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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?

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.

Quote from: DoctorBeaver on 19/03/2009 11:16:36I 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.

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.

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.

Quote from: LeeE on 20/03/2009 12:04:23You'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.

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.

Quote from: LeeEHowever, 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?

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.

Another good link on falling into a Black Hole (it's not habit forming []) : ...sorry, you cannot view external links. To see them, please REGISTER or LOGIN

Quote from: LeeE on 21/03/2009 19:28:06The 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.

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. []

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.

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, 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.

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?

... 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.

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.

Quote from: LeeE on 23/03/2009 14:30:36... 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 ?

Quote from: LeeE on 23/03/2009 14:57:15The 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*.

QuoteAs 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.

Quote from: Vern on 21/03/2009 23:57:17Thanks 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 r_{0}, we get 1 - 1 = 0.

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

I think I'll just waddle off somewhere and eat worms....sorry, you cannot view external links. To see them, please REGISTER or LOGIN

Quote from: DoctorBeaver on 24/03/2009 01:49:38I think I'll just waddle off somewhere and eat worms....sorry, you cannot view external links. To see them, please REGISTER or LOGINWatch out for worm-holes []

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?

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?