Imprimir Republish


Taming black holes

Rio de Janeiro physicists propose an experiment that could help to review the basic laws of the universe

INSTITUTO DE ASTROFÍSICA DE CANÁRIASRepresentation of a black hole: in search of the limits of gravity and the subtleties of the universeINSTITUTO DE ASTROFÍSICA DE CANÁRIAS

The recipe for the creation of a laboratory of one of the most fascinating cosmic structures is ready: black holes, gigantic compacted masses, coming from the collapse of stars, with gravitational attraction so intense that they absorb all in their surroundings, including light. With relatively simple materials – a type of Van de Graff generator, a device that generates static electricity, and, when touched, makes your hair stand on end, and a special type of plastic capable of reflecting light -, physicists at the Brazilian Center of Physics Research (CBPF), in Rio de Janeiro, are guaranteeing that the black holes, according to a proposal that they themselves have put together, could be tamed. Not to suck in material, but to trap light, and by analogy, this would permit a more detailed understanding of how similar cosmic bodies operate, whose properties turn them even more difficult to study because of the distance at which they are found – the true black hole nearest to us can be found in the center of theMilky Way, around thirty thousand light years from the Earth.

The prospect of turning black holes more friendly much like a modern car, is a form of reviewing the laws of physics. The processes that occur in the interior of these structures are extreme examples of interactions between elementary particles, practically impossible to be visualized in particle accelerators, in which the gravitational attraction between the particles can be disregarded. From this point one can explain the worldwide race to see who can be the first to tame black holes and it is estimated that the experimental results should be produced in a maximum period of five years.

In January, the physicist Ulf Leonhardt, from University of Saint Andrews, in the United Kingdom, published in Nature his proposal for the creation of an artificial black hole, founded on the so-called catastrophe quantum theory, a form of the dispersion of light that explains the most trivial phenomena, such as the rainbow. In a more recent proposal, published electronically in May, William Unruh, from the British Colombia University in Canada, showed how one might make sonorous black holes, capable of capturing sonorous waves, which would also demonstrate the power of these cosmic objects.

But almost four years ago, in November of 1998, there were two Brazilians, Mario Novello and José Salim, from the Cosmology and Experimental Physics Laboratory of Atlas Energies (Lafex) of the CBPF, who published in the Physical Review D a proposal for the creation of artificial black holes of the electromagnetic and non-gravitational type, capable of absorbing photons – light particles – that are close to them. During 2000, the mechanism suggested by the Brazilians was given in detail in another article published in Physical Review D – and there is yet another paper on its way, written in conjunction with researchers from the Federal University of Itajubá, Minas Gerais.

Distinctive proposals
“Novello’s research complements my own and can be adjusted with perfection to the exciting area of the study of artificial black holes”, says Leonhardt. The Swedish researcher appeared at a seminar sponsored by the CBPF in October of 2000 and assisted in a lecture given by Novello about the effects of quantum vacuum on an electromagnetic field, which was shown to be decisive for his very own work. Quantum vacuum, far from representing a simple empty space, is a space in which sub-atomic particles collide, appear and disappear constantly. In Novello’s opinion, the languages adopted under the two possible situations are different: the Swede is a physicist who studies the quantum state of materials, concerned with the detailed behavior of atomic structures, while the Brazilians stick to the study about the behavior of photons in quantum vacuum.

Leonhardt’s experiment involved the use of an ultra cold gas or crystal, which can remain transparent according to the type of light shone upon it – it is what is called induced electromagnetic transparency. By shining over this material different quantities of light, it is possible to create a non-transparent region in the central part and regions that are more transparent on the periphery. Another ray of light, on striking at an angle within the material, is going to propagate and reduce its velocity, until it completely stops when the material has become opaque. This region simulates, in electromagnetic terms, the effect of event horizons, the limit of a black hole, on the ray of light.

“I prefer the language of the structure of space-time, which allows for a re-formulation much deeper than the simple triviality of the process of the construction of a black hole”, says Novello. Essentially space-time is the means through which the events occur, as well as making up one of the key concepts of the Special Theory of Relativity, formulated by the German physicist Albert Einstein (1879-1955) at the beginning of the last century. By following along this trail, the CBPF research group is inquiring into the fundamentals of the theory of gravity in its geometrical aspects, untouched for over a century.

In the black hole project, the CBPF team are exploring the consequences of research through the propagation of luminous waves carried out by another German physicist, Werner Heisenberg (1901-1976), during the 60’s. Normally the photons propagate themselves in a linear fashion, without depending on the means through which they travel, according to the routes defined by the universal laws of gravity, which are true for any body in the universe, from atomic particles to stars.

Abnormal behavior
However, Heisenberg’s studies indicated that, as a consequence of oscillations in quantum vacuum, when the energy and other properties of an electrical field vary, over a very short time interval, the photons behave in a different manner: they act upon the environment that they pass through and modify it; in compensation, the environment acts upon the photons, in a type of interaction. This is the so-called non-linear behavior, through which the light particles detect a species of additional covering on the earth, denominated metric effect, and they distinguish this additional covering from the gravity covering, defined as a curvature of space in the Theory of Relativity.

“As well as the curvature of space, brought on by gravitational attraction, which follows universal laws, the photons perceive an additional curvature, drawing forth a new geometry of the world, to complete the description given by Einstein”, clarifies Novello. “This additional curvature of space is only felt by the photons, as if for them time-space were not the same thing. Therein lies the clue jumped upon by the Brazilian researchers: “If photons in non-linear situations lead to an additional modification of the geometry of the world, it is probable that one of these modifications imitates a black hole.” From this conclusion, it would be enough to simulate in the laboratory the situations in which the photon behaves in an anomalous manner – or non-linear as the physicists say – and, everything going well, one will reach the approximation of a black hole.

One of the ways for observing the exceptional behavior of photons would be through an experimental apparatus with a dielectric fluid – so called because it would be capable of modifying the trajectory of the light. Water itself manages to deviate light: a knife inside a glass of water appears to be broken because the propagation of the photons in the air and in the water take place in a different manner. But both in the water and in the glass and in the organic crystals, which also demonstrate this property, the intensity of their action does not depend on the value of the electrical field to which they are submitted.

Reviewing Einstein
In a different way, the experiment presupposes a dielectric fluid whose reply varies according to the intensity of the applied electrical field – for this reason called a non-linear type. This viscous liquid – a solution with polarized polymers (molecules with two poles, one negative and the other positive) – does the same thing as the water with the knife, but with light. As yet the cost of the prototype that they wish to construct is uncertain – it depends on the characteristics of the materials, to be defined by another group of physicists, the experimentalists.

The physicists from Rio are convinced that the work is worthwhile because with it they may effectively question the pre-suppositions of the Theory of Relativity proposed by Einstein. For the German scientist, the universe is a model of a space curve, and the curvature is brought about by the mass of the stars. It is as if we picked up a very soft rubber sponge, representing the universe, and in its center we placed a lead ball that would be our Sun. The mass of the ball makes the sponge sink and form a depression in its surroundings. If one now picks up a smaller ball, this is symbolizing the Earth. If it is launched in the direction of the lead ball, starting from a certain distance it is going to move around lead ball following the line of depression that it has brought about. For Einstein, it is this curvature of space that explains the action of gravity. For the physicists who want to build a black hole, there may well be a lot more subtleties in the universe.