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Old 01-08-2012, 02:54 PM
 
Location: Fairfax
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Quote:
Originally Posted by plwhit View Post
We agree black holes suck everything around it into it.

How are you so sure nothing comes out of a black hole?

I didn't realize mankind had discovered everything there is to know about the Universe, when did that occur?
To even talk about science we have to make some assumptions. If regular matter spewed out of a black hole, it wouldn't be much of a black hole would it?
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Old 01-08-2012, 03:03 PM
 
Location: Wilsonville, OR
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You could not shine a flashlight behind you because the photons emitted by it no longer have any worldlines that don't point directly into the singularity.
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Old 01-08-2012, 03:04 PM
 
5,203 posts, read 8,205,785 times
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Quote:
Originally Posted by decafdave View Post
Nothing spews out of black holes, although I can understand how quasars caused the confusion here. Anything that is "burped out" has not yet fallen into the event horizon. The tremendous radiation that is emitted comes from the accretion disk, which is a high pressure bottleneck of matter/energy competing to enter the event horizon.

However, none of these gamma rays or x-rays originated from within the black hole.
Quasar - Wikipedia, the free encyclopedia

Hawking radiation, is an entirely different matter, and if it exists is completely un-observable in an active black hole (the single quantum particle would be swamped by matter coming in the other way).
When I mentioned 'burping', it was meant figuratively. Yes, matter that's spewed out is from the accretion disk, but there's more going on than just that. When too much material is attracted by the gravitational pull of a black hole, it's got to go somewhere. While there's no question that particles and matter are ejected from the accretion disk, an excess amount of particles are likely to expand or encompass the black hole from the equatorial zone (where the accretion disk is located) and spread out toward the poles which results as energetic jets. This behavior seems to be related to black holes that are actively feeding. It relates to both the amount of material being attracted by the black hole as well as the spin of a black hole. Black holes like that are known as Kerr black holes.

On the other hand, not all black holes rotate on their access or have an accretion disk, and can draw in matter from all directions. These are known as Schwartzchild black holes. Matter attracted by Schwartzchild BH's might be sprayed out over the entire surface at the event horizon primarily leaving behind the Hawking radiation as the last gasp of that matter which would not be as noticable as Kerr BH's. Detecting a Schwartzchild BH is possible with luck by gravitational lensing as it passes over background stars, etc.

Some of this was touched on in a previous thread.
http://www.city-data.com/forum/scien...ive-black.html


Quote:
Time slows down even close to Earth. GPS satellites have to contend with extra micro seconds every day because of their speed and lower gravity due to distance.

Back to my original question, since we consider photons as timeless, and the matter/energy right AT the event horizon would look timeless to the outside observer, it must be traveling at exactly the speed of light. An observer in a spaceship passing through the event horizon would see the entire future history of the universe play out (as long as the black hole continues to exist).

But, the instance that matter/energy passes the event horizon it should be traveling faster than the speed of light towards the singularity. Craziness ensues:

1. Does time go in reverse? How would this play out for the "inside" observer?
2. Is this breach in the law of physics allowed because the event horizon "hides" it from the outside universe?
Cosmic censorship hypothesis - Wikipedia, the free encyclopedia
3. In a supermassive black hole, there is very little tidal force and a person could easily survive for hours beyond the event horizon. How is he going to observe time as a superluminal object?

I think these things give credence to the idea that anything inside black holes are in a separate universe given the different set of laws.
Your initial question was about what goes on inside a black hole once past the event horizon. There are some ideas that are based on what we know about the effects of gravity. But there is much that ccan only be left to the imagination. We don't know what happens as particles break up inside and gets closer to the singularity.

I'm not sure I understand your point about photons being timeless. There's no evidence of that, although the speed of light in a vacuum is considered a point where time completely stops, in so far as we know. However, there are conditions where light can travel slower than 186,000 miles per second, such as passing through water or passing through gasses. Light doesn't aways travel at top speed. The gravitational pull of a black hole doesn't have to be faster than the speed of light. It's just more powerful than the escape velosity of photons.

With regard to black holes and photons, it's worth noting that photons are particles whereas the effect of black holes is gravitational. Gravity is a force, not a particle. Extreme gravity trumps photons. As such, light cannot escape the gravitational pull of a black hole once inside the event horizon.

Let's take a look at your list of questions (these are just my opinions):

1. Does time go in reverse? How would this play out for the "inside" observer?
Personally, I doubt time goes in reverse inside a black hole. It's generally suggested that time just stops or that it has no longer has any meaning. Whether time absolutely ends or not is unknown. That starts getting into Planck Time, which is very difficult to wrap your brain around. If I'm not too far off track, a Planck Time 'tick' is a billionth of a billionth of a billionth of a billionth of a billionth of a second. If there's anything beyond Planck Time, it's beyond our experience and has no meaning for us.

If an observer could survive inside a black hole, he probably wouldn't see anything except blackness. Everything inside a black hole would be stretched and breaking apart.

2. Is this breach in the law of physics allowed because the event horizon "hides" it from the outside universe?
Cosmic censorship hypothesis - Wikipedia, the free encyclopedia
"Cosmic censorship" is an hypothesis without a formal statement and is more of a research program proposal. That said, it's always possible there could be "breaches" in the laws of physics. There are a lot of things we don't know. We have yet to fully understand exactly why the Big Bang banged and why it resulted into the universe as it has. We still don't understand the nature of Time, or whether Dark Energy exists. We don't know exactly what happens inside the event horizon of a black hole. I don't know if we'll ever cross that threshold any more than whether we'll ever know what's beyond the limits of universe. We're not even sure exactly what the universe is. The point is that our knowledge is always subject to change.

3. In a supermassive black hole, there is very little tidal force and a person could easily survive for hours beyond the event horizon. How is he going to observe time as a superluminal object?
I have my doubts survival beyond the event horizom of a supermassive black hole would last for hours. I think the first video I posted suggested that survival would more likely be around 7 seconds before you're stretched and compressed into a noodle.

As for the observer, there'd be no visual points of reference to determine the passing of time, apart from thinking: "Not good! Not good! This is it! I'm never going to make it out of......."
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Old 01-08-2012, 03:10 PM
 
5,203 posts, read 8,205,785 times
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Quote:
Originally Posted by decafdave View Post
So again, if matter is supposedly falling into the singularity at sub-light speed, then I don't understand why you couldn't shine a flashlight behind you as you fall.
Sure, you could shine a flashlight behind you. The problem is that the light would not be able to escape to the outside since the photons would be falling into the black hole right along with you and your flashlight. Evn if you were falling head first and shined the light toward your face, all you'd see is blackness because the photons are falling inward in front of you. They couldn't travel back to your face.
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Old 01-08-2012, 03:24 PM
 
Location: Westwood, MA
3,608 posts, read 4,774,914 times
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Quote:
Originally Posted by decafdave View Post
If you'll read the op, you'll see that my statements were really questions.

That said, doesn't the twisted geometry around a black hole necessitate that the escape velocity be higher than the speed of light? As far as I know, scientists haven't come to the conclusion that the escape velocity inside the event horizon is infinite. The escape velocity at the horizon is c. So you're saying that immediately inside it jumps to infinity?

So again, if matter is supposedly falling into the singularity at sub-light speed, then I don't understand why you couldn't shine a flashlight behind you as you fall.
It's sometimes difficult to determine if something is a question or a statement laid out like a question. I apologize for my misunderstanding.

You're thinking about the geometry in an intuitive but incorrect way and that leads to your confusion. Inside the event horizon, the light-like and time-like paths are all directed toward the singularity. Any direction you shine a flashlight, the light path will be bent around by gravity and eventually direct itself toward the singularity. It's totally independent of the observer velocity. Even if weren't, you're forgetting special relativity--the speed of light is the same regardless of observer, so the velocity of the transmitter is ultimately irrelevant.
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Old 01-08-2012, 07:24 PM
 
Location: Fairfax
2,880 posts, read 6,225,879 times
Reputation: 1231
Quote:
Originally Posted by NightBazaar View Post
When I mentioned 'burping', it was meant figuratively. Yes, matter that's spewed out is from the accretion disk, but there's more going on than just that. When too much material is attracted by the gravitational pull of a black hole, it's got to go somewhere. While there's no question that particles and matter are ejected from the accretion disk, an excess amount of particles are likely to expand or encompass the black hole from the equatorial zone (where the accretion disk is located) and spread out toward the poles which results as energetic jets. This behavior seems to be related to black holes that are actively feeding. It relates to both the amount of material being attracted by the black hole as well as the spin of a black hole. Black holes like that are known as Kerr black holes.

On the other hand, not all black holes rotate on their access or have an accretion disk, and can draw in matter from all directions. These are known as Schwartzchild black holes. Matter attracted by Schwartzchild BH's might be sprayed out over the entire surface at the event horizon primarily leaving behind the Hawking radiation as the last gasp of that matter which would not be as noticable as Kerr BH's. Detecting a Schwartzchild BH is possible with luck by gravitational lensing as it passes over background stars, etc.

Some of this was touched on in a previous thread.
http://www.city-data.com/forum/scien...ive-black.html
Just a misunderstanding then. You are absolutely correct that not all of the mass/energy near a super-massive black hole ends up inside the event horizon. These bottle-necks create quasars.



Quote:
Originally Posted by NightBazaar View Post
...

I'm not sure I understand your point about photons being timeless. There's no evidence of that, although the speed of light in a vacuum is considered a point where time completely stops, in so far as we know. However, there are conditions where light can travel slower than 186,000 miles per second, such as passing through water or passing through gasses. Light doesn't aways travel at top speed. The gravitational pull of a black hole doesn't have to be faster than the speed of light. It's just more powerful than the escape velosity of photons.
That assumption (definitely aware that it's only an assumption) is that since time slows down increasingly as you approach c as an asymptote, then it must stop completely at the actual speed of light. This is the idea behind the conjectured "Tachyons" which would violate causality if they actually existed.

I don't think there's anything significant about slowing light down using water or another medium. In the new medium, whatever speed light is traveling at IS the new "top speed" of the universe.

I'm not sure if I can agree with this: "The gravitational pull of a black hole doesn't have to be faster than the speed of light. It's just more powerful than the escape velosity of photons." The escape velocity of photons = the top speed in the universe. Whatever speed light is traveling at inside the BH, then that is the new c, not 186,000 miles/sec.

Quote:
Originally Posted by NightBazaar View Post

With regard to black holes and photons, it's worth noting that photons are particles whereas the effect of black holes is gravitational. Gravity is a force, not a particle. Extreme gravity trumps photons. As such, light cannot escape the gravitational pull of a black hole once inside the event horizon.

Let's take a look at your list of questions (these are just my opinions):

1. Does time go in reverse? How would this play out for the "inside" observer?
Personally, I doubt time goes in reverse inside a black hole. It's generally suggested that time just stops or that it has no longer has any meaning. Whether time absolutely ends or not is unknown. That starts getting into Planck Time, which is very difficult to wrap your brain around. If I'm not too far off track, a Planck Time 'tick' is a billionth of a billionth of a billionth of a billionth of a billionth of a second. If there's anything beyond Planck Time, it's beyond our experience and has no meaning for us.

If an observer could survive inside a black hole, he probably wouldn't see anything except blackness. Everything inside a black hole would be stretched and breaking apart.

2. Is this breach in the law of physics allowed because the event horizon "hides" it from the outside universe?
Cosmic censorship hypothesis - Wikipedia, the free encyclopedia
"Cosmic censorship" is an hypothesis without a formal statement and is more of a research program proposal. That said, it's always possible there could be "breaches" in the laws of physics. There are a lot of things we don't know. We have yet to fully understand exactly why the Big Bang banged and why it resulted into the universe as it has. We still don't understand the nature of Time, or whether Dark Energy exists. We don't know exactly what happens inside the event horizon of a black hole. I don't know if we'll ever cross that threshold any more than whether we'll ever know what's beyond the limits of universe. We're not even sure exactly what the universe is. The point is that our knowledge is always subject to change.

3. In a supermassive black hole, there is very little tidal force and a person could easily survive for hours beyond the event horizon. How is he going to observe time as a superluminal object?
I have my doubts survival beyond the event horizom of a supermassive black hole would last for hours. I think the first video I posted suggested that survival would more likely be around 7 seconds before you're stretched and compressed into a noodle.

As for the observer, there'd be no visual points of reference to determine the passing of time, apart from thinking: "Not good! Not good! This is it! I'm never going to make it out of......."
Good points overall.

About point 1: I think my idea stems from stuff I've read about the dimensions possibly inverting inside the black hole. That is, instead of 3 space and 1 time dimension, it changes to only 1 space dimension and 3 of time. Horrifically confusing, but the 1 dimension of space makes a little bit of sense because of the "all roads lead to the singularity" idea. If I can remember where I read about that I'll post a link to it.

About point 3: I disagree with the claim that someone would be spaghettified inside a super-massive BH.
I think this depends on the distance from the singularity. In a stellar mass BH, this would happen very quickly, maybe even before you hit the event horizon. But it's believed that you would encounter no discomfort when passing the event horizon of a galactic center black hole. At some point, spaghettification would occur, but it would be whenever you get close to the actual singularity. You'd still be doomed, but the difference in the tug at your feet vs. at your head would be negligible....at first.

This source tackles this:

BLACK HOLES by Ted Bunn

"For a very large black hole like the one you're falling into, the tidal forces are not really noticeable until you get within about 600,000 kilometers of the center. Note that this is after you've crossed the horizon. If you were falling into a smaller black hole, say one that weighed as much as the Sun, tidal forces would start to make you quite uncomfortable when you were about 6000 kilometers away from the center, and you would have been torn apart by them long before you crossed the horizon. (That's why we decided to let you jump into a big black hole instead of a small one: we wanted you to survive at least until you got inside.)"

Here's how to maximize your survival time
Maximizing Survival Time Inside the Event Horizon of a Black Hole
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Old 01-09-2012, 09:21 PM
 
5,203 posts, read 8,205,785 times
Reputation: 3188
Quote:
Originally Posted by decafdave View Post
Just a misunderstanding then. You are absolutely correct that not all of the mass/energy near a super-massive black hole ends up inside the event horizon. These bottle-necks create quasars.
No big thing. I'm not always the greatest writer. Thanks for the reminder to clarify myself.


Quote:
Originally Posted by decafdave View Post
That assumption (definitely aware that it's only an assumption) is that since time slows down increasingly as you approach c as an asymptote, then it must stop completely at the actual speed of light. This is the idea behind the conjectured "Tachyons" which would violate causality if they actually existed.

I don't think there's anything significant about slowing light down using water or another medium. In the new medium, whatever speed light is traveling at IS the new "top speed" of the universe.

I'm not sure if I can agree with this: "The gravitational pull of a black hole doesn't have to be faster than the speed of light. It's just more powerful than the escape velosity of photons." The escape velocity of photons = the top speed in the universe. Whatever speed light is traveling at inside the BH, then that is the new c, not 186,000 miles/sec.
I disagree that if light can travel below 186,000 mps that it means it's a new constant. All it means is that nothing known in the universe, except light, can travel at 186,000 mps. That's the maximum. It doesn't violate c, nor does a slower speed represent a new c. It represents the top speed in a vacuum where nothing else is present to interfere which is the idea condition. There have been experiments showing that as photons pass through a gas (I can't remember off hand whch gas), it slows down, then resumes it's speed again once it get through. Perhaps the photons are still traveling at c but bump into the gas particles causing it to take longer to move from Point A to Point B. Other experiments have also shown that it takes light longer to pass by objects, like the Sun, because of how gravity warps spacetime. Gravitational lensing is another example. Light doesn't always travel in a straight line. It's just one of the ways the universe works.

Back to the black holes, once photons have passed the event horizon, they're on a one way trip in the direction of the singularity. There's no escape. As explained, the reason has nothing to do with how fast photons can travel. It's because the strength of the BH's gravitational attraction is so intense that light can't escape it. Perhaps the photons are still traveling at 186,000 mph inside, but if you tried to shine a light behind you toward the outside, the photons, along with everything else, would never make it out.

There have been some ideas regarding freefall. I don't have a problem about that, other than to say that freefalling into a black hole is probably not going to be the same as freefalling from a plane on Earth.


Quote:
Originally Posted by decafdave View Post
About point 1: I think my idea stems from stuff I've read about the dimensions possibly inverting inside the black hole. That is, instead of 3 space and 1 time dimension, it changes to only 1 space dimension and 3 of time. Horrifically confusing, but the 1 dimension of space makes a little bit of sense because of the "all roads lead to the singularity" idea. If I can remember where I read about that I'll post a link to it.

About point 3: I disagree with the claim that someone would be spaghettified inside a super-massive BH.
I think this depends on the distance from the singularity. In a stellar mass BH, this would happen very quickly, maybe even before you hit the event horizon. But it's believed that you would encounter no discomfort when passing the event horizon of a galactic center black hole. At some point, spaghettification would occur, but it would be whenever you get close to the actual singularity. You'd still be doomed, but the difference in the tug at your feet vs. at your head would be negligible....at first.

This source tackles this:

BLACK HOLES by Ted Bunn

"For a very large black hole like the one you're falling into, the tidal forces are not really noticeable until you get within about 600,000 kilometers of the center. Note that this is after you've crossed the horizon. If you were falling into a smaller black hole, say one that weighed as much as the Sun, tidal forces would start to make you quite uncomfortable when you were about 6000 kilometers away from the center, and you would have been torn apart by them long before you crossed the horizon. (That's why we decided to let you jump into a big black hole instead of a small one: we wanted you to survive at least until you got inside.)"

Here's how to maximize your survival time
Maximizing Survival Time Inside the Event Horizon of a Black Hole
Regarding Point 1:
That dimensions may invert to 1 of space and 3 of time is a new one on me. A singularity would have a spatial dimension of zero, in effect that it becomes infinitely smaller. As for time, it too extends to infinity. If the speed of light is the maximum speed in the universe, then for practical reasons it too reaches zero time because it too becomes infinite. That doesn't mean that you would necessarily fall infinitely inside a black hole. I'd guess there's a core in there at some point, but that's just an intuitive thought, and intuitive thoughts aren't always correct.

Regarding Point 3:
I agree that how large a black hole would have an effect on how quickly you'd be spaghettified. With a Kerr type black hole, you'd be vaporized long before you ever reached the event horizon.

The links you included are interesting, but not without flaws. I looked at the research paper, "No way Back: Maximizing survival time below the Schwartzchild event horizon". While the points are well made, it's primarily a mathematical exercise based on ideal conditions.

For example, the authors state the following in "3 Setting Up the Problem":
"In this paper, only purely radial motion will be considered and the faller will be assumed to be impervious to the significant inertial and tidal forces it will suffer on its journey."

In effect, it assumes the faller is indestructable. That's fine for working out the mathematical problem, but pretty meaningless in a realistic sense. It also only considers Schwartzchild black holes, not Kerr black holes. I didn't quite get the point of the example about firing up the rocket engines. Is it to travel in faster? Or to turn around and slow the descent? I'm also not certain of your view of the relationship between the speed of light and the gravitational attraction of a black hole inside the event horizon.
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Old 01-09-2012, 09:55 PM
 
Location: Fairfax
2,880 posts, read 6,225,879 times
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NightBazaar, I'll have to give you a full reply when I'm not wiped (and watching the LSU/Alabama game).

But, regarding the speed of light, I know that different mediums can slow it down. While technically "c" denotes the speed of light in a vacuum, when light passes through gas, for example, that new speed is the new speed of light. Let's say it's 50% of c. Well, nothing in the universe can go through that gas (hitting the same particles, of course) faster than that.
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Old 01-09-2012, 10:42 PM
 
Location: Westwood, MA
3,608 posts, read 4,774,914 times
Reputation: 4663
Quote:
Originally Posted by decafdave View Post
NightBazaar, I'll have to give you a full reply when I'm not wiped (and watching the LSU/Alabama game).

But, regarding the speed of light, I know that different mediums can slow it down. While technically "c" denotes the speed of light in a vacuum, when light passes through gas, for example, that new speed is the new speed of light. Let's say it's 50% of c. Well, nothing in the universe can go through that gas (hitting the same particles, of course) faster than that.
Lots of things exceed the speed of light through a given medium. When charged particles do it they emit Cherenkov radiation (the mystic blue glow of radioactive materials). The only speed of light that can't be exceeded is that of the vacuum.
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