Collaborative Research: Measuring G with a Magneto-Gravitational Trap

引力是科学家用数学方法描述的第一种力，用来解释月球、行星和恒星的运动。几百年后，引力仍然被认为是最鲜为人知的力。在物理学的不同理论中，它不能被一致地描述，甚至它的强度也鲜为人知。用来量化引力强度的牛顿引力常数，可能是测量最差的宇宙基本性质。这个项目寻求极大地提高我们对这个常量的认识，这是自1798年亨利·卡文迪什(Henry Cavenish)实验以来最显著的技术变化，卡文迪什使用扭转天平进行测量。由该奖项资助的测量可能在物理学和天文学的许多领域都有价值，正在开发的新实验工具可能会导致新的仪器，用于测量极小的力和加速度，用于研究地球和惯性导航。此外，这些实验所需的对细节的关注使它们成为未来STEM工作人员的特殊培训场地。该项目的最终目标是开发一种新的系统来测量牛顿引力常数G，并使G测量到前所未有的精度(百万分之10或更高)。该方法利用了最近开发的光学机械系统：在超高真空下悬浮在磁引力陷阱中的二氧化硅微球。在摆动时间法中，将利用微球的机械振荡来确定当场质量靠近捕获粒子时振荡频率的变化。该系统具有多种功能，使其几乎是精密测量的理想之选，包括可低于1赫兹的振荡频率、与周围环境隔离以及充当内置探头以校正漂移的其他自由度。之所以选择拟议的衡量战略，是因为它对科学界透明。首先，系统的简单性使其易于理解和分析。其次，大多数数据将包含在记录的图像序列中；在重新分析组件时几乎没有隐藏的反馈环路或其他困难。为了确保对新测量的信心，所有数据和分析代码都将被存储起来，并免费提供给其他研究人员。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Gravity was the first force mathematically described by scientists as an explanation for the motion of the moon, planets, and stars. Hundreds of years later, gravity is still considered to be the most poorly understood force. It cannot be consistently described across different theories in physics, and even its strength is poorly known. The Newtonian constant of gravitation, which quantifies the strength of gravity, is perhaps the most poorly measured fundamental property of the universe. This project seeks to greatly improve our knowledge of this constant with the most significant change in technique since the experiments of Henry Cavendish in 1798, who used a torsion balance for his measurements. The measurement funded by this award may be of value across many areas of physics and astronomy, and the new experimental tools being developed may lead to new instruments for measuring extremely small forces and accelerations for use in studying the earth and for inertial navigation. Further, the attention to detail required in these experiments makes them an exceptional training ground for tomorrow's STEM workers.The ultimate goal of this project is to develop a new system for measuring the Newtonian constant of gravitation G, and to make a measurement of G to unprecedented accuracy (10 parts per million or better). The approach leverages a recently-developed optomechanical system: a silica microsphere suspended in a magneto-gravitational trap under ultra-high vacuum. The mechanical oscillation of the microsphere will be used in the time-of-swing method to determine G from the change in oscillation frequency when field masses are brought near the trapped particle. The system has multiple features that make it nearly ideal for precision measurements, including an oscillation frequency that can be made less than 1 Hz, isolation from the surrounding environment, and other degrees of freedom to act as a built-in probe to correct for drifts. The proposed measurement strategy was chosen for its transparency to the scientific community. First, the simplicity of the system makes it simple to understand and analyze. Second, most of the data will be contained in sequences of images which are recorded; there are almost no hidden feedback loops or other difficulties in reanalyzing components. To ensure confidence in the new measurement, all data and analysis code will be stored and made freely available to other researchers in their entirety.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.