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At the beginning of the last century, the universe was considered as identical throughout the cosmos. 1 meter on earth was necessarily equal to 1 meter in the other end of the universe, as 1 second remained always 1 second when that we are in the universe. The space possessed 3 dimensions: the height, the width and the depth. But during the 20 me century, we are going to realize that the universe is not as simple as it appears to it and that our understanding is going to collide with another dimension: the Fourth, the space-time. A small return behind is imperative:

The speed finished of the light

It is in 1889 that an American physicist, Albert Michelson, by measuring the speed of light discovered a surprising thing. What about is the speed of the light source, the light always goes to 300 000 Kps. To explain that take an example:

A train runs in 100 kph. Inside a child releases an electric motor car which runs in 10 kph in the same direction as the train. A cow in its meadow watching passing the train, would see if walls were transparent a small blue automobile running in 110 kph with compare to her while it advances of 10 kph with compared to the child. Totally normal.

Now, replace the small blue car by a beam of light and imagine that the speed of the train is 100 000 kps. With the same first reasoning, we would think that the speed of light, seen by the cow, is equal at the speed of the train + the speed of light; or: 300 000 + 100 000 = 400 000 kps. Now the cow, which nevertheless is not crazy, (we made the test of the ESB) but just perplexed, sees the beam of light in the same speed as the kid in the train. What appears much less normal.

The restricted relativity

It is at the beginning of the last century, that Albert Einstein, German physicist, considered this enigma: Why is the speed of light is always the same about is the speed of the observer? he emitted a assumption which was going to revolutionize our conception of our environment: the space and the time contract in very big speeds.

See an example of the contraction of time

Except the contraction of space-time, a very big speed involves an increase of the mass. No body can reach(affect) the speed of light without what its mass would become infinite. The light is a compound to part: it is constituted by photons, particles devoid of mass.
In his restricted relativity, Albert Einstein discovered a new form of energy: the energy of mass. Any still bodies possess an energy. We does not notice it because it is not emitted(uttered) except in the case of a nuclear fission ( nuclear bomb). The quantity of energy of any bodies is given by the famous formula:

E is the energy of mass
M is the mass of the object
C is the speed of light

The general relativity

In 1913, Albert Einstein, thanks to the restricted relativity, invented a new theory to explain the gravitation. He discovered that massive bodies as earth or sun act on the frame of space-time. So the mass of the sun deforms the space and the time around him by digging it as a ball of metal on an elasticated tissue. Planets, which turn around him, go really in a straight line. But being obliged to follow the lines of space, they cross (go through) so a circular trajectory quite as the cyclist who without changing direction marries the banked corners of the track of the cycle-racing track. This is only a metaphor, the track has only two dimensions, the space-time possesses four and we are very incapable to imagine four curved dimensions. The more the mass is important, the more the "hollow" is deep, the more planets go fast and the more the time also passes fast .
The deformation of time and of the space is so the consequence of two phenomena: the speed and the quantity of mass. However these effects are not perceptible to us in the life of every day. So that that is the case it is necessary that speeds and masses brought into play is considerable. So that the time slows down in a measurable way it is necessary that the speed is at least equal to a 1/10-th of that of the light. This time which is elasticated, is not an abstract time. It is the physical time, that whitch controls the ageing of our bodies: two persons can indeed age at different rhythms if them circles differ.
The deformation of the space by a mass was verified in 1919, during an eclipse of the sun. Measures allowed to show that the beams of a star situated behind plan of the eclipse were well and truly diverted by the impressive mass of the sun. What validated Albert Einstein's general theory of relativity. The dilation of time it was verified in the 60s by synchronizing two atomic clocks. One of them was placed in a plane of the NASA flying from very big speeds. Returned on ground, the clock of the plane delayed a fraction of a second with regard to the other one stayed on earth...

Let us imagine a world in four dimensions...

( Added Part the 26 febrary 2002)

Can we see a world in four dimensions?

Here is the world in 3 dimensions that we know.
If you are capable to add a fourth dimension, you would obtain, no doubt, the Nobel prize!

How then to imagine the fourth dimension?

First of all, take a world in 2 dimensions, characterized by the length and the width. One obtains a plan.

Put on this plan a star (the star is indeed on in 3 dimensions, but let us consider that the plan).
Under the mass of the star, the plan forms a hollow in another dimension than we name the fourth and which is imperceptible to us. We see the right plan while it is bent with the 4-th dimension.

In fact, a curved mass of advantage a plan which is already bent. In our world in 3 dimensions, what seems to us a straight(right) line, is in four dimensions a curve

Take the case of a spaceship going practically at the speed of light. In our plan with the fourth dimension, the vessel will pass by the another road which is not perceptible in our world in 3D red line)

Being seen the previous plan, we sees well that the road with big speed is shorter. But then how to explain that the time which passes in the vessel is different from the time which passes outside? (See the journey of Jaro)
In this, a key sentence: the space and the time are inextricable!
In the diagram opposite, the scale is valid for both representation.
It is for that about that we speaks about deformation of space-time.

Some precision...
- To facilitate the understanding and especially the diagram, I have to represent the route of the vessel by a line. In fact, the vessel if it just goes a little less fast than the light, its route will be slightly curled.
- The vessel, if it is in another dimension, it lives there no not less in one circles in 3 dimensions
- On the plan n2, one saw that a mass bent our plan. So in quoted(esteemed) by an important mass, one enters another dimension. I see you coming. You go to say me that the husband of Mat should often be in another dimension... And I shall not say you the opposite!