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Black Holes Disputed
JScarpace writes: "Researchers at the Los Alamos National Laboratory in New Mexico and at the University of South Carolina in Columbia have proposed the existence of "gravastars" which are bubbles of superdense matter. If they are correct, the idea of a black hole with a singularity at the center may be just a fantasy."
From the outside, these objetcs would look exactly the same as the black holes that most astrophysicists currently believe in. The only difference is that there's no actual hole in the center, just a very dense lump of matter. If you got sucked into one, you'd be spread out over its surface, not stretched into a long string.
A "singularity" is a point at which the gravitational force is infinite. This logically doesn't even make sense, so it's no wonder that it's disputed.
Cryptnotic
My other first post is car post.
And now every single Linux user on the planet will chime in with their own expert opinion on this topic
/., because that is what you will get alot of. For better or worse people are free to post here even if they aren't an expert.
But isn't that the point of slashdot?
I mean, this is a discussion forum, and most people here want to read and post.
Perhaps if that bugs you, you shouldn't read
Michael
There is no cryptographic solution to the problem where the intended receiver and the attacker are the same entity.
Escape velocity not only depends on the mass, but also on the distance from the center. In a black hole, escape velocity only exceeds the speed of light if you get closer than the event horizon.
Now, if for some reason the necessary mass would not fit into the event horizon, no black hole could occur. This new theory stipulates that if you have such a huge mass, it will actually form a hollow sphere where much of the mass is actually concentrated outside of the event horizon. Now, a hollow sphere has the following "interesting" properties (or would have, in classical mechanics):
- outside the spere it is the same as for a point mass: mM/r^2
- within the shell it would be approximately linear in r: mM*(r-r_inner)/r_outer^2/(r_outer-r_inner)
- inside, it would be zero
Probably this is not 100% exact, as we're in a relativistic context here, rather than a classical one, but we can still presume that gravity inside the sphere would be much weaker than outside.(approximative formula, for "thin" shells)
This would basically mean that you would not have an escape velocity exceeding the speed of light anywhere:
Say no to software patents.
Just b/c our understanding of physics breaks down at the singularity doesn't mean it does not exist (remember we can't describe in physical terms just what the first few picoseconds of the big bang where like - the physics just can't cope with the amount of matter/energy involved).
But in the same way, just because our understanding of physics breaks down at the singularity / start of the big bang level, we cant be sure that the "laws" of thermodynaics are "violated" at the scale and energies involved at this theoretical gravastar state.
TO do so the matter woudl have to exceed the speed of light. Right.
Why not? how many times does everyone have to be surprised by physics before its finally conceded that there are no "LAWS" of physics.
As far as we are concerned, there is only our theoretical understanding and our observations, and thats all. Anything else that exists iin the universe (whatever that is), continues to exist whether we observe it and theorize about it or not.
If you approach science in this way, it becomes an open persuit instead of a closed one, which makes it ultimately more fruitful.
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Secondly, black hole theory is a mess and only looks acceptable to modern eyes due to familiarity. The singularity in the system is a BIG clue that it's wrong.
I'm not saying that the gravastar idea is right, and the temperature issue is a big question mark, but no one has given any reason in the last 30 years as to why we should accept the current BH theory other than it looks good on paper and the "problems" will be solved one day. Soon. Not yet, no, but I'm sure someone will clear it up. Probably.
TWW
"Encyclopedia" is to "Wikipedia" what "Library" is to "Some people at a bus stop"
Actually, going by entropic laws, it would seem that the Universe is better described in say, 700 constants, than say, 6 constants.
...but no one has given any reason in the last 30 years as to why we should accept the current BH theory other than it looks good on paper and the "problems" will be solved one day.
:-)
But the reason these constants _are_ of prime importance is because as a solution to certain tensor calculus equations in relativity, and these constants have been observed to be unattainable, but have been observed. Ofcourse, it is entirely possible like how we once thought that the speed of sound could not be exceeded, we may still be wrong about the speed of light and absolute zero, but that is a remote possibility because no particle in the world has been observed to have c nor have absolute zero (now don't get me started on photons.... as I read somewhere, your guess is as good as mine on what they are).
Good point. But you are forgetting one important point - there has been _some_ evidence showcasing possible black hole like behaviour, which cannot be explained by gravistar theory, atleast not yet. Example - Event horizon, dense areas which are surrounded by matter with an invisible core, and so on. In fact, Chandra has observed the existence of an Event Horizon in M82.
If you have done any amount of tensor calculus & quantum physics related mathematics (which I'm assuming you have), you'll know that Black Holes can be described with considerable ease in a Riemann plane, than gravistars.
Think of the implications these guys are suggesting --
1. You have submanifolds which would overlap as more matter gets in, and so the relativistic frame would in itself be a function carrying many frames. Assuming a standard rate of expansion for each of these frames, you can imagine the number of frames which would be in existence by now.
2. The gravitational effects caused by a tending mass are described in general relativity. These use a mere 16 coupled hyperbolic-elliptic nonlinear partial differential equations, called the Einstein field equations. Now, you have a solution for these called Bertotti-Robinson Solution, and when these are applied to a Black Hole, they work out just fine. This, despite assuming a uniform magnetic field.
However, you will realise owing to the submanifolds, you may not be able to apply the same to a gravistar. It'd be way too complex. And Bertotti-Robinson have been proved
3. Despite what the say about the Schwarzschild Black Hole, the exterior solution for such a black holes _has_ been proved, and it conforms to the field equations proposed by Einstein.
Now these are independent results to the same set of equations. I think I'd rather trust Einstein than these guys
Anyways, it would be interesting to watch how this would get on. I'm not against this theory, just that there _seem to be_ far too many unanswered questions.
>Anyone see the problem with that? The first
>problem is that no reason is given for the
>airstream over the top to have to meet up
>with the airstreem under the bottom. Why
>can't it just flow straight back?
See here for one of many explanations of the Kutta condition, one of the foundational principles of aerodynamics. This has nothing to do with an explanation for the layman. Basically, it states that the air MUST meet smoothly at the back of the wing.
Logically, if you spend some time thinking about the flow, you cannot possibly construct a situation where the air above the wing somehow slips past the air below. Remember that a jet moves so fast that its wing is only passing through a portion of the air for fractions of a second - it's simply not possible to make the air move fast enough to slip like this.
This principle has been demonstrated NUMEROUS times. You can demonstrate it very easily with a line of smoke through which a wing passes, among a zillion other simple experiments.
--Brandon / Split Infinity Music
"That doesn't make sense."
Nobody ever said quantum mechanics made sense, either (and if they did, they're lying). But not making sense doesn't mean it's not right.