One of Einstein's old tutors, a man 의해 the name of Minkowski showed that the special theory of relativity could be expressed in an interesting way.
The world we live in consists of four dimensions, the three 우주 dimensions and one that is not exactly time but is related to time (it is in fact time multiplied 의해 the square root of -1). This is not at all easy to understand but it means that space-time as we call it has some rather weird properties. In particular, when 당신 옮기기 through one of the 우주 dimensions 당신 also travel, unwittingly, through time. 당신 do not notice this, indeed as far as 당신 are concerned nothing happens to 당신 at all, but someone observing 당신 would say that 당신 have travelled through time. Of course, we are always travelling through time, but when 당신 travel through 우주 당신 travel through time 의해 less that 당신 expect. The most famous example of this effect is the "Twins Paradox".
All the effects of special relativity, such as the slowing down of clocks and the shrinking of rods follow from the above. In fact, it is often better to think of some things, such as electromagnetic fields as being four-dimensional objects. However, the important thing to remember for the moment, is: when 당신 옮기기 through 우주 당신 are compelled to 옮기기 through time but, when 당신 옮기기 through time (which of course 당신 are always doing) 당신 do not have to 옮기기 through space.
So, what does this have to do with gravity? It is quite simple! When a mass is present in the above space-time it distorts it so that whilst it remains true that travelling through 우주 causes 당신 to travel through time, travelling through time now causes 당신 to 옮기기 (accelerate) through space. In other words just 의해 existing, 당신 are compelled to 옮기기 through 우주 - this is gravity.
The particular advantage of this theory of gravity (General Relativity) is that it explains, at a stroke, all the observed properties of gravity. For example the fact that it acts equally on all objects and substances becomes obvious when 당신 thing of gravity as a distortion of space-time rather than a force.
Imagine that 당신 are in free space, away from any planets 또는 stars, when suddenly a planet is created quite close to you. 당신 would not be aware that anything is happening to you, 당신 would feel no force, but 당신 would find that 당신 started to accelerate towards the planet. This is just like the case where 당신 travel through space, 당신 are not aware that 당신 have also travelled through time but people observing 당신 are.
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