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: 2207801
• 负责人: Charles Hoyle
• 金额: $ 12.79万
• 依托单位: Humboldt State University Foundation
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-07-01 至 2025-06-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2207801&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 the effort would then help understand the current discrepancies among existing experimental results. 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. 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 finish building 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. Incidentally, using attractor masses that are transparent in the vissible/near infrared will permit a much more precise determination of the mass distribution. 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 three methods will also shed light in the possible overlooking of systematic effects.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

在自然界的所有基本常数中，万有引力常数 G 的已知精度最低。当前围绕 G 知识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，并且与最精确的实验的不确定性相差约 40 倍。此外，了解 G 的真实值在各个领域都很重要，因为它对于在量子引力理论中统一广义相对论和量子力学是必要的。此次合作促成的项目将进行仔细控制的计量实验，测量精度将达到百万分之一。由于过去G测定之间的部分差异可以追溯到所使用的方法，因此该小组将在同一设备内结合不同的方法来确定G，希望从每种方法中获得高精度的G值，但期望使用不同方法获得的值将模仿社区的当前情况，即不同的方法，无论多么精确，都会产生不同的结果。通过在同一设备中进行实验，这项工作将有助于理解现有实验结果之间的当前差异。除了广泛的科学兴趣之外，本科生和研究生也是该项目成功不可或缺的一部分。他们将接受实验物理学和精密测量技术的培训。该项目将从一个联邦政府认可的乡村拉美裔服务机构招募人才，为来自不同背景的第一代大学生和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保持联系，增强他们对不同学术文化的接触并提供交流机会。 该项目将建立一个扭摆设施，专用于在同一设备内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。由于不同实验组最近的测量结果分散广泛，或者精度较低，因此商定的 G 值仍然难以确定。精密测量界认为测量值的分散性和测量精度相对较低是需要解决的问题。该项目将根据之前扭摆实验中引入的想法完成系统的构建，但将通过设备的多模式性质扩大测量的范围和广度。在主模式中，G 将通过测量在存在精心设计的吸引子质量（也在单独的转盘上旋转）的情况下在转盘上旋转时防止扭摆纤维扭曲所需的角加速度来确定。这种角加速度反馈模式已经产生了迄今为止最精确的 G 测量，但只执行了一次。与之前的工作相比，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。顺便说一句，使用在可见光/近红外范围内透明的吸引子质量将允许更精确地确定质量分布。使用相同的设备，G将通过测量存在吸引子质量的扭摆的谐振频率的变化来确定，并且通过测量摆的热感应振荡来去除吸引子质量。在第三种方法中，当吸引子质量处于两个不同位置时，G 将通过大幅度确定摆的谐振频率变化来确定。每种技术的测量预计相对误差约为 2 ppm。这三种方法还将揭示可能忽视的系统效应。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。