Collaborative Research: Multi-Mode Apparatus to Resolve the Discrepancy Concerning Big G

合作研究：解决大G差异的多模式装置

• 批准号: 1707985
• 负责人: Ricardo Decca
• 金额: $ 42.5万
• 依托单位: Indiana University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-05-01 至 2022-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1707985&HistoricalAwards=false
• 关键词: Collaborative; Research; Multi; Mode; Apparatus

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.

在自然界的所有基本常数中，万有引力常数G是已知的精度最低的。目前围绕着G知识的不确定性的情况令基础物理学和精密测量界感到困惑。世界上最好的实验产生的值彼此不相容，其不确定度大约是最精确的实验的40倍。此外，了解G的真值在各个领域都很重要，因为这是努力将广义相对论与量子引力理论中的量子力学统一起来所必需的。通过这一合作实现的项目将是进行精心控制的计量实验，其中测量的精度将在百万分之几。由于过去对G的测定之间的部分差异可以追溯到所使用的方法，专家组将在同一仪器内结合不同的方法来确定G，希望从每种方法获得高精度的G值，但期望使用不同的方法获得的值将模拟社区的当前情况，即不同的方法，无论多么精确，产生不同的结果。随着实验在相同的仪器中进行，我们的努力将有助于理解现有实验结果之间的当前差异。该项目将建立一个扭摆设备，专门用于在同一设备中使用三种不同的实验技术以前所未有的灵敏度测量牛顿引力常数G。由于不同实验小组最近的测量结果分散得很广，或精度较低，因此仍难以达成一致的G值。精密测量界认识到测量值的差异和测量的相对较低的精度是需要解决的问题。这个项目将建立一个基于以前扭摆实验中介绍的想法的系统，但将通过仪器的多模式性质来扩展测量的范围和广度。在主模式中，G将通过测量扭转摆在转盘上旋转时保持光纤不扭曲所需的角加速度来确定，而转盘上存在精心设计的吸引器质量(吸引器质量也在单独的转盘上旋转)。这种角加速度反馈模式产生了迄今为止最精确的G测量，但它只执行了一次。与以前的工作相比，所提出的系统将通过使用先进的测量和表征技术来实现更小的计量误差。用同样的装置，通过测量扭摆的共振频率随吸引子质量的变化来确定G，通过测量摆的热致振荡来确定G。在第三种方法中，当吸引子质量在两个不同的位置时，通过大幅测定摆的共振频率的变化来确定G。每种技术预计提供的测量相对误差约为2ppm。在这个项目中进行的测量将引起物理学和计量学不同领域的科学家的广泛兴趣，这种方法可能会解释为什么以前的实验导致G的测量结果不一致。除了广泛的科学兴趣外，本科生和研究生将是该项目成功不可或缺的一部分。他们将接受实验物理和精密测量技术方面的培训。该项目将通过从联邦承认的农村拉美裔服务机构招聘人才，为第一代大学生和来自不同背景的本科生提供培训和教育，该机构在校园内的研究机会有限。来自三所不同大学的学生将进行接触，增加他们对不同学术文化的接触，并提供交流机会。作为拟议活动的一部分，将制作与武力原则有关的示范，并在社区聚会、招募活动和课堂环境中使用。