# Are black holes, dark matter, and dark energy subject to entropy and/or the conservation law? **URL:** \ **Category:** Factual Questions\ **Created:** [August 15, 2009, 5:33pm UTC](https://boards.straightdope.com/t/are-black-holes-dark-matter-and-dark-energy-subject-to-entropy-and-or-the-conservation-law/506533 "2009-08-15T17:33:29Z")\ **Posts on this page:** 5\ **Page:** 2
**Author:** ![Zoe](https://avatars.discourse-cdn.com/v4/letter/z/a4c791/32.png) [@Zoe](https://boards.straightdope.com/u/Zoe)\ **Post date:** [August 16, 2009, 6:09am UTC](https://boards.straightdope.com/t/are-black-holes-dark-matter-and-dark-energy-subject-to-entropy-and-or-the-conservation-law/506533/21 "2009-08-16T06:09:19Z")
Pardon me. In rereading the OP, I see that Dark Matter _and_ Black Holes are both topics of discussion. Sorry. ---
**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:** [August 16, 2009, 9:48am UTC](https://boards.straightdope.com/t/are-black-holes-dark-matter-and-dark-energy-subject-to-entropy-and-or-the-conservation-law/506533/22 "2009-08-16T09:48:44Z")
> [@Zoe](#): > > Would all of the Laws of Physics be assumed to be true of Dark Matter based on what is true in 4% of the known universe of non-Dark Matter? I have no opinion on this. I am asking what position science would hold at this time of not knowing much of anything about DM. Well, the thing about why conservation of energy is such a fundamental law is the weakness of the assumptions that go into its derivation – basically, you just have to assume that physics works the same tomorrow as it did yesterday (or, somewhat more accurately, that the laws describing a physical system are invariant under continuous time translations), and, via what’s known as [Noether’s theorem](http://en.wikipedia.org/wiki/Noether%27s_theorem), the direct consequence is that energy is conserved (it occurs to me that this might illustrate the problems for global energy conservation in an expanding universe – because there, the physical description is not the same regardless of time, since, well, it’s bigger tomorrow; however, locally, there is no such effect: the space between me and my bed isn’t expanding, and neither are we getting any further away from the sun). And it’s not the case that there isn’t ‘much of anything’ known about dark matter – it’s known that it must interact gravitationally, i.e. have mass (else, it wouldn’t account for the anomalous rotational velocity distribution in galaxies it is supposed to explain), that it doesn’t interact electromagnetically (else, it wouldn’t be ‘dark’, since it would interact with radiation), and some other constraints, as well (I believe it must also be colour-neutral, though I’m not absolutely certain about that). So, what you do is try and dream up extensions to the standard model (or theories replacing it completely, while being at least as compatible with present experimental evidence) that include candidate particles that fit these constraints, and see what other properties these would have according to your model. Then, ideally, if your candidates aren’t already ruled out by some observations, you set up experiments to test whether there are particles with these properties, and if the predictions your model makes are in concordance with the data these experiments yield, you might be onto something. That last part, though, is still some way away. ---
**Author:** ![tim314](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tim314/32/3468_2.png) [@tim314](https://boards.straightdope.com/u/tim314)\ **Post date:** [August 16, 2009, 2:43pm UTC](https://boards.straightdope.com/t/are-black-holes-dark-matter-and-dark-energy-subject-to-entropy-and-or-the-conservation-law/506533/23 "2009-08-16T14:43:16Z")
> [@SandyHook](#): > > I think the problem with this line is in the dividing by the b = zero thing. What you get when you divide by 0 isn’t infinity, it’s indeterminate. So C wouldn’t be infinite, it would meaningless. A/0 is undefined (not the same as indeterminate), but you can say that the limit of A/x goes to infinity as x goes to zero (for positive A). When we talk about something being infinite we almost always actually mean “the limit goes to infinity”. In contrast, 0/0 is indeterminate, because it could be any value. For instance, x/x goes to 1 as x goes to 0, so we could claim 0/0 = 1. But x[sup]2[/sup]/x goes to 0 as x goes to 0, so we could claim 0/0 = 0. ---
**Author:** ![Tom\_Tildrum](https://avatars.discourse-cdn.com/v4/letter/t/e95f7d/32.png) [@Tom\_Tildrum](https://boards.straightdope.com/u/Tom_Tildrum)\ **Post date:** [August 16, 2009, 2:53pm UTC](https://boards.straightdope.com/t/are-black-holes-dark-matter-and-dark-energy-subject-to-entropy-and-or-the-conservation-law/506533/24 "2009-08-16T14:53:37Z")
> [@otorophile](#): > > I think it should be **physicists** have problems with infinity. I believe that **Chronos** has said in previous threads that the currently-prevailing view is that the universe is infinite. ---
**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:** [August 16, 2009, 11:30pm UTC](https://boards.straightdope.com/t/are-black-holes-dark-matter-and-dark-energy-subject-to-entropy-and-or-the-conservation-law/506533/25 "2009-08-16T23:30:19Z")
> [@](#): > > and some other constraints [on dark matter], as well (I believe it must also be colour-neutral, though I’m not absolutely certain about that) So far as we know, everything must be color-neutral, regular and dark matter alike. If you grab the colored quarks in a hadron and try to pull them apart, you’ll end up with a new colorless hadron in each hand. And the entire Universe may or may not be infinite (the simplest model consistent with the known evidence is that it’s infinite, but a finite Universe requires only a slightly less simple model), but the _observable_ Universe, which is all that physics really need concern itself with, is definitely finite. [Previous page](https://boards.straightdope.com/t/are-black-holes-dark-matter-and-dark-energy-subject-to-entropy-and-or-the-conservation-law/506533.md?page=1)