The Nature of Time

Book Description

This book reviews and contrasts contemporary and historical perceptions of time from scientific and intuitive human points of view. Ancient and modern clocks, Augustinian ideas, the deterministic Newtonian universe, biological clocks, deep time, thermodynamics, quantum mechanics, and relativity all contribute to the perspective. The focus is on what can be inferred from established technologies and science as opposed to futuristic speculation.

Chapter 1 describes clocks, including the cesium atomic clocks establishing the current global time standard, a history of clock development, biological clocks, phylogenetic trees, radioactive dating, and astronomical methods to determine the age of the universe. Chapter 2 poses ancient questions about time not fully addressed by an understanding of the technical nature of clocks. An early summary of some of these questions as described by Augustine in the 3rd century CE is followed by a description of how Newton, 1300 years later, introduced a conception of time which provided some answers, such as the nature of an infinitesimally short present. Implications concerning the reality of events in the past, present, and future are also discussed. The Newtonian picture is contrasted with the intuitive human one and the possibilities of time travel and temporal recurrence are briefly discussed. Chapter 3 introduces the second law of thermodynamics and addresses how it is compatible with a time-reversible Newtonian description of a universe, even though it appears to define an arrow of time. The nature of entropy and its relation to coarse graining and emergence play a central role in the discussion. Chapter 4 discusses ways in which quantum mechanics has altered the Newtonian perspective, accounting for various interpretations of the meaning of quantum mechanics with regard to time. Chapter 5 describes basic elements of special relativity and their implications for the nature of time. Examples of time dilation and the changing order of space, such as separated events in different frames, are described. The examples are chosen to avoid evocation of currently unattainable technologies. An afterword in chapter 6 reviews questions raised by Augustine and summarizes how the development of science since then has addressed them.

This book was originally developed for an interdisciplinary seminar for beginning undergraduates at the University of Minnesota. It uses a small amount of algebra, mainly in supplementary appendices, and does not assume any prior knowledge of physics, chemistry, biology, or astronomy. In contrast to many semipopular books on time, it avoids speculation either about engineering (techno-optimism) or physical theory (strings, loop quantum gravity, black hole entropy). Instead, it takes a more grounded approach and describes what is currently known (and not known) to help both students and the general reader make better sense of time.

中文：

书名：时间的本质

本书从科学和直观的人类角度回顾和对比了当代和历史对时间的看法。古代和现代的时钟，奥古斯丁思想，确定性的牛顿宇宙，生物钟，深度时间，热力学，量子力学和相对论都有助于透视。重点是可以从既定的技术和科学中推断出什么，而不是未来的推测。

第1章介绍了时钟，包括建立当前全球时间标准的铯原子钟，时钟发展史，生物钟，系统发育树，放射性测年以及确定宇宙年龄的天文方法。第2章提出了有关时间的古老问题，而对时钟的技术性质的理解并没有完全解决。如奥古斯丁在公元3世纪所描述的那样，对其中一些问题进行了早期总结，然后描述了1300年后的牛顿如何引入了时间概念，该概念提供了一些答案，例如无限短的本质礼物。还讨论了过去，现在和未来事件的现实含义。牛顿图像与直观的人类图像进行了对比，并简要讨论了时间旅行和时间递归的可能性。第3章介绍了热力学第二定律，并论述了它如何与宇宙的时间可逆的牛顿描述兼容，即使它似乎定义了时间箭头。熵的性质及其与粗粒化和涌现的关系在讨论中起着核心作用。第4章讨论了量子力学改变牛顿观点的方式，解释了对量子力学关于时间的含义的各种解释。第五章介绍了狭义相对论的基本要素及其对时间本质的影响。描述了时间膨胀和空间变化顺序的示例，例如不同帧中的分离事件。选择这些示例是为了避免唤起当前无法实现的技术。第6章的后记回顾了奥古斯丁提出的问题，并总结了此后科学的发展如何解决这些问题。

这本书最初是为明尼苏达大学初学者的跨学科研讨会而开发的。它使用少量的代数，主要是在补充附录中，并且不假定任何物理，化学，生物学或天文学的先验知识。与许多有关时间的半语言书籍相反，它避免了对工程学 (技术乐观) 或物理理论 (字符串，循环量子引力，黑洞熵) 的猜测。相反，它采用了一种更扎根的方法，并描述了当前已知 (和未知) 的内容，以帮助学生和普通读者更好地了解时间。