Saturday, 1 February 2014

Hawking, Black Holes and Evolving Universes

Stephen Hawking: "There Are No Black Holes" - Nature

When one of the creators of the Black Hole theory questions one of the fundamental principles of black holes, people take notice.

Stephen Hawking has just published an online paper entitled Information Preservation and Weather Forecasting for Black Holes, which has yet to be peer-reviewed, in which he casts doubt on the idea that nothing can escape from a black hole and that all information about the matter which falls into one will be destroyed. He didn't actually say what the over-simplified headline implies but he does question whether they are truly black.

The assumptions behind the idea of a black hole are assumptions of Einsteinian relativity - that a sufficient large mass will collapse under its own gravity to form a singularity of near-infinite density and near-zero volume. However, below a certain size, the laws of quantum mechanics apply, not those of relativity, and so far it has proved difficult to reconcile these two theories into one Grand Unified Theory - the present holy grail of theoretical physics.

There is no escape from a black hole in classical theory, but quantum theory enables energy and information to escape.

Stephen Hawking, University of Cambridge, UK
Hawking's new thinking concerns the so-called 'event horizon' which is, in relativity terms, where the velocity of light just fails to be sufficient for it to escape from the gravity of a black hole. Crossing the event horizon was believed to be a one-way process. However, this is also where relativity gives way to quantum mechanics and Hawking now says the quantum fluctuation in the event horizon will be so wild that there is no definite horizon.

Hawking has attempted to reconcile the event firewall phenomenon with relativity. The firewall was discovered two years ago by theoretical physicist Joseph Polchinski of the Kavli Institute and his colleagues, who realised that this quantum fluctuation would create an effective firewall around a black hole. This firewall conflicts with relativity which says the laws of the Universe apply everywhere in the Universe so a hypothetical astronaut falling into a black hole would not notice anything unusual. This firewall would certainly be noticeable.

The picture Hawking gives sounds reasonable. You could say that it is radical to propose there’s no event horizon. But these are highly quantum conditions, and there’s ambiguity about what space-time even is, let alone whether there is a definite region that can be marked as an event horizon.

Don Page, Physicist, University of Alberta in Edmonton, Canada
What he now proposes is an indistinct 'apparent' horizon in which matter attempting to escape the black hole is held suspended. In the 1970s Hawking showed the black holes can evaporate by 'Hawking Radiation' as pairs of virtual particles forming on the event horizon can have one inside the horizon which can't escape, and one outside the horizon which can. They are thus unable to mutually annihilate, leaving one particle to become real and so radiating a small quantity of the mass of the black hole away.

This radiation still occurs so, unless they take in more matter, black holes shrink over time. This means that black holes can no longer be regarded as things from which no matter can escape and in which all information is destroyed, because a shrinking black hole will also shrink its apparent horizon, releasing the suspended matter.

To me, this is where things start to get really interesting.

In 1992, theoretical physicist Lee Smolin proposed in his book, The Life of the Cosmos, the possibility that universes evolve by Darwinian evolution by arising inside a black hole of a 'parent' universe. This mechanism is also supported by theoretical physicist, Lawrence M. Krauss. This would mean that universes that are good at making black holes are also good at making new universes.

Darwinian evolution is inevitable if three conditions apply:

  • Inheritance of information.
  • Imperfect replication of that information.
  • Differential selection of those variants.

It would be delicious to think that a mechanism proposed in the infancy of modern biology, and which has been called one of the most profound in all of science, were to be the one which best explained why there are living things to evolve in the first place.

Now, as Victor J. Stenger has pointed out in his book, The fallacy of Fine Tuning, where he systematically dismantles the creationist notion that the Universe is so finely tuned for life to exist that the possibility of this being so without the intervention of their magic friend is almost zero, that this Universe has almost certainly produced more black holes than it has human beings. It would therefore be more sensible (and more honest) to argue that, if the Universe is designed for something it is designed for making black holes. The fact that the right conditions for allowing long-chain carbon molecules to form on a planet where water exists in its three physical states around a sun which has been radiating energy for long enough for life to evolve, are those which also allow black holes to form, is fortuitous but nothing more than that. In short, living things are a byproduct of making black holes. And how could we be discussing it in a Universe in which it were not so?

But Smolin's evolving universes theory suffered from one major obstacle which some saw as insurmountable. If all information was destroyed in the replication process, the information which set the initial conditions so the baby universes could produce black holes like their parents did could not be inherited. It was left as a tantalizing possibility pending it being shown that there was some way information could pass through the t=0 conditions in a Big Bang and into the newly formed universe, to be passed on again to a descendant universe. Without inherited characteristics, Darwinian evolution is impossible.

If Hawking's new thinking is accepted and all information is not destroyed in a black holes, that objection to Smolin's proposal will have been removed.

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2 comments :

  1. Maybe it's a quibble, but the only way an astronaut could fail to notice a change if he fell into a black hole would be if said astronaut was a dimensionless point.

    Here's what I wrote on the subject back in 2011:

    Hollywood movies apart, no astronaut would be advised to try and dive into a black hole. Let’s suppose someone fell into one feet-first. As this intrepid (and suicidal) adventurer fell, the gravity around his feet would be many times greater than the gravity at his head, because his feet are closer to the black hole and the distance between them and his head would mean that the gravity affecting his feet is greater by the square of his height (the Inverse Square Law, again). This is true of all gravity, but most gravitational fields are so weak that it doesn’t matter. However, since the gravity well of a black hole is so strong, the difference in pull along the length of his body would stretch him out like a piece of chewing gum; as he fell into the event horizon, he’d be drawn into something resembling a thread, hundreds of kilometres long.

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    Replies
    1. I think time differences due to these differences in gravity take care of that. Although to an outside observer he may appear to stretch out with the spaghetti effect, to his head and feet, because time slows closer with higher gravity, they appear to be moving at the same speed.

      Of course, an outside observer would not be able to observe anything inside the classical event horizon, but you know what I mean. :-)

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