Fundamental Physics and Cosmology

“这项奖励是根据2009年美国复苏和再投资法案（公法111-5）资助的。”暴胀宇宙学，结合弦理论的最新发展，指出了一个主要的范式转变：从一个几乎均匀和各向同性的宇宙到一个极端不均匀的“多元宇宙”，其中大部分体积仍然处于爆炸性暴胀膨胀的状态。我们生活在一个有限的“泡沫”中，膨胀已经结束，其他具有不同性质的泡沫正在不断形成。这项研究的一个主要目标是了解如何通过观测来检验这种多元宇宙的设想。在一个永远膨胀的多元宇宙中，所有可能的事件都会发生无数次。除非我们学会如何比较这些无穷大，否则我们根本无法做出任何预测。这就是所谓的“度量问题”。为了确定多重宇宙的概率度量，将研究不同的度量处方，以检查内部不一致和与数据的冲突。一些措施候选人已经以这种方式被排除在外，希望没有那么多可行的处方满足一些最低要求。Garriga和Vilenkin最近提出了另一个想法。他们推测，暴胀多元宇宙的动力学在未来无限空间被全息编码，在那里它被一个低维欧几里得场论所描述。然后在该理论中通过施加紫外线截止来定义该测量。这是一个有吸引力的方法，因为它开启了从第一原理推导出度量的可能性。对多元宇宙场景最壮观的观测测试将是直接观察我们的气泡与另一个气泡的碰撞。我们将研究这种碰撞的观测效应，以及我们近距离探测到这种碰撞的可能性。提出的研究的另一个主要主题是研究拓扑缺陷的演化和观测特征，拓扑缺陷可以在早期宇宙的相变中大量产生。这里的主要焦点将放在宇宙弦网络和“项链”上，由弦连接的单极子组成，从观测的角度来看，这是最有希望的缺陷。数值模拟和解析模型将用于研究弦网络的演化，其结果将用于对引力波、高能粒子通量和其他可观测效应进行准确预测。对拓扑缺陷的检测将打开一扇新的窗口，让我们了解宇宙的早期历史和极高能量下的粒子物理学。更广泛的影响是，拟议的研究将与研究生和博士后合作完成。私家侦探将继续努力向公众传达调查结果。这尤其适用于多元宇宙的世界观，它具有超越物理学的深远影响。PI已经为非专业人士写了一本名为《许多世界合而为一》的书，他的作品在美国、欧洲、俄罗斯和日本的许多报纸和杂志上都有特写，并在许多流行书籍中出现。

"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)."Inflationary cosmology, combined with recent developments in string theory, is pointing to a major paradigm shift: from a nearly homogeneous and isotropic universe to an extremely inho-mogeneous "multiverse", where much of the volume is still in the state of explosive inflationary expansion. We live in a finite "bubble" where inflation has ended, and other bubbles with diverse properties are constantly being formed. A major goal of the proposed research is to learn how this multiverse scenario can be tested observationally. All possible events will happen an infinite number of times in an eternally infllating multiverse. Unless we learn how to compare these infinities, we will not be able to make any predictions at all. This is known as "the measure problem". To determine the probability measure of the multiverse, different measure prescriptions will be studied to check for internal inconsistencies and for conflict with the data. Some measure candidates have already been ruled out in this way, and the hope is that there aren't that many viable prescriptions satisfying some minimal set of requirements.Another idea to be pursued has recently been suggested by Garriga and Vilenkin. They conjecture that the dynamics of the inflationary multiverse is holographically encoded at the future infinity, where it is described by a lower-dimensional Euclidean field theory. The measure is then defined by imposing an ultraviolet cutoff in that theory. This is an attractive approach, as it opens the possibility of deriving the measure from first principles. The most spectacular observational test of the multiverse scenario would be a direct observation of a collision of our bubble with another one. Observational effects of such a collision and the probability for us to be close enough to detect one will be investigated.Another major topic of the proposed research is the study of the evolution and observational signatures of topological defects, which can be copiously produced at phase transitions in the early universe. The main focus here will be on cosmic string networks and on "necklaces", consisting of monopoles connected by strings, which are the most promising defects from the observational point of view. Numerical simulations and analytic modeling will be used to study the evolution of string networks, and the results will be used to make accurate predictions for gravitational waves, high-energy particle fluxes, and other observable effects. Detection of topological defects would open a new window into the early history of the universe and into particle physics at extremely high energies. The broader impacts are that the proposed research will be done in collaboration with graduate students and postdocs. The P.I. will continue his efforts to communicate the results to the general public. This especially applies to the multiverse worldview, which has far-reaching implications beyond physics. The PI has already written a book for lay-persons called "Many Worlds in One" and His work has been featured in numerous newspaper and magazine articles in US, Europe, Russia, and Japan, and in many popular books.