How do Black Holes exist with Relativity? [Archive]

RJBeery

05-27-09, 06:53 PM

I enjoy studying QM, but my knowledge of black holes is basically limited to the high school explanations as depicted below.

http://farm3.static.flickr.com/2451/3570613811_c32a05e432.jpg

As a body approaches the event horizon the gravitational forces on that body accelerate it to a velocity approaching c. The math implies that mass crossing the event horizon is actually moving faster than the speed of light. This is expressly forbidden by special relativity, but I had always assumed that general relativity somehow provided the answer via curved space-time that allowed such speeds to be obtained "in appearance only"...or something.

After reading a couple of (non grad-level) books on GR, the problem has not been resolved for me. Sticking strictly to my SR knowledge, my interpretation of black holes has been that they never actually form; as matter begins its collapse from a neutron star, for example, that matter becomes "frozen in time" as its velocity approaches c. I'm pretty sure the SR time dilation math shows that the "outside world" clocks move to infinity during a black hole's formation, yet we seem to readily postulate that black holes currently exist...

Can someone that understands black holes please explain?:confused:

quantum_wave

05-27-09, 07:13 PM

http://en.wikipedia.org/wiki/Gravity

There is a General Relativity section in this Wiki link that discusses the various solutions to the EFEs which is interesting.

I know your question goes beyond this simple explanation and I don't think anyone really understands black holes beyond the mathematical solutions. The physical nature of black holes varies depending on how they form and on their motion, mass, etc., but it is shown mathematically that the solutions to the equations predict various types of black holes except the inflation solution as far as I know.

RJBeery

05-27-09, 11:22 PM

I don't think anyone really understands black holes beyond the mathematical solutions.
You know, I really hope that isn't the case. I was given the distinct impression by a few members on this forum that any confusion I have had relating to black holes was a result of my personal naivete, and that the answers were readily available with some effort. Fine, I did some research. I've even enrolled in some Physics courses back at my alma mater, UNL. Unfortunately the answers I'm looking for don't seem to be addressed in anything short of higher graduate level, so I'm asking for pointers, specifically from...

Guest254 (http://www.sciforums.com/showthread.php?t=67582#20), BenTheMan (http://www.sciforums.com/showthread.php?t=67582#23), Prometheus (http://www.sciforums.com/showthread.php?t=67582#24), and most eagerly from AlphaNumeric (http://www.sciforums.com/showthread.php?t=67582#31) who charmingly asked me to "put a sock in it" for asking questions...

Let's keep the questions simple:

1) Does the math show that, from a stationary point far from the BH, an object "never" crosses that black hole's event horizon? I'm talking about calculating when it will happen, as opposed to trying to "observe" it happening.

2) As a related question, does the math show that, from the frame of the body of mass crossing the event horizon, the "outside world's clock" progresses to infinity in an instant?

3) If the answer to 1 and 2 are yes (which I believe they are but until recently have always assumed that GR resolved this somehow), then HOW can we postulate that black holes exist today? In other words, if the creation time for black holes from our perspective is infinite, how can ANY exist from our perspective? :bugeye:

Thanks in advance

Dinosaur

05-27-09, 11:31 PM

The posted high school explanation & diagram do not seem correct to me.

First: c is a velocity & accelerative forces cannot be said to approach c because the units do not match. The following does not make senseAs a body approaches the event horizon the accelerative forces on that body approach c.As an object approaches the event horizon, the escape velocity approaches c, which means that at the event horizon not even a light ray can escape from the fierce gravitational forces. In General Relativity jargon, the geometry of the space time continuum at the horizon does not allow any outward paths.

An important issue vaguely mentioned above: In any physics equation, the units must match or there has been a mistake. Note the following.Velocity is Distance / Time

Acceleration is Distance / Time2

The following is a valid equation.
Distance = InitialDistance + IntitialVelocity*Time + Acceleration*Time2

Using the metric system: Velocity units are Centimeters / Seconds & acceleration units are Centimeters / Seconds 2. Therefore velocity multiplied by time has centimeters for units & acceleration multiplied by time2 also has centimeters for units.Thus units for the above formula are centimeters = centimeters + centimeters + centimeters. If the units in a formula do not match as illustrated in the above example, something is incorrect. Perhaps meters or inches were used in one term & centimeters in another. Perhaps there is a mistake in the formula itself.

The following does not seem correct.Inside the horizon, space is being pulled faster than the speed of light (c).Once again, c is a velocity. I do not that space inside the horizon is moving rather than being warped or having extreme curvature. I do not think that anything inside the horizon is moving faster than c, and objects inside are surely not moving as fast as c.

BTW: Outside of black holes, there is expansion of the universe. I do not think they refer to this as space moving. In some sense, more space is generated between galaxies. This effectively results in galaxies moving farther apart. The galaxies can be thought of as moving, but space itself is not usually referred to as moving. At huge distances from Earth, the expansion results in galaxies receding from us faster than the velocity of light. Galaxies receding at c or faster are said to be outside our observable universe: They can have no interaction with us. In some sense, they are not moving faster than c with respect to us: The space between us & them is increasing due to the expansion.

Do not worry if some of the above seems a bit mind boggling. It is counterintuitive, but not as counterintuitive as Quantum Physics.

RJBeery

05-27-09, 11:36 PM

Dinosaur: you're right, I understand that acceleration and velocity are not the same. I need more experience in getting my thoughts into words succinctly. Ignore the HS explanation, and ignore my first post entirely if you wish. Please read post #3...

jmpet

05-27-09, 11:46 PM

The only way black holes are Relativity-compliant is if they exude energymass over time to form a zero.

James R

05-27-09, 11:47 PM

The math implies that mass crossing the event horizon is actually moving faster than the speed of light.

That's not quite right. If you were in a spaceship falling into a large black hole, you would not notice anything unusual as you crossed the event horizon. You would not judge your speed to be faster than the speed of light.

What somebody a long way from the hole sees as you fall in is that you appear to slow down as you approach the event horizon. This is actually due to the fact that time near the event horizon runs slower than time far from the hole. In fact, from the point of view of a distant observer, nothing falling into a black hole ever reaches the event horizon. But at the same time, the light from the object falling in slowly fades out as it is red-shifted - think of this as the apparent colour of the object gradually becoming redder until the object itself fades from view into blackness.

It's really important to keep in mind the difference between frames of reference of a distant observer looking at the hole and of somebody in freefall into it. What they see is quite different, partly due to the effects of the different space and time curvature near the hole, and partly due to the behaviour of light propagating outwards from the hole to the distant observer.

Sticking strictly to my SR knowledge, my interpretation of black holes has been that they never actually form; as matter begins its collapse from a neutron star, for example, that matter becomes "frozen in time" as its velocity approaches c.

The "freezing in time" effect is the same effect as described above. Any infalling object (such as the surface of a star) will appear from a long distance away to fall more and more slowly as it approaches the event horizon, so that it never quite gets there. But this appearance is only the appearance from the outside. If you jumped on the star's surface, you'd quickly find yourself well past the event horizon and on your way to the centre of the hole.

RJBeery

05-27-09, 11:53 PM

James R: I am appreciative, but you've given the same pop-sci explanation that I've read many times which I understand completely, and I had always assumed that it was a watered down answer for the masses. Please read post #3...

James R

05-28-09, 12:05 AM

1) Does the math show that, from a stationary point far from the BH, an object "never" crosses that black hole's event horizon?

Yes, provided that you're careful to measure time using a clock that is stationed far from the BH.

2) As a related question, does the math show that, from the frame of the body of mass crossing the event horizon, the "outside world's clock" progresses to infinity in an instant?

No. There's nothing special about the event horizon from the point of view of a frame co-moving with the body.

3) If the answer to 1 and 2 are yes (which I believe they are but until recently have always assumed that GR resolved this somehow), then HOW can we postulate that black holes exist today? In other words, if the creation time for black holes from our perspective is infinite, how can ANY exist from our perspective? :bugeye:

When we talk about the "creation time" for a black hole, we mean the time at which an event horizon formed. If you're looking at a collapsing star, that time is approximately when the radius of the star due to gravitational collapse becomes less than the Schwarzschild radius of a black hole of equivalent mass. You can calculate a time that will be close enough without worrying about relativistic effects.

James R: I am appreciative, but you've given the same pop-sci explanation that I've read many times which I understand completely, and I had always assumed that it was a watered down answer for the masses. Please read post #3...

Of course it's watered down for the masses. The masses don't know the tensor calculus and differential geometry required to understand the theory in its full glory. Nor can concepts like the Schwarzschild metric and the results that follow from that be easily explained without at least some knowledge of partial differentiation, a decent understanding of algebra and so on - and even with that a small leap of faith is required unless you want to go the whole hog and learn general relativity properly.

Dinosaur

05-28-09, 12:40 AM

R J Beery: Do not dispair about understanding black holes. The General Relativity mathematics is formidable & without some prerequiste courses you might never understand it.

However, explanations & diagrams with little or no mathematics can provide a reasonable understanding of the characteristics of black holes. Some explanations for non-experts are misleading or down right erroneous due to being edited by journalists who only thought they understood what some expert told them. This is true in fields other than physics & occurs in many "books for the layman." Scientific American articles are almost always good translations of what some expert said or wrote. In many cases, they are written by the expert rather than by some journalist with little real understanding.

Your question about when an object crosses the event horizon is a good one. This issue is almost always misunderstood due to a literal translation of the mathematics into ordinary English or some other natural language.

Yes the mathematics indicates time slowing down as the horizon is approached. This is from the viewpoint of a distant observer. From the point of view of an observer falling toward the horizon, he will observe himself being torn apart rather quickly. There is a Scifi story about twins who were telepathic & used for faster than light communications over interstellar distances. In the story, one twin is on a space ship which gets sucked into a black hole. His twin back on earth goes crazy because he can sense his brother's agony as he is being torn apart. Due to the time slowdown effects, the twin on Earth is aware of his brother's agony for days, weeks, years although the brother died very fast from his own point of view.

Back to an explanation of why distant observers can see black holes growing due to matter being pulled in. The explanation is as follows. The numbers used are made up, not to be taken seriously. Imagine some stars being pulled toward a black hole with a horizon radius of 100 miles.

Suppose the black hole has a certain mass which we will call InititialMass.

Note that stars or other objects do not usually fall directly toward a black hole. They usually start getting their path of motion pulled into an orbit around the black hole. The gravititational forces start tearing the orbiting stars apart, resulting in a disk of matter swirling around the black hole. Such a disk is a bit like the rings around Saturn, but more like our solar system before the planets formed from a disk of matter surrounding the sun.

Matter in the swirling disk starts getting pulled closer & closer to the event horizon.

Now suppose than the horizon radius is 105 miles for a black hole with InitialMass + OneSolarMass.

If OneSolarMass gets pulled in closer than 5 miles from the event horizon, you get a black hole with a 105 mile horizon radius.A distant observer could (in principle) see the horizon radius increase from 100 to 105 miles and observe matter falling into a black hole (but not the original black hole). Note that such an observer never saw any matter reach the original horizon which had a radius of 100 miles.

I am not sure than in practice we can observe black holes growing or directly measure/observe an event horizon. I think the most we can do is calculate the horizon radius by observing (measuring velocites & paths of) objects orbiting the black hole.

I think we can be certain that black holes in galactic centers grow over periods of decades, centuries, or thousands of years. We might even be able to calculate (estimate) the rate of growth for some black holes.

RJBeery

05-28-09, 02:20 AM

“
Originally Posted by RJBeery
James R: I am appreciative, but you've given the same pop-sci explanation that I've read many times which I understand completely, and I had always assumed that it was a watered down answer for the masses. Please read post #3...
”
Of course it's watered down for the masses. The masses don't know the tensor calculus and differential geometry required to understand the theory in its full glory. Nor can concepts like the Schwarzschild metric and the results that follow from that be easily explained without at least some knowledge of partial differentiation, a decent understanding of algebra and so on - and even with that a small leap of faith is required unless you want to go the whole hog and learn general relativity properly.
I didn't mean to sound rude, if that's how you took my response. Your answer is consistent with everything that I've read, and I do not doubt that you have a more sophisticated answer than you gave. What I was saying is, basically, give me the REAL answer, gore and all (if there is one).

No. There's nothing special about the event horizon from the point of view of a frame co-moving with the body.
OK, here I do have a problem. Are you sure that an accelerated frame (i.e. the guy falling into the black hole) would not calculate a speeding up of clocks in distant frames? You're making me question my understanding, which is good, but I'm fairly certain that a body approaching an event horizon would see distant clocks moving at a rate approaching infinity.

When we talk about the "creation time" for a black hole, we mean the time at which an event horizon formed.
You're presuming that the event horizon IS formed. I am suggesting, through logic stated above, that the black hole never reaches that point. What this would mean is that the required Schwartzchild radius is never *quite* reached for a given mass...

Dinosaur: your posts are thought provoking, thanks.

prometheus

05-28-09, 03:39 AM

I didn't mean to sound rude, if that's how you took my response. Your answer is consistent with everything that I've read, and I do not doubt that you have a more sophisticated answer than you gave. What I was saying is, basically, give me the REAL answer, gore and all (if there is one).

Assuming the Schwarzschild metric ds^2 = -f(r) dt^2 + \frac{dr^2}{f(r)} + r^2 d \Omega^2 where f(r) = 1- \frac{r_S}{r}. To work out the time taken for an object to fall into a black hole from the point of view of an observer at infinity you evaluate \int dt and from the point of view of the infalling observer you evaluate \int ds. You'll find the former is infinite while the latter is finite.

You're presuming that the event horizon IS formed. I am suggesting, through logic stated above, that the black hole never reaches that point. What this would mean is that the required Schwartzchild radius is never *quite* reached for a given mass...

Suppose you have a setup like this: a thin spherical shell of matter that has mass M is collapsing to form a black hole. For an external observer they will never see a black hole formed because the horizon is a coordinate singularity as JamesR has explained. This doesn't mean that a black hole is not formed because from the point of view of the shell there is a finite time at which it collapses inside it's own horizon and another finite time where a singularity is formed.

You may think that this is unsatisfactory but think about it in the following way. From the point of view of the shell, the geometry is dynamic - that is it's radial position is changing with time. You can transform to coordinates where the shell is stationary but the curvature changes as a function of time. At infinity the geometry is static - the observer sees the Schwarzschild metric and the collapse does not affect him. As far as the observer at infinity is concerned the mass he's looking at at r = 0 could be a blob of gas, a star, a shell or a black hole. It makes no difference. A precise statement of this is known as Gauss' law for gravity - the gravity of a mass distribution of total mass m in free space is the same as for a point mass m located at the centre of mass of the distribution. In the example above the centre of mass is r = 0 and a point mass is what you would call a singularity.

In summary, even though the observer at infinity doesn't ever see a black hole formed it doesn't matter because the gravity he sees is the same. Observers whose observations depend of whether a black hole is "really" there or not will see a black hole being formed.

BobG

05-28-09, 04:48 AM

Assuming the Schwarzschild metric ds^2 = -f(r) dt^2 + \frac{dr^2}{f(r)} + r^2 d \Omega^2 where f(r) = 1- \frac{r_S}{r}. To work out the time taken for an object to fall into a black hole from the point of view of an observer at infinity you evaluate \int dt and from the point of view of the infalling observer you evaluate \int ds. You'll find the former is infinite while the latter is finite.

I saw this calculation when I was taught a bit of GR. What I didn't understand was why the co-ordinate time dt is the time measured by a stationary observer at infinity. Is it just because you are integrating from infinity?

prometheus

05-28-09, 06:20 AM

The Schwarzschild metric in the coordinates I've given describe an observer at infinity. I should clarify that you integrate over a geodesic and in this case you're looking at radial infalling geodesics. The time coordinate is the time experienced by an observer at infinity, while the "s - time" or the proper time is the time experienced by an observer following the geodesic being integrated over.

The reason we choose to use the time of an observer at infinity as a coordinate is because that observer would be inertial, ie would not need to be accelerating to stay at the same radial distance from the centre of the black hole, and it's basically the only coordinate that non inertial observers can agree on.

AlphaNumeric

05-28-09, 08:14 AM

and most eagerly from AlphaNumeric (http://www.sciforums.com/showthread.php?t=67582#31) who charmingly asked me to "put a sock in it" for asking questions...
I have no problem with people asking honest questions but it's my experiience that you aren't asking questions because you want a point clarified, you ask questions because you are trying to lead into a "Aha! That proves it's inconsistent!" moment about either quantum mechanics or general relativity. You say you're 'studying QM' but something tells me you aren't reading the textbooks an undergraduate studying QM would be reading. I read layman pop science books before going to uni and since then I've actually done QM and know the huge gapping difference between the two metods of 'studying' QM.

quantum_wave

05-28-09, 08:15 AM

You know, I really hope that isn't the case. I was given the distinct impression by a few members on this forum that any confusion I have had relating to black holes was a result of my personal naivete, and that the answers were readily available with some effort. ...
There can be impatience and condescending from people who view the picture mathematically knowing that those who don’t do the math can’t see the picture in the same way they see it, i.e. mathematically. On the other hand it is difficult to explain the physical picture when it comes to black holes. The two groups do not completely communicate because they are viewing different pictures, i.e. the mathematical picture and the physical picture. Either you do the math and are satisfied that there is no physical explanation yet for what the math leads to, or you think through the physics to see where our understanding ends and the unknown begins.

When you get to the point of departure from what we know, the physical answers are no longer available. To go beyond that point a new understanding of the physical universe is required. However math can go anywhere, even places that the real universe cannot go.

In my speculative view, time stops for everything that enters a black hole relative to an outside observer for reasons that are not science but are speculation. Anything that has entered a black hole has been accelerated and is in the process of being compressed physically to the point that its mass reaches a limit of maximum energy density. This limit can be exceeded mathematically but not physically.

If that object is being accelerated then that limit occurs before the object reaches the speed of light because nothing physical can reach that speed except light. But mass can enter a black hole and it cannot escape. Once inside, the physical compression of acceleration becomes the physical compression of objects within a growing massive object, i.e. heat and pressure. Heat and pressure within a black hole eventually compress the mass to that maximum limit of energy density. In my view, matter ceases to function at that limit because every particle requires adequate space to function and the physical particle gets compressed to the point that there isn’t enough physical space to function. Physical mass is compressed to physical energy inside the black hole as more and more mass enters.

That statement is not science, it is my speculation about the physical picture that is not told mathematically because the math can take objects to the speed of light at which the physical universe becomes energy and the math bumps into infinity.

The speculative reason that I say, “in my view time stops in a black hole relative to an outside observer”, is because mass in a black hole is converted to energy and energy is timeless. However the current scientific view is that energy in the state that I am referring to, i.e. the dense state, does not exist and so it is not addressed scientifically and it doesn't comply mathematically.

prometheus

05-28-09, 09:16 AM

...the physical picture that is not told mathematically because the math can take objects to the speed of light at which the physical universe becomes energy and the math bumps into infinity.

I'm not going to go through your post line by line and I'm sure this is not the only one, but this is not what happens mathematically. If you want to understand the mathematics and talk about it you should take the time to learn it first.

In my speculative view...

In general terms, this is the problem with your approach to physics. You haven't come up with a new paradigm and you haven't discovered a new interpretation of GR, you are simply wrong and yet you seem to regard your own opinions above all. The Schwarzschild metric is very well understood now and has been experimentally tested thoroughly. You should get it out of your head that you can do something of value without learning the basics.

quantum_wave

05-28-09, 09:42 AM

I'm not going to go through your post line by line and I'm sure this is not the only one, but this is not what happens mathematically. If you want to understand the mathematics and talk about it you should take the time to learn it first.

In general terms, this is the problem with your approach to physics. You haven't come up with a new paradigm and you haven't discovered a new interpretation of GR, you are simply wrong and yet you seem to regard your own opinions above all. The Schwarzschild metric is very well understood now and has been experimentally tested thoroughly. You should get it out of your head that you can do something of value without learning the basics.
Maybe you are right. What I am wrong about then is that If the mathematicians were to calculate the black holes as if there was a limit to the maximum possible energy density, i.e. a new constant, then the math would work. Mass would convert to energy at the maximum energy density (not recognized by science) and even energy at the maximum energy density requires space in proportion to the equivalent mass.

So what you say I am wrong about is that mass converts to energy when compressed to a limit of maximum energy density?

prometheus

05-28-09, 10:36 AM

Maybe you are right. What I am wrong about then is that If the mathematicians were to calculate the black holes as if there was a limit to the maximum possible energy density, i.e. a new constant, then the math would work. Mass would convert to energy at the maximum energy density (not recognized by science) and even energy at the maximum energy density requires space in proportion to the equivalent mass.

So what you say I am wrong about is that mass converts to energy when compressed to a limit of maximum energy density?

I have no idea what the hell you are on about.

quantum_wave

05-28-09, 11:11 AM

If RJBeery doesn't object to me explaining it to you on his thread, I'll be glad to. It is a question to you about energy density and if there is space required for individual fundamental particles to function, i.e. are fundamental particles actually points in space or do they occupy a finite volume of space. Let's wait to see if RJB wants it discussed here.

RJBeery

05-28-09, 04:08 PM

I have no problem with people asking honest questions but it's my experiience that you aren't asking questions because you want a point clarified, you ask questions because you are trying to lead into a "Aha! That proves it's inconsistent!" moment about either quantum mechanics or general relativity.
Yes, sometimes I do this. Believe it or not, this is a healthy process for Science, ESPECIALLY if the questions make you ponder. If you find yourself defending popular dogma by blinding yourself to reason then you have done nothing but transform Science into a Religion.

Look at the ass-reaming quantum_wave just got for posting his personal speculation about how mass is dealt with in black holes...
you are simply wrong and yet you seem to regard your own opinions above all. The Schwarzschild metric is very well understood now and has been experimentally tested thoroughly. You should get it out of your head that you can do something of value

This response is BULLSHIT and does not foster creative thinking. In fact it completely stifles new ideas from anyone without a thick skin. What ever happened to...

Prometheus: "that's interesting, QW, but how would you explain the disparity between the math calculations and your proposal?"

A little change in tone gets the same message across without the responder looking like an asshat.

Quantum_wave, of course I'd like to learn more about your speculative theory. On my first pass it sounded like some kind of super-fusion threshold that results in a complete conversion of matter to energy that you're proposing...

Now, back to my question:

Assuming we're all in agreement that the distant observer calculates that matter never crosses the event horizon, how can that observer postulate that black holes currently exist*? If, from that frame, black holes take an infinite amount of time to form, then why do we speculate that they already have? Avoiding black hole singularity formation has some benefits, including Relativity compliance, Universal homeomorphism, and avoidance of information loss.

NOW, to Ben, Alpha, Prometheus, Guest and anyone else out there having an aneurysm because "this is not what we were taught in school", ask yourself if my LOGIC makes sense before you begin the ass-reaming. :D

* It is very important to distinguish between a fully-formed traditional black hole which possesses an event horizon and a "black hole condition" where the outside effects are virtually indistinguishable yet the singularity is never actually formed.

prometheus

05-28-09, 04:47 PM

This response is BULLSHIT and does not foster creative thinking. In fact it completely stifles new ideas from anyone without a thick skin. What ever happened to...

Prometheus: "that's interesting, QW, but how would you explain the disparity between the math calculations and your proposal?"

A little change in tone gets the same message across without the responder looking like an asshat.

Think of my response how you like, but you've got to remember that the Schwarzschild metric has been known since 1916. People a lot smarter than you or I or even quantum wave I dare say have been thinking about the implications and predictions for more than 90 years. All experiments devised to test Schwarzschild have supported it. I posit that it is not creative thinking that is required at this stage, but some understanding.

Your problem is that you've got this view of physics from your armchair that we just think about stuff and come up with crazy ideas. When I read a brief history of time I wondered what sort of imagination physicists must have to come up with such lunacy and it still seems to work. The reality is that theoretical physicists spend 99% of their research time slogging through the mathematics of a particular theory or model or whatever. When a result is obtained, then do we try and interpret what it means.

If quantum wave feels like an asshat then that's good, because that's how he is behaving, and you as well. If you can't take it from someone who works on GR type models every day how the discipline works (I'm not even talking about the explanation I gave that you have ignored) and insist on making up bollocks to try and make yourself feel clever then you are far worse than an asshat.

prometheus

05-28-09, 05:01 PM

Assuming we're all in agreement that the distant observer calculates that matter never crosses the event horizon, how can that observer postulate that black holes currently exist?

As has been carefully explained to you, an observer at an infinite distance observes an object approaching the horizon but never crossing it. It doesn't matter because the only real observable from infinity is the mass of the combined black hole and object. Go back and read post 12 again and read the wiki article on Gauss law for gravity.

If, from that frame, black holes take an infinite amount of time to form, then why do we speculate that they already have?

Another thing that's been carefully explained to you is that in the frame of a collapsing shell or fluid sphere, the collapse takes a finite time to fall inside the horizon and another finite time to form a singularity. Hawking and Penrose have showed that in GR a collapsing body must form a singularity if it collapses inside it's own horizon. This is non negotiable.

Avoiding black hole singularity formation has some benefits, including Relativity compliance, Universal homeomorphism, and avoidance of information loss.

But it's wrong, so it's completely pointless. Asshat.

RJBeery

05-28-09, 05:12 PM

Prometheus: you are right, I didn't thank you for your very detailed explanation of black holes. THANKS, I really appreciate you taking the time to respond. The reason I didn't reply to it directly is because you gave me no new information - you corroborated my current understanding of black holes. At a distance, the black hole takes an infinite time to form. This single verification is all I needed to justify my question:
Assuming we're all in agreement that the distant observer calculates that matter never crosses the event horizon, how can that observer postulate that black holes currently exist*? If, from that frame, black holes take an infinite amount of time to form, then why do we speculate that they already have? Avoiding black hole singularity formation has some benefits, including Relativity compliance, Universal homeomorphism, and avoidance of information loss.

It's a simple question. Grab your balls and allow yourself to postulate a response that doesn't come from your textbook. Hell go make a second log in identity first if you're worried about being treated like you treated quantum_wave. ;)

prometheus

05-28-09, 05:18 PM

Have you not considered that the textbook might be right?

RJBeery

05-28-09, 05:35 PM

Obviously the veracity of the textbooks is my presumption when I read them. When I find an inconsistency my first reaction is that the textbook has been watered down for readability, and that a higher level explanation would resolve everything (so far, I have not found that higher level explanation for this question). I also consider the possibility that it was written by someone that did not question what *they* read in a textbook a generation earlier...

prometheus

05-28-09, 05:52 PM

I'll put it another way - have you considered that it's your understanding that is deficient?

RJBeery

05-28-09, 06:22 PM

Yes, I have considered this, why do you think I posted this thread?! I don't know to what extent you are the forum's black hole authority, but your fingers-in-the-ears reaction tells me that you don't know the answer either.

I take that back, maybe you think you've given me an answer? You said:
Another thing that's been carefully explained to you is that in the frame of a collapsing shell or fluid sphere, the collapse takes a finite time to fall inside the horizon and another finite time to form a singularity. Hawking and Penrose have showed that in GR a collapsing body must form a singularity if it collapses inside it's own horizon. This is non negotiable.
Yes, from the shell's perspective the black hole takes a finite amount of time to form according to the math. I do not dispute this. HOWEVER, do you believe that there currently exists a singularity at the center of the Milky Way? I know this is a popular theory in Astrophysics. If the answer is YES, then, in your mind, time-reverse it's creation to the point just prior to the singularity formation. Now, play it forward again through the present day. Has sufficient time passed from our perspective for the singularity to form? What does the math say?

quantum_wave

05-28-09, 06:51 PM

Thanks RJ, but instead of accepting your gracious offer to explain my post to Prometheus on your thread it is unnecessary to expose you and your thread to the expected immature and unprofessional responses that are getting pretty well known. I have dealt with stodgy ( http://www.answers.com/topic/stodgy) people on my ongoing threads about QWC for over a year it seems, and no one from the stodgy set has ever shown any interest in alternative thinking.

My invitation is open to all to visit my thread and here is a recent post written after a series of circus clown posts from the stodgy set:

http://www.sciforums.com/showpost.php?p=2263931&postcount=72

I would welcome you and anyone who can think logically to jump in after post #72 and participate. Getting anyone’s views on what I am asking would be nice, but of course I would ask that you show some maturity. Post #72 & #73 represent the beginning to a series of reasonable and responsible steps of speculation that clearly explain my idea. Prometheus and others could have easily dispatched me to oblivion if they had addressed the ideas using their own reasonable and responsible logic which must certainly trump my feeble effort. But no, only ad homs and displays of inflated self worth.

James R

05-28-09, 10:49 PM

RJBeery:

What I was saying is, basically, give me the REAL answer, gore and all (if there is one).

It's not clear to me whether you want me to reproduce the relevant mathematics, which is of course readily available in any introductory text on general relativity. On the one hand, that appears to be what you're asking for, but on the other hand I'm getting mixed messages because you appear to be telling prometheus and others to throw away their textbooks.

OK, here I do have a problem. Are you sure that an accelerated frame (i.e. the guy falling into the black hole) would not calculate a speeding up of clocks in distant frames?

That's not what I said. Specifically, you asked whether external clocks would be seen as speeding up infinitely, so that time passed "in an instant", according to somebody falling through the event horizon. My answer to that was "no". External clocks would be seen as running faster, but not infinitely faster.

You're presuming that the event horizon IS formed. I am suggesting, through logic stated above, that the black hole never reaches that point.

If you're viewing the situation from a long way away, you're right. If there is any "preferred time" to look at black hole formation, however, it is probably the proper time of the infalling matter. Since infalling matter falls to the centre of the hole in a finite proper time, that suggests to me that the black hole is formed in finite time. But I don't think it's necessary to labour the point:

What this would mean is that the required Schwartzchild radius is never *quite* reached for a given mass...

As seen from the outside, yes. No problem.

RJBeery

05-28-09, 11:10 PM

Specifically, you asked whether external clocks would be seen as speeding up infinitely, so that time passed "in an instant", according to somebody falling through the event horizon. My answer to that was "no". External clocks would be seen as running faster, but not infinitely faster.
Again, JamesR, I am open to being corrected, but I'm pretty sure that the body approaching the event horizon calculates that the "distant time clocks" continue to speed up with an infinite acceleration, not just "some" acceleration...

“
What this would mean is that the required Schwartzchild radius is never *quite* reached for a given mass...
”
As seen from the outside, yes. No problem.
Ahh but that's the crux of my argument! In order to postulate that black holes currently exist one must presume that the frame to cross the event horizon currently exists!

James R

05-28-09, 11:25 PM

Again, JamesR, I am open to being corrected, but I'm pretty sure that the body approaching the event horizon calculates that the "distant time clocks" continue to speed up with an infinite acceleration, not just "some" acceleration...

I don't think that is right, but I admit that it's possible that I am wrong.

In order to postulate that black holes currently exist one must presume that the frame to cross the event horizon currently exists!

Are you claiming that black holes don't exist, then? Is that what this is about?

If black holes don't exist, how do you explain active galactic nuclei, the object Sagittarius A*, the many sources of huge radio emission that are observed and which can be shown to be produced from regions of space too small to be anything other than a black hole?

What's your alternative theory?

Dinosaur

05-29-09, 01:25 AM

R J Beery & James R: Have either of you taken time to analyze post #4? That post describes how a black hole can grow in finite time without a distant observer seeing matter reach an event horizon.

The following has a logical error. Assuming we're all in agreement that the distant observer calculates that matter never crosses the event horizon, how can that observer postulate that black holes currently exist ? If, from that frame, black holes take an infinite amount of time to form, then why do we speculate that they already have?I agree that a distant observer can correctly calculate that he will never see matter reaching or crossing an event horizon. I claim that this does not lead to the conclusion that Black holes take an infinite time to form from the point of view of that distant observer.

My explanation in post #4 indicates that the distant observer can (in some sense) see & calculate that the radius of a black hole event horizon can grow without matter actually crossing the original event horizon or any other event horizon associated with the growing black hole.

Can you point out an error in that analysis?

Crunchy Cat

05-29-09, 02:35 AM

As a body approaches the event horizon the gravitational forces on that body accelerate it to a velocity approaching c.

I don't recall that being true.

The math implies that mass crossing the event horizon is actually moving faster than the speed of light. This is expressly forbidden by special relativity, but I had always assumed that general relativity somehow provided the answer via curved space-time that allowed such speeds to be obtained "in appearance only"...or something.

Mass can never move at the speed of light (or more). It would require a minimum of infinite energy to do so and no such beast is available in our universe. What does happen is space is warped and dragged beyond the event horizon... and that can exceed the speed of light with ease.

After reading a couple of (non grad-level) books on GR, the problem has not been resolved for me. Sticking strictly to my SR knowledge, my interpretation of black holes has been that they never actually form; as matter begins its collapse from a neutron star, for example, that matter becomes "frozen in time" as its velocity approaches c. I'm pretty sure the SR time dilation math shows that the "outside world" clocks move to infinity during a black hole's formation, yet we seem to readily postulate that black holes currently exist...

We can observe black holes so the whole paragraph is pretty much invalid.

Can someone that understands black holes please explain?:confused:

After the event horizon, space warps and drags right into the singularity... in other words all paths from all directions lead to the singularity. Once mass hits the singularity it effectively melts into its most fundamental parts and squishes together.

AlphaNumeric

05-29-09, 04:56 AM

quantum_wave

05-29-09, 10:10 AM

When I read RJ say 'Homeomorphism' I can't help but think "I bet he doesn't know what that actually means". Other than that it's typical crank stuff, the "Oh you don't think, you just defend the dogma. You need to think about black holes", as if noone in the 90 years of GR has done that. Cranks are a lot less original than they think, they don't realise this because they never make the effort to find out what's been done before.If only you had a grasp of reality yourself :). I can't help but think you didn't think before you slushed out that piece of drivel you seem to think was a post. Did you know you can just keep quiet if you don't have anything to contribute?

prometheus

05-29-09, 10:30 AM

If only you had a grasp of reality yourself :). I can't help but think you didn't think before you slushed out that piece of drivel you seem to think was a post. Did you know you can just keep quiet if you don't have anything to contribute?

If you stuck to that rule yourself I can't help thinking that your 1000 odd posts would be more like 10. AN is doing cutting edge research in physics, something you can only dream of.

quantum_wave

05-29-09, 10:48 AM

If you stuck to that rule yourself I can't help thinking that your 1000 odd posts would be more like 10. AN is doing cutting edge research in physics, something you can only dream of.And what part of the cutting edge work was his useless post to a guy that has requested his helpful input?

prometheus

05-29-09, 12:59 PM

The explanation of the OP is on the first page of this thread and both of you are ignoring it in favour of waffling about rubbish and claiming it's physics. RJ and you never request helpful input - you simply want people to pat you on the head and tell you that your ideas about physics are useful and interesting, neither of which they are. My recommendation for getting the above is to paint a picture of your house and show it to your mum.

quantum_wave

05-29-09, 01:02 PM

Not true in the slightest. Obfuscation on your part and another wasted post that we have to take as an example of your lack of maturity.

RJBeery

05-29-09, 01:19 PM

Are you claiming that black holes don't exist, then? Is that what this is about?

I'm not claiming anything, but my speculation was basically summarized earlier:
* It is very important to distinguish between a fully-formed traditional black hole which possesses an event horizon and a "black hole condition" where the outside effects are virtually indistinguishable yet the singularity is never actually formed.

Note that this "virtual indistinguishability" from a traditional black hole is my response to Dinosaur and Crunchy Cat:

My explanation in post #4 indicates that the distant observer can (in some sense) see & calculate that the radius of a black hole event horizon can grow without matter actually crossing the original event horizon or any other event horizon associated with the growing black hole.
We can observe black holes so the whole paragraph is pretty much invalid.

Finally, to AlphaNumeric:
When I read RJ say 'Homeomorphism' I can't help but think "I bet he doesn't know what that actually means".
You know what saddens me? There are only a few people on this forum whose knowledge truly impresses me and you are one of them. Every once in a while someone will ask a very deep math question, and you will quickly churn out a beautifully elegant answer. I do not doubt that you *get* mathematics. Your problem is that's your only language (the same is true with Ben, but his skills do not match yours); that's why the two of you talk about "doing Physics". You don't DO Physics, you STUDY Physics; you DO the math that we suspect underlies the Physics. Math is the only way you can relate to Physics which is why you will probably never substantially help Physics progress. It takes creative genius, while you are a very well educated automaton. I know you work on a campus somewhere, and you do research. Good! I don't WANT you to fail. Hell I'd love it if you came up with the "next big idea", but I suspect any truly edgy research you are involved in has you as the math cruncher rather than the spearhead of the project.

RJBeery

05-29-09, 06:21 PM

ripleofdeath

05-30-09, 05:17 AM

philosophically postulating for a moment...

gravity is an unknown "reality"...

dark matter is an unknown "reality"

speeds greater than what we currently measure(light) are an unknown "reality"

matter at speed creates gravity...

mass is relative to gravity by speed(supposedly although i suspect this is more soo a symptomatic environmental).

what are we challenging... ?

"our reality" ... ?

i suggest this as a concept...
we set aside the presumption of light being an absolute speed
we set aside the presumption of reality being clinically factualised

i suspect we need to approach the situation dynamically to be able to encompass realities which on the surface oppose each others existence.

quantum_wave

06-02-09, 10:35 AM

Now, if the personal attacks have run their course, I'll recap my thought:

At the very "instant" that gravity overcomes the neutron degeneracy pressure, and the first particle begins its descent into a singularity, I am questioning whether or not it ever gets there. I believe it does not. This does not prevent other mass from falling into the "neutron-star-just-on-the-brink-of-collapse", and I believe that Newton's Shell Theorem ensures that we could not tell the difference...My comments are of small value in addressing the theoretical physics that you address, but I do have some comments that might give you something to respond to so you can advance from your recap.

I'm not alone in thinking that time stops somewhere in conjunction with the formation of a black hole. My view is that matter as we know it ceases to exist and becomes a different and unobservable form of timeless energy. So the "instant" that you describe when that particle crosses the threshold is the same instant that I describe as the point where matter ceases to function and becomes a part of that timeless energy that resides inside the black hole.

I say the black holes exists but the matter that goes into them crosses the threshold, no longer functions as a particle and is no longer experiencing time.

Guest254

06-05-09, 05:30 PM

At the very "instant" that gravity overcomes the neutron degeneracy pressure, and the first particle begins its descent into a singularity, I am questioning whether or not it ever gets there. I believe it does not. This does not prevent other mass from falling into the "neutron-star-just-on-the-brink-of-collapse", and I believe that Newton's Shell Theorem ensures that we could not tell the difference...
Having just arrived in this forum from a link in another thread, and having seen my name in lights in this thread, I feel compelled to storm on in and call you stupid.

Do the calculation. You are essentially asking "if you do the calculation, is my guess correct?" People have told you no. People have told you how to do the calculation. The only remaining option is for you to do the calculation.

If you are at all interested in the answer, and in black holes in general, you'll be willing to put in the time and effort to learn the tiny amount of GR needed to do such calculations. Such calculations are basic exercises for undergraduates studying their first course in GR. I predict that you will make no such effort - you're not interested in actually doing science, you just want to come on internet forums and play pretend.

RJBeery

06-05-09, 07:06 PM

Do the calculation. You are essentially asking "if you do the calculation, is my guess correct?" People have told you no. People have told you how to do the calculation. The only remaining option is for you to do the calculation.
What calculation are you referring to? I have done the math which is why I asked the following three questions. It appears to me that you are the one doing the presuming.
1) Does the math show that, from a stationary point far from the BH, an object "never" crosses that black hole's event horizon? I'm talking about calculating when it will happen, as opposed to trying to "observe" it happening.

2) As a related question, does the math show that, from the frame of the body of mass crossing the event horizon [sitting on the collapsar's surface as it forms], the "outside world's clock" progresses to infinity in an instant?

3) If the answer to 1 and 2 are yes (which I believe they are but until recently have always assumed that GR resolved this somehow), then HOW can we postulate that black holes exist today? In other words, if the creation time for black holes from our perspective is infinite, how can ANY exist from our perspective?

James R

06-06-09, 03:39 AM

I have done the math ...

You have? Please post it.

Guest254

06-06-09, 04:46 AM

Indeed, I'd love to see your efforts. Show us all the mathematics...

RJBeery

06-06-09, 12:37 PM

Indeed, I'd love to see your efforts. Show us all the mathematics...
To what end? I don't seek your respect; I'm looking for an answer to question #3. If you take issue with question #1, for example, then say so first, otherwise it gives the appearance that you don't know the answer but are putting nothing on the line by acting like you do. With respect, yours is not the mind that I'm probing.

common_sense_seeker

06-06-09, 01:10 PM

(Q)

06-06-09, 01:28 PM

D H

06-06-09, 01:37 PM

In other words, if the creation time for black holes from our perspective is infinite, how can ANY exist from our perspective?
You're playing semantical games, RJ. An outside observer does see infalling mass slow down as it approaches the event horizon. This outside observer also sees the light from that infalling mass redshift and dim. From the outside, infalling mass appears to be freeze in place and turn black at the event horizon. This is why another name for black hole is "frozen star". That the picture seen by the infalling mass is completely different: Welcome to relativity.

Just because the the external view says mass appears to freeze at the event horizon does not mean that black holes cannot be said to exist. The conclusion does not follow.

RJBeery

06-06-09, 02:44 PM

Just because the the external view says mass appears to freeze at the event horizon does not mean that black holes cannot be said to exist. The conclusion does not follow.
Semantic games, maybe, but it's not intentional - it's a sincere question based on common sense. I'm not asking whether or not black holes exist in any frame; I'm asking why many folks (astrophysicists?) apparently believe that black holes currently exist in our frame.

Even if no singularity exists in our frame I was suggesting that the outside appearance of an "almost black hole", as its radius comes infinitisimally close to the Schwarzschild radius, would be virtually indistinguishable from a fully formed one (ala Shell Theorem). As I said in an earlier post, I've always assumed that GR "took care of this" in some way that would allow distant singularities to form in our frame, but I cannot find how this issue is resolved.

AlphaNumeric

06-07-09, 04:14 AM

There´s also the notion of a blackhole eclipsing another blackhole; if a quantum or particle theory of gravity is pictured, then it would seem logical to think that there would be a gravity shielding effect, yet the mathematical mainstream view states that there wouldn´t be.Actually, things like charge shielding in quantum electrodynamics is a well known concept and it's pivotal to understanding the concepts behind renormalisation, the differences between observed charge and bare charge. Gravity is not so straight forward because it's always attractive.

You simply can't claim "mainstream hasn't looked at that" or "It doesn't view things like that" because you have proven time and again you have no clue what mainstream physics is.

Guest254

06-07-09, 04:45 AM

To what end? I don't seek your respect; I'm looking for an answer to question #3. If you take issue with question #1, for example, then say so first, otherwise it gives the appearance that you don't know the answer but are putting nothing on the line by acting like you do. With respect, yours is not the mind that I'm probing.
So you're unable to do the mathematics now?
I have done the math.
What does this mean then? Could you please indicate where you've "done the math". I think you're a fibber...

Burada

06-07-09, 09:58 AM

D H

06-07-09, 11:04 AM

Semantic games, maybe, but it's not intentional - it's a sincere question based on common sense. I'm not asking whether or not black holes exist in any frame; I'm asking why many folks (astrophysicists?) apparently believe that black holes currently exist in our frame.
Your argument appears to be along the lines of "from our perspective mass does not form a singularity, therefore black holes cannot exist". If that is your argument, it is a semantic game and nothing else. In your eyes the only kind of thing we could call a black hole is a naked singularity. General relativity tells us that the event horizon shields us from seeing the singularity. So what is your beef?

AlphaNumeric

06-07-09, 11:31 AM

In our frame, and anyone else's above the event horizon, zero emissions of any kind are observed coming from the region closer to the middle of the black hole than where the event horizon is said to be in GR, so that region is completely black because while the region just above the event horizon does seem to contain matter which we can just about see dimly that's something GR people never denied. So if you define a black hole to be a non-radiating object then you do see such an object of size and structure precisely as GR says, it's just you see a haze of time dilated, dimmed material around it which arises from objects falling in and the gravitational effects preventing you from seeing them actually cross the horizon. Doesn't mean you can't observe a cut off distance for such 'haze'.

RJBeery

06-07-09, 01:23 PM

Your argument appears to be along the lines of "from our perspective mass does not form a singularity, therefore black holes cannot exist". If that is your argument, it is a semantic game and nothing else. In your eyes the only kind of thing we could call a black hole is a naked singularity. General relativity tells us that the event horizon shields us from seeing the singularity. So what is your beef?

It's not really my 'argument' because I'm not defending anything, it was a question based on my stated understanding of black holes. Practically speaking the Universe would look the same either way, so the question is more philosophical, I guess. I'm not sure I'd call it purely a 'semantic game and nothing else' though - this isn't just an issue of claiming that black holes don't exist because we can't see them. The math suggests shows that the black hole forms at t=infinity from our frame.

{dt \over dr} = {dt \over d\tau} {d\tau \over dr} =

- \sqrt {r \over 2M} \left( {1- 2M \over r }\right) ^{-1}

As r approaches 2M, coordinate time t (of the distant observer) approaches infinity.

In our frame, and anyone else's above the event horizon, zero emissions of any kind are observed coming from the region closer to the middle of the black hole than where the event horizon is said to be in GR, so that region is completely black because while the region just above the event horizon does seem to contain matter which we can just about see dimly that's something GR people never denied. So if you define a black hole to be a non-radiating object then you do see such an object of size and structure precisely as GR says, it's just you see a haze of time dilated, dimmed material around it which arises from objects falling in and the gravitational effects preventing you from seeing them actually cross the horizon. Doesn't mean you can't observe a cut off distance for such 'haze'.
Yes, we could redefine a black hole to be a non-radiating object rather than an region containing an actual singularity, and we would all agree that black holes indeed exist today. As I mentioned, the shell theorem would make an "almost" black hole appear identical to one containing a singularity and the Universe's appearance would remain unchanged.

D H

06-07-09, 01:55 PM

You are conflating the black hole with the singularity. You are playing semantics.

Your shell theory argument has two major flaws. The first: How do you know the shell theory is valid in a non-Newtonian universe? The shell theory is predicated on gravity following an inverse square law and space being Euclidean. The second flaw is that the density of shell would be so high that small chunks of the shell would form black holes themselves. The shell would break up into a bunch of tiny black holes that would fall into each other to form a larger black hole.

Guest254

06-07-09, 02:37 PM

The math suggests shows that the black hole forms at t=infinity from our frame.

{dt \over dr} = {dt \over d\tau} {d\tau \over dr} =

- \sqrt {r \over 2M} \left( {1- 2M \over r }\right) ^{-1}

As r approaches 2M, coordinate time t (of the distant observer) approaches infinity.
I'm terribly confused. In your opening post you tell us all your understanding of black holes is limited to illustrations aimed at high-school students, and yet now you're telling us the solutions to variational problems on curved manifolds. Is this your mathematics, or someone else's? (The equation you've posted is relevant for an observer in r>2M watching the motion of an infalling massless particle with no angular momentum).

It doesn't really matter, given it's clear you don't understand what's written. Had you known what you're on about, or even studied the tiniest bit of GR, you'd know that if you want to describe physics in a neighbourhood of the event horizon, then the standard Schwarzchild coordinates are no good. There's no globally defined chart, and in particular the standard coordinates are no good at r=2M. Kruskal coordinates are convenient for such a job.

Maybe now I've given you a convenient coordinate system to use, you'd like to show us the corresponding calculation.

RJBeery

06-07-09, 05:49 PM

Guest254: Umm, no, I didn't "rediscover" the Schwarzschild metric or this derivative; you would prefer I did? I didn't post that to prove something to you, and my responses are not directed toward you. When I said "yours is not the mind I am probing" I was politely saying your knowledge/participation does not interest me, thanks. :shrug:

You are conflating the black hole with the singularity. You are playing semantics.

Your shell theory argument has two major flaws. The first: How do you know the shell theory is valid in a non-Newtonian universe? The shell theory is predicated on gravity following an inverse square law and space being Euclidean. The second flaw is that the density of shell would be so high that small chunks of the shell would form black holes themselves. The shell would break up into a bunch of tiny black holes that would fall into each other to form a larger black hole.

On your first point, isn't it well established that shell theorem isn't completely valid in Relativity? I wasn't suggesting otherwise; I was speculating on why we observers on Earth might see regions that have characteristics of what we call a black hole, even if no singularity "currently" resides within it. On your second point, I think you're right in a sense in that the entire region within the Schwarzschild radius would be "on the cusp" of collapse but when you say that tiny black holes would form you are speaking from a frame local to the collapsar, which again would have a distant coordinate time of infinity...

Guest254

06-07-09, 06:10 PM

RJBeery

06-07-09, 06:34 PM

I felt it unlikely that you'd actually done the mathematics. I think I said to you a while back that I'd translate some physics from some mathematics for you, if you'd meet me half way and learn some basic general relativity. Unsurprisingly, it seems you've bailed on your side of the bargain.

For the love of God - why don't you people spend your time a little more productively by actually learning about the areas of physics you like to harp on about!!
Then I've got some good news for you. I've been reading books (some pop-sci and some a bit more advanced), and tomorrow is my first day back at UNL for Physics. Unfortunately, dealing with old, unhappy graduates who try to derive their self-worth by pointing out how stupid others are is not something that I intend to do after I finish my degree. :(

Guest254

06-08-09, 05:50 AM

Then I've got some good news for you. I've been reading books (some pop-sci and some a bit more advanced), and tomorrow is my first day back at UNL for Physics. Unfortunately, dealing with old, unhappy graduates who try to derive their self-worth by pointing out how stupid others are is not something that I intend to do after I finish my degree. :(
So does this mean you can do some basic relativity? After all, you've told us that you'd already done the maths - from which we can only infer you're able to do the relevant GR calculations.

I've given you a convenient coordinate system to use (google Kruskal coordinates), so when you feel like flexing your GR muscles, let us know and post the calculations here.

RJBeery

06-08-09, 01:14 PM

So does this mean you can do some basic relativity? After all, you've told us that you'd already done the maths - from which we can only infer you're able to do the relevant GR calculations.

I've given you a convenient coordinate system to use (google Kruskal coordinates), so when you feel like flexing your GR muscles, let us know and post the calculations here.
Slow down, chief. You said
Do the calculation. You are essentially asking "if you do the calculation, is my guess correct?" People have told you no. People have told you how to do the calculation. The only remaining option is for you to do the calculation.
What calculation were you referring to, specifically? And in what post did "people" tell me how to do it? And who claims that the calculation is wrong...you? I showed the equation from which I deduced that the distant observer calculates the black hole to form at t=infinity. Why you think this means that I'm claiming to know more than I do I have no idea. I know there are other coordinate systems (Kruskal, Lemaitre, et al); are you saying that if the calculation is made in Kruskal coordinates that the infinitely distant observer will calculate a finite time for the black hole formation?

AlphaNumeric

06-08-09, 01:53 PM

RJBerry, you're the one who said you've done the math. Now you seem to be back tracking and saying "Where did anyone tell me how to do it?". Well if you understand the formulae you posted you'd know how to do it. And well done on being able to Google for other well known coordinates in GR, now let's see if you can do something with them.

Guest254

06-08-09, 03:06 PM

What calculation were you referring to, specifically?
In response:
1) Does the math show that, from a stationary point far from the BH, an object "never" crosses that black hole's event horizon?
I have done the math.
You have claimed an event does not happen, i.e. a particle cannot cross the event horizon. This is false. It is a simple exercise to go to the frame of an infalling test particle and show the time experienced by that particle until it crosses the event horizon is finite. You say you've done the math - then you should know this.
And in what post did "people" tell me how to do it?
I have given you a coordinate system valid in a neighboorhood of the event horizon - this means there are no coordinate singularities in the region in which you want to do physics.
And who claims that the calculation is wrong...you?
You've done no calculation.
I showed the equation from which I deduced that the distant observer calculates the black hole to form at t=infinity.
Makes no sense.
Why you think this means that I'm claiming to know more than I do I have no idea.
Show us your calculation. You have the Schwarzchild metric and a variational principle, so if you've done the calculation you've derived the relevant geodesic equations and done some integrals. Show us.
I know there are other coordinate systems (Kruskal, Lemaitre, et al); are you saying that if the calculation is made in Kruskal coordinates that the infinitely distant observer will calculate a finite time for the black hole formation?
Firstly, I don't believe for a second you're at all familiar with those things. But prove me wrong - answer your own question. I don't think you'll be able to...

Why do you people do this?

Burada

06-08-09, 04:18 PM

RJBeery

06-09-09, 12:55 AM

Guest254: I said the event does not happen from a particular frame, not that it does not happen at all, and I've been very clear about this. From what I can tell, Kruskal coordinates are not defined at r=infinity so the infinite observer issue is not resolved, and your ignorance is shining through your arrogant visage by telling me otherwise. I have no interest in bantering with you or the "competant (http://www.sciforums.com/showthread.php?p=2274575)" AlphaNumeric - I've told you this more than once so please go away.:bugeye:

Guest254

06-09-09, 02:31 AM

Guest254: I said the event does not happen from a particular frame, not that it does not happen at all, and I've been very clear about this.
1) Does the math show that, from a stationary point far from the BH, an object "never" crosses that black hole's event horizon? I'm talking about calculating when it will happen, as opposed to trying to "observe" it happening.
It now seems that you're unaware that time is frame dependent concept - I assumed you knew some basic special relativity, but perhaps I was too kind.

From what I can tell, Kruskal coordinates are not defined at r=infinity so the infinite observer issue is not resolved, and your ignorance is shining through your arrogant visage by telling me otherwise. I have no interest in bantering with you or the "competant (http://www.sciforums.com/showthread.php?p=2274575)" AlphaNumeric - I've told you this more than once so please go away.:bugeye:
What's this? No calculation? Well if you people are anything, it's predictable.

AlphaNumeric

06-09-09, 05:46 AM

I have no interest in bantering with you or the "competant (http://www.sciforums.com/showthread.php?p=2274575)" AlphaNumeric - I've told you this more than once so please go away.:bugeye:And we're into full blown crank territory now. You make claims you can't back up, you can that pointed out by people who can do the things you claimed you could and so all you can do it point at the fact I didn't go back and use the Firefox spell checker on my post. As if my spelling is relevant to the fact I was talking about competency in physics. For instance, I can do all the calculations Guest is asking you to do and which you claimed you'd either done or could do. I'm competent at it. Shame the same can't be said for you.

thinking

06-09-09, 04:17 PM

for black-holes to even exist means that gravity over-whelms the nature of the particles involved , one dimensionally , from one direction , either above or below the galactic globular center point

however I tend to focus on the particles themselves from an hydraulic point of view

in all fluid hydraulics you can only squeeze so far until you can only squeeze down so far and then the particles push back

hence a " black-hole " is not really possible , since a black-hole suggests the collapse of matter down to non existence or singularity

Burada

06-09-09, 04:36 PM

quantum_wave

06-09-09, 04:45 PM

Hello Thinking. Don't forget that a particle has a tiny amount of energy and the internal forces are finite. Think about how much energy and force can be brought to bear on the particles by the internal heat and pressure exerted by a massive body that GR would define as a black hole. No particle could withstand such compression without undergoing significant change I wouldn't think.

We have no way of knowing the physics that is possibly taking place within the event horizon of a black hole but mathematically they are derived from Einstein's field equations and there are lots of reasons to believe that they do exist.

Dinosaur

06-10-09, 02:04 AM

RJ: Your posts indicates that you lack an understanding of how a Black Hole forms. The concept is very simple.

For a given amount of mass, the radius of a black hole event horizon can be calculated. I am sure that a search could locate tables relating radius to mass for black holes which do not rotate & have no charge.

When (if) 3-4 or more stellar masses are crushed by gravity into a volume less than that indicated by the calculated event horizon radius, a black hole with an event horizon is formed. The calculations relating what can be measured/seen by a distant observer are not applicable prior to the formation of the black hole & accompanying event horizon.

The above analysis does not require doing the calculations. It only requires thinking a bit.

Aside from any analysis, we have observational evidence of existing black holes. It is crazy to deny that they can form in finite time. They have formed in finite time. To the best of our knowledge, the universe is about 13-14 billions years old & there are a lot of black holes, many formed long after the birth of the universe.

To back up the views expressed in this thread, you must provide far more cogent arguments than you have so far posted. Without better arguments/analysis than you have shown so far, you deserve to be considered an intelligent crack pot or a naive child-like personality who has read & misunderstood some dumbed down articles on the subject.

D H

06-10-09, 06:42 AM

Moderator action:

The thread "black-holes do they even exist" was merged into this thread because that thread raised exactly the same issue as that raised in this already existing thread. Please do not open multiple threads on this same topic.

RJBeery

06-10-09, 07:42 PM

Dinosaur: I guess I'll reply to you although I don't believe you have read all of my posts (or maybe I wasn't clear enough). Otherwise you would give me credit for more understanding than you have. Frankly I am baffled that I must resort to using TEX (first time so go easy!) than qualitatively asking my questions in order for anyone to understand me, but here it goes...
RJ: Your posts indicates that you lack an understanding of how a Black Hole forms. The concept is very simple.

For a given amount of mass, the radius of a black hole event horizon can be calculated. I am sure that a search could locate tables relating radius to mass for black holes which do not rotate & have no charge.
r = { 2Gm \over c^2 } , with G = gravitational constant, m = mass of body; very straight forward. The "3-4 stellar masses" you refer to are determined by the mass required to generate sufficient gravitational forces to overcome the neutron degeneracy pressure.
When (if) 3-4 or more stellar masses are crushed by gravity into a volume less than that indicated by the calculated event horizon radius, a black hole with an event horizon is formed.
In the frame local to the formation, I agree with this.
The calculations relating what can be measured/seen by a distant observer are not applicable prior to the formation of the black hole & accompanying event horizon.
I don't know what you mean by "are not applicable". The Schwarzschild line element is described by

ds^2 = - \left( {1-{2M \over r}} \right) dt^2 + \left( {1 - {2M \over r}} \right) ^{-1} dr^2 + r^2 d\theta^2 + sin^2\theta\phi^2

where the Schwarzschild coordinates are given by (t, r, \theta, \phi). Granted, this is pretty heady stuff, but we don't need it to pose my question!

A derivative of this is

{dt \over dr} = {dt \over d\tau} {d\tau \over dr} = {- \sqrt {r \over 2M}} \left( {{1-2M} \over {r}} \right) ^{-1}

which describes the calculated coordinate time of an object approaching the black hole by the infinitely distant observer. Note that the observer is "infinitely distant" to simplify the equations such that he experiences no gravitation from the black hole, but the conclusions are similar for any body not traveling towards the event horizon ("static observers" I believe they are called). I did not derive this calculation, as some here believe that I should've to "prove" myself. I am not posting these things to show how far I can piss, I was only looking for discussion on the topic and an answer to my question. However, anyone with a bit of common sense can see that when r approaches x(=2M) you get

- {{x} \over ({1-x})}

Now as the radius approaches zero (as would be required "just before" the singularity initially forms), t moves to infinity. That's it. From the frame of any static observer the black hole apparently never forms (or more precisely, forms at t=infinity). D H calls it games of semantics, and if you want to blow off the question in that manner it is your prerogative, yet the question remains. The only frame in which the singularity forms is one which contains a body that actually makes the journey, and that by definition presumes that a crossable event horizon already exists!

Guest254 and AlphaNumeric claim that Kruskal coordinates magically resolve this problem. I initially deferred to their greater mathematical knowledge, but when I looked into it it appears that Kruskal coordinates are not defined at r = infinity which, unfortunately, is where our observer resides!

Aside from any analysis, we have observational evidence of existing black holes. It is crazy to deny that they can form in finite time. They have formed in finite time. To the best of our knowledge, the universe is about 13-14 billions years old & there are a lot of black holes, many formed long after the birth of the universe.
Arrgh, I have dealt with this issue many times in this thread. The mass in this "black hole region" remains, and the gravitational effects would still be felt. Instead of being trapped "forever", light would be detained "longer and longer", approaching an infinite time (yet all light would eventually escape).

Somehow I feel like my simple question ("Why do we believe singularities exist today from our frame?") has been inflated to being some fully fleshed out theory that I'm defending. This is not the case; I'm just asking questions and applying common sense and logic to what knowledge I can gain. If someone were to give me a satisfactory answer (or, if not, then at least acknowledge that the question is a valid one!) then I would be most grateful.

you deserve to be considered an intelligent crack pot or a naive child-like personality who has read & misunderstood some dumbed down articles on the subject.
Et tu, Brute? Don't go there.

James R

06-10-09, 09:24 PM

Somehow I feel like my simple question ("Why do we believe singularities exist today from our frame?") has been inflated to being some fully fleshed out theory that I'm defending. This is not the case; I'm just asking questions and applying common sense and logic to what knowledge I can gain. If someone were to give me a satisfactory answer (or, if not, then at least acknowledge that the question is a valid one!) then I would be most grateful.

I'm not sure that you phrased your original question as "Why do we believe singularities exist today from our frame?" I'd have to check.

My answer to that question is: we don't know if singularities exist at all. A singularity is a mathematical artifact that shows where our theoretical knowledge stops. In fact, the event horizon of a black hole is a type of singularity, in that external time goes to infinity at the horizon (as you have pointed out). However, this is a removable singularity - it arises only because of the particular choice of coordinates. The singularity at the centre of the hole is a non-removable singularity - it appears in ALL coordinate systems. Whether it is physically "real" depends on the details of quantum gravity, which we do not yet know.

If you are asking whether we can know, from outside a black hole, whether a singularity has formed at its centre, the simple answer is no, we can't know that. If that's true, then why do "we" believe that central singularities exist from our outside frame of reference. Answer: Maybe "we" don't all believe that. Maybe some of us know the limits of the theories we are using and don't make unwarranted assumptions.

Does that help?

RJBeery

06-10-09, 10:09 PM

James R: Yes, it does help quite a bit, thank-you. My original question (question 3 in post #3) was "how can we postulate that black holes exist today?" and in that question I was defining a black hole as a region containing a singularity, although defining a black hole as a region with an event horizon is the same thing to me (i.e. one implies the other).

And you're right, I didn't mean to imply that everybody believed something, one way or the other. Later I said
I'm asking why many folks (astrophysicists?) apparently believe that black holes currently exist in our frame.
Note: "many folks" apparently = just about every poster in this thread (including one who "felt compelled to storm on in" and call me "stupid"), except you and myself, so I don't think the assumption was completely unwarranted.:shrug:

D H

06-11-09, 02:21 AM

I'm not sure that you phrased your original question as "Why do we believe singularities exist today from our frame?" I'd have to check.

That is not the question RJ asked. You are helping RJ move the goalposts. The title of the thread is "How do Black Holes exist with Relativity". No mention of singularities. In post #3 he asked
HOW can we postulate that black holes exist today? In other words, if the creation time for black holes from our perspective is infinite, how can ANY exist from our perspective?
No mention of singularities. The first mention of the word singularity doesn't occur until post #12 by prometheus. RJ didn't mention singularities until post #21.

My original question (question 3 in post #3) was "how can we postulate that black holes exist today?" and in that question I was defining a black hole as a region containing a singularity, although defining a black hole as a region with an event horizon is the same thing to me (i.e. one implies the other).
Those are very different things. Most respectable physicists, when asked whether they really think that a singularity does indeed lie at the heart of a black hole or if the fact that general relativity admits singularities indicates there is something wrong with general relativity, will agree with the latter. Ask these same physicists whether they agree or disagree with the conjecture that black holes exist and almost all will agree that black holes do exist. Just because there is a potential problem with what happens at the very heart of a black hole does not mean that black holes don't exist.

The question "Do black holes really exist" is a frequently asked question. The answer is here, in the physics FAQ: http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/fall_in.html

and here, at the black holes FAQ:
http://cosmology.berkeley.edu/Education/BHfaq.html#q4

You can find similar answers all over the internet. This question is also addressed in several books on general relativity. This leads me to wonder whether you are trolling.

In an earlier post you asked about an almost black hole. An object sent to the surface of this almost black hole will of course be compressed to the size of a grain of sand. Suppose someone discovers a gravity shield so that a capsule can be lowered to the surface of this almost black hole. Suppose that the capsule is outfitted with a powerful light source that shines forever at a constant illumination. As the capsule descends the light from the capsule will be redshifted and dimmed. Assume the light source is powerful enough so that we can see the capsule even when it is resting on the surface. What would we see in the case of (a) the almost black hole remaining an almost black hole forever versus (b) the capsule's mass triggers a gravitational collapse?

In the first case, the light from the capsule, while redshifted and dimmed, will be constant in frequency and intensity once the capsule reaches the surface. If we observed the capsule forever and counted the photons emitted from it, we would count an infinite number of photons.

In the second case, the light from the capsule will continue to redshift and dim as time passes. It will not reach a steady state. Any sensing device that has a lower frequency limit will detect a last photon from the capsule in a finite amount of time. The capsule will "wink out". Suppose we have a sensing device that is not frequency limited. While this device will see photons coming from the capsule forever, it will only count an finite number of photons. The capsule did, after all, cross the event horizon in a finite interval of time, so only a finite number of photons were emitted by the capsule before it crossed the event horizon.

AlphaNumeric

06-11-09, 03:19 AM

A derivative of this is

{dt \over dr} = {dt \over d\tau} {d\tau \over dr} = {- \sqrt {r \over 2M}} \left( {{1-2M} \over {r}} \right) ^{-1}
No, a particular derivative of one of the metric entries is that. That is not 'a derivative of the metric'. And no, it's not heady stuff, it's pretty much the first non-trivial thing you do in a GR course. You have yet to show you actually grasp the equations you're posting.

Guest254 and AlphaNumeric claim that Kruskal coordinates magically resolve this problem. I initially deferred to their greater mathematical knowledge, but when I looked into it it appears that Kruskal coordinates are not defined at r = infinity which, unfortunately, is where our observer resides!As Guest said (and is a well known fact) there's no globally defined coordinate system in the Schwarzchild space-time. Kruskal coordinates are used to cross event horizons in a consistent manner, they are not used at large distances. Anyone whose ever drawn the Penrose diagram for the Schwarzchild metric will have used them.

Guest254

06-11-09, 03:43 AM

I don't know what you mean by "are not applicable". The Schwarzschild line element is described by

ds^2 = - \left( {1-{2M \over r}} \right) dt^2 + \left( {1 - {2M \over r}} \right) ^{-1} dr^2 + r^2 d\theta^2 + sin^2\theta\phi^2

where the Schwarzschild coordinates are given by (t, r, \theta, \phi). Granted, this is pretty heady stuff, but we don't need it to pose my question!

A derivative of this is

{dt \over dr} = {dt \over d\tau} {d\tau \over dr} = {- \sqrt {r \over 2M}} \left( {{1-2M} \over {r}} \right) ^{-1}

Now convinced that you're simply copying and pasting things you don't understand. Classic stuff.
Guest254 and AlphaNumeric claim that Kruskal coordinates magically resolve this problem. I initially deferred to their greater mathematical knowledge, but when I looked into it it appears that Kruskal coordinates are not defined at r = infinity which, unfortunately, is where our observer resides!
There is no such place as "r=infinity" - hell, the statement "r=infinity" makes no sense. Physicists sometimes use the abuse of language "an observer at infinity", to mean there is an observer very far away and as such we can approximate certain integrals by taking the upper limit to infinity, assuming things converge fast enough.

We have told you about Kruskal coordinates because you are say you are interested in some physics in the neighbourhood of an event horizon. The Schwarzschild metric has a coordinate singularity in this region, so we have offered you a better set of coordinates to do calculations with - i.e. to make your life easier. However, it's become apparent that you're not doing any calculations, because you don't understand even the most basic parts of general relativity.

From your subsequent posts it has become apparent that you have some severe conceptual misunderstandings of even basic special relativity. It is without doubt, that from a local frame in r>2M (note I'm saying r>2M, not "r=infinity", since any large enough radius illustrates the point), it would appear that it takes an in falling test particle an infinite amount of time to reach the event horizon. However, if one does the *incredibly simple* calculation from the frame of the in falling test particle, the time experienced by that particle to reach the event horizon is, low and behold, finite. I would urge you to derive the necessary equations from first principles, then do the relevant integrals, but it's become apparent that you're not capable of doing so (despite having told everyone you'd "done the math").

There isn't even an issue here - it's just that your complete lack of basic knowledge makes it incredibly difficult to understand these things. If you were actually interested in these things, you'd go away and spend some time learning the basics. But you wont, because that's not what cranks do. Learning and understanding takes effort and intelligence - it's just far easier for you to from from one wiki article to the next, coming on places like this, and play pretend.

RJBeery

06-11-09, 02:02 PM

D H: I define a black hole as a region with a singularity. Do you have an alternative definition? To me it is a contradiction to say that singularities do not exist in a frame yet black holes do.
In other words, I find the following questions equivalent regardless of my first mention of a singularity:
HOW can we postulate that black holes exist today? In other words, if the creation time for black holes from our perspective is infinite, how can ANY exist from our perspective?
vs

Why do we believe singularities exist today from our frame?

Also, if it's the case that this is a well known contradiction between BH and GR then why in the hell did it take over 80 posts for anyone to even admit that the question was a valid one? I've been called a stupid cranky crackpot with no knowledge and no motivation to learn, yet in the end it appears that I've been asking about a well known issue? What the hell is wrong with some people on this forum? And no, I have not seen those links before, and I did NOT know this was a well-known issue with astrophysicists, but I do now and thanks for the reference.

There's no globally defined chart, and in particular the standard coordinates are no good at r=2M. Kruskal coordinates are convenient for such a job.
are you saying that if the calculation is made in Kruskal coordinates that the infinitely distant observer will calculate a finite time for the black hole formation?
<no response>
From what I can tell, Kruskal coordinates are not defined at r=infinity so the infinite observer issue is not resolved,
There is no such place as "r=infinity" - hell, the statement "r=infinity" makes no sense
If the infinite observer calculation cannot be used in Kruskal coordinates then why did you give me the reference? To waste my time?
With respect, yours is not the mind that I'm probing.
your knowledge/participation does not interest me
please go away
TAKE A HINT :D

D H

06-11-09, 02:37 PM

D H: I define a black hole as a region with a singularity. Do you have an alternative definition?
How about the blatantly obvious definition that
a black hole is a region of space in which the gravitational field is so powerful that nothing, including light, can escape its pull.

To me it is a contradiction to say that singularities do not exist in a frame yet black holes do.
Just because you don't understand something doesn't mean it is wrong.

That general relativity admits singularities is indicative that there might be a problem with general relativity. This is one of the motivating factors for string theory, loop quantum gravity, and other theories that are attempting to find a common ground between general relativity and quantum mechanics. On the other hand, sans a few crackpots, physicists do not deny the concept of gravitational collapse. There were a few holdovers until astronomers observed things that look and act exactly like the theoretical description of a black hole.

Moderator comments
You are playing semantic games. This thread is on short notice. It will head to the cesspool in 48 hours unless you can convince me otherwise.

RJBeery

06-11-09, 02:50 PM

D H: You want to cesspoll a thread which deals with what you said was a well-known issue between BH and GR; an issue so foundational that it has contributed to the impetus for string theory and loop quantum gravity; an issue that some participants were clearly unaware of? Do what you want but I'm not seeing this as a cesspool candidate.

D H

06-11-09, 03:03 PM

You are not addressing fundamental issues. You are addressing semantic issues, and well-known semantic issues at that. I provided a couple of links that address this very question in post #81. Read them. I specifically addressed your question about distinguishing a "near black hole" from a black hole in post #81. The two are very different beasts. Read post #81 and read the links cited therein.

RJBeery

06-11-09, 03:09 PM

I did NOT know this was a well-known issue with astrophysicists, but I do now and thanks for the reference.
I thanked you for the links, they are interesting. I'm basically done here so thanks to everyone for continuing (or affirming) my understanding, and for putting up with my ego. :p

Guest254

06-11-09, 03:54 PM

If the infinite observer calculation cannot be used in Kruskal coordinates then why did you give me the reference? To waste my time?
There is no such thing as an "infinite observer", or "an observer at infinity". I just explained this to you. And I also explained to you why I told you Kruskal coordinates should be used in a neighbourhood of the event horizon. And still no calculations... this is all too predictable.

You've essentially got your knickers in a twist because this thread has served as a showcase for your complete ignorance of basic results from relativity. Pull up your socks and deal with it...

AlphaNumeric

06-12-09, 04:01 AM

D H: I define a black hole as a region with a singularity. Do you have an alternative definition? To me it is a contradiction to say that singularities do not exist in a frame yet black holes do.That's not the definition GR people use. You can have black holes without singularities.

If the infinite observer calculation cannot be used in Kruskal coordinates then why did you give me the reference? To waste my time?IF you'd ever actually done any GR you'd know about coordinate patches. The Schwarzchild spherical coordinates are not valid at the horizon so you use Kruskal to cross the horizon in a controlled manner and then the spherical coordinates become valid again. You swap from spherical to Kruskal and back, using each one in the realm where you know they work. That's the basic concept of coordinates in manifolds.

I'm basically done herDone lying?

RJBeery

06-12-09, 02:33 PM

That's not the definition GR people use. You can have black holes without singularities.

Yes, D H helped me realize this too, thanks. I had assumed that the singularity's existence was a presumption in the black hole's existence, which is why I interchanged {black hole, event horizon, singularity} in my questions. I wasn't trying to 'move the goal posts', I had considered all variations of my question to be equivalent. Discussing the singularity is really a red herring, though, because removing it from the black hole's definition does not resolve the issue. The problem remains if the question refers to "an event horizon", or, using D H's definition, "a region of space in which the gravitational field is so powerful that nothing, including light, can escape its pull."

As I said, I'm vaguely familiar with coordinate patches, and I understand the concept. Quick question for you (I'm speaking to AlphaNumeric) - and this is a sincere question to which I do not know the answer - what do the Kruskal coordinates say about the time it takes a body to cross the event horizon as calculated by a static observer? I am now talking about an observer "hovering" over the horizon as opposed to an infinitely distant observer...

jsaldea12

07-04-09, 07:04 PM

Did Dr. Einstein mentioned or made comment about the black hole during his lifetime? I seem to miss it. Because in his later life, Dr. Einstein commented: "I do not know anymore my relativity..".

Moderator, Whatever I post (pertaining to Big Bang or cosmoligical constant) is honest-to-goodness scientific search..So i hope you open posted articles "Man-made nuclear bomb: one best evidence of Big Bang" and "Cosmologival constant or Big Bang". thank you.and regards..

jsalea12

7.5.09 ..

jsaldea12

07-04-09, 11:07 PM

Please permit me to re-phrase. pertaining that illustration showing a black hole inside a cone-shaped hole (spacetime). To put plainly, the classic example of spacetime gravity of Dr. Einstein is like a trampoline wherein an object dropped in will cause a dip in the trampoline, the heavier the object dropped in, the deeper the dip. IS THIS EINSTEIN GENUINE ILLUSTRATION OF HIS SPACETIME GRAVITY? That dipping deeper and deeper into spacetime (as body collapses to a blackhole). Because, in retrospect, Einstein commented, “I cannot anymore recognize my relativity..” The classic trampoline illustration appears impossible in actual outer space. There is a more realistic interpretation of spacetime gravity of Dr. Einstein that goes hand-in-hand with attraction gravity of Newton.. .

.

Regards.

Jsaldea12

75.09

D H

07-05-09, 12:01 AM

The next nonsensical post will get a warning, jsaldea12.

The correct quote is "Since the mathematicians have invaded the theory of relativity, I do not understand it myself anymore." It was intended to be taken humorously. You have taken it seriously and you have misstated the quote in a manner that illustrates a key misunderstanding on your part of how science works. While a theory is often named after the originator, it does not belong to the originator: It is in the public domain.

Regarding the rubber sheet analogy: It is an analogy. The intent of the analogy is to illustrate the concept of gravitation to the mathematically disabled.

RJBeery

07-05-09, 02:17 PM

jsaldea: As D H said, the trampoline/rubber sheet analogy is just way to help people get the concept, it doesn't really mean anything. It's flawed and confusing to some because it uses gravity (which is what's causing the "dip") to explain gravity. IMO a better analogy is to stretch the center of the rubber sheet, then tie it in a knot on itself like a balloon, and let it go. What you are left with is an area of tension surrounding the knot that lessens as you move further away. It's much easier to imagine that in three dimensions than the former analogy...

AlphaNumeric

07-08-09, 08:53 AM

The problem remains if the question refers to "an event horizon", or, using D H's definition, "a region of space in which the gravitational field is so powerful that nothing, including light, can escape its pull."Is there a difference since an event horizon is pretty much that definition.

As I said, I'm vaguely familiar with coordinate patches, and I understand the concept. Quick question for you (I'm speaking to AlphaNumeric) - and this is a sincere question to which I do not know the answer - what do the Kruskal coordinates say about the time it takes a body to cross the event horizon as calculated by a static observer? I am now talking about an observer "hovering" over the horizon as opposed to an infinitely distant observer...If you're unfamiliar with how to compute such a thing then I question your claim you understand coordinate patches and how to do such things in the usual spherical coordinates of the Schwarzchild metric.

The answer is pretty straight forward, as Kruskal coordinates are so useful precisely because they say everything is finite in and around the event horizon of a black hole.