50 Billion Suns! -The Biggest Single Object in the Universe !

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Offline dlorde

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« Reply #50 on: 19/03/2009 21:53:30 »
I think I've remembered what that Blue Curtain thing is all about. It's from the perspective of an observer falling into the EH. Does that sound better?

I don't see it myself [;)]

If you're falling towards the EH, you're accelerating. You'll be accelerating away from everything further out, so if you look back, it will all be red-shifted. Everything in front of you (toward the EH) is accelerating away from you into the BH, so that should be red-shifted too. So where does the blue light come in? Maybe if you were stationary at the EH, you'd see stuff coming in toward you as blue-shifted...

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Offline DoctorBeaver

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« Reply #51 on: 19/03/2009 23:52:58 »
dlorde - I don't remember the details of it. It was at least 4 years ago and I didn't know much about physics in those days (I still don't, but I knew even less then). It didn't really sink in.
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Offline dlorde

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« Reply #52 on: 20/03/2009 01:33:24 »
dlorde - I don't remember the details of it. It was at least 4 years ago and I didn't know much about physics in those days (I still don't, but I knew even less then). It didn't really sink in.
OK, I was just curious.

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Offline itisus

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« Reply #53 on: 20/03/2009 05:46:16 »
"That's a hundred thousand tredagrams, and you'll never get the chance to use that word in relation to anything else."

It's a lot less than a googleplex though, and there is one of those in Mountain View.  I've been in Mountain View a few times; it's no big deal.

It's late, but my scratch paper gives about 10^(-8) grams /m^3.  Air at sea level is on the order of kg/m^3.

I have wondered whether the universe should be considered a black hole.  Nothing escapes unless it is evaporating, its size is unknown but much larger than 50 billion suns, and the usual Schwarzschild interior solution is dubious.

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Offline LeeE

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« Reply #54 on: 20/03/2009 12:04:23 »
I think I've remembered what that Blue Curtain thing is all about. It's from the perspective of an observer falling into the EH. Does that sound better?

I don't see it myself [;)]

If you're falling towards the EH, you're accelerating. You'll be accelerating away from everything further out, so if you look back, it will all be red-shifted. Everything in front of you (toward the EH) is accelerating away from you into the BH, so that should be red-shifted too. So where does the blue light come in? Maybe if you were stationary at the EH, you'd see stuff coming in toward you as blue-shifted...

You've got to remember the time-dilation effects too.
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline Vern

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« Reply #55 on: 20/03/2009 13:25:17 »
The Event Horizon is a region around a black hole that marks the boundary where light closer in can never exit the black hole. Why does that fact give the boundary special properties?  The natural laws should still apply. A steel rod part way past the EH should still allow its internal construct to follow a force on the outside part that pulled it out of the EH.

I think we globally describe the event horizon then in our minds, give it special properties that the General theory of Relativity does not give it.

We like to say that, once past the event horizon, nothing can escape. Maybe that should be modified to say that nothing operating under its own momentum can escape.

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Offline dlorde

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« Reply #56 on: 20/03/2009 20:51:15 »
You've got to remember the time-dilation effects too.
OK, please explain, I don't see how time-dilation would cause an observer falling into the BH to see blue-shifted light.

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Offline dlorde

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« Reply #57 on: 20/03/2009 20:54:50 »
The Event Horizon is a region around a black hole that marks the boundary where light closer in can never exit the black hole. Why does that fact give the boundary special properties?  The natural laws should still apply. A steel rod part way past the EH should still allow its internal construct to follow a force on the outside part that pulled it out of the EH.

I think we globally describe the event horizon then in our minds, give it special properties that the General theory of Relativity does not give it.

We like to say that, once past the event horizon, nothing can escape. Maybe that should be modified to say that nothing operating under its own momentum can escape.
Yes, there is no special property at the EH, it's simply the point at which the escape velocity is > c. An observer falling through the EH wouldn't notice anything - assuming the BH is large enough that tidal forces don't rip him apart  [;)]

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Offline Vern

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« Reply #58 on: 20/03/2009 22:05:40 »
That was my thinking exactly. However, we seem to be thinking of the EH as the singularity itself. It seems to me that the EH would be some distance from the singularity.


Wiki article explaning the Schwarzschild radius

Quote from: the article.
In 1916, Karl Schwarzschild obtained an exact solution[1][2] to Einstein's field equations for the gravitational field outside a non-rotating, spherically symmetric body (see Schwarzschild metric). The solution contained a term of the form 1 / (2M − r); the value of r making this term singular has come to be known as the Schwarzschild radius. The physical significance of this singularity, and whether this singularity could ever occur in nature, was debated for many decades; a general acceptance of the possibility of a black hole did not occur until the second half of the 20th century.

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Offline DoctorBeaver

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« Reply #59 on: 21/03/2009 08:48:47 »
Apparently you don't actually need a singularity for an event horizon to form. If the mass is spread over a large enough area you could still get an EH. I've seen this theory proposed for the universe. It was referred to as a brown hole (sounds a bit dodgy, that).
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Offline LeeE

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« Reply #60 on: 21/03/2009 19:28:06 »
The Event Horizon is a region around a black hole that marks the boundary where light closer in can never exit the black hole. Why does that fact give the boundary special properties?  The natural laws should still apply. A steel rod part way past the EH should still allow its internal construct to follow a force on the outside part that pulled it out of the EH.

I think we globally describe the event horizon then in our minds, give it special properties that the General theory of Relativity does not give it.

We like to say that, once past the event horizon, nothing can escape. Maybe that should be modified to say that nothing operating under its own momentum can escape.

The event horizon isn't a region but a boundary.  It doesn't occupy a volume of space but separates two regions of space that have different characteristics.  In the region of space outside the event horizon the rate of time is greater than zero but reduces as one gets closer to the event horizon.  Exactly at the event horizon, the rate of time reduces to zero.  What happens on the other side of the event horizon is anyone's guess, and a guess is all anyone can give you, but one thing for sure is that you couldn't poke a steel rod through it.

It's debatable that the steel rod could even actually reach the event horizon, for if space is distorted just as time is, there may be an infinite amount of space compressed around the event horizon, in which case you could fall forever and never reach the event horizon, not only from your point of view, in a slow time-frame, but also from the point of view of an observer, who would seem to see you perpetually receding from them, both shrinking and fading from sight.  Like I said though, this interpretation of the distortion of space-time around a black hole is open to debate.

However, one thing is for sure, if the rate of time reduces to zero at the event horizon we cannot talk of anything happening inside it for there appears to be no time, from our point of view, on the other side of the event horizon for anything to happen within.
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline LeeE

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« Reply #61 on: 21/03/2009 19:44:22 »
You've got to remember the time-dilation effects too.
OK, please explain, I don't see how time-dilation would cause an observer falling into the BH to see blue-shifted light.

Although light produced closer to the event horizon than the observer is red-shifted, effectively reducing it's frequency when viewed by the observer, the time-dilation experienced by the observer means that less time has passed for the observer, which has the effect of raising the frequency of the light.

Also, iirc, I think the main factor for the Blue curtain effect is that matter falling into the BH produces gamma frequency light, which after the red-shift and time-dilation factors are taken in to consideration, ends up as blue in the visible spectrum.   Or something like that.
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline Vern

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« Reply #62 on: 21/03/2009 20:33:11 »
Quote from: LeeE
However, one thing is for sure, if the rate of time reduces to zero at the event horizon we cannot talk of anything happening inside it for there appears to be no time, from our point of view, on the other side of the event horizon for anything to happen within.
Are you sure about this? It seems that time should be zero at the singularity. How does time get to be zero at the Event Horizon?

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Offline LeeE

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« Reply #63 on: 21/03/2009 20:55:38 »
Quote from: LeeE
However, one thing is for sure, if the rate of time reduces to zero at the event horizon we cannot talk of anything happening inside it for there appears to be no time, from our point of view, on the other side of the event horizon for anything to happen within.
Are you sure about this? It seems that time should be zero at the singularity. How does time get to be zero at the Event Horizon?

Have a look at:

http://en.wikipedia.org/wiki/Gravitational_time_dilation#Outside_a_non-rotating_sphere

for the simplest solution (outside a non-rotating sphere).  The formula is pretty simple and it shows that at the Schwarzchild radius you end up with 0.

Interestingly, there's another solution just below, for inside the event horizon, but it doesn't deal with how anything can actually pass that zero-time boundary, and while the outside solution might be provable, the inside solution isn't; if someone were to be able to get inside to prove it, they couldn't convey that proof back to us.
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline Vern

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« Reply #64 on: 21/03/2009 23:57:17 »
Thanks for the link LeeE. I notice that the Schwarzchild radius is part of the equation. It is not immediately obvious to me that t = 0 at that radius. I don't doubt that it might, I just notice that many folks think that t = 0 closer in toward the singularity. I'll have to do some arithmetic.  [:)]

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Offline dlorde

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« Reply #65 on: 22/03/2009 01:11:29 »
The event horizon isn't a region but a boundary.  It doesn't occupy a volume of space but separates two regions of space that have different characteristics.
In the region of space outside the event horizon the rate of time is greater than zero but reduces as one gets closer to the event horizon.  Exactly at the event horizon, the rate of time reduces to zero.  What happens on the other side of the event horizon is anyone's guess, and a guess is all anyone can give you, but one thing for sure is that you couldn't poke a steel rod through it.
Not really - the time dilation experienced by objects at the EH is relative to the outside observer. Because of the extreme curvature of spacetime, external observers can't see beyond the event horizon in space or time, but the only thing special about spacetime at that point is the amount of curvature it has. From outside, we can't see inside because at that point the curvature is too great, but the curvature is smooth. If the black hole is sufficiently large (e.g. 10 million x solar mass), the curve will be shallow enough at the EH that an observer falling through the EH would not be ripped apart by the tidal forces, and would, in principle (ignoring radiation, etc) be able survive for some time on the other side before being pulled apart.

Quote
It's debatable that the steel rod could even actually reach the event horizon, for if space is distorted just as time is, there may be an infinite amount of space compressed around the event horizon, in which case you could fall forever and never reach the event horizon, not only from your point of view, in a slow time-frame, but also from the point of view of an observer, who would seem to see you perpetually receding from them, both shrinking and fading from sight.  Like I said though, this interpretation of the distortion of space-time around a black hole is open to debate.
Again, that's not accurate, there is no special discontinuity at the EH - the singluarity sits at the bottom of almost infinitely deep gravity well - we don't know what's near the bottom or if there is one, but spacetime is being effectively stretched down into this well. Space-time may be compressed at the singularity, but no-one knows. But outside the singularity tidal forces will pull objects apart in the direction of travel and compress them across it (spaghettisation) as the gravity differentials across them strengthen as space-time stretches. Other than that (ouch), and some odd visual distortions, not a lot is different.

Quote
However, one thing is for sure, if the rate of time reduces to zero at the event horizon we cannot talk of anything happening inside it for there appears to be no time, from our point of view, on the other side of the event horizon for anything to happen within.
That doesn't mean that an observer falling through the EH experiences that time distortion. It is possible to predict what they might experience right up until they approach the region of singularity. In 'The Emperor's New Mind' (pp 433,434), Roger Penrose describes what an observer B, falling into a BH, away from an observer A outside the EH, would experience:

".. It should first be pointed out that there will be nothing whatever noticeable by B at the moment of his crossing the horizon. He glances at his watch ... and he sees the minutes pass regularly by. He can look back at A, and will find that A remains continuously visible the whole time. He can look at A's own watch, which appears to be proceeding in an orderly and regular fashion. Unless B has calculated that he must have crossed the horizon, he will have no way of knowing it. ... The second law [of thermodynamics] will hold sway just as much inside a BH as it does elsewhere. The entropy in B's vicinity is still increasing, right up to the time of his final crunch." Penrose should know - he helped Hawking develop the physics of BHs.

ISTM that in principle, it would be possible to drop down a cable or tether across the EH from orbit around a BH - but of course, you couldn't pull it back. In practice, the tether would have to be incredibly strong, and if it didn't break, it would start pulling you in towards the EH well before it got there. Once it reached the EH, you'd have to let go or be pulled in with it.

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Offline om

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« Reply #66 on: 22/03/2009 05:16:26 »
Detailed studies of the properties of ordinary nuclei reveal strongly repulsive interactions between neutrons.

[See: "Neutron repulsion confirmed as energy source", Journal of Fusion Energy 20, 197-201 (2003)].

http://www.omatumr.com/abstracts2003/jfe-neutronrep.pdf

These studies show that neutron-emission from a neutron star "may release up to 1.1%-2.4% of the nuclear rest mass as energy".  By comparison, only about 0.8% of the rest mass is converted to energy in Hydrogen fusion and only about 0.1% of the nuclear rest mass is converted to energy in fission.

Therefore massive, energetic celestial objects are probably not black holes at all, but neutron stars that are highly energized by repulsive interactions between neutrons.

With kind regards,
Oliver K. Manuel
http://www.omatumr.com/

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Offline dlorde

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« Reply #67 on: 22/03/2009 10:33:24 »
Another good link on falling into a Black Hole (it's not habit forming  [;)]) : Fall Into A Black Hole
« Last Edit: 22/03/2009 18:01:38 by dlorde »

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Offline DoctorBeaver

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« Reply #68 on: 22/03/2009 10:57:54 »
There's a problem with your link. You got http:// twice. Try editing it.

It's an interesting article but I'll have to read it a few times to fully absorb it.
« Last Edit: 22/03/2009 11:11:57 by DoctorBeaver »
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Offline om

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« Reply #69 on: 22/03/2009 13:50:08 »
DoctorBeaver,

Thanks for your comment.  Try this link to: "Neutron repulsion confirmed as energy source", J. Fusion Energy 20 (2003) 197-201,

www.omatumr.com/abstracts2003/jfe-neutronrep.pdf


If it doesn't work, see: "Nuclear systematics: III. The source of solar luminosity", Journal of Radioanalytical & Nuclear Chemistry, Vol. 252, No. 1 (2002) 3-7

www.omatumr.com/abstracts2001/nuc_sym3.pdf

With kind regards,
Oliver
www.omatumr.com/index.html


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Offline Vern

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« Reply #70 on: 22/03/2009 13:53:39 »
Another good link on falling into a Black Hole (it's not habit forming  [;)]) : Fall Into A Black Hole
It seems to still not work when edited.

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Offline yor_on

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« Reply #71 on: 22/03/2009 15:12:03 »
Ah, Vern, wrong dude :)
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Offline Vern

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« Reply #72 on: 22/03/2009 15:38:27 »
Well; I don't know; the link did have, http://http://, doubled like that. But I fixed it in the quote and the link still didn't work. However the home site is really nice [:)]

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Offline dlorde

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« Reply #73 on: 22/03/2009 18:05:06 »
Sorry guys, it's fixed now. Looks like this forum software adds the http prefix automatically.

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Offline LeeE

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« Reply #74 on: 22/03/2009 21:07:37 »
The event horizon isn't a region but a boundary.  It doesn't occupy a volume of space but separates two regions of space that have different characteristics.
In the region of space outside the event horizon the rate of time is greater than zero but reduces as one gets closer to the event horizon.  Exactly at the event horizon, the rate of time reduces to zero.  What happens on the other side of the event horizon is anyone's guess, and a guess is all anyone can give you, but one thing for sure is that you couldn't poke a steel rod through it.
Not really - the time dilation experienced by objects at the EH is relative to the outside observer. Because of the extreme curvature of spacetime, external observers can't see beyond the event horizon in space or time, but the only thing special about spacetime at that point is the amount of curvature it has. From outside, we can't see inside because at that point the curvature is too great, but the curvature is smooth. If the black hole is sufficiently large (e.g. 10 million x solar mass), the curve will be shallow enough at the EH that an observer falling through the EH would not be ripped apart by the tidal forces, and would, in principle (ignoring radiation, etc) be able survive for some time on the other side before being pulled apart.

While the degree of time-dilation is relative to the observer, as it must be unless when compared with a hypothetical space-time frame outside of our universe, it doesn't mean that the effect is not real.  Experiments, both with moving clocks and with clocks in different gravitational potential, show that different amounts of time have passed for the two separated clocks when they are subsequently brought back together.  The difference in the duration of time that has passed for the two separated points of view is not illusory.  Thus, as something approaches an event horizon, the absolute amount of time that passes for the approaching object is less than the absolute amount of time that has passed for a distant observer, and when the approaching observer reaches the event horizon zero time will pass for it.  At this point, the ratio between the rate and duration of time for the approaching observer and that for the distant observer becomes infinite, and from that point onwards, physics breaks down.  Yes, the approaching observer will not be aware that time is running slow, at least from their point of view, in their own space-time frame; they will not 'feel' that they are running slow, and neither, when/if they reach the event horizon, will they realise that no time is passing for them, because everything will have stopped.  Even though the difference can only be expressed in relative terms, if one set of values equals zero the difference is absolute.

If the approaching observer only closely approaches the event horizon, and then returns to the distant observer, their two space-time frame can be reconciled because the difference between the rates and durations of time that have passed for both of them will be finite.  If the approaching observer were to be able to actually reach the event horizon, however, the difference between the two rates and durations cannot be reconciled because for the approaching observer, they will both be zero.

I think that the other two points you raise are dependent upon your first point.
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline LeeE

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« Reply #75 on: 22/03/2009 21:18:26 »
Thanks for the link LeeE. I notice that the Schwarzchild radius is part of the equation. It is not immediately obvious to me that t = 0 at that radius. I don't doubt that it might, I just notice that many folks think that t = 0 closer in toward the singularity. I'll have to do some arithmetic.  [:)]

This is the equation:



cutting straight to the shortened form, to save time, when the distance r from the center of the object is equal to the Schwarzchild radius r0, we get 1 - 1 = 0.
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline yor_on

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« Reply #76 on: 22/03/2009 23:58:23 »
Just a thought. according to the Schwarzchild metric the inside of the EV (event horizon) will, if observed from the inside, be almost limitless in distance if I understand it right. When we have a spinning black hole using the Kerr metric I presume the same. But then we have the spin too? That must add to the distances as seen from the inside, won't it?  Won't all geodesics  become infinitely long there as it forms a spiraling motion?? Not that you would notice it while being in there, but if one could observe it from the outside? (I know you can't though, still?:)
« Last Edit: 23/03/2009 00:02:02 by yor_on »
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Offline Vern

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« Reply #77 on: 23/03/2009 00:18:59 »
Okay; I am a convert [:)] According to the accepted equations t = 0 at the event horizon. But it seems now that nothing could ever reach the event horizon. I think mostly in terms of computer simulation since that is what I've done most of my life, and I can't imagine a program that could simulate something getting past the event horizon.

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Offline dlorde

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« Reply #78 on: 23/03/2009 14:12:43 »
While the degree of time-dilation is relative to the observer, as it must be unless when compared with a hypothetical space-time frame outside of our universe, it doesn't mean that the effect is not real.
Certainly it's real, the external observer measures the time of the infalling observer slowing, and their image dimming and reddening. From the external observer's POV, the faller never reaches the EH.

Quote
Thus, as something approaches an event horizon, the absolute amount of time that passes for the approaching object is less than the absolute amount of time that has passed for a distant observer, and when the approaching observer reaches the event horizon zero time will pass for it.
Yes - from the POV of the distant observer. This is relativistic physics at the extremes, but it only breaks down completely at the singularity.

Quote
Yes, the approaching observer will not be aware that time is running slow, at least from their point of view, in their own space-time frame; they will not 'feel' that they are running slow, and neither, when/if they reach the event horizon, will they realise that no time is passing for them, because everything will have stopped.
Only with respect to the distant observer. The approaching observer will notice no change in time in his local vicinity, as my quote from Penrose describes.

Quote
Even though the difference can only be expressed in relative terms, if one set of values equals zero the difference is absolute. If the approaching observer only closely approaches the event horizon, and then returns to the distant observer, their two space-time frame can be reconciled because the difference between the rates and durations of time that have passed for both of them will be finite.
And the visitor to the edge of the EH would have aged considerably less than the outside universe - the distant observer and his planet would probably be ancient history by the time he returned (all depending on how close the observer got to the EH).

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If the approaching observer were to be able to actually reach the event horizon, however, the difference between the two rates and durations cannot be reconciled because for the approaching observer, they will both be zero.
I'm with Penrose on this one - he developed the physics of BHs. I can't pretend to have the maths to work it out myself, so when he says the EH is simply the point where the curvature of spacetime routes light into a circular path, and that an approaching observer can, in principle, fall through it without noticing significant change, I'll take his word - unless, of course, there have been developments in BH physics in the years since, that have changed that description - but I haven't heard of any.


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Offline LeeE

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« Reply #79 on: 23/03/2009 14:30:36 »
Vern:

I think that whether something can actually reach the event horizon or not depends upon how space is warped in the region of the BH.

If space is linear in the direction of the BH, that is, along a straight line passing through the center of the BH, and is only warped around the BH so that an orbit feels like a straight line, then I can't see any reason why something could not reach the event horizon.  In this case, the distance traveled, as measured by both the approaching object and the distant observer would agree.  This would be akin to an observer on Earth* a distant observer agreeing with an observer in the ISS that the ISS was at the same altitude above the Earth.

If space is non-linear along that line though, then moving say, one metre nearer as viewed by a distant observer, might actually equate to moving more than one meter for the approaching object.  If this is so, and the amount of spatial warping matches the amount of temporal warping, then it seems to me that at the point where the rate of time drops to zero the amount of space becomes infinite and the object can never reach the event horizon.  In this case, an observer in close orbit around a BH would disagree with a distant observer regarding their altitude above the event horizon.

As time is non-linear along a path through the center of the BH, I'm inclined to believe that space is non-linear along that path too.

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« Last Edit: 24/03/2009 13:49:51 by LeeE »
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline LeeE

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« Reply #80 on: 23/03/2009 14:57:15 »
dlorde:

Outside of the event horizon, physics is no different to any other gravity well and just as something accelerates as it falls in to the Earth's gravity well, it will accelerate as it falls towards an event horizon; it will not seem to slow down.  The only slowing that will be apparent to a distant observer is if the falling object is periodically sending a signal back to the observer at a constant rate i.e. the falling object flashes a light once every second.  Then you will find that the amount of time between successive flashes increases, showing that the rate of time for the falling object has slowed.

The reduced amount of time that passes for the falling object is not just from the point of view of the distant observer.  If this were so, then two synchronised clocks, one staying with the distant observer and the other traveling close to the BH before returning, would show the same elapsed time when the traveling clock returned; the clock experiments that have been performed, both moving and in different gravitational potentials show that this is not so and there is an absolute difference in the amount of time that has passed for the two clocks.

You then seem to go on and agree that different amounts of time will pass for the two different locations, so I can't see how you can say that it will only be from the POV of the distant observer.

As much as I respect Penrose, I have to work stuff out for myself, and if I come to different conclusions, so be it.
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline LeeE

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« Reply #81 on: 23/03/2009 15:01:44 »
Just a thought. according to the Schwarzchild metric the inside of the EV (event horizon) will, if observed from the inside, be almost limitless in distance if I understand it right. When we have a spinning black hole using the Kerr metric I presume the same. But then we have the spin too? That must add to the distances as seen from the inside, won't it?  Won't all geodesics  become infinitely long there as it forms a spiraling motion?? Not that you would notice it while being in there, but if one could observe it from the outside? (I know you can't though, still?:)

Yes, the equation for inside the event horizon is interesting, but it's even more hypothetical, and imo, more questionable than the conditions outside it.  However, if both equations actually do apply, then they must be reconcilable with each other; the implications of one must be accounted for in the other because they are both dealing with the same single object.
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline dlorde

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« Reply #82 on: 23/03/2009 15:30:00 »
... If this is so, and the amount of spatial warping matches the amount of temporal warping, then it seems to me that at the point where the rate of time drops to zero the amount of space becomes infinite and the object can never reach the event horizon.
If an object approaching the BH can never reach the event horizon, doesn't this suggest that a BH, once formed, will not increase in mass, as no mass can reach it... ? Wouldn't this lead to a dense shell of mass trapped at the EH ?

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Offline dlorde

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« Reply #83 on: 23/03/2009 15:38:53 »
The reduced amount of time that passes for the falling object is not just from the point of view of the distant observer.  If this were so, then two synchronised clocks, one staying with the distant observer and the other traveling close to the BH before returning, would show the same elapsed time when the traveling clock returned; the clock experiments that have been performed, both moving and in different gravitational potentials show that this is not so and there is an absolute difference in the amount of time that has passed for the two clocks.

You then seem to go on and agree that different amounts of time will pass for the two different locations, so I can't see how you can say that it will only be from the POV of the distant observer.
Different amounts of time will pass in each location *relative to the other*.

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As much as I respect Penrose, I have to work stuff out for myself, and if I come to different conclusions, so be it.
Fair enough.

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Offline LeeE

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« Reply #84 on: 23/03/2009 15:50:51 »
... If this is so, and the amount of spatial warping matches the amount of temporal warping, then it seems to me that at the point where the rate of time drops to zero the amount of space becomes infinite and the object can never reach the event horizon.
If an object approaching the BH can never reach the event horizon, doesn't this suggest that a BH, once formed, will not increase in mass, as no mass can reach it... ? Wouldn't this lead to a dense shell of mass trapped at the EH ?

Yes, so it would seem, or rather, just outside the EH.  For the distant observer though, the amount of mass inside that volume of space, which appears to be finite from their point of view, would appear to increase.
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline LeeE

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« Reply #85 on: 23/03/2009 16:13:35 »
The reduced amount of time that passes for the falling object is not just from the point of view of the distant observer.  If this were so, then two synchronised clocks, one staying with the distant observer and the other traveling close to the BH before returning, would show the same elapsed time when the traveling clock returned; the clock experiments that have been performed, both moving and in different gravitational potentials show that this is not so and there is an absolute difference in the amount of time that has passed for the two clocks.

You then seem to go on and agree that different amounts of time will pass for the two different locations, so I can't see how you can say that it will only be from the POV of the distant observer.
Different amounts of time will pass in each location *relative to the other*.

If you're just comparing two different rates, of anything in fact, one rate can be related to another different rate, but with time we're dealing with something having a rate that is always either positive, or zero, and once it's zero any comparison seems to be absolute and not relative.

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As much as I respect Penrose, I have to work stuff out for myself, and if I come to different conclusions, so be it.
Fair enough.

Just to be clear, I'm not saying that I'm right and he is wrong, just that until I can see where I've made a mistake I have to work on the basis that I'm right.  I've been wrong plenty of times, so won't be surprised if I find that I'm wrong again, but it won't be until I can see where I'm wrong.  I think that's the same for most people, really.
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline om

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« Reply #86 on: 23/03/2009 16:34:43 »
Serious readers of this forum may want to consider:

1. Evidence from Case Western Reserve University [Science (21 June 2007)] that Black Holes do not exist:

http://sciencenow.sciencemag.org/cgi/content/full/2007/621/1, and

2. A 2007 discussion published in Nature about interactions between neutrons in massive celestial objects:

blogs.nature.com/news/blog/2007/05/the_biggest_bang_of_them_all.html

In my opinion, repulsive interactions between neutrons:

a.) Rule out the existence of Black Holes, and
b.) Explain otherwise "mysterious" explosions of massive cosmic objects.

With kind regards,
Oliver K. Manuel
Emeritus Professor
Nuclear and Space Studies
myprofile.cos.com/manuelo09
www.omatumr.com/


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« Reply #87 on: 23/03/2009 17:52:44 »
Thanks for the link LeeE. I notice that the Schwarzchild radius is part of the equation. It is not immediately obvious to me that t = 0 at that radius. I don't doubt that it might, I just notice that many folks think that t = 0 closer in toward the singularity. I'll have to do some arithmetic.  [:)]

This is the equation:



cutting straight to the shortened form, to save time, when the distance r from the center of the object is equal to the Schwarzchild radius r0, we get 1 - 1 = 0.

LeeE, You are right in that Schwarzchild metric defines time as being zero as seen from a 'stationary observer' being at the event horizon. But to me that seems more of a theoretical limit? As I understand it, this is a situation that won't exist as there is no way to place an observer stationary at the EV, the definition of a EV is a 'point of no return'. When you're there you won't be able to 'hover' without expending a lot of energy in the opposite direction, and from the point of the in-falling observer there is nothing stopping him from falling further in towards that black hole. If I was observing him I expect that there would be a 'last moment' where light was reflected from that person, falling in.

That light I would expect to be both distorted and redshifted, but, it would still hit my retina at 'c' so that image wouldn't, as some imply, 'freeze' at that EV (event horizon). There is no 'hovering' allowed there, neither for the person falling in, nor for any light obeying spacetimes geodesics. So that last 'reflection' will arrive to the 'stationary observer' outside and then there would be no more reflected light emitted from that in-falling person.

From the situation of the person falling in it seems trickier though, one might argue that, as seen from the point of the in-falling observer, time would would 'slow down' allowing the universe to 'die' before he ever reached that EV. But that won't hold from our stationary observers point of view I think. He will observe this person disappearing from our view and so draw the conclusion that he have passed what he saw as the EV.

Why I think so goes back to my thought experiment with a 'stationary' relative Earth super-telescope watching a our spacecraft leave earth toward a star and then come back. That spacecraft, even if being extremly close to light speed in space, will have the same 'time dilation' as we observe at a black hole, you could say that the ship represents the in-falling observer and our telescope represents the observer outside the gravity well (black hole). To say that the observer of the in-falling person would observe, from his frame of reference, that this person would freeze in space due to the time dilation caused by the black hole seems to me to be equivalent to expecting that our spacecraft, as observed from our super telescope, would 'freeze' in space.

If that was a fact, I believe that this ship never would be able to make that journey, as seen from the telescopes (stationary observers) point of view. And all discussions about length contraction seems then to be a exercise in futility as any 'stationary observer' only would experience that spacecraft passing it at near 'c' as being frozen in time. So I expect the in-falling 'observer' to pass, what the 'staionary observer' outside the gravity well will observe to be, the Event Horizon.

---------

When it comes to the Kerr metric for a spinning black hole there will be framedragging added to the situation though. But we're not talking about that as I understands it? Anyway :) I might be wrong in my 'comparison' between those two situations, but even without that 'comparison' I see no real problem for the guy at the EV to keep falling as that is the only way he can take, as seen from his frame of reference.
« Last Edit: 23/03/2009 18:27:59 by yor_on »
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« Reply #88 on: 24/03/2009 01:49:38 »
I think I'll just waddle off somewhere and eat worms.

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« Reply #89 on: 24/03/2009 14:08:27 »
om:

I had a look at the first article you mentioned, and found: "As Einstein demonstrated in his Theory of General Relativity, a passenger inside a spaceship traveling toward a black hole would feel the ship accelerating, while an outside observer would see the ship slow down."

Which is just wrong.  A passenger falling towards a gravity well doesn't feel acceleration.  What Einstein pointed out was that when someone falls off a roof they feel nothing until they hit the ground.  Apart from the increasing speed of the air passing by them, they feel nothing.  Well, perhaps fear too.

As viewed by a distant observer, the ship will only appear to slow down (while it's actually accelerating) if space is compressed along the path of the craft, so that while the craft may actually travel, say 100m, a distant observer will measure that amount of space as less than 100m.  If this is so though, then we're back to a potentially infinite amount of space around the event horizon, which then can't ever be reached.  In fact, rather than slow down, the craft would appear to recede from the distant observer, as it is actually getting further away.
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline LeeE

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« Reply #90 on: 24/03/2009 14:52:33 »
Yor_on:

Quote
in that Schwarzchild metric defines time as being zero as seen from a 'stationary observer' being at the event horizon

It's the other way around; the observer at, or close to, the event horizon won't be aware of any slowing.  Rather, from their point of view, they will seem to be running at 'normal' time and everything else in the universe will seem to speed up.

Actually, I think that trying to work out what happens directly at the event horizon may not be the best way to find the answer.  Working out some solutions outside the event horizon will show the direction that things are going without having to deal with any zero values anywhere - all the physics will be 'normal'.

So instead, let's imagine sending a craft on a sling-shot voyage around the BH so that it returns back to the distant observer.  Now, when both the traveling craft and the distant observer are back in the same frame of reference, we find that less time has passed for the traveling craft.  They've started from the same frame of reference and ended in the same frame of reference, but different periods of time have elapsed for them.

Although it requires calculus to find the actual elapsed time for the traveling craft, because the rate of time will be changing during it's voyage, we can see that the elapsed time will relate to the degree of time-dilation that it experiences, and we know that if it's path is closer to the event horizon the degree will be greater and if it's further away it will be less, which is all that the equation tells us, so all we really need do is to plot several values for r to see which way t0 is going.

We can then try reducing r to be infinitely small, so that the craft comes as close to the event horizon as possible without actually touching or crossing it.  When the craft returns from this journey to compare the elapsed times, what are we going to find?

Yes, I agree that there won't be a frozen image of them - that's just silly.
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline LeeE

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« Reply #91 on: 24/03/2009 14:54:23 »
I think I'll just waddle off somewhere and eat worms.



Watch out for worm-holes  [;)]
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline DoctorBeaver

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« Reply #92 on: 24/03/2009 17:31:19 »
I think I'll just waddle off somewhere and eat worms.



Watch out for worm-holes  [;)]

Stop picking on me  [:-'(]
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« Reply #93 on: 24/03/2009 21:29:18 »
I may have got it all backwards then?

Sorry LeeE, I got the impression that you said that the in-falling observer wouldn't get past that EV? But here you seem to say exactly the same as I think too "from their point of view, they will seem to be running at 'normal' time " and so they will, as seen from their frame of reference, just keep falling in. What I reacted on was the statement that "t = 0" at the eventhorizon. How exactly do you see that idea?
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Offline erickejah

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« Reply #94 on: 24/03/2009 21:37:46 »
wow!!! would this formula has anything to do with this?
Fg=GMm
         r2
where G=6.67*10^-11

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« Reply #95 on: 25/03/2009 00:19:54 »
Not sure, you are talking about the gravitational force between two frames of reference I presume? Why don't you enlighten me :)
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Offline erickejah

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« Reply #96 on: 25/03/2009 01:57:38 »
yes, [:D].
that is how we calculate the force of attraction between bodies. That is what my teacher said. But how did the scientific people like you figured out this??
and how is this other equation:

related to this one [???]

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« Reply #97 on: 25/03/2009 11:54:30 »
Tell me Eric, what is your point here?
To ridicule others by what ability you might have with manipulating numbers?
Or do you have a a 'cleaner' agenda with those formulas?
Like proving some point you haven't bothered to mention perhaps?
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Offline LeeE

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« Reply #98 on: 25/03/2009 15:40:35 »
I may have got it all backwards then?

Sorry LeeE, I got the impression that you said that the in-falling observer wouldn't get past that EV? But here you seem to say exactly the same as I think too "from their point of view, they will seem to be running at 'normal' time " and so they will, as seen from their frame of reference, just keep falling in. What I reacted on was the statement that "t = 0" at the eventhorizon. How exactly do you see that idea?

Yes, they'll think that time is running normally for them, but at the point where t0 = 0, they'll stop thinking; their rate of thinking will slow and stop, so they won't be aware that they've stopped thinking.

Go back to close paths outside the event horizon; the traveler isn't aware that less time has passed for them when they return to the same frame of reference as the distant observer, even though the absolute amount of time that has passed for both is different.  The only difference is that instead of the absolute difference being finite, if they could return from the point where t0 = 0, the absolute ratio would seem to be infinite.

I think this just actually complicates the issue though.  The actual reason that I think they couldn't reach the event horizon is that it may be infinitely far away in spatial terms, regardless of how time-dilation effects the relative energy that's seen to be expended, say by a battery powered light inside the craft, by both the local and distant observers. 

Energy is highly time dependent and the amount that seems to be being used should differ between the observers due to time-dilation, so for example, if the craft were to hover above the event horizon, expending energy to maintain it's position against gravity, the amount required should seem different to the observers even though the amount should be absolute and just dependent on the masses and distances involved.
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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« Reply #99 on: 25/03/2009 15:43:03 »
Tell me Eric, what is your point here?
To ridicule others by what ability you might have with manipulating numbers?
Or do you have a a 'cleaner' agenda with those formulas?
Like proving some point you haven't bothered to mention perhaps?

I was wondering that too.  We're discussing time-dilation, not forces.  I fail to see the point.
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!