Looking at the above diagram we first see a beam of light (in blue) issuing from point "B" on a given
galaxy"A-B". Now each of the light rays making up the beam are deviated from their
straight line course into a curve by the gravitational forces from the galaxies cluster
just below. An observer on a faraway galaxy receive the light rays thinking that they are coming
from up above : the other point "B" on the image galaxy. We can say that because the same thing
is happening at point "A" and every others "points sources of light" making up the reel galaxy.
To help us understand what we just said, see in the following diagrams what happens when we look
at our self in a mirror. Why do we see our image in the mirror? The first diagram
explain the image formation for a single "point light source". See the beam of light emitted from the
point source and how its light rays bounce back on the mirror.
![diagramme d'un miroir](miroir/bmp1.jpg)
B) Analogy with glass mirror
Can you see the analogy with the gravitational mirror? Instead of bouncing back from a mirror
surface, the rays are deviated by gravity. In the glass mirror above we see that all of the rays
bouncing off the mirror converge towards a point (behind the mirror). This is the image of the
point source of light and as you experimented before, it seems reel. We find that the same thing
happens to the light deviated by gravity in a Gravitational Mirror.
Any objet is visible because each of the points making up its surface radiate light. It is the
summation of all the light rays reflected by a mirror that form an image of a given object. In
the following diagram to keep it simple we show only one of the rays bouncing off the mirror to
form the virtual image
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![diagramme d'un miroir](miroir/1miroir.jpg)
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As we just said, in the case of a gravitational mirror, the light does not bounce back, but
is deviated by gravity. Of course we are not saying there is a physical mirror of any sorts out
in space. It is only to help understand what is happening that we will draw one in the following
diagram. Just below we reproduce the first diagram shown above at the beginning but this time we
added the imaginary gravitational mirror surface. Here is how we drew it: take a point on a galaxy,
take one light ray radiated from the point but instead of following the curvature we extend it in a straight line as if
there was no gravity to deflect it. We do the same thing at the other end where the observer
is located. We prolonged the light ray at the same angle that he receives it. Because of physical
proprieties ( see calculations ) for a given ray, the angle at the observer location
is the same as its opposing angle when it left the galaxy. We show the two line forming an
isosceles triangle. By repeating the same for the other rays, we obtain a family of isosceles
triangles. The imaginary Gravitational Mirror is the line joining the summit of all the triangles
.
![diagramme d'un miroir gravitationnel](miroir/bmp5.jpg)
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We done this to show the analogies in the functioning of a Gravitational Mirror and a Glass
Mirror. Now we see that for a gravitational mirror, the light rays give the impression of bouncing off an imaginary mirror. This allow us to
use the Glass Mirror theories in the construction of our model for the Universe.
We can ask ourselves is it possible for the light to submit to such a deviation? Look at
what happens near a black hole, the following is from an independent source:
![diagramme d'un trou noir ref: http://nrumiano.free.fr/Fetoiles/t_noirs.html](miroir/trou_noir.gif)
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Obviously we can not see a black hole, by definition the light can not escape it. If a light
ray tries to do so it is drawn back in the black hole by gravitational forces.
Conclusion
In a gravitational mirror the light does not bounce back a surface, but it is deviated by
gravity. No there is no physical mirror out in space but the effect of gravity on light is just as if there was one.
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