# Dark Matter and Dark Energy **URL:** \ **Category:** Factual Questions\ **Created:** [December 13, 2016, 12:58am UTC](https://boards.straightdope.com/t/dark-matter-and-dark-energy/774572 "2016-12-13T00:58:15Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Enola\_Straight](https://avatars.discourse-cdn.com/v4/letter/e/dec6dc/32.png) [@Enola\_Straight](https://boards.straightdope.com/u/Enola_Straight)\ **Post date:** [December 13, 2016, 12:58am UTC](https://boards.straightdope.com/t/dark-matter-and-dark-energy/774572/1 "2016-12-13T00:58:15Z")
Dark Matter > **[Dark matter](https://en.wikipedia.org/wiki/Dark_matter)** > > Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe. Dark matter is called "dark" because it does not appear to interact with the electromagnetic field, which means it does not absorb, reflect, or emit electromagnetic radiation and is, therefore, difficult to detect. Various astrophysical observations – including gravitational effects which cannot be explained by currently accepted theories of gravity unless more matter is present Dark Energy > **[Dark energy](https://en.wikipedia.org/wiki/Dark_energy)** > > In physical cosmology and astronomy, dark energy is an unknown form of energy that affects the universe on the largest scales. The first observational evidence for its existence came from measurements of supernovas, which showed that the universe does not expand at a constant rate; rather, the universe's expansion is accelerating. Understanding the universe's evolution requires knowledge of its starting conditions and composition. Before these observations, scientists thought that all forms Two... Looking at these representations of the distribution of matter in the universe… [![](http://www.paranormalmagazine.co.uk/wp-content/uploads/2010/02/dark-matter.jpg) ](http://www.paranormalmagazine.co.uk/wp-content/uploads/2010/02/dark-matter.jpg) [http://breakingenergy.com/wp-content/uploads/sites/2/2015/05/dark-matter.jpg](http://breakingenergy.com/wp-content/uploads/sites/2/2015/05/dark-matter.jpg) I’ve noticed that there are bubble-like voids between galaxy clusters. If dark matter and dark energy are in fact two halves of the same coin, could it be stated that dark matter collects more dark matter…gravity…and dark energy generates more dark energy…some kind of spacio-genesis? ---
**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:** [December 13, 2016, 2:08am UTC](https://boards.straightdope.com/t/dark-matter-and-dark-energy/774572/2 "2016-12-13T02:08:16Z")
> [@](#): > > If dark matter and dark energy are in fact two halves of the same coin… We have no particular reason to believe this to be true, as the only thing they have in common, in our current understanding, is that we know so little about either. But there are plenty of things that we know little about, so it’s not all that remarkable a coincidence. > [@](#): > > …could it be stated that dark matter collects more dark matter…gravity…and dark energy generates more dark energy…some kind of spacio-genesis? These are actually both true, or at least approximately so, though I rather suspect that that’s an accident. Dark matter is matter and has gravity, and so it’ll attract other matter (of all sorts). Clumps of dark matter will attract more dark matter, and will also attract baryonic matter, and likewise baryonic matter will attract both more baryonic and dark. Meanwhile, dark energy, so far as we can tell, has a constant density in space, regardless of the expansion (or contraction) of space. And it causes the Universe to expand. As the Universe expands, one could say that “more space is created”, and since that space is just as full of dark energy as anywhere (and anywhen) else in the Universe, there’s more dark energy, too. The voids you see don’t really have much to do with dark energy: Since it’s inherently uniform, it won’t cause clumping. Matter (of any sort) will, though. And though any kind of matter works for this, there’s a lot more dark matter, so it’s responsible for most of the clumping. The voids are just places where there isn’t a clump. ---
**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:** [December 13, 2016, 2:08am UTC](https://boards.straightdope.com/t/dark-matter-and-dark-energy/774572/3 "2016-12-13T02:08:01Z")
> [@](#): > > If dark matter and dark energy are in fact two halves of the same coin… We have no particular reason to believe this to be true, as the only thing they have in common, in our current understanding, is that we know so little about either. But there are plenty of things that we know little about, so it’s not all that remarkable a coincidence. > [@](#): > > …could it be stated that dark matter collects more dark matter…gravity…and dark energy generates more dark energy…some kind of spacio-genesis? These are actually both true, or at least approximately so, though I rather suspect that that’s an accident. Dark matter is matter and has gravity, and so it’ll attract other matter (of all sorts). Clumps of dark matter will attract more dark matter, and will also attract baryonic matter, and likewise baryonic matter will attract both more baryonic and dark. Meanwhile, dark energy, so far as we can tell, has a constant density in space, regardless of the expansion (or contraction) of space. And it causes the Universe to expand. As the Universe expands, one could say that “more space is created”, and since that space is just as full of dark energy as anywhere (and anywhen) else in the Universe, there’s more dark energy, too. The voids you see don’t really have much to do with dark energy: Since it’s inherently uniform, it won’t cause clumping. Matter (of any sort) will, though. And though any kind of matter works for this, there’s a lot more dark matter, so it’s responsible for most of the clumping. The voids are just places where there isn’t a clump. ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [December 13, 2016, 2:26am UTC](https://boards.straightdope.com/t/dark-matter-and-dark-energy/774572/4 "2016-12-13T02:26:09Z")
There’s an article on the voids in this month’s Discover, but it’s beyond a paywall. I found it an interesting read. [http://discovermagazine.com/2016/dec/nothing-really-matters](http://discovermagazine.com/2016/dec/nothing-really-matters) ---
**Author:** ![Asympotically\_fat](https://avatars.discourse-cdn.com/v4/letter/a/e47c2d/32.png) [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)\ **Post date:** [December 13, 2016, 3:37am UTC](https://boards.straightdope.com/t/dark-matter-and-dark-energy/774572/5 "2016-12-13T03:37:24Z")
Whatever the form of dark energy (i.e. quintessence, cosmological constant, phantom energy), if you have a region where dark energy dominates that region expands and the the total dark energy in that region increases. I suppose that could be described as generating more dark energy. When studying the accumulation of matter on large scales, there’s no reason to distinguish between cold dark matter and normal visible matter, except to say that CDM makes up the majority of matter. Whether the matter density of a region increases or not is a more complicated question as it involves perturbation theory, but it is true that if a region is dense enough its density will increase until it collapses and becomes gravitationally bound. ---
**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:** [December 13, 2016, 2:38pm UTC](https://boards.straightdope.com/t/dark-matter-and-dark-energy/774572/6 "2016-12-13T14:38:56Z")
> [@](#): > > When studying the accumulation of matter on large scales, there’s no reason to distinguish between cold dark matter and normal visible matter, except to say that CDM makes up the majority of matter. And except that the visible matter is a lot easier to study, being, well, visible. And there’s also the matter that dark matter probably has a lot less self-interaction than visible matter, which makes certain kinds of clumping less likely.