If one believed that the universe had a beginning，the obvious question was：What happened before the beginning？ What was God doing before He made the world？ Was He preparing Hell for people who asked such questions？ The problem of whether or not the universe had a beginning，was a great concern to the German philosopher，Immanuel Kant. He felt there were logical contradictions，or Antinomies，either way. If the universe had a beginning，why did it wait an infinite time before it began？ He called that the thesis. On the other hand，if the universe had existed forever，why did it take an infinite time to reach the present stage？ He called that the antithesis. Both the thesis，and the antithesis，depended on Kant’s assumption，along with almost everyone else，that time was Absolute. That is to say，it went from the infinite past，to the infinite future，independently of any universe that might or might not exist in this background.
This is still the picture in the mind of many scientists today. However in 1915，Einstein introduced his revolutionary General Theory of Relativity. In this，space and time were no longer Absolute，no longer a fixed background to events. Instead，they were dynamical quantities that were shaped by the matter and energy in the universe. They were defined only within the universe，so it made no sense to talk of a time before the universe began.
If the universe was essentially unchanging in time，as was generally assumed before the 1920s，there would be no reason that time should not be defined arbitrarily far back. Any so-called beginning of the universe，would be artificial，in the sense that one could extend the history back to earlier times. Thus it might be that the universe was created last year，but with all the memories and physical evidence，to look like it was much older. This raises deep philosophical questions about the meaning of existence. I shall deal with these by adopting what is called the positivist approach. In this，the idea is that we interpret the input from our senses in terms of a model we make of the world. One can not ask whether the model represents reality，only whether it works. A model is a good model if it first，interprets a wide range of observations，in terms of a simple and elegant model. And second，if the model makes definite predictions that can be tested，and possibly falsified by observation.
We do not yet have a good theoretical understanding of the observations that the expansion of the universe is accelerating again，after a long period of slowing down. Without such an understanding，we can not be sure of the future of the universe. Will it continue to expand forever？ Is inflation a law of Nature？ Or will the universe eventually collapse again？ New observational results and theoretical advances are coming in rapidly. Cosmology is a very exciting and active subject. We are getting close to answering the age old questions. Why are we here？ Where did we come from？
Thank you！
根据中非Boshongo人的传说，世界太初只有黑暗、水和伟大的Bumba上帝。一天，Bumba胃痛发作，呕吐出太阳。太阳灼干了一些水，留下土地。他仍然胃痛不止，又吐出了月亮和星辰，然后吐出一些动物，豹、鳄鱼、乌龟，最后是人。
这个创世纪的神话，和其他许多神话一样，试图回答我们大家都想问的问题：为何我们在此？我们从何而来？一般的答案是，人类的起源是发生在比较近期的事。人类正在知识上和技术上不断地取得进步。这样，它不可能存在那么久，否则的话，它应该取得更大的进步。这一点甚至在更早的时候就应该很清楚了。例如，《创世纪》把世界的创生定于公元前4004年10月23日上午9时。另一方面，诸如山岳和河流的自然环境，在人的生命周期里改变甚微。所以人们通常把它们当作不变的背景。要么作为空洞的风景已经存在了无限久，要么是和人类在相同的时刻被创生出来。
但是并非所有人都喜欢宇宙有个开端的思想。例如，希腊最著名的哲学家亚里士多德，相信宇宙已经存在了无限久的时间。某种永恒的东西比某种创生的东西更完美。他提出我们之所以看到发展处于这个情形，那是因为洪水或者其他自然灾害，不断让文明回复到萌芽阶段。信仰永恒宇宙的动机是想避免求助于神意的干涉，以创生宇宙并起始运行。相反的，那些相信宇宙具有开端的人，将开端当作上帝存在的论据，把上帝当作宇宙的第一原因或者原动力。
如果人们相信宇宙有一个开端，那么很明显的问题是，在开端之前发生了什么？上帝在创造宇宙之前在做什么？他是在为那些诘问这类问题的人准备地狱吗？德国哲学家伊曼努尔·康德十分关心宇宙有无开端的问题。他觉得，不管宇宙有无开端，都会引起逻辑矛盾或者二律背反。如果宇宙有一个开端，为何在它起始之前要等待无限久。他将此称为正题。另一方面，如果宇宙已经存在了无限久，为什么它要花费无限长的时间才达到现在这个阶段。他把此称为反题。无论正题还是反题，都是基于康德的假设，几乎所有人也是这么办的，那就是，时间是绝对的，也就是说，时间从无限的过去向无限的将来流逝。时间独立于宇宙，在这个背景中，宇宙可以存在，也可以不存在。
直至今天，在许多科学家的心中，仍然保持这样的图景。然而，1915年爱因斯坦提出他的革命性的广义相对论。在该理论中，空间和时间不再是绝对的，不再是事件的固定背景。相反的，它们是动力量，宇宙中的物质和能量确定其形状。它们只有在宇宙之中才能够定义。这样谈论宇宙开端之前的时间是毫无意义的。
如果宇宙随时间本质上不变，正如20 世纪20年代之前一般认为的那样，就没有理由阻止在过去任意早的时刻定义时间。人们总可以将历史往更早的时刻延展，在这个意义上，任何所谓的宇宙开端都是人为的。于是，情形可以是这样，这个宇宙是去年创生的，但是所有记忆和物理证据都显得它要古老得多。这就产生了有关存在意义的高深哲学问题。我将采用所谓的实证主义方法来对付这些问题。在这个方法中，其思想是，我们按照我们构造世界的模型来解释自己感官的输入。人们不能询问这个模型是否代表实在，只能问它能否行得通。首先，如果按照一个简单而优雅的模型可以解释大量的观测；其次，如果这个模型作出可能被观察检验，也可能被证伪的明确预言，这个模型即是一个好模型。
……
我们观察到，宇宙的膨胀在长期的变缓之后，再次加速。对此理论还不能理解清楚。缺乏这种理解，对宇宙的未来还无法确定。它会继续地、无限地膨胀下去吗？暴胀是一个自然定律吗？或者宇宙最终会再次坍缩吗？新的观测结果，理论的进步正迅速涌来。宇宙学是一个非常激动人心和活跃的学科。我们正慢慢接近这个古老问题的答案：我们为何在此？我们从何而来？
谢谢各位。
导读
2006年6月19日，世界科学大师斯蒂芬·霍金教授参加在人民大会堂举行的国际弦理论大会开幕式，并作“宇宙的起源”主题讲座。霍金，现任英国剑桥大学应用数学及理论物理学系教授，当代最重要的广义相对论和宇宙论家，是本世纪享有国际盛誉的伟人之一，被称为在世的最伟大的科学家，还被称为“宇宙之王”。
单词注解
vomit [5vRmit] v.喷出；吐出
constant [5kCnstEnt] adj.固定的，不变的
eternal [i(：)5tE：nl] adj.永久的，永恒的；无穷的
assumption [E5sQmpFEn] n.假定，设想
falsify [5fC：lsi7fai] v.篡改；伪造；歪曲
collapse [kE5lAps] v.崩溃，瓦解
诵读名句
If one believed that the universe had a beginning，the obvious question was：What happened before the beginning？
If the universe was essentially unchanging in time，as was generally assumed before the 1920s，there would be no reason that time should not be defined arbitrarily far back.
New observational results and theoretical advances are coming in rapidly. Cosmology is a very exciting and active subject.
