When most people believed in an essentially static and unchanging universe, the question of whether or not it had a beginning was really one of metaphysics or theology. One could account for what was observed equally well on the theory that the universe had existed forever or on the theory that it was set in motion at some finite time in such a manner as to look as though it had existed forever. But in 1929, Edwin Hubble made the landmark observation that wherever you look, distant galaxies are moving rapidly away from us. In other words, the universe is expanding. This means that at earlier times objects would have been closer together. In fact, it seemed that there was a time, about ten or twenty thousand million years ago, when they were all at exactly the same place and when, therefore, the density of the universe was infinite. This discovery finally brought the question of the beginning of the universe into the realm of science.
Hubble’s observations suggested that there was a time, called the big bang, when the universe was infinitesimally small and infinitely dense. Under such conditions all the laws of science, and therefore all ability to predict the future, would breakdown. If there were events earlier than this time, then they could not affect what happens at the present time. Their existence can be ignored because it would have no observational consequences. One may say that time had a beginning at the big bang, in the sense that earlier times simply would not be defined. It should be emphasized that this beginning in time is very different from those that had been considered previously. In an unchanging universe a beginning in time is something that has to be imposed by some being outside the universe; there is no physical necessity for a beginning. One can imagine that God created the universe at literally any time in the past. On the other hand, if the universe is expanding, there may be physical reasons why there had to be a beginning. One could still imagine that God created the universe at the instant of the big bang, or even afterwards in just such a way as to make it look as though there had been a big bang, but it would be meaningless to suppose that it was created before the big bang. An expanding universe does not preclude a creator, but it does place limits on when he might have carried out his job!
Metaphysics 形而上學
Impose 強加
Preclude 排除
當大部分人相信一個本質上靜止不變的宇宙時，關於它有無開端的問題，實在是一個形而上學或神學的問題。按照宇宙存在無限久的理論，或者按照宇宙在某一個有限時刻，以給人的印象似乎是已經存在了無限久的樣子啟動的理論，我們可以同樣很好地解釋所觀察到的事實。但在1929年，埃德溫·哈勃作出了一個具有里程碑意義的觀測，即是不管你往那個方向看，遠處的星系正急速地遠離我們而去。換言之，宇宙正在膨脹。這意味著，在早先星體相互之間更加靠近。事實上，似乎在大約100億至200億年之前的某一時刻，它們剛好在同一地方，所以那時候宇宙的密度無限大。這個發現最終將宇宙開端的問題帶進了科學的王國。
哈勃的發現暗示存在一個叫做大爆炸的時刻，當時宇宙的尺度無窮小，而且無限緊密。在這種條件下，所有科學定律並因此所有預見將來的能力都失效了。如果在此時刻之前有過些事件，它們將不可能影響現在所發生的一切。所以我們可以不理它們，因為它們並沒有可觀測的後果。由於更早的時間根本沒有定義，所以在這個意義上人們可以說，時間在大爆炸時有一開端。必須強調的是，這個時間的開端是和早先考慮的非常不同。在一個不變的宇宙中，時間的端點必須由宇宙之外的存在物所賦予；宇宙的開端並沒有物理的必要性。人們可以想像上帝在過去的任何時刻創造宇宙。另一方面，如果宇宙在膨脹，何以宇宙有一個開端似乎就有了物理的原因。人們仍然可以想像，上帝是在大爆炸的瞬間創造宇宙，或者甚至在更晚的時刻，以便它看起來就像發生過大爆炸似的方式創造，但是設想在大爆炸之前創造宇宙是沒有意義的。大爆炸模型並沒有排斥造物主，只不過對他何時從事這工作加上時間限制而已！
閱讀更多 讀書看劇記單詞 的文章
