English: • LEFT: A large mass (blue) belongs to the positive sector where it creates a positive curvature. It also produces a positive gravitational lensing effect on the image of a distant positive mass m(+), making photons of positive energy φ(+) converging around the large mass. This large positive mass induces on the contrary a negative curvature in the negative sector. Hence, although being invisible, its apparent mass in the negative sector is felt as if it was negative.

• RIGHT: a large mass (red) belongs to the negative sector where it creates a positive curvature. Such a mass being in the negative sector, it appears as being invisible but induces a negative curvature in the positive sector. It produces a negative gravitational lensing effect on the image of a distant little mass

m(+), making photons of positive energy φ(+) diverging around the invisible but apparent large negative mass.