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

在自然界的所有基本常数中，G，即万有引力常数，是已知的最不精确的。围绕G知识的不确定性的现状困扰着基础物理学和精密测量界。世界上最好的实验产生的值是相互不相容的，相差约40倍的最精确的实验的不确定性。此外，知道G的真实值在许多领域都很重要，因为它是统一广义相对论和量子力学的量子引力理论的必要条件。通过这种合作实现的项目将进行仔细控制的测量实验，测量精度将达到百万分之一。由于过去G值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仪器内结合联合收割机不同的方法来测定G，希望从每种方法中获得高度精确的G值，但期望使用不同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。通过在同一装置上进行实验，我们的努力将有助于理解现有实验结果之间的差异。该项目将建立一个扭摆装置，专门用于在同一装置上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。一个商定的G值仍然难以捉摸，因为不同实验组最近的测量结果分散得很广，或者精度很低。精确测量界认为，测量值的分散和测量精度相对较低是需要解决的问题。该项目将建立一个系统的基础上，在以前的扭摆实验中介绍的想法，但将扩大范围和广度的测量仪器的多模式性质。在主模式中，G将通过测量角加速度来确定，所述角加速度是在存在精心设计的吸引子质量（其也在单独的转盘上旋转）的情况下使扭摆的纤维在转盘上旋转时保持不扭曲所需的。这种角加速度反馈模式产生了迄今为止最精确的G测量，但它只执行过一次。与以前的努力相比，该系统将实现更小的计量误差，通过使用先进的测量和表征技术。使用相同的装置，G将通过测量存在吸引子质量的扭摆的共振频率的变化来确定，并且通过测量摆的热致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将通过摆的共振频率的变化的大幅度确定来确定。预计每种技术都能提供相对误差约为2ppm的测量结果。该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，该方法可能揭示为什么以前的实验导致G的测量不一致。除了广泛的科学兴趣，本科生和研究生将是该项目成功的组成部分。他们将接受实验物理和精密测量技术的培训。该项目将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，从一个农村，联邦政府认可的西班牙裔服务机构招聘，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接触，提高他们接触不同的学术文化，并提供网络机会。作为拟议活动的一部分，将在社区聚会活动、招募活动和课堂环境中开发和使用与部队原则有关的演示。

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.