Search for Deviations from Newtonian Gravity at Micron Scale (A Continuation Proposal)

现代理论试图弥合粒子物理学公认的模型（“标准模型”）的尺度与引力变得与自然界中所有其他力一样强的尺度（比原子的大小小约23个数量级）之间的差距，预测牛顿定律在更长的长度尺度上的修正，高达1毫米。 最近，已经有几个实验设计来检测或限制牛顿定律在这个宏观长度尺度上的偏差。在斯坦福大学，我们已经建立了这样一个基于低温探针的实验，以测量相距20微米量级的质量之间低至阿托牛顿的力。在我们的实验中，低温氦气轴承被用来旋转一个磁盘包含一个驱动质量模式的交替密度下的一个小的测试质量安装在微机械悬臂梁。两者之间的任何质量相关力将在测试质量上产生随时间变化的力，从而产生悬臂随时间变化的位移。理论物理学的圣杯是提供一个紧凑而优雅的理论，统一所有的自然力。虽然电磁力（带电粒子之间的力），强（将原子核保持在一起的力）和弱（与原子核的某些衰变相关的力）的理解很好，但重力，人类可能经历的第一种力，却知之甚少，将其与其他力统一起来构成了巨大的智力挑战。 这一领域的新理论见解使研究人员有机会尝试通过精确的“桌面”实验为这一研究领域做出贡献。在斯坦福大学，我们利用物理学、化学、材料科学和工程学中的先进技术，建造了一种仪器，可以测量比正常尺度小20多个数量级的力。设计、建造、测试和在真实的实验中使用这样一个装置的挑战迫使我们提出许多解决工程问题的优雅方案。这不仅使参与该项目的学生受益，也使其他在不同领域工作的研究人员受益。例如，我们为该项目开发的微型杠杆现在被用作扭矩磁力计，用于测量纳米样品的磁性。在另一个例子中，我们在实验中发现的控制旋转转子速度的解决方案与辐射施加压力的基本物理定律有关。

Modern theories attempt to bridge the gap between the scale of the accepted model for particle physics (the 'Standard Model'), and the scale at which the force of gravity becomes as strong as all other forces in nature (about 23 orders of magnitudes smaller than the size of an atom), predicting modifications to Newton's law at much longer length scales, up to 1mm. Recently, there have been several experiments designed to detect or constrain deviations from Newton's law at this macroscopic length scale. At Stanford we have built such an experiment based on a low temperature probe to measure forces as low as attoNewton between masses separated by distances on the order of 20 micrometers. In our experiment a cryogenic helium gas bearing is used to rotate a disc containing a drive mass pattern of alternating density under a small test mass mounted on a micromachined cantilever. Any mass-dependent force between the two will produce a time-varying force on the test mass, and consequently a time-varying displacement of the cantilever. The holy grail of theoretical physics is to provide a compact and elegant theory that unifies all forces of nature. While the Electromagnetic (force between charged particles), Strong (force that holds the nucleus together), and Weak (force associated with certain decays of nuclei) forces are well understood, the force of gravity, the first force that human beings probably experienced, is poorly understood, and unifying it with the other forces poses an enormous intellectual challenge. The new theoretical insight in this field gave researchers an opportunity to try and contribute to this field of research through precision, 'table-top' experiments. At Stanford University we utilized advanced techniques used in physics, chemistry, materials science, and engineering to build an apparatus that can measure forces that are more than twenty orders of magnitudes smaller than the force measured by a normal scale. The challenge to design, to construct, to test, and to use in a real experiment such an apparatus forced us to come up with many elegant solutions to engineering problems. This benefitted not only the students working on the project, but also other researchers working in different fields. For example, the miniature cantilevers that we developed for the project are now being used as torque magnetometers for measuring magnetic properties of nano-samples. In another example, a solution we found for controlling the speed of a spinning rotor in our experiment bears on a fundamental physics law of pressure exerted by radiation.