View Full Version here: : matter bettween 2 event horizons

scuba cat
24-11-2010, 03:53 PM
Theoretically, say some dense stable matter was between two cross sections of two event horizons, like a ven-diagram.
Now say that the black holes forming the event horizons are moving away from each other. What would happen to the matter when the event horizons no longer cross?


24-11-2010, 05:59 PM
Interesting question. Here's what I think.
I would assume that any matter inside an event horizon is already lost to the Black Hole. Thus, there would be no "normal" matter in the intersection of the event horizons. In fact, the combined event horizons would be distorted at the contact face, initially perhaps the shape of a dumbbell. I would also assume that with the event horizons already merging, it would be impossible for the black holes to separate i.e. they would merge into a black hole with a larger event horizon.
Someone else might have a different take on the scenario.

Regards, Rob

24-11-2010, 06:20 PM
In the observer's frame of reference overlapping event horizons cannot occur.

Consider an object emitting photons near the edge of the event horizon of black hole A. Suppose black hole A is brought into close proximately of black hole B. Now according to GR the object cannot pass inside the event horizon of black hole B as the photons from the object become infinitely red shifted in the observer's frame of reference. The "closest" the object can approach is the edge of the event horizon of black hole B.
In other words the horizons cannot overlap. In fact if the horizons "touch" this is equivalent to the black holes merging with the event horizon expanding out to the sum of the combined black hole masses.



24-11-2010, 06:39 PM
Ok … interesting …

So in our holographic universe, it seems overlapping 'Cosmic Horizons' can't occur either (for the same reason) …

(Just thought I'd say that … even though the term 'holographic universe' appears to arouse concerns).


24-11-2010, 07:49 PM
There are similarities between a black hole's event horizon and a cosmic event horizon. To an observer at distance from the black hole or an observer at the centre of the cosmic horizon, velocity = c and change in time = 0 at the horizon.

However, I think there are differences.
With black holes, the event horizon is created by mass "compressed" into a critical volume by gravity. Light does not have enough energy to escape from the horizon's surface. Combining two black holes increases the mass and the size of the event horizon but the effect is the same. I'm not sure if Steven is suggesting that the merger would be instantaneous if the horizons touch. I wonder if this is the case, as the event horizons would be gravitationally distorted first with perhaps an ill-defined contact point.

Cosmic event horizons are brought about by objects exceeding the speed of light due to expansion away from the observer's location. I don't see any reason that these event horizons could not overlap (but not merge) for observers in two separate frames of reference. If each observer's universe can be defined by their cosmological horizon, as in the holographic principle, then it is still possible for information to be passed from one observer's universe to the other where they intersect.

Regards, Rob

24-11-2010, 08:38 PM

The event horizon is independant of space-time distortion. It is a property of the time component of the Schwarzchild metric. You can create an event horizon by accelerating a clock in flat Minkowski space. The horizon itself doesn't undergo "distortion" by gravity.

If an object is subjected to tidal forces at the event horizon, it's due to a small radius event horizon being close to the singularity where space time curvature is more pronounced. The horizon itself doesn't cause the distortion nor is the horizon itself distorted.



24-11-2010, 09:52 PM

Not according to this ...
Read section on Dynamical black holes. Interesting movie attached.

Regards, Rob

25-11-2010, 06:01 AM

The distortion of the event horizon is a property of angular momentum not gravity. In the case of dynamical black holes one needs to consider the angular momentum of the black holes rotating around a centre of mass.

Consider the effects of intrinsic angular momentum on horizons.
A Kerr black hole is a rotating black hole and has 2 horizons, one is similar to the Schwarzschild event horizon, the other is is a flattened sphere that extends out from the equatorial region of the black hole. The faster the black hole rotates the greater the dimensional change effects on each horizon.

A general statement about the effect of angular momentum on horizons is also found in your reference under "Black hole parameters".



25-11-2010, 06:46 AM
As an aside, here's a really cool video taken from some modelling they're doing of black hole collisions (http://www.physorg.com/news194881040.html), (dated June 4, 2010) !

If interested, the accompanying paper is here (http://arxiv.org/abs/1003.0873)

They analyse the deformations, recoil 'kicks' and geometries surrounding the collision, shown in the video.


25-11-2010, 08:33 AM

Interesting debate. I would suggest that the distortion of the event horizon would be a combination of both angular momentum and gravity. In my mind, it is reasonable to assume that two close black holes would create immense mutual gravitational disturbances that would deform the event horizon. After all, it is mass and hence gravity that defines the black hole's event horizon in the first place. The upper diagram in Craig's reference (previous post) indicates this distortion as the two black holes approach each in linear fashion (no orbital physics involved).

Regards, Rob

25-11-2010, 08:58 AM
Wow .. interesting exercise !

I notice from the paper I cited, the two approaching holes are of different sizes (radii) and thus, differences in the tidal forces because of this (?)

I guess the more interesting case would be for two approaching holes of the same radii.

The paper deals more with the effects of the momentum transfers and recoils, upon impact.


25-11-2010, 11:58 AM
Interesting for its simplicity ...

The Schwarzschild radius is the radius of the event horizon of a black hole.
If the mass of two separate black holes is m1 and m2, then the Schwarzschild radii are:
r1 = 2G m1/c^2 and r2 = 2G m2/c^2

The combined mass of the two merged black holes is m1+m2.
Its Schwarzschild radius r = 2G (m1+m2)/c^2 = 2G m1/c^2 + 2G m2/c^2
which is simply r = r1 + r2

Very nice!


25-11-2010, 12:30 PM
Yes .. very simple, Rob ! Neat ! Hides the complexity very nicely !

I'm still thinking about the cosmic horizon side of things (I notice Steven's steering clear of this …that's OK … those String Theorists hijacked it all from quantum mechanics, any way ;) )

I think its actually simpler for me to think of all this from holographic/cosmic horizons perspective, as long as gravity isn't a factor.



25-11-2010, 01:48 PM

The event horizon has no physical reality in the black hole's frame of reference. It only exists to an observer outside the horizon. It cannot be distorted by gravity because it doesn't exist to the black hole.

For a nonrotating black hole, it takes an infinite amount of time for an object moving in a radial direction to cross the horizon (hence the term event horizon). If the event horizon is well away from the singularity the tidal forces on the object are small. The object appears to come to a grinding stop at the horizon but remains intact. In the black hole's frame of reference the object is perfectly free to travel towards the singularity to be eventually destroyed by tidal forces.

For a rotating black hole if the object approaches at an angle except along the axis of rotation, the object will appear to spiral towards the flattened horizon. At this horizon it will appear to orbit forever.
However like the nonrotating black hole, the object will actually pass through the horizon along a radial path and be destroyed by tidal forces.

The role of angular momentum as can be seen plays a very unfamiliar part when it come to event horizons.



25-11-2010, 02:00 PM
Ok .. so time for a question …

What happens to the matter inside the smaller radius BH as it approaches one of a larger size ?
(Hypothetical, of course). Surely the matter is distorted by tidal forces ..(?)

If this is the case, then can this distort its event horizon before collision ?
(I guess this is very hypothetical).


25-11-2010, 02:16 PM

Looks like we need some observational evidence.
It is the reality of the event horizon relative to an outside observer that is relevant here. In my opinion, the event horizon will appear to be distorted by the gravity of the interacting black holes to an observer outside the horizon.

Regards, Rob.

25-11-2010, 03:45 PM

The search for observational evidence by definition contradicts GR.
If gravity does in fact distort the event horizon, then one can argue it is impossible to define the Schwarzschild radius for low mass black holes as the event horizon is well within the tidal forces of a black hole and is therefore distorted.



25-11-2010, 04:48 PM
You may as well be arguing about how many angels can dance on a pin!
At best hypothetical at worst absurd!

If you fall into a giant black hole you will not be turned into spaghetti but just float as you have orgasmic revelations just before you die!

Climbing dangerous mountains is just so passe.


25-11-2010, 06:15 PM
Agreed. Bit like a discussion when everyone has overly imbibed. Immensely meaningful at the time but complete nonsense when you sober up.

25-11-2010, 06:59 PM
Sorry Bert and Chris;

I have found this thread to contain a lot of very useful information.

I would like to thank Steven and Rob, as I have learnt heaps, and so too will others, particularly if they read the attachments and then review the posts.

Next time I hope both Bert and Chris contribute constructively as I know you both can.

Cheers and Regards.

25-11-2010, 11:39 PM
Bert and Chris,

And thanks for the inane comments.

Would it have been more justifiable to turn the discussion into a mathematical thread given that neither of you would be able to comprehend it?

The statements made in this thread are perfectly valid. It's not the case of being right, wrong or inapplicable. It's shows that people are prepared to think and offer an interpretation to a concept that is not straightforward.

Rob and Craig.
Thanks for your contributions in this thread.



26-11-2010, 09:17 AM
Thanks Craig and Steven for your time and contributions. As usual, I found it educational and enjoyable.

Who is to say what is impossible or ridiculous in science? It is through imagination, hypothesis, observation/research and analysis that the boundaries of the impossible can be tested.

I am reminded of the following three "laws" made by the eminent Arthur C. Clarke:
When a distinguished but elderly scientist states that something is possible, he is almost certainly right; when he states that something is impossible, he is probably wrong.
The only way of discovering the limits of the possible is to venture a little way past them into the impossible.
Any sufficiently advanced technology is indistinguishable from magic.

Regards, Rob

26-11-2010, 11:06 AM

I've been thinking, (and calming down a bit), but I'm left with a question for you..

What exactly do you see about our discussion that is 'nonsense' ?
It seemed completely the opposite to me.

… I'm just intrigued, now.


27-11-2010, 08:11 PM
This is best summary of our knowledge and our approach to science I have hear in long time

28-11-2010, 05:10 PM
Let me first deal with Craig's question. I have degrees in five disciplines including physics and astrophysics (postgrad) and also arts (philosophy). I think therefore that I have a reasonable understanding of the many theories put forward to explain the world as it exists today. Unlike Steven I make no arrogant claims that any of my ideas or statements, nor the statements of anybody else, are perfectly valid. Indeed it must be wonderful for Steven to inhabit such a position of perfect knowledge. What I can do as indeed all reasonably intelligent human beings will do, is decide what for me makes sense about the world and as a result reject other data of hypothesis as non-sensical. Without tending to use the word in a perjorative sense I thus categorise certain hypotheses as "nonsense" maining that they make no sense to me. This is not to say that they are not worthy of intellectual effort but more on that later.

As an interested observer of religion and other descriptions of the way the world is like, for instance "intelligent design" and astrology there have been many sophistocated arguments put forward to justify such positions. I would assume that like me most here would generally reject such positions as "nonsense" but in reality the majority of people do not share these views.

Now I, and probably you, reject these views, mainly because they are simply not scientific, and that contradicts our fundamental belief in science as a paradigm by which we interpret the world. Science however, is not something we can glibly define. With respect to Clark his three laws in no way define "Science" and both intelligent design and astrology would both easily pass his definitions. To put this sort of specious nonsense forward is really pretty demeaning to the scientific method.

Further, to say that we should not judge on what is and what is not science is also fraught with danger as that attitude will see intelligent design taught alongside evolution in schools, and chasing the diminishing science research dollar.

I will not go into the philosophy of science as that would turn this post into a tome but you will instrinsically know that a scientific hypothesis is only validated by its verifiability. It is more complex than this but you get the picture as you have probably seen the movie.

We would therefore dismiss hypothesis like the existance of God, natural selection and astrology as unverifiable and reject them as nonsense given our scientific intellectual and cultural bias, although as I remind you the majority of human beings do not fall into this category.

Following from this it seems to me the height of arrogance to let the so called scientific community led by people motivated by selling books to venture from what is science to what is pure speculation. This has been heightened over the last 30 years in which the theorists have been given their heads in constructing completely unverifiable theories based on mathematic abstraction, mostly based around string theory and black holes because these exiting ideas first and foremost sell books. Again I wont go there, but you will have seen the movie. Indeed it became unfashionable for a long time, although it is changing now due to the fact that physics has languished for around 20 years, to examine the fundamentals of the assumptions we have made for so long. The very nature of mass, what is a particle, what is time, why does GM predict what it does and so on and so forth.

Before I go on here, let me state as I did in my original post I have no problem with pure speculation for speculation's sake, just as I have no problem with people waxing lyrical on other tenuous and non provable speculations. On the contrary it is quite a pleasant exercise to luxuriate in such intellectual meanderings but ultimately as I said one must accept that at base level the fundamental premises are flawed and accept that as a matter of current fact, rather than take a pious position of intellectual superiority.

It therefore concerns me that this thread took on that guise of actually being based on anything tangible rather than speculation.

What do we know about Black Holes. Well again I could write a tome on the basic and arrogant assumptions we make in regard to our interpretation of the EM date we recieve in our little planet in our infinitessimally small region of a huge universe, but I wont go there. Instead I will assume all of these assumptions are correct. Based on this what do we know.

We know black holes exist.

We know that general relativity explains in general terms how a black hole can come to exist.

We know that beyond the event horizon under our current understanding of the laws of physics we cannot know what is contained within the event horizon.

We know that mathematically we can define models for the nature of black holes and their singularities and as a result we can speculate on matters such as entropy, informations exchange, quantum fluctuations and so on and so forth. this all inevitably having to do with the event horizon.

There are many such mathematical models allowing for a variety of conditions including angular momentum and collision scenarios.

Not withstanding such models under our current laws of physics we cannot ever know the very nature of physics beyond the event horizon of a black hole and moreover, astrophysical measurements can never reveal this information.

So let me count the ways :-

Rob said "There are similarities between a black hole's event horizon and a cosmic event horizon". WTF. This is like saying "There are similarities between heaven and the Kingdom of Allah". As Bert says if you were able to visit a black hole event horizon you would no longer be able to measure where or what you were and the cosmic event horizon is merely a fictional place which by definition you can never visit.

Then Steven says boldly "The event horizon is independant of space-time distortion. It is a property of the time component of the Schwarzchild metric. You can create an event horizon by accelerating a clock in flat Minkowski space. The horizon itself doesn't undergo "distortion" by gravity." Now I defy anybody including Hawking itself to make any sense of these statements. What he means to say is that by one mathematical model (probably his own) this statement is correct, but even then I suspect the math will not reflect the hyperbole. Notwithstanding this Steven asserts every opinion he has is perfectly valid and it seems that when others comment they are inane. This sounds very much like the fundamentalist viewpoint expressed by non scientists to me. I am right so you must be wrong. And yes, a few papers and a little math backing up your arguments would not go astray, but even then there are so many theories of black holes that I have no doubt any argument could be adequately supported.

And so it goes on, back and forward, until Bert quite rightly calls a spade a spade to which he gets dumped upon from a great height. How dare he tell us to stop imbibing and go home.

So gentleman, I applaud your prognostications, just as I applaud the latest Harry Potter movie, but let us not delude ourselves into thinking they are anything but pure speculation and certainly let us not delude ourselves into thinking there is anything scientific about them.

28-11-2010, 06:12 PM

Thank you, for what I am assuming, was your reply to my question:
"What exactly do you see about our discussion that is 'nonsense ?"

I believe your outright opinion interjected into the midst of a conversation where all of the participants were doing their best to contribute to this thread, and where all participants were very well aware of the hypothetical nature of the topic, was what I found was frankly, rude behaviour. Also, I for one, find opinions of little value in this forum (my own included).

I have no idea of your background and frankly, I don't really care.

I am interested in positive contributions, which add value to this site, and its threads.

So far, I am yet to see anything of this nature from your fingertips.

I look forward to anything you may have to offer in the future, (other than opinions).

The folk you have attacked in your response are very highly valued here, because of their long histories of unending contributions. They also have a depth of insight and professional industry experience in these topics. Their academic backgrounds are also very sound and their generosity is exhibited every day, by them 'walking the talk'.

Once we've become familiar with your contributions, we may be able to say the same of you.

Frankly, I look forward to that day.


28-11-2010, 07:24 PM

Every time anyone posts he/she is expressing an opinion. It appears that you only regard opinions as positive if they are in accord with yours.

I attacked no one - only expressed views on statements made by others. On the other hand you and Steven used the words "inane" and "rude" in regard to myself and others these words representing value judgements against individuals that I would never make.

Having said that I have no wish to rock the boat with opinions that threaten the status quo and I have no wish to participate in a crude slanging match of invective. Accordingly you will not hear from me again.

All the best

28-11-2010, 08:25 PM
Of course you didn't attack anyone. Stating that the opinions of others as being nonsense is definitely not an attack. Neither is the attempt to portray me as an arrogant individual flouting an opinionated view. Who in fact has the opinionated view.

Neither are your posts inane. The author of this thread is now fully enriched by your posts, which were on topic, contained valuable insights, offended no one and is a source of learning.
Definitely not inane.

You must be a grossly misunderstood individual.

28-11-2010, 11:38 PM

I read your rather long reply in an attempt to find something constructive to warrant my time on it. Contrary to your opinion that everything about black holes is pure speculation, I thought you did a reasonable job in stating a few tangibles about them.

In dealing with any contentious scientific matter one always strives to find the current boundary between the established and the hypothetical. Years ago, black holes were a hypothetical, now they are pretty much established. There is an extraordinary amount of evidence to support their existence. The physics of event horizons is largely mathematical but their are physical observations that support what we know about them.
What happens inside a black hole is hypothetical but perhaps we might know one day. If no-one were to speculate, science would come to a standstill.

There are many people who spare their time to contribute to these threads. I would say without hesitation that it is their enthusiasm about astronomy and their willingness to help and educate that keeps these threads going.

Each and every person is entitled to a viewpoint on any particular aspect of science. The expectation is that any viewpoint is a constructive argument either for or against the viewpoints stated. I don't think that I have ever read a post and asked for that person's qualifications to answer. A thinking person should have learnt much more than the contents of his degree from years gone by. Often individuals have a particular interest and a lot of accumulated knowledge around it. Most of us can put the jigsaw puzzle together when we're given the right pieces. Invariably posts will refer us somewhere we can verify or rebut the claims.

I always deliberate about any comment I make in a post and welcome any constructive feedback.

Regards, Rob