# Black holes may not exist!

Discussion in 'Physics & Math' started by RJBeery, Jan 24, 2014.

1. ### RJBeeryNatural PhilosopherValued Senior Member

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First of all, I disagree. If many posters claim that my arguments MUST be wrong because black holes DO exist...without addresses the arguments themselves...and it turns out that black holes do not exist...then in a perfect world apologies would follow.

As far as you're concerned, przyk, I appreciate that you give me what are probably the most reasonable and informed responses on this site and particular subject. That being said, I'd like to see the math behind a finite spacelike separation between an outside observer and portions of the causal present singularity. This isn't trolling - I really want to see it - because I have a problem with the idea that we share a causal present with ANY portion beyond an event horizon, let alone the singularity...

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Again, if GR BHs dont exist then I would like to see an explanation as to the observations put down to BHs.
BHs of sorts [called Dark Stars] were even theorised to exist in Newtonian mechanics, and way back in the late 1700's

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November 27, 1783: John Michell anticipates black holes:

We think of black holes as a 20th century invention, dating back to 1916, when Albert Einstein first published his theory of general relativity and fellow physicist Karl Schwarzschild used those equations to envision a spherical section of spacetime so badly warped around a concentrated mass that it is invisible to the outside world. But the true “father” of the black hole concept was a humble 18th century English rector named John Michell–a man so far ahead of his scientific contemporaries that his ideas languished in obscurity, until they were re-invented more than a century later.

http://www.aps.org/publications/apsnews/200911/physicshistory.cfm
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John Michell's Newtonian governed objects, called Dark Stars, differs from the more likely GR variety, in that, there is no Schwarzchild limit, and just below the parameter where the particles of light are turned back, there exists a solid surface.
The Schwarzchild limit of course, once reached, sees further collapse to a Singularity as compulsory.

7. ### RJBeeryNatural PhilosopherValued Senior Member

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If the event horizon does not "exist" today in GR then it never will. That means that there is no event horizon to reach; it's just a region of asymptotically slowing time and increasing pressure/gravity.

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Also from the article, Hawking says....
“The correct treatment,” Hawking says, “remains a mystery.”

All in all, a typical journalist attempt at sensationalism with the headline....But a good article just the same.
And nowhere is there any inference that BH's do not exist [other then the sensationalistic headline] just a few speculative pedantic details, which was virtually admitted to here....
" He titled it, whimsically, 'Information preservation and weather forecasting for black holes', and it has yet to pass peer review."

I'm sure Hawking at his age, has his tongue just very slightly planted in his cheek.

9. ### RJBeeryNatural PhilosopherValued Senior Member

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If your point is that black holes exist because Hawking didn't explicitly say otherwise in this article, I would disagree; if your point is that no one knows for sure, then I would of course agree...

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My point is that in my opinion BH's do 100% exist. The details have not yet been completely finalised.
Those that think they don't, need to explain the effects we see by some other means.

11. ### RJBeeryNatural PhilosopherValued Senior Member

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*sigh*

I agree that an area with enough concentrated mass will grow dark from asymptotic redshifting and slow down from asymptotic time dilation. This does not mean that an event horizon has formed.

12. ### przyksquishyValued Senior Member

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For points inside the event horizon, with the exception of the singularity itself, it's actually very easy to see without doing any intensive math. For any spacelike curve $x^{\mu}(\lambda)$ expressed in terms of some parameter $\lambda$ starting at $\lambda_{0}$ and ending at $\lambda_{1}$, the spacetime distance is just the integral

$s \,=\, \int_{\lambda = \lambda_{0}}^{\lambda = \lambda_{1}} \mathrm{d}s \,=\, \int_{\lambda_{0}}^{\lambda_{1}} \mathrm{d} \lambda \sqrt{g_{\mu\nu} \frac{\mathrm{d}x^{\mu}}{\mathrm{d}\lambda} \frac{\mathrm{d}x^{\nu}}{\mathrm{d} \lambda}} \,.$​

A simple example you could consider is just to draw a horizontal line on a Kruskal diagram starting at some Kruskal (spacelike) coordinate $u_{0}$ inside the event horizon and ending at some Kruskal coordinate $u_{1}$ outside the event horizon, at some fixed Kruskal time coordinate $v \,>\, 0$. If you use the Kruskal coordinate $u$ itself as the line parameter, then $\frac{\mathrm{d}v}{\mathrm{d}u} \,=\, 0$ and $\frac{\mathrm{d}u}{\mathrm{d}u} \,=\, 1$, and the spacetime distance just becomes

$\begin{eqnarray} s &=& \int_{u_{0}}^{u_{1}} \mathrm{d}u \sqrt{g_{vv} \Bigl( \frac{\mathrm{d}v}{\mathrm{d}u} \Bigr)^{2} \,+\, g_{uu} \Bigl( \frac{\mathrm{d}u}{\mathrm{d}u} \Bigr)^{2}} \\ &=& \int_{u_{0}}^{u_{1}} \mathrm{d}u \sqrt{g_{uu}} \,. \end{eqnarray}$​

At this point, you could crack open a textbook or consult Wikipedia to find out exactly what $g_{uu}$ is for the black hole metric in Kruskal coordinates (NB: it's a function of $v$ and $u$), substitute it in, and try to calculate the integral to get an exact value. In the case of an eternal black hole, Wikipedia says it's

$g_{uu} \,=\, \frac{32 G^{3} M^{3}}{r} e^{- r / 2GM}$​

with $r \,=\, r(v,\, u)$ defined implicitly by $v^{2} \,-\, u^{2} \,=\, ( 1 \,-\, r/2GM ) e^{r/2GM}$. But for our purposes this is more detail than we need. The only thing you need to notice about $g_{uu}$ is that it is finite everywhere except on the singularity (where $r \,=\, 0$). Consequently, the spacetime interval is the integral of a finite function over a finite domain (unless you somehow managed to draw an infinitely long line on a piece of paper, $u_{1} \,-\, u_{0}$ is finite), which will obviously produce a finite value.

13. ### przyksquishyValued Senior Member

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No, said posters would really owe you apologies regardless of whether black holes exist.

14. ### TrooperSecular SanityValued Senior Member

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An apology? You're not referring to me, are you?

Sorry, but I think there are black holes...and that's that.

Jesus Christ, RJ, what are you after, a Penthouse subscription?

15. ### brucepValued Senior Member

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The 'Black holes may not exist' is sensationalism made for you. This is the predicted firewall

T_Unruh = h*g_conventional/4(pi)^2*k_Boltzmann*c [eq.1]

g_conventional/c^2 = (M*c^2/r^2)(1-2M/r)^-1/2

g_shell = g_conventional/c^2 = (M_meters*c^2/r^2)(1-2M/r)^-1/2 [eq.2]

Substituting [eq.2] into [eq.1]

T_Unruh = [h*M_meters*c] / [4(pi)^2*k_B*r^2 (1-2M/r)^1/2)]

Let r > 2M the Schwarzschild event horizon. Account for the redshift measured from remote coordinates
(1-2M/r)^1/2 / 1-2M/r)^1/2 =1

T_Hawking=[h*c*M_meters/4(pi)^2*k_Boltz*(2M_meters)^2]

T_Hawking = h*c/16(pi)^2*k_Boltz*M_meters

This is the part that predicts the 'firewall'

g_shell = g_conventional/c^2 = (M_meters*c^2/r^2)(1-2M/r)^-1/2 [eq.2]

It says g_shell and the Hawking temperature go to infinity at r=2M.

The apparent horizon is a dynamic horizon where distance r=2M fluctuates with a change in system mass. It's not fixed but it's still a coordinate singularity. The limits still apply but the distance, r=2M, isn't fixed because the black hole is dynamic. I already showed you the direct evidence for the black hole at Cygnus x_1. Your argument was the event horizon couldn't be reached because you think the only way to trace that path is from remote coordinates. This physics is about what happens locally to an object approaching r=2M and concludes 'it's fried' before it can crossover the apparent horizon. The infinity thing doesn't hold much water since the horizon is a coordinate singularity. IE: it can be transformed away by using different coordinates. I'm sure they use a different method to predict the actual firewall temperature at r=2M since it's surely not infinite.

16. ### LaurieAGRegistered Senior Member

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http://www.cscamm.umd.edu/tiglio/GR2012/Syllabus_files/EinsteinSchwarzschild.pdf

17. ### TrooperSecular SanityValued Senior Member

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BH's do exist, and I don't believe Hawking is saying they do not. Until at least someone can give a better solution,
As I noted earlier, he has titled titled it, whimsically, 'Information preservation and weather forecasting for black holes', and it has yet to pass peer review."

Again, at his age, I reckon Hawking has his tongue at least slightly planted in his cheek.
[He has been known for his humour.

19. ### brucepValued Senior Member

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Hawking is a rock star so he likes to say stuff like that. He means the classical GR description doesn't exist as real natural phenomena. He predicted that 40 years ago when he was analyzing [looking for holes] in Jacob Bekestein black hole thermodynamics. What he found was black holes should radiate in the thermal spectrum. Considered a theoretical path towards quantum gravity. The apparent horizon predicts 'when the mass of the black hole changes so does the distance r=2M'. I've been wondering about the consequences of the Hawking Temperature derivation for 20 years. The classical answer is the inertial blackholenaut falling into the black hole won't detect a radiation bath. Using 'a quantum model' the physics predicts they will [don't know any details for that]. I haven't read Hawkings paper [don't think it exists yet] but I've read about the firewall and apparent horizon.
Just to clarify something. GR is a classical theory and doesn't predict any quantum natural phenomena. It's not in the GR domain of applicability. Whenever you get the opportunity to evaluate a black hole using quantum mechanics it's a step forward for the research.

20. ### OnlyMeValued Senior Member

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Hawking posted a preprint of the paper the quote came from, it was mentioned and linked in the OP Nature Article link.

Here is a direct link, http://arxiv.org/abs/1401.5761. It is a short response to the earlier "firewall" concept, not so much a response to the paper itself, which is also referenced in the OP Nature link.

21. ### FarsightValued Senior Member

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RJ: don't pay any attention to this. It's smoke and mirrors. Kruskal Szekeres coordinates are nonsense. Imagine I had a clock that was going slower and slower and slower. Then imagine I "defined" some new time coordinate such that one second was one tick of that clock. That's effectively what Kruskal-Szekeres coordinates do. Guys like pryzk end up thinking you can put a stopped observer in front of a stopped clock, and the observer sees it ticking as normal. Then he'll throw a load of equations at you and try to blind you with maths. Look at his first line: For points inside the event horizon. There are no points inside the event horizon. It takes forever to cross the event horizon. We've been through this before. See the diagram on the left. The infalling observer goes to the end of time and back, and is in two places at once. It's garbage. It is total tosh.

But don't let this persuade you that black holes don't exist. They do. They just aren't like what people say they're like.

22. ### Walter L. WagnerCosmic Truth SeekerValued Senior Member

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Thanks for the historical reference, quite interesting.

We can infer something 'black', small, and of very large mass, in the center of our Milky Way about which numerous stars are in orbit. The orbits have been observed and plotted, as here:

http://www.bing.com/videos/search?q...&mid=E8C36A1666B3BA11E699E8C36A1666B3BA11E699

For lack of a better term, we can call that very large, dark mass a "black hole".

I believe Hawking has already had his share of 15 minutes of fame. He must be 'egocentric' to be constantly trying to write about black holes to get his name out there.

23. ### FarsightValued Senior Member

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Can somebody remind me about Hawking's contribution to physics? Only I'm having a spot of bother remembering what it is.