TESTS OF GRAVITY LAWS
Tests of Gravity Laws
Most gravity tests confirm the validity of general relativity, but windows remain open for deviations. One possibility is to improve the precision, for example in the space tests of the equivalence principle by MICROSCOPE or of the redshift law by ACES.
Another possibility involves ranges poorly tested today, that is short or long ranges. The first window, corresponding to distances below a fraction of a millimeter, is explored by Casimir tests of the gravity law. The second window, corresponding to distances beyond the size of planetary orbits in the solar system, is related to the puzzling questions of dark matter and dark energy observed in astrophysics and cosmology.
Space test of the equivalence principle : MICROSCOPE
The MICROSCOPE satellite was launched on April 25th 2016 from Kourou. It is a micro-satellite of the french space agency CNES with a payload provided by ONERA , in a collaboration with GeoAzur (CNRS / Observatoire de Côte d’Azur) and European partners.
All attempts to theoretical unification of general relativity and quantum physics lead to modifications of the theory. They introduce violations of the equivalence principle which is the basis of the theory of general relativity. This principle, well tested in experiments on Earth, will see its accuracy greatly improved by the MICROSCOPE space experiment.
Serge Reynaud is part of the Science Working Group that oversees the data analysis of the mission with the primary aim to test the principle of equivalence, and also secondary aims in fundamental physics and improved knowledge of Earth’s gravity field or orbital environment perturbations.
Our group has worked on the active techniques used to control noise, in particular the cold damping developed by MICROSCOPE to reduce thermal noise. Using a quantum network theory developed previously, we calculated the sensitivity limits of the capacitive accelerometers developed at ONERA and proved that the cold damping mechanism did provide an effective damping without adding thermal fluctuations.
- Quantum theory of fluctuations in a cold damped accelerometer, F. Grassia, J.-M. Courty, S. Reynaud, P. Touboul, European Physical Journal D 8 (2000) 101 [in the arXiv]
Quantum tests of general relativity
Atomic clocks and high-performance time and frequency links, atom interferometers and classical accelerometers are today able to measure frequency, time, and distances, and furthermore to track the motion of massive bodies, quantum particles, and light to accuracy levels never reached before. These instruments achieve their ultimate performance in space, where the clean environment and the free-fall conditions become essential for identifying tiny deformations in space–time that might bring the signature of new physics or new fundamental constituents.
In collaboration with Christophe Salomon (LKB) and Peter Wolf (SYRTE), we have discussed the perspectives for new tests of general relativity based on recent technological developments with atomic clocks as well as new ideas. In particular, we presented the scientific motivations of the space project ACES.
- Testing General Relativity with Atomic Clocks, S Reynaud, C Salomon, P Wolf, Space Science Review 148 233 (2009)
We have also proposed to perform clock comparisons between a ground clock and a remote spacecraft equipped with an ultrastable clock, rather than only ranging to an on-board transponder. Optimization of this technique would lead to significant improvements on present bounds on gravitational waves in an interesting frequency range. The interest of this approach is illustrated by the SAGAS project which aims to fly an ultra stable optical clock in the outer solar system.
- Bounds on gravitational wave backgrounds from large distance clock comparisons, S. Reynaud, B. Lamine, L. Duchayne, P. Wolf, M.-T. Jaekel, Phys. Rev. D 77 122003 (2008)
- Quantum physics exploring gravity in the outer solar system: the SAGAS project, P Wolf, CJ Borde, A Clairon, L Duchayne, A Landragin, P Lemonde, G Santarelli, W Ertmer, E Rasel, FS Cataliotti, M Inguscio, GM Tino, P Gill, H Klein, S Reynaud, C Salomon, E Peik, O Bertolami, P Gil, J Paramos, C Jentsch, U Johann, A Rathke, P Bouyer, L Cacciapuoti, D Izzo, P De Natale, B Christophe, P Touboul, SG Turyshev, J Anderson, ME Tobar, F Schmidt-Kaler, J Vigue, AA Madej, L Marmet, MC Angonin, P Delva, P Tourrenc, G Metris, H Mueller, R Walsworth, ZH Lu, LJ Wang, K Bongs, A Toncelli, M Tonelli, H Dittus, C Laemmerzahl, G Galzerano, P Laporta, J Laskar, A Fienga, F Roques and K Sengstock, Exp. Astron. 23 651-687 (2009)
In collaboration with European colleagues involved in the space mission STE–QUEST, we have given a detailed analysis of its scientific objectives dedicated to different aspects of the Einstein Equivalence Principle. Using atomic clocks, matter wave interferometry and long distance time/frequency links, they provide fascinating science at the interface between quantum mechanics and gravitation that cannot be achieved, at that level of precision, in ground experiments. We have especially emphasized the specific strong interest of performing Equivalence Principle tests in the quantum regime, by using quantum atomic wave interferometry.
- Quantum tests of the Einstein Equivalence Principle with the STE-QUEST space mission, B Altschul, QG Bailey, L Blanchet, K Bongs, P Bouyer, L Cacciapuoti, S Capozziello, N Gaaloul, D Giulini, J Hartwig, L Iess, P Jetzer, A Landragin, E Rasel, S Reynaud, S Schiller, C Schubert, F Sorrentino, U Sterr, JD Tasson, GM Tino, P Tuckey, P Wolf, Advances in Space Research 55 501 (2015)
Extensions of general relativity
Metric extensions of general relativity preserve the equivalence principle, which is verified at a high accuracy level, but they correspond to a metric which may differ (slightly) from that predicted from the Einstein-Hilbert equation.
They provide a natural framework for discussing the validity of general relativity in the solar system. A key criterion for considering these extensions is of course that they remain compatible with the many observations which agree with the predictions of general relativity in the solar system.
They may also suggest new effects to be looked for in existing observations as well as in new dedicated missions.
A general review with numerous references
- Tests of general relativity in the solar system, S. Reynaud, M. -T. Jaekel, International School of Physics Enrico Fermi (Varenna, 2007), in Atom Optics and Space Physics, p. 203-217 (Societa Italiana de Fisica & IOS Press, 2009) [in the arXiv]
This work is performed in close collaboration with Marc-Thierry Jaekel of the Laboratoire de Physique Théorique (LPT) de l’ENS.
Space probes and proposals for new missions
The Doppler tracking of Pioneer 10 & 11, during their travel to the outer solar system, did prove that the scientific analysis of navigation data of space probes could improve our knowledge of the gravity field at large distances, provided that the effect of non gravitational forces be properly controlled. An international collaboration investigated the Pioneer Anomaly under the auspices of the International Space Science Institute (ISSI, Bern) to recover and analyse the data with the purpose of characterizing in the best manner the significance of the observations. This had also led to define the relevant questions to be addressed by future missions.
In collaboration with other groups specialized in data analysis of space probes (Royal Observatory of Belgium, Bruxelles; Systèmes de Référence Temps Espace, Observatoire de Paris; Université Notre Dame de la Paix, Namur; Laboratoire de Physique Théorique de l’ENS, Paris; Institut de Mécanique Céleste et de Calcul des Ephémérides, Observatoire de Paris), we have worked on the data analysis of already flown probes as well as on the preparation of the data analysis of forthcoming missions.
- Radioscience simulations in General Relativity and in alternative theories of gravity, A. Hees, B. Lamine, S. Reynaud, M. -T. Jaekel, C. Le Poncin-Lafitte, V. Lainey, A. Füzfa, J. -M. Courty, V. Dehant, P. Wolf, Classical and Quantum Gravity 29 235027 (2012)
The discussions about the Pioneer anomaly has led to proposals for new space missions using the presently available techniques which are much more precise than those used at the time of Pioneer 10 & 11. In particular, using accelerometers for measuring the non gravitational forces acting on the probe would lead to an unambiguous way of testing the gravity law at the solar system scale.
Proposals have been submitted to the European Space Agency (ESA), as responses to the Cosmic Vision calls, with principal objectives dedicated to fundamental physics (test of the gravity laws at the solar system scale).
- Odyssey: a solar system mission, B Christophe, PH Andersen, JD Anderson, S Asmar, P Berio, O Bertolami, R Bingham, F Bondu, P Bouyer, S Bremer, JM Courty, H Dittus, B Foulon, P Gil, U Johann, JF Jordan, B Kent, C Laemmerzahl, A Levy, G Metris, O Olsen, J Paramos, JD Prestage, SV Progrebenko, E Rasel, A Rathke, S Reynaud, B Rievers, E Samain, TJ Sumner, S Theil, P Touboul, S Turyshev, P Vrancken, P Wolf, N Yu, Experimental Astronomy 23 529 (2009)
- OSS (Outer Solar System): a fundamental and planetary physics mission to Neptune, Triton and the Kuiper Belt, B Christophe, LJ Spilker, JD Anderson, N Andre, SW Asmar, J Aurnou, D Banfield, A Barucci, O Bertolami, R Bingham, P Brown, B Cecconi, JM Courty, H Dittus, LN Fletcher, B Foulon, F Francisco, PJS Gil, KH Glassmeier, W Grundy, C Hansen, J Helbert, R Helled, H Hussmann, B Lamine, C Laemmerzahl, L Lamy, R Lehoucq, B Lenoir, A Levy, G Orton, J Paramos, J Poncy, F Postberg, SV Progrebenko, KR Reh, S Reynaud, C Robert, E Samain, J Saur, KM Sayanagi, N Schmitz, H Selig, F Sohl, TR Spilker, R Srama, K Stephan, P Touboul, P Wolf, Experimental Astronomy 34 203 (2012)
The addition of an ultra stable optical clock on board a probe going to the outer solar system would allow one to characterize all the aspects of the gravity field. This idea led to the ambitious SAGAS project which used atomic sensors.
- Quantum physics exploring gravity in the outer solar system: the SAGAS project, P Wolf, CJ Borde, A Clairon, L Duchayne, A Landragin, P Lemonde, G Santarelli, W Ertmer, E Rasel, FS Cataliotti, M Inguscio, GM Tino, P Gill, H Klein, S Reynaud, C Salomon, E Peik, O Bertolami, P Gil, J Paramos, C Jentsch, U Johann, A Rathke, P Bouyer, L Cacciapuoti, D Izzo, P De Natale, B Christophe, P Touboul, SG Turyshev, J Anderson, ME Tobar, F Schmidt-Kaler, J Vigue, AA Madej, L Marmet, MC Angonin, P Delva, P Tourrenc, G Metris, H Mueller, R Walsworth, ZH Lu, LJ Wang, K Bongs, A Toncelli, M Tonelli, H Dittus, C Laemmerzahl, G Galzerano, P Laporta, J Laskar, A Fienga, F Roques, K Sengstock, Experimental Astronomy 23 651 (2009)
Another idea has been studied, consisting in embarking instruments such as electrostatic accelerometers dedicated to gravity tests, on missions essentially devoted to the exploration of the outer solar system. This has led to our participation in proposals aiming at exploring the outer planets Uranus or Neptune.
- The science case for an orbital mission to Uranus: Exploring the origins and evolution of ice giant planets, CS Arridge, N Achilleos, J Agarwal, CB Agnor, R Ambrosi, N Andre, SV Badman, K Baines, D Banfield, M Barthelemy, MM Bisi, J Blum, T Bocanegra-Bahamon, B Bonfond, C Bracken, P Brandt, C Briand, C Briois, S Brooks, J Castillo-Rogez, T Cavalie, B Christophe, AJ Coates, G Collinson, JF Cooper, M Costa-Sitja, R Courtin, IA Daglis, I De Pater, M Desai, D Dirkx, MK Dougherty, RW Ebert, G Filacchione, LN Fletcher, J Fortney, I Gerth, D Grassi, D Grodent, E Grun, J Gustin, M Hedman, R Helled, P Henri, S Hess, JK Hillier, MH Hofstadter, R Holme, M Horanyi, G Hospodarsky, S Hsu, P Irwin, CM Jackman, O Karatekin, S Kempf, E Khalisi, K Konstantinidis, H Kruger, WS Kurth, C Labrianidis, V Lainey, LL Lamy, M Laneuville, D Lucchesi, A Luntzer, J MacArthur, A Maier, A Masters, S McKenna-Lawlor, H Melin, A Milillo, G Moragas-Klostermeyer, A Morschhauser, JI Moses, O Mousis, N Nettelmann, FM Neubauer, T Nordheim, B Noyelles, GS Orton, M Owens, R Peron, C Plainaki, F Postberg, N Rambaux, K Retherford, S Reynaud, E Roussos, CT Russell, A Rymer, R Sallantin, A Sanchez-Lavega, O Santolik, J Saur, K Sayanagi, P Schenk, J Schubert, N Sergis, EC Sittler, A Smith, F Spahn, R Srama, T Stallard, V Sterken, Z Sternovsky, M Tiscareno, G Tobie, F Tosi, M Trieloff, D Turrini, EP Turtle, S Vinatier, R Wilson, P Zarkat, Planetary and Space Sciences 104 122 (2014)
- Neptune and Triton: Essential pieces of the Solar System puzzle, A Masters, N Achilleos, CB Agnor, S Campagnola, S Charnoz, B Christophe, AJ Coates, LN Fletcher, GH Jones, L Lamy, F Marzari, N Nettelmann, J Ruiz, R Ambrosi, N Andre, A Bhardwaj, J Fortney, CJ Hansen, R Helled, G Moragas-Klostermeyer, G Orton, L Ray, S Reynaud, N Sergis, R Srama, M Volwerk, Planetary and Space Sciences 104 108 (2014)
New instruments for new missions
When proposals for space missions have been proposed to space agencies, in particular in answer to the Cosmic Vision calls at the European Space Agency (ESA), their scientific and technological content has been extensively studied by the collaborations and partly submitted to technical assessment study by the european or national space agencies.
During this process, it became clear that new instruments had to be developed in advance of new mission proposals with the aim of assessing the feasibility of new techniques of measurement before the selection process.
Our group has been involved in the development by ONERA of bias correction for electrostatic accelerometers in order to make them suitable for outer space missions.
- Electrostatic accelerometer with bias rejection for gravitation and Solar System physics, B Lenoir, A Lévy, B Foulon, B Lamine, B Christophe, S Reynaud, Advances in Space Research 48 1248-1257 (2011)
- Unbiased acceleration measurements with an electrostatic accelerometer on a rotating platform, B Lenoir, B Christophe, S Reynaud, Advances in Space Research 51 188 (2013)
- Experimental demonstration of bias rejection from electrostatic accelerometer measurements, B Lenoir, B Christophe, S Reynaud, Measurement 46 1411 (2013)