News: Do black holes really exist?

By Phil Plait | June 19, 2007 9:28 am

Black holes are weird. Really weird.

But you know this. Infinitely small, with huge gravity, warpers of time and space; they’re simply cool to astronomer and the public alike.

Everything about them is interesting. They form when massive stars explode in titanic supernovae, they sit in the centers of big galaxies (like ours!) with masses millions or billions of times that of the Sun, and if they’re feeding on material around them they can form disks of swirling material which can easily outshine the rest of the galaxy combined.

But do they really exist?

No astronomer doubts that these gravitational objects actually exist. But astronomers Tanmay Vachaspati, Dejan Stojkovic, and Lawrence Krauss at Case Western Reserve University have written a new paper which has thrown a monkey in the wrench about the exact, well, "surface" of a black hole. Here’s how this works.

When a massive star ends its life, the core collapses. As the core shrinks, its surface gravity increases (that is, the gravity you would feel if you were standing on its surface). This means the escape velocity increases as well — this is how fast an object would have to move to be able to break free and escape to infinity. For the Earth it’s about 11 km/sec (7 miles/sec), and for the Sun it’s about 600 km/sec (400 miles/sec). The escape velocity of a body depends on how massive it is and how big it is. For a given mass, a smaller body has a higher escape velocity.

So as the core of the star shrinks, the escape velocity increases. At some point, if the core has enough mass, the escape velocity reaches the speed of light. This means that if you are standing there on the core’s surface, you would need to move at the speed of light to escape (actually, the situation is more complicated than this, but I’m simplifying). It’s like an infinitely deep hole; any matter in it cannot get out.

If the core shrinks just a wee bit more, not even light can escape. To an outside observer, the core becomes black. So let’s see, it’s a hole, and it’s black. What should we call such a thing?

Anyway, the theory is that the mass inside the black hole shrinks all the way to a point, an object of infinitely small size, called a singularity. The region around it where the escape velocity equals the speed of light is called the event horizon. And this is where things get sticky.

Einstein showed that as gravity increases, your clock runs slower. Literally, if you have two people, one guy up high above a black hole, and another guy close in, the guy outside sees the close-in guy’s clock running slower. Literally, time flows more slowly near an object with gravity, and the stronger the gravity the slower time flows relative to an outside observer. For a black hole, time literally stretches to infinity at the event horizon. Clocks stop. Update: Well, I was being glib. Actually they continue to slow, ever approaching stopping but never actually reaching it. I was trying to simplify, but oversimplified — I make similar comments below in this entry, so where you read that things stop, think of it as "slowing almost to but never quite reaching zero". Read the comments thread below for details.

This brings up a very interesting situation. If time takes forever to flow, then how does a black hole ever form? Imagine the core collapsing, and you’re looking at it from far away. You see it getting smaller, but the collapse also appears to be going more slowly because of the time dilation. Like Zeno’s paradox, you see the escape velocity approach the speed of light, but you’ll never see it actually get to the speed of light! Time would stretch out infinitely, and the collapse of the core would appear to you to stop.

No black hole.

But it gets worse. Years ago, Stephen Hawking discovered that black holes can in fact "leak" out mass. It’s very complicated, and has to do with entropy and quantum mechanics, so forgive me if I leave out details. Let’s just say that black holes can evaporate, and go from there.

From the black hole’s viewpoint, time flows just fine. It starts to form, and it starts to very slowly lose mass through Hawking radiation. Over time, billions of years or more, it eventually evaporates away.

But from your point of view, high above the black hole, the event horizon never quite actually forms. It gets closer and closer, remember, but slower and slower. Yet the Hawking radiation isn’t really affected by this. So the two effects compete: the event horizon never totally forms because it would take an infinite amount of time, but during that time the hole is losing mass. So the black hole will actually evaporate before it ever really becomes a black hole.

If you throw something, let’s say a wad of paper, into the black hole, you would actually see the black hole evaporate (if you could wait long enough) before you’d see the paper wad get to the event horizon. So the black holes loses mass faster than it can gain mass and the event horizon can never actually form.

This idea makes scientists nuts. And this is what the new paper is about. Some people have thought that if you take quantum mechanics into account, this paradox may be resolved. What the authors appear to have shown is that QM doesn’t help. The black hole itself, the event horizon, never really forms.

However, have a care here: there is still a massive, dense, highly gravitational object there! So we still have what are essentially black holes in the cores of galaxies and forming when stars explode and all that, it’s just that, technically, well, they aren’t actually black holes.

Get it?

I will note that this is how I understand the situation, and I may have it wrong. This is very complicated stuff! This paper is by no means the last word on the subject — even the experts argue incessantly about it, and I’m no expert. This is a very interesting situation, and I’m quite sure that it is nowhere near being resolved. I have many friends who study black holes and I’m sure they’ll have quite the reaction to this story. If I hear more I’ll post again. I guarantee that this idea won’t, ah, evaporate on its own anytime soon.

CATEGORIZED UNDER: Astronomy, Cool stuff, Science

Comments (104)

  1. Daffy

    A layman’s question: since, as I understand it (and I will never understand it), at quantum level time does not really exist anyway, would that not solve the problem?

  2. baric

    I was under the impression that time at the black hole only *appears* to stop to an outside observer, simply because they are receiving no more information (photons) from the hole.

    Inside the event horizon, however, the black hole is churning away regardless of what an outside observer can or cannot see.

  3. Sounds like it’s time to do an experiment.

    I’ll get the straws and paper, somebody else get the space ship ready. We’re going to the ultimate spitball target.

  4. Kirk

    Now my head hurts. :-)

  5. For a black hole, time literally stretches to infinity at the event horizon. Clocks stop.

    I’m going to have to read the paper, but I’m pretty sure that you have it wrong. Saying “time stops” at the event horizon of the black hole is expressing a misunderstanding of relativity. I don’t know what the paper is about, having not read it, but I do know that this way of talking about it is wrong.

    It is true that the Schwartzschild t coordinate — that coordinate which is the same as time for a distant observer at rest with respect to a black hole — goes to infinity for any object whose path crosses the event horizon. However, that does not mean you can include that “time stops” at the event horizon of the black hole. Indeed, drawing that parallel is the classic mistake of relativity, and similar to the mistake that creates all sorts of seeming “paradoxes” in special relativity.

    In relativity, you can’t compare times unless you’re at the same point in space. Simultaneity of two events in special relativity is the classic example of this. Two events that are simultaneous for one observer are not simultaneous for a second observer moving with respect to the first. The two observers will only agree that the two events are simultaneous if they happened at the same point in space.

    The Schwartzschild t coordinate is a bad coordinate to use at the event horizon of a black hole, just as an “inverse radial” coordinate p=1/r is a bad coordinate to use at the origin of a 2d plane.

    One way to decide if it takes an infinite amount of time for something to fall into a black hole (using just classical GR, not thinking about QM) is to consider the following thought experiment. Suppose Person A is falling into a black hole. Person B is somewhere outside watching. Given unlimited resources (i.e. don’t worry about your energy budget), could Person B wait an arbitrary amount of time and still go in and rescue Person A? The answer is “no.” You can’t answer this with Schwartzschild coordinates, because they hit a coordinate singularity at the event horizon, but you can answer it with Kruskal-Szerkes coordinates. All you have to do is draw a spacetime diagram to show that the event of Person A crossing the event horizon is eventually not in the future light-cone of Person B.

    It *does* take an infinite amount of time for the last photon emitted by Person A just before he crosses the event horizon to esacpe to infinity. It only takes a finite amount of proper time (i.e. as measured on his watch) for Person A to cross the black hole, and the answer of the thought experiment above is also clear. Given that it’s not even really meaningful in relativity to say that “time stops” for the person falling into the black hole, I would say given the three things mentioned above it’s not colloquially meaningful either. The first one is the only one that would lead to that colloquial meaning, and I don’t think it’s good enough given the other misconceptions that the “time stops” statement suggests.

    Consider another experiment. This one is just in special relativity. You are at rest, and your friend, initially at rest with respect to you, accelerates away at 1g. You only have a finite amount of time with which you can send a signal to your friend. From the point of view of your friend, your watch slows down, slows down, until it seems to stop; for the rest of eternity, all the signals she reaches from you are the ever more time-dilated and ever more redshifted signals you send up until that last final moment.

    Does time stop for you? No; it’s just the relativity of space and time that is causing this to happen. But the signals your friend receives from you are exactly the same as if she had been at rest outside a black hole, and you were falling in. In one case, the final time is determined by the initial separation and the acceleration, and in the other case, the final time is determined by the proper time when you cross the event horizon.


  6. Chip

    Probably the phrase “black hole” will continue to stick even though the understanding of its nature changes. Sort of like the phrase “atonal music” is still in use today though the musician who first created it (Schoenberg) insisted that technically it isn’t “atonal”. Some writers have used the phrase “galactic engine” to describe active dense cores of galaxies; a metaphor for an on-going dynamic process that’s still running.

  7. PK

    Daffy, in QM time is a parameter in the theory, rather than an observable. This does not mean time does not exist in QM.

    baric, indeed the in-falling observer will cross the event horizon in finite time. However, the paradox is still there because we are observers who are far enough away so that the curvature due to the real black holes do not affect our clocks.

  8. Rob and baric have it right. You’re making the same mistake as the standard misinterpretations of special relativity. You’re trying to say your observations (far from the event horizon) tell you accurately what’s going on at the horizon itself, and they just don’t. If you’re standing at the horizon you’ll fall through it with no problems at all. In fact, for a large enough hole you won’t even notice that you’ve crossed it from local observations.

    Now, we do know from experiments that clocks “slow down” in a gravity well, but you’re confusing the observational effects of a horizon with the gravitational effects on proper times. Again, for a large enough hole the local curvature at the horizon (the “amount of gravity there”) can be almost zero. That is, a clock might slow no more than it does on the Earth’s surface compared to one in orbit. It’s the outside observer that sees a drastic slowdown, and that’s purely because of the horizon effects, not because of the gravity there.

    In a nutshell: gravitational effects like clocks running slow are determined purely locally by the amount of curvature of spacetime at a given point. Horizon effects like you describe are determined globally by geometric and topological properties spread out over large regions of spacetime.

  9. Phil

    I think my brain just melted.

  10. Rob, baric, John– right. One problem with writing a popular-level article like this is how to simplify things without oversimplifying things. Of course, an observer falling into the event horizon sees no problems at all, but I don’t think that’s critical for understanding the apparent paradox. It’s not the observer at the horizon who sees a paradox; it’s the observer far away. And this is issue that appears to be just what the paper is dealing with: an observer far from the event horizon and what they see. And according to the paper, this observer sees the black hole evaporate before the event horizon ever fully forms. That’s the key issue.

    I probably shouldn’t have said that time stops; it asymptotically slows down for an outside observer. I was oversimplfying. :-)

  11. Gary Ansorge

    The reference to Zeno’s paradox reminds me of a class room discussion of that very paradox, wherein the instructor gave this example:
    “Assume you are entering a room where your girlfriend is sitting on a couch next to the opposite wall. As you enter the room you cut the distance between you by one half in some time equal to T. After some time, 1/2T, you cut the distance in half again. After 1/4T it’s cut in half again. Thus you can see you’ll never get to your girlfriend,,,

    ,,,and from the back of the room came a voice saying,”Yeah, but I can get close enough for all practical purposes,,,”

    Gary 7

  12. There is a confusion of frames here, I think. To the black hole, it collapses just fine, objects fall in just fine, and its evaporation rates reflect the matter inflow and the size of the collapsed black hole. To an observer at infinity, what they will see is the matter of a star collapsing till the outer shell appears to asymtotically slow the collapse at 1 R_s, but at the same time photons from it get infinitely redshifted, so to an outside observer a black hole still ‘forms’; perhaps not in its completely collapsed state, but the edge of what you can still see is completely “black” at one Schwarzchild Radius. Furthermore, Hawking Radiation still behaves as if it was the completely collapsed object, because that depends on QM near the event horizon, and the physical object actually is completely collapsed. So it evaporates as if it was a fully collapsed black hole.

    Now what about the paper wad?

    Well, you throw it in and it appears to stop as it approaches the horizon (OK, I’ve been saying 1 R_s because I’m assuming a spherically symmetric non-rotating black hole, but eh, close enough), but the black hole still gains mass because the wad still enters the black hole and so the Hawking radiation is still controlled by the total mass of the black hole. The wad does appear to slow down and stop — but! the thing dissapears from view, anyway, as it gets infinitely redshifted.

    Of course, this is just the way to fix it conceptually. Mathematically there isn’t a problem either; while the Schwarzchild solution blows up at 1 R_s for the t and r coordinates, if you use an alternate coordinate system like the Kruskal system, you can see there is no actual singularity at 1 R_s — its just a ‘coordinate singularity’.

    Is the paper a preprint? Because this sort of ‘paradox’ seems to be just a problem in conceptualization in reconciling different frames. I may repost as I get time after I read the paper.

  13. Gary Ansorge

    Addendum: I’ve wondered for some time, if we have a particle/space craft traveling at very high velocity, as its V approaches C, it must eventually acquire enough mass/energy to form its own event horizon however, if we then slow it back down, its mass/energy becomes insufficient to maintain the event horizon and ,,,what happens then? Does the matter contained within the event horizon escape all at once or,,,?

    GAry 7

  14. Mister Earl

    From the frame of the paper wad, wouldn’t it appear that time were accelerating for everyone else as it fell? I.E. see suns coalesce and detonate in milliseconds, faster and faster as it dropped in? But having throught for a minute longer, there, the paper wad isn’t actually there that long. I suppose that it would see “ahead” a microscopically small amount, as light that would never have struck it is pulled into the event horizon. Also, the way I, uh, “See it in my head”, the view would change drastically for mister paper ball as well. As the fabric of space is scrunched up towards the event horizon, as the paper ball falls… let me rephrase this. Wording it right escapes me, as I am no scholar. Let’s say the field of view for the paper ball is transcribed onto a sphere, which the paper ball is in the center of, as it falls into the black hole. At first, the BH would occupy only a circular portion of that sphere of view. But, while falling in, that sphere would grow and warp, I think, and eventually hit a point where one half of the sphere of view is occupied by the BH. Falling more would compress the view of the rest of the universe into less than a half of the sphere of view, and to the paper ball, the BH would appear to be warping around it!

    I’m probably waaay off, here, but am I at least barking up the right tree? It seems to me that at the moment before complete black-out, all the incoming light visable to the paper ball would be coming into the sphere of view from a single point, like a non-monochromatic laser.

  15. Okay, let’s see if I can understand this from a philosophical perspective.

    With one paradox, you have “If a tree falls, and no one is around to hear it, does it make a sound?” Of course, the answer is yes. The air still vibrates (sound), but there are no ears to hear it.

    This one sounds more like “If a black hole forms, and we can’t see it, does it really exist?” My gut reaction is to say, yes. It takes the sun’s light eight minutes to reach us, so we never see it as it currently is. The black hole is preventing light from escaping and showing what is going on inside the event horizon, but that still doesn’t stop what is going on inside from happening.

    Yes, I super-mega-oversimplified, but hopefully someone can better say what I’m trying to get at.


    PS. If I’m wrong, someone please correct me. I love paradoxes and learning.

  16. “But from your point of view, high above the black hole, the event horizon never quite actually forms. It gets closer and closer, remember, but slower and slower. Yet the Hawking radiation isn’t really affected by this. So the two effects compete: the event horizon never totally forms because it would take an infinite amount of time, but during that time the hole is losing mass. So the black hole will actually evaporate before it ever really becomes a black hole.”

    That doesn’t make sense.

    It seems to me that masses forming a black hole would need to reach a certain threshold of density in relation to how much it eats (so to speak) before the evaporation rate would exceed its accumulation rate. So it would have to get freakin’ huge or lose its lunch before it would start dying.

    Taking time dilation into account, I see two options in my completely limited understanding of black holes:

    1. What we see as a black hole’s evaporation really exists as its birth in reverse and inside out (since time would – again, from our perspective – go backward faster, the closer to the “center” of the black hole).


    2. The theory about black holes birthing universes has some, er, weight to it, and the black hole evaporation we see really comes from surface tension of spacetime going back to equilibrium after the universe chunk breaks off. Rather like how bubble solution wobbles a bit and flattens out after creating a bubble that then flies off on its own.

    Hm…not exactly mutually exclusive, now that I write them next to each other.

    Or, I suppose, I’ve just completely misunderstood the whole thing and they just die. In any event, it should result in some decent reading material as the experts try to sort this one out.

  17. PK

    Gary, the gravitating (and inertial) mass m is independent of the velocity of the particle. I know some people say that the mass increases as the velocity v gets larger, but without the maths this can be very a misleading statement. What happens is that as v gets larger, the mass seems to get larger, but the momentum is also larger. The invariant mass is the difference between the two (squared), and this always stays the same. Hence the “invariant”.

    You may object that Lorentz contraction will increase the mass density, but again you need to look at the mass density with respect to four-volumes in space and time. Again, this is invariant for inertial observers.

  18. Joshua Zucker

    To follow up on PK’s explanation,
    reminds us that things aren’t so simple, and in particular that black holes don’t just form based on mass density; that’s just a static, spherically symmetric solution. If things are moving, momentum affects things too.

  19. Joshua, good point. In the paper, they appear to be looking at a static, non-rotating black hole, which literally cannot exist in nature. I will admit the math of the paper is well beyond me. I will be asking some friends of mine soon about this! I also want to see what they say about what I wrote. Like I said in the comment above, I want to simplify, but not oversimplify.

  20. Daffy
  21. And according to the paper, this observer sees the black hole evaporate before the event horizon ever fully forms. That’s the key issue.

    I believe this issue was actually solved at some point in the past. For this thought experiment, let’s pretend for the moment that the event horizon has already formed. Firstly, if you throw a wad of paper into a non-evaporating Black Hole, you’ll “see” it hit the horizon at time-coordinate infinity.

    However, for an evaporating Black Hole what instead has been found to happen is that the time-coordinate for the outside observer doesn’t actually diverge – it instead ends up being precisely the time when the Black Hole finally evaporates completely.

    Now, time-delay also affects all the particles escaping through Hawking Radiation, so they’re slowed down as well. Since they’re close to the event horizon, they get slowed down a lot. In fact, almost all of them are delayed enough that you won’t see them until after the time of evaporation, after which you’ll see a slow stream coming out.

    So, here’s the final sequence of events, as seen by an observer:

    1. Wad is thrown in. As it approaches the black hole, time is stretched out for it, so it reflects back photons at a slower and slower rate. It fades from view during this time as the flux of photons decreases.
    2. At the time of evaporation, the last photons from the wad are detected coming back, and the first particles from Hawking Radiation (there’s actually a bit of overlap here).
    3. After the first point in evaporation, more of the particles from radiation can be seen until they all at some time far in the future.

    To extend this to the collapse of a star itself, there’s really no problem. You’d see the star collapse and keep slowing and fading on its collapse. If it’s light enough to evaporate, you’ll see the collapse complete at the time of complete evaporation, and right after this you’ll see the first particles created via Hawking Radiation.

  22. DrFlimmer

    I love this stuff! Black holes are one thing why I’m studying (astro-)physics now and I can’t wait until I’m able to deal with it a bit more and deeper as I can do now!

  23. Stark

    Infophile – so if that’s the case then from the internal reference of an evaporating black hole… does it only exist for a moment?

    I’m not sure that’s clear so let me try it this way. Assuming I have a craft that can survive the ride (impossible, I know) and I fly into a black hole (which is evaporating) then my frame of reference would therefore be moving closer to that of the singularity. Would I then experience the singularity winking out of existence just as I reached the event horizon?

    That is, after all, what an observer sees from an external reference right? The last of my photons that can escape, do escape, and then the black hole itself has evaporated and is no longer a black hole.

    So, if this is the case then is it safe to say that from the internal reference of the singularity it only exists for the very briefest amount of time?

  24. zandar

    call me naive, but I really doubt if real time and space work in such a manner that photons from point a would take forever to reach point b. Relativity is something for which we have only a child’s grasp. One day, or perhaps never, the real nature and identity of black holes will be realized and the math will fit perfectly. Keep trying, humanity.

  25. PK

    zandar, the maths already fit perfectly. It’s just that the correct physical interpretation seems counterintuitive.

    I think this is why so many people (some would say crackpots) try to prove that Einstein was wrong and relativity is flawed. However, there is no reason why our intuition, which is based on everyday experiences, should hold under the extreme circumstances of high relative velocities or strong gravitational fields. Part of getting a physics degree is to come to grips with this new intuition.

  26. Michael Welford

    Years ago I spent many hours with the book Gravitation by Misner, Thorne and Wheeler. ( Note: Wheeler is the one who coined the term “black hole”. ) Now you get the benefit of the 5% or so that I actually understood.

    Time does come nearly to a stop ( as seen by folks far away ) at the surface of a star collapsing to form a black hole, and for folks far away the formation of the event horizon is infinitely far in the future. If you have the misfortune to be on the star as it collapses the you see the collapse occur in finite time. As Rob Knop noted, if folks far away wait too long they will no longer be able to effect the collapsing object. This because you or your probes will also be slowed as you approach the forming black hole.

    All this has been understood for a long time and was suggested by the old name for black holes: “frozen star”. As the BA has observed elsewhere, “words have impact” and the label “black hole” has led to an emphasis on horizons to the extent that basic facts of black hole formation are ignored. So even quite knowledgable individuals never learn them.

    Here’s irony for you. The best explanation of the basic facts about black hole formation that I’ve ever seen occurs in Gravitation in a dialogue meant to justify the label “black hole”. But, the label “black hole” itself leads to many of those basic facts being ignored! I favor the name “collapsar”, myself.

    In recent years some astrophysicists have claimed that magnetic fields can significantly retard the formation of black holes. I dunno. This stuff is way over my head. But if you’re interested go to Wikipedia and look up ‘Magnetospheric eternally collapsing object”.

  27. Bryan D.

    Boy this Black Hole stuff makes me think of Schrödinger’s cat for some reason. :)

  28. niin

    If it take forever to reach the event horizon, then two black holes can never merge into one big black hole.
    How do you explain the super massive black hole at the center of the galaxy?
    Why do you think, that Hawking radiation is not affected by time?

  29. DenverAstro

    Im sorry, I apologize in advance but I just have to say it…

    I KNOW Black Holes exist, my ex-wife had one and it had a HELL of an escape velocity! hehehe

    Im just a graphic designer and web developer with a amature hobbyist interest in astronomy…this stuff is way too hairy for me :o) But it is just interesting as heck. I thought they had confirmed the existance of Black Holes observationally by the effects of all the stuff around them. Dust and gas falling into them and heating up enough to emit X-Rays and whatnot. Is that wrong?

  30. Here’s a sort of off-topic question:

    Do the expressions “infinitely small” and “infinitely large” have any scientific meaning, or are they only convenient ways to talk about things that are big or small beyond measure?

  31. I object to the use of hypothetical black holes as the dumping ground for office waste! The wad of paper should be recycled, not used to litter a majestic cosmic feature! And no spitting tobacco into black holes either!

  32. Ah, so there are yet more contradictions to Black Holes than previosuly imagined. Perhaps we need some more Dark Stuff to balance the equations? Really, isn’t it just time to go back to the drawing board, admit that cosmology is in crisis, and start over! Black Holes? Utter drivel!

  33. Alice says : Black Holes? Utter drivel!

    So, if you don’t understand how the carburetor works then obviously the car doesn’t exist?

    I have a question about this .. if the stuff falling in never truly reaches the ‘black hole’ what happens to it? If you have entire suns and solar system falling in then would that just create multiple blackholes as all that mass crushes together while racing for the singlularity?

  34. George Jones

    I may have missed it, but it seems to me that everyone here has missed the main (and controversial) point of the paper: *no* observer (hovering, freely falling, blasting away with rocket *towards* the surface of the collapsing object, etc.) experiences an event horizon because there is no event horizon to experience.

    This contasts with the standard view: stationary observers hovering above the collapsing object never see the event horizon form, but an observer sitting on the surface of the black hole ends up inside an event horizon, and a freely falling observer also can cross this event horizon.

    From the paper: “The infalling observer never crosses an event horizon, not because it takes an infinite time, but because there is no event horizon to cross. As the infalling observer gets closer to the collapsing wall, the wall shrinks due to radiation back-reaction, evaporating before an event horizon can form. The evaporation appears mysterious to the infalling observer since his de tectors don’t register any emission from the collapsing wall Yet he reconciles the absence of the evaporation as being due to a limitation of the frequency range of his detectors. Both he and the asymptotic observer would then agree that the spacetime diagram for an evaporating black hole is as shown in Fig. 9. In this picture a global event horizon and singularity never form. A trapped surface (from within which light cannot es cape) may exist temporarily, but after all of the mass is radiated, the trapped surface disappears and light gets released to infinity.”

  35. Bryan: Schrödinger’s Cat has more to do with Hawking’s resolution of the information problem. Basically, as a black hole evaporates can you get back the information of what fell in? His solution is that really the universe exists in a superposition of the states where a black hole forms and those where it doesn’t, and you can get all the information back from the latter.

  36. Remek

    My question is:

    How can a black hole *not* have any rotation?
    I mean, none at all. Isn’t that extremely remote, almost impossible in reality?

  37. Wow. I think I shouldn’t have had that last swallow of rum before I read this. Or should it be that I need some more rum?

    My brain hurts…

  38. It seems to me that it makes absolutely no sense to say “no event horizon ever forms, because distant observers never see it happen.” Relativity paradoxes are strongly connected to confused ideas about what is simultaneous (same time, but separated in space) and, um, simul-place-e-ous (same place, but separated in time). Unless the observer is actually present at both events, his opinion cannot be relied upon, because other observers will disagree.

    Now, George Jones pointed out that the paper asserts that there ARE no observers who are present at the formation of the horizon, which is a totally different and radical assertion, that I can’t understand or believe in right now …

    Remek: No, it’s pretty much impossible for a black hole to form with no rotation, at least naturally. All the contraction mechanisms tend to create angular momentum.

    A sufficiently powerful intelligent race could probably set things up to form a black hole with as little rotation as desired — but even then it might be impossible to reach zero, or at least to be sure of reaching zero.

  39. dan

    man, that was awesome.
    i need a cigarette.

  40. Folcrom

    It doesn’t seem so complicated to me.
    From the perspective of the Black Hole,
    it is niether here nor there what the outside observer sees.
    It is was it and cares not, whether the observer sees it or not.

  41. BH1602

    I thought the whole point of Zeno’s paradox is that it isn’t really a paradox at all. It’s more like a joke. You can prove ad absurdum that an arrow can’t go through an infinite number of points, but then you can still go out and shoot an arrow into a target. Similarly, if a black hole is there, then it got there. You can prove it isn’t there because it didn’t get there, but it’s still there. So the proof that it can’t have formed may be logical, but it isn’t accurate. Not only THAT, but can you prove you’re not a duck?

  42. Folcrom

    Two characters sitting in space.
    One called “Steller Core” the other called “Observer”

    Steller Core:
    Im collapsing!
    Im collapsing!

    So you are!

    Steller Core eventually collapses into a singularity and gives rise to another character “Black Hole”, yet “Observer” sees it not.

    Black Hole:
    I am, I exist!

    Steller Core, you still collapsing?

    Steller Core:
    Im collapsing!
    Im collapsing!

    Steller Core, your boring!
    You say you are collapsing, but you never fully collapse!
    The saga never ends, should I watch for eternity!

    Black Hole:
    I am I exist!

    Observer sees him not.

  43. Jingo

    Bit of a different flavour of question. Love the NASA/ESA drawing of the rotating hole, but shouldn’t there be some sort of red-shift to the infalling material close to the horizon?

  44. Murff

    I still have trouble grasping all that matter compressed to such a small size. Would a Singularity be smaller than a proton? breadbox? Rhode Island?

    I can understand matter compressing dramatically, but why/how can it possibly compress that far?

    Time to go do some reading!

  45. PK

    Murff, a singularity is really a mathematical point with infinitesimally small size. How matter can collapse that far is still a mystery, and indicates that this is a regime where general relativity breaks down. It is thought that quantum gravity will come to the rescue when it is properly developed.

  46. No matter how much time it takes, you’d never quite make it there, stylish footwear aside.

    Zeno’s Pair of Doc’s

    I’m so, so sorry. But the nature of the paper was about to make my head pass the Chandrasekhar limit.

  47. Michelle Rochon

    …*Sniffs* Hmm, smells like my brain’s on fire. I think it shorted while I read this…

  48. tussock

    So what they’re saying isn’t just that when observers at distance see us go futureward before we cross the event horizon, it’s when _any_ observer, anywhere, inertial, rotating, whatever, when they see a body approach what they see as the event horizon, it doesn’t cross it from their point of veiw, it just goes futureward.

    It actually seems intuitive now I’ve thought about it. If an observer is inside the standard definition event horizon, what _they_ see as the event horizon (the radius from inside which light cannot reach them other than via Hawking radiation) is necisarily inside their current distance from the gravitational centre. It must be.

    So from the veiw of the distant observer, a faller emits ever more red-shifted light as his time rate slows and he passes into the incomprehensibly distant future. From the veiw of the falling observer, only a few seconds pass for our distant friend as we are blasted apart by the burst of a giant star turning itself into pure energy, aka Hawking radiation (or more likely spagettified first).

    So the star collapses and radiates away completely in a couple of seconds (from it’s own point of view), it just takes a very long time indeed for that information to reach the rest of us. Of course information is preserved, it’s never lost.

    All a rather neat way of thinking about it. Be interesting to know if it’s accurate.

  49. niin

    Hawking radiation is normally though to work on pre-formed black holes.
    How can Hawking radiation evaporate the non-formed black holes?
    Why can’t light escape the non-formed black holes?

  50. Gary Ansorge

    I think we should be hearing from either Roger Penrose or Prof Hawking about this.

    I’m pretty sure I’m not competent to comment on this aspect of black holes however, as far as detecting the event horizon is concerned, it seems to me that the emphasis on detection is misplaced. Of course we can’t “see” the event horizon. Since light can’t escape, there is no “seeing”. As far as matter collapsing to “infinite” density is concerned, what we really mean is “density so high as to be approaching a really large number but never really getting there,,,”. The assumption about infinite density requires there be no limit to the frequency of energy and we don’t know that for a fact. aside: E is proportional to plancks constant times the frequency and as E=MC^2 therefore MC^2=Plancks constant times the frequency. Thus we see that mass and frequency are directly proportional,,,and related by Plancks constant.

    Matter is assumed to collapse inside the black hole because the force carrying particles of electromagnetism cannot exceed light speed, as they would have to do in order to propagate uphill, so there is nothing to keep the matter from collapsing inward however, there may be some other mechanism to prevent the matter from collapsing all the way to zero radius, as in some limiting frequency to electromagnetic phenomena, ie, when the frequency gets high enough, that’s enough to overcome relativistic limitations. At this point in time we just don’t know and it’s gonna take someone with a far greater grasp of Quantum mechanics than I have to figure this out,,,
    ,,,but that don’t keep me from speculating,,,

    Gary 7

  51. Infophile – so if that’s the case then from the internal reference of an evaporating black hole… does it only exist for a moment?

    I’m not sure that’s clear so let me try it this way. Assuming I have a craft that can survive the ride (impossible, I know) and I fly into a black hole (which is evaporating) then my frame of reference would therefore be moving closer to that of the singularity. Would I then experience the singularity winking out of existence just as I reached the event horizon?

    That is, after all, what an observer sees from an external reference right? The last of my photons that can escape, do escape, and then the black hole itself has evaporated and is no longer a black hole.

    So, if this is the case then is it safe to say that from the internal reference of the singularity it only exists for the very briefest amount of time?

    I think the problem you’re having here is that you still think that multiple observers would see things the same way. In fact, it’s the core tenet of Relativity that this isn’t true. In this case, while an outside observer would “see” the Black Hole existing fully-formed for only a moment (if it does ever evaporate, otherwise they’d never “see” it fully-formed), an observer who falls in would see that moment stretch out to a long length of time in which the Black Hole exists.

    Back on what the paper actually says: It seems to me that what they’re trying to say is that during the formation of the Black Hole, the Hawking Radiation should be much greater since the amount of mass below the even horizon is much less. However, there are a few things they seem to be neglecting:

    1. Hawking Radiation only works because of the existence of the event horizon. Without it, you can’t split up the worldline of the pair-production-created particles so that one falls in while the other escapes. Additionally, if there’s anything but zero energy density outside the horizon, the radiation can go in either direction, so there’s no reason it has to evaporate. (Note that here I’m talking about where the event horizon will be in the future, since this occurs during formation.) Also, since we have the CMB everywhere, there’s never actually zero energy density outside that event horizon, and the flow of energy in because of it is why massive Black Holes never evaporate.

    2. Hawking Radiation isn’t the only thing contributing to mass flow across the horizon. All the mass being pushed in by the collapsing star is a huge part of it, too, and this is orders of magnitude greater than the Hawking Radiation. Once enough of this is inside, the horizon forms.

  52. Thomas Love

    Perhaps all astronomers believe in black holes, but I’m a physicist and I don’t believe black holes exist. They are a relic of General relativity, which is a theory of gravity only. There are other much stonger forces in nature which would keep singularities from developing. Then again, I don’t believe there was a big bang (that’s creationism moved back a few billion years) and the universe is not expanding (general relativity is not a theory of light).

  53. Stark

    Infophile – Thanks, that helped my understanding a great deal and my brain has now quit hurting me out of spite.

  54. To T. Love, above.

    What do you propose as alternatives to black holes, BB, and expansion? Keep in mind that GR is demonstrably correct to one part in 10 to the 22nd.

  55. BH1602 asked:

    Not only THAT, but can you prove you’re not a duck?

    I do not weigh the same as a witch (I happen to have an Aunt who is one), therefore I am not a duck.

    Seamyst asked:

    Wow. I think I shouldn’t have had that last swallow of rum before I read this. Or should it be that I need some more rum?

    I’m about to do an experiment on that. I’ll get back to you.


  56. Ataullah

    sooooooo…….who do you guys think will win the 2008 NBA finals!?

  57. miller

    I once asked a friend how gravitons escape from a black hole. He started talking, but I couldn’t tell what he was saying.

  58. Jeff the Addled

    i is in ur brain pwning ur cells

  59. PK

    A black hole does not produce gravitons, unless the black hole is in a close orbit with another heavy object. In this case the gravitational waves are produced outside the event horizon, and they have no trouble reaching us.

    It is very much like electrostatics: a charge does not produce light (photons) unless it is accelerating. That does not mean there is no electric field.

  60. George Jones

    The global, observer-independent Penrose diagrams of all of spacetime in Figures 8 and 9 of the paper illustrate well the differences between the standard view and the paper’s view. Figure 8 (same as page 419 of Carroll’s text) has an event horizon and a singularity; Figure 9 has no event horizon and no singularity. Since these are global, observer-independent diagrams, the paper puts forth the view that no observer see an event horizon or a singularity.

  61. Irishman

    JanieBelle said:
    > I do not weigh the same as a witch (I happen to have an Aunt who is one), therefore I am not a duck.

    JanieBelle, you rock!

  62. :)

    Thanks, Irishman. You’re pretty spiffy yourself.


  63. Folcrom

    I weight the same as a Witch!
    I must be duck!

  64. I haven’t read the paper yet, and it’s quite possible that they’ve come up with something really novel this time.

    But it’s worth noting that arguments of this sort–claims that black holes cannot exist, based on some argument (often quantum-mechanical) having to do with time dilation at the event horizon–come up every couple of years or so and are generally mistaken. (The last one came from George Chapline who had some sort of weird theory about how black holes were really “dark energy stars”; I did not find it convincing and neither, seemingly, did most physicists who work on this stuff.)

    Your summary of the argument about time dilation and Hawking radiation is identical to one I came up with about 21 years ago as a college freshman, and I had a lot of fruitless arguments with physics professors about it before I realized that at least according to the standard treatments it was wrong.

  65. NR

    There is a certain sense of knowledge in all aspects surrounding current black hole “theories” that is misleading. No one really knows if any of the things we discuss in our current best “proved” theories do apply inside a real black hole. What we have is just an “educated guess”, at best. As this paper might show (sorry, didn’t read it yet), we do not even agree on what we can see (or have) on the outside of the thing.

    Sure, time contraction is an effect that we experience outside the thing when we measure events that we might expect to see near it (those really affected by it’s gravitational force). But we don’t really know how time events are related inside and outside the thing or even if that relation is possible in someway. As far as we know, it is not possible. So, saying that events inside the horizon of the thing are slower, faster or do run at the same rate then outside is as meaningless as saying that “yellow” just tastes nice. From our point of view those things occur “outside” our universe and comparing times is meaningless: a star can take the rest of the time this universe has available to shrink inside the horizon (so, no GR paradox…;-) or can do it in the Plank time. For us, that’s history and we cannot know it.

    After that thing shrink bellow the horizon size (even if it does ever form) the “practical” effect will be the same one we see today (in theory there’s a big difference, but we don’t really have a theory that completely explains the situation). But the implications are different: if the event horizon never forms, then, in theory, we can see through it and the thing can no longer be called a black hole. I mean, the horizon forms when the escape velocity is equal to the light speed. And if it never forms then the escape velocity will always be a little less the “c”. If so then is not only the Hawkings radiation that will evaporate it’s mass: the thing will be throwing away (for a big hole) huge amounts of “highly red shifted” radiation (whatever that might be). This would be detectable…

    But for a really, really big hole time contraction and space distortion would be small near the event horizon, let’s say not bigger then near our Sun. In this case, if the event horizon never forms and light can came out, than we might see normal radiation, without a real high shift, caming out of it… what would make it look like any normal (quasi) star object out there.

    Wouldn’t this be the end of black holes as we know them today?

    PS. Got to read that paper, it might explain how light remains inside the thing when there is no event horizon…

  66. …Looking at the paper itself, I notice that the authors at least recognize that the radiation they’re talking about is *not* conventional Hawking radiation, and they acknowledge the traditional treatment of the subject that is markedly different from what they claim. That gives me some confidence that they’re not making an elementary mistake.

    However, it’s worth noting that the case they’re looking at is a greatly simplified toy model: a collapsing domain wall in an unrealistic field theory that supports such things, rather than a collapsing star. Personally, I have my doubts that their result is going to hold for all possible cases of collapsing matter, since the formation of an event horizon is such a global property: it’s hard to see how dramatic events prior to the formation of an event horizon could happen if, say, the black hole has the mass of a galaxy and an extremely low density.

  67. There is a certain sense of knowledge in all aspects surrounding current black hole “theories” that is misleading. No one really knows if any of the things we discuss in our current best “proved” theories do apply inside a real black hole. What we have is just an “educated guess”, at best. As this paper might show (sorry, didn’t read it yet), we do not even agree on what we can see (or have) on the outside of the thing.

    Sure, but there’s a general sense, which I think is correct, that any modification of current theory to make black holes not exist would be very strange indeed, stranger than the existence of black holes.

    The reason is that according to general relativity (which holds in all domains we have tested) the existence of an event horizon is a global property of the spacetime rather than a local one, and local physics at the event horizon itself can be completely unexotic. So GR might break down near the singularity, but it’s hard to see how things could drive it out of its domain of application at the event horizon in all cases where an event horizon can form; locally, the event horizon can be a not-very-special place.

    Jacques Distler pointed out when he heard of Chapline’s earlier ideas that they required faster-than-light communication, so that a patch of spacetime near the event horizon can even know that an event horizon is in danger of forming so as to produce the necessary anti-event-horizon reaction.

  68. 0x0b0b

    Cheers!! I marked this discussion and knew it would be bearing fruit in a day or two. There is more info here than I can digest! Reading this blog has inspired me to read all sorts of physics realted stuff in the past year. What happens if you are going the speed of light and you turn your headlights on? These though experiments are great, and I haven’t seen too many DUH responses at all.

    The term singularity seems to me as the same as saying that time stops. The observer in the singularity wouldn’t notice the distortion in length any more than he would notice the time dilation.

    While we are playing with the classic extreme conditions… I read that entropy has a minimum surface area. If there is a limit to the ammount of information that a single particle can hold, then we can’t keep smashing atoms into smaller parts, there must be a lower bound t that.

    If this is true, volume would truely be a relativistic effect and be a derived metric depending on an observer and his measuring sticks and the direction they are pointed. We don’t see volume mentioned in any of these types of discussions becuase it would be completley misleading using all of these different coordinate systems (that I don’t understand anyow) and different time-space tranlsations that it takes to make up the points of a 4 dimentional volume.

    I think that the last couple of comments have bent to the direction that the guy falling into the singularity observes life as usual, and that the outside observer does not see an spahgettification. He sees the guy stop in time.

  69. 0x0b0b

    Addendum: Sorry I forgot my point.. That is of course we don’t ever see the event horizon form. It never does to us. DUH

  70. John

    This is ludicrous! Yes – from the outside observer it LOOKS like anything that approaches the black hole slows down to infinity – but looks can be deceiving – its only the light from the object that slows down (that the observer can see). The actual object itself continues on towards the black hole – never to return.
    Eg) say if someone blew up the sun – but to you its looks like the sun is fine. Wait 8 minutes and then you will realize you were wrong. (But in this case you would have to wait forever-but were always wrong)

  71. icemith

    Most (well, 99% +/- x) of the above comments I have no arguments with, namely because I am struggling to understand it, I just have to accept what is said.

    But I do have some questions or ideas that need clarification, so I hope I can even express them with some semblence of credibility.

    • There was mention earlier of “fade”, that light would fade to ?? (nothing or at least invisibility). Would this be really a Red-shift? And it drops down to an invisible frequency that we cannot see, or our instruments cannot register, meaning that, although it is still there, it is un-observable?

    •Black Hole concept. If the current depiction, as exemplified by the name itself, is portrayed as the ubiquitous whirlpool, or even the newer idea as in the first image at the head of this blog, then I cannot see it without the colorful rendition as it should be. There would be a graduated color rendition of the outer “lips” of the blackhole “funnel” as the color shift of light that does reach us, changes depending as to whether the spin of the BH is receding or advancing relative to our observing position. Of course in the actual vicinity of the singularity where light could not escape it would be black as usual.

    Or is a BH better depicted as a sphere, not a funnel, and material is falling towards it from all directions? The same coloration would exist again depending on the spin of the BH – receding/advancing etc, giving a technocolor view. Even from a polar view.

    • Now for an advance on the previous ideas. What about a “binary” set-up? Two BHs approaching each other, spinning as usual, would mutually effect each other, and the stronger would cause the other to slow down. It would reach a static, zero position and then probably spin the other way. Or would it? Or is the first proposal nonsense anyway? ( I haven’t thought about the effect if both are spinning in the same direction, though I suppose the spin would add before combining.)


  72. There was mention earlier of “fade”, that light would fade to ?? (nothing or at least invisibility). Would this be really a Red-shift? And it drops down to an invisible frequency that we cannot see, or our instruments cannot register, meaning that, although it is still there, it is un-observable?

    That’s part of it. An object falling into a gravitational well acts just like an object accelerating away from you. So, image such an object, which is shooting out 1 photon per second (just imagine it, don’t quibble) and accelerating away from you. When its speed is a significant fraction of the speed of light, in the time between photons being shot out, its moved a fair bit away from you. This means that the second photon has to travel farther to reach you than the first, so it takes longer to get to you. Add this extra time it spends traveling to the one-second delay before it’s sent, and it gets to you after more than a second has passed.

    As the object gets very close to the speed of light, this delay approaches infinity. This means that the number of photons you’ll receive in a given amount of time approaches zero, so the intensity of the light from the object also approaches zero. In this sense, the object “fades” in that the intensity of the light from it fades to zero. Of course, there’s nothing stopping redshift from also occuring at the same time, so there are two factors making it harder to see.

  73. kroosing 2 '37'

    Zeno’s paradox is indeed a farce, because it is not about the hare and the tortoise, but about the human activity of measuring their consecutive positions -consequential to their speeds- by means of a unit. When the hare closes in on the tortoise, at a certain point the distance will become smaller that the unit and the hare passes from a negative distance to a positive (he comes ahead).

    Now the paradox is created by decreasing the unit ad infinitum, but decreasing the unit comes down to introducing negative acceleration for the hare, as such creating a new situation: Zeno’s hare doesn’t slow down because your ruler shrinks.

    But that’s just my kind of logic and I don’t know how this applies to black holes but it looks like what Philip says: “a confusion of frames”.

    Love this dicussion though. It feels like … well, deeply spiritual 😉 But hey, if there will ever be any physical reality to religion, it will have to be at the other end of a black hole, hopefully acquiring enough escape velocity to break free from the singularity. Way too fundamentalist that is.

  74. niin

    why do the speed of stuff falling into the black hole approach the speed of light?

  75. icemith

    Thanks infophile, but I am also curious as to what happens (to the maths reckoning) if one works with the concept of “wave” theory as pertainong to light emission, instead of photons, or even packets of them?

    Or is that theory now obsolete?


  76. Keith

    Niin, he said “acts just like” something getting closer to the speed of light. In his example it’s someone accelerating away from you. In the case of a black hole, it’s gravity slowing the photons (the more gravity, the more they are slowed). From the point of view of an external observer the two effects are equivalent.

  77. Ken G

    Very high level of discussion here, with what seems like the correct perspective about the global nature of the event horizon mentioned many times. The paper may be right or it may be wrong, but I don’t see it as solving any “problems”– the universe will be one way or the other whether we see it as a “problem” or not. Indeed, shouldn’t we be asking ourselves if it is even a part of scientific thought to ask the question whether or not Black Holes “really exist”? The scientific question is, which is the best model for understanding these objects, one that invokes an event horizon or one that does not. As usual, all we will ever be able to do is make observations to answer that, and we will never know what “really exists”. It is not a philosophical question, it is a question of which model best explains the observations. So– what observations are we talking about?

  78. niin

    He never said anything about slowing photons.
    Infophile said: “As the object gets very close to the speed of light, this delay approaches infinity.”
    Why would the object get very close to the speed of light?

  79. AMOObserver

    I think our universe is inside an event horizon.

  80. scotchtape

    What actually happens to the person falling into the alleged black hole? Does this that, were I to fall into a black hole, it would evaporate before I reached the almost-singularity, leaving me alive, but billions of years in the future? Or would I die right away but no one would ever see me die?

  81. tussock

    Scotchtape: for the black hole to evaporate, it must turn it’s mass into energy. That’s a lot of energy, so much that you certainly will not survive it all passing you on the way out if it happens quickly from your perspective. Also with the spagettification, very nasty tidal effects eventually. Other problems too.

    Also, not billions of years, but billions of billions of billions, of billions, give or take.

    And you would die pretty quickly from your perspective (blown apart by the complete mass to energy conversion of a large star as it’s time-perspective aligns with yours), but super slow and way big far in the future from the perspective of a distant observer.

  82. RussT

    Einstein was on the right track, BUT he did not have enough information to structure SR and thus GR correctly!

    Einstein knew nothing about ‘Exotic Matter’/Non-Baryonic Dark Matter, SMBH’s, or Voids.

    And, even before that ‘science’ made some VERY BIG decisions that pertained to the ‘universe as a whole’, without having ‘enough’ information!

    So, when they say that ‘The Laws Of Physics’ break down at ‘singularities’, they are correct!

    That simply means that the ‘singularity’ ‘inside’ black holes is just ‘FINE”, BUT the Laws of Thermodynamics NOT allowing anything to go ‘through’ MBH’s (Not steller ones, they are NOT powerful enough to go all the way through space/time) does ‘blow up’ and should never have been made a LAW!

    SO, the “Naked Singularity” simply cannot even exist (Cosmic Censorship is true!), and “Science” has unwhittingly ONLY been looking at ONE side of the equation from the very beginning!

    The BB Naked Singularity “closes” the system from anything outside, and our universes SMBH’s are ‘closed’ at their Singularities, from anything leaving the system.

    SO, just Time reverse a SMBH ‘straight out’ of that ‘other universe’ to ours (an Einstein-Rosen Bridge), each of ‘their SMBH’s’ equalling one of our Voids, and that is where the “Exotic Matter” is entering ‘our universe’ and makes up ALL of our NON-Baryonic Dark Matter ‘space’ and is traveling at “c” in every/all directions (96%, yes this =’s DM/DE). That is actually Gravity/Point Particles. Lisa Randall/Gravity “Leaking” to our universe.

    Now comes the tricky part…that means that ALL of ‘space’ is gravity, traveling at “c”, and that is actually the “Strings”/That become Branes, and when that Gravity ‘collides’, THAT makes our SMBH’s and the High Energy Gamma Radiation that makes the electrons/protons for each galaxy.

    That, quite simply, is “AN OPEN SYSTEM” the ‘Science’ not only has NEVER even looked at, BUT has defined so incorrectly/tightly, that it is actually CAREER SUICIDE for it even to be suggested!

    Oh, BTW, the time diemma goes away at the event horizon here as well.

  83. icemith

    Phew, after that , what can I say?


  84. Ivan


    What happens if you are going the speed of light and you turn your headlights on?

    If you are going at the speed of light… your time has stopped to all others.. so it kind of woult take you eternity to get those lights on 😉

    An other Ivan.

  85. Nelson

    Wouldn’t space itself be swallowed up by a black hole as it passed from one region to another?

  86. poctsrqgdbh

    The rambling, accusatory style and loose grasp of facts and theory in RussT’s comment reminds me of Gene Ray’s Unsurprisingly, it also gets quite a few points on John Baez’ crackpot index (and 30 points alone for suggesting that ‘in his later years, Einstein was groping his way toward my explanation’!).

    To anyone reading this, check out that crackpot index. It’ll make you laugh, but it works pretty well; it’s very much “ha-ha only serious”:

    So called “exotic/dark matter”, etc. are unobserved phenomena that are predicted by theory. If Einstein (or anyone) had known about those things, the body of theory they historically developed would already describe these phenomena, and no modification would be necessary. Your accusation unwittingly supposes the validity of the theory you attack.

    Science makes “decisions that pertain to the universe as a whole without having enough information” you say? No; science DESCRIBES the PARTS of the universe we have already observed. Newton failed to describe relativistic velocity because he had not observed such velocities, not because he was stupid or because he considered and decided against it. Scientific laws are descriptive, not authoritative. Laws tend to be generalized with correcting terms added rather than make wrong turns followed by U-turns. Mistakes are usually “too vague” or “fails to describe a few newly discovered cases” and not “totally, unequivocally wrong”. Should Newton never have called his descriptions of motion “Laws” simply because he might not have had all the information, even though they described all the information he could observe?

    The rest of the post smacks of an author who had skimmed “The Elegant Universe” and thought themself and expert on cosmology, or M-theory at least. One of the principle objections to the superstring description is that its predictions are not observable, even if some do happen to be testable hypotheses in principle. Why wouldn’t you hold string theory to this standard if you would hold Newton, Maxwell, Einstein et al. to it?

    “Oh, BTW, the time diemma goes away at the event horizon here as well.”
    And I’m sure you would be able to to recognize that derivation if it bit you on your face, AND talk about its assumptions, in just as offhand a manner.

    If everything is quite quite so obvious to you, perhaps you would care to fill in Dr. Witten, Dr. Greene, Dr. Randall, and others on the details. Phil would probably like to know too, since you’ve made such a claim on his ‘blog.
    @ Nelson:
    That’s really an ill-framed question in the first place. Space (spacetime, ahem) isn’t a ‘thing’ to reside within a black hole or contain thermal energy or other such things familiar from experience with matter. When we say “fabric”, it’s for lack of a better word, and unfortunately also of a better analogy. Space doesn’t fall into a black hole and stay, as do things like matter. Spacetime is distorted by the mass of the matter in the black hole, just as it is distorted by any other matter; it’s a question of degree and not kind. As a massive body moves through spacetime, the spacetime near it distorts in ways we can describe with physical ‘laws’ (mathematical models!). Whether that body’s escape velocity is greater or smaller than the speed of light is a side issue, and an academic and arbitrary one with admittedly interesting observable effects.

  87. Logan

    so is the stuff in a black hole like string theory type stuff??? but like string theory by string theory??? lol

    And with time *slowing down to almost a stop but not quite reaching there* since it exists doesn’t it mean that it needs to be going at the same speed or what every you want to call it as everything else is happening.

    Or does time not really exist and we just want to say when something happens.

    As everyone else has said “i think my brain just melted!”

  88. Logan

    instead of happening i should have said going

  89. G...G

    jingo your joke is laim- is it a joke? Jainebelle i agree with you and Nelson no, no your so wrong in so many ways.

  90. OW OW OW OW OWreading the main thing then robs then everyone else’s OWWWWWW haha i kinda understood what ya all said AND I”M 13!!!!!!!!!! YAY ME

    i had a thought: what if a blackhole is just a matter converter yeah with the dense gravity and such but when it gets sucked in the matter gets converted into energy then spit out as the jet stream of energy; so now we know how its formed and were it goes after its sucked in………..did that make any sence?

  91. Seehart

    There is a distinction between an event happening and me finding out that an event has occurred.

    Correct me if I am wrong, but my understanding is that what I see now is distinct from what I consider to be happening now in my reference frame. To illustrate, consider a really trivial SR case. When I look at Alpha Centauri in my telescope, I consider what I see to be what happened 4.37 years ago in my frame of reference, not what is happening now in my frame of reference. I know that what is happening now at Alpha Centauri will take 4.37 years to reach me. (I am ignoring the difference in velocity between myself and Alpha Centauri, so both are in the same inertial from of reference).

    Likewise, what I see now when I look at a black hole is not what I consider to be happening now in my frame of reference. When I look at a (forming) black hole I see things slow down asymptotically to zero. This has been described as an “optical illusion” caused by the fact that photons take longer to reach me as the escape velocity approaches c. This seems to be a misleading, though partially correct, description.

    My current understanding is that the passage of time actually slows down near the (forming) event horizon in the frame of reference of a distant observer, even after taking into consideration the travel time of the photons. This is tricky because two distinct (not even complementary) phenomena imply the observation of things slowing down, the optical illusion caused by ever increasing travel time of photons on the one hand, and relativistic time dilation on the other. Or do I have it wrong? Are these two phenomena complementary rather than distinct?

    A related source of confusion is sometimes seen in sci-fi B movies, when you hear phrases like “…meanwhile, back in the present….” What the heck does “meanwhile, back in the present” mean? Anyway, if the time dilation at the event horizon is merely an “optical illusion” due to the fact that I have to wait forever to actually see the black hole form, even though I know that really it has already formed, then I can say things like “meanwhile, back at the black hole”. Otherwise, I have to say that as far as I am concerned, the black hole will never form.

    I don’t think that it is quite correct to say this: “Hey, it looks like that neutron star is almost frozen. But that’s just because I’m looking at what happened millions of years ago. The photons describing what’s happening now will never reach me since it is a real black hole by now.”

    More correct would be this: “Hey, it looks like that neutron star is almost frozen. But that’s just because I’m looking at what happened millions of years ago. The photons describing what’s happening now will take a very long time to reach me. Nevertheless, my understanding of physics tells me that even now, it is not yet a real black hole.”

    If it is the case that black holes do not form in finite time in my frame of reference, then it is also the case that no information leaves my version of the universe. No matter how long I wait, it is possible in principle for any object (including any part of the collapsing neutron star) to suddenly decide to send me a message (since escape velocity is not yet c), which I will eventually receive. Therefore I will never experience the phenomenon of information loss.

    If my version of the universe (i.e. the universe as described by my frame of reference) will never lose information to black holes, then what about that wad of paper? Well, the wad of paper experiences nothing special when crossing the event horizon. All the information of the universe is available to the wad of paper, so the wad of paper has nothing to complain about (other than being mercilessly shredded). Unless I improperly combine these two distinct frames of reference into one interpretation, I don’t see the problem. What observer can say that information is being lost?

    Let me put it another way. Assuming that I can easily create a 20 solar mass neutron star destined for collapse in my lab and I have nearly Godlike powers of perception (subject to the limitations of quantum mechanics) what experiment can I do that detects the phenomenon of information loss? Quantum mechanics demands that we pick no more than one observer to witness our experiment. It seems to me that it would be completely improper for me to consider the frame of reference of an in-falling observer when attempting to model what will happen in my experiment with me as the observer.

  92. Seehart

    My confusion about physics times my incertitude that I am not a duck is greater than h. Therefore, since I am a witch, and I want to understand physics better, I should not weigh myself.

  93. Seehart

    Please excuse the typos.

    First paragraph should end with “… so both are considered to be in the same inertial /frame/ of reference).”

    The main thing that I would particularly like to get confirmation on is this: Time dilation approaching infinity at the event horizon is a fact in present time, in the reference frame of a distant observer (as opposed to an artifact of waiting for light to arrive).

  94. Amilius

    In resume black holes are weird, full of mysteries, beyond the understanding of the commoner. Just like any religious dogma you can only crouch your head and believe the dogma. Any heretic will be excommunicated. Specially the one that demonstrate that the dogma contradicts itself. We are doomed to remain outside the understanding of the sacred ‘mysteries’… forever XD

  95. Has anyone calculated the amount of mass required to form a black hole lately? It’s an exercise that would greatly clarify the premise of this article. An event horizon cannot be observed until a black hole is created nor can a singularity be examined. Until it is created on paper anyway. This would eliminate the search for ‘dark matter’ also I believe.

  96. Bob Black Hole

    Black holes are really cool. Would someone please jump in one with a video camera taped to their head so we can see what it’s like? :)

  97. Dmitry

    I blame spacetime coordinates for everything. To a normal person time is something that has happened and no longer exists, so you can’t go back there. Not for clever people. It’s a point on a graph. Look there’s warping of spacetime, draw that curve that way, stack those equations and you’ll go back and see your great-great grandma – I read something like that in Hawking’s “Brief History”. Black holes and singularities is like hardcore religion – may not make total sense, but it must be true – see that big fat Book explains everything. And you can’t really explain it in everyday language – “you are confusing goobledygook with gobbledygook, here’s a few clever terms you don’t know, but I do, hope I make myself clear”. Simply your vaunted theory is breaking down and leading to ridiculous conclusions: small scale physics and large scale physics don’t stack up – it is a wellknown fact.

  98. Rajas

    Well, since time is relative, and since time doesn’t really stop, to an external observer, the black hole doesn’t really stop forming, but to someone inside the black hole, time is passing just as quickly as it was, no difference, and hence the black hole forms, only the photons don’t get out and tell us what’s happening (murder story, lol).

  99. tony

    As a firm believer in the plasma cosmology model, I think the concept of the “galactic engine” makes so much more sense. I think it is only a matter of time (probably 50 years or more) before black holes, dark matter, and dark energy are finally laid to rest where they belong…in the overactive imaginations of mathemeticians.

  100. peter

    black holes are a theory!!!!!!!!!! only exist only on paper, ya talking like one has been witnessed or recorded.


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