higher dimensional gravity". Physical Review D. 64 (8): 083004. arXiv: hep-ph/0012011 . Bibcode:2001PhRvD..64h3004U. doi:10.1103/PhysRevD.64.083004. S2CID   119455304.
  15. ↑ Uzan, Jean-Philippe (2007). "The acceleration of the universe and the physics behind it". General Relativity and Gravitation . 39 (3): 307–342. arXiv: astro-ph/0605313 . doi:10.1007/s10714-006-0385-z. S2CID   118989708.
  16. ↑ Cusin, Giulia; Pitrou, Cyril; Uzan, Jean-Philippe (2017-11-28). "Anisotropy of the astrophysical gravitational wave background: Analytic expression of the angular power spectrum and correlation with cosmological observations". Physical Review D. 96 (10). American Physical Society (APS): 103019. arXiv: 1704.06184 . doi:10.1103/physrevd.96.103019. ISSN   2470-0010. S2CID   118967586. arXiv preprint
  17. ↑ Cusin, Giulia; Dvorkin, Irina; Pitrou, Cyril; Uzan, Jean-Philippe (2018). "First Predictions of the Angular Power Spectrum of the Astrophysical Gravitational Wave Background" (PDF). Physical Review Letters. 120 (23): 231101. arXiv: 1803.03236 . Bibcode:2018PhRvL.120w1101C. doi:10.1103/PhysRevLett.120.231101. PMID   29932710. S2CID   49379620. . See also the CNRS journal article: Ter Minassian, Vahé (2018-06-19). "Décrypter la rumeur des cataclysmes cosmiques". Le Journal. CNRS.
  18. ↑ Fleury, Pierre; Larena, Julien; Uzan, Jean-Philippe (2015). "The theory of stochastic cosmological lensing". Journal of Cosmology and Astroparticle Physics. 2015 (11): 022. arXiv: 1508.07903 . Bibcode:2015JCAP...11..022F. doi:10.1088/1475-7516/2015/11/022. S2CID   118389041.
  19. ↑ Fleury, Pierre; Larena, Julien; Uzan, Jean-Philippe (2017). "Weak Gravitational Lensing of Finite Beams" (PDF). Physical Review Letters. 119 (19): 191101. arXiv: 1706.09383 . Bibcode:2017PhRvL.119s1101F. doi:10.1103/PhysRevLett.119.191101. PMID   29219481. S2CID   206302118.
  20. ↑ Uzan, Jean-Philippe (2010). "Tests of general relativity on astrophysical scales". General Relativity and Gravitation. 42 (9): 2219–2246. arXiv: 0908.2243 . Bibcode:2010GReGr..42.2219U. doi:10.1007/s10714-010-1047-8. S2CID   14667139.
  21. ↑ Ruiz-Lapuente, Pilar, ed. (2010). "Chapter 1. Dark energy, gravitation and the Copernican principle by Jean-Philippe Uzan". Dark Energy: observational and theoretical approaches. pp. 3–47. Bibcode:2010deot.book.....R. arXiv preprint
  22. ↑ Uzan, Jean-Philippe (2016). "The big-bang theory: Construction, evolution and status". arXiv: 1606.06112 [astro-ph.CO].
  23. ↑ Uzan, Jean-Philippe; Clarkson, Chris; Ellis, George F. R. (2008). "Time Drift of Cosmological Redshifts as a Test of the Copernican Principle" (PDF). Physical Review Letters. 100 (19): 191303. arXiv: 0801.0068 . Bibcode:2008PhRvL.100s1303U. doi:10.1103/PhysRevLett.100.191303. PMID   18518435. S2CID   31455609.
  24. ↑ Pereira, Thiago S.; Pitrou, Cyril; Uzan, Jean-Philippe (2016). "Weak-lensing B-modes as a probe of the isotropy of the universe". Astronomy & Astrophysics. 585: L3. arXiv: 1503.01127 . Bibcode:2016A&A...585L...3P. doi:10.1051/0004-6361/201527258. S2CID   118463946.
  25. ↑ Uzan, Jean-Philippe; Aghanim, Nabila; Mellier, Yannick (2004-10-27). "Distance duality relation from x-ray and Sunyaev-Zel'dovich observationsof clusters". Physical Review D. 70 (8). American Physical Society (APS): 083533–083539. doi:10.1103/physrevd.70.083533. ISSN   1550-7998. S2CID   119430471.
  26. ↑ Ellis, George F. R.; Poltis, Robert; Uzan, J. P.; Weltman, Amanda (2013). "Blackness of the cosmic microwave background spectrum as a probe of the distance-duality relation". Physical Review D. 87 (10): 103530–103535. arXiv: 1301.1312 . doi:10.1103/PhysRevD.87.103530. S2CID   118469478.
  27. ↑ Luminet, Jean-Pierre; Weeks, Jeffrey R.; Riazuelo, Alain; Lehoucq, Roland; Uzan, Jean-Philippe (2003). "Dodecahedral space topology as an explanation for weak wide-angle temperature correlations in the cosmic microwave background". Nature. 425 (6958): 593–595. arXiv: astro-ph/0310253 . Bibcode:2003Natur.425..593L. doi:10.1038/nature01944. PMID   14534579. S2CID   4380713.
  28. ↑ Bernardeau, Francis; Uzan, Jean-Philippe (2003-06-04). "Inflationary models inducing non-Gaussian metric fluctuations". Physical Review D. 67 (12). American Physical Society (APS): 121301. arXiv: astro-ph/0209330 . doi:10.1103/physrevd.67.121301. ISSN   0556-2821. S2CID   118875651. arXiv preprint
  29. ↑ Pitrou, Cyril; Uzan, Jean-Philippe; Bernardeau, Francis (2010). "The cosmic microwave background bispectrum from the non-linear evolution of the cosmological perturbations". Journal of Cosmology and Astroparticle Physics. 2010 (7): 003. arXiv: 1003.0481 . Bibcode:2010JCAP...07..003P. doi:10.1088/1475-7516/2010/07/003. S2CID   118452299.
  30. ↑ Pereira, Thiago S.; Pitrou, Cyril; Uzan, Jean-Philippe (2007). "Theory of cosmological perturbations in an anisotropic universe". Journal of Cosmology and Astroparticle Physics. 2007 (9): 006. arXiv: 0707.0736 . Bibcode:2007JCAP...09..006P. doi:10.1088/1475-7516/2007/09/006. S2CID   119143078.
  31. ↑ Pitrou, Cyril; Uzan, Jean-Philippe; Bernardeau, Francis (2008). "Cosmic microwave background bispectrum on small angular scales". Physical Review D. 78 (6): 063526. arXiv: 0807.0341 . Bibcode:2008PhRvD..78f3526P. doi:10.1103/PhysRevD.78.063526. S2CID   56073123.
  32. ↑ C. Pitrou, T.S. Pereira & J.-P. Uzan, Predictions from an anisotropic inflationary era, JCAP 04, 004 (2008)
  33. ↑ Bernardeau, Francis; Kofman, Lev; Uzan, Jean-Philippe (2004). "Modulated fluctuations from hybrid inflation". Physical Review D. 70 (8): 083004. arXiv: astro-ph/0403315 . Bibcode:2004PhRvD..70h3004B. doi:10.1103/PhysRevD.70.083004. S2CID   119411642.
  34. ↑ Mukohyama, Shinji; Uzan, Jean-Philippe (2013). "From configuration to dynamics: Emergence of Lorentz signature in classical field theory". Physical Review D. 87 (6): 065020. arXiv: 1301.1361 . Bibcode:2013PhRvD..87f5020M. doi:10.1103/PhysRevD.87.065020. S2CID   119307685.
  35. ↑ "Prix Paul Langevin". Société Française de Physique (sfpnet.fr).
  36. ↑ "Gretz-Armainvilliers: arboretum du Val des Dames". Coleur Jardin.
  37. ↑ "(35391) Uzan = 1997 XN3 (entry on page 16)" (PDF). WGSBN Bulletin. 1 (1). Working Group Small Bodies Nomenclature, International Astronomical Union.
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