# What does "infinite density" mean? **URL:** \ **Category:** Factual Questions\ **Created:** [May 2, 2001, 4:31pm UTC](https://boards.straightdope.com/t/what-does-infinite-density-mean/64101 "2001-05-02T16:31:18Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![WIGGUM](https://avatars.discourse-cdn.com/v4/letter/w/ce7236/32.png) [@WIGGUM](https://boards.straightdope.com/u/WIGGUM)\ **Post date:** [May 2, 2001, 4:31pm UTC](https://boards.straightdope.com/t/what-does-infinite-density-mean/64101/1 "2001-05-02T16:31:18Z")
I just read an article on black holes and it explained that they have a point of “infinite density”. Now, I have a hard enough time wrapping my brain around the idea of “infinity”, but this one really threw me. How can something be infinitely dense? Does this infinitely dense point have any volume? I would think that if it was infinitely dense, it wouldn’t take up any space. So what’s the deal, and could I possibly say infinite enough times? Infinitely thankful, WIGGUM ---
**Author:** ![Johanna](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johanna/32/8318_2.png) [@Johanna](https://boards.straightdope.com/u/Johanna)\ **Post date:** [May 2, 2001, 4:37pm UTC](https://boards.straightdope.com/t/what-does-infinite-density-mean/64101/2 "2001-05-02T16:37:04Z")
Wouldn’t that refer to an asymptotic line whose limit is infinity? ---
**Author:** ![barking\_frog](https://avatars.discourse-cdn.com/v4/letter/b/96bed5/32.png) [@barking\_frog](https://boards.straightdope.com/u/barking_frog)\ **Post date:** [May 2, 2001, 5:46pm UTC](https://boards.straightdope.com/t/what-does-infinite-density-mean/64101/3 "2001-05-02T17:46:54Z")
Correct me if I’m wrong, but black holes are not infinitely dense. As long as you have enough mass inside a small enough volume of space, you will have a black hole. Mathematically speaking, if R \< 2GM/c^2 where G is the gravitational constant, M is mass, and R is the radius, then you will have a black hole. ---
**Author:** ![WIGGUM](https://avatars.discourse-cdn.com/v4/letter/w/ce7236/32.png) [@WIGGUM](https://boards.straightdope.com/u/WIGGUM)\ **Post date:** [May 2, 2001, 6:31pm UTC](https://boards.straightdope.com/t/what-does-infinite-density-mean/64101/4 "2001-05-02T18:31:43Z")
The article I read can be found here: [http://abcnews.go.com/sections/scitech/DailyNews/spinningholes010501.html](http://abcnews.go.com/sections/scitech/DailyNews/spinningholes010501.html) and says the following; > [@](#): > > Scientists believe the black hole Strohmayer studied formed when a star grew to such > bulk it collapsed upon itself. The resulting collapsed matter formed a single point of > **infinite density** that sucks in surrounding matter and even light. ---
**Author:** ![Saltire](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saltire/32/553_2.png) [@Saltire](https://boards.straightdope.com/u/Saltire)\ **Post date:** [May 2, 2001, 6:42pm UTC](https://boards.straightdope.com/t/what-does-infinite-density-mean/64101/5 "2001-05-02T18:42:10Z")
I guess it is wrong to say that a black hole is infinitely dense. A black hole includes the area enclosed by the event horizon, so it has volume. If the event horizon were to shrink to a point (presumably through Hawking radiation), the hole would disappear. What the article probably was trying to describe wasn’t the whole black hole, but the singularity at its center. Some would describe that as infinitely dense, since it does have some mass and does not have any volume. However, most math mavens would hesitate to use that description. At a singularity, density is not defined. Same as with any division by zero. ---
**Author:** ![cjclark](https://avatars.discourse-cdn.com/v4/letter/c/7bcc69/32.png) [@cjclark](https://boards.straightdope.com/u/cjclark)\ **Post date:** [May 2, 2001, 7:28pm UTC](https://boards.straightdope.com/t/what-does-infinite-density-mean/64101/6 "2001-05-02T19:28:35Z")
In some sense this is all rather a moot point. The reason that the term “infinitely dense” often is thrown around when speaking of black holes is that there is nothing stopping the catastrophic collapse of the object. A black hole has reached a state where physics knows of nothing that could resist the gravitational collapse. According to our currently understood laws of physics (perhaps it is better to say, “our current models”) since there is nothing to stop it, the object would in fact be crushed to a point of zero-volume. The name “singularity” is a common mathematical term to describe a point where a function goes ga-ga. If you do the calculations for a black hole, this zero-volume result is a mathematical sigularity. This “object” has also come to bear the name “sigularity” in its own right. Now, why is this all moot? Because this “singularity” is unobservable. No information can cross a black hole’s event horizon. The old (and inaccurate) saying, “Nature abhors a vacuum,” can be applied to black holes. “Nature abhors a naked sigularity.” To spare us the trouble of having to deal with points in space with infinite density, nature conveniently hides them away behind a event horizon where they can never be observed. So, is there a point of infinite density at the center of a black hole? The real answer is that it is not a meaningful question. In a very real sense, nothing that is behind the event horizon exists in our universe except for its gravitational (and rotational, blah-blah) influence. ---
**Author:** ![bughunter](https://avatars.discourse-cdn.com/v4/letter/b/aeb1de/32.png) [@bughunter](https://boards.straightdope.com/u/bughunter)\ **Post date:** [May 2, 2001, 9:34pm UTC](https://boards.straightdope.com/t/what-does-infinite-density-mean/64101/7 "2001-05-02T21:34:48Z")
Well, a lot of hyperbole is being tossed about, but it’s really rather simple. The reason they say it’s “infinite density” is because the singularity of the black hole is predicted to be a point. (It is likely no one will ever verify this first hand, or if they do, that they will be able to tell us about it.) In other words, it has no volume, yet it has rest mass. Since density is mass divided by volume, then you have the rather unique circumstance where the universe is trying to divide by zero.