At least that is what is supposed to happen, but you can always question the competence of the person who carried out the observation.
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!)
The eventual goal of science is to provide a single theory that describes the whole universe. However, the approach most scientists actually follow is to separate the problem into two parts. First, there are the laws that tell us how the universe changes with time. (If we know what the universe is like at any one time, these physical laws tell us how it will look at any later time.) Second, there is the question of the initial state of the universe. Some people feel that science should be concerned with only the first part; they regard the question of the initial situation as a matter for metaphysics or religion. They would say that God, being omnipotent, could have started the universe off any way he wanted. That may be so, but in that case he also could have made it develop in a completely arbitrary way. Yet it appears that he chose to make it evolve in a very regular way according to certain laws. It therefore seems equally reasonable to suppose that there are also laws governing the initial state.
Competence 能力
Devise 設計
Omnipotent 無所不能的
至少被認為這遲早總會發生的，問題在於人們有無才幹去實現這樣的觀測。
實際上經常發生的是，所設計的新理論確實是原先理論的推廣。例如，對水星的非常精確的觀測揭露了它的運動和牛頓理論預言之間的很小差異。愛因斯坦的廣義相對論所預言的運動和牛頓理論略有不同。愛因斯坦的預言和觀測相符，而牛頓的預言與觀測不相符，這一事實是這個新理論的一個關鍵證據。然而我們在大部分實際情況下仍用牛頓理論，因為在我們通常處理的情形下，兩者差別非常小。（牛頓理論的另一個巨大的優點在於，它比愛因斯坦理論容易處理得多！）
科學的終極目的在於提供一個簡單的理論去描述整個宇宙。然而，大部分科學家遵循的方法是將這問題分成兩部分。首先，是一些告訴我們宇宙如何隨時間變化的定律；（如果我們知道在任一時刻宇宙是什麼樣子的，則這些定律即能告訴我們以後的任一時刻宇宙是什麼樣子的。）第二，關於宇宙初始狀態的問題。有些人認為科學只應過問第一部分，他們認為初始狀態的問題應是形而上學或宗教的範疇。他們會說，全能的上帝可以隨心所欲地啟動這個宇宙。也許是這樣。但是，倘若那樣，他也可以使宇宙以完全任意的方式演化。可是，看起來他選擇宇宙以一種非常規則的、按照一定規律的方式演化。所以，看來可以同樣合理地假定，也存在著制約初始狀態的定律
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