The general theory of relativity is a complex mathematical theory, but its description of black holes is surprisingly simple. A stable black hole can be described by only three properties: its mass, electric charge and rotation. Since black holes are unlikely to have a large charge, in fact, only two properties are required. If you know the mass and rotation of a black hole, you know everything you need to know about a black hole.
This property is often generalized as a theorem. In particular, the theorem states that once matter falls into a black hole, the only characteristic that can have is mass. In any case, the Event Horizon of the black hole is completely smooth, without any additional features.
But for all its strength, the general theory of relativity has a problem with quantum theory. This is especially true of black holes. If the previous theorem is correct, then the information about the object inside the black hole is destroyed when the object crosses the event horizon. Quantum theory states that information can never be destroyed. Thus, the real theory of gravity contradicts the real theory of quanta. This leads to problems such as the firewall paradox, which cannot decide whether the event horizon should be hot or cold.
To resolve this contradiction, several theories have been proposed, often including extensions to the theory of relativity. The difference between the standard theory of relativity and these modified theories can only be noticed in extreme situations, which makes their observational study difficult. But a new article in Physical Review Letters shows how they can be studied through the rotation of a black hole.
Many modified relativity theories have an additional parameter that is not in standard theory. Known as a massless scalar field, it allows the Einstein model to connect to quantum theory in such a way that it does not contradict each other. In this new work, the team investigated how such a scalar field is associated with the rotation of a black hole. They found that at low speed, the modified black hole is indistinguishable from the standard model, but at high speed, the scalar field allows the black hole to have additional characteristics.
The theory of Einstein’s general theory of relativity has so far passed all the tests in the field of observations, but most likely it will collapse in the most extreme conditions of the Universe. Studies like this show how we could discover the following theory.