Thursday, February 22, 2018

Intriguing black hole research

A paper came out in January talking about that old black hole chestnut - the breakdown of physics inside of them, and the cosmic censorship idea that we'd never know about it anyway.

Here's an explanation of the paper from some physics site I'm unfamiliar with, and I'll extract the first couple of paragraphs:
Is the future predictable? If we know the initial state of a system exactly, then do the laws of physics determine its state arbitrarily far into the future? In Newtonian mechanics, the answer is yes. Similarly in electromagnetism: if one knows the initial state of the electric and magnetic fields exactly, then Maxwell’s equations determine their state at any later time. In quantum mechanics, if the initial wave function is known exactly, then Schrödinger’s equation can be used to predict the wave function at any later time. However, new research by Vitor Cardoso from the University of Lisbon, Portugal, and colleagues [1] suggests that this predictability of the laws of physics can fail in general relativity. The researchers find that it might be possible for a star that undergoes gravitational collapse to form a black hole containing a region in which physics cannot be predicted from the initial state of the star.

General relativity asserts that spacetime is dynamical, with its dynamics dictated by Einstein’s equation. Just as the initial state of a particle is specified by its position and velocity, an initial state for spacetime is specified by the geometry of space at some instant of time, as well as by its rate of change. Given such initial data, a fundamental theorem in general relativity [2] states that there is a so-called maximal Cauchy development. This is the largest spacetime that is uniquely determined by the initial data. But is it all of spacetime? In other words, could the maximal Cauchy development be a subset of a larger spacetime? By definition of the maximal Cauchy development, this larger spacetime could not be predicted from the initial data. This scenario would represent a failure of determinism: one would not be able to use the initial data to predict the state of spacetime arbitrarily far into the future.
 Another article trying to explain it (and I suspect, not as accurately) is here.

One thought that is not mentioned in either paper - could this potentially tie in, in any way, with the idea that our universe is actually inside of a black hole?    If so, could it be a way in which our universe is not deterministic?   Just a thought....

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