Are Black Holes Really Black?

The history of black holes is fraught with controversies and twists and turns. Black holes are supposed to be places where information is lost, where the known laws of physics will break down and will cease to apply. Nobody can say with certainty what will or will not happen inside a black hole. Therefore the existence of black holes has been contested and even resisted by those physicists who still try to retain what has been called the Newtonian or classical viewpoint of sceintific determinism, according to which once we know the angle, spin, position, mass, and velocity of an object, its pathway through space can always be precisely determined. Of course, the finding of quantum mechanics has already dealt a severe blow to such Newtonian or Laplacian determinism  because according to Heisenberg's principle of uncertainty, in quantum mechanics, only the probability that a particular event will happen at a specific point in time is certain and determined such that the more certainly we know about the position of a particle, the more uncertain will we know about its momentum and vice versa. When anything is sucked into the black hole, even the certainty of the operation of the wave functions of quantum mechanics may become inapplicable because, like everything else, they too will be sucked into the huge force of gravity of that unknown and unknowable black hole. All the information contained they contain will be lost too!

 

In 1976, Stephen Hawking announced that black holes may not be completely black because black holes may also emit radiation. The uncertainty principle has already taught us that even what was previously regarded as the vacuum of empty space may not be truly empty: it is teeming with the frenzy of quantum jitters of virtual particles momentarily erupting into existence and then as quickly got annihilated by each other. This kind of activity may also occur just outside the "event horizon" of a black hole.  There, the force of gravity might inject energy into a pair of virtual photons and tear them just far enough apart that one of them will get sucked into the black hole. If so, the remaining photon, having lost its photino to the abyss of the black hole, will no longer have a partner to finish off the normal mutual annihilation and might get a "push" from the force of gravity such that as its partner gets drawn into the black hole, it itself will shoot outward away from the black hole and therefore, to an observer watching from afar outside of the "event horizon", the feverish activity will appear as a steady stream of radiation emitting from the black hole. And the black hole may glow! Hawking shows that the strength of the radiation will be exactly the same as predicted by the laws of black hole physics and those of thermodynamics. Therefore even black holes may have entropy and may have a temperature! If so, black holes are not entirely black! Hawking's calculations show that the less massive a black hole is, the higher will be its temperature and the greater will be the amount of radiation it emits.  Radiation is a form of energy. According to Einstein's theory of relativity, energy and mass are interchangeable. That means that as energy escapes from a black hole, its mass will decrease. If so, even a black hole may evaporate with time! If it does so, then the distance from the centre of gravity of that black hole to the "event horizon" will also slowly shrink and when the Schwarzschild radius decreases, the regions of space formerly cut off by the "magic sphere" and included within that "magic sphere" may re-enter the perceivable cosmic space and again become visible. A question then arises. Will the information previously "swallowed" by the black hole re-emerge into the visible universe as the black hole evaporates? There is no consensus amongst physicists on what the proper answer should be.  According to Brian Greene, Hawking held that black holes destroy information forever but John Preskill of the CIT thinks that the information will re-emerge as the black hole radiates and shrinks. But whatever the truth may be, so far, scientists have been unable to detect such posited radiation from a low mass black hole!

 

At a lecture in Amsterdam in June 1997, Hawking acknowledged that as a result of the findings of string theory, there might be a way for the information to re-emerge because information can be stored and recovered from the constituent branes. But Andrew Strominger in an interview in December, 1997, thought that the conclusion may be "premature" and his colleague Vafa agreed. He said he was "agnostic" because it could turn out either way.

 

There is still another problem with black holes: what happens to spacetime at the centre of the black hole? According to Schwarzschild, the enormous mass and energy crushed together at the centre of the black hole will cause even space and time to be infinitely curved, if we can still trust the theory of relativity to be applicable and since once something has crossed the "event horizon", it will be irresistibly drawn towards that centre of the black hole and since nothing can travel faster than the speed of light, the time which has been sucked in, will also come to an end. But other scientists think that the possibility exists that there might be some "worm hole" through which something may escape into another "universe" such that when time in our universe comes to an end, the time in the next attached universe will just begin!