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Observing a black hole's singularity


Mr Skeptic
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Someone suggested that you could observe a black hole's singularity, briefly before your inevitable death, by passing through the event horizon to look at it. As I understand it, so long as the black hole is big enough, you could survive the tidal forces that would be acting on you getting close to the event horizon.

 

Now, my question is this: even if you were to go inside a black hole, I understand that the things there are falling faster than the speed of light toward the singularity. Wouldn't this mean that you wouldn't actually be able to see where you were falling?

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Now, my question is this: even if you were to go inside a black hole, I understand that the things there are falling faster than the speed of light toward the singularity. Wouldn't this mean that you wouldn't actually be able to see where you were falling?

That definitely seems most logical. It's not as if photons would be unable to escape from within the event horizon yet they'd somehow be able to reach the inner wall of the event horizon no problem.

 

As for seeing nothing ahead of you once inside the event horizon, just turn around. Better view :P

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Someone suggested that you could observe a black hole's singularity, briefly before your inevitable death, by passing through the event horizon to look at it. As I understand it, so long as the black hole is big enough, you could survive the tidal forces that would be acting on you getting close to the event horizon.

 

Now, my question is this: even if you were to go inside a black hole, I understand that the things there are falling faster than the speed of light toward the singularity. Wouldn't this mean that you wouldn't actually be able to see where you were falling?

 

I don't know if things are falling faster than the speed of light.

 

My understanding is that things falling in a black hole, at maximum speed (the moment before hitting the inner wall), you would be travelling at 99.99% speed of light. I think this may also depend on the size of the black hole. But then that brings in another good point.

 

As an observer falls towards the theoretical singularity he would approach

'c'. As the observer approaches 'c' time would slow down, basic relativity. This would make the fall take an extremely long time to an observer (assuming /he/she could survive the tidal forces).

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I would think the frame of reference is implied here because of the topic title. But it is good that you bring up that point. From what I was saying, it would be the velocity of the observer as compared to the theoretical singularity of the black hole.

 

I of course cannot prove that the observer would be travelling 99.99% the speed of light, but I would think that would be the maximum that the observer would be travelling at. My point is that I don't think the observer would fall into a black hole and surpass the speed of light.

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I would think the frame of reference is implied here because of the topic title. But it is good that you bring up that point. From what I was saying, it would be the velocity of the observer as compared to the theoretical singularity of the black hole.

 

I of course cannot prove that the observer would be travelling 99.99% the speed of light, but I would think that would be the maximum that the observer would be travelling at. My point is that I don't think the observer would fall into a black hole and surpass the speed of light.

 

As far as I can guess, for you on Earth observing someone falling into a BH, the poor guy would appear traveling at 99,99% c. Only relativistic calculations would show what would be his experience. After all, looking back to you, he would say that you are the one traveling at 99,99% C. All is relative.

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Doesn't matter. As long as GR 'holds', Natural Law remains Invariant wrt all FsOR. At the 'breakdown' point, the issues become moot from a physical POV, and all that's left is speculation.

 

This is an easy way in order to avoid the question. It is not a difficult one. Everything stays in the frame of accepted physics since our guy is out of the BH at speed less than C. I do not agree that we are dealing with speculations.

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I would think that all you could see would be black as the light would be going inwards and none would be visible as no light would be coming out for you to see, the Event Horizon is only visible to Observers from the outside would not be noticed by you , But your personal time as you go in would be slowed down, so perhaps you would never arrive in the centre....

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I would think that all you could see would be black as the light would be going inwards and none would be visible as no light would be coming out for you to see, the Event Horizon is only visible to Observers from the outside would not be noticed by you , But your personal time as you go in would be slowed down, so perhaps you would never arrive in the centre....

 

As I said before, only calculations will tell.

The good & more interesting question is what the guy will see looking back. He will see the Earth moving at 99,99% C. And he would assume intuitively that people on Earth are experiencing weird phenomenas such as the impossibility to speed up. Which we know is not the case. So, where is the catch?

_You could assume that Relativity tells that the guy near a black hole would actually know that he is moving at speed near C, because he will experience some phenomena (the impossibility of speeding up) so that he could measure his own speed. Wrong, because his own time will change also, so that he will not experience anything weird, and not be able to measure his own speed. But in this case, there would be no impossibility for him to speed up (accelerate), as there is no impossibility for us to speed up. Which looks contrary to intuition, but not contrary to Relativity. Because the guy's new speed (after acceleration) as measured from his point of vue (FOR) would be only a fraction of C (0,00000000000000000000000........1) of C as measured from Earth.

The point is that our guy would experience nothing weird due to his speed.


Merged post follows:

Consecutive posts merged

But he would experience something due to the fact a BH is a gravitational well. http://en.wikipedia.org/wiki/Gravitational_well

 

That means our guy at the BH proximity would be in a state of free fall in a huge gravitational well. Instead of walking on the Moon, where his body wheights less than on Earth due to the lower gravity on the Moon, in the BH case the human body would turn into billions & billions of tons. Knowing that the human body can stand acceleration only a few g's ("a constant 16 g for a minute, however, may be deadly. from http://en.wikipedia.org/wiki/G-force#Human_tolerance_of_g-force), I suppose our guy would be dead before reaching the BH event horizon. Or am I wrong somewhere?

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I have no idea, being black holes do not emit light, I do not think you would be able to see anything. I think the only thing you may be able to see is looking outward, but if you pass the event horizon, would you be able to see anything outside of it.

 

From what I know, everything in a black hole ends up in the singularity correct? Yet black holes are able to be given thermodynamic properties via hawking radiation I think, so would that mean that something, even if its just friction is occurring in a black hole? Yet I do not think you could ever test anything, or test any calculations of what physics actually occur past the event horizon because as far as I know very limited information can escape one.

 

If thermodynamics in someway holds for black holes, then to me that means something is indeed occurring in them, or that they are not frozen balls of incredible gravity forming some end of the universe. Saying that I still cannot fathom a human being actually experiencing anything past becoming one with the singularity:eek: So I would have to think, or imagine that nothing would be witnessed.

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...

That means our guy at the BH proximity would be in a state of free fall in a huge gravitational well. Instead of walking on the Moon, where his body wheights less than on Earth due to the lower gravity on the Moon, in the BH case the human body would turn into billions & billions of tons. Knowing that the human body can stand acceleration only a few g's ("a constant 16 g for a minute, however, may be deadly. from http://en.wikipedia.org/wiki/G-force#Human_tolerance_of_g-force), I suppose our guy would be dead before reaching the BH event horizon. Or am I wrong somewhere?

 

Well just to have a concrete example, suppose it is a billion solarmass BH, like you find at the core of some galaxies. Some galaxies' BH are bigger than that, but take a billion solar for round numbers.

 

Someone falling towards the event horizon would not feel any acceleration and not be stressed. Free fall is zero G. The sucker is too big to generate tidal forces on you at this point. It pulls your feet with about as much force as it pulls your kidneys or your brain or your ears. You are small compared to it, like a point particle, so no tidal stretching and no feeling of acceleration.

 

And you would fall thru the horizon without noticing it. It wouldn't hurt.

Now you are inside. You don't feel any tidal stretching yet. There is a long way to fall, on the order of two billion miles or three billion kilometers.

You don't feel like you weigh "billions & billions of tons".

You are still in free fall, which means zero G.

 

So you have some time to look around and see and think before you start to feel uncomfortable and start to get shredded by tidal forces (unequal attraction on different body parts). It is an interesting question what do you SEE. Because the hole geometry bends light in funhouse ways. Your world is going to be optically distorted.

 

Somebody else should discuss this. I haven't thought about the visual experience. intuitively, the central singularity would not be something you can SEE. It would be like in your future, and you can't see your future. But you would be able to see lots of other stuff. Like maybe busloads of Japanese tourists that fell in at the same time you did, all taking pictures of each other. Or used television sets that somebody dropped in because he couldn't figure out what else to do with them. And the stars outside the event horizon, behind you. You could see lots of stuff. But because of the funny optics I can't intuitively picture it.

The way I'm thinking about it, if your feet are pointing down inwards, then your visual world becomes more and more concentrated into a 360 degree band around your head at eye-level. Looking around you at eye-level you see stuff. But tilting your head to look up you see less and less (and it is redshifted to invisibility) and tilting your head to look down you also see less and less (and it is redshifted). So the tourist busses and broken television sets all around you increasingly concentrated at eye-level.

 

Someone who has thought this through may hopefully take over. I know Andy Hamilton at the U of Colorado has done some graphics showing what it looks like to fall into a BH. Some of Andy's stuff is online. Maybe someone here has checked that site out.

 

BTW, someone might check this estimate---I estimate that if you were taken near the event horizon of a billion solar BH and dropped thru your fall from the horizon to the singularity would last about 6000 seconds (by your own subjective time sense.)

That's called your proper time. The time as you experience it, the clock that your body processes are running on. 6000 seconds according to your own wrist-watch if you wear one.

Since I'm not being precise and am not so sure of my estimate, maybe I better say "something over an hour" of subjective time.

Edited by Martin
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Martin wrote:

(..)

Someone falling towards the event horizon would not feel any acceleration and not be stressed. Free fall is zero G. The sucker is too big to generate tidal forces on you at this point. It pulls your feet with about as much force as it pulls your kidneys or your brain or your ears. You are small compared to it, like a point particle, so no tidal stretching and no feeling of acceleration.

 

And you would fall thru the horizon without noticing it. It wouldn't hurt.

Now you are inside. You don't feel any tidal stretching yet. There is a long way to fall, on the order of two billion miles or three billion kilometers.

You don't feel like you weigh "billions & billions of tons".

You are still in free fall, which means zero G.

(..)

 

Thank you Martin.

 

Michel wrote:

Or am I wrong somewhere?

 

Of course Michel is wrong.

 

My post standed for 7 days without any remark. You saved the honour Martin.

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But tilting your head to look up you see less and less (and it is redshifted to invisibility) and tilting your head to look down you also see less and less (and it is redshifted).

 

Wouldn't the stuff above you be blue-shifted?

 

Anyhow, it does seem like we never get to see the singularity, even jumping into the black hole.

 

I know Andy Hamilton at the U of Colorado has done some graphics showing what it looks like to fall into a BH. Some of Andy's stuff is online. Maybe someone here has checked that site out.

 

http://casa.colorado.edu/~ajsh/schw.shtml

 

Interesting stuff.

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Related question:

What is the state of matter in a BH?

I understand that BH is a very massive object. More massive than the Earth. But the Earth is a solid object, and we are not falling into the Earth, we are walking upon its surface because it is made of solid rock. If a BH is more massive than the Earth, I suppose it must be harder than rock. Isn't it?

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Related question:

What is the state of matter in a BH?

I understand that BH is a very massive object. More massive than the Earth. But the Earth is a solid object, and we are not falling into the Earth, we are walking upon its surface because it is made of solid rock. If a BH is more massive than the Earth, I suppose it must be harder than rock. Isn't it?

 

A black hole can be of any mass, from that of a subatomic particle to millions of suns. An object is a black hole if its mass is condensed beyond the point where any known force can resist its own gravity and prevent it from collapsing into itself indefinitely. Because of this, relativity predicts that all of the mass of a black hole becomes concentrated in a single point of infinite density. Most likely this is not the actual case due to quantum effects, but what actually happens is not resolved.

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Wouldn't the stuff above you be blue-shifted?

 

No Sir, I think not. It seems like it would, at first sight. But the photons from outside that came in thru the horizon after you are having a hard time catching up with you and are actually redshifted. As I recall, Andy Hamilton explains that somewhere at the Boulder black hole site.

 

 

 

You are absolutely right! It is interesting indeed. Hard. But Andy's a determined and visual explainer.

 

====================

Intuitively, you are closer to center so you are pulling away from the stuff that fell in after you, and the stuff ahead of you is closer to center so it is pulling away from you. This is just halfwitted Newtonian intuition, not to take literally, but it sort of explains why both the stuff ahead and the stuff behind is redshifted.

Edited by Martin
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Related question:

What is the state of matter in a BH?

I understand that BH is a very massive object. More massive than the Earth. But the Earth is a solid object, and we are not falling into the Earth, we are walking upon its surface because it is made of solid rock. If a BH is more massive than the Earth, I suppose it must be harder than rock. Isn't it?

 

Jupiter is also more massive than earth, and it is made of largely hydrogen. Same with the sun.

 

A black hole is as "hard" as you can make something, because you can't break one apart no matter how hard you hit it, and you certainly can't scratch it.

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... concentrated in a single point of infinite density. Most likely this is not the actual case due to quantum effects, but what actually happens is not resolved.

 

This is the key thing. It what is so interesting.

Gravity=geometry. Quantum gravity = quantum (therefore uncertain) geometry.

 

When QG is used to analyze what happens in a black hole, typically the singularity goes away and is replaced by something else. But so far different researchers have not resolved the issue of what.

 

In order to resolve, it must be possible to test ideas. For instance, the different QG models of BH collapse must lead to different predictions about gammaray bursts, say. If gammaray bursts are radiation from a BH collapse event. Then one must make detailed observations of the bursts in order to confirm or eliminate models.

 

If anyone is curious about the current QG research into BHs, they can look up papers on arxiv.org by various authors. Three young researchers that come to mind are

Kevin Vandersloot

Dah-wei Chiou

Leonardo Modesto

Personally I would not bother with any papers from before 2007 because the quantum black hole research is in transition. It is a high-risk area of research. There is so far no stable authoritative treatment that I know of.

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Jupiter is also more massive than earth, and it is made of largely hydrogen. Same with the sun.

 

A black hole is as "hard" as you can make something, because you can't break one apart no matter how hard you hit it, and you certainly can't scratch it.

 

Intuitively, that makes a BH look like a very solid block of matter, not a gaseous or liquid substance that can swallow anything (although attracting anything). But I never heard of any such description. All I have read about BH mention horizon & no surface. Actually, when describing the radius of a BH, I don't know what it means.

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I'll probably get thrown off for this .... Lol.

 

Michel, it can't be a 'block'. That is a 'cube'. Although it is still unclear how to describe the physical properties of a BH, until fairly recently, it was considered an infinitely dense object with ZERO dimensions. An infinitely small point. It has also been described as a 'ring' with ZERO thickness if the BH is rotating. That is how the math, and GR characterized it to my knowledge.

 

Now it seems that more scientists are considering the possibility that it has actual dimensions.

 

Describing a BH by it's 'radius' means the Schwarzschild Radius.

 

From Wiki:

 

The Schwarzschild radius of an object is proportional to the mass. Accordingly, the Sun has a Schwarzschild radius of approximately 3 km[3], while the Earth's is only about 9 mm, the size of a peanut. That is, if all the mass of the Sun (or Earth) were contained in a sphere with a radius of 3 km (or 9 mm for the Earth), then the volume of the Sun (or Earth) would continue to collapse into a singularity, due to the force of gravity.

 

An object smaller than its Schwarzschild radius is called a black hole. The surface at the Schwarzschild radius acts as an event horizon in a non-rotating body. (A rotating black hole operates slightly differently.) Neither light nor particles can escape through this surface from the region inside, hence the name "black hole". The Schwarzschild radius of the (currently hypothesized) supermassive black hole at our Galactic Center would be approximately 7.8 million km.

 

I'm sure I have mentioned this before, but if we could park our space ship a few hundred miles outside the event horizon of a BH with an ACTUAL physical diameter of a MILLION kilometers and stare directly at it ... we would see nothing. The light coming from the stars BEHIND the BH would bend around the gravitational well, so it would no different than looking at any starry section of space. ( This assumes it is not 'feeding' ... no jets of radiation coming from the poles ... and that there is no accretion disc to give away the location.)

 

Hope this answer is helpful.

Edited by pywakit
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...

Now it seems that more scientists are considering the possibility that it has actual dimensions. Describing a BH by it's 'radius' means the Schwarzschild Radius.

 

Misleading. The singularity AND the event horizon with its Schwarzschild radius have always been parts of the classical description. There has been no shift by "more scientists considering" some possibility. The Schw. radius has been with us since the 1918 work of Karl Schw. The event horizon was already a big deal in the 1970s with Bekenstein entropy and Hawking radiation.

 

 

I'm sure I have mentioned this before, but if we could park our space ship a few hundred miles outside the event horizon of a BH with an ACTUAL physical diameter of a MILLION kilometers and stare directly at it ... we would see nothing. The light coming from the stars BEHIND the BH would bend around the gravitational well, so it would no different than looking at any starry section of space. ( This assumes it is not 'feeding' ... no jets of radiation coming from the poles ... and that there is no accretion disc to give away the location.)

 

Misinformation.

 

Already with a stellar BH, like the 30 solarmass one in Andy Hamilton's graphic illustrations, looking in the direction of the BH you see something HUGELY DIFFERENT from an ordinary patch of starry sky.

 

This assumes the BH is not "feeding" but is completely quiet. A quiet BH still reveals its presence by gross optical distortion of whatever is behind it.

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Maybe someday we will know the answer, but for know we can only speculate what a black hole is all about. One thing is for shure, there is a lot of energy inside a black hole, If we could send a probe into the center of our own galaxay,where we suspect there is a black hole, Only then will we know. I dont think it will be in our life time though

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Misleading. The singularity AND the event horizon with its Schwarzschild radius have always been parts of the classical description. There has been no shift by "more scientists considering" some possibility. The Schw. radius has been with us since the 1918 work of Karl Schw. The event horizon was already a big deal in the 1970s with Bekenstein entropy and Hawking radiation.

 

Never argue with a man smarter than you. Lol. And you are certainly smarter. But you are speaking of purely mathematical constructs. Please correct me on this Martin. Classical GR says a BH is infinitely small. QM says it CAN'T be infinitely small. Just very tiny.

 

Researchers have continued to push the arbitrary 'theroetical' mass limit. The latest is 50 billion solar masses. But GR puts no such upper limits on mass. ( to my knowledge )

 

If QM is correct, and infinitely small is not possible, then how large a structure would a BH be that contained 40,000,000,000,000,000,000,000 solar masses?

 

This is 200 billion galaxies times 200 billion solar mass average per galaxy.

 

I can't find the research paper I read from one of the universities. I'm sorry. I should have copied it. But in it the astrophysicist speculated on extreme ultra BHs having rather large physical dimensions.

 

I will continue the search for the paper.

 

Misinformation.

 

Already with a stellar BH, like the 30 solarmass one in Andy Hamilton's graphic illustrations, looking in the direction of the BH you see something HUGELY DIFFERENT from an ordinary patch of starry sky.

 

This assumes the BH is not "feeding" but is completely quiet. A quiet BH still reveals its presence by gross optical distortion of whatever is behind it.

 

Sure won't argue this one. Thank you for correcting me Martin. I am not up to speed on gravitational lensing. I should have known better, and I am more than embarrassed by my mistake. My apology Michel. Typical layman ...

 

Beautiful shots, BTW Martin. Hubble pics, I mean. Glad I have high resolution screen!

Edited by pywakit
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l constructs. Please correct me on this Martin. Classical GR says a BH is infinitely small. QM says it CAN'T be infinitely small.

 

In classical general relativity the singularity (not quite so easy to define) at the centre of a black hole is a point- infinitesimally small. This is not usually taken to the the "extent" of a black hole. (Again, extent is not so easy to define). The "size" or "extent" is taken to be the Schwarzschild radius (x2 for a diameter etc). For sure it is the Schwarzschild radius that seems to be the interesting thing for the physics.

 

Now, quantum mechanics presumably smears the singularity inside a black hole. This would then regulate the divergence in the curvature/matter density.

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