New developments in string theory

我们对物理宇宙的理解建立在两块基石上：量子力学和广义相对论。量子力学使用统计概念来描述亚原子粒子，以预测它们的行为。相比之下，爱因斯坦的引力理论--广义相对论--使用时空几何精确描述了天文尺度上的物理学。将这两种理论及其截然不同的自然观统一在一个单一的框架内，仍然是21世纪理论物理学家面临的突出的根本问题。弦理论是这一探索的主要候选者。弦理论的显著特征不是将基本粒子视为类点粒子，而是它们向一个方向延伸，即“弦”。这种方法的一个值得注意的特性是，重力是这些理论的一个必要组成部分。然而，统一的量子引力理论的负担是一致地描述所有尺度上的物理，从亚原子到天文尺度。目前，我们的知识不足以回答弦理论是否真的实现了这一目标，因此仍有大量工作要做，以了解这种极其丰富和复杂的结构及其物理含义。我的大部分研究涉及研究这些新想法如何在实验中得到检验。例如，物质的粘性特征可能在粒子加速器实验或宇宙学观测中被揭示。一个精辟的例子是“宇宙超弦”：早期宇宙中产生的微细弦，通过宇宙膨胀伸展到宏观尺寸。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.