# What is inside a black hole? **URL:** \ **Category:** Factual Questions\ **Created:** [January 29, 2009, 4:30pm UTC](https://boards.straightdope.com/t/what-is-inside-a-black-hole/483570 "2009-01-29T16:30:45Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [January 29, 2009, 11:29pm UTC](https://boards.straightdope.com/t/what-is-inside-a-black-hole/483570/21 "2009-01-29T23:29:44Z")
\>Gravitationally, they look like any other object of similar mass. A nitpick, and a minor one at that: Gravitationally, items of the same mass give gravitational fields that are similar at a given distance only to a first order or approximation. Gravitational fields have various details to them, though. For example, recall that spacecraft orbiting planets or moons demonstrate dynamic behavior that let us deduce details of the overall and local structure of those planets or moons. The hardest homework problem I ever succeeded in doing involved comparing different level analyses of the gravitational field of an almost but not quite uniformly dense, almost but not quite spherical, body. I bet swapping a same-mass black hole with the Earth would make the Moon behave noticeably differently within a human lifetime. Whether doing that with the Sun would make Earth behave noticeably differently, I don’t want to guess. The only way I can think of that the force of a black hole doesn’t behave like other things we have witnessed, would be that black holes should impose way impressive tidal forces on objects that get too close to them. You could get your feet half as far from a black hole as your head, which you can’t do with a planet. While it lasted, the pull along the length of your body would be spectacular. But that’s just because a black hole is compact enough to let you position yourself this way. And, we never witness such extreme things, because we don’t do this painful experiment. There are, though, ways to use gravitational fields to distinguish between the natures of some of these animals. ---
**Author:** ![Frylock](https://avatars.discourse-cdn.com/v4/letter/f/ce7236/32.png) [@Frylock](https://boards.straightdope.com/u/Frylock)\ **Post date:** [January 29, 2009, 11:49pm UTC](https://boards.straightdope.com/t/what-is-inside-a-black-hole/483570/22 "2009-01-29T23:49:12Z")
**Whack-a-Mole** suggested that from the point of view of an object falling into a black hole’s singularity, it takes an infinite amount of time to reach that singularity. (Incidentally, I recall having read this somewhere as well. If I had to bet, I would bet I read it in the book _Stephen Hawking’s Universe_ long long ago.) **MikeS** said this is not true–that “the singularity is always in the future” just means the singularity is inescapable. But **Stranger on a Train** also addressed **Whack-A-Mole** ’s comment, and seemed to be agreeing that it _is_ true–that “the singularity is always in the future” in the sense that the meeting with it is never in the present. Which is it, then? Or did I misread someone? -FrL- ---
**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\ **Post date:** [January 30, 2009, 12:05am UTC](https://boards.straightdope.com/t/what-is-inside-a-black-hole/483570/23 "2009-01-30T00:05:21Z")
If you fall into the singularity, you – or rather, whatever tidal forces have turned your constituent particles into – do encounter the singularity after a finite amount of time; that the singularity is always in your future only means that there exists no path that does not meet it beyond the event horizon. The often-repeated ‘it takes forever to fall into a black hole’ only is true from the point of view of external observers – to those, due to gravitational time dilatation, an object approaching the event horizon seems to asymptotically slow down to a standstill just before actually encountering it (of course, its light will also be redshifted beyond visibility, so you couldn’t look at a black hole and see all the stuff that ever fell in just kinda hang around at the event horizon). However, the object falling in knows nothing of this – in fact, it can’t even tell when it crosses the horizon. ---
**Author:** ![Frylock](https://avatars.discourse-cdn.com/v4/letter/f/ce7236/32.png) [@Frylock](https://boards.straightdope.com/u/Frylock)\ **Post date:** [January 30, 2009, 12:26am UTC](https://boards.straightdope.com/t/what-is-inside-a-black-hole/483570/24 "2009-01-30T00:26:58Z")
> [@Half\_Man\_Half\_Wit](#): > > The often-repeated ‘it takes forever to fall into a black hole’ only is true from the point of view of external observers – to those, due to gravitational time dilatation, an object approaching the event horizon seems to asymptotically slow down to a standstill just before actually encountering it (of course, its light will also be redshifted beyond visibility, so you couldn’t look at a black hole and see all the stuff that ever fell in just kinda hang around at the event horizon). However, the object falling in knows nothing of this – in fact, it can’t even tell when it crosses the horizon. Actually, that’s what I was remembering, I think. I got my frames of reference mixed up. -FrL- ---
**Author:** ![Ring](https://avatars.discourse-cdn.com/v4/letter/r/6a8cbe/32.png) [@Ring](https://boards.straightdope.com/u/Ring)\ **Post date:** [January 30, 2009, 2:57am UTC](https://boards.straightdope.com/t/what-is-inside-a-black-hole/483570/25 "2009-01-30T02:57:10Z")
> [@Half\_Man\_Half\_Wit](#): > > But, if one looks at the whole process a little closer, one finds that for this to be allowed to happen, the particle that fell into the black hole must actually have had _negative_ total energy, and thus its falling into the event horizon has effectively reduced the black hole’s total energy – by just the amount that’s now being carried away by the other particle! What **Half Man Half Wit** said is absolutely correct, however a couple of other points. Even though the total energy of the infalling particle is negative the energy of the particle itself is still positive. And another way to look at is that the hole via its tidal gravity has expended enough energy to create two real particles (from the virtual particle pair) but only gets the energy of one particle back. Effectively radiating a particle. ---
**Author:** ![Altair33](https://avatars.discourse-cdn.com/v4/letter/a/e79b87/32.png) [@Altair33](https://boards.straightdope.com/u/Altair33)\ **Post date:** [January 30, 2009, 3:28am UTC](https://boards.straightdope.com/t/what-is-inside-a-black-hole/483570/26 "2009-01-30T03:28:13Z")
Has anyone ever figured out the minimum IQ you need to have to be able to understand stuff like general relativity and particle physics? I like to think I’m a pretty smart guy and I have a law degree from a good school, but this stuff goes way over my head. Oh sure, I can parrot back the stuff I’ve read like “massive objects warp spacetime” but I don’t really understand, for example, how space and time can be the same thing. It’s fascinating stuff as long as you are content with only understanding every few sentences you read. ---
**Author:** ![Ring](https://avatars.discourse-cdn.com/v4/letter/r/6a8cbe/32.png) [@Ring](https://boards.straightdope.com/u/Ring)\ **Post date:** [January 30, 2009, 3:40am UTC](https://boards.straightdope.com/t/what-is-inside-a-black-hole/483570/27 "2009-01-30T03:40:53Z")
> [@Altair33](#): > > Has anyone ever figured out the minimum IQ you need to have to be able to understand stuff like general relativity and particle physics? I like to think I’m a pretty smart guy and I have a law degree from a good school, but this stuff goes way over my head. Oh sure, I can parrot back the stuff I’ve read like “massive objects warp spacetime” but I don’t really understand, for example, how space and time can be the same thing. It’s fascinating stuff as long as you are content with only understanding every few sentences you read. You’ll have to judge for yourself how reputable this site is. > [@](#): > > According to these tables, the average IQ of a physics PhD student is about 130. For comparison, english/literature PhD students average about 120 and sociology PhD students only 115. (115 is the average for college students in general, so the typical sociology TA is no smarter than the students in his or her class 😉 Amazingly, the average grad student in education (109) is below the average for college students! > **[Physics still pulls them in...](https://infoproc.blogspot.com/2005/12/physics-still-pulls-them-in.html)** > > There is much concern among physicists that our field is no longer getting the same share of the brightest students as in the glory days (e.... ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [January 30, 2009, 3:48am UTC](https://boards.straightdope.com/t/what-is-inside-a-black-hole/483570/28 "2009-01-30T03:48:49Z")
> [@Altair33](#): > > Has anyone ever figured out the minimum IQ you need to have to be able to understand stuff like general relativity and particle physics? I like to think I’m a pretty smart guy and I have a law degree from a good school, but this stuff goes way over my head. Oh sure, I can parrot back the stuff I’ve read like “massive objects warp spacetime” but I don’t really understand, for example, how space and time can be the same thing. It’s fascinating stuff as long as you are content with only understanding every few sentences you read. I guarantee you most physicists couldn’t get through a court opinion without specialized help. I’ve had the misfortune to read hundreds of medical journal articles and they are often incomprehensible. Interest, aptitude, and prolonged study are the key in almost every field. I grok most concepts in advanced physics without an advanced degree. I can’t explain them the way the physicists do but I’ve read about each advance over the past 40 years and I’ve read all the good popular books explaining the concepts by going back to the beginning and leading me through the logic. I’m not coming at it suddenly from the outside and trying to let it sink in by deep end immersion. Law is no different. How many threads have there been in which Gfactor quotes yards of law jargon and people have to ask for a simple explanation. Anybody else’s jargon is impenetrable until you can find the time to hack a pathway through it with the aid of a good translator. That doesn’t make you less smart. The only group that really is smarter than everybody else is writers. 😛 ---
**Author:** ![Ring](https://avatars.discourse-cdn.com/v4/letter/r/6a8cbe/32.png) [@Ring](https://boards.straightdope.com/u/Ring)\ **Post date:** [January 30, 2009, 4:48am UTC](https://boards.straightdope.com/t/what-is-inside-a-black-hole/483570/29 "2009-01-30T04:48:44Z")
**Exapno** I don’t doubt you grok the concepts, but that’s the easy part. Until you grok the Mathematics you don’t really understand why you don’t understand it. So. How are you at groking the math? Actually I found that groking the math wasn’t as difficult as groking the notation, especially indicial notation. That shit almost killed me. And the real physicists here are still so far out my league that I need a telescope to even see them. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [January 30, 2009, 6:36am UTC](https://boards.straightdope.com/t/what-is-inside-a-black-hole/483570/30 "2009-01-30T06:36:50Z")
> [@Ring](#): > > **Exapno** I don’t doubt you grok the concepts, but that’s the easy part. Until you grok the Mathematics you don’t really understand why you don’t understand it. > > So. > > How are you at groking the math? > > Actually I found that groking the math wasn’t as difficult as groking the notation, especially indicial notation. That shit almost killed me. Or as the old saw attributed to Thomas Edison goes, genius is 1% inspiration and 99% perspiration. The primary characteristic of most “geniuses” is that they’re wonks; that is, that they are able to focus in and study the intimate details of some field (or subfield) in such detail and depth that their knowledge of it is intimate and vastly exceeding that which any dilettante could hope to approach. This is not to say that it doesn’t take a modicum of intelligence to understand the mathematics behind general relativity, but once you get past the notation (which, as **Ring** notes, is fiendishly difficult to interpret) the math is relatively straightforward…just very, very, very tedious to work through for any significant problem. And at least GR gives answers that are more or less intuitive (once you accept the underlying premises of the theory). This places it in contrast with quantum mechanics, where you just have to accept that the math just because it happens to work, not because it makes any kind of sense. Of course, an understanding of advanced physics based upon analogized explanations is just that; comprehension based on comparative similarity. A practical mastery of the material comes when you can concoct a scenario, develop a predictive model, and match your answers to reality. Stranger ---
**Author:** ![Rigamarole](https://avatars.discourse-cdn.com/v4/letter/r/77aa72/32.png) [@Rigamarole](https://boards.straightdope.com/u/Rigamarole)\ **Post date:** [January 30, 2009, 8:47am UTC](https://boards.straightdope.com/t/what-is-inside-a-black-hole/483570/31 "2009-01-30T08:47:01Z")
What I don’t understand is why, if black holes have a tendency to suck everything in their surroundings into them, even light, how have they not swallowed up the universe by now? ---
**Author:** ![Der\_Trihs](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/der_trihs/32/233_2.png) [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)\ **Post date:** [January 30, 2009, 12:07pm UTC](https://boards.straightdope.com/t/what-is-inside-a-black-hole/483570/32 "2009-01-30T12:07:15Z")
> [@Rigamarole](#): > > What I don’t understand is why, if black holes have a tendency to suck everything in their surroundings into them, even light, how have they not swallowed up the universe by now? The inverse square law, and orbits. Gravity becomes weaker with distance; so once everything nearby has been pulled in ( or thrown away ) only objects that drift nearby are significantly tugged on by the hole. And in order to actually be pulled in, an object has to hit the hole. Just as planets can orbit the Sun without being “sucked in” and immolated, objects can orbit or just fly by a black hole. > [@mlees](#): > > So. Will the “merge” of this pair be spetacular? From what I recall, and from my googling while an enormous amount of energy is released, it’s almost all in the form of invisible gravity waves. ---
**Author:** ![Frylock](https://avatars.discourse-cdn.com/v4/letter/f/ce7236/32.png) [@Frylock](https://boards.straightdope.com/u/Frylock)\ **Post date:** [January 30, 2009, 12:17pm UTC](https://boards.straightdope.com/t/what-is-inside-a-black-hole/483570/33 "2009-01-30T12:17:42Z")
> [@Rigamarole](#): > > What I don’t understand is why, if black holes have a tendency to suck everything in their surroundings into them, even light, how have they not swallowed up the universe by now? Because not everything is within some black hole’s “surroundings,” so to speak. As long as you stay away from the event horizon of a black hole, you’re good to go. Everything that hasn’t been captured by a black hole by now, then, is all the stuff that hasn’t come within the event horizon of a black hole. It’s not suprising that there’s so much stuff left, since the volume bound by event horizons of black holes is a tiny fraction of the volume of space in the universe. -FrL- ---
**Author:** ![Anne\_Neville](https://avatars.discourse-cdn.com/v4/letter/a/b9e5f3/32.png) [@Anne\_Neville](https://boards.straightdope.com/u/Anne_Neville)\ **Post date:** [January 30, 2009, 1:54pm UTC](https://boards.straightdope.com/t/what-is-inside-a-black-hole/483570/34 "2009-01-30T13:54:07Z")
> [@Anne\_Neville](#): > > I want this book. So badly I can taste it (It tastes like chicken). Today’s my birthday, and I’m hoping it is waiting at home for me… It was! I’m enjoying it immensely. > [@Stranger on a Train](#): > > Or as the old saw attributed to Thomas Edison goes, genius is 1% inspiration and 99% perspiration. I can tell you that this is true of majoring in physics. You really do a lot of slogging through problem sets, or at least I did when I was getting my undergrad degree in physics. And then there are the labs. I would say that “being willing and able to put in a lot of time doing the work for your classes” is at least as important as raw intelligence for a physics major. It really isn’t a matter of reading something like “space and time are the same thing” and immediately and intuitively understanding what that means- it’s doing a lot of problems where you have to treat space and time the same way. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [January 30, 2009, 2:52pm UTC](https://boards.straightdope.com/t/what-is-inside-a-black-hole/483570/35 "2009-01-30T14:52:22Z")
> [@Rigamarole](#): > > What I don’t understand is why, if black holes have a tendency to suck everything in their surroundings into them, even light, how have they not swallowed up the universe by now? This was explained waaaaay back in post #7. ---
**Author:** ![billfish678](https://avatars.discourse-cdn.com/v4/letter/b/7bcc69/32.png) [@billfish678](https://boards.straightdope.com/u/billfish678)\ **Post date:** [January 30, 2009, 3:08pm UTC](https://boards.straightdope.com/t/what-is-inside-a-black-hole/483570/36 "2009-01-30T15:08:03Z")
> [@Anne\_Neville](#): > > It was! I’m enjoying it immensely. > > I can tell you that this is true of majoring in physics. You really do a lot of slogging through problem sets, or at least I did when I was getting my undergrad degree in physics. And then there are the labs. I would say that “being willing and able to put in a lot of time doing the work for your classes” is at least as important as raw intelligence for a physics major. It really isn’t a matter of reading something like “space and time are the same thing” and immediately and intuitively understanding what that means- it’s doing a lot of problems where you have to treat space and time the same way. In my graduate school, there was a minimum they required on the standardized tests (the math ones). It wasnt a HARD rule to be admitted, if you could convince them some other way that you could grok the math at the required level, they would consider that. But, having said that, years of experience had shown them that statistically speaking, if you didnt test at some fairly above average math level, you just werent going to be able to cut it in the program. And these professors seemed to be the nice ones that WANTED more folks in the program, not some elitist snobs looking for any reason to keep folks out. For what its worth. ---
**Author:** ![billfish678](https://avatars.discourse-cdn.com/v4/letter/b/7bcc69/32.png) [@billfish678](https://boards.straightdope.com/u/billfish678)\ **Post date:** [January 30, 2009, 3:49pm UTC](https://boards.straightdope.com/t/what-is-inside-a-black-hole/483570/37 "2009-01-30T15:49:27Z")
> [@Stranger\_On\_A\_Train](#): > > Neutron stars (and other exotic hypothetical celestial bodies like quark stars) are still theoretical. Because of the tendency of unbound neutrons to decay it is unclear how such a body would behave or exactly what type of matter it would be composed of. Mass inside of a singularity, compressed by the curvature of space into an unimaginably small point, much denser than even quarks pressed “edge to edge”. We can’t really say what form mass takes in that form; indeed, a black hole can in many ways be considered a giant composite quantum particle. > Stranger I thought neutron stars (like black holes) were fairly well confirmed observationally ? As to how they work detail wise (like black holes), thats a whole nuther issue . ---
**Author:** ![Anne\_Neville](https://avatars.discourse-cdn.com/v4/letter/a/b9e5f3/32.png) [@Anne\_Neville](https://boards.straightdope.com/u/Anne_Neville)\ **Post date:** [January 30, 2009, 4:00pm UTC](https://boards.straightdope.com/t/what-is-inside-a-black-hole/483570/38 "2009-01-30T16:00:54Z")
[quote=“billfish678, post:36, topic:483570”] In my graduate school, there was a minimum they required on the standardized tests (the math ones). It wasnt a HARD rule to be admitted, if you could convince them some other way that you could grok the math at the required level, they would consider that. [quote] I went to grad school in astronomy, not physics. Maybe there was some minimum score on the math GRE, but nobody ever talked about it. I remember the math section of the GRE being really easy, though- supposedly, it’s easier than the math SAT. We did also have to take the physics GRE, which was definitely not easy. It’s not an IQ test, though. It’s a physics test, and supposedly scores vary quite a bit based on where you did your undergrad degree. > [@Exapno Mapcase](#): > > I grok most concepts in advanced physics without an advanced degree. I can’t explain them the way the physicists do There are lots of physicists who aren’t very good at explaining things, too. ---
**Author:** ![martu](https://avatars.discourse-cdn.com/v4/letter/m/e0b2c6/32.png) [@martu](https://boards.straightdope.com/u/martu)\ **Post date:** [January 30, 2009, 4:30pm UTC](https://boards.straightdope.com/t/what-is-inside-a-black-hole/483570/39 "2009-01-30T16:30:50Z")
Do Black Holes grow? ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [January 30, 2009, 5:07pm UTC](https://boards.straightdope.com/t/what-is-inside-a-black-hole/483570/40 "2009-01-30T17:07:08Z")
> [@martu](#): > > Do Black Holes grow? Sure. If the Black Hole has something to “feed” off of it will grow. For instance, occasionally there is a star orbiting a black hole and the black hole is siphoning off material from the star. Since the black hole is gaining mass it is growing. Eventually the BH will completely consume the star (or the companion star, if of the right size, may form into a black hole too…eventually the two black holes would merge making one bigger one). [Previous page](https://boards.straightdope.com/t/what-is-inside-a-black-hole/483570.md?page=1) [Next page](https://boards.straightdope.com/t/what-is-inside-a-black-hole/483570.md?page=3)