正在看《时间简史》，以我目前的理解，这本书从亚里士多德时期，人们认为地球是平的，是宇宙的中心开始说起，然后，人类认识到地球是圆的，再然后，人们对宇宙和时间的起源的认识，等等，一直到现在。包括了人类在各个阶段对宇宙和时间的认识的重要理论。
@20210322 补充
之前，我一直以为《时间简史》会很高深，一直不敢看，现在看了大约四分之一了，而且看的英文版，感觉就是用中学物理的技能在讲解宇宙的奥秘，甚至是初中物理。语言通俗易懂，又风趣，还包括了一些名人的趣事。可以当成一本关于人类探索宇宙的传记体小说来看。五星推荐。
一共12章：
1，我们的宇宙图像
2，时空
3，不断扩展的宇宙
4，不确定性原则
5，基本粒子与自然力
6，黑洞
7，黑洞不是那么黑
8，宇宙的起源与命运
9，时间之箭
10，虫洞和时间旅行
11，物理学的统一
12，结论
1, Our Picture of the Universe
2, Space and Time
3, The Expanding Universe
4, The Uncertainty Principle
5, Elementary Particles and the Forces of Nature
6, Black Holes
7, Black Holes Ain’t So Black
8, The Origin and Fate of the Universe
9, The Arrow of Time
10, Wormholes and Time Travel
11, The Unification of Physics
12, Conclusion
读书笔记：《时间简史》
读书笔记：《时间简史》
上次由 Mia2014 在 周一 3月 22, 2021 11:50 pm，总共编辑 2 次。
《时间简史》读书笔记：Q&A 1-2
1, 爱因斯坦的相对论推翻了牛顿的重力理论，为什么我们还在学习牛顿的万有引力定律？
简单概括：我们通常处理的情况中，根据牛顿的理论预测的结果和相对论预测的结果只有极小极小的差异，可以忽略不计，而且，牛顿的理论比爱因斯坦的相对论简单的多。
在实践中，经常发生的是设计出一种新的理论，它实际上是对先前理论的扩展。 例如，对水星的非常精确的观测表明，它的运动与牛顿的重力理论的预测之间存在细微的差别，爱因斯坦的相对论预测的运动与牛顿的理论稍有不同。 爱因斯坦的预言与观察到的事实相吻合，而牛顿却没有，这一事实是对新理论的关键确认之一。 但是，我们仍然将牛顿理论用于所有实际目的，因为在我们通常处理的情况下，牛顿的预测与广义相对论的预测之间的差异非常小。 （牛顿的理论还具有很大的优势，即与爱因斯坦的理论相比，它的工作简单得多！）
In practice, what often happens is that a new theory is devised that is really an extension of the previous theory. For example, very accurate observations of the planet Mercury revealed a small difference between its motion and the predictions of Newton’s theory of gravity, Einstein’s general theory of relativity predicted a slightly different motion from Newton’s theory. The fact that Einstein’s predictions matched what was seen, while Newton’s did not, was one of the crucial confirmations of the new theory. However, we still use Newton’s theory for all practical purposes because the difference between its predictions and those of general relativity is very small in the situations that we normally deal with. (Newton’s theory also has the great advantage that it is much simpler to work with than Einstein’s!)
2, 霍金的理论会推翻爱因斯坦的相对论么？
简单概括：像爱因斯坦用相对论将相互矛盾的牛顿的理论和麦克斯韦的光是恒定的、绝对的理论结合起来一样，引力量子理论在努力将相互矛盾的相对论和量子力学结合起来。霍金应该是对这个引力量子理论做了很大贡献。
今天，科学家用两种基本的局部理论来描述宇宙：相对论和量子力学。它们是本世纪上半叶的伟大智力成就。广义相对论描述了万有引力和宇宙的大规模结构，即这种结构的尺度从几英里到一亿亿亿亿（1后面有二十四个零）英里，可观测宇宙的大小。另一方面，量子力学以很小的规模处理现象，例如百万分之一英寸。但是，不幸的是，这两种理论彼此之间是不一致的-它们不可能都是正确的。当今物理学的主要努力之一，也是本书的主要主题，是寻求将两者结合在一起的新理论 — 引力量子理论。我们还没有这样的理论，距离理论还有很长的路要走，但是我们已经知道它必须具备的许多特性。我们将在后面的章节中看到，我们已经对引力量子理论必须进行的预测有相当多的了解。
Today scientists describe the universe in terms of two basic partial theories — the general theory of relativity and quantum mechanics. They are the great intellectual achievements of the first half of this century. The general theory of relativity describes the force of gravity and the large-scale structure of the universe, that is the structure on scales from only a few miles to as large as a million million million million (1 with twenty-four zeros after it) miles, the size of the observable universe. Quantum mechanics, on the other hand, deals with phenomena on extremely small scales, such as a millionth of millionth of an inch. Unfortunately, however, these two theories are known to be inconsistent with each other — they cannot both be correct. One of the major endeavours in physics today, and the major theme of this book, is the search for a new theory that will incorporate them both — a quantum theory of gravity. We do not yet have such a theory, and we may still be a long way from having one, but we do already know many of the properties that It must have. And we shall see, in later chapters, that we already know a fair amount about the predictions a quantum theory of gravity must take.
简单概括：我们通常处理的情况中，根据牛顿的理论预测的结果和相对论预测的结果只有极小极小的差异，可以忽略不计，而且，牛顿的理论比爱因斯坦的相对论简单的多。
在实践中，经常发生的是设计出一种新的理论，它实际上是对先前理论的扩展。 例如，对水星的非常精确的观测表明，它的运动与牛顿的重力理论的预测之间存在细微的差别，爱因斯坦的相对论预测的运动与牛顿的理论稍有不同。 爱因斯坦的预言与观察到的事实相吻合，而牛顿却没有，这一事实是对新理论的关键确认之一。 但是，我们仍然将牛顿理论用于所有实际目的，因为在我们通常处理的情况下，牛顿的预测与广义相对论的预测之间的差异非常小。 （牛顿的理论还具有很大的优势，即与爱因斯坦的理论相比，它的工作简单得多！）
In practice, what often happens is that a new theory is devised that is really an extension of the previous theory. For example, very accurate observations of the planet Mercury revealed a small difference between its motion and the predictions of Newton’s theory of gravity, Einstein’s general theory of relativity predicted a slightly different motion from Newton’s theory. The fact that Einstein’s predictions matched what was seen, while Newton’s did not, was one of the crucial confirmations of the new theory. However, we still use Newton’s theory for all practical purposes because the difference between its predictions and those of general relativity is very small in the situations that we normally deal with. (Newton’s theory also has the great advantage that it is much simpler to work with than Einstein’s!)
2, 霍金的理论会推翻爱因斯坦的相对论么？
简单概括：像爱因斯坦用相对论将相互矛盾的牛顿的理论和麦克斯韦的光是恒定的、绝对的理论结合起来一样，引力量子理论在努力将相互矛盾的相对论和量子力学结合起来。霍金应该是对这个引力量子理论做了很大贡献。
今天，科学家用两种基本的局部理论来描述宇宙：相对论和量子力学。它们是本世纪上半叶的伟大智力成就。广义相对论描述了万有引力和宇宙的大规模结构，即这种结构的尺度从几英里到一亿亿亿亿（1后面有二十四个零）英里，可观测宇宙的大小。另一方面，量子力学以很小的规模处理现象，例如百万分之一英寸。但是，不幸的是，这两种理论彼此之间是不一致的-它们不可能都是正确的。当今物理学的主要努力之一，也是本书的主要主题，是寻求将两者结合在一起的新理论 — 引力量子理论。我们还没有这样的理论，距离理论还有很长的路要走，但是我们已经知道它必须具备的许多特性。我们将在后面的章节中看到，我们已经对引力量子理论必须进行的预测有相当多的了解。
Today scientists describe the universe in terms of two basic partial theories — the general theory of relativity and quantum mechanics. They are the great intellectual achievements of the first half of this century. The general theory of relativity describes the force of gravity and the large-scale structure of the universe, that is the structure on scales from only a few miles to as large as a million million million million (1 with twenty-four zeros after it) miles, the size of the observable universe. Quantum mechanics, on the other hand, deals with phenomena on extremely small scales, such as a millionth of millionth of an inch. Unfortunately, however, these two theories are known to be inconsistent with each other — they cannot both be correct. One of the major endeavours in physics today, and the major theme of this book, is the search for a new theory that will incorporate them both — a quantum theory of gravity. We do not yet have such a theory, and we may still be a long way from having one, but we do already know many of the properties that It must have. And we shall see, in later chapters, that we already know a fair amount about the predictions a quantum theory of gravity must take.
上次由 Mia2014 在 周六 3月 20, 2021 1:38 pm，总共编辑 1 次。
《时间简史》读书笔记：Q&A 3-4
3，牛顿是坐在苹果树下被苹果砸了头么？
牛顿的灵感来自苹果撞击他的头部，这个故事几乎可以肯定是假的。 牛顿本人只说过，重力的念头是在他“沉思地坐着”并且“因苹果掉落而引起的”。
The story that Newton was inspired by an apple hitting his head is almost certainly apocryphal. All Newton himself ever said was that the idea of gravity came to him as he sat “in a contemplative mood” and “was occasioned by the fall of an apple.”
4，根据牛顿的理论，上帝就没地方住了么？
简单概括：根据牛顿的定律，静止和运动都是相对的，没有绝对的静止，也就没有绝对的空间，因为空间的位置也是相对的，这和他相信上帝的存在的观念是相悖的。
亚里士多德的思想与伽利略和牛顿的思想之间的最大区别在于，亚里士多德相信一种较好的静止状态，如果没有任何力量或冲动，任何身体都会吸收这种静止状态。 特别是，他认为地球静止了。 但是根据牛顿定律，没有唯一的静止标准。 同样可以说，相对于身体A，身体A处于静止状态，而身体B则以恒定速度运动，或者说身体B处于静止状态，而身体A处于运动状态。 ……
缺乏绝对的静止标准意味着无法确定在不同时间发生的两个事件是否在空间中的同一位置发生。 ……
牛顿非常担心缺乏所谓的绝对位置或绝对空间，因为它不符合他关于绝对神的观念。 实际上，他拒绝接受绝对空间的缺失，即使这是他的定律所意味的。
The big difference between the ideas of Aristotle and those of Galileo and Newton is that Aristotle believed in a preferred state of rest, which any body would take up if it were not driven by some force or impulse. In particular, he thought that the earth was at rest. But it follows from Newton’s laws that there is no unique standard of rest. One could equally well say that body A was at rest and body B was moving at constant speed with respect to body A, or that body B was at rest and body A was moving. … …
The lack of an absolute standard of rest meant that one could not determine whether two events that took place at different times occurred in the same position in space. ……
Newton was very worried by this lack of absolute position, or absolute space, as it was called, because it did not accord with his idea of an absolute God. In fact, he refused to accept lack of absolute space, even though it was implied by his laws.
牛顿的灵感来自苹果撞击他的头部，这个故事几乎可以肯定是假的。 牛顿本人只说过，重力的念头是在他“沉思地坐着”并且“因苹果掉落而引起的”。
The story that Newton was inspired by an apple hitting his head is almost certainly apocryphal. All Newton himself ever said was that the idea of gravity came to him as he sat “in a contemplative mood” and “was occasioned by the fall of an apple.”
4，根据牛顿的理论，上帝就没地方住了么？
简单概括：根据牛顿的定律，静止和运动都是相对的，没有绝对的静止，也就没有绝对的空间，因为空间的位置也是相对的，这和他相信上帝的存在的观念是相悖的。
亚里士多德的思想与伽利略和牛顿的思想之间的最大区别在于，亚里士多德相信一种较好的静止状态，如果没有任何力量或冲动，任何身体都会吸收这种静止状态。 特别是，他认为地球静止了。 但是根据牛顿定律，没有唯一的静止标准。 同样可以说，相对于身体A，身体A处于静止状态，而身体B则以恒定速度运动，或者说身体B处于静止状态，而身体A处于运动状态。 ……
缺乏绝对的静止标准意味着无法确定在不同时间发生的两个事件是否在空间中的同一位置发生。 ……
牛顿非常担心缺乏所谓的绝对位置或绝对空间，因为它不符合他关于绝对神的观念。 实际上，他拒绝接受绝对空间的缺失，即使这是他的定律所意味的。
The big difference between the ideas of Aristotle and those of Galileo and Newton is that Aristotle believed in a preferred state of rest, which any body would take up if it were not driven by some force or impulse. In particular, he thought that the earth was at rest. But it follows from Newton’s laws that there is no unique standard of rest. One could equally well say that body A was at rest and body B was moving at constant speed with respect to body A, or that body B was at rest and body A was moving. … …
The lack of an absolute standard of rest meant that one could not determine whether two events that took place at different times occurred in the same position in space. ……
Newton was very worried by this lack of absolute position, or absolute space, as it was called, because it did not accord with his idea of an absolute God. In fact, he refused to accept lack of absolute space, even though it was implied by his laws.
《时间简史》读书笔记：广义相对论里，速度加快，时间为什么变慢？人也会随之老得慢么？
5, 广义相对论里，速度加快，时间为什么变慢？
评：相对论说时间变慢的依据或者打的比方是光速变慢。时钟用的电磁波，电磁波在真空中的传播速度等于光速，速度变快，电磁波也变慢，时钟变慢。这个是有实验依据的。
但是，时钟变慢，人就老得慢了么？想象一下，据称，人体有个生物钟，也是用的电磁波。如果一个细胞只能传输n次电磁波，每次都老化一点点，那么，电磁波传输变慢，每次的间隔加长，老化的就慢一点，也就实现了时间变慢，人也老得慢了。
下面是《时间简史》上的解释：
广义相对论的另一个预测是，在像地球这样的大物体附近，时间似乎应该变慢。 这是因为光的能量与其频率（即每秒光的波数）之间存在关系：能量越大，频率越高。 当光在地球引力场中向上传播时，它会失去能量，因此频率会降低。 （这意味着一个波峰到另一个波峰之间的时间增加了。）
1962年使用在水塔顶部和底部安装的一对非常精确的时钟对这一预测进行了测试。 发现靠近地球底部的时钟运行较慢，这与广义相对论完全吻合。 现在，随着基于卫星信号的非常精确的导航系统的出现，在地球上不同高度的时钟速度的差异具有相当大的实际重要性。 如果忽略了广义相对论的预测，那么所计算出的位置将错几英里！
所以，如果一对双胞胎，一个在山上，一个在海平面上，山上的那个时间会过的比地面上的快些，会比地面上那个老一点。因为越靠近地球，地球重力越大，速度加快，时间变慢。
Another prediction of general relativity is that time should appear to run slower near a massive body like the earth. This is because there is a relation between the energy of light and its frequency (that is, the number of waves fo light per second): the greater the energy, the higher the frequency. As light travels upward in the earth’s gravitational field, it loses energy, and so its frequency goes down. (This means that the length of time between one wave crest and the next goes up.) This prediction was tested in 1962, using a pair of very accurate clocks mounted at the top and bottom of a water tower. The clock at the bottom, which was nearer the earth, was found to run slower, in exact agreement with general relativity. The difference in the speed of clocks at different heights above the earth is now of considerable practical importance, with the advent of very accurate navigation systems based on signals from satellites. If one ignored the predictions of general relativity, the position that one calculated would be wrong by several miles!
评：相对论说时间变慢的依据或者打的比方是光速变慢。时钟用的电磁波，电磁波在真空中的传播速度等于光速，速度变快，电磁波也变慢，时钟变慢。这个是有实验依据的。
但是，时钟变慢，人就老得慢了么？想象一下，据称，人体有个生物钟，也是用的电磁波。如果一个细胞只能传输n次电磁波，每次都老化一点点，那么，电磁波传输变慢，每次的间隔加长，老化的就慢一点，也就实现了时间变慢，人也老得慢了。
下面是《时间简史》上的解释：
广义相对论的另一个预测是，在像地球这样的大物体附近，时间似乎应该变慢。 这是因为光的能量与其频率（即每秒光的波数）之间存在关系：能量越大，频率越高。 当光在地球引力场中向上传播时，它会失去能量，因此频率会降低。 （这意味着一个波峰到另一个波峰之间的时间增加了。）
1962年使用在水塔顶部和底部安装的一对非常精确的时钟对这一预测进行了测试。 发现靠近地球底部的时钟运行较慢，这与广义相对论完全吻合。 现在，随着基于卫星信号的非常精确的导航系统的出现，在地球上不同高度的时钟速度的差异具有相当大的实际重要性。 如果忽略了广义相对论的预测，那么所计算出的位置将错几英里！
所以，如果一对双胞胎，一个在山上，一个在海平面上，山上的那个时间会过的比地面上的快些，会比地面上那个老一点。因为越靠近地球，地球重力越大，速度加快，时间变慢。
Another prediction of general relativity is that time should appear to run slower near a massive body like the earth. This is because there is a relation between the energy of light and its frequency (that is, the number of waves fo light per second): the greater the energy, the higher the frequency. As light travels upward in the earth’s gravitational field, it loses energy, and so its frequency goes down. (This means that the length of time between one wave crest and the next goes up.) This prediction was tested in 1962, using a pair of very accurate clocks mounted at the top and bottom of a water tower. The clock at the bottom, which was nearer the earth, was found to run slower, in exact agreement with general relativity. The difference in the speed of clocks at different heights above the earth is now of considerable practical importance, with the advent of very accurate navigation systems based on signals from satellites. If one ignored the predictions of general relativity, the position that one calculated would be wrong by several miles!