# space traveling singularty **URL:** \ **Category:** Factual Questions\ **Created:** [April 1, 2003, 1:34pm UTC](https://boards.straightdope.com/t/space-traveling-singularty/165694 "2003-04-01T13:34:17Z")\ **Posts on this page:** 12\ **Page:** 2

**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [April 2, 2003, 2:09am UTC](https://boards.straightdope.com/t/space-traveling-singularty/165694/21 "2003-04-02T02:09:16Z")

Black holes don’t magically “break the laws of physics”. It is more accurate to say, our current understanding of the laws of physics can’t predict exactly what happens to the mass at the center of a black hole. Relativity predicts that it collapses into a point of zero volume and infinite density, which is really saying that our math fails at that point. Our best guess about what really happens is that quantum effects become important at a very small but non-zero radius. Just what we don’t know, and would like to. ---

**Author:** ![\_Tim](https://avatars.discourse-cdn.com/v4/letter/_/e47c2d/32.png) [@\_Tim](https://boards.straightdope.com/u/_Tim)\ **Post date:** [April 2, 2003, 4:14am UTC](https://boards.straightdope.com/t/space-traveling-singularty/165694/22 "2003-04-02T04:14:43Z")

A black hole travelling close to the speed of light observed by a ‘stationary’ observer will look **exactly** like what a ‘stationary’ black hole would look like to an observer travelling close to the speed of light. I mean that in a strict, mathematical sense: the two situations are literally indistinguishable. ‘stationary’ is simply a matter of perspective, and is an arbitrary choice. That’s what relativity means… ---

**Author:** ![bryanmcc](https://avatars.discourse-cdn.com/v4/letter/b/eada6e/32.png) [@bryanmcc](https://boards.straightdope.com/u/bryanmcc)\ **Post date:** [April 2, 2003, 3:04pm UTC](https://boards.straightdope.com/t/space-traveling-singularty/165694/23 "2003-04-02T15:04:31Z")

And what does that look like, **(Tim)**? I guess that puts the singularity back in the center of the event horizon, but wouldn’t the event horizon be foreshortened in the direction of travel, approaching a disk as the observer approaches the speed of light? ---

**Author:** ![shea241](https://avatars.discourse-cdn.com/v4/letter/s/439d5e/32.png) [@shea241](https://boards.straightdope.com/u/shea241)\ **Post date:** [April 2, 2003, 4:10pm UTC](https://boards.straightdope.com/t/space-traveling-singularty/165694/24 "2003-04-02T16:10:12Z")

I know this might sound stupid but does anybody know how big a singularity accually is. What I mean is… is it an accual spot in space takeing uponly one spot in space no width no length just a single spot in space. Or does it have length and width maybe it is the size of this period. ---

**Author:** ![Earthworm\_Jim](https://avatars.discourse-cdn.com/v4/letter/e/f07891/32.png) [@Earthworm\_Jim](https://boards.straightdope.com/u/Earthworm_Jim)\ **Post date:** [April 2, 2003, 5:27pm UTC](https://boards.straightdope.com/t/space-traveling-singularty/165694/25 "2003-04-02T17:27:55Z")

Many of the answers so far seem to regard the black hole itself as an object (re a ‘black hole’ gaining mass, spinning, etc). I thought a black hole wasn’t an object in and of itself - isn’t a black hole an area defined by the mass of the singularity? Wouldn’t the behavior of a black hole be governed by the behavior of the singularity? And, as a tangent, infinite density is not the same as infinite mass, is it? ---

**Author:** ![Urban\_Ranger](https://avatars.discourse-cdn.com/v4/letter/u/e9c0ed/32.png) [@Urban\_Ranger](https://boards.straightdope.com/u/Urban_Ranger)\ **Post date:** [April 2, 2003, 5:57pm UTC](https://boards.straightdope.com/t/space-traveling-singularty/165694/26 "2003-04-02T17:57:22Z")

> [@](#): > > \*Originally posted by bryanmcc \* > Care to expand upon that? I thought most physicists (including Stephen Hawking, if I’m not mistaken) believe that naked singularities are forbidden. Could it perhaps be that in order for the singularity to become naked, it would have to rotate faster than the speed of light, and so is forbidden? The Cosmic Censorship is nothing more than a hypothesis. According to Roy Kerr, there is a mathematical solution to Einstein’s GR equations for a rotating black hole with a ring-shaped event horizon. ---

**Author:** ![g8rguy](https://avatars.discourse-cdn.com/v4/letter/g/7cd45c/32.png) [@g8rguy](https://boards.straightdope.com/u/g8rguy)\ **Post date:** [April 2, 2003, 7:21pm UTC](https://boards.straightdope.com/t/space-traveling-singularty/165694/27 "2003-04-02T19:21:39Z")

A few comments, if I may. 1. **shea** , no one knows how big a singularity is. In classical GR, it’s just a point. But quantum mechanics plays a role in there somewhere, and we don’t know how yet. Presumably, it’s not in fact a point, but I don’t believe anyone can tell you how big it really is. 2. **Beelzebubba** , infinite density is not the same as infinite mass, no. Why do you ask? 3. Yes, there is a solution for a rotating black hole, just as there is a solution for a charged black hole (and, for that matter, a rotating charged black hole). I don’t remember the conditions, if any, on what angular momentum a Kerr black hole would have to satisfy lest the singularity be revealed. ---

**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [April 3, 2003, 7:07am UTC](https://boards.straightdope.com/t/space-traveling-singularty/165694/28 "2003-04-03T07:07:52Z")

If it is, in fact, a singularity, then it’s a point, by definition. Most relativists suspect that it’s actually a very small region, perhaps of order the Planck size, but we won’t know until we have a good, working quantum theory of gravity, which is rather the Holy Grail of physics at the moment. And the censorship condition on black holes is that q[sup]2[/sup] + a[sup]2[/sup] \< M, where q is the charge, a is the angular momentum per unit mass, and M is the mass of the hole. Units are chosen in such a way that Newton’s, Einstein’s, and Coulomb’s constants (G, c, and k[sub]e[/sub]) are all 1. Actually, if there exist magnetic charges, or any other sort of charges, you need to add extra terms to the left side of that inequality, but the form is the same. Typical astrophysical black holes are expected to have all charges much less than the mass, but considerable angular momentum. Most are expected to have a equal to about .9 M, or so, and the stars which become black holes very often have a two or three times greater than M (the extra angular momentum is carried away in matter ejected in the supernova and in gravitational waves). A Kerr black hole, by the way, has a ring singularity, but the event horizon is still topologically a sphere. ---

**Author:** ![Hombre](https://avatars.discourse-cdn.com/v4/letter/h/ecb155/32.png) [@Hombre](https://boards.straightdope.com/u/Hombre)\ **Post date:** [April 3, 2003, 8:11am UTC](https://boards.straightdope.com/t/space-traveling-singularty/165694/29 "2003-04-03T08:11:06Z")

Chronos, “If it is, in fact, a singularity, then it’s a point, by definition.” Isn’t that a mathmatical definition? I asumed the OP was refering to actual matter that has been compressed (allowing Planck). If you are assuming that that compressed matter has no 3D measurements, aren’t you opening the door for a 4th (or more) diminsion(s)? I believe singularity is a handy way to communicate very complicated and yet understood concepts. ## Re: micco - "quote: ## Originally posted by shea241 How would the event horizon effect the singularty if at the speed of light there could be no event horizon. I say this because if it’s going the speed of light then shouldn’t the light thats in front of the direction the singularity is heading get sucked into the singularity and anything behind the singularity would now be following behind the singularity. This is like the intro-to-relativity problem that asks what happens if a car is going the speed of light and turns on its headlights. The answer (I believe) is that they work normally because the speed of light is constant even in a moving reference frame." Does this work EVEN at the speed of light? Finally, sorry if I missed the answer, but does a moving (to a stationary observer) BH have a eliptoid EH? ---

**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [April 3, 2003, 10:39am UTC](https://boards.straightdope.com/t/space-traveling-singularty/165694/30 "2003-04-03T10:39:10Z")

Some stuff on Kerr black holes [here](http://www.astronomical.org/astbook/blkhole.html) I was wrong, it is not the event horizon which is oblate, it is a region called the_ergosphere_ - in this region it is possible to escape, but it is not possible to avoid being dragged round by the rotating singularity inside the event horizon. However, a relativistic black hole should be contracted in the direction of travel to a stationary observer, but would appear normal to a co-travelling observer… and you can’t turn your lights on at the speed of light because no time passes. ---

**Author:** ![Earthworm\_Jim](https://avatars.discourse-cdn.com/v4/letter/e/f07891/32.png) [@Earthworm\_Jim](https://boards.straightdope.com/u/Earthworm_Jim)\ **Post date:** [April 3, 2003, 12:33pm UTC](https://boards.straightdope.com/t/space-traveling-singularty/165694/31 "2003-04-03T12:33:10Z")

> [@](#): > > \*Originally posted by g8rguy \* > **Beelzebubba** , infinite density is not the same as infinite mass, no. Why do you ask? > \*\* No good reason 🙂 For a split second there I thought I had discovered the **Physics of the New Order** [sup]TM[/sup] - The infinite mass of a black hole means it’s always travelling at light speed!!! Then I thought “Hang about - that’s density, not mass, and the one is not the other” And it made it into my post. Maybe I’ll start a conspiracy theory and work it in somehow. Y’know, for grins 🙂 ---

**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [April 3, 2003, 7:47pm UTC](https://boards.straightdope.com/t/space-traveling-singularty/165694/32 "2003-04-03T19:47:10Z")

> [@](#): > > Isn’t that a mathmatical definition? I asumed the OP was refering to actual matter that has been compressed (allowing Planck). If you are assuming that that compressed matter has no 3D measurements, aren’t you opening the door for a 4th (or more) diminsion(s)? I believe singularity is a handy way to communicate very complicated and yet understood concepts. The point is, there’s… something at the center of the black hole. According to General Relativity, it’s a true mathematical singularity. In quantum gravity, it might turn out to be really compressed, but not quite a singularity. If that’s the case, then it’s still plenty weird, but not nearly as weird as a true singularity. And both the ergosphere and the event horizon are oblate in a Kerr black hole, the ergosphere is just more oblate. As for driving at the speed of light and turning on your headlights, the question is meaningless. An object with rest mass just plain can’t go the speed of light, and once you start assuming things which can’t happen, you can come to absolutely any conclusion at all. [Previous page](https://boards.straightdope.com/t/space-traveling-singularty/165694.md?page=1)