Talk:Black hole/Archive 2

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This is an archive of past discussions. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page.

Contents 1 LinkFix dump 2 Black holes as supercomputers 3 Horizon confusion 4 Hubble measures first proven black hole in Andromeda 5 Falling into a black hole 6 Infinite energy sink 7 Black hole unitarity paragraph needs to be corrected 8 Hawking radiation and entropy 9 Talkpage length 10 Break up a black hole from the inside? 11 GR prohibits BH formation 12 Eternal black holes and non-eternal black holes 13 Tunneling 14 Singularity and time 15 Event Horizon and Time Travel 16 I don't get it 17 Potentially useful figures

LinkFix dump

See also User:Ambush Commander/LinkFix dump

LinkFix dump for "Black hole", no edits made:

Black hole (disambiguation) ! Disambiguation Page
Gravitational field % Gravity
Active galactic nuclei % Active galaxy
John Wheeler % John Archibald Wheeler
Russian (language) % Russian language
Supermassive black holes % Supermassive black hole
Active galactic nuclei % Active galaxy
Radioastronomy % Radio astronomy
M87 % Elliptical Galaxy M87
Bulge ! Disambiguation Page
Particle accelerators % Particle accelerator
John Wheeler % John Archibald Wheeler
Scout rocket experiment % Gravity Probe A
Red-shift % Redshift
Theory of Relativity % Theory of relativity
Chaos ! Disambiguation Page
Media % Mass media
Marble (toy) % Marbles
Reissner-Nordström metric % Reissner-Nordström black hole
Occam's razor % Occam's Razor
Dark-energy star % Dark energy star
IMBHs % Intermediate-mass black hole
Dark-energy star % Dark energy star

Ah... links to fix... — Ambush Commander^(Talk) 16:10, August 14, 2005 (UTC)

Black holes as supercomputers

I reverted an edit that said this:

Some physicists, including Stephen Hawking, have recently concluded that black holes could act as natural supercomputers of incredible speed and power.

Is this true? I need someone to verify. — Ambush Commander^(Talk) 15:44, August 16, 2005 (UTC)

Sounds like high quality BS to me!--Light current 02:25, 30 September 2005 (UTC)

It's a partly-correct statement, if I understand correctly. The actual idea came up in a number of "limits to computation" articles, with the idea being that a black hole's size was exactly small enough that if it was performing calculations at the maximum rate allowed by its contained rest energy, signals would be able to propagate completely across the hole between computations, making it the ultimate serial computer. Systems that weren't as compact (i.e., that weren't black holes) would have to have some degree of parallel computation if performing at their peak theoretical capacity, which limits the types of problems that you can solve. To the best of my knowledge, nobody's actually found a plausible way to make black holes perform useful computation. --Christopher Thomas 21:13, 25 November 2005 (UTC)

Horizon confusion

In a recent Horizon documentary the entropy formula of black holes was given, but their version did not feature the Boltzmann constant k. What is correct? ThomasWinwood 07:58, 16 September 2005 (UTC)

In Planck units, the formula is A/4. In the article, it is not written in any particular system of units, hence all the constants (which go to one in Planck units). –Joke137 14:51, 16 September 2005 (UTC)

Hubble measures first proven black hole in Andromeda

• http://www.newscientistspace.com/article.ns?id=dn8025
• http://www.theregister.co.uk/2005/09/21/hot_stars/
• detail at http://www.universetoday.com/am/publish/blue_halo_stars_blackhole.html?2092005

This needs added to the Have we found them? section.

Please note that there is nothing radically new here. Other black holes were proven to exist in the past -- this is just the latest of many, but it happens to have got a lot of publicity because the NASA Hubble public relations department have made a big deal (in order to help save Hubble). In particular, astronomers have been watching stars zipping close to the last stable orbit around the black hole in the centre of the Milky Way for two decades. Hubble doesn't have the resolution or wavelength coverage to look at that, so it doesn't get the benefit of the NASA Hubble public relations department ;-) Rnt20 14:39, 22 September 2005 (UTC)

Falling into a black hole

I think Rnt20's edit about falling into a black hole is incorrect or at least incorrectly phrased. The three space-like directions do not become time-like, as general relativity is defined on a metric of a given signature (e.g. - + + +). That doesn't even make sense. What does happen is that in the usual Schwarzschild coordinates, the radial and time-like directions exchange. This is called a coordinate singularity, and has nothing to do with the physical situation being described. The Eddington-Finkelstein coordinates and Kruskal coordinates do not have this kind of behavior.

In Schwarzchild coordinates the radial and time components of the metric change sign once past the event horizon, this implies that you cannot avoid moving in a direction of decreasing r no more than you could avoid moving in a direction of increasing t outside the black hole. r is now a timelike direction, and t is spacelike. Obviously nothing happens to the θ or φ directions. --Jpowell 21:42, 28 February 2006 (UTC)

The real condition of being inside a black hole was described by Hawking in the 1960s and involves the formation of something called a "trapped surface". Essentially, you can tell a singularity is there (and that you're going to hit it) by drawing a sphere around the singularity and looking at the "congruences" of geodesics going outwards and inwards from the sphere. If they are both contracting, then you know there's a singularity. –Joke137 13:28, 23 September 2005 (UTC)

Ok that does sound better. My memory of General Relativity lectures is a bit hazy, I have to say. Rnt20 14:18, 23 September 2005 (UTC)

Infinite energy sink

How can it be that a black hole is an infinite energy/mass sink? At some point the mass/energy must escape. Where does it go to?--Light current 00:48, 29 September 2005 (UTC)

I'm not an expert in the area, but you might want to read about Hawking radiation. The idea there is that the black hole very, very slowly evaporates due to quantum effects. —HorsePunchKid→龜 02:12, 29 September 2005 (UTC)

I think stuff can enter a BH quicker than HawkRad can radiate it away!--Light current 10:59, 29 September 2005 (UTC)

Yes, until there's no more stuff outside the black holes. Then they'll radiate themselves out of existance, but it takes something like 10⁵⁰ years--at that point, the universe will be uniformly-distributed heat, entropy wins, and that's that. So, what's wrong with that? I admit it's a bummer, but other than that... -- SCZenz 11:09, 29 September 2005 (UTC)

Well I dont see how a black hole electron can interact with other things as we know real electrons do. For instance how do BHEs emit photons if they're black holes. Don has a lot to explain!

I seem to be on the wrong talk page here. Sorry I thought this was Black hole electron land!--Light current 02:34, 30 September 2005 (UTC)

It's hard to tell them apart sometimes. ;) -- SCZenz 08:37, 30 September 2005 (UTC)

Any charged object, including a black hole, that undergoes acceleration emits photons as a result of the interaction causing the acceleration. This is due the disturbance the object's charge makes in the field of virtual photons that carries the electromagnetic force. The energy comes from whatever potential energy source is being tapped to allow the acceleration. Two co-orbiting charged black holes would have their orbits degrade as a result of this emission, for instance. Even two non-charged co-orbiting black holes will emit orbital energy as gravity waves. Accelerating charges to produce photons just provides an additional loss mechanism in this context. --Christopher Thomas 18:39, 15 November 2005 (UTC)

Black hole unitarity paragraph needs to be corrected

Hawking's argument is not represented correctly here.

see here for details.

Also his article has been accepted in Phys. Rev. D

see here

so it has been reviewed, but it is fair to say that many physicists are not convinced.

Count Iblis 15:16, 17 October 2005 (UTC)

Hawking radiation and entropy

It is said that

In 1971, Stephen Hawking showed that the total area of the event horizons of any collection of classical black holes can never decrease.

If I understand this correctly, inclusion of Hawking radiation should modify this statement to say that "the sum of the entropy connected to the event horizon's area and the entropy due to the leaving radiation, can never decrease". Right? I think that ought to be mentioned, since it took at least me some time to figure out what happened to the (supposedly non-diminishing) event horizon area for a shrinking black hole... \Mike(z) 20:11, 25 October 2005 (UTC)

I think the key word there is "classical." A "classical" black hole does not radiate, because that's a quantum mechanical process. All the sentence says is that black holes have a property (area) that's like entropy in that it never decreases; Hawking later showed that this quantity can decrease if entropy is produced elsewhere (i.e. in radiated particles), strongly implying that black hole area (times some constant) is entropy. -- SCZenz 22:18, 25 October 2005 (UTC)

Seth Lloyd of MIT has a new paper showing that Hawking radiation contains information. So far this is a news article at PhysicsWeb. -MegaHasher 21:17, 2 March 2006 (UTC)

A number of papers have been written about the subject. To the best of my knowledge, none of these are accepted as definitely correct, because without a complete theory of quantum gravity, many approximations are needed in order to model Hawking radiation, raising the possibility that the approximations mangle something important. See Hawking radiation and trans-Planckian problem for more information. Discussion of black hole entropy and Hawking radiation is probably best done at black hole information paradox. --Christopher Thomas 21:38, 2 March 2006 (UTC)

Talkpage length

This page appears to be long enough to create the black hole otherwise known as an archive.

I agree to this anonymous and undated comment; but also the main article reaches a critical size. This is especially annoying if someone wants to edit the first lines which are not in a (sub)section, and for reverting (frequent!) vandalism (needs edit of the complete article). OK, it's already a featured article, so we can expect it won't grow much any more, but nevertheless this will happen.

To reduce the article's size, I see as one possibility to move the FAQ to a separate page: In fact there is much redundancy (all "What is a ...." questions are explained previously, often with almost identical wording), and even if the FAQ makes up "only" about 2.5 pages in my browser, I think the density of text is so high that it represents a considerable part of the article's size.— MFH:Talk 13:44, 16 March 2006 (UTC)

I'm not sure what the point of the FAQ is - it seems like a less precise summary of the information in the main article... Kjl 00:04, 17 March 2006 (UTC)

Break up a black hole from the inside?

This is probably an elementary idea, but what if you sent something into a black hole with the sole purpose of destroying it? Say, an advanced bomb or payload of anti-matter. Nothing can escape the event horizon, but if you break it up from the inside, won't the gravimetric forces have to decrease as the chunks separate?

Someone else here can probably provide a better answer, but the thing to remember is that what's inside the event horizon of a black hole is not just a really dense ball (like a neutron star, for example). The mass is actually concentrated at (mathmatically, anyway) a single point, called a singularity. How do you blow up a singularity? As a rough analogy, if I want to destroy a piece of string, I can cut it up into tiny pieces and scatter them around. But if the string has no length to begin with, how am I going to cut it apart? I'm not saying it's impossible, since that's far too strong a word, but I certainly can't picture how you'd go about it. —HorsePunchKid→龜 04:38, 29 October 2005 (UTC)

If it's really a singularity, you can't blow it apart. Of course, we don't know what singularities really are without a theory of quantum gravity, but I find it pretty unlikely that anything could break up whatever it really is, or keep it from recollapsing if it did. Certainly antimatter won't do it. While I won't make a prediction about physics and technology thousands of years from now, this sounds even harder than making a stable macroscopic wormhole. -- SCZenz 05:45, 29 October 2005 (UTC)

QG will probably allow for spontaneous break up of a black hole. Black holes can evaporate, so the amplitude for a black hole to emit a mini black hole is very likely larger than zero.Count Iblis 21:32, 29 October 2005 (UTC)

There may be something known as a reverse black hole... Stuff just goes out into the universe again from there. The "Big Bang" may be caused by a reverse black hole in another "universe" which is already there. Anyway, what defines the "edge" of a universe?

Apparently you'd see a reverse black hole (a "white hole") as you crossed the event horizon of a proper black hole, since everything entering the black hole behind you would appear to come from a single direction due to the intense curvature of space. As for the "edge" of the (possibly infinite) Universe, I'd put money on the Hubble distance as being the common answer. (where space expands faster than light can cross it). Tzarius 11:57, 17 November 2005 (UTC)

This is covered at Talk:Big bang. The big bang could be argued to be the time-reversal of the _formation_ of a black hole, but is not a white hole (time reversal of a black hole post-formation). In practice, it's expected that our predictions of what happened break down past the time when the universe approached the Planck temperature, so the interpretation provided by general relativity doesn't completely hold. As for whether falling into a black hole sends you out a white hole at the other end, this turns out not to be the case. Some of the links at the end of the black hole article explain why. Short version is that if you include the original stellar collapse that created the black hole, you can't draw a consistent spacetime diagram of a black hole/white hole pair.--Christopher Thomas 22:11, 17 November 2005 (UTC)

GR prohibits BH formation

An edit by 130.184.202.187 states that GR prohibits BH formation. This is a misunderstanding of general relativity. By definition, you cannot receive information from inside a black hole, and so information from the event horizon takes an infinite amount of time to propagate away. This is a statement of what it means to be a black hole. Nonetheless, just because a black hole cannot be probed doesn't mean it doesn't form. These issues are subtle, but the edit as stated is misleading and doesn't do the issue justice. –Joke137 17:16, 14 November 2005 (UTC)

Anon could have been thinking of the recent publication by Chapline which was mentioned in Nature in which he does claim that GR prohibits black hole formation. Perhaps that paper should be mentioned in this article, but only with some strongly worded caveats that the scientific community soundly rejects Chapline's hypotheses, methods, and conclusions, and that his model differs with standard physics in foundational ways. -Lethe | Talk 19:22, 14 November 2005 (UTC)

It is also relevant to the new Hawking paper, in which his argument appears to be, very roughly, that only evolutions which do not form black holes seem to contribute to the Euclidean path integral for gravity. –Joke137 20:03, 14 November 2005 (UTC)

what's relevant to the new paper? The statement by anonymous that GR doesn't allow black hole formation? -Lethe | Talk 22:40, 14 November 2005 (UTC)

Yes. Hawking, in a sense, uses this fact to show that in anti-de Sitter space, only geometries in which the black hole never actually forms contribute to the Euclidean path integral. Still, for practical purposes we should clasically still think of the black hole as forming, because, for one, it is not yet clear what the Hawking calculation actually means for the real universe. –Joke137 18:40, 15 November 2005 (UTC)

I think the point was not that you can't receive information from inside a black hole, but rather that as the matter falls in towards the event horizon it never gets there because time slows down for it. So it isn't really a black hole, it's a partially formed black hole. If you fell into the partly formed black hole, as you approach the event horizon you'd see the black hole finish forming under you. (Hypothetically if it was still emitting something to see it by.)

I'm not a scientist, but my understanding is that since you can't say that distant events are simultaneous, you can equally well interpret this as "time slows down for matter falling into the event horizon" and "time moves normally, but the distance gets very large, so you see the matter fall in only long after it does". Which means that whether the black hole formed yet is purely a matter of interpretation. Is this anywhere near correct? Ken Arromdee 05:27, 15 November 2005 (UTC)

Ken, that was indeed the argument, but that argument is wrong. If you are falling with the material that will form the black hole and are communicating with me using light signals, then I won't be able to receive any information from you after a certain time, T, on your clock. But you will continue to receive information from me after your clock indicates T (until the time you are destroyed by the singularity). I will continue to receive information about you till eternity on my clock, but that information is about you before your clock indicates T.Count Iblis 12:38, 15 November 2005 (UTC)

What does it mean to "not receive information", though? If I'm falling with the black hole material and you can't receive any information from me after T on my clock, does that mean that

• you can't receive information from me because time has slowed down for me and falling in takes an infinite time by your clock (though a finite time by my clock), or
• you can't receive information from me because although it takes a finite time for me to fall in, the distance travelled by the information gets infinitely large?

I was under the impression that these are both equally accurate descriptions, so whether I've fallen in yet depends on what reference frame you pick. Ken Arromdee 15:45, 15 November 2005 (UTC)

The second version you give is the one that provides the most insight into what's actually happening. If I send a radar pulse down into the hole towards where I see your image, it won't reach you, because you passed the horizon long before I even sent the radar pulse. In other words, the time I read from the clock your image is carrying doesn't tell me what time you are experiencing in my reference frame when I receive the light - it tells me what time you were experiencing _when you emitted the light in the image_. This is a very important distinction. Depending on what convention you use to define how you measure when a distant event occurred, you get different answers about when exactly the horizon was crossed, but you cross it, and the black hole forms, in finite time even from an outside observer's point of view. See point 3 on the FAQ linked from the bottom of black hole, and check the [Schwarzschild Geometry page] from the "falling into a black hole" site that used to be linked from this article. --Christopher Thomas 18:34, 15 November 2005 (UTC)

That FAQ, which I've seen before, says this: "At large distances t *does* approach the proper time of someone who is at rest with respect to the black hole. But there isn't any non-arbitrary sense in which you can call t at smaller r values "the proper time of a distant observer," since in general relativity there is no coordinate-independent way to say that two distant events are happening "at the same time." The proper time of any observer is only defined locally."

That sounds like what I was saying before: you can interpret it as time slowing down for someone falling into the black hole, it's just that your choice is arbitrary. In one reference frame it takes forever to fall in but the light reaches an outside observer quickly; in another one, falling in is quick but the light takes forever to reach the outside observer.

I don't understand the idea that time slowing down is *wrong*, as opposed to a valid, but less useful, interpretation. Ken Arromdee 18:54, 15 November 2005 (UTC)

Time does slow down. If you tie a clock to a rope, lower it down to _near_ the surface of the horizon, then haul it back up, it'll read slower than a clock that you kept with you far from the hole. This is only a meaningful test, however, when you are able to haul the clock back, or to exchange signals with it. That is not the case for an infalling object, as a photon sent in after it won't ever reach it. Check the spacetime diagrams on the site I linked above to see why - that's why I linked that site. An observer lowered on a rope to just above the event horizon won't be able to contact someone who fell in previously. They'll instead see the previous victim recede, getting even closer to the horizon.

If you want a different way of thinking about it that might feel more intuitive to you, consider a black hole as "sucking in" space itself. Anything falling in, gets sucked in. The signals they send out take longer than expected to reach a distant observer, because despite travelling at C, they're running on a treadmill. This emission can take an arbitrarily long time, which is why you continue to see an image of infalling objects arbitrarily long after they were dropped. Light emitted from within the horizon is sucked into the singularity despite propagating away from it at C, as the swatch of space it's moving in is moving FTL relative to an outside observer. If you try to lower something through the horizon on a cable that's stationary relative to a distant observer, your cable disintegrates when it touches the horizon because the force-carrying particles binding it together are sucked away. While this is an incomplete way of looking at a black hole (it doesn't give you the insights looking at it as curved spacetime does), it's correct as long as you define your coordinates properly, and is good for giving a qualitative feel for what's happening. --Christopher Thomas 19:17, 15 November 2005 (UTC)

I hate to say this, but I still don't get it.

Suppose I drop in a clock. But instead of a rope there's a little rocket engine attached which fires when the clock is an inch away from the event horizon, propelling the clock back out. When I get the clock back I'll find that more time has passed in the outside world than for the clock.

Now I reprogram the engine to fire when the clock is a *half* inch away from the event horizon. When I get the clock back I'll get it back later than in the first case.

I repeat the same experiment, constantly setting the rocket to fire when the clock's even closer and closer to the event horizon. So I keep getting the clock back later and later.

Couldn't I make the clock come back arbitrarily far in the future, just by firing arbitrarily close to the event horizon? So an object that is outside the event horizon, but close to it, could have its time slowed by an unbounded amount. If the clock is slowed by an unbounded amount when it gets closer to the event horizon, wouldn't the same be true for objects that fall in without coming out? Ken Arromdee 21:44, 15 November 2005 (UTC)

The difference is that a dropped object is freely falling, while an object tied to the end of a rope (or hovering on a rocket) is not (it's experiencing an accelerating force that exactly cancels the black hole's gravitational acceleration). The worldlines followed are very different (the falling object follows a geodesic, while the object experiencing acceleration has its worldline curved away from the geodesic). Thus, while you can dangle an object on a string over a black hole, pull it back after as much time as you feel like, and have the clock show as little time as you like, this scenario isn't the same as the scenario where you have an object _dropped_ into the hole.

Giving a more detailed description would involve drawing diagrams, which I don't have time for this evening. Ask on Wednesday if you're still not sure what I'm talking about, and if the diagrams in the cited web page aren't helping. --Christopher Thomas 23:01, 15 November 2005 (UTC)

So an object tossed into a black hole in a parabolic orbit whose periapsis is just outside the event horizon, will not experience any slowing of time because it is in free fall? Ken Arromdee 00:18, 17 November 2005 (UTC)

An object tossed into a near-approach orbit around a black hole will experience time dilation both from SR and GR effects, but the amount will be different than that experienced by an object you held stationary (relative to a distant observer) at that altitude. In practice, you can't actually get as close with an orbiting object as you can lowering an object on a rope - inwards of something like (4/3) the event horizon radius, tangential motion pushes you inwards instead of outwards, making stable orbits impossible. If you want hard numbers for time dilation in specific scenarios, I'm afraid you're going to have to hunt down an astrophysicist and get them to do the number crunching for you. I can only give the qualitative version.--Christopher Thomas 00:42, 17 November 2005 (UTC)

Actually, those who say that black holes can exist in a finite time to an external observer are the ones who are misunderstanding GR. In the viewpoint of collapsing matter, only a finite time is necessary for collapse inside the event horizon. BUT ... to an EXTERNAL observer, gravitational time dilation approaches infinity as the collapsing matter approaches the event horizon. Thus, to the EXTERNAL observer, the time it takes to actually collapse is infinite. Thus, if the universe really has a finite age, black holes do not exist. —The preceding unsigned comment was added by 130.184.202.187 (talk • contribs) .

This is a misconception. The reason why it turns out to be a misconception are explained above, so I'm not going to spell them out again. The very, very short version is that "it looks like the falling object is still there" doesn't mean it's still there. You have to take light propagation time into account, and light propagates strangely near black holes. --Christopher Thomas 22:03, 17 November 2005 (UTC)

Eternal black holes and non-eternal black holes

Can something about eternal black holes and non-eternal black holes be added to this article or be the subject of a new article? I'd do it, but I'm not knowledgeable enough them. This is part of the missing articles project. Another encyclopedia has a (very short) article about them. -- Kjkolb 12:45, 25 November 2005 (UTC)

I believe this is referring to the "remnant" proposal for what happens after black hole evaporation. The description as-stated at the linked glossary is missing something pretty critical (for one thing, an object with no mass has no gravitational field, and so can't be "contained" by it; for another, without a gravitational field, it wouldn't absorb other matter). The idea behind remnants was that the black hole information paradox could be solved if you assumed that some type of particle or spatial defect remained after the hole's mass went away, and this object contained all of the information that had apparently been lost by the evaporation.

If I understand correctly, this is not the currently favoured view of what happens, though without a really good treatment of quantum gravity, nobody can really say what _does_ happen. The type of solution I heard most about in years past was to assume that some mechanism kept information about infalling matter bound at the surface of the hole, and that this left an imprint on the outgoing Hawking radiation. The type of solution that seems to be in vogue now is to find some way of showing that the event horizon and singularity never actually form. Hawking claimed to have a proof of this recently, but I don't think it's been universally accepted yet. --Christopher Thomas 21:21, 25 November 2005 (UTC)

Tunneling

The article presently contains a statement that Hawking evaporation is a form of quantum tunnelling. My understanding is that this is not the case. Quantum tunneling refers to a particle traversing a barrier due to the fact that its wavefunction is nonzero in the region of the barrier (decays exponentially, as opposed to a sharp cutoff to zero). Hawking evaporation is a completely different mechanism involving the peculiar behavior of virtual particles in the strongly-curved spacetime near the horizon. Tunneling, by contrast, would involve the wavefunction of matter in the singularity itself (which is undefined but bounded within an arbitrarily small volume, if I understand correctly). The two are analogous in that the end result of either would be mass loss from the hole, but that's about as far as it goes. --Christopher Thomas 02:37, 6 December 2005 (UTC)

It is still a tunneling phenomenon. Let me try to explain this. In ordinary non-relativistic quantum mechanics you can have a single particle evolving from state x to y while classically it had to pass through z, even though it lacks the energy to be found at z. We call this tunneling, because the particle appears to "tunnel" through the "forbidden" state z.

Quantum field theory is just "ordinary" quantum theory applied to fields. The Hamiltonian has the same form as that of harmonic oscillators. The energy levels are equally spaced and are interpreted as states containing 0, 1, 2,... etc. particles.

Any process in quantum field theory involving "virtual particles" is exactly analogous to the tunneling in the non-relativistic case. The virtual particle states are precisely the "forbidden" intermediary states the system seems to tunnel through. Count Iblis 13:19, 6 December 2005 (UTC)

Singularity and time

Please excuse my intrusion to your facinating thoughts in this area, as I am a relative newbie, however...

1. If the singularity is the disintergration of all matter as we know it, would there still be Time?
2. Would the beginning of Time itself best discribe the edge of the universe?
3. How about a merging supermassive binary grey hole? Hmmm.. Andy 19:46, 19 December 2005 (UTC)

Welcome to Wikipedia. I've moved your comment to a new subsection; you can start one by adding a title heading that ==looks like this== on its own line. If you'd prefer it to be in the "breaking up a singularity" subsection, by all means move it back.

The short answer is that the singularity isn't so much "the disintegration of all matter as we know it", as a point where our mathematical models of black holes produce undefined values. This is usually interpreted as an indication that the models are incomplete, as opposed to an actual location where some of the laws of physics break down. As for time, the relative rate of time flow for objects at the singularity is undefined. It could be considered the endpoint of the infalling object's worldline (as there is a well-defined time of impact from the infalling object's point of view), but my understanding is that this is a somewhat misleading conclusion to draw (as the impact event's spacetime coordinates aren't well-defined from an external observer's point of view).

As for the "beginning of time", most models of the big bang that I'm aware of don't define an explicit boundary, instead stopping at the point where our understanding of the physics underlying the model of the universe breaks down (the point at which the fundamental forces are unified and a theory of everything is expected to apply). Other models describe the big bang as the decay of a false vacuum state, and some of these define their coordinate systems such that time as experienced within this universe starts at a boundary corresponding to the light-cone of the expanding decay region in the parent universe, but this just pushes the problem back, and I'm not sure how rigorous or accepted the description I'm recalling was. The short answer is that we do not presently have an ironclad theoretical description of a beginning or ending of time that I'm aware of (spacetime is assumed to be a surface without tears).

You're going to have to reference whatever object you're calling a "grey hole" before I can comment on your third point. For black holes, all that an external observer sees happening is that they merge into one object with the combined mass and angular momentum of the parent objects, and lose a lot of angular momentum and gravitational potential energy in the form of gravity waves as they spiral into each other. --Christopher Thomas 21:39, 19 December 2005 (UTC)

Event Horizon and Time Travel

Hello, I am not a user of wikipedia, however, I wished to address something. Because the gravitational pull of the black hole is so strong, if you were to "hover" just outside the event horizon of a black hole, then a form of time dilation would occur and, in essence, because time would be moving so much slower, it would be like traveling to the future, although in reality you would have just aged more slowly. I feel that this should be mentioned. —The preceding unsigned comment was added by 24.10.164.230 (talk • contribs) .

Of course. It's easy to forget to include some of the many and strange effects of relativity. I guess that's why there's so many 'wrong' interpretations of black holes (among the general population). Tzarius 22:05, 20 December 2005 (UTC)

I don't get it

http://www.xdr.com/dash/blackholes.html

The gyst of the article above is that for the person falling into the black hole time slows down so much, he can never actually fall into the black hole, even in his own reference frame. His clock will never go beyond time T, and actually he will only reach time T after an infinite amount of time has passed "outside".

Someone criticized my adding the above link to the black holes page directly under the external links. Fine, sorry. Someone else wrote:

• quote

Sources for scientific articles are expected to be from refereed journals, or from well-regarded experts in the field. I'm afraid your personal web page about black holes is neither. Also, the interpretation you discuss is already discussed extensively on the talk page (it's an illusion, and the reasons why it's an illusion are described in detail). Please check talk-page discussion before modifying an article, and please only use refereed sources if it's a science article.

• unquote

Ok, so I looked here which I presume is the "talk page" and didn't find the extensive discussion. Nor did the word "illusion" appear anywhere. I suppose it does now though...

I'm truly looking for enlightenment. Anyone who has any insight as to why my way of looking at is wrong, please explain!

[10 minutes later] I read the stuff about if a person were to suspend a clock on a rope down close to the event horizon, then pull it back up, time would pass on the clock, also if the clock were to come back out under its own power. Christopher argued this was not the same because the clock was experiencing acceleration, and that would be what caused the time dilation. My answer to that is this: That would be an *additional* cause for time dilation on the clock. Just being in that place at that time would be enough to dilate time. It doesn't matter if you're firing your rocket to escape or if you're suspended on a string. If you're there you've slowed down.

I think the asymptotic time warp to 0 is correct -- it solves so many problems. No singularity, no problem with entropy, etc. You don't need to invent solutions like Gravastars to escape the singularity problem.

If you do the math, you find that if you track things from the infalling object's reference frame, you don't end up with a discontinuity until the object hits the singularity itself. The apparent halting of the infalling object from a distant observer's point of view is an artifact of the geometry of spacetime. Light emitted after passing the horizon doesn't reach the outside observer, as the light-cones are warped to point inwards, and light emitted just before crossing it is delayed an arbitrarily long time, giving the illusion of asymptotic approach. This is already described by several people, though it seems that thread has been moved to the Talk:Black_hole/Archive_1 page linked from the top of this page. Alternative ways of describing this effect are also listed on that page. While originally scientists thought something strange happened at the surface of black holes along the lines of what you describe, this was later shown to be a problem with the coordinate system being used, rather than a feature of the horizon itself. See Schwarzschild metric for a discussion of this. --Christopher Thomas 19:31, 26 December 2005 (UTC)

Do the math: We all know what the math says -- that the victim falling into the black hole keeps right on going in his reference frame. He doesn't stop. However my point is that that would take an infinite amount of time outside for him to complete the fall. Here's an example. Suppose you construct a mass of some magical substance that is absolutely incompressible but has mass. You keep dropping this substance into the big mass, little by little. Finally you stop when the escape velocity on the surface of the mass is c minus some tiny amount. Then you drop your clock onto the surface of the mass. You look at the clock. What does it do? It's moving veeeery veeeery slowly. It's almost red-shifted to black, but you can just make it out. Time has actually slowed down in there. You can make it slow down by an arbitrary amount by how much mass you dropped into the pile. You can make it slow down by so much that 10^10^10 years must pass before the clock can advance one nanosecond. Now suppose it's sitting there like that, all stable, time slowed down very much -- then you "turn off" the magical property that makes it uncompressible. Say you turn off the stasis field. :^) (reference to Larry Niven books). So now the mass starts to fall into itself -- or does it? Time has slowed down already, so it doesn't fall very fast. In fact as it falls, the escape velocity gets closer to 'c'. Closer and closer and closer. But as it gets closer, time is slowing down even more. I submit that no mass can ever form in such a way that the escape velocity can exceed 'c'. And it takes infinite time to even achieve 'c' escape velocity.

If you want to "do the math", it's right there at Schwarzschild metric, as I pointed out. If you want a qualitative description, then - as was mentioned in the talk thread I pointed you at already - you have to recognize than an object being _held_ at a distance above the horizon is in a very different situation than an object freely falling towards the hole (or freely collapsing, if you're considering a shell or uniform sphere of matter). Holding it still requires violent acceleration, just as holding you still on the surface of the earth requires acceleration to warp your worldine into a non-geodesic path. The violence of the acceleration required directly correlates with the depth in the hole's gravity well; start freely falling, and no matter what altitude you start at, you cross the horizon in a finite length of time from the point of view of an observer falling with the collapsing surface, and at the point of crossing, have received signals corresponding to a finite span of time passing in the outside universe. Drop a reflective ball into the black hole, and shine a timing signal at it, and the reflected signal you get back never passes a certain time code (from your clock), no matter how long you wait and listen to the red-shifted return signals. If you don't want to go to Schwarzschild metric and do the math yourself, one of the physics experts lurking here can explain it to you, as I've given as good a description as I can without breaking out xfig and drawing a spacetime diagram. --Christopher Thomas 08:09, 28 December 2005 (UTC)

According to the sci.physics faq at http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/fall_in.html the freezing of time for an object falling in is an illusion. However, it also says that the illusion is caused by the paths of light rays and that it may take an unlimited amount of time for the light rays to get out. If so, how can "Drop a reflective ball into the black hole, and shine a timing signal at it, and the reflected signal you get back never passes a certain time code (from your clock)" be true? The reflected signal should be able to get back an arbitrary amount of time in the future, long past any time code on your clock.

The reflected signal is received by the distant observer at a time arbitrarily far in the future. The observed _timestamp_ on the returned signal, encoded into the signal at its time of _emission_ never passes a certain finite value, no matter how long you wait to receive the signal. Does this clarify what I'd written? --Christopher Thomas 18:11, 29 December 2005 (UTC)

Okay, so suppose the reflective ball has a clock inside it and is sending out timestamped light too. So when you look at the pairs of timestamps on the light you get back, the observer timestamp will be associated with an onboard timestamp of at most a certain maximum value? And on the other hand, if you have a rocket hovering arbitrarily close to the event horizon and you do the same thing, the observer timestamp might be associated with an onboard timestamp of arbitrarily far in the future (depending on how close to the event horizon it's hovering)? Ken Arromdee 20:49, 29 December 2005 (UTC)

Yes, that is my understanding of how this type of system works. I'm still waiting for one of the GR physicist lurkers to give a more easily-understood description of these scenarios (I realize that my own explanations are often unclear). --Christopher Thomas 22:06, 29 December 2005 (UTC)

The FAQ also says "the Schwarzschild coordinate called t goes to infinity when I go through the event horizon" and "At large distances t does approach the proper time of someone who is at rest with respect to the black hole. But there isn't any non-arbitrary sense in which you can call t at smaller r values "the proper time of a distant observer." That seems to imply that there is indeed an interpretation where time slows down infinitely (relative to a distant observer) for an object falling in, but that choosing this interpretation is arbitrary. Ken Arromdee 15:42, 29 December 2005 (UTC)

I agree that this is an interpretation that is useful for some purposes. However, I disagree with the statement that this interpretation prevents black holes from forming in the first place, which is what started this dispute (anon added their web page with a claim to this effect to the "external links" section of the article). --Christopher Thomas 18:11, 29 December 2005 (UTC)

Christopher, thanks very much for engaging in this discussion. I don't see much point in my studying the math involved enough to work with the equations and come up with the solution you're describing -- because I'll grant the result is what you're saying. You're saying the party line. I'm saying, why can't a time warp effectively stop time completely? Yes, it's a finite length of time to fall all the way in, but in that reference frame time just stops advancing. Suppose you have a mass. The mass is so great that at some point away from the center, the escape velocity is very close to 'c'. At that point time has slowed down -- whether or not something at that point is "standing" on the mass itself and enjoying the acceleration, or whether it is free-falling. You can tell time has slowed down because a pulse of light sent from that point still has to climb out of the gravity well and get red-shifted.

I'd like to pose a hypothetical question: what if what I'm suggesting is actually a reflection of reality?

• The sun ejects 1/3 as many neutrinos as it should, so our confidence in our theories can't be too high
• Quasars seem to be strangely bright for their presumed distance -- maybe quasars are nearby partially black holes
• No one has been able to merge general relativity with quantum gravity -- gravitons and whatnot
• Gravity waves have never been detected
• Whether or not a black hole continues collapsing into a singularity would not affect any of the observations of black-hole like objects seen with telescopes. This black hole that stops because time has stopped would still, from the outside world, feel, taste, smell, sound and look like someone else's black hole with a singularity
• This black hole would have no problem with missing entropy -- because the mass that has fallen into the hole to form the hole in the first place is still there, all in its original positions, still in the act of falling in. You can't represent a black hole with just 3 numbers -- mass, charge + angular momentum.
• All of the work Hawking has done on black holes would have been an unfortunate waste of time -- just like ancient monks arguing over how many angels can dance on the head of a pin. Yes it's a tragedy but history's full of that.
• Lots and lots of contemporary physicists would have to collectively say "Doh!" because they've been buying into and teaching and happily explaining what would have turned out to be a fairy tale.
• How long is the right amount of time for the scientific community to pursue a dead end before backing up and trying something else?
• The main point to get past is this: Couldn't time slow down so much so that even if it takes time X to fall all the way into the singularity, you never actually get there -- you're caught at say X/10 frozen in time. If you can just visualize that you'd see my whole point.

I _understand_ the approach you're using - it's the same one originally used by Karl Schwarzschild to produce the "frozen star" interpretation of black holes, before it was realized that this was just an artifact of the coordinate system he was using (as discussed at Schwarzschild metric). Both the "frozen star" model, and the reasons why it's an illusion, are well-understood. Because the "party line" description of black holes is derived directly from the equations of general relativity, it is important to understand that your claim that the "party line" description is in error is a claim that general relativity itself is in error. There is a large amount of experimental evidence that confirms the predictions of general relativity to considerable precision under less extreme conditions. Certainly, black holes are expected to behave differently from the manner that general relativity predicts, but it's neither in the way you're describing or for the reasons you're describing (it's because quantum gravity effects are expected to become significant). --Christopher Thomas 19:01, 28 December 2005 (UTC)

Perhaps the whole debate is moot. The only picture anyone's ever going to get of a black hole is what it looks like from the outside. I think I'd rather believe in my version of what's inside + be proved wrong later by unshakable evidence to the contrary than blindly just give up because I'm unwilling to work through the math.

GR - I like GR. I think if you allow something to contract past the Schwarzschild radius then the only way anything could make sense is if space warps/stretches as described. But if things can't actually contract past the S.R. because of the time dilation, you don't need to resort to the pathological warping of space -- things never get so far out of hand.

Christopher: Thanks very much for your commitment to this discussion. What I'd encourage you to do since you obviously have the theoretical background + math experience is to examine the problem from the point of view of trying to prove me right instead of the opposite. Suppose you succeed -- that really would be a step forward :^). —The preceding unsigned comment was added by 70.32.171.199 (talk • contribs) .

What you appear to be failing to realize is that what you're proposing isn't just a different way of interpreting the visible behavior of black holes, but a direct violation of general relativity, with measurable consequences (you see different results when sending time-coded radar pulses after the infalling object, for example). I'm not going to try to "prove you right" unless you can present reasons beyond just aesthetic ones as to why you consider GR to be in error in the way that you propose. The burden of proof is upon the person making the most extraordinary claim (in this case, that the predictions of GR don't hold, in a regime where it looks like they should). Also, be aware that you can sign your posts with four ~ marks to produce a timestamped signature. --Christopher Thomas 00:50, 29 December 2005 (UTC)

The entire argument against my viewpoint is that from the reference frame of the victim falling into the black hole it takes a finite amount of time for him to fall. I grant that -- that would be the result of doing the math. My point is how you interpret that result. Just because it takes a finite amount of time doesn't mean that amount of time is guaranteed to pass in that reference frame. Example: The 1979 movie "The Black Hole", has a run time 98 minutes according to imdb. If I watch 60 minutes of the movie then pause my dvd player forever, what do I know? It's a 98 minute movie, therefore it must complete in 98 minutes according to time within the movie? That's irrelevant if I never push play again. The characters in the movie would be unable to detect that time has stopped, they'd be completely unaware of this.

Along that same example, suppose after the video passes the 60 minute mark I hit a button to slow down the playback rate by 50%. Then every 5 seconds according to my clock I hit the button again, slowing down playback by 50%. The video will effectively stop. It's always moving forward but it can never pass the 60 minute + 5 second mark. --David Ashley 01:22, 29 December 2005 (UTC)

General relativity theorists have not interpreted the result to mean that black holes can't form, if that's what you're getting at; only that their collapse can't be fully observed by a stationary observer. Once you let someone fall into the black hole, without ever stopping them, things are completely different, as Chris points out.

Please keep in mind that the talk page is foremost for discussing changes to the article, and we cannot in any case add claims to the article that are not backed up by formal peer review. Gazpacho 03:42, 29 December 2005 (UTC)

Hmph. I thought "discussion" meant actual discussion. Don't get into the habit of being a Wikipedia Nazi. You'll probably find lots and lots and lots of activity going on that doesn't fit into what people expected when building this thing. Welcome to anarchy. David Ashley 03:46, 29 December 2005 (UTC)

After playing around with Wikipedia I uncovered a very good reason why this is a perfect place for this discussion. It seems every 2 weeks someone asks this same question that I'm asking. So if it turns out I am incorrect, whatever explanation you can bring to bear on convincing me can be quite useful as a contribution to the article itself -- to deter other people from posing the same question. So it seems like this exercise is actually A Good Thing. If people reading an article are left with the same questions, maybe that means someone should answer the question in the article. David Ashley 05:09, 29 December 2005 (UTC)

Well I guess it's time for me to repeat the question then... I'm afraid I don't get it either. I had it described to me this way once, can someone tell me if it's right/wrong? Two astronauts head out to a black hole and one of them jumps in. Well, jumps towards it. Lets say they're both waving at each other with a frequency of 1hz, you know, goodbye, see you on the other side, etc etc. The guy falling in and looking out sees his pal seeming to wave at him faster and faster. At the same time, the guy watching his partner fall in sees his partner seeming to wave more and more slowly. Now eventually the guy falling in would see his friend on the outside either running out of air and choking or leaving, and then, a short while later (in his refernce frame) he sees tourists from the "future" coming to watch the guy who fell into a black hole, and sees all the kids with their wide-open eyes going "oooo" but everything would seem to be going very fast. To the tourists, who are coming to visit hundreds/thousands of years later (or longer) the guy seems to have come to a virtual standstill in mid-handwave (he has also become very very dim but we'll ignore that for simplicity). As the ill-fated astronaut falls towards the black hole, he sees the entire "future" of the universe flash before his eyes, because it is taking him a literal eternity (from the outside's frame of refernce) to fall in. But to his frame of refence, time doesn't seem to slow (quite obviously), it's just that things on the "outside" speed up, such that the time for him to reach the black hole is an eternity elsewhere in the universe.

A couple questions, beyond the basic one of "am I completely off-base."

1. If this is an accurate description, does this mean it would take him an eternity to reach the event horizon or the singularity of the black hole? I'm inclined to say the event horizon since no light would escape once he reaches the event horizon (and he would thus tun completely black rather than just dim)
2. The way I think about it, the reason the astronaut gets dimmer is because the same amount of light (or number of photons) is spread over a larger amount of time, such that the # of photons per second that reaches the outside world keeps getting smaller and smaller. I would then assume that the same is true the other way around, in other words the light from the fellow astronaut, the other stars, the tourists, etc etc would hit the astronaut in a smaller and smaller amount of time, so for the astronaut falling in, would the outside universe seem to get brighter and brighter? and as he approached the event horizon, and the entire future of the universe flashed before his eyes, would it simply become a extremely bright flash? Would it be imperceptible, sufficient to give him a nasty sunburn, or enough to vaporize him? I'm inclined to say vaporize, but I may be off-base here as well.

I hope my description is right... that's pretty much as complicated as it can be if I'm expected to get my head around it ;) --AK7 22:03, 22 January 2006 (UTC)

Potentially useful figures

I've created two figures that may be useful for a description of events that occur when an object falls into a black hole. These were created using "xfig", so they'd have to be redrawn by someone with decent Photoshop-fu or GIMP-fu before being suitable for use in the article. I hope that these figures are useful to editors of this article.

It is important to note that things look very different in different coordinate systems. These figures reflect what seems to happen from a distant observer's point of view, if I understand correctly. --Christopher Thomas 19:30, 29 December 2005 (UTC)

If new versions of these figures are uploaded, you might want to avoid making the duplicate-word mistake I missed twice on the "radar pulse" filename... --Christopher Thomas 19:57, 29 December 2005 (UTC)

The pictures look good, but I don't think they prove anything. It's like you're saying, "Given that the event horizon forms, this is what would happen..." I dispute the event horizon forms in the first place. An infinite amount of time can pass outside and the event horizon is still trying to form. Couldn't a time warp exist such that the forward passage of time, for all practical purposes, just stops? David Ashley 03:26, 30 December 2005 (UTC)

I keep trying to tell you, the only way an effect like that could happen is if the equations of relativity are _wrong_. In order to demonstrate that that is a viable scenario, you're going to have to 1) write new equations that describe the situation you think occurs, 2) prove that they produce the same effects as GR under less extreme conditions (i.e. match all of the experiment data that currently supports the GR equations), and 3) provide some kind of explanation as to why you feel the principles the GR equations embody (that C is always measured to be a given value regardless of reference frame, and that inertial and gravitational acceleration are indistinguishable) don't hold for the cases where your equations violate them. People have _tried_ doing this, sometimes with interesting results ("doubly-special relativity" is a really neat idea, for instance), but saying "I think this looks nicer" doesn't cut it, as the equations of GR weren't just pulled out of thin air. It takes more than handwaving to back up a claim that they don't apply.

What the pictures themselves are intended to do is not to prove, but to _explain_ in a layman-accessible manner, what exactly it is that GR describes happening near a black hole. In this case, they say that the collapsing star's matter follows the "infalling object P" curve on the second plot. For a nonrotating spherically symmetrical collapsing body, any given layer of matter doesn't care whether or not an event horizon has formed under it yet, only how much mass is under it, so if you accept that this is what the diagram looks like with an event horizon in place, you're going to have a hard time justifying a statement that it's not what happens during implosion to a black hole. If you instead dispute that this is what happens in the scenario where an event horizon has already formed, we're back to my first paragraph.--Christopher Thomas 06:50, 30 December 2005 (UTC)

Christopher, I don't think you're really seeing my point at all. You don't even seem to be reading my examples. You're absolutely certain the common theory is correct and I'm just an ignorant layman that you're not even considering it. Just consider this one single example: pretend that neutrons are sufficiently uncompressible such that I can keep packing them together until I create a nonrotating, spherical mass with an escape velocity just one iota less than 'c'. Can you picture that? Time is slowed down vastly on the surface of that sphere. By adding mass I can arbitrarily slow down time on the surface. Couldn't I then add enough mass such that for all practical purposes time has stopped on the surface? Tell me what's wrong with this picture? David Ashley 08:01, 30 December 2005 (UTC)

Because you couldn't add more mass when there's no time in which to do it? Tzarius 11:11, 30 December 2005 (UTC)

That's exactly the result I'm after -- that time slowing down is a roadblock to further increases in the escape velocity. David Ashley 17:03, 30 December 2005 (UTC)

I already _have_ told you what's wrong with that picture, when you first gave an incompressible sphere example. In order to keep your sphere from collapsing, you need to apply an extremely powerful _acceleration_ to its material. This has two effects. First, it affects the amount of time dilation occurring (due to the equivalence of inertial and gravitational acceleration). A freely-falling shell without resistance to compression has a different amount of time dilation. Among other things, this means that the matter you add to the rigid sphere follows a worldline that lets it intersect the accelerating worldline of the shell of matter at the sphere's surface. Secondly, it requires infinite compressive strength to halt the collapse as the mass of the sphere approaches that needed to form an event horizon. This means that at some point you're forced to transition between a "rigid body" scenario and a "freely falling body" scenario for any material with finite compressive strength. If you start with a rigid shell at rest a small distance above the horizon radius, sure, it may take longer for the collapse to start, but it only takes an infinite amount of time if your object starts off stationary arbitrarily close to the horizon radius, which doesn't happen for any material with finite compressive strength.

The fact that you didn't give a response showing understanding of this explanation the first time around, and the fact that you don't appear to realize that your proposal involves replacing GR as a model of gravity, and the fact that you're unwilling to produce a mathematical description of how you propose gravity works near black holes, are the things that give me the most concern in this discussion. I _do_ read your examples, and I _do_ understand where you're coming from - it just turns out that that approach to thinking about black holes doesn't quite work, for reasons which I've tried repeatedly to explain to you, and which you can also find at Schwarzschild metric or in any textbook on the subject. --Christopher Thomas 17:50, 30 December 2005 (UTC)

You say "If you start with a rigid shell at rest a small distance above the horizon radius, sure, it may take longer for the collapse to start, but it only takes an infinite amount of time if your object starts off stationary arbitrarily close to the horizon radius, which doesn't happen for any material with finite compressive strength." That sounds to me like a yes response to my incompressible sphere example. Nevermind that real material isn't incompressible, the whole thing is hypothetical anyway. What I was after was that my understanding of time dilation on the surface of a massive body was correct, which I think you're confirming. So now I understand your argument against my scenario is that the infalling mass would already have velocity -- it's not starting from a stationary state. The fact that it has this downward velocity then means it will take a finite amount of time to complete its fall, in its reference frame. I think that wouldn't change anything--as the mass gets denser and the escape velocity gets closer to 'c', time dilation must increase. It would just move faster towards a state of suspended animation, if that makes any sense.

With my scenario you don't have any black/white transition. With the traditional scenario the event horizon forms and then things get really crazy once stuff goes inside. Follow this progression: 1) Incompressible massive sphere with escape velocity on surface close to 'c' takes infinite amount of time to gain enough mass to form an event horizon -- you agree. 2) Instead of incompressible sphere, make it normal neutrons that you've dropped onto it one by one until it starts to collapse on its own -- This time the surface of the sphere will have downward velocity as it collapses. However as it approaches the point where an event horizon forms, time is dilating so it takes longer and longer (outside) for the collapse to progress. Yes in its reference frame it takes finite time to complete the fall, but it still can't complete because time progression slows to zero asymptotically. 3) Then generalize the concept to any infalling mass with arbitrary starting velocity and configuration. Whenever an event horizon _would_ form, it is also dilating time in such a way as to retard the formation.

There isn't any difference in the math that I'm proposing, there isn't any _different_ math involved, it would just be GR and SR + time dilation + whatnot. The only difference is how you look at the results. You say in the reference frame of the falling matter it takes a finite amount of time to complete its fall to a point mass. I say "That's correct, but that doesn't mean it will really happen because the advance of time itself can stop for all practical purposes." The math describing the reference frame of the infalling mass will involve a function of t. At t(X) this happens, at t(Y) this happens, at t(Z) this happens. But at the same time t just isn't advancing happily. While t goes from Y to Z, the universe outside will have withered and burned out and died, and still t won't have reached Z.

Anyway my enthusiasm for this debate is waning, as I'm sure yours is also. I don't really have any emotional attachment to this point of view. All I'm really after is the human race Figuring It Out, meaning coming up with an accurate model of what's going on with all the observed phenomena. I think we ought to have figured it out by now, but we haven't. So could it be that at some point in the past (say in the 1920's or the 1960's) the scientific community took a wrong turn, and since then they've been piling incorrect theory on top of incorrect theory, packed with fudge factors + special cases and exceptions and shaky math in order to try to make sense of things? The scientific method is supposed to be always encouraging testing, examining everything, including long held to be true beliefs and understandings, but in practical terms people are people, why invest time in re-examining something that everyone just _knows_ to be true -- it has been around for 80 years, right? Living with accepting long held beliefs would be perfectly fine -- _if_ we were in a utopian situation where we could explain everything and there are no mysteries. But we're not there yet, are we? David Ashley 18:52, 30 December 2005 (UTC)

Well this is an interesting turn of events. Time has Geometry. This is a new theory that debunks the whole thing. Big stuff. David Ashley 00:46, 7 February 2006 (UTC)

This is, in fact, nothing of the sort. Try reading it again. The page you link to 1) correctly notes that spacetime is not Euclidean (that's the "not just a big box with three space axes and one time axis" part), and 2) correctly notes that you have several options for defining where the time axis is, constrained only by the geometric properties of spacetime. Point 1) is part of the foundation of General Relativity. This is why spacetime is described as a Riemannian manifold instead of a Cartesian-style space. Point 2) is part of the foundation of Special Relativity, which says that inertial frames that move relative to each other have different ideas of how "space" and "time" are defined (related by the Lorentz transformation). In General Relativity, this is further constrained by the idea of directions on the manifold being "space-like", "time-like", or "light-like", with the easiest way to tell the difference being that in a coordinate system defined on a local approximately Euclidean patch of spacetime, the timelike coordinate has a minus sign in front of it in the equations.

You also seem to be missing the point about what science is all about. Nobody is claiming that General Relativity is a completely correct model of reality. In fact, we know quite well where it breaks down (at the energies at which gravity and the other forces are unified, at particle energies approaching the Planck energy, at the singularity in a Schwarzschild black hole, and at the Cauchy surface in other types of black hole). The problem with your statements has been that you appear to be disagreeing with the majority of scientists in your interpretation of what the equations of GR predict. How the model described by the equations diverges from reality is an open question. What the model itself predicts near event horizons is not. Do you understand this distinction?--Christopher Thomas 04:48, 7 February 2006 (UTC)

AFM's new website is up here: [1] Christopher: I don't think you've read all his lectures. AFM asserts a black hole is a wormhole to a point elsewhere in the universe, and at that point there is a white hole. All the matter streaming into the black hole ends up spraying out of the white hole. There is no singularity inside the black hole. The black hole only exists as long as sufficient matter continues to fall into it. All I can say is AFM's theories match what I'd rather have for the underlying machinery for the universe, such as 1) No singularities, 2) No big bang ever occured, 3) Red shift in distant objects is not caused because they're receding rapidly, 4) Quasars are not especially bright, they're much closer than originally assumed, 5) Dark matter is a myth made up to prop up incorrect theories, 6) Elegance + simplicity backed up by empirical evidence. David Ashley 00:43, 17 February 2006 (UTC)

So you're admitting that you think GR is wrong because you dislike it's predictions? Science isn't about picking and choosing how you think the world should operate. We need to look at the evidence, and right now the evidence is that GR is a perfectly good theory within certain experimental bounds and conditions. --Jpowell 00:17, 3 March 2006 (UTC)

Hi David, this is old news. See this image:

These are called a Penrose diagrams. The future is at the top, the past at the bottom. The upper left hand side shows the geodesically complete Schwarzschild solution for a black hole also contains a white hole and, sort of, a wormhole between them. Light travels at 45° angles in these diagrams. The diamond on the left could represent our universe, the one on the right an alternate universe. Unfortunately, it is impossible to go, or even communicate, from one to the other. So the matter going into the black hole just goes into the black hole. The more realistic model is the picture on the lower left, which shows a star collapsing to form a wormhole. There is no white hole in this picture. You'll also notice that after a certain point, it is impossible to prevent the black hole from forming because you can't get to the event horizon before it has formed. The picture on the right does not show a black hole at all. –Joke 01:08, 17 February 2006 (UTC)