Monday, November 25, 2013

A skeptical view of black holes

A reader writes:
I am skeptical about black holes, because they involve infinity. There is an opinion that they don't actually solve Einstein's equations.
There is a lot of evidence for black holes, where they are defined:
A black hole is a region of spacetime from which gravity prevents anything, including light, from escaping.
Belief in such objects dates back two centuries, and has little to do with relativity. If the mass is sufficiently concentrated, the gravity will be sufficiently strong to contain light.

Relativity teaches that the black hole has a boundary, called the event horizon or Schwarzschild radius, and a singularity at the middle. Furthermore, nothing inside the event horizon is observable to anyone on the outside. In particular, the singularity is not observable.

Physics has other infinities that are not observable. For example, the electron is widely assumed to be a point particle, in which case it has infinite density, and the charge concentration gives it infinite energy. These infinities are not observable, and the usual explanation is QED renormalization.

Getting back to my reader's comment, does a rational skeptic really need to believe in physical infinities that can never be observed? I say no. I believe in black holes right up to that event horizon. Discussion of what happens inside the event horizon is just metaphysical fluff that is outside the scope of science. You can say anything you want, and no one can ever prove you right or wrong. Not even in principle, according to relativity.

Likewise, there is no real reason for anyone to believe in the electron infinities. The infinity renormalization schemes may be the most convenient way to calculate electron scattering, but there could well be new physics on other scales to prevent the infinities, such as string theory. As long as the infinities are not observable and not truly required by the theory, there is no reason anyone has to believe in them.


  1. Physical Points are not something you can ever observe except diagrammatically, they are not actually real, by definition they have no physical extension at all, and can be assigned no numeric value. A point particle can have no physical extension and thus, no actual physical movement or momentum/mass, much less physical collision, is possible without contradiction of all said terms by definition. A mathematical point is a numerically diagrammed point, and is not equivalent to a physical point, as it must (by definition) have at least one dimension (a distance from zero) which should be a warning sign right there that it is always at least one dimension removed from actual equivalence with a physical point in reality. You can also assign as many dimensions as you like to your mathematical point, doing so just reinforces the fact that your mathematical point is not equivalent to a physical point, and has no relation to describing a physical point in reality.
    "There is a lot of evidence for black holes where they are defined..." which means only in avid speculation. Relativity teaches no such thing as 'black hole event horizons', David Hilbert did with his mucking about with empty space time containing no matter. Black holes only have been shown to exist within science fiction and Ric=0 spacetime mathematical spaces (in which there is no matter, which is meaningless even as a model). Please read or listen to Stephen J. Crothers before bringing up the Schwarzchild radius as almost no one in physics knows or can agree with what it 'r' really is, and most are just parroting each other because of what they were taught in school, not because they understand its definition or derivation. There are over a dozen contradictory definitions of what 'r' is, and all of them wrong. You are also confusing a 'Black Hole' (which is specifically defined within a highly non-linear framework of Einstein's GR) with the over two hundred year old 'Black Body' (which is also specifically defined within a linear framework of Newton's gravity equations). As a thought experiment or concept, one of them can have an escape velocity, the other can not, one is based on the flawed logic of a singularity, the other is just an extremely dense gravitational object of measurable size. They are not equivalent concepts, Mr. Crothers goes to great pains to explain why, and the fact that most in physics are blithe to the differences explains much of the confusion.