Black holes remain an object of mystery for both experts and millions of science fans. Let us dig a little dipper into the unknown in this review. Experts do not understand the state of matter at the centre of a black hole, although it appears more certain (although not entirely certain for all black hole masses, according to some quantum gravity models such as asymptotic safety) that black holes should exist. According to a new review just published, Dr Pinochet mentions: "Given the great interest that black holes arouse among non-specialists, it is important to analyse misconceptions related to them. According to the author, the most common misconceptions are that: (1) black holes are formed from stellar collapse; (2) they are very massive; (3) they are very dense; (4) their gravity absorbs everything; and (5) they are black."
Black holes, almost certainly appear to exist at all sizes both in theory and according to observations. (A black hole hasn't been created at the lab yet as the energies required are too high). In particular we know about mini black holes with the size of an atom, stellar sized black holes, and huge black holes at the centres of the galaxies. Among these 3 categories, there exist strong indirect observational evidence for the last two categories, but mini black holes haven't yet been observed (according to theory they should have a very short lifespan and evaporate emitting gamma rays). Neither of course LHC succeeded in producing mini black holes, although there was a hope according to some theories.
In theory it is certain, (at least according to Einstein's theory) that if there is a strong enough force, this force could compress any amount of matter into a black hole, even if this amount of matter was to be a single proton. Since, according to our current understanding all black holes evaporate - with time being proportional to their mass - they should not be considered really "black". If the whole Universe could transform into a black hole somehow, this would mean (apart from the unknown physics), that the law of increasing entropy would be violated. Therefore the law of thermodynamics appears to be more powerful than the unknown physics and it seems that black holes evaporate and obey the law of entropy which wants the Universe to become a more and more chaotic system. The second law of thermodynamics itself is the theory of Big Bang. It predicts an initial state of maximum order. Cosmological observations confirm (entirely independently), that the Universe is expanding with acceleration, which again confirms the second law of thermodynamics, or perhaps the second law of thermodynamics is awarded one more Nobel prize for predicting the observations of supernovae of 1998, which proved that our Universe is expanding with acceleration, and hence it will never collapse again forming loops of expansion and contraction. Although there exists a huge pile of unknown physics, it depends on our intellect to set aside the principles that should certainly hold true under any conditions, even at the most mysterious parts of the Universe, and let these principles to safely guide us into the deepest parts of the unknown.