TESTS OF GRAVITY LAWS
Tests of Gravity Laws
Most gravity tests confirm the validity of general relativity, but windows remain open for deviations. One way to progress on these questions 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 way is to study 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, has seen its accuracy improved by a factor 10 by the recent preliminary results announced by the MICROSCOPE space experiment. Analyzing the full data at the end of the mission should lead to a further improvement by another factor 10.
- MICROSCOPE Mission: First Results of a Space Test of the Equivalence Principle, P. Touboul et al, Phys. Rev. Letters 119 231101 (2017)
Quantum tests of general relativity
Atomic clocks, high-performance time and frequency links and atomic interferometers 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.
In collaboration with Christophe Salomon (LKB) and Peter Wolf (SYRTE), we have discussed the perspectives for new tests of general relativity with atomic clocks. 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 ultra stable 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 interesting frequency ranges. 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 different aspects of the Einstein Equivalence Principle, tested by using atomic clocks, matter wave interferometry and long distance time/frequency links. They correspond to fascinating science at the interface of quantum physics and gravitation that cannot be studied in ground experiments.
- 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 may correspond to a metric differing (slightly) from that predicted from the standard theory. They provide a natural framework for discussing the validity of general relativity.
Of course these extensions have to remain compatible with the number of observations which agree with the predictions of general relativity in the solar system. They may however suggest new effects to be looked for in existing observations or in new dedicated missions.
A general review with numerous references can be found in
- 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.
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 also worked on the data analysis of already flown probes or 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)
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 to recover and analyse the data with the purpose of characterizing in the best manner the significance of the observations and also to define the relevant questions for future missions.
These discussions have led to proposals for new space missions which would be much more accurate than at the time of Pioneer 10 & 11. Using accelerometers for measuring the non gravitational forces acting on the probe would in particular lead to an unambiguous test of gravity laws at the solar system scale. Proposals have been submitted to the European Space Agency (ESA), with principal objectives dedicated to this test of 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 make possible a complete characterization of all aspects of the gravity field. This idea led to the ambitious SAGAS project based on 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)
More modest ideas have also been studied, consisting in embarking instruments such as electrostatic accelerometers on missions mainly devoted to the exploration of the outer solar system.
- 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 new space missions have been proposed, their scientific and technological content has been studied by the proposing collaborations and also by technical assessment at the european (ESA) or national (CNES) space agencies. During this process, it became clear that new instruments had to be developed in advance of missions with the aim of assessing the feasibility of new techniques of measurement before the selection process.
We have been involved in the development of bias correction for electrostatic accelerometers (derived from the ONERA expertise). This development has proven that these instruments were indeed 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)