Black Holes Don't Exist?

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.

Comments

Re:The obvious question:

[logicnazi]

Two comments. First the matter of naked singularities is of some debate...in fact it was the subject of a bet between kip thorne and steven hawking which was settled recently. Certain very specific simulations seemed to show that naked singularities could exist...but there are doubts that this simulations are actually physically realizable. More may have been done since I heard about it please correct me if I am wrong. Secondly very many smart physicists belive in black holes so it is nothing to be dismissed lightly. It seems, both from your summary and the article that many of these rejections are based in some specific time frame. Indeed in the frame of some object (I forget which) the mass never actually reaches the event horizon. So in a suitably choosen reference one might try to claim black holes cannot exist. However, I asked Kip Thorne this question in lecture and if I understood his response correctly it was that yes in some time frame the event horizon is never reached but because of the singular nature of the black hole this infinite time in one frame can be only a finite time in a differnt frame forcing us to take the concept of a black hole seriously. If it is our time frame where the object takes an infinite amount of time to fall into the black hole then one might succesfully argue they don't concern us (they exist but only in our infinite future)...but I don't remember which time frame it is and I may just be entierly misinterpreting what was said. But the point being very smart physiucists have not been ignoring these problems and it seems highly unlikely that "simple" arguments could disprove their existance at this junture.

Re:World-wide Moderation

[Anonymous Coward]

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...

[efuseekay]

>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.

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.

Oh, an errata and one more note

[efuseekay]

It's 10^(15) g/cm3 not -15. (silly me)

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.

The obvious question:

[re-geeked]

Do any known observations include phenomena that can only be attributed to singularities, as opposed to just really, really dense objects?

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:

[krlynch]

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.

Re:The obvious question:

[tesserae]

I've got the paper open in PDF format, and am trying to read it...

What he appears to claim is:

1. 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...

2. 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)

3. 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)

4. 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...

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Another argument + HyperDrive idea( /. patented )

[RedLaggedTeut]

Not sure that this is one of his arguments, but I always wondered whether space time would't bend faster ( slowing down time ) in the presence of more gravity such that you could never observe a black hole from the outside, only matter that comes closer and closer to the event horizon, never quite reaching it.

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.

URL for the paper

[bcrowell]

The preprint is here.

Common misconception

[bcrowell]

Sounds like you're echoing a common misconception about black holes, that they suck everything in like a vacuum cleaner. Actually, it's quite hard to fall into a black hole -- the event horizon makes a small target. You're more likely to swing past and fly back out.

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:ECO vs black hole -- does it matter?

[tesserae]

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 ... maybe his theory would make different, testable predictions about the x-ray spectra that have been observed for matter falling into black-hole candidates?

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).

I'm also unclear on how you can have a permanent ("eternal") gravitational field pattern if all the mass is gone...???

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...

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