Why do black holes have such strong gravity?

By Phil Plait | July 22, 2008 8:00 am

At the end of one of my favorite movies of all time, The War of the Worlds (the 1953 version, the only version, there was no remake, I can’t hear you, lalalalalalalala), the narrator says that it’s the littlest things that are important, alluding to the microbes that (spoiler alert) wipe out the aliens.

I always hated that voice-over at the end, actually. But he’s right. In this case, big things might be stars, and little things are black holes.

OK, so what does this have to do with anything? Well, in my live video chat, Cate Mato asked, "Why is the gravity from a black hole so much stronger than the star from which it forms?"

That’s a good question. I have a good answer. Maybe you’ve already figured it out, but just in case, here’s my response. And I get to plug my book! Bonus.

CATEGORIZED UNDER: Astronomy, DeathfromtheSkies!, Science

Comments (67)

  1. I always hated that voice-over at the end, actually.

    I’m not surprised, because not only are the microbes thanked, but a certain deity that “in His wisdom” put the microbes there.

  2. Ryan

    Oh come on, the remake (aside from Tom Crazy) wasn’t all THAT bad. You at least had Morgan Freeman doing the voice overs.

  3. jc

    Nice explanation. I somehow managed to make it through high school without anyone ever explaining the WHY of the inverse square law and it’s amazing how much stuff like this just fell into place when I looked it up on my own and realized it was related to the surface area of a sphere at a given radius. It’s such an important concept that applies to gravity, magnetism, light, radio and anything else that propagates spherically from a point source that you’d really think somewhere along the line it would have been explained. There’s a nice little graphic here if anyone else had such pathetic science teachers. http://hyperphysics.phy-astr.gsu.edu/Hbase/Forces/isq.html

  4. Robbie

    Phil Plait: “At the end of one of my favorite movies of all time, The War of the Worlds (the 1953 version, the only version, there was no remake, I can’t hear you, lalalalalalalala)”

    Lies! You positively reviewed the remake.


  5. TheBlackCat

    I don’t think you have to write a spoiler alert for a 1953 movie based on a 1898 book, but that’s just me.

  6. Incanus

    Morgan Freeman doing the narration and Tim Robbins’ performance was about the only 2 things that saved that movie.. still it could have been worse

  7. “squishy brain of science”… love it! :)

  8. Aramael

    Hey, if it’s not Jeff Wayne’s musical version with Richard Burton, I don’t want to hear about it.

  9. DaveS

    Ditto the Jeff Wayne. Truest to the book.

    Phil, what do you mean by “the black hole is only X wide”? I thought black holes were singularities, with no physical size at all? In supposition, of course, since you can’t look inside the event horizon.

  10. Ian Menzies

    Phil, what do you mean by “the black hole is only X wide”? I thought black holes were singularities, with no physical size at all? In supposition, of course, since you can’t look inside the event horizon.

    I’d say that if someone is talking about the size (in space) of a black hole, they are referring to the extent of the event horizon, since, as you noted, you can’t look inside. Also, the event horizon depends only upon the mass and angular momentum of the black hole.

  11. Cameron

    You mean closer to the center of mass, not the surface, right?

  12. Another vote here for Jeff Wayne and Richard Burton (Come on, Thunderchild!).

  13. Nice explanation.

    So is it possible that dark matter and black holes are related?

  14. Sorry, but I just can’t stand watching Tom Cruise. Knowing what he believes, and what he supports, I refuse to give him any more of my money to support his whacked out beliefs. Finding out Wil Smith is walking down the same road was quite disappointing (although he denies it).

  15. Ben

    Haha, dinky. That’s great!

  16. Nice explanation. I’ve been asked this before (as I’m known as a bit of an astronomy geek) and my explanation was basically the same. Nice to know I was 100% right!

    And I agree with Michael L – to this day I haven’t watched a single TC movie (apart from Minority Report but that was only because I was at a friend’s house and he insisted on watching it.) Same goes for Travolta, again with the single exception of Blow Out. That was an excellent film (only watched it on TV though.)

  17. Viewer 3

    Shameless plug.

    But good explanation.

    But if the force affecting everything beyond its event horizon doesn’t change, why are galaxies formed around black holes instead of stars of the same mass (pre-collapse) as the black holes if the only force that changes is felt when moving closer?

  18. madge

    Is there something Michael L and I DON’T agree on? I don’t think so :)
    TC should be denied not only the oxygen of publicity but the oxygen of oxygen too!

  19. KC

    Viewer 3:

    Black holes come in a variety of sizes. Those in the center of galaxies are supermassive black holes of mind numbing heft. The one at the center of our galaxy is thought to be between 3 and 4 million times the mass of the Sun. Think of it: The equivalent of 4 million suns squeezed into a space smaller than the earth’s orbit. But compared to the universe’s record holder, that’s a regular pipsqueak. The largest supermassive black hole on record is about 18 billion times the mass of the sun. It was weighed by observing the orbit of a smaller companion black hole that “only” weighs 100 million solar masses.

    No one’s quite sure how these ginormous black holes form. It’s still a puzzle of astronomy.

  20. If I only allowed myself to partake of entertainment produced by people who share my own religious/political/moral/etc. beliefs, or even just hold beliefs that are “acceptible” to me, I’d have to spend an awful lot of time staring at the ceiling…

  21. Charles


    That’s true, and we should all give folks the benefit of the doubt. But….some people escape even the benefit of the doubt and are still unsupportable. [Mental edit here: MUST NOT USE EXAMPLE THAT PROVES GODWIN'S LAW. AGAIN.] For me, Cruise is one of those people because his beliefs and the organization he supports have caused real people real harm. I choose not to enable him to do more of that with my money.

    Plus, he’s as much a physical midget as he is a mental midget.

  22. IBY

    You will never forget the remake, HAHAHAHAHA :)

  23. Viewer 3

    KC: Good stuff, but I’m saying that if they’re formed from collapsed stars, then why aren’t galaxies formed around stars that size pre-collapse? If the gravitational pull beyond the BH’s event horizon is unchanged regardless of whether the star is in regular form or black-hole form, then why don’t we see galaxies rotating around single stars, which is essentially equal in mass to their black-hole counterparts?

  24. BMcP

    If you burrow yourself very deep into the earth to the core (setting aside the unlikely ability to “dig” through the hot mantle and liquid outer core) and thus closer to the center of the Earth’s mass, would the gravity you feel increase?

  25. Cameron

    No, as you tunnel down farther, the gravity you feel will actually decrease until you reach the core where it would essentially be zero. As you go down, there is less and less mass within your radius from the center of the Earth. Gravity is at the maximum at the surface.
    If someone would be willing, they could point out the appropriate mathematical relations, but I’m too lazy to pull out my old physics book.

  26. Viewer 3

    And as far as Tom Cruise goes, I think people overreact to him to an extreme degree. First, he’s one of the best actors of our time. If you refuse to acknowledge his work because of his beliefs, you’re just an idiot. If you think that by “not watching his work” that you’re somehow “boycotting his beliefs and now allowing him to capitalize on your minuscule contributions of viewing time and/or your .1 of a cent that will make it into his pocket by purchasing a DVD of one of his films”, then you also need to have your head examined, even if you attempt to defend it by calling it a “matter of principle”. Give me a break.

    Sure, there are parts of his beliefs that can be considered “harmful” and have caused harm in the past and continue to do so. But I highly doubt that Cruise supports “harming people”, even if it is an indirect consequence created by others in the “organization” that he supports. And I’m sure he would denounce any of the classic Nazi-eqsue stories or murder and fear-mongering that has been known to take place in the name of his religion. Like most people with religious beliefs, Cruise has good intentions, and believes that his “way” is the best and only way to help people live. As with any religion, if it works for him and others, and they genuinely feel that they are helping others and themselves in the best and only way they know, then at worst they are simply disillusioned. And disillusioned he is, but there are many who would consider pretty much any religious person as such.

    And I’m amazed at how many people not only suddenly pretend that he’s a terrible actor, but also attack his intelligence. I admit, I have no idea how someone like him could’ve gotten caught up in that pseudo-religion, but if the packaging is right, and you’re surrounded by just the right people at just the right time, who knows what one would eventually get sucked into. But at least I’m aware that Cruise is a very smart guy, he wouldn’t be where he is if he wasn’t. I’m not the guy’s biggest fan, I’d just prefer to be fair to people instead of jumping on the bandwagons from watching entertainment shows and internet articles. Seriously, just give the guy a break and enjoy his art (well, what’s left of it). It’s the equivalent of boycotting Brokeback Mountain because you don’t want to “support gay people spreading HIV”.

    And yes, I’ve had to listen EXTENSIVELY to the list of Cruise’s beliefs and things he’s done, so I’d rather not hear “Well in 2003 he said this in this interview and said that he supported this by doing this with his wife”.

    Now for the love of all that is holy, someone answer my black hole question!

  27. Cameron

    @Viewer 3
    We don’t see galaxies forming around star-sized black holes because they’re simply too small. The black holes at the center of galaxies are thousands or millions of times the mass of even the largest stars.

    Someone might need to correct this next part, but I don’t think galaxies form around black holes, rather black holes are more or less the result of mass falling to the middle of galaxies.

    Also, Tom Cruise is definitely not one of the best actors of our time. “you. complete. me.”

  28. Esmitt

    Why do we know that block holes are only a couple of miles across? What’s the evidence?

  29. Phil mentioned that if the Sun were to become a black hole, the Earth would still experience the same gravity.
    This got me thinking on a tangent:

    How many blackholes that we know of have a planetary system? Is it possible despite the preceding stellar explosion and turmoil in the region? If so, how can we detect the presence of such a planet? I ask because I’m not sure one of the usual methods of measuring the wobble of the blackhole due to the planet’s gravity is going to work as the effect of planet’s gravity on the black hole is negligible.

    If the answer is in the negative, how can we rule out the possibility of such a system.

  30. Joseph

    When it comes to black holes, I always think of the graphic of a star sitting in a nice round dent in space-time compared to a black hole practically (or actually?) punching a hole through. So if I’m understanding this right, since both objects are the same mass they “sink” to the same level in space-time. An object can easily “roll” into and out of the gradual dent made by the star (possibly hitting it) but the well-like walls of the black hole’s dent are just too steep past the event horizon.

  31. BMcP

    @Cameron says: No, as you tunnel down farther, the gravity you feel will actually decrease until you reach the core where it would essentially be zero. As you go down, there is less and less mass within your radius from the center of the Earth. Gravity is at the maximum at the surface.
    If someone would be willing, they could point out the appropriate mathematical relations, but I’m too lazy to pull out my old physics book.

    That’s okay, I understand what you are saying, in the most basic terms, the deeper I go, surpass more and more of the Earth’s mass and the amount (and radius) of mass from me to the exact center is smaller, thus the gravity is smaller.

  32. If you managed to tunnel down to the centre of the Earth, all the mass would be all around you in equal proportions. The sum total of the gravitational pull at that point would cancel out to zero, and you would be effectively weightless. Of course it is imposible to actually get to the centre of the Earth because of the intense pressure and heat.

    Cameron has it right about stellar mass black holes: they would by definition have too little mass to form a galaxy. I can’t see any fault with his(?) logic either concerning galaxies forming or accreting around supermassive black holes. They are the result, not the cause.

    I don’t “overreact” to Tom Cruise, I simply don’t react to him at all. I have seen him in Minority Report (as I stated) and thought him a competent actor, but nothing more. But as a person, I simply don’t like the man, and would not go out of my way to watch anything he’s in. The fact he’s a scientologist does not do him any favours in terms of his “star appeal”. OTOH, there are plenty of actors I do admire (e.g. the other Tom, of the Hanks variety) . I can only watch so many movies in my lifetime; I tend to favour those with actors I like.

  33. Cameron

    No the exact center does not change. The only thing that changes is your distance (radius) from it. The more mass between you and the center, the more gravity you’ll feel. The less mass between you and center, the less gravity you’ll feel.

    Hope that helps.

  34. Cameron

    Thanks Elwood Herring, you said it better. And yes, it is “his” logic.

  35. CanadianLeigh

    @ Viewer 3, I have to agree with Michael and Madge. I don’t care what TC’s beliefs are or Will Smith’s for that matter. They are not “great” actors. Will Smith ruined I Robot for me. These guys are examples of not acting. When they are in a movie, all you can see is their personalities, not the character’s personality they are supposed to portray. The sign of a great actor or actress is when you buy into the role so well that you forget who they really are until the credits.

  36. Cusp

    None of the movies have anything on the book!

    HG was the greatest sci-fi writer **EVER**

  37. CanadianLeigh

    @ Cusp, I enjoy lots of sci-fi writers and it is rare that a movie comes anywhere near a good book and human imagination. You have to dial down your expectations a little when staring at a screen. I still don’t like it when a good movie is ruined by a big ego on screen.

  38. Viewer 3

    So from what I gather, the types of black holes in the center of galaxies are not of the star-collapse variety. Which makes sense, and I look forward to the discovery of how the supermassive ones are formed.

    And wow, I honestly haven’t heard too many people serious discredit TC as not one of the great actors of our day, other than the mindless, pseudo “film buffs” that sit around watching Citizen Cane all day. He’s had plenty of flops, more flops than someone like Hanks. And of course Hanks is easier to respect as both an actor as a person. But TC’s earlier work has indeed had some great performances, and I’ve yet to see anyone else put him in the same category as someone like Will Smith. But to each their own.

  39. TheBlackCat

    So from what I gather, the types of black holes in the center of galaxies are not of the star-collapse variety. Which makes sense, and I look forward to the discovery of how the supermassive ones are formed.

    They may have originally been one, or perhaps many, star-collapsed black holes but because the center is so dense with stars they just kept growing in size. Although I am not entirely sure about that.

  40. quasidog

    Great clip BA. SO you didn’t like the new WotW hey? :P I didn’t mind it. I don’t like Tom Cruise either but when he is on screen I forget about it all, all of his, weirdness. He is a decent actor anyway.

    BTW .. Dark Knight Rocked … gonna review it ?

  41. John

    Great explanation! I do agree with the other posters – HG is the best, and his books obviously are better than any movie. TC – just an actor…

    I like this link: http://www.fourmilab.ch/gravitation/foobar called “bending spacetime in the basement”. It is an experiment that a middle school kid could do to explore gravity and the inverse square law.


  42. Huwbert

    Cool! I like these videos. You explain very well.

    Keep doing them. :-)

  43. Crudely Wrott

    I like the idea that the advent of a black hole is mostly a matter of accretion over a long time accompanied by radical change in a relatively short time. Process over phenomenon.

    In the case of a central galactic black hole, it seems likely it got its start from some seed event; an actual stellar collapse yielding a modestly sized black hole, orbiting neutron stars merging, or some other event that concentrated matter near to, or sufficient for the formation of a singularity. Or, failing that, something close. Subsequent events might be influenced by such a concentration of mass (in a small volume!) or the subsequent events might be influenced by the concentrated mass.

    One way or another enough mass accumulates in a small enough volume that gives it all an extraordinary influence on other masses in close range. Say, less than an average planetary orbit (don’t quote me, I’m a generalist wrt astronomy). As objects are attracted gravitationally with respect to their centers of mass, the increased density of any mass increases its orbital velocity; the speed at which some other mass can establish an orbit about a common center of gravity. Take a given mass, compute its orbital velocity, shrink the radius of the mass by some factor and compute orbital velocity again. By shrinking the size you have increased the density and have created a deeper and more steeply sloping gravity well.

    A poor analogy would be the difference between a mean rooster and a mosquito. Keep a respectable distance between yourself and the rooster and things will be OK. Same with the mosquito, but for one thing. You and the rooster can see each other at considerable distance and notice the attention of the other; you and the mosquito must get much closer to experience mutual “awareness.” Thus, if you spend a lot of time around roosters and mosquitoes, you are much more likely to be slapping at mosquitoes than roosters. And you can quote me on that because it this case I am am (was) a specialist.

  44. RobertB

    When the crappy Cruise version of WotW came out in theaters there were two direct-to-DVD versions that came out within the same week.

    There was a C. Thomas Howell version titled “H.G. Wells’ War of the World” that while it had typical Sci-Fi Channel movie of the week production values was actually better than the Cruise version. Avoid the ‘sequel’ “War of the Worlds 2: The Next Wave” it was totally unwatchable *BEEP*.

    There other version titled “The War of the Worlds” had laughable production values, public access grade Special FX, and poor acting but it was VERY faithful to the original book which actually made it worth watching despite their production budget of three dollars.

    And the “by the humblest things that God, in his wisdom, has put upon this earth.” comes from the book.

  45. RobertB Says: “When the crappy Cruise version of WotW came out in theaters there were two direct-to-DVD versions that came out within the same week.”

    I’m glad you mention that, so that I wouldn’t have to. The first one you mention was by David Michael Latt, and was really a horror movie version with lots of gory makeup. The Tim Hines version(the one with the $3 budget) was actually started before the Spielberg version, but after four years of struggling with it, they released it when they ran out of money. All three of these are compared in a sidebar at the end of the WotW chapter in “The Saucer Fleet.”

    > And the “by the humblest things that God, in his
    > wisdom, has put upon this earth.” comes from the book.”

    That’s true, but it wasn’t at the end of the book, nor was it the concluding moral as it is in the movie(s). I go over this at some length, but here’s a little teaser from the end of the chapter for those who can’t wait three more months before the book comes out:

    H.G. Wells was a renowned atheist. His point in mentioning God in that sentence, which Pal and Lyndon either didn’t get, or deliberately ignored, was to give it an ironic twist. Far from being the concluding moral of the book (the sentence appears more than ten pages from the end), he goes on to describe how bacteria had been killing people since our earliest ancestors, and that billions of human deaths over the millennia had developed our immunity to most of them. The true purpose of that statement was an attack on mankind’s hubris in thinking of itself as the master of the world; the endpoint, in fact the entire point, of evolution. Wells wanted to take us down a notch or two, to show that the human brain and abstract thinking, of which we are so proud, were completely helpless against this foe, which had no problem completely undoing 10,000 years of civilization in only a few weeks. We were eventually saved by animals at the far opposite end of the evolutionary scale.

    - Jack

  46. Wells wanted to take us down a notch or two, to show that the human brain and abstract thinking, of which we are so proud, were completely helpless against this foe, which had no problem completely undoing 10,000 years of civilization in only a few weeks. We were eventually saved by animals at the far opposite end of the evolutionary scale.
    Especially considering the hubris of the British Empire of the 1890s.

  47. 1) I thought were were not allowed to call them black holes any more on the grounds it was considered racialy offensive now.

    2) When will Phil’s book becoming out in the UK? Will it initially be in hardback and how long for paperback?

  48. I got another question concerning gravity. It’s sure we won’t be able to reach the core of the earth, as the pressure would be to big. But what would happen, if we would dig a whole in a planet with a cooled down core? As we dig the gravity should weaken shouldn’t it? And if we reach the core of the planet, will there be zero gravity? As gravity is “produced” by mass, but the mass would be all around us. Or will the gravity be maximized, because the space is curved and we are at the most curved point?

  49. Torbjörn Larsson, OM

    Phil, your videos are veritable black holes for BA readers. (I mean of the attraction type – I’m sure the information gets out by Hawking radiation or something such. :-P )

    But when you say that we won’t notice the sun forming a black hole gravitationally, I dunno. The collapse will have mass accelerating into the hole (or possibly away from the star, if it’s a supernova collapse). That should mean gravitation radiation. Albeit AFAIU the quadrupole moment of a mass sphere changing radius is essentially zero, so it is deviations from symmetry that will give off some.

    @ Sarat:

    How many blackholes that we know of have a planetary system? Is it possible despite the preceding stellar explosion and turmoil in the region? If so, how can we detect the presence of such a planet?

    The very first planetary detection were of (very small) planets orbiting a pulsar, a neutron star. Apparently the explosion formed a new protoplanetary disk, which resulted in (tiny) planets.

    It isn’t a far stretch to propose that black holes may form similar systems if they too are results of supernova explosions. But I assume we would need an accompanying neutron star (i.e. a black hole-neutron star pair) to detect them thusly.

    @ Hanno:

    As we dig the gravity should weaken shouldn’t it? And if we reach the core of the planet, will there be zero gravity?

    Quite correct; read the thread, where your question is asked and answered several times over.

  50. Hanno: simple answer, yes.

    Longer answer: If in the future we find an asteroid or dead moon that we could drill into, we would find that any gravitational pull the body has would gradually weaken the further we drill into it.

    It actually happens already right here on Earth. Miners who work deep underground weigh slightly less than they do on the surface. I believe it can actually be measured too, but since the deepest mine ever dug on Earth is still comparitively a mere pinprick, the difference is exceedingly small and requires very accurate scales.

  51. For an interesting take on why the Martians succumbed to our bugs at the end of TWOTW check out this short story podcast at Escapepod.

    *whiney mode on*
    Hey Phil, I posted this yesterday and it went into moderation and then completely disappeared. Hope you don’t think I was spamming?
    *whiney mode off*

    I also said something like that I found Tom Cruise a “good” actor but his performances tended to be overwrought, exaggerated and unbelievable… the same goes for his movie acting.

  52. I always thought that the remake would of been a better movie if it wasn’t associated with War of the Worlds in any way shape or form.

  53. SJC

    Plait’s discussion of black holes is spurious.

    The notion of black holes voraciously gobbling up matter, twisting spacetime into contortions that trap light, stretching the unwary into long spaghetti-like strands as they fall inward to ultimately collide and merge with an infinitely dense point-mass singularity, has become a mantra of the astrophysical community, so much so that even primary-school children know about the sinister black hole, waiting patiently, like the Roman child’s Hannibal, for an opportunity to abduct the unruly and the misbehaved. There are almost daily reports of scientists claiming that they have again found black holes again here and there. It is asserted that black holes range in size from micro to mini, to intermediate and on up through to supermassive behemoths. Black holes are glibly spoken of and accepted as scientific facts and it is routinely claimed that they have been detected at the centres of galaxies. Images of black holes having their wicked ways with surrounding matter are routinely included with reports of them. Some physicists even claim that black holes will be created in particle accelerators, such as the Large Hadron Collider, potentially able to swallow the Earth, if care is not taken in their production. Yet despite all this hoopla, contrary to the assertions of the astronomers and astrophysicists of the black hole community, nobody has ever found a black hole, anywhere, let alone ‘imaged’ one. The pictures adduced to convince are actually either artistic impressions (i.e. drawings) or photos of otherwise unidentified objects imaged by telescopes and merely asserted to be due to black holes, ad hoc.

    The alleged signatures of the black hole are an infinitely dense point-mass singularity and an event horizon. Scientists frequently assert that the escape velocity of a black hole is that of light in vacuum and that nothing, not even light, can escape from the black hole. In fact, according to the same scientists, nothing, including light, can even leave the black hole. But there is already a serious problem with these bald claims (black holes are also alleged to have “no hair”). If the escape velocity of a black hole is that of light, then light, on the one hand, can escape. On the other hand, light is allegedly not able to even leave the black hole; so the black hole has no escape velocity. If the escape velocity of a black hole is that of light in vacuum, not only can light both leave and escape, material objects can also leave the event horizon, but not escape, even though, according to the Theory of Special Relativity, they can only have a velocity less than that of light in vacuum. This just means that if the black hole has an escape velocity then material bodies can infact leave the black hole and eventually stop and fall back to the black hole, just like a ball thrown into the air here on Earth with an initial velocity less than the escape velocity for the Earth. So the properties of the alleged black hole event horizon are irretrievably contradictory.

    What of the infinitely dense point-mass singularity at the heart of the black hole? It is supposed to be formed by irresistible gravitational collapse so that matter is crushed into zero volume, into a ‘point’, a so-called ‘point-mass’. One recalls from high school that density is defined as the mass of an object divided by the volume of the object. If the mass is not zero and the volume is zero, as in the case of a black hole singularity, one gets division by zero. But all school children know that division by zero is not allowed by the rules of mathematics. Nonetheless, black hole proponents divide by zero! Furthermore, black holes are allegedly obtained from Einstein’s General Theory of Relativity. It is called the General Theory because it is a generalisation of his Special Theory of Relativity. As such, General Relativity cannot, by definition, violate Special Relativity, but that is precisely what the black hole does. Special Relativity forbids infinite densities because, according to that Theory, infinite density implies infinite energy (or equivalently that a material object can acquire the speed of light in vacuo), which contradicts the fundamental postulate of Special Relativity. Therefore General Relativity also forbids infinite densities. But the point-mass singularity of the black hole is allegedly infinitely dense, in violation of Special Relativity. Thus the Theory of Relativity actually forbids the existence of a black hole.

    What else of the event horizon of the black hole? According to the proponents of the black hole it takes an infinite amount of time for an observer to watch an object (via the light from that object, of course) to fall down to the event horizon. So it therefore takes an infinite amount of time for the observer to verify the existence of an event horizon and thereby confirm the presence of a black hole. However, nobody has been and nobody will be around for an infinite amount of time in order to verify the presence of an event horizon and hence the presence of a black hole. Nevertheless, scientists claim that black holes have been found all over the place. The fact is nobody has assuredly found a black hole anywhere – no infinitely dense point-mass singularity and no event horizon. Some black hole proponents are more circumspect in how they claim the discovery of their black holes. They instead say that their evidence for the presence of a black hole is indirect. But such indirect “evidence” cannot be used to justify the claim of a black hole, in view of the fatal contradictions and physically meaningless properties associated with infinitely dense point-mass singularities and event horizons. One could just as well assert the existence and presence of deep space unicorns on the basis of such indirect “evidence”. It is also of great importance to be mindful of the fact that no observations gave rise to the notion of a black hole in the first place, for which a theory had to be developed. The black hole was wholly spawned in the reverse, i.e. it was created by theory and observations subsequently misconstrued to legitimize the theory. Reports of black holes are just wishful thinking in support of a belief; not factual in any way.

    Another fatal contradiction in the idea of the black hole is the allegation that black holes can be components of binary systems, collide or merge. Let us, for the sake of argument, assume that black holes are predicted by General Relativity. The black hole is fundamentally described by a certain mathematical expression called a line-element (which is just a fancy name for a distance formula, like that learnt in high school) that involves just one alleged mass in the entire Universe (just the alleged source of a gravitational field), since the said distance formula is a solution for a spacetime allegedly described by Einstein’s static equations in vacuum (or, more accurately, in emptiness), namely Ric = 0. One does not need to know anything at all about the mathematical intricacies of this equation to see that it cannot permit the presence of one black hole, let alone two or more black holes. The mathematical object denoted by Ric is what is called a tensor (in this case it’s Ricci’s tensor, and hence its notation). The reason why Ric = 0 is because in Einstein’s General Theory of Relativity all matter that contributes to the source of the gravitational field must be described by another tensor, called the energy-momentum tensor. In the case of the so-called static vacuum field equations the energy-momentum tensor is set to zero, because there is no mass or radiation present by hypothesis. Otherwise Ric would not be equal to zero. So the alleged black hole can interact with nothing, not even an ‘observer’. Ric = 0 does not describe a two body problem, only, allegedly, a one body problem (and hence quite meaningless). One cannot just introduce extra objects into a given solution to Einstein’s field equations because his theory requires that the curvature of spacetime (i.e. the gravitational field) is due to the presence of matter and that the said matter, all of it, must be described by his energy-momentum tensor. If the energy-momentum tensor is zero there is no matter present. Einstein’s field equations are non-linear, so the ‘Principle of Superposition’ does not apply. In other words, one cannot obtain a solution to Einstein’s field equations for some specified configuration of matter and thereafter just insert additional lumps of matter into the spacetime for that solution. All configurations of matter each require an associated energy-momentum tensor particular to it and a solution to the field equations for each configuration. Before one can talk of relativistic binary systems it must first be proved that the two-body system is theoretically well-defined by General Relativity. This can be done in only two ways:

    (a) Derivation of an exact solution to Einstein’s field equations for the two-body
    configuration of matter; or

    (b) Proof of an existence theorem.

    There are no known solutions to Einstein’s field equations for the interaction of two (or more) masses, so option (a) has never been fulfilled. No existence theorem has ever
    been proved, by which Einstein’s field equations even admit of latent solutions for such configurations of matter, and so option (b) has never been fulfilled either. Since Ric = 0 is a statement that there is no matter in the Universe, one cannot simply insert a second black hole into the spacetime of Ric = 0 of a given black hole so that the resulting two black holes (each obtained separately from Ric = 0) mutually interact in a mutual spacetime that by definition contains no matter! One cannot just assert by an analogy with Newton’s theory that two black holes can be components of binary systems, collide or merge, because the ‘Principle of Superposition’ does not apply in Einstein’s theory. Moreover, General Relativity has to date been unable to account for the simple experimental fact that two fixed bodies will approach one another upon release. So from where does the matter allegedly associated with the solution to Ric = 0 come, when this is a statement that there is no matter present? The proponents of the black hole just put it in at the end of their calculations, a posteriori and ad hoc, in violation of their starting hypothesis that Ric = 0, and to top it off, they do so by introducing a Newtonian relation.

    Curiously it is frequently claimed that Newton’s theory of gravitation also predicts a black hole. What is actually alluded to is the theoretical Michell-Laplace Dark Body, which has an escape velocity equal to or greater than the velocity of light in vacuo, but which is nonetheless not a black hole. The basis for the claim resides in the fact that the critical radius for the Michell-Laplace Dark Body is given by the same mathematical expression as that for the so-called “Schwarzschild radius” of a black hole. But this is not surprising, because this “radius” was effectively inserted into the distance formula for
    Ric = 0 (called the “Schwarzschild solution”), along with matter, a posteriori and ad hoc. However, in the space of Newton’s gravitation, the radius of the Michell-Laplace Dark Body is the radial distance from the centre of mass of the object, but in the space of the “Schwarzschild solution” the “Schwarzschild radius” it is not a radial distance at all, by reason of the non-Euclidean geometry of Einstein’s gravitational field. Furthermore, the black hole is allegedly produced by irresistible gravitational collapse, but the Michell-Laplace Dark Body does not involve irresistible gravitational collapse; the black hole irresistibly collapses into an infinitely dense point-mass singularity but the Michell-Laplace Dark Body does not (its density is finite); no light and no material body can even leave the black hole let alone escape, but light and material bodies can leave the Michell-Laplace Dark body, and at its critical radius light can escape from it; the black hole has an event horizon but the Michell-Laplace Dark Body has no event horizon; the black hole has no escape velocity whereas the Michell-Laplace Dark Body has an escape velocity; no observer, no matter how close to the event horizon, can see a black hole, but there is always a class of observers that can see the Michell-Laplace Dark Body (an observer only needs to be close enough to it); there is no upper limit to the speed of an object in Newton’s theory, but no material body can acquire the speed of light in vacuo in Einstein’s theory; in the case of a black hole for Ric = 0, such as the “Schwarzschild” black hole, an observer can’t be present in its spacetime which is by definition empty, but an observer can always be present in the space of the Michell-Laplace Dark Body because its space is not empty by definition; the ‘Principal of Superposition’ applies in the case of the Michell-Laplace Dark Body but does not apply in any case of a black hole; and the centre of mass of a body is not a physical object in Newton’s theory nor Einstein’s theory. So the Michell-Laplace Dark Body does not possess the tell-tale signatures of the alleged black hole, and so it is not a black hole. Thus, Newton’s theory also does not predict black holes.

    Finally, although the fundamental solution to Ric = 0 is usually called the “Schwarzschild solution”, despite its name, it is not in fact Schwarzschild’s solution. Schwarzschild’s actual solution forbids black holes. The frequent claim that Schwarzschild found and advocated a black hole solution is patently false, as a reading of Schwarzschild’s papers on the subject irrefutably testify. False too are the claims that he predicted an event horizon and that he determined the “Schwarzschild radius” (i.e. the alleged “radius” of the black hole event horizon). Schwarzschild actually had nothing to do with the black hole, but attaching his name to it lends the notion an additional façade of scientific legitimacy.

    1. Karl Schwarzschild, On the gravitational field of a mass point according to Einstein’s theory, Sitzungsber. Preuss. Akad. Wiss., Phys. Math. Kl, 189, 1916,

    2. Karl Schwarzschild, On the gravitational field of a sphere of incompressible fluid according to Einstein’s theory, Sitzungsber. Preuss. Akad. Wiss., Phys. Math. Kl., 424, 1916,

    3. G. C. McVittie, Laplace’s alleged ‘black hole”, The Observatory, v.98, 272, 1978,

    4. Stephen J. Crothers, A Brief History of Black Holes, Progress in Physics, v.2, 54-57, 2006, http://www.ptep-online.com/index_files/2006/PP-05-10.PDF

  54. How is it that black holes are spoken about like they’re more than simply a theory, or in fact a wild conjecture?

    No-one has ever seen nor imaged a black hole. ALL of the images we are fed are either artist’s representations (cartoons) or images of areas THOUGHT to contatin a black hole.

    They are a mathematical construct, and even then they violate the very laws of mathematics which are supposedly used to support them.

    If density is a measure of mass/volume, and the volume of a black hole is zero, (point mass) that means we are effectively dividing by zero, TOTALLY FORBIDDEN BY ANY MATHEMATICAL LAWS!!! – Unless of course a PhD is a licence to break such laws…

    Please explain this in simple terms, after all it is a very simple problem yet ALWAYS overlooked by proponents of the black holes.

    Cheers, Dave Smith.

  55. Buzz Parsec

    A little freshman physics: 1) the gravitational field of a spherically symmetric body anywhere outside that body (including on the surface) is exactly the same as that of a point source of equal mass located at the center of it. 2) The gravitational field of a spherical shell of matter is zero at any point inside the shell. (The net force of the nearby bits pulling in one direction is exactly the same as the more massive but more distant far away bits pulling in the other direction, so everything cancels.) It takes calculus to prove these two statements, AFAIK, but maybe someone’s come up with a clever algebraic proof. A third point is the net gravitational field of a collection of objects is the sum of their individual fields. This is called the principle of superposition, and I think it’s one of those things that seems obvious at first glance, but is devilishly hard to prove. In any case, the proof is in the pudding; i.e. it works! Given those three propositions, think about what happens as you descend a tunnel dug down into the Earth. You can compute the gravity at any point by regarding the earth as the superposition of two objects, one a sphere including all the Earth that is still below you, and the other a spherical shell consisting of all the Earth above you, the part that’s farther from the center than you currently are.
    Since the spherical shell part has no net field, the gravity you feel at any point is
    just that due to the part below your feet. That will always be less than the surface gravity of the Earth, given a reasonable density distribution [1], and will always reach zero at the center, because the mass between you and the center will become zero at that point.

    [1] If the Earth had a very dense core (e.g. lead or uranium) surrounded by a thick layer of very light material, e.g. Nerf, then the gravity might actually go up as you descended through the Nerf layer, because the amount of mass below you wouldn’t change much, as the distance decreased, and the force is proportional to M/r^2. But it takes a really extreme mass distribution to do that. For example, the Earth’s atmosphere is thin enough that gravity increases all the way down to the surface, even though at the surface the atmosphere no longer counts as part of the total mass of the earth in determining it’s gravity.

  56. Buzz Parsec

    Dave Smith and SJC both posted after I had written my post but long before I submitted it (I got distracted by real work), so I’m not following up myself… :-)

    Dave, density is a defined quantity of macroscopic objects that breaks down at very small scales (you can’t adequately define the density of an atomic nucleus either), so the fact that it breaks down at a gravitational singularity as well doesn’t mean much. General Relativity and Quantum Mechanics both break down at that point. Just because the theory (or theories) break down doesn’t mean the phenomenom isn’t real. It just means we need better theories. Reconciling GR and QM is one of the great current unsolved problems of physics. Similar problems arose in QM, and were solved by a mathematical trick (renormalization) that avoided dividing by zero. Unfortunately, the same trick doesn’t work with GR.

    The flaws in GR and QM don’t mean they’re invalid, any more than Special Relativity (or General Relativity, for that matter) mean that you can’t use Newton’s laws to navigate to the Moon. You just have to know where they apply, which for GR, is anywhere outside the event horizon of a black hole (and most of the space inside it, too.)

    As for SJC’s comments, SHEESH!! I don’t know where to begin, with his history (which is incorrect), or his physics (which is non-sensical) or his logic, which is non-existent. I only managed to wade through about a third of his post, but in case anyone is fooled by it or wants to ask a legitimate question based on it, I’ll try to clarify.

    Historically, he implies there’s a vast conspiracy of astronomers and astrophysicists who insist on promoting the idea that black holes exist despite a total lack of evidence, apparently because they’re really cool and you can get a lot of attention talking about them gobbling down galaxies by the score and creating cool pictures of the process out of whole cloth. Nothing of the sort. Black holes were first hypothesized about 75 years ago, but it wasn’t until the late 1960′s or early 1970′s that astronomers first began to suspect that they might be the engine powering quasars and other active galaxies. But it took about 20 years to accumulate enough evidence to convince most astronomers that black holes really exist (some still aren’t convinced.) The most compelling evidence is in the form of velocity curves of stars orbiting very close to black holes, and in gravitational lensing effects. You don’t need a photograph to prove black holes exist, you need data, usually in the form of spectra.

    His physics is equally bogus. Escape velocity is dependent on the distance from a mass. At the event horizon, the escape velocity (at least when calculated naively using Newtonian gravitational theory) is the speed of light. Inside the event horizon (but still miles from the singularity for a solar-mass black hole, and millions of miles from it for a galactic core style super massive black hole) is *greater* than the speed of light. There’s been lots of work down studying various mechanisms to try to climb out of a black hole, and the bottom line is nothing works (except, possibly, Hawking radiation.) SJC isn’t proposing things no one else has ever thought of.

  57. SJC

    Parsec has not understood anything I posted. Parsec should prove that the two-bpody problem has been formulated and solved by General Relativity. He should prove that Special Relativity permits infinite density. He should prove that the “Schwarzschild radius” is a radius. He should prove that Ric = 0 is not an empty spacetime. He should give the coordinates of any infinitely dense point-mass singularity of a black hole. He should give the coordinates of any event horizon of a black hole. He should prove that the definition of escape velocity prevents anything from leaving an object, such as a black hole. He should prove that black holes can be components of binary systems. He should prove that the history of black holes I have given (in my citation) is “incorrect”, especially since I cite the historical documents. He should prove that it does not take an infinite amount of time for an observer to confirm the presence of an event horizon. He should prove that if the speed of light inside the event horizon is greater than the speed of light (in vacuo) then no object with a speed less than the escape velocity cannot leave (bearing in mind the definition of escape velocity). He should prove that vague assertions that physics “breaks down” is a scientific rebuttal. He should prove that what I have posted is not “real work”. He should give us all a rigorous demonstration that matter can be superimposed into the spacetime of Ric = 0 despite there being no matter present by definition. Indeed, he should prove that the ‘Principle of Superposition’ applies in Einstein’s General Theory of Relativity. Plait should also provide the necessary proofs and demonstrations. The usual hand waving is not scientific method.

  58. SJC

    Parsec should also prove that “Schwarzschild’s solution” is Schwarzschild’s solution (which it isn’t) and prove that Schwarzschild’s actual solution predicts black holes (which it doesn’t) and prove that Schwarzschild obtained and advocated a black hole solution (which he didn’t) and that Schwarzschild even breathed a single word about black holes (which he didn’t). The facts about Karl Schwarzschild can be verified by anybody simply by reading Schwarzschild’s original two papers on the subject, links to which I have provided in my first post. Parsec should also prove that General Relativity is able to account for the simple experimental fact that two fixed bodies will attract one another upon realse, since there is no known solution to Einstein’s field equations for that simple configuration of matter. Plait should also provide these additional proofs.

  59. MacMac

    Plait and Parsec are just repeating the standard mantra being dispensed daily by professors who have painted themselves into a corner. The few who experience some nauseating worries about it don’t know how to get out of it without shaming themselves unacceptably, but most take the same position as L. T. More did when first introduced to Einstein’s work, quote:

    “Thomas F. Glick, ed., The Comparative Reception of Relativity (Kluwer Academic Publishers, 1987), ISBN 9027724989.”
    In the Preface by Stanley Goldberg, “The Assimilation of Relativity in America”, he writes, quote:
    “…  While Lewis and Tolman were endeavoring to convince their colleagues that the theory was empirical and practical, those Americans who did comment on the theory ridiculed it as errant nonsense. L.T. More, Professor of Physics at the University of Cincinnati, teased relativists on the grounds that if they were right then the sun was melting away at an incredible rate and that when a man caught a baseball, the mass of both the ball and the man’s hand should change. But he became deadly serious when he thundered that the “electronicist theories” were a throwback representing an attempt to undermine the three century struggle which science had waged to purge itself of metaphysics, that is, nonsense. …” .

    History is about to repeat itself. Plait and Parsec would be well advised to invest some brainjuice in a thorough study of Stephen Crother’s papers at . You will find the logic, mathematics and geometry to be flawless. No fudge factors. The problem might be that this is at a level that could cause your brains to creak and groan a lot before you get it.

    Mind you, we still have no way of knowing if the universe ultimately can be described in terms of the mathematics and geometry humans are capable of.

    Here’s another quote for you:

    In the introduction to his Nobel Lecture on 8 December 2005 at Karolinska Institutet in Stockholm, Sweden, Dr Barry Marshall from Perth, Western Australia made reference to a famous statement by historian Daniel Boorstein:

    “The greatest obstacle to knowledge is not ignorance, it is the illusion of knowledge”.

    He was alluding to the many years of rejection, snubbing and even ridicule he and his colleague and fellow Nobel Prize Laureate Dr Robin Warren had to endure before their discovery was accepted as the truth; a micro-organism, Helicobacter Pylori, could in fact live in the acidic stomach environment and was in fact casually linked to peptic ulcers.

  60. Torbjörn Larsson, OM

    Life intervened, but finally returning to old threads FWIW:

    @ SJC:

    Parsec should prove

    Why would any of those derivations be applicable to the question whether black holes are sufficiently experimentally verified or not? His description of physics and its history (check for example with the standard reference “Gravitation” by Misner, Thorne, Wheeler) is on the money; yours is not.

    @ MacMac:

    L.T. More, Professor of Physics at the University of Cincinnati, teased relativists

    Again, relevance? In spite of More’s misunderstandings relativity is now universally accepted.

    Which, of course, brings the question why you don’t accept it, especially since you have no scientific problems with it to present.

  61. SJC

    Larsson is wrong. The physics of Plait and Parsec is incorrect. Larsson should, along with Plait and Parsec, just provide the proofs required. Also, my history of the physics is dead accurate. Larsson’s claims are demonstrably false on this head too. A simple history, verified by the historical documents, is here:


    Differing to the authority of Misner, Thorne and Wheeler is not science, just hand waving, as usual. Their book contains much demonstrable nonsense. They don’t even understand escape velocity, and that the Principle of Superposition does not apply in Einstein’s theory. On top of that they don’t even know Schwarzschild’s actual solution and they don’t even know what the variable ‘r’ denotes in their corrupted version of Schwarzschild’s solution, and so they don;t even know elementary differential geometry. All this is easily verified by reading their silly book.

    We cannibals await the proofs of the preachers (but they will not come, because Plait, Parsec, Larsson et al. cannot provide them, and instead just tell us that black is white).

    Nobody has found an infinitely dense point-mass singularity and nobody has found an event horizon, and so nobody has found a black hole anywhere. All claims for the discovery of black holes are false. And since infinite density is forbidden by the Theory of Relativity, black holes are inconsistent with that Theory.

  62. SJC

    Deferring: in the previous, just in case Larsson resorts to typos as a method of rebuttal.

  63. Al

    Substitute “neutron star” for black hole and nothing Phil Plait says is wrong …
    is SJC denying neutron stars ?
    Now make the mass larger and larger – you get a an escape velocity that approaches the speed of light, but you have things orbiting this object and things coming in being accelerated. If they get near c, then they must be radiating a lot of energy so they cannot maintain that velocity to escape, and they must get to c+ to escape.
    So eventually most objects that come close get slowed down and fall in – eventually something must happen .. does it explode or does it collapse. I don’t know, I don’t have the energy to even look at the mathemetics or theory, but when the escape velocity is c something strange must happen.My money is with the theorists, because we can see the results of the gas being pulled apart and they tell me it matches the theoretical predictions of having a supermassive small object – maybe not a singularity, but definitely something with a Schwartzchild radius.

  64. Al

    ably the ravings of someone with too much 1997 Shiraz in his system, but anyway …

  65. Angela Rorkes

    This was really helpful to my daughter in grade 9(the video). Thanks, Mr.Plait!


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