Thursday, April 12, 2007

Black hole science - interpretation needed

Regular readers know that I scan papers appearing on arxiv about black holes. They are often not easy to understand, to say the least. In fact, I half suspect that even other scientists outside of very narrow fields may find it an effort to follow most papers too. Here's a couple of recent examples:

The existence of closed timelike curves (CTCs) presents a clear violation of causality. In some cases these CTCs can be disregarded because to have them one ought to have an external force acting along the whole CTC, process that will consume a great amount of energy. The energy needed to travel a CTC in Godel universe is computed in [1]. For geodesics this is not the case since the external force is null, therefore the considerations of energy does not apply in this case and we have a bigger problem of breakdown of causality.

Following so far? Well, no, nor am I, but it sort of sounds significant, doesn't it? This was just the introduction to the paper, which actually found this:

In the present work we study the existence and stability under linear perturbation of CTCs in the spacetime associated to slowly rotating black hole (BH) pierced by a spinning string. We find that presence of the black hole makes possible to transform the CTCs present in the spinning string metric alone that are stable into CTGs. We also find sufficient conditions to have stable CTGs. This conditions are not very restrictive and can be easily fulfilled.

So, I gather that they think they have found a way that something which violates causality can be made around a black hole. If you are looking for some actual interpretation of what this means in real life, in language anyone can understand, it ain't in the paper.

Here's another obscure paper that may, or may not, be significant.

A new theorem for black holes is established. The mass of a black hole depends on where the observer is. The horizon mass theorem states that for all black holes: neutral, charged or rotating, the horizon mass is always twice the irreducible mass observed at infinity. The
horizon mass theorem is crucial for understanding the occurrence of Hawking radiation. Without black hole radiation, the Second Law of Thermodynamics is lost.

I have no idea what they are talking about, but in the paper, the authors use an exclamation mark, which means it must be significant (I think):

In each case, we found that the horizon mass is always twice the irreducible mass observed at infinity. The conclusion is surprising. The electrostatic energy and the rotational energy of a general black hole are all external quantities. They are absent inside the black hole!

This is also said to be relevant to Hawking Radiation, a matter of continuing interest due to the heavy reliance on it by the CERN people in figuring out what micro black holes will do.

By the way, the engineers and scientists at CERN made a mistake that recently caused a bit of a bang:

A £2 billion project to answer some of the biggest mysteries of the universe has been delayed by months after scientists building it made basic errors in their mathematical calculations.

The mistakes led to an explosion deep in the tunnel at the Cern particle accelerator complex near Geneva in Switzerland. It lifted a 20-ton magnet off its mountings, filling a tunnel with helium gas and forcing an evacuation.

Let's hope they do their work on what happens to micro black holes a bit more carefully.

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