I'd been intending to put up a geek post about this but I'd been holding off until that fuller explanation was published, which is supposed to be sometime this month. And because his presentation left a number in the audience shaking their heads either in wonder, confusion, or surprise, I also wanted to wait for some analysis and reactions in order to get (and give) a better idea of what's going on here.
Others, however, haven't waited and in the course of not waiting have seriously mashed the issues.
One misunderstanding that keeps coming up is the actual nature of the claim Hawking said he was retracting, based on a misunderstanding of modern physics. One article, for example, said that black holes defy "subatomic theory [which] says matter can be transformed but never fully destroyed." Another said that the standard notion of black holes had violated "a fundamental tenet" of physics, which is that time can run "backward" as well as "forward." In each case, the assertion was Hawking was rescuing standard physics from the problems presented by black holes.
The trouble is, both of those premises are wrong. First, the idea that matter can't be destroyed - conservation of mass - got tossed nearly a century ago by Einstein. Matter can be "destroyed" by being changed into energy. (If it couldn't, nuclear weapons, for one thing, would not work.) It's the conservation of mass-energy that's maintained, and black holes do not violate that.
Sidebar: Nukes aside, it's actually good for us that matter can be changed into energy; if it couldn't, no life would ever have developed on Earth. The fusion reaction that powers the Sun, while actually somewhat more complicated, can be expressed simply this way: Under the tremendous heat and pressure at the core of the Sun, a hydrogen atom (one electron, one proton) fuses with a neutron to produce a deuterium atom (one electron, one proton, one neutron) and two deuterium atoms fuse into a helium atom (two electrons, two protons, two neutrons). Even though a helium atom would appear to be exactly the same as two deuterium atoms, it's total mass is actually slightly less. That difference is the mass that has turned into energy in the reaction. Multiply by the incredible number of times such reactions are occurring and you have a star on which all life here ultimately depends.
As for time, it's true that most physicists accept the idea that time is reversible. But the idea is still debatable, as can be told by the number of debates that go on about it: Some assert that time does indeed "flow" in one "direction" and the laws of thermodynamics prove it, while there are others who even argue that time does not exist, it's merely an artifact of the expansion of space. More importantly, the reversibility of time is not a "fundamental tenet" of physics, it's a simplifying assumption that allows physical processes to be examined without regard to which "direction" time is "going." In fact, it was discovered nearly 50 years ago that the degeneration of a subatomic particle known as a K-meson (or kaon) is not time invariant. That is, the process is not always reversible in time. (This lead to the development of CPT invariance, but we're getting way too complex here.)
The dispute in which Hawking was involved did not relate to the "destruction" of matter or the reversibility of time; it had to do with information. Simply put, the question was, as black holes age and dissipate, as physicists now believe they eventually do, could you examine what comes out of them and reconstruct what went in?
Hawking maintained that no, you couldn't, that any information about what went into a black hole was irretrievably lost and what eventually emerged was random radiation. Others disputed that, insisting that was impossible, that information can't be destroyed - which is a fundamental tenet of modern physics.
Hawking has now said that the information survives: "If you jump into a black hole, your mass energy will be returned to our universe, but in a mangled form, which contains the information about what you were like, but in an unrecognizable state." That last phrase may be of the things that got some in the audience shaking their heads because it hints that the information may be there but unrecoverable.
If that's what he means, it appears on the surface to come close to splitting the difference: Yes, the information is there, but no, you can't recover it, so in a sense everyone is right. According to the New York Times, which had a pretty decent article on his announcement, Hawking is applying quantum principles describing an "apparent" black hole coexisting with a real one (don't - you'll only get a headache; I understand the basic principles, if not the math, and it still makes my eyes hurt), the dissolution of which, which can happen easily because after all it's not really there (I told you, don't), would mean the radiation thus released would be to some degree correlated with that from the real black hole, allowing a means for information to escape. (I warned you.)
The problem is, "nobody knows how to weigh the different possibilities in such a quantum calculation," Dr. Sean Carroll of the University of Chicago told the Times.
I'm curious to see if what Hawking has come up with is something akin to the idea described by the Heisenburg Uncertainty Principle, which holds that it's impossible to accurately know both the position and momentum of a subatomic particle and that the more precisely you know one, the less precisely you know the other. In this case, perhaps something like the greater the correlation here, the less the correlation there. But that's just blue-skying. We'll have to wait a bit to find out.
That, however, has not kept some from passing immediate and ignorant judgments, which is why I've said all this now.
Thanks to Brad DeLong, I hear that Gregg Easterbrook, author of the right wing's favorite environmental tract, A Moment on the Earth, has used his New Republic Online column to trash not only Hawking, but both astronomy and physics in general. DeLong does a good demolition job on the fool here, but I wanted to add some of my own comments.
Easterbrook variously describes Hawking's work as "saying kooky things," "mumbo-jumbo," "claptrap," and "considerable nonsense," adding that in general, "physicists have the status once held by medieval priests." Of course, the fact that a lot of Hawking's work has been validated by others and the whole business operates on the very far edges of our comprehension of the universe doesn't phase him. He doesn't get it, so it must be nonsense. Valid science = Gregg Easterbrook's level of understanding.
In which case, we're in a lot of trouble. To show just how low his level of understanding is, he goes on to mock the Big Bang theory because it "don't do especially well on the common-sense test." Hell, I don't think a gyroscope does well on the common-sense test, but that doesn't keep us from using them in all sorts of ways. His contempt is based on the statement that physics can't definitively answer the question of what came "before" the Big Bang. True, it can't - some say there simply was no "before" or at least it's meaningless to talk about a before; others say that yes, there was a before in the sense there was the quantum vacuum, a state of potential without existence in which it's meaningless to talk of time because these was no change (careful of that headache); still others say that "before" in the quantum vacuum was much as today, seething with "virtual particles" popping into and out of existence, so in a way you could talk about time; others say our universe is simply an outgrowth of a previous state so time did not start with the Big Bang; others.... You get the idea. Since it's all based on mathematical models with an enormous number of possible solutions and we don't currently have the technology to test the predictions, no, science can't say what came "before" - if anything did. (We might have the ability to test at least some ideas within the decade, however.)
But notice that important phrase "test the predictions." What makes for a solid scientific hypothesis is not only that it explains observed phenomena but that it makes predictions about future observations. That is, it provides a means by which it can be tested. Once a hypothesis is confirmed by observation, it can take on the respected title of "Theory." The Big Bang - more specifically, the Inflationary Model of the Big Bang - is a theory. It has explained observations, accurately predicted later findings, and has stood up to challenge. Easterbrook may choose to disbelieve it, but the fact is, it works. And until and unless someone comes up with something that works better, it will remain a linchpin of astronomy, its separation from "common sense" be damned as wholly irrelevant.
You want to get removed from "common sense?" Try this: force from nothing. Literally. Nothing. It's called the Casimir Effect and it has been experimentally demonstrated. Hang two facing mirrors very close to each other in a vacuum and you will find they move toward each other as if they were attracted. Where does the force come from? From the quantum vacuum. All fields have variations, none are absolutely stable. These quantum-level variations can be described as "virtual particles" popping into and out of existence. But such a particle will have a specific electromagnetic wavelength associated with it and can only exist if the space allows for an integer multiple of that.
Huh?
Okay, try it this way. Imagine you have a tube 1" across and 10" long. You also have a supply of dowels that are a fraction under 1" across (so they'll slip into the tube) but of varying length. You want to exactly fill the tube with dowels of the same length. You can do that if the dowels are 1/2" long or 2" or 5" or any other number evenly divisible into 10 - but you can't do it with dowels that are 3" or 4" long. Likening it to subatomic particles, we could say that a particle of wavelength 2" could exist in the tube (there would be five of them) But one of 4" can't (because you can't have 2.5 particles, only whole ones).
In the Casimir effect, what happens in essence is that when the mirrors are close together, enough wavelengths are excluded that the pressure from the virtual particles striking the backs of the mirrors exceeds that of those striking their faces (because there are so many more of them) to a degree sufficient to be observed as a force. And thus you have an observable force generated from nothing. How's that for failing the common-sense test, Gregg? And again, this is something that has been repeatedly demonstrated and in fact is being studied because of its possible effect on nanotechnology.
But to show just how childish Easterbrook's understanding really is, consider his discussion of gravity under Einstein, which I'll have to quote for you to get the full effect.
Einstein speculated that the mass of every object causes space-time to curve, and then less massive objects roll downward on the curvature, and that's where gravity comes from. But wait, even if space is curved by mass, why do objects roll down the curvature - what pulls them? Your guess is as good as the next PhD's.Isaac Newton had developed a working theory of gravity that involves bodies pulling on each other with a force related to their masses and the distance between them. It worked well enough to explain the motion of bodies on the Earth, as well as the motions of the planets. (It still works well enough for applications up to and including space shots.) But Einstein realized that as velocity increased in accelerated systems (i.e., ones in which things are not moving at constant speeds in straight lines - in other words, the real world), Newton's predictions break down - so he searched for an underlying principle that would encompass but reach beyond Newton. It became his General Theory of Relativity, otherwise referred to as his theory of gravity.
Put as simply as possible, Einstein argued first that space and time are not separate entities but are linked. That is, instead of there being three dimensions of space and one of time, there is four-dimensional spacetime. He further argued that spacetime is warped by the presence of mass, and the greater the mass, the greater the warping. Masses moving through spacetime in the straightest lines possible would tend to follow the warps, with smaller warps causing less acceleration (change in motion) than bigger warps - so objects of lesser mass would tend to move toward objects of greater mass. Gravity, then, becomes an artifact of the warping of four-dimensional spacetime in the presence of mass.
Right.
Okay, here's a common way of trying to imagine this. Picture a sheet of rubber stretched out flat and suspended in the air. Now drop steel balls of various sizes and weights on the sheet, making depressions of various depths. In this simplified model, the smaller, less massive balls will tend to roll down into the deeper depressions of the larger, more massive balls.
But wait, what does that sound like? Yes! Like Easterbrook's description of the theory! What our genius has done is to equate a two-dimensional model with actual four-dimensional spacetime - that is, he has equated a simplified picture of a complex principle with the principle itself! For someone struggling to understand a difficult idea, that's understandable and forgivable. For someone who presents himself as a science writer, it's a bonehead blunder that undermines any remaining claim he may have tried to lay to credibility.
He may not know black holes, but he is certainly some kind of hole.
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