The concept of the thing we call a Black Hole today was born more than two hundred years. A Cambridge scientist, John Michele had written a study about it in 1783, but the name we know is given by an American physicist, John Wheeler in 1967.

According to the generally admitted theory massive object are collapsing at the end of their life. If the mass is big enough, even the particles are not able to resist to this gravitational collapse and the spherical object becomes so small, that we can observe only its gravitational field.

Theory also sais that something can get so close to the mass, that it would need to start faster then the light being able to escape from the gravitational potential of that object. The boundary of this sphere is called Event Horizon.

There are guesses what the region behind the Event Horizon looks like. Is there another Universe? Can we travel faster then light going through these holes?

I don't want to make guesses, just tell how light reach this area.

This is a well known fact the gravity of celestial body bends the light. Einsten's theory says that the bending of the light in the gravitation is the question of geometry. The light goes strait, only the space-time is curved. For better understanding draw a straight line on a paper, then you fold it to a cone. Having a look at in the cone, you can see your straight light bending around the centre of the cone. The space-time around the mass bends similarly, like a cone. As we close to the centre, this gravitation cone becomes steeper and steeper.

These effects can be observed near any massive spherical object. But we may have two difficulties with the observation.

Firstly: some objects, especially stars have their own light that prevents us from seeing anything. For example we can see the gravitation effect of our sun only in case of total eclipse, as British scientists did in 1919 to proof the property of Einsten's theory. Another problem occurs if the spherical object is not small enough. Imagine that we put a big ball in our little cone, we will not see our straight line bending around its centre. That’s why we deal with black holes. They have no light or significant radiation and they are heavy, dense and small. So they will not disturb our observation.

So we see the light bending around the black hole, but we know in the space-time it goes along a straight line from its source to the observer. It means the light can come back along the same straight line.

Shortly if two points of the space can be connected with a straight line, the light is able to go from either of them to the other. If we are not able to send a light ray from one to another, it means this kind of straight line does not exist, so the light will also fail to reach the first point from the other one. We could say: „They do not see each-other."

And what if the world has changed? If the straight path does not exist any more, and we cannot send our light ray back. No doubt, we would be in trouble. Our light could really be trapped by a black hole.

But we are lucky. The space-time curvature caused by theoretical black holes does not change in time. It means the paths of light rays will not move.

Well, let’s imagine a simple case.

Let's send a light-ray towards the Black-Hole, and let's put a mirror in the way of our light ray so that it would go back along the same straight path as it came. Upon the symmetry of the example to reach the mirror and to come back will last the same length of time. We can put this mirror anywhere. We will learn that the closer we put the mirror to the boundary of the black hole, the longer we have to wait the light ray to return. The reason is that closing to the black hole our space-cone goes steeper and steeper, and looks like a pipe. Our light ray has to travel more and more to return. The gravitational red-shift will strengthen this effect too.

Now let’s put our mirror behind the event horizon. It is well known that the light cannot return from there. But why? We can say that it takes infinite time the light to reach the mirror and return. So we’ll never see it again.

Another interpretation is even simpler. It sets out from the fact that if a light reached the mirror along a straight line, then it must be able to return along the same path. Let’s have a look at our cone, which is infinitely steep at a defined distance from the centre, just like a pipe. This cone has no point closer to the centre than this radius. So we cannot draw a straight line passing by this boundary. The region behind the event horizon is not part of the space-time, so no light and no information can be lost here.

We know by now that the black holes should evaporate their material and energy. This is not surprising knowing that their material is not behind the event horizon.

So the question in the title should sound like this: Can we reach the infinity?

György Szondy

gyorgy_szondy@hotmail.com