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