João Lopes Costa, a professor at ISCTE-IUL and researcher at BRU-IUL, who is member of an international team of mathematicians and physicists, has studied black holes in an expanding universe. The results, published in an article in Physical Review Letters, show that, using Einstein's theory of general relativity, it is not always - under specific conditions - possible to determine the future of space-time within these black holes.

The work shows that black holes - astrophysical objects that can be generated by the implosion of stars - must, in extreme situations, contain a region where the physical conditions are not fixed by their initial state. This idea goes against the conjecture of the Strong Cosmic Censorship, which stipulated that there is an intrinsic determinism in calculating the exact state of a physical system at any point in the future, as long as we know its initial state perfectly. Thus, given the theory of general relativity: a precise knowledge of space geometry and its tendency to change in the present, we are able, at least in theory, to predict exactly how space-time will develop. Due to this causal relationship, Einstein's theory is considered by most physicists to be deterministic.

From the theoretical point of view, it is expected that what Einstein called singularity should be formed within a black hole, derived from the destruction of the "Cauchy horizon". As the British physicist Roger Penrose explained in the 1970s, a mechanism within general relativity - a censorship - made it impossible to create Cauchy horizons. In the case of an electrically charged black hole, Penrose calculated that even a small disturbance in the initial conditions of the star in the implosion would eventually destroy the Cauchy horizon and thus produce a singularity.

As João Lopes Costa explains, this rule is now called into question, as under some circumstances the singularity imposed by cosmic censorship is not formed. The researcher's team considered that the net effect of two opposing influences on the Cauchy horizon - the amplification of any small disturbance by the immense gravity of a black hole, on the one hand, and the dampening effect of the external environment of the black hole, on the other. The results show that, in fact, a singularity appears on the Cauchy horizon in most cases, as expected. However, sometimes (when the black hole is highly electrically charge) the Cauchy horizon remains intact... that is, Einstein's theory seems to be unable to predict the future in some situations!

While not being a common area of ​​study at ISCTE-IUL, it is extremely important that we can contribute to a better understanding of the Universe!

See the article here.