廣義相對論的*相對* 的意義何在

廣義相對論的"相對"就是相對於狹義相對論

廣義相對論（英文General relativity）係物理理論，愛因斯坦寫，一九一六年發

表。廣義相對論係狹義相對論，推而廣之。佢考慮到萬有引力，同時間空間嘅

關係。廣義相對論中，時空已非平面幾何，而係曲面幾何，引力查實係時空曲

面。時空曲率，係物質或者放射嘅動量及能量有關。
廣義相對論好多預測，引力拖慢時間，引力透鏡，引力紅移，黑洞等等，都得

以證實。
廣義相對論，並非宇宙唯一描述。另一啲理論，如量子力學，點樣同廣義相對

論夾得埋，係現時物理研究主要課題之一。

Please read the following excerpt taken from "physicsworld.com newswire" today:

"In General Realtivity (GR)(廣義相對論) the speed of light is locally invariant, that is if you measure the speed of light at your location you'll always get the value c. However if you measure the speed of light at some distant location you may find it to be less than c. The obvious example of this is a black hole, where the speed of light falls as it approaches the event horizon and indeed slows to zero at the event horizon.

The reason we may measure the speed of light at a distant location to be less than c is because space/time is curved by mass/energy. The co-ordinates that you use for measuring space/time will not match the co-ordinates a distant observer uses, and that's why the two of you measure different values for the speed of light. To calculate the speed of light at some distant point you need to solve Einstein's equations to find out how space/time curves relative to your co-ordinate system.

Be absolutely clear what you're calculating: the speed of light in your co-ordinate system i.e. the result you get applies only to you. Other observers in other places will calculate a different value, and every observer everywhere will find the local speed of light to have the same value of c."

Simply speaking, measuring space-time depends on the relative coordinate systems. Gravity is a result of warping of space-time and hence depends on such relative coordinate systems.