| NSF Org: |
PHY Division Of Physics |
| Recipient: |
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| Initial Amendment Date: | April 5, 2017 |
| Latest Amendment Date: | December 1, 2021 |
| Award Number: | 1708024 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Pedro Marronetti
pmarrone@nsf.gov (703)292-7372 PHY Division Of Physics MPS Directorate for Mathematical and Physical Sciences |
| Start Date: | May 1, 2017 |
| End Date: | April 30, 2023 (Estimated) |
| Total Intended Award Amount: | $55,000.00 |
| Total Awarded Amount to Date: | $55,000.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
1 HARPST ST ARCATA CA US 95521-8222 (707)826-4189 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
CA US 95518-1185 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): |
Gravity Exp. & Data Analysis, OFFICE OF MULTIDISCIPLINARY AC |
| Primary Program Source: |
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| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.049 |
ABSTRACT
Of all the fundamental constants of nature, G, the universal gravitational constant, is known with the least precision. The current situation surrounding the uncertainty in the knowledge of G is puzzling the fundamental physics and precision measurement communities. The world's best experiments yield values which are incompatible with one another and differ by about 40 times the uncertainty of the most precise experiment. Furthermore, knowing the true value of G is important in various fields, as it is necessary in efforts to unify general relativity with quantum mechanics in a quantum theory of gravity. The project enabled by this collaboration will be to carry out carefully controlled metrological experiments where the precision of the measurements will be in the part-per-million. Since part of the past discrepancies between determinations of G can be traced back to the methodology used, the group will combine different approaches to determine G within the same apparatus, hoping to obtain highly precise values of G from each approach, but with the expectation that the values obtained using different methodologies will mimic the current situation in the community, namely, that different methodologies, no matter how precise, yield different results. With the experiments carried out in the same apparatus our effort would then help understand the current discrepancies among existing experimental results.
The project will establish a torsion pendulum facility dedicated to measuring the Newtonian gravitational constant G with unprecedented sensitivity using three different experimental techniques within the same apparatus. An agreed upon value for G remains elusive as recent measurements by different experimental groups have scattered widely, or have had low precision. The spread in measured values and the relatively low precision of the measurements is recognized by the precision measurement community as something that needs to be addressed. This project will build a system based upon the ideas introduced in previous torsion pendulum experiments, but will expand the scope and breadth of the measurements by the multi-mode nature of the apparatus. In the primary mode G will be determined by measuring the angular acceleration needed to keep a torsion pendulum's fiber from twisting while it rotates on a turntable in the presence of carefully designed attractor masses (that also rotate on a separate turntable). This angular acceleration feedback mode has yielded the most precise measurement of G to date, yet it has only been performed once. Compared to previous efforts, the proposed system will achieve smaller metrology errors by using advanced measurement and characterization techniques. Using the same apparatus, G will be determined by measuring the change in the resonant frequency of the torsion pendulum with the attractor masses present and removed by measuring the thermally induced oscillation of the pendulum. In the third approach, G will be determined by large amplitude determination of the change in the resonant frequency of the pendulum when the attractor masses are at two different positions. Each technique is expected to provide a measurement with a relative error of approximately 2 ppm. The measurements performed within this project will be of broad interest to scientists in diverse fields of physics and metrology, and the approach may shed light on why previous experiments have resulted in discrepant measurements of G. In addition to broad scientific interest, undergraduate and graduate students will be integral to the success of the project. They will be trained in experimental physics and precision measurement techniques. The project will provide training and education for first-generation college students and undergraduates from diverse backgrounds by recruiting from a rural, federally-recognized Hispanic Serving Institution that has limited research opportunities on campus. Students from three different universities will be in contact, enhancing their exposure to different academic cultures and providing networking opportunities. As part of the proposed activities, demonstrations associated with the principles of forces will be developed and used at community gathering events, recruiting events and in classroom environments.
PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
An apparatus to improve the determination of the gravitational constant G was designed and its construction started. Precision machining was used to minimize the effect of misplacing of mechanical components. Nevertheless, positions and dimensions of all parts were determined using a Coordinate Measuring Machine (with a resolution of 1 micron) and their effects were taken into account.
A system with two turntables was designed and built. The outer turntable allows to position the attractor masses in 16 different configurations, and their position, geometry and density are characterized to minimize metrological errors. Furthermore, the apparatus is housed in an environment where the temperature is controlled to better that 5mK, and the changes in the composition of the atmosphere are monitored to minimize the effects of variations induced by temperature changes or changes in the buoyant forces. The apparatus allows to measure G using three different modes, simplifying the analysis of systematic effects.
While a measurement of G was not yet realized in this project, it is expected it has laid out the work to produce a determination of this fundamental constant with about a part-per-million error. This would be the best determination of G so far.
High school students, undergraduate and graduate students, and a postdoc have joined forces and will continue to work in this project to make it a reality. A total of five Cal Poly Humboldt students contributed to this project and presented their work at several national conferences. These students from diverse backgrounds have continued with successful careers in STEM.
Last Modified: 05/03/2023
Modified by: Charles D Hoyle
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