Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Kauffmann on 24/10/2014 04:27:53
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I've been giving a brief thought to some of the characateristics of black holes described by modern physics and I have 3 observations that may be pertinent and worth discussing.
1. It's impossible to see towards the singularity of a black hole even beyond the horizon, why? because if the horizon represents the frontier where gravitational acceleration equals c, then anywhere beyond that point only makes acceleration even greater than c. You could only see the singularity once you've hit it.
2. On the note of the 1st point, if gravitational acceleration equals c at the horizon, then wouldnt that mean that beyond the horizon, a black hole is capable of accelerating objects beyond c?
3. If gravitational wells make time go slower, wouldn't that mean that the gravitational well of a black is strong enough as to make time passage inside of a black hole for an outside observer go asymptotically to 0? Meaning that such force will make time inside the horizon for an outside observer to virtually stop. Taking, maybe trillions of years to even get close to the singularity. This means that there might be no such singularity and/or that most of the mass inside all recent black holes be not in the singularity, but on it's way to it.
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1. It's impossible to see towards the singularity of a black hole even beyond the horizon, why?
Because all worldlines ( which originate inside the horizon stay within the horizon and thus inside the black hole.
If you don't know what a worldline is see:
http://en.wikipedia.org/wiki/World_line
... because if the horizon represents the frontier where gravitational acceleration equals c, ...
That's not possible. Acceleration and c are different things. The former is acceleration having units of m/c2 whereas the later has units m/s.
... then anywhere beyond that point only makes acceleration even greater than c. You could only see the singularity once you've hit it.
This sentence makes no sense to me. Can you further clarify what you mean by it?
2. On the note of the 1st point, if gravitational acceleration equals c at the horizon, then wouldnt that mean that beyond the horizon, a black hole is capable of accelerating objects beyond c?
Even it that sentence made sense the answer would be no since nothing can go faster than c.
3. If gravitational wells make time go slower, wouldn't that mean that the gravitational well of a black is strong enough as to make time passage inside of a black hole for an outside observer go asymptotically to 0?
As reckoned by an observer who is outside the event horizon, the closer a clock is to the event horizon the slower it runs (i.e. ticks). It the clock is just a smidgen away from the event horizon then the clock will appear to be frozen and not ticking at all.
Meaning that such force will make time inside the horizon for an outside observer to virtually stop.
No. It's not the force that is responsible for the clock slowing down, it's the gravitational potential that's related to the rate at which the clock ticks.
Taking, maybe trillions of years to even get close to the singularity.
As observed by whom?
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1. It's impossible to see towards the singularity of a black hole even beyond the horizon, why? because if the horizon represents the frontier where gravitational acceleration equals c, then anywhere beyond that point only makes acceleration even greater than c. You could only see the singularity once you've hit it.
That's if a singularity actually exists. Have a read of The Formation and Growth of Black Holes (http://mathpages.com/rr/s7-02/7-02.htm) by Kevin Brown. He refers to two interpretations of GR, one of which leads to the "frozen star" concept. He doesn't favour this, but I think it's correct.
2. On the note of the 1st point, if gravitational acceleration equals c at the horizon, then wouldnt that mean that beyond the horizon, a black hole is capable of accelerating objects beyond c?
I don't think it is c actually. The local force of gravity relates to the gradient in the "coordinate" speed of light at that location. And at the event horizon, the coordinate speed of light is zero. We were talking about this sort of thing on another forum, and one of the guys emailed a physics professor with a scenario I proposed:
You're standing on a gedanken planet holding a laser pointer straight up. The light doesn't curve round, or slow down as it ascends, or fall down. It goes straight up. Now I wave my magic wand and make the planet denser and more massive. The light still doesn't curve round, or slow down as it ascends, or fall down. I make the planet even denser and more massive. The light still doesn't curve round, or slow down as it ascends, or fall down. I make the planet even denser and more massive, and take it to the limit such that it's a black hole. At no point did the light ever curve round, or slow down as it ascends, or fall down. So why doesn't the light get out?
The answer was this:
As the planet's mass approaches the black hole limit, the signal emitted from the surface will seem to move more and more slowly away from the surface (and will also be seen to be increasingly red-shifted as observed from infinity). When the surface of the planet coincides with the black hole's event horizon, the signal will stop moving outward from the surface (and the redshift observed at infinity will go to infinity). So light no longer escapes.
Light doesn't get out because the coordinate speed of light is zero at the event horizon. And it can't go lower than that. So there's no gravitational acceleration beyond the event horizon.
3. If gravitational wells make time go slower, wouldn't that mean that the gravitational well of a black is strong enough as to make time passage inside of a black hole for an outside observer go asymptotically to 0?
Yes. Hence the "frozen star" black-hole concept. This dates back to Oppenheimer.
Meaning that such force will make time inside the horizon for an outside observer to virtually stop. Taking, maybe trillions of years to even get close to the singularity. This means that there might be no such singularity and/or that most of the mass inside all recent black holes be not in the singularity, but on it's way to it.
Yep. Like Pmb said it's potential rather than force. And as per the above, whatever fell in might not be on its way anywhere.
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"So there's no gravitational acceleration beyond the event horizon."
Oh! So you mean the acceleration gradient beyond the horizon equals 0? Or the well doesn't curve any further than c?
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Sorry PmbPhy, but I think you didn't get anything. I mean, try not to think so strictly in scientific terminology.
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Sorry PmbPhy, but I think you didn't get anything.
I got what was able to be "got" from what you said and the way you said it. You weren't very clear. For example, when you wrote
1. It's impossible to see towards the singularity of a black hole even beyond the horizon, why? because if the horizon represents the frontier where gravitational acceleration equals c, then anywhere beyond that point only makes acceleration even greater than c. You could only see the singularity once you've hit it.
You, quite literally, can see towards the singularity since seeing towards something means that you can see things in the direction of the singularity and if there are things between the singularity and you then you can see them if they're illuminated. For example: if I say I can "see towards" the moon then it means that I'm looking in the direction of the moon. If it was the summer of 1969 then I could see Apollo 11 heading to the moon. That's because the spacecraft is in-between you and the moon.
It's for those reasons that it's not literally impossible to see things towards the singularity. If you're talking about things inside the event horizon then it doesn't have to be towards the singularity not to be seen.
Just because you can't "see" it, it doesn't mean that it can't be detected. We know it's there. It may no be radiating photons but it does generate a gravitational field and it's for that reason we can detect it. It's misleading to think that just because we can't use light to detect something then it isn't there.
I mean, try not to think so strictly in scientific terminology.
You're kidding, right? Why shouldn't I think so strictly in scientific terminology? You understand that this is a science forum, right? Its the goal for physicists such as myself who try to help people understand physics to attempt to get the people we're trying to help to think strictly in scientific terms. Only then can the real meaning get through. E.g. you weren't speaking strictly in scientific terminology and that's how you made the mistake of confusing speed with acceleration.
If you don't like what I write then don't read it. But remember that you're not the only one reading these posts. They're going to be here as long as the forum exists and someone could come back to this thread 5 years from now and read it. Those people will mostly want strict scientific terms to be used.
Frankly I can't understand what you're problem is with such terminology and what it has to do with what I posted. Please clarify that for me, will you? Thanks. :)
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Don't see where you find Pete to be ambivalent. He's perfectly clear here, and perfectly correct as far as I see? You need to read up on the subject.
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Ah forget it
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Ah forget it
You should be clearer. If you meant that at the event horizon an instantaneous reading of acceleration gives a value equal to c in that instant that is different. The value of c as stated is simply a speed and involves no acceleration. Gravitational acceleration is s^2 a per second per second measure. As Pete stated c is inviolate so stating that c can be exceeded breaks the laws of physics. What you got wrong is that at the event horizon escape velocity equals c and not g.
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Ah! So you mean the acceleration gradient beyond the horizon equals 0?
Yes. If I could set you down at the event horizon, you wouldn't fall down.
Or the well doesn't curve any further than c?
It's like the well is bottomed out. See this image (http://scienceblogs.com/startswithabang/files/2009/11/dec07_1_10.gif). The black bit in the middle is where the "coordinate" speed of light is zero. It can't go lower than that. And because the speed of light is zero, your light clock stops, along with the electrochemical signals in your brain. So you can't see anything.
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Ah! So you mean the acceleration gradient beyond the horizon equals 0?
Yes. If I could set you down at the event horizon, you wouldn't fall down.
Or the well doesn't curve any further than c?
It's like the well is bottomed out. See this image (http://scienceblogs.com/startswithabang/files/2009/11/dec07_1_10.gif). The black bit in the middle is where the "coordinate" speed of light is zero. It can't go lower than that. And because the speed of light is zero, your light clock stops, along with the electrochemical signals in your brain. So you can't see anything.
What people generally tend to neglect is that although escape velocity equals c the gravitational acceleration is a different beast altogether. On earth escape velocity is around 11.2 km/s whereas gravitational acceleration is a very small fraction of this at 9.81 metres per second every second. I have run calculations for dense masses and the results are very interesting. If you really think you are going to set someone down at the event horizon you have a strange idea of placing objects. I wouldn't let you into a china shop.
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Interestingly, if kinetic energy is taken from mass by gravitation then the more dense a mass gets then the slower the flux of energy. However at some point it will have lost significant gravitational energy because of the strength of the field. If enough is lost the effects of time dilation and any possible length contraction will start to subside. There will be a point of no return where the reversal of dilation is unstoppable and results in an energetic explosion when all the dilated energy flux speeds up all at once. Hence the big bang and the ripples of early gravitation in the CMB.
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You should take a look at Friedwardt Winterberg's firewall. See this:
http://www.znaturforsch.com/aa/v56a/56a0889.pdf
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You should take a look at Friedwardt Winterberg's firewall. See this:
http://www.znaturforsch.com/aa/v56a/56a0889.pdf
I can see his point about the internal masses. I currently have no way to quantify this type of hypothesis. I am currently on the fence about a number of things. I will have to reject some ideas and am trying to decide which.
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Mighty interesting fellas
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If you Google " black hole magnetic field" you will find a research article by Berkeley dated 4 June which claims that there is evidence that the magnetic field is so strong around some 70 super massive black holes that it more than counters gravity. Probably all super massive black holes at the centre of galaxies will prove to be magnetic hubs as predicted by magnoflux CliveS