Evidence for an evaporating black hole?

Quantum field theory in curved space-time predicts that black holes have a finite lifetime, proportional to the mass of the black hole. The larger the black hole, the longer it takes to evaporate. This prediction is widely believed because of the theoretical plausibility of the connection it makes between thermodynamics and curved space-time, but it is, nevertheless, an unverified speculation. However, a team of astronomers analysing archive data from the Parkes radio telescope in Australia, have discovered a very short, but very powerful burst of radio-wavelength radiation, estimated to have originated from a source 3 billion light years away. The signature of this radio burst has never previously been seen, and, indeed, the sensitivity of many radio telescopes is insufficient to detect such short bursts.

The astronomers speculate that the radiation may be the 'last gasp' of an evaporating black hole. Personally, I wonder if it could just be a statistical fluctuation in the data...

Shut-up and calculate!

Mr Multiverse, Max Tegmark, wrote an article in New Scientist a couple of weeks ago, advocating once more the notion that the physical universe is nothing more than a mathematical structure. The 'director's cut' version of this article can now be freely downloaded.

I have much sympathy with Tegmark's position, but I would personally say that the physical universe is an instantiation of a mathematical structure, not a mathematical structure itself. It's the difference between an individual thing and a type of thing.

I would also question Tegmark's insistence that a final theory of everything should be bereft of any interpretational 'baggage', by which he means not only observational and experimental terms and phrases, but also non-mathematical theoretical terms such as 'mass' and 'charge'. How does this work when a theory has multiple mathematical formulations, as is generally the case? For example, in quantum theory, the state of a system can be represented by a vector in a Hilbert space in one formulation, and by a positive normalized linear functional upon the self-adjoint part of a C*-algebra in another formulation. If we are to literally equate the state of a system with part of a mathematical structure, from which formulation are the structures to be taken?

Naked singularities

Exactly how shy is the universe? Does the universe permit naked singularities? It seems that there may now be an observational means of answering this question.

To understand what a naked singularity is, it is first necessary to recognise that space-time singularities come in two forms: spacelike singularities and timelike singularities. The former are consistent with determinism, whilst the latter are not. Even if one specifies the state of the entire 3-dimensional universe at a moment in time, if timelike singularities exist, then the state of the universe at a moment in time is insufficient to predict what will emerge in the future from the timelike singularity. Note that the Schwarzschild space-time for a non-rotating, electrically neutral black hole, and the corresponding space-time for a white hole, both possess spacelike singularities.

However, the maximally extended Kerr space-time for a rotating black hole contains a timelike singularity. Whilst this is strictly inconsistent with determinism, those Kerr space-times which possess a physically realistic angular momentum, contain an event horizon which prevents the unpredictable output from the singularity reaching the outside world. In contrast, a naked singularity is a timelike singularity which is not confined within an event horizon.

The family of Kerr space-time solutions to the Einstein field equations are such that the event horizon disappears if the angular momentum-to-mass ratio exceeds a certain extremal value. Arguments have thus raged for some years over whether a naked singularity could form by a physically realistic process, or whether it is merely a theoretical artifact.

Arlie Petters (Duke University) and Marcus Werner (University of Cambridge) now suggest that the space-time of such a rapidly spinning, naked singularity, would form a distinctive gravitational lens, enabling astronomers to spot such an object, if it exists, in our own galaxy.