# Dark energy and dark matter [duplicate]

Our galaxies are speeding apart from each other and that is because of dark energy, but we don't know where it comes from right? If I'm not mistaken could dark matter have dark energy? (If they are the same thing please correct me.) Matter has gravity so could dark matter have dark energy, so sense there is more dark matter is that why our galaxies are being pushed apart?

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## marked as duplicate by Emilio Pisanty, Qmechanic♦Sep 20 '13 at 19:59

Does this answer your question? –  Michael Brown Mar 21 '13 at 23:22
@Michael Brown - Just a little bit but not really. –  Kevril Mar 21 '13 at 23:28
How about this good (as in actually accurate) faq? Specifically the following quote: "What’s the difference between dark energy and dark matter? Completely different. Dark matter is some kind of particle, just one we haven’t discovered yet. We know it’s there because we’ve observed its gravitational influence in a variety of settings (galaxies, clusters, large-scale structure, microwave background radiation)." (cont.) –  Michael Brown Mar 21 '13 at 23:42
I think the wikipedia articles on dark energy and dark matter do answer this question. –  zhermes Mar 21 '13 at 23:43
Possible duplicate: physics.stackexchange.com/q/33466/2451 –  Qmechanic Mar 21 '13 at 23:46

You seem to be caught up on the word "dark." The reasons both things are called "dark something" represents our incomplete knowledge. Beyond this, dark matter and dark energy are no more related than Superman is related to superconductivy, or lightbulbs are related to light exercise.

Dark matter is the term for what appears to be gravitating mass spread out throughout space (but clustering around galaxies) that doesn't interact much if at all with light, thus making it very hard to detect directly.

Dark energy is related to the observation that the universe's expansion is accelerating, which would happen if the universe were filled uniformly with a non-interacting "fluid" whose pressure $P$ is related to its density $\rho$ by $P = -\rho c^2$.

It is rather difficult to argue dark matter is not related to some underlying substance (though some still pursue that line of reasoning), even though we don't know quite how that substance fits in with our understanding of everything else. On the other hand, dark energy is really more of a catch-all for a phenomenon, rather than a description of material stuff that you could collect in a jar.

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+1 for the lightbulb analogy! –  Mark Mitchison Mar 22 '13 at 1:43
Next question: can superman achieve superconductivity? –  Mindwin Aug 18 at 21:52

As others have already stated, dark energy and dark matter are most likely two completely separate phenomena. Most (but certainly not all) cosmologists and particle physicists think that dark matter is likely to be some beyond-the-standard-model particle that doesn't interact with anything besides gravity and maybe the weak force. I also heard a talk at AAS about how there is some (still-sketchy) evidence that dark matter might interact with itself via some sort of "dark force".

The simplest explanation of dark energy is the vacuum energy of space, i.e. what is left over once you take out everything else. This so called "cosmological constant" model of dark energy has so far been very successful, although there is a little bit of tension growing between CMB measurements and supernovae measurements that might favor more exotic dark energy models.

Of course, some people have developed cosmological models where dark energy and dark matter are unified as some sort of dark fluid, but so far there are no observations which explicitly favor these models. In addition, the simplicity gained by "unifying" dark matter/energy is typically lost by the addition of more parameters which are required to fit the data.

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Dark mater is related to phenomena observed about the rotational motion of stars around galaxies, which can be in our neighbourhood. Dark energy is related to the accelerated rate of expansion of the universe and is observed in $\gamma$-photons coming from the remotest galaxies in the universe. I.e. dark energy appears to be a sheer volume effect acting as negative pressure, it does not seem to be a negative gas density pressure. This is why the accelerated rate of expansion is observed at the vast distances between the milky way and the remotest galaxies in the universe. If it relates to a known constant of nature, that would be the cosmological constant which was introduced by Einstein in his field equations, for reasons unrelated to the accelerated expansion.

There is another phenomenon observed recently, the so called Dark flow, associated with the observed accelerated flow of mater in the universe towards a particular direction, but it does not relate to the overall accelerated expansion of the universe. The adjective Dark is used to describe something we don’t really understand, as it has been said in previous answers.

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What caused the Big Bang is dark energy, a strange energy expanding the universe, that's why I chose it.

For dark matter my theory was that as E=mc2, the dark energy can be converted into dark matter. For the properties of dark matter of it being like a ghost(it can pass right through anything).

Dark matter could have an atom that is different from others that might be smaller,﻿ small enough to pass through your body.

Dark matter and energy is basically matter and energy that is ample in the universe that doesn't interact with light making it hard to detect, so it is why the universe looks dark but is transparent.

The reason for dark energy being the cause of the big bang is that, 1, it is one type of energy, 2, it expands the universe, which makes it likely that it expanded the singularity to cause it and 3, it still continues to expand the universe from the start.

Dark matter, as I said, could be a type of matter that has a atom which has different properties, like anti-matter.It could have originated from dark energy as E=mc2, so it is one of the possible origins.

For the origins of dark energy, it is the energy in the singularity that expanded the universe into existence with it's contents.

For the equation is,

(Dm=Dark matter, De=Dark energy)

De=Dmc2, expansion of space=De=Dmc2

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This is merely self-promotion of one's own crackpot theories. This neither explains anythingj, nor does it make any mathematixcal nor observational sense. Nor does its makes some greammatieacalle senses : ) . . . –  Dimensio1n0 Sep 18 '13 at 12:43