Relevance of the weak equivalence principle and experiments to test it: Lessons from the past and improvements expected in space

Nobili, A. M.; Anselmi, Alberto

doi:10.1016/j.physleta.2017.09.027

Cited by 21 publications

(30 citation statements)

References 73 publications

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“…If so, the unexplained improvement by a factor 1.9 might be due to an increase of the quality factor of the gold wires by 1.9 2 = 3.6 times for the same system in the same conditions, except for the fact that the frequency of the signal has increased (with faster rotation) by 3.53 times. It is quite interesting that a similar improvement has been observed with the ground demonstrator of the proposed GG experiment in space: with a frequency increase by 2.16 times, the quality factor (for the same system, except for rotation), was found to increase by 2.24 times ( [4], Sec. 8).…”

Section: Microscope First Test Of the Equivalence Principle In Spsupporting

confidence: 65%

“…Instead, RTB are sensitive to ∆a = 10 −15 ms −2 at a signal frequency of 0.84 mHz for both the Be-Ti and Be-Al composition dipoles tested ( [2,3], Table 3). Despite 70 times less sensitivity, MICROSCOPE's early test is 10 times better thanks to the larger driving signal from Earth in orbit versus RTB on ground [4].…”

Section: Microscope First Test Of the Equivalence Principle In Spmentioning

confidence: 99%

“…The improvement occurs despite a sensitivity to differen-arXiv:1803.03313v2 [gr-qc] 17 Jul 2018 tial accelerations about 70 times worse than RTB at similar frequency. In favor of the space test is the much larger driving signal from Earth by almost 500 times at low altitude as compared to RTB on ground (∼ 8 ms −2 versus 0.0169 ms −2 at most) [4]. Having RTB superseded mass dropping tests by several orders of magnitude, despite a driving signal almost 600 times weaker ( 0.0169 ms −2 versus 9.8 ms −2 ) the very large factor yet to gain in low Earth orbit and the success of MICROSCOPE strongly indicate that the next leaps in precision tests of the WEP shall occur in space.…”

Section: Introductionmentioning

confidence: 99%

“…If care is taken in flying an experiment somewhat more sensitive than ground balances, the improvement achievable in space can be impressive. Rapid rotation of the spacecraft and consequent up-conversion of the signal to high frequency, at which thermal noise is low and integration time is short, are the main drivers of the "Galileo Galilei" (GG) space experiment to test the equivalence principle to 10 −17 without invoking cryogen-ics ( [14][15][16][17], [4]).…”

Section: Introductionmentioning

confidence: 99%

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Testing the equivalence principle in space after the MICROSCOPE mission

Nobili

Anselmi

2018

Phys. Rev. D

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Tests of the Weak Equivalence Principle (WEP) can reveal a new, composition dependent, force of nature or disprove many models of new physics. For the first time such a test is being successfully carried out in space by the MICROSCOPE satellite. Early results show no violation of the WEP sourced by the Earth for Pt and Ti test masses with random errors (after 8.26 d of integration time) of about 1 part in 10 14 , and systematic errors of the same magnitude. This result improves by about 10 times over the best ground tests with rotating torsion balances despite 70 times less sensitivity to differential accelerations, thanks to the much stronger driving signal in orbit. The measurement is limited by thermal noise from internal damping in the gold wires used for electrical grounding, related to their fabrication and clamping. This noise was shown to decrease when the spacecraft was set to rotate faster than planned. The result will improve by the end of the mission, as thermal noise decreases with more data. Not so systematic errors. We investigate major nongravitational effects and find that MICROSCOPE's "zero-check" sensor, with test masses both made of Pt, does not allow their separation from the signal. The early test reports an upper limit of systematic errors in the Pt-Ti sensor which are not detected in the Pt-Pt one, hence would not be distinguished from a violation. Once all the integration time available is used to reduce random noise there will be no time left to check systematics. MICROSCOPE demonstrates the huge potential of space for WEP tests of very high precision and indicates how to reach it. To realize the potential, a new experiment needs the spacecraft to be in rapid, stable rotation around the symmetry axis (by conservation of angular momentum), needs high quality state-of-the-art mechanical suspensions as in the most precise gravitational experiments on ground, and must allow multiple checks to discriminate a violation signal from systematic errors. The design of the "Galileo Galilei" (GG) experiment, aiming to test the WEP to 1 part in 10 17 unites all the needed features, indicating that a quantum leap in space is possible provided the new experiment heeds the lessons of MICROSCOPE.

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Section: Microscope First Test Of the Equivalence Principle In Spsupporting

confidence: 65%

Section: Microscope First Test Of the Equivalence Principle In Spmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Testing the equivalence principle in space after the MICROSCOPE mission

Nobili

Anselmi

2018

Phys. Rev. D

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“…In a space test such as Microscope, which is not a mass dropping experiment [7,10], the offset vectors between the centers of mass of the test bodies -being due to construction and mounting errors-are fixed with the apparatus and therefore follow its rotation, allowing the gravity gradient effect to be distinguished from a violation signal. In mass dropping tests with AIs, in which a large number of drops is needed, each one with its own initial conditions, the assumption that the mismatch vectors between the two atom species are fixed with the apparatus cannot be taken for granted.…”

mentioning

confidence: 99%

Systematic errors in high-precision gravity measurements by light-pulse atom interferometry on the ground and in space

Nobili

Anselmi

Pegna

2020

Phys. Rev. Research

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We focus on the fact that light-pulse atom interferometers measure the atoms' acceleration with only 3 data points per drop. As a result the measured effect of gravity gradient is systematically larger than the real one, an error almost unnoticed so far. We show how it affects the absolute measurement of the gravitational acceleration g as well as ground and space experiments based on gradiometers such as those designed for space geodesy, the measurement of the universal constant of gravity and the detection of gravitational waves. Tests of the weak equivalence principle need two different atom species. If both species can be operated with the same laser the error reported here cancels out. If not, the fractional differences in pulse timing and momentum transfer set the precision of the test at unacceptable levels and severely limit the atoms' choice, whereby most tests use isotopes of the same Rb atom which differ by two neutrons only.Light-pulse Atom Interferometers (AIs) are based on quantum mechanics. As the atoms fall, the atomic wave packet is split, redirected, and finally recombined via three atom-light interactions at times 0, T , 2T . The phase that the atoms acquire during the interferometer sequence is proportional to the gravitational acceleration that they are subjected to.It has been shown ([1], Sec. 2.1.3) that although one might think that the phase shift depends on quantum mechanical quantities ". . . this is merely an illusion since we can write the scale factor [between the phase shift and the gravitational acceleration] in terms of the parameters we control experimentally, i.e. Raman pulse vector k and pulse timing T . It then takes the form kT 2 . . . . We can simply ignore the quantum nature of the atom and model it as a classical point particle that carries an internal clock and can measure the local phase of the light field." In the same reference it is demonstrated that both the exact path integral approach and the purely classical one lead to the same exact closed form for the phase shift and free fall acceleration measured by the AI, which is then expanded in power series of the local gravity gradient γ for convenience [1]. The only remaining sign of the atom-light interaction -which cannot possibly appear in the classical model where there is no such interactionis the recoil velocity. However, it neither appears in the phase shift actually measured by AIs because they are operated symmetrically so as to cancel it out (or make it smaller than the initial velocity errors) [2,3]. Thus, the classical approach gives excellent predictions of the phase shift measured by the interferometer, while including the quantum mechanical details related to the internal degrees of freedom is needed to account for smaller effects, such as the finite length of the light pulses.We focus on the fact that AIs measure the atoms position along the trajectory only 3 times per drop (in correspondence of the 3 light pulses), unlike laser interferom-eters in falling corner-cube gravimeters which make hundreds to ...

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The General Theory of Relativity and Its Tests in the Solar System

Ciufolini

2024

Recent Progress on Gravity Tests

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Relevance of the weak equivalence principle and experiments to test it: Lessons from the past and improvements expected in space

Cited by 21 publications

References 73 publications

Testing the equivalence principle in space after the MICROSCOPE mission

Testing the equivalence principle in space after the MICROSCOPE mission

Systematic errors in high-precision gravity measurements by light-pulse atom interferometry on the ground and in space

The General Theory of Relativity and Its Tests in the Solar System

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