Exploring a Frontier of Experimental Gravitation

引力自由落体的普遍性，广义相对论（爱因斯坦的引力理论）的潜在对称性，将以前所未有的精度和普遍性进行检验。有两个强有力的理由来验证这种对称性。首先，广义相对论不是一个量子理论，目前关于量子引力的观点自然会违反自由落体的普遍性，这可能是实验上可以实现的。这些场的发现将对我们对引力的理解乃至宇宙学的理解产生深远的影响。其次，通过寻找对广义相对论认为是精确的对称性的违反，人们可以探测到新的、超弱的、非引力场。目前的宇宙学观点认为，宇宙中的大部分能量可能都与这些场有关。虽然这种超弱场通常会被引力掩盖，但它们是可以探测到的，因为它们通常违反了自由落体的普适性。拟议的测试需要不断改进仪器，以探测受地球、太阳、大尺度宇宙结构或大型铀实验室源吸引的测试物体加速度的微小差异。测试体包括Be、Al、Ti、Cu、Pb，外加成分分别接近地核和月球的天体。三种不同的扭力平衡仪器，最初是在以前的国家科学基金会的支持下开发的，将被升级并用于这项工作。这些仪器的组合将测试汤川长度范围从1厘米到无穷远的自由落体的普遍性，差分加速度分辨率低至10-13厘米/秒。扭力平衡仪器将采用电子自旋极化摆和吸引子来探测自旋相关力。此外，牛顿常数G将使用一种新技术进行测量，该技术避免了以前测量中的重要误差来源。最近关于G的结果非常分散，证明了对这个基本常数进行几次独立测量的必要性。该技术应该能够确定G的精度为1 / 105。

The Universality of Gravitational Free Fall, the underlying symmetry of general relativity (Einstein's theory of gravity), will be tested with unprecedented precision and generality. There are two strong reasons for testing this symmetry. First, general relativity is not a quantum theory and current ideas about quantum gravity naturally produce violations of the Universality of Free Fall that may be experimentally accessible. Discovery of such fields would have profound consequences for our understanding of gravity and perhaps of cosmology. Second, by searching for violations of a symmetry that general relativity holds to be exact, one can probe for new, ultra-weak, non-gravitational fields. Current ideas in cosmology suggest that much of the energy in the universe may be tied up in such fields. Although such ultra-weak fields would normally be obscured by gravitational forces, they are detectable because they generically violate the Universality of Free Fall. The proposed tests require the continued improvement of instruments for detecting tiny differences in the accelerations of test bodies attracted toward the earth, the sun, large-scale cosmological structures, or toward a massive uranium laboratory source. The test bodies include Be, Al, Ti, Cu, Pb, plus bodies having compositions close to the earth's core and the moon respectively. Three different torsion-balance instruments, initially developed under previous NSF support, will be upgraded and employed in this work. The combination of these instruments will test the Universality of Free Fall for Yukawa length scales from 1 cm to infinity with differential acceleration resolutions down to 10-13 cm/s2. The torsion balance instruments will be adapted to probe for spin-dependent forces by using an electron-spin polarized pendulum and attractor. In addition, the Newtonian constant G will be measured using a new technique that avoids important sources of error in previous measurements. Recent results for G have scattered widely, demonstrating the necessity of several independent measurements of this fundamental constant. The technique should be capable of determining G to a precision of 1 part in 105.