Their measurement had been sheer luck, or a case of knowing the result they wanted to get, not an uncommon occurrence in science. The light deflection has, however, been accurately confirmed by a number of later observations.
Another prediction of general relativity is that time should appear to 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 of light per second):
the greater the energy, the higher 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.) To someone high up, it would appear that everything down below was making longer to happen. 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!
Newton’s laws of motion put an end to the idea of absolute position in space. The theory of relativity gets rid of absolute time. Consider a pair of twins. Suppose that one twin goes to live on the top of a mountain while the other stays at sea level. The first twin would age faster than the second. Thus, if they met again, one would be older than the other. In this case, the difference in ages would be very small, but it would be much larger if one of the twins went for a long trip in a spaceship at nearly the speed of light. When he returned, he would be much younger than the one who stayed on earth.
Satellite 衛星
他們的測量純屬是運氣，或是已知他們所要得的結果的情形，這在科學上是普遍發生的。然而，光偏折被後來的許多次觀測準確地證實。
另一廣義相對論的預言是，在像地球這樣的大質量的物體附近，時間顯得流逝得更慢一些。這是因為光能量和它的頻率（每秒鐘裡光振動的次數）有一關係：能量越大，則頻率越高。當光從地球的引力場往上走，它失去能量，因而其頻率下降（這表明兩個波峰之間的時間間隔變大）。從在上面的某個人來看，下面發生的每一件事情都顯得需要更長的時間。利用一對安裝在一個水塔的頂上和底下的非常準確的鐘，這個預言在1962年被驗證到。發現底下的那隻更接近地球的鐘走得更慢些，這和廣義相對論完全一致。地球上的不同高度的鐘的速度不同，這在目前具有相當的實用上的重要性，這是因為人們要用衛星發出的信號來作非常精確的導航。如果人們對廣義相對論的預言無知，所計算的位置將會錯幾英里（1英里=1.609公里）！
牛頓運動定律使空間中絕對位置的觀念告終。而對論擺脫了絕對時間。考慮一對雙胞胎，假定其中一個孩子去山頂上生活，而另一個留在海平面，第一個將比第二個老得快。這樣，如果他們再次相會，一個會比另一個更老。在這種情形下，年紀的差別非常小。但是，如果有一個孩子在以近於光速運動的空間飛船中作長途旅行，這種差別就會大得多。當他回來時，他會比留在地球上另一個人年輕得多。
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