 No SingularityFor decades physicists have worried about the breakdown of the equations of general relativity that occur in the centre of a black hole.They have called this problem "the singularity". Relativistic physics appears to divide by zero - when modelling gravitational collapse! As astronomical objects which appear to be black holes have been identified, the problem has intensified. Several solutions to this problem have been proposed: One is to think that there will be repulsive forces that engage at some point. these may prevent a singularity from forming - or may prevent gravitational collapse from resulting in a black hole in the first place. However, so far observations of distant dense spinning objects, and particle accelerators have shown no sign of such a force. However, there is another pretty simple resolution to this problem that does not invoke any new physics that relatively few seem to appreciate to this day. This is the idea that the inside of black holes is outside this universe. The inside of a black hole - including its hypothetical singularity - does not exist. Nothing ever penetrates the black hole event horizon.
VideoI explain the idea on camera
QuotesThis idea has been promoted from time to time. For example:Nothing that falls into a black hole will ever reach the event horizon, so there is no information paradox. This is also true for the matter of the original star that formed the black hole. There is no singularity inside and, in fact, there is no inside. ...and...
Some people say that black holes are portals to other worlds or other dimensions, but good old mathematicians (as in people who dedicate there lives to math) know that there is nothing inside black holes. ...and...
As long as the black hole exists, the event horizon is always in the future of anything that falls inside. The moment anything reaches the event horizon is the moment when the black hole finishes evaporating and the event horizon disappears. So a trajectory into the black hole just comes out on the other side after what is a short time for an object following that trajectory (if your wavelength is longer, you might come out a little bit earlier).
Solution receptionHowever, this solution is still not widely accepted. It seems that few have given a convincing counter to the counter-argument that an infalling observer only takes a finite time - as measured by a clock they are carrying - to cross the event horizon.The solution to that seems pretty obvious - at least to me. By the time the infalling observer reaches the event horizon, the black hole has evaporated. This happens because of relativistic time dilation - which slows the passage of time for those near to black holes - a relatively well-understood effect. So: the infalling observer never reaches the horizon - because the hole evaporates before it is reached. To quote from the "What happens to you if you fall into a black hole? document: "If the black hole is mortal, you'll instead see those events happen closer and closer to the time the black hole evaporates. Extrapolating, you would calculate my time of passage through the event horizon as the exact moment the hole disappears!" Exactly. In-falling observers never reach the event horizon. Nor does anything else. Black holes evaporate before anything ever reaches their "horizon". There are a number of fancy explanations of why observers can go through - but these all appear to be nonsensical rationalisations. New Scientist has had a [good explanation] of all this on its site by Andreas Keller. The article is dated 2nd December 2006. Alas, these days the page is only available to subscribers. Fortunately, the idea was written up formally by Tanmay Vachaspati, Dejan Stojkovic and Lawrence Krauss in 2007 - in a paper entitled Observation of Incipient Black Holes and the Information Loss Problem - which is available online. This paper was all over the news as solving the black hole information loss paradox. Also, Lawrence Krauss is a celebrity physicist - which probably helped to promote the paper. Though he has been described as "the Woody Allen of cosmology". Anyway, so far, few people seem to have absorbed these results. To quote from the paper:
The infalling observer never crosses an event horizon, not because it takes an infinite time, but because there is no event horizon to cross. ...and...
Here we find that the shell, even as it collapses, radiates away its energy in a finite amount of time. With some assumptions about the metric close to the incipient horizon, we conclude that the evaporation time is shorter than what would be taken by objects to fall through a black hole horizon. This leads us to the conclusion that the asymptotic observer will see the evaporation of the collapsing shell before he can see any objects disappear. This solution is somewhat related to the idea of Eternally Collapsing Objects (ECOs). Alas, these seem rather mis-named - they do not really collapse "eternally" - because they eventually evaporate. For more details about them, see the references below.
HypothesisMy hypothesis about what happened is that physicists calculated the finite subjective time to the event horizon for an infalling observer before it was known that black holes evaporate.This went into the textbooks, and was not properly revisited once it was widely appreciated that black holes were thermodyanamic entities that radiate heat - and so are likely to eventually evaporate. This situation was not properly cleared up until around 2006.
Fall outHawking radiation is utter nonsense. Nothing ever falls into a black hole in the first place, no nothing ever needs to escape from one. Holes evaporate due to perfectly ordinary thermal radiation generated by the process of spaghettification.The hypothetical Singularity at the centre of a black hole is no longer inside the universe - and so does not cause any problems. The Black hole information loss paradox is trivially resolved. No information is lost inside black holes - since no information ever enters into black holes in the first place. The No-hair theorem is nonsense. The Event horizon does not exist, never forms, or remains infinitely far away - depending on how you look at it. It is never observed or reached by any kind of observer - and nothing ever penetrates it. It is true that there is a region that is separated causally from the rest of space and time. However, that region is not part of the universe. Since it is not part of the universe, there is an important sense in which it does not exist. Nothing ever penetrates such regions. The Penrose–Hawking singularity theorems turn into argments reminiscent of angels dancing on the head of a pin. Naked singularities are nonsense. The cosmic censorship hypothesis is not needed. The black hole "inner horizon" is an unnecessary concept. The fancy stories about black holes as wormholes are not needed either. What about the whole concept of a black hole itself? The original idea was of a dark object - that not even light can escape from. However, matter can escape from the objects under discussion - so they are not really "black". I expect that we will keep the "Black hole" terminology for these objects. It has already survived the discovery that these objects emit radiation. The name is not really right - but it is well established, and is not too far from the truth.
Experimental testsThe model described here uses standard relativity theory, with no changes. It makes all the same predictions. As many people know the gravitational force on the surface of a planet is the same as if its mass was concentrated at its centre. The same idea means that a black hole has the same gravitiational field irrespective of whether its mass is on its surface, or concentrated at its centre.This model proposes that Hawking radiation is nonsense: black holes radiate due to ordinary thermal processes. However, both hypotheses concerning the radiation apparently predict something close to black body radiation - which for a black hole means a very low intensity of radiation. The details may differ - see the [Vachaspati/Stojkovic/Krauss paper for how - but we would probably need a small artificial black hole to look for any differences experimentally. The New Scientist coverage in 2007 - Do black holes really exist? - suggested the need for expermental tests. However, this rather misses the point. The "singularity" interpretation arises not from a different theory or observations - but from doing the maths in existing relativity theory incorrectly. Correct calculations with the existing theory show that nothing ever penetrates the black hole event horizon - and so black holes do not have an inside. Of course, it remains possibile that the existing gravitational theories are wrong - but for the moment, we should probably take them seriously until we have something better.
The traditional black hole theory is nonsense"Conventional" black hole theories postulate a singularity where the laws of physics break down. It combines two reversible theories (GR and QM) to produce an irreversible event horizon - which things can fall into, but can't come out of. It postulates a hypothetical partitioning of spacetime and matter into causally disjunct regions with incredibly poor supporting evidence. It has external and infalling observers observing different temporal sequences. In short, the theory is rather obviously a load of nonsense - which nobody should have seriously entertained in the first place.
ReversibilityBoth general relativity and quantum mechanics are reversible theories - except at general relativity's "singular" points. Combining these two theories and getting a microscopically irreversible outcome at the event horizon is a clear sign that you have made an elementary mathematical mistake. A hole that things can fall into - but not out of - is not a possible solution to this type of math problem - since it violates microscopic reversibility. In the correct interpretation, reversibility is maintained everywhere.It may be true that more things move towards black holes than move away from them. However, that is due to the second law of thermodynamics. The same law that explains why more meteorites land on the earth than levitate away from it. That is macroscopic - not microscopic - irreversibility - and that is perfectly acceptable.
The Bekenstein boundConventional ideas about black holes violate the Bekenstein bound if applied to the interior of a black hole. They produce a point of infinite density - the hypothetical singularity - where the laws of physics are supposed to break down. In the correct interpretation, the Bekenstein bound holds. Black holes expand as more matter falls towards them - and the Bekenstein bound is approached near the event horizon - but never reached.The idea that the matter of a black hole is concentrated on its surface combines neatly with the idea that there is an upper limit to the density of matter in the universe to explain why the mass of a black hole is proportional to its surface area. That fact is mysterious under the interpretation that the mass of a black hole is concentrated at its centre - but simple and obvious if the mass is concentrated on its surface.
Hawking's mistakeHawking realised (correctly) that black holes would have a temperature, and so might evaporate if left in a dark place for long enough. He tried to reconcile general relativity with quantum mechanics. However, he didn't take general relativity seriously enough. In general relativity, space-time curves. Hawking didn't apply quantum mechanics on the curved space - or he would have found that nothing ever got near the event horizon. That seems likely to have been a mistake. Take the space-time curvature of general relativity seriously, and the event horizon remains at infinity - and so there is no Hawking radiation.Vachaspati, Stojkovic and Krauss honour Hawking in their paper - describing the radation that is produced by black holes as "pre-Hawking radiation". However, that radiation is really perfectly ordinary - and has nothing to do with Hawking's proposed mechanism of black hole radiation. I think it is better to recognise that Hawking's idea was a terrible mistake - one that has caused confusion and problems for decades - and to put some appropriate distance between his ideas and the correct interpretation.
Physics scandalThat physicsts entertained these awful ideas for so long seems to be quite an embarassment.It seems at least as embarassing as the Copenhagen "collapse" hypothesis. The Copenhagen situation illustrates that there is a precident for physicsts seriously entertaining terrible ideas for extended periods of time.
2015 updateIn 2014, Hawking published Information Preservation and Weather Forecasting for Black Holes. His new proposal features no singularities or "event horizons behind which information is lost". It represents an endorsement by Steven of many the main ideas which had been published here years before.
ReferencesEternally collapsing objectsWikipedia articlesGravastars - a different, not so promising hypothesisMore hole scepticism (pretty confused, IMHO) |