Collaborative Research: Measuring G with a Magneto-Gravitational Trap

万有引力是第一个被科学家用数学方法解释月球、行星和恒星运动的力。几百年后，引力仍然被认为是最不为人所知的力。它不能在不同的物理理论中被一致地描述，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，可能是宇宙中最难以测量的基本属性。该项目旨在通过自1798年亨利·卡文迪什（Henry Cavendish）使用扭力天平进行测量以来技术上最重大的变化，极大地提高我们对这一常数的认识。由该奖项资助的测量可能在物理学和天文学的许多领域具有价值，正在开发的新实验工具可能会导致用于测量极小力和加速度的新仪器，用于研究地球和惯性导航。此外，这些实验所要求的对细节的关注使它们成为未来STEM工作者的特殊培训基地。该项目的最终目标是开发一种测量牛顿引力常数G的新系统，并使G的测量精度达到前所未有的水平（百万分之十或更高）。该方法利用了最近开发的光机械系统：悬浮在超高真空磁引力阱中的二氧化硅微球。当场质量接近被捕获粒子时，微球的机械振荡将用于摆动时间法，从振荡频率的变化来确定G。该系统具有多种功能，使其几乎是精确测量的理想选择，包括振荡频率可以小于1hz，与周围环境隔离，以及作为内置探头纠正漂移的其他自由度。选择拟议的测量策略是因为它对科学界是透明的。首先，系统的简单性使其易于理解和分析。其次，大部分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回路或其他困难。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，并将其完整地免费提供给其他研究人员。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.