New developments in string theory

我们对物理宇宙的理解建立在两个基石上：量子力学和广义相对论。量子力学用统计概念来描述亚原子粒子来预测它们的行为。相比之下，广义相对论，即爱因斯坦的引力理论，利用时空几何在天文尺度上提供了对物理的精确描述。将这两种理论及其截然不同的自然观统一在一个框架内，仍然是21世纪理论物理学家面临的突出的基本问题。弦理论在这一探索中处于领先地位。弦理论的显著特征是，与其说基本粒子是点状的，不如说它们是向一个方向延伸的，即“弦”。这种方法的一个值得注意的特性是，引力是这些理论的必要组成部分。然而，统一量子引力理论的负担是在从亚原子到天文尺度的所有尺度上一致地描述物理。目前，我们的知识还不足以回答弦理论是否真的实现了这一目标，因此还有大量的工作要做，以了解这个非常丰富和复杂的结构及其物理含义。我的大部分研究都涉及到如何通过实验来检验这些新想法。例如，物质的弦特性可能在粒子加速器实验或宇宙学观测中得到揭示。“宇宙超弦”提供了一个深刻的例子：在早期宇宙中产生的微观弦，通过宇宙膨胀被拉伸到宏观大小。这样的弦可以通过天文观测看到。

Our understanding of the physical universe rests on two corner-stones: quantum mechanics and general relativity. Quantum mechanics describes subatomic particles using statistical notions to predict their behavior. In contrast, general relativity, Einstein's theory of gravity, provides a precise description of physics on astronomical scales using spacetime geometry. Unifying these two theories and their remarkably dissimilar views of nature in a single framework remains the outstanding fundamental question for theoretical physicists in the twenty-first century. String theory stands as the leading candidate in this quest. The distinguishing feature of string theory is that rather than regarding elementary particles as point-like, they are extended in one direction, i.e., "strings." A noteworthy property of this approach is that gravity emerges as a necessary ingredient of these theories. Yet the burden of a unified quantum theory of gravity is to consistently describe physics on all scales, from subatomic out to astronomical scales. At present, our knowledge is inadequate to answer whether string theory truly fulfills this goal and so a great deal of work remains to understand this remarkably rich and complex structure and its physical implications. Much of my research involves studying how these new ideas may be tested experimentally. For example, the stringy character of matter may be revealed at particle accelerator experiments or in cosmological observations. One incisive example would be provided by "cosmic superstrings": Microscopic strings created in the early universe and stretched to macroscopic sizes by cosmological expansion. Such strings could be seen with astronomical observations.