Black Holes Don't Exist? 38
An Anonymous Coward sends this link about a physicist who is trying to prove that black holes can't exist. It'll be a shame if he succeeds; this would eliminate one major plot element that sci-fi writers have been able to rely upon for years.
Re:The obvious question: (Score:1)
--
shades of the cosmological constant (Score:1)
Re:The obvious question: (Score:1)
In any event (and this is not my specialty, so take this with the standard grain o' salt), the reason that a collapsar is expected to stop collapsing at neutron-star stage is that the neutron degeneracy pressure (basically, the Pauli Exclusion Principle in action) is able to resist the mutual gravitational forces up to some limit -- by calculation, 1.4 to 1.8 solar masses, although it appears that a value of 2.3 solar masses has been observed [washington.edu]. Clearly, though, greater densities can exist, because if the limiting mass is exceeded the collapse continues -- to form a black hole, if you accept the present standard formulations of the problem. It's just that we don't know of a stronger force than neutron degeneracy, which will be able to resist the gravitational collapse. During the formation event (typically a supernova), if the collaspe forces (gravitation, implosion) exceed the neutron degeneracy forces, there's nothing to stop the continued collapse (through higher densities) to a black hole. Our lack of knowledge doesn't mean there's not a further stable state, though -- only that we don't know about it. Some scientists have speculated that a further point might exist in a quark star [sciencemag.org], which would consist (at least in its core) of free strange quarks. But some models [raytheon.com] of quark stars end up with lower densities than neutron stars... the problem is that we just don't know enough, yet.
(BTW, there's good info here [umd.edu] on neutron stars, from a specialist.)
---
Re:So What? (Score:1)
As Dr. Mitra points out in his paper, what's really been demonstrated is that there's something more dense than a standard-model neutron star -- which I believe is an accurate assessment. He explicitly addresses (and allows for) the existence of things more dense than that, however -- he just "forbids" them from forming event horizons and turning into black holes. If black holes are "allowed", present theory doesn't provide for anything between neutron-star density and black holes, though: a collapse past neutron-star density just "keeps going."
IIRC the paper in Science revealing the compact massive object in our own galaxy's center actually made the statement that it was more dense than a neutron star -- and therefore could only be a black hole. (Of course, after that they simply called it "the black hole"...).
---
Re:The obvious question: (Score:2)
Hume Hates You (Score:1)
Re:Hume Hates You (Score:1)
If you can see the object, then the good Dr. is right, as an event horizion has not formed and light is escaping :-).
Re:The obvious question: (Score:1)
In its own frame of reference the falling object never reaches the event horizon. For an outside observer the time to reach the event horizon is finite.
Re:World-wide Moderation (Score:2)
So you don't like what the scientist is trying to do .. doesn't mean its not important. Science is not about trying to find out what we want to hear - thats called religion. If you have proof that black holes do exist, let us know, until then scientists are free to try disprove them. Scientists doing research like this are an important part of science, scientific assertions must be verifiable.
Scientific results don't have to be popular, just verifiable. Typical fucking /. idiot moderator style, moderating something down just because you don't like what they're saying.
It's rather more complicated than that... (Score:2)
Well, it's not due to "higher densities".
First, 2 facts to clear up some of the stuff of the previous post(s):
(a) Neutron stars always have densities that are less than nuclear density (i.e. the density of a nuclei, about 10^-15 g/cm3). The point is that there is no "smooth" transition from finite to infinite density : the collapse is catastrophic and highly unstable.
(b) The standard calculation of a "chandrasekhar mass" of a neutron star uses the so-called Oppenheimer-Volkoff equation (which Mitra is questioning : I have not read his paper since I'll let the bigger guns shoot him. There are _a lot_ of crazy people out there....), combined with an equation of state for fermions. In a standard "non-GTR" calculation, a mass of about 6 solar masses is obtained for collapse to BH. In a proper OV-GTR calculation, a mass of about 2.5 solar masses is obtained.
Now, my point : "mass densities" no longer has any meaning at high gravitational fields since the fermions no longer just contribute mass, their mass contributes to increasing curvature which modify the metric. This relationship is highly nonlinear (kind of a "feedback" thingie I suppose. In standard white dwarf Chandra mass calculation, the metric is always fixed in the weak-field Newtonian limit). Usually, in the weak-field limit, increasing density will increase the degeneracy pressure, so adding mass to a fixed radii will increase the pressure. However, in strong fields adding mass pass a certain point will actually reduce pressure because of the OV equation :
dp/d(rho) = (m(R)+4piR^3)/R(R-2m(R)) (set G=c=1 as usual, and rho = density)
Note the denominator R-2m(R). Usually in weak fields, dp/d(rho) >1, since R>2m(R) so adding mass will add pressure. However, at a certain fixed m(R), R2m(R), and adding mass will _decrease_ the pressure instead.
It turns out that the critical density when this happens actually is less than the nuclear density.
Re:So What? (Score:1)
"Why is this such a big deal?"
I haven't noticed anybody around here claiming that this is a big deal. Just another bit of scientific research that some /. readers may find interesting, but certainly not "a big deal". Did someone here tell you it was a big deal?
Oh, an errata and one more note (Score:2)
There is a singularity in the OV equation at R=2m(R). This is a result of the coordinate system we uses, and is not a physical singularity so no worries.
how can he prove it? (Score:1)
ECOs and Gravity Waves (Score:1)
Several years back, I read an idea which was far more to my liking. It was based on a theory by Roger Penrose(1), which states that the fabric space-time, as we know it, is comprised of much smaller, multi-dimensional space-times. These building block space-times are incredibly small; in fact, they exist on the order of the planck length(1.6161x10^-35 m). The idea proposed was that collapsing stars would get "stuck" in this fabric and would never possess any measurement smaller than that of the planck length. In essence, they become *really* tiny ECOs.
(1)This is a bit ironic, given that Penrose gave the first "proof" that singularities *must* exist.
If I understood his question correctly, RedLaggedTeut asked if the space-time curvature around a black hole would make it impossible to view.
The nature of a black hole is such that it cannot be viewed. It is an absence, not a presence, so there is nothing to view, hence it is black. I cannot provide any information regarding curvature rate, but if I had to conjecture, I would say that space-time does not bend more quickly in the presence of increased gravity. If I remember correctly, two supermassive stars, but of different masses, will collapse at the same rate. This would indicate to me that collapse is regulated by the structure of space-time. However, someone from
http://www.physlink.com [physlink.com] may be able to provide a more accurate and far more knowledgable answer.
Re:Hume Hates You (Score:1)
---------
Plan to be spontaneous tomorrow
Re:World-wide Moderation (Score:1)
Re:The obvious question: (Score:1)
-------
Plan to be spontaneous tomorrow
Query: Can you never see a black hole? (Score:1)
I've just watched Stargate :D (Yeah I know, that kind are hardly a found of serious info, but the show is kind of cozy)
and in one episode a team is caught on the ground when a black hole suddenly worms in the solar system where the planet is located. And the hole is visible from the ground - at least for the first few seconds.
--
Yes, they do (Score:1)
So What? (Score:1)
The obvious question: (Score:4)
E.g. Hawking radiation, as theorized, would seem to require an event horizon, but would it look any different than radiation from accreting matter? If so, have these differences been observed?
Re:The obvious question: (Score:3)
The short answer is "NO": there are no observations that can only be attributed to singularities. But, then again, there are no observations that CAN be attributed to singularities. That's what the singularity theorems say: gravitational collapse (even in GTR) can not result in a "naked" singularity, that is, a singularity which is not hidden from view. In the case of non-extreme black holes, the singularity would be hidden from view by the event horizon; and all known extreme black hole solutions are unstable, so they probably can't ever be formed in the first place! Unfortunately, I don't think these "no-go", or "cosmic censorship" theorems have been proven (although I don't really know, since I haven't followed the field closely in the last year or so).
It must be pointed out that the "singularity" that we are talking about at the bottom of the black hole probably doesn't actually exist, even in the absence of the censorship theorems - the existence of a singularity (or non-removable infinities) tells us simply that we don't know what happens in the neighborhood of the points. In this context, it means that the local space-time curvature in the neighborhood of the classically predicted infinity exceeds the value at which you need to consider the quantum properties of gravity - i.e. we need a quantum theory of gravity.
I haven't read this paper that is referenced, but I would guess that either: 1) the paper doesn't say what the article says that it says, or 2) the guy is a kook. I say this since thousands of physicists over the last 80 odd years have done the mathematical proof that black holes exist in GTR (and in fact, they exist in any metric theory of gravity, I believe); that is not the same as saying that you can physically create a black hole, but most astophysicists don't see a reason why it wouldn't happen - the dynamic (computer based) models show the formation of black holes under realistic conditions that we KNOW exist in the universe does occur: put enough material in a small enough area, and you get a black hole...and once you have one, they are stable. The other thing to note is that GTR properly predicts the evolutions of stars, the existence of white and brown dwarfs, and the existence of neutron stars...the exact same equations that predict the existence of black holes.
Hawking radiation is a quantum effect that leads to stuff "tunneling out of the black hole", but it occurs at a phenomenally miniscule rate for any black hole of the type formed in stellar collapse. It is a long, but straightforward derivation based on GTR and quantum field theory. Hawking radiation would only be visible in the final stages of evaporation of very light black holes that would only have formed at the time of the big bang.
Another argument + HyperDrive idea( /. patented ) (Score:5)
Same thing as for the astronauts twins .. (http://www.phys.virginia.edu/classes/252/srel_twi ns.html)
the astronaut will not age at all when hitting the schwarzchild radius, so a black hole would be perfect if it existed .. And rate of slowdown of time is sqrt(1-v/c) .. which is the same effect that prevents matters from reaching light speed.
Interestingly, this effect seems to be like the doppler effect for sound waves. Continue thinking along that line, that would mean you can't go past light speed because that would mean breaking invisible links that existed between matter.
Continuing that thought, you might be able to go above light speed if you could make yourself completely invisible from all or most forces and other emissions, like light waves.
No idea how you could do that - so its just replacing one riddle by one that isn't much easier.
Now to continue daydreaming, that would also explain what happened at the philadelphia experiment - the ship cloaked, someone sneezed, and they ended up somewhere else - most likely in outer space.
I should end this with a REALLY funny note, but I got none.
Re:Another argument + HyperDrive idea( /. patented (Score:1)
footnote 2: the other theory what would happen to a ship that successfully conducted a perfect philadelpia experiment would be that it ended up in its own little universe - without a decent source of power to pop out again.
URL for the paper (Score:3)
Alternate Views page (Score:1)
That would also explain... (Score:1)
Re:Alternate Views page (Score:1)
Re:The obvious question: (Score:4)
What he appears to claim is:
- Within the formal General Theory of Relativity, a trapped surface (a surface formed by light moving radially outward, which is not expanding because of the gravitational field inside the surface) cannot exist. This appears to imply that the mass inside the surface goes to zero as the radius goes to zero...
- The proper radial length goes to infinity as the radius goes to zero, so the collapse process continues indefinitely (he refers to Eternally Collapsing Objects -- ECOs)
- Because there is no trapped surface and the collapse itself takes infinitely long, all the mass interior to the collapse is radiated away as electromagnetic energy (he refers to Eternally Collapsing Objects -- ECOs)
- There can therefore be no "naked singularity" problem, because a finite-mass Schwartzschild black hole doesn't form: the mass "escapes" during the collapse.
He does allow for massive compact objects, however, even with densities larger than that of a static neutron star -- and claims that the infinitely-long accretion time prevents the gravitational radiation from being observed. He allows for exotic equation-of-state matter ("quark stars") and points out that extremely large magnetic fields are possible if black holes aren't allowed -- which might explain some of the more exotic species of high-energy objects, like gamma bursters and so on.For the most part, what he's doing is beyond me -- my degree's in physics, but it's been a long time, and this is esoteric stuff. But the flavor of it is this: past work has made several incorrect simplifying assumptions, and when the physics and math are done correctly, black holes can't exist. It'd take me a year to check his math, though, so I'm going to stop right here.
Interesting stuff -- this will be very controversial, and we should know shortly whether or not he's made a trivial error. If not, the arguments will take years...
---
I've been saying this very thing for quite some (Score:1)
Re:The obvious question: (Score:1)
ECO vs black hole -- does it matter? (Score:1)
One thing I'd wonder about is whether the spacetime outside an ECO is predicted to be any different than the spacetime outside a black hole. After all, at large distances I don't see how the field can be anything but a Newtonian 1/r2. Maybe close up the field would be different -- so maybe his theory would make different, testable predictions about the x-ray spectra that have been observed for matter falling into black-hole candidates?
I'm also unclear on how you can have a permanent ("eternal") gravitational field pattern if all the mass is gone...???
Re:So What? (Score:1)
There are a bunch of very solid candidates for several-solar-mass black holes. Basically you look for a binary star where x-rays are coming out due to infalling matter being pulled off of the "normal" (giant) companion. In a binary, the masses can be determined. If the mass is beyond a certain amount (I've forgotten, 3 solar masses?), it can't be a standard-model neutron star.
Also, there is a many-million-solar-mass object at the center of our galaxy which is much too compact to be a standard-model neutron star, and which it's been proven can't be anything like a dense star cluster or anything.
So until today, I think if you'd asked any well-informed astronomer, the answer would have been, "Why of course black holes have been proven to exist."
Common misconception (Score:3)
Primordial black holes (as opposed to black holes formed from stellar evolution) are an interesting topic, but it's not clear that any ever formed (searches for micro-holes have turned up negative), and even if they did, they wouldn't necessarily have devoured everything around.
Re:how can he prove it? (Score:1)
I would take a brave notion and suggest that maybe, just possibly this guy who wrote this article is VERY FUCKING SMART and has spent a GREAT DEAL OF TIME THINKING AND STUDYING AND.... doing the "Math"
Re:ECO vs black hole -- does it matter? (Score:2)
You've got me on that one. I'd doubt it -- basically what he's arguing is that the trapping surfaces never form, so there's no event horizon and such. The physics of black holes is different inside the event horizon (if that's a meaningful statement), not outside.
That said, he does predict some different physics: magnetic fields would probably dominate after a while (classic black holes don't have a magnetic field), and you'd see the continuing collapse and evolution of the massive body after a supernova, for example -- which becomes relevant with the present model of a gamma burster (he actually addresses some of this in the paper, making predictions about observations).
The mass goes to zero as the radius goes to zero, and for sufficiently-massive starting bodies, this takes "forever" -- and he actually discusses the concept of a "zero-mass singularity" (although he calls it something different -- I don't have the paper up now) as the limiting case for unbounded t. I couldn't follow that one, though... For cases we're likely to encounter, I'd suspect that the rate of mass loss through radiation would be low enough that you'd not notice the slow change in mass within the measurement sphere -- and of course that mass (if it's spherically symmetric) is equivalent to a singularity of equal mass. I'd expect him to say that gravitational field strength does slowly decay with time -- but very slowly. For all I know, it'd be indistinguishable from Hawking radiation...
---
Re:So What? (Score:1)
--
Re:I've been saying this very thing for quite some (Score:1)
Unfortuneately, scientists have *never* like to have their view of the universe questioned. Even if this guy is right, Hawking and the rest of the Black Hole Team (members who are still alive) will passionately fight to the death to prove him wrong, 'cause, if he's right it will mean *they* were wrong.