Slashdot Mirror
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.
If you see this, please respond because I want to be corrected. One thing you said, about having densities higher than neutron stars, can't be true. I remember reading (somewhere) that as the density increases, the 'stiffness' of the matter increases, as does the speed of sound through it. If the density reached a certain limit, sound would travel through it faster than light speed, which can't be; so that's the limit of a neutron star and anything more dense must be a more condensed form of matter (black hole).
--
Soma: because a gramme is better than a damn.
The most eye-catching line in Mitra's paper is towards the end. He claims that string theory is having trouble admitting black holes, so folks are trying to fudge it. "However, ironically, string theorists, at this moment are guided by the erroneous notion that GTR yields BH with M>0, and are struggling to wiggle out of this result by modifying the definition of event horizon into the socalled "stretched horizon"." Before Hubble (the astronomer, not the satellite) claimed to have observational evidence that the universe is expanding, Einstein produced equations that showed that the universe had to be expanding (or contracting). But, big Al didn't have the courage to trust the mathematics, and he introduced the "cosmological constant," a fudge factor to allow a non-expanding universe. After Hubble later released his results, Einstein called the cosmological constant his greatest professional mistake. It seems that string theorists may have been introducing fudge factors of their own to allow singularities. Wouldn't it be neat if they should have just trusted the mathematics, too? Upon re-reading this post, it seems to be hard on Einstein, but it's not intended to be. He's the man!
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. 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, which would consist (at least in its core) of free strange quarks. But some models 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 on neutron stars, from a specialist.)
---
---
Politics is about making compromises. Religion isn't. --Michael Horton
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"...).
---
---
Politics is about making compromises. Religion isn't. --Michael Horton
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.
If you liked this thought maybe you would find my blog nice too:
But just because that something cannot be explained by any other means, does that necessarily require whatever random theory may explain the phenomenon to be true? In the 1500s, people KNEW the earth was flat; it of course wasn't, but the point is that a widely accepted assumption is not a fact. The only proof that a black hole exists is to actually find one. If ever a body was found that exhibited all the properties of a black hole, and was without a trace of doubt a black hole, then it would be proven that black holes exist.
Indeed in the frame of some object (I forget which) the mass never actually reaches the event horizon.
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.
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.
>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.
Mode (3) smart-aleck mode. Press * to return to main menu.
"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?
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.
Mode (3) smart-aleck mode. Press * to return to main menu.
whats wrong with tis guy?has he been nippin' at the cough syrup or somethin'. black holes have to exist.All a blackhole is is a dead star that is so dense that it absorbs everything. Now, is he saying that they don't exist or that they don't suck up light waves?
what is this for? oh well
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 may be able to provide a more accurate and far more knowledgable answer.
Seriously, this is possibly the worst written article I have ever read. Now, if one were to post the article from "Foundations of..." I would be much happier. I mean, is it too much to ask for some punctuation?
I might be misunderstanding you, but I believe that is backwards; In it's own frame of reference a falling object will reach the event horizon, and if you happen to be in this object, and are still alive to look back the way you came in, you will see the universe ending behind you. That is, if the Big Crunch theory is right. Otherwise I can't guess what you might see. To an outside observer, on the other hand, the object will never reach the event horizon, and, in fact, wont even appear to be moving. That's just the way I understand it, and I, of course, hold no degrees in any physics, but that is the way it seems to make sense. I've been reading some very interesting stories about just this idea, as told by Greg Egan. I particularly like his short story, "The Planck Dive". You can find his stuff at http://www.netspace.net.au/~gregegan/index.html
-------
Plan to be spontaneous tomorrow
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.
--
If Google really cared they would fix Android Chrome to reflow text, instead of discriminating
And they prevent free trade of information on the internet, by sending certain IP's into them.
Why is this such a big deal? It's not like black holes were ever proved in the first place. And it's not like they still can't be used in sci-fi. God only knows the number of scientific inaccuracies in movies like that, what's another one going to hurt? All in all I think that this article should be appreciated; opposing views help to discern fact from fiction. Additionally, the lack of any proven existing black holes did hurt the theory to begin with. My only question is: What about wormholes? Is there any other way that spacetime could tear without blackholes (or similar phenomenons)? Would this kill one of the ten dimensional superstring theories, since it relies on six of our dimensions being trapped in another universe that broke off of our own just after the big bang?
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?
"You can't get something for nothing." - my grandfather, on the stock market and Reaganomics.
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.
I'm still trying to figure out what people mean by 'social skills' here.
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.
I'm still trying to figure out what people mean by 'social skills' here.
Find free books.
check this out for some more stuff on disproving black holes http://mist.npl.washington.edu/AV/altvw100.html
This is my sig. The post is over.
That might also explain why all the particle wave functions in the universe did't collapse into the first black hole that formed.
time now and I've got the time-stamped messageboards to prove it. That's not to mention the dozens of people so inspiried by my message that they emailed me saying I was a freaking idiot... But the fact remains, no object following the laws of physics can do the things a black hole is credited with. I know I'm being light on real facts here but my theory is quite legenthy and most likely lost on this crowd. If you would really like to know more, feel free to email me... If you can't figure out how to email me, you proably don't need to.
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...???
Find free books.
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.
Find free books.