View Poll Results: Are we in a BH with one of the cosmic horizons serving as BH event horizon?
Yes, in my opinion we are. 13 14.29%
No. 59 64.84%
No opinion. 19 20.88%
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We are in a Schwarzschild black hole--T or F?


by marcus
Tags: black, holet, schwarzschild
jal
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#127
Apr16-08, 07:56 PM
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P: 640
http://arxiv.org/abs/hep-th/0603133
Naturalness of the Vacuum Energy in Holographic Theories
Authors: Csaba Balazs, Istvan Szapudi
(Submitted on 17 Mar 2006)
Based on the cosmic holographic conjecture of Fischler and Susskind, we point out that the average energy density of the universe is bound from above by its entropy limit. Since Friedmann's equation saturates this relation, the measured value of the cosmological energy density is completely natural in the framework of holographic thermodynamics: vacuum energy density fills the available quantum degrees of freedom allowed by the holographic bound. This is in strong contrast with traditional quantum field theories where, since no similar bound applies, the natural value of the vacuum energy is expected to be 123 orders of magnitude higher than the holographic value. Based on our simple calculation, holographic thermodynamics, and consequently any future holographic quantum (gravity) theory, resolves the vacuum energy puzzle.
foolosophy
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#128
May1-08, 11:30 AM
P: 35
If we are in fact living in a black hole then te BLACK HOLES we are describing within our own reality arent really balck holes but something else entirely.

You have set up a convoluted argument - close to a mathematical paradox by posing the question in that way.

And in any case there is no way of knowing.

A few points though come to mind -

If we are indeed living in a black hole, then why is it expanding?

Why are we proposing a BIG BANG cosmological model?

Why arent we detecting any material or energy that should be entering our little black hole via the event horizon?

What exactly is the Cosmic Backgound radiation then?
jal
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#129
May1-08, 01:55 PM
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P: 640
My quest started by a simple question, How is the universe made and how does it works?
As you can see in my blog, many have asked this question and there are many different approaches to try to get an answer.
I get my pleasure from seeking the answers.
I have not found the answer but Im still looking.
jal
foolosophy
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#130
May1-08, 10:11 PM
P: 35
The Socratic method is over 2500 years old and involves the gaining of wisdom and knowledge via the asking of questions - its still a fundamental basis for education and teaching throughout the world today.

foolosophy
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#131
May17-08, 11:20 PM
P: 35
confusing the location of the event horizon with the actual singularity itself is a common miss interpretation of what a Black hole is.
jmcgrady
jmcgrady is offline
#132
May18-08, 08:15 PM
P: 5
Quote Quote by marcus View Post
...How can we tell we arent in a BH? A LARGE black hole containing thousands of galaxies.

We if we were there would be a direction towards the collapse point, and in that direction galaxies would be redshifted because they would be accelerating faster, ahead of us, and in the reverse direction (behind us) galaxies would also be redshifted because we would be accelerating faster and escaping from them! And in the plane of direction which are abeam of us, sideways from that collapse direction (to port and starbord so to speak) galaxies would be BLUE shifted, cause we are all getting closer to each other as we approach the collapse point.
What if the Milky Way was at the centre of the BH? Say the universe is a bounded sphere. And that there is a greater density of galaxies near the centre - so much so that the schwarzschild BH criteria are met some distance from the centre such that the radius is less than 13.7 billion light years but greater than X billion light years. Would this explain why we see most galaxies as red shifted?
jal
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#133
Jun5-08, 04:04 PM
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P: 640
Leonid V. Verozub, will be making a presentation at the NEB-XIII Poster Session http://www.astro.auth.gr/~neb-13/program-posters.pdf
http://www.astro.auth.gr/~neb-13/programme.html
Here is his latest paper.
http://arxiv.org/abs/0805.0313v1
On accelerated Universe expansion
Authors: Leonid V. Verozub
(Submitted on 2 May 2008)
Abstract: It is shown that observed peculiarities of the Universe expansion are an inevitable consequence of the gravitational force properties following from gauge-invariant gravitation equations considered in detail in an author's paper in Annalen der Physik, v.17, 28 (2008).
jonmtkisco
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#134
Jun5-08, 06:39 PM
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Hi Jal,

Do you know if it's possible to get the Verozub paper from Ann. Phys. (Berlin) 2008? Apparently that's where he describes his underlying equations.

His solution for gravitational acceleration changing sign at a large distance and then declining to zero at infinity sounds like a good conceptual match for a kinematic-GR model. Then gravity can be the source of all kinematics in the universe.

At least it's worth understanding in more detail.

Jon
jal
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#135
Jun5-08, 09:04 PM
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P: 640
I can only access his papers by "clicking" on his name. I did not check out the rest of his papers. Maybe there is something there.
jal
jonmtkisco
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#136
Jun6-08, 01:15 PM
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HI jal,

It turns out he has a dozen or so papers on arXiv, all playing around with the same idea. His math is pretty inaccessible.

Jon
yuiop
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#137
Jun17-08, 09:51 AM
P: 3,966
Quote Quote by marcus View Post
......from post#40...

and around big bang time, stuff was WAY denser than Schwarzschild requires, so why didnt the universe collapse then and there? Because it was expanding so fast.
.......
Hi Marcus,

I normally hang around in the relativity forum (but I am by no means a relativity expert) and while playing around with Schwarzschild solutions I made a discovery that I think is very relevant to this thread and may provide an alternative answer to the question you pose here.

The equation for coordinate acceleration in the exterior Schwarzchild solution is:

[tex]a '=\frac{GM}{R^2}\left(1-\frac{R_s}{R}\right)[/tex]

When R is greater than the Schwarzschild radius the gravitational acceleration is positive towards the mass as you would expect. When R is less than the Schwarzchild radius the gravityational acceleration is negative and directed outwards towards the event horizon. if for example all the mass of the universe was originally confined to radius of R=Rs/10 then the outward acceleration is -900 GM/Rs^2. If the mass was confined to R=Rs/1,000 then the outward acceleration is -999,000,000 GM/Rs^2. Obviously, the outward gravitational acceleration gets considerably larger as original density increases.

Now if we look at the coordinate velocity of photon falling from infinity the equation is:

[tex]c '= c\left(1-\frac{R_s }{R}\right)[/tex]

and for R>Rs the coordinate velocity is always less than c, the velocity of light at infinity. Below the Schwarzchild radius the coordinate velocity of light get larger than c and is negative. This value for R<Rs is the speed of light falling from the centre outwards towards the event horizon. So for a universe with an extreme initial density photons (and particles with mass) move outwards towards the Schwarzchild radius at velocities much greater than c. In other words the outward expansion would very rapid until the universe reached the size of its own Schwarzchild radius. In fact the expansion would be arbitarily high and only limited by the initial density. The greater the initial density the greater the initial expansion. This would be very like the inflation that is thought to have occured early in the history of the universe. For falling particles the coordinate velocity is given by:

[tex]v ' = c\sqrt{{Rs \over R}} \left(1-\frac{R_s}{R} \right)[/tex]

One possible objection to this idea is that the coordinate velocity of the outward moving particles becomes zero at the Schwarzchild radius bring everything to a stop. I think this issue can be resolved by considering a universe with an initially flat spacetime. The rapid expansion of the particles within the Schwarzschild volume sends a gravitational shock wave that ripples outwards. Gravity waves have no difficulty passing event horizons and carry energy away with them. The loss of energy from the Schwarschild volume reduces the Schwarschild radius, releasing the particles trapped at the event horizon. The process is self destructive and the event horizon dissappears.

If dark energy is ignored this model would basically oscillate, with the universe expanding and collapsing to point and then expanding again. With dark energy it may never collapse.

I came to this conclusion while investigating the interior Schwarzschild solution that enables you examine what happens to a black hole as it forms and found that normal stable black holes do not have a singularity of infinite density at the centre but are a thin shell of matter just outside the event horizon.


For more equations and background on these ideas, see these threads:

http://www.physicsforums.com/showthr...=238839&page=2 post #19 onwards.

http://www.physicsforums.com/showpos...2&postcount=17

http://www.physicsforums.com/showthr...=223730&page=2 post#19

I hope these ideas are of interest. The nice thing about them is that they basically fall straight out of the Schwarzschild solutions. I am not saying dark energy does not exist or that the Schwarschild solutions might have to be modified a bit to allow for expanding spacetime, but I am saying that that even without those things the Schwarzschild equations do not imply the universe would be trapped in a black hole even when there technically enough mass within a given radius to be a black hole. In fact, examination of the solutions show the universe would be very different if we were inside a black hole.
yuiop
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#138
Jun19-08, 04:10 AM
P: 3,966
Quote Quote by kev View Post
One possible objection to this idea is that the coordinate velocity of the outward moving particles becomes zero at the Schwarzchild radius bring everything to a stop. I think this issue can be resolved by considering a universe with an initially flat spacetime. The rapid expansion of the particles within the Schwarzschild volume sends a gravitational shock wave that ripples outwards. Gravity waves have no difficulty passing event horizons and carry energy away with them. The loss of energy from the Schwarschild volume reduces the Schwarschild radius, releasing the particles trapped at the event horizon. The process is self destructive and the event horizon dissappears.
I just found a counter argument to my above statement. Damn!
http://en.wikipedia.org/wiki/Birkhof...em_(relativity)

Birkhoff's theorem states a pulsating spherical mass can not give off gravitational waves. That seems reasonable as the gravitaional filed of a sperical object always looks like a point source outside the mass of the body.

There are however any number of potential ways that the mass trapped in a shell at the Schwarzschild radius can escape. The loss of a single atom or photon by Hawking radiation or quantum tunelling would start the destruction of the event horizon. This is even more likely as there is no CMB radiation adding to the mass/energy of the Schwarzschild mass at this epoch. The other method is to observe that the escape velocity at the event horizon is c and that during the inflation period the velocities of exceed c as explained in my last post.

So for those who cherish the notion that if the universe is expanding, that it must have been smaller and denser at some time in the past, GR can cope with that. For those that dont like that notion, you can take comfort with thought of a universe that started infinite in volume and mass and then continued expanding.


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