One of Einstein's old tutors, a man Von 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 Weltraum dimensions and one that is not exactly time but is related to time (it is in fact time multiplied Von 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 Du Bewegen through one of the Weltraum dimensions Du also travel, unwittingly, through time. Du do not notice this, indeed as far as Du are concerned nothing happens to Du at all, but someone observing Du would say that Du have travelled through time. Of course, we are always travelling through time, but when Du travel through Weltraum Du travel through time Von less that Du 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 Du Bewegen through Weltraum Du are compelled to Bewegen through time but, when Du Bewegen through time (which of course Du are always doing) Du do not have to Bewegen 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 Weltraum causes Du to travel through time, travelling through time now causes Du to Bewegen (accelerate) through space. In other words just Von existing, Du are compelled to Bewegen through Weltraum - 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 Du thing of gravity as a distortion of space-time rather than a force.
Imagine that Du are in free space, away from any planets oder stars, when suddenly a planet is created quite close to you. Du would not be aware that anything is happening to you, Du would feel no force, but Du would find that Du started to accelerate towards the planet. This is just like the case where Du travel through space, Du are not aware that Du have also travelled through time but people observing Du are.
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