Gravitational Physics via Lunar Laser Ranging: Optimizing Data Quality

重力，最明显的自然力，实际上是最弱的基本力，因此也是最不容易检验的。爱因斯坦的广义相对论是我们目前对引力的最好描述，但它与量子力学从根本上是不兼容的，很可能在未来被更完整的理论所取代。一种修正后的理论将预测太阳系中的微小偏差，这些偏差可能会对我们对整个宇宙的理解产生深远的影响。月球激光测距(LLR)是指从望远镜发射的短激光脉冲从美国宇航员和苏联登陆者放置在月球上的反射器上反弹。几十年来，通过高精度绘制月球轨道的形状，月球激光测距产生了各种领先的重力测试。该小组建议继续利用阿帕奇点天文台的月球激光测距操作(Apollo)进行前沿观测，以努力使重力经受迄今最严格的测试。阿波罗位于新墨西哥州南部一座9200英尺的山顶上，它引入了一种新的毫米精度测量月球轨道的系统。然而，到目前为止，不完整的模型无法确认其准确性。因此，除了继续观测活动外，该小组还将寻求建立一个校准系统，以确保阿波罗达到其毫米测量目标。拟议的工作将在许多方面使更广泛的社区受益。在智力方面，提高我们对引力的认识可以为各种各样的宇宙学家、天体物理学家、粒子物理学家和弦理论家提供信息。这一努力还将有助于地球和行星科学，特别是通过超导重力仪产生的测量。阿波罗团队将继续参与教育和外展活动，毫无疑问，将继续通过印刷、网络、广播和电视媒体吸引公众兴趣。在有助于阿波罗卓越观测的其他属性中，常规到分钟级的所有五个月球反射器极大地提高了我们测量月球方位和身体变形的能力。这些信息可以更准确地确定月球质心的路径，从而促进基本重力的测试。同时，更高精度的距离测量，以及来自阿帕奇点天文台的超导重力仪和2.5公里外高质量全球定位系统(GPS)站的数据，将通过揭示必须纳入模型的微妙的地球动力学，极大地提高我们对天文台相对于地球重心(重力测试所需)的瞬时位置的理解。LLR测量提供了对强等价原理、牛顿引力常数的时间变化率、引力磁学、平方反比定律和首选框架效应的最佳可用测试。除了这些经典的引力测试，阿波罗还将允许测试与暗能量、额外维度和违反洛伦兹不变性有关的物理学新概念。这里提出的很大一部分工作是建立一个基于铯原子钟标准、低抖动短脉冲激光器和精密间隔计数器的绝对校准系统。该系统将提供对阿波罗基本测量的独立检查，潜在地识别故障并确认其相应的补救措施。

Gravity, the most evident force of nature, is in fact the weakest of the fundamental forces, and consequently the most poorly tested. Einstein's general relativity, which is currently our best description of gravity, is fundamentally incompatible with quantum mechanics and is likely to be replaced by a more complete theory in the future. A modified theory would predict small deviations in the solar system that could have profound consequences for our understanding of the Universe as a whole. Lunar laser ranging (LLR), in which short laser pulses launched from a telescope are bounced off of reflectors placed on the moon by U.S. astronauts and Soviet landers, has for decades produced various leading tests of gravity by mapping the shape of the lunar orbit to high precision. The group proposes to continue conducting leading-edge observations with the Apache Point Observatory Lunar Laser-ranging Operation (APOLLO), in an effort to subject gravity to the most stringent tests yet. APOLLO, situated atop a 9,200 ft summit in Southern New Mexico, introduces a new regime of millimeter-precision in measuring the lunar orbit. However, incomplete models are thus far unable to confirm the accuracy. The group will therefore seek to build a calibration system to ensure that APOLLO meets its millimeter measurement goal, in addition to continuing the observation campaign. The proposed work will benefit the broader community in a number of ways. On the intellectual front, improving our knowledge of gravity informs a diverse range of cosmologists, astrophysicists, particle physicists, and string theorists. The effort would also contribute to Earth and planetary science, especially via measurements produced by the superconducting gravimeter. The APOLLO team will continue a track record of engagement in education and outreach activities, and will no doubt continue to attract public interest through print, web, radio, and television media.Among other attributes that contribute to APOLLO's superior observations, routine ranging to all five lunar reflectors on timescales of minutes dramatically improves our ability to gauge lunar orientation and body distortion. This information allows a more precise determination of the path for the Moon's center of mass, thereby facilitating tests of fundamental gravity. Simultaneously, higher precision range measurements, together with data from a superconducting gravimeter at the Apache Point Observatory and from a high-quality Global Positioning System (GPS) station 2.5 km away, will greatly improve our understanding of the instantaneous location of the Observatory with respect to the Earth's center of mass (needed for the gravitational tests) by exposing subtle Earth dynamics that must be incorporated into the model. LLR measurements provide the best available tests of the strong equivalence principle, the time-rate-of-change of Newton's gravitational constant, gravitomagnetism, the inverse-square law, and preferred frame effects. In addition to these classical gravitational tests, APOLLO will permit testing of new ideas in physics relating to dark energy, extra dimensions, and violations of Lorentz Invariance. A large part of the effort proposed here is the construction of an absolute calibration system based on a cesium clock standard, a low-jitter short-pulse laser, and a precision interval counter. This system will provide an independent check of APOLLO's fundamental measurement, potentially identifying faults and confirming their pursuant remediation.