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: 1707993
• 负责人: Stefan Ballmer
• 金额: $ 12万
• 依托单位: Syracuse 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 2020-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1707993&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.

在自然的所有基本常数中，g（普遍的引力常数）的精度最低。围绕G知识不确定性的当前情况使基本的物理和精确测量社区感到困惑。世界上最好的实验产生的值彼此不兼容，大约是最精确实验的不确定性的40倍。此外，在各个领域中了解G的真实价值很重要，因为在重力理论中统一与量子力学的一般相对性的努力是必要的。该协作启用的项目将是进行仔细控制的计量实验，其中测量的精度将在每百万的零件中。由于可以追溯到所使用的方法学之间的一部分过去差异，因此该组将结合不同的方法来确定在同一设备内的G，希望从每种方法中获得高度精确的G值，但是期望的是，使用不同方法获得的值将模仿社区中的当前情况，即，无论多么精确，不同的方法都会产生不同的结果。通过在同一设备中进行的实验，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转的摆动设施，该设施专门用于测量具有前所未有的敏感性的牛顿重力常数G设备。由于不同实验组的最新测量已广泛散布或精确度较低，因此G的商定价值仍然难以捉摸。精确度量群落中的测量值和测量值相对较低的精度为需要解决的问题。该项目将根据先前的扭转摆实验中引入的想法建立一个系统，但会扩大测量的范围和广度，并通过设备的多模式性质。在主要模式下，G将通过测量扭转摆纤维所需的角度加速度来确定，而在精心设计的吸引子质量的情况下，它在转盘上旋转（也可以在单独的转盘上旋转）。迄今为止，这种角度加速反馈模式对G产生了最精确的测量，但仅执行一次。与以前的努力相比，提出的系统将通过使用高级测量和表征技术实现较小的计量误差。使用相同的设备，G将通过测量扭转摆的谐振频率的变化与存在的吸引子质量的变化来确定，并通过测量沉淀的热诱导的振荡去除。在第三种方法中，当吸引子质量处于两个不同的位置时，将通过大幅度确定摆的谐振频率的变化来确定G。预计每种技术的相对误差约为2 ppm。该项目中执行的测量值将引起各种物理和计量领域的科学家的广泛关注，并且该方法可能会阐明为什么先前的实验导致G的差异。除了广泛的科学兴趣，本科生和研究生外，将是项目成功的组成部分。它们将接受实验物理和精确测量技术的培训。该项目将通过从农村，联邦认可的西班牙裔服务机构招募，为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。来自三个不同大学的学生将接触，增强他们对不同学术文化的接触并提供网络机会。作为拟议活动的一部分，将在社区收集活动，招募活动和课堂环境中开发和使用与部队原则相关的演示。