<p>Yes, as mentioned elsewhere, it is possibly possible. Dark matter particles may be intrinsically unstable (though having long lifetimes, which are at least significantly longer than Hubble time).</p>

<p>Check for more info here:
<a href="http://arxiv.org/abs/1307.6434" rel="nofollow">http://arxiv.org/abs/1307.6434</a></p>

CC BY-SA 3.0
2014-01-14T14:40:34.403Z
Could it be exotic in such a way that it becomes hydrogen, similarly to how hydrogen turns into helium through fusion? Then if ordinary visible matter turns into dark matter somehow, it would be a full circle.
frodeborli
CC BY-SA 3.0
2014-01-14T14:47:03.767Z
There wouldn't be a full circle, due to first and second laws of thermodynamics: ordinary matter would need a lot of energy to transform back into dark matter particles. But DM can create some ordinary matter, hypothetically.
Alexey Bobrick
CC BY-SA 3.0
2014-01-14T16:54:59.017Z
Hmm... Thus requiring it to accumulate energy for billions of years. By the way, DM could be a chemical element at the end of the periodic table "anti radioactive" which then splits to become hydrogen. I just want it to be full circle because it would almost guarantee the creation of life by chance, and enable civilizations that are billions of years old and a lot more, but I'm on very thin ice here... :)
frodeborli
CC BY-SA 3.0
2014-01-14T19:12:53.080Z
What do you mean "..due to dark matter accumulating energy." ?
astromax
CC BY-SA 3.0
2014-01-14T20:20:40.317Z
DM is certainly not made of chemical elements with baryonic composition of the atomic nucleus, no matter how strange. That's ruled out by Planck data.
Gerald
CC BY-SA 3.0
2014-01-14T22:15:25.917Z
I don't know possible mechanisms for how dark matter could turn into hydrogen. I also don't know mechanisms which would allow matter to become dark matter. But if that somehow was possible, then that has a lot of implications for both the past and the future of the universe.
frodeborli
CC BY-SA 3.0
2014-01-15T08:24:23.717Z
@astromax To me, the basis for the question is somewhat philosophical and is basically about if DM could be the origin or the end of ordinary matter, or even better if DM is *both*, creating a full circle. A full circle would of course require a lot of energy. Then I'm simply asking if that energy could be accumulated over billions of years.
frodeborli
CC BY-SA 3.0
2014-01-15T15:24:44.043Z
@frodeborli I have no idea what you mean by "A full circle would of course require a lot of energy." And no, my question is not a philosophical one - I'd like clarification from AlexeyBobrick regarding his statement about the "dark matter accumulating energy".
astromax
CC BY-SA 3.0
2014-01-15T15:47:04.807Z
@astromax: oh, it was a comment on a phrase in the question mentioning DM decaying because of some energy accumulation. I have modified the question after to make it more scientifically robust but haven't updated my answer.
Alexey Bobrick
CC BY-SA 3.0
2014-01-15T16:03:49.280Z
@AlexeyBobrick Ah, I understand.
astromax
CC BY-SA 3.0
2014-01-15T20:36:55.940Z
@astromax By full circle, I meant that matter goes from dark matter, to hydrogen, to other elements then back to dark matter once it had accumulated the energy it would need to do that. It's not a scientific statement, just an idea. There seem to be a lot of strange matter in the world, so why not?
frodeborli
CC BY-SA 3.0
2014-01-14T13:58:16.677Z
2014-01-15T15:47:17.730Z
2014-01-15T15:47:17.730Z
Alexey Bobrick
<p>Dark matter is actually matter. Real matter, just that we can not observe it.</p>

<p>Part of it is actually cold hydrogen, and even cold dust.</p>

<p>Other parts of it are actually different particles that may decay. But that does not mean formation of new Hydrogen. To form Hydrogen you need both a proton and an electron to get bound together, and this implies they meeting, which is very difficult in low density regions like those of extragalactic dark matter.</p>

CC BY-SA 3.0
2014-01-14T14:43:19.743Z
Pure hydrogen and "dust" should be observable, but dark matter is only indirectly observed.
frodeborli
CC BY-SA 3.0
2014-01-14T14:44:31.150Z
Well, protons are ionised hydrogen. And given that IGM is very hot and significantly ionised, protons to contribute to hydrogen.
Alexey Bobrick
CC BY-SA 3.0
2014-01-14T19:11:06.417Z
Dark matter behaves the same way as mass does (gravitationally speaking), but it is absolutely not simply dust and gas that we have a hard time seeing. Dust and gas still interact electromagnetically (that is, emit photons; albeit at lower frequencies if cold). Dark matter appears not to interact electromagnetically. They are completely different categories.
astromax
CC BY-SA 3.0
2014-01-17T16:45:44.203Z
@astromax, in fact, some part of what is called DM can come from our incomplete knowledge of IGM or even from not so easily observable outer parts of spiral galaxies.
Alexey Bobrick
CC BY-SA 3.0
2014-01-17T16:49:48.213Z
So you're saying that part of the "dark matter" that has is out there is matter that we simply cannot see well enough? If so, I couldn't agree with you LESS: http://physics.stackexchange.com/questions/78873/does-the-term-dark-matter-apply-to-nonluminescent-bodies-which-still-interact/78882#78882
astromax
CC BY-SA 3.0
2014-01-18T02:29:54.740Z
I agree completely with @astromax. Part (not all, of course, and probably not the main part) of the dark matter is just unobservable ordinary matter that is detected only due to gravitational effects. Hence the name.
Envite
CC BY-SA 3.0
2014-07-24T08:47:05.290Z
@astromax is saying that dark matter comes from **non-baryonic** matter. The point is that it isn't ordinary matter we are "missing", it is a new type of matter that doesn't interact the same way that normal (i.e. baryonic) matter interacts.
Aaron
CC BY-SA 3.0
2014-07-24T12:43:48.627Z
@Aaron this is not how Dark Matter is defined in Astronomy, when we make rotation profiles for galaxies. Dark matter is ordunary matter, but just dark=unobservable.
Envite
CC BY-SA 3.0
2014-07-24T18:26:04.467Z
@Envite That is absolutely incorrect. Astronomer's do not define dark matter as cold gas, dust, or the like, which is simply unobservable.
astromax
CC BY-SA 3.0
2014-07-24T23:14:29.717Z
https://en.wikipedia.org/wiki/Baryonic_dark_matter
Envite
CC BY-SA 3.0
2014-07-29T19:10:40.860Z
From your link: "Both indicate that the amount of baryonic dark matter is much smaller than the total amount of dark matter." Therefore, baryonic dark matter has a very small impact on our understanding of dark matter and while you can mention that there is baryonic matter that we can't observe, it is not the answer to the question.
Aaron
CC BY-SA 3.0
2014-01-14T13:59:30.687Z
2014-01-14T13:59:30.687Z
Envite
<p>Is it possible that dark matter particles are unstable and the existing dark matter will decay in the long run and turn into hydrogen, for example? What would be possible mechanisms for such a decay?</p>

<p>Could some of the hydrogen we observe be "new" hydrogen, i.e. be the product of dark matter decay?</p>

<dark-matter><dark-energy><hydrogen>
Could dark matter particles be unstable?
frodeborli
# Could dark matter particles be unstable?

(Asked by: username_0 on 2014-01-14)

Is it possible that dark matter particles are unstable and the existing dark matter will decay in the long run and turn into hydrogen, for example? What would be possible mechanisms for such a decay?

Could some of the hydrogen we observe be "new" hydrogen, i.e. be the product of dark matter decay?

**Tags:** dark-matter, dark-energy, hydrogen

---

## 2 answers

### Answer by username_1 on 2014-01-14. Score: 4

Yes, as mentioned elsewhere, it is possibly possible. Dark matter particles may be intrinsically unstable (though having long lifetimes, which are at least significantly longer than Hubble time).

Check for more info here:
<http://arxiv.org/abs/1307.6434>

> **Comments:**
> **username_0**: Could it be exotic in such a way that it becomes hydrogen, similarly to how hydrogen turns into helium through fusion? Then if ordinary visible matter turns into dark matter somehow, it would be a full circle.  
> **username_1**: There wouldn't be a full circle, due to first and second laws of thermodynamics: ordinary matter would need a lot of energy to transform back into dark matter particles. But DM can create some ordinary matter, hypothetically.  
> **username_0**: Hmm... Thus requiring it to accumulate energy for billions of years. By the way, DM could be a chemical element at the end of the periodic table "anti radioactive" which then splits to become hydrogen. I just want it to be full circle because it would almost guarantee the creation of life by chance, and enable civilizations that are billions of years old and a lot more, but I'm on very thin ice here... :)  
> **username_2**: What do you mean "..due to dark matter accumulating energy." ?  
> **username_3**: DM is certainly not made of chemical elements with baryonic composition of the atomic nucleus, no matter how strange. That's ruled out by Planck data.  
> **username_0**: I don't know possible mechanisms for how dark matter could turn into hydrogen. I also don't know mechanisms which would allow matter to become dark matter. But if that somehow was possible, then that has a lot of implications for both the past and the future of the universe.  
> **username_0**: @astromax To me, the basis for the question is somewhat philosophical and is basically about if DM could be the origin or the end of ordinary matter, or even better if DM is *both*, creating a full circle. A full circle would of course require a lot of energy. Then I'm simply asking if that energy could be accumulated over billions of years.  
> **username_2**: @frodeborli I have no idea what you mean by "A full circle would of course require a lot of energy." And no, my question is not a philosophical one - I'd like clarification from AlexeyBobrick regarding his statement about the "dark matter accumulating energy".  
> **username_1**: @astromax: oh, it was a comment on a phrase in the question mentioning DM decaying because of some energy accumulation. I have modified the question after to make it more scientifically robust but haven't updated my answer.  
> **username_2**: @AlexeyBobrick Ah, I understand.  
> **username_0**: @astromax By full circle, I meant that matter goes from dark matter, to hydrogen, to other elements then back to dark matter once it had accumulated the energy it would need to do that. It's not a scientific statement, just an idea. There seem to be a lot of strange matter in the world, so why not?  

---

### Answer by username_4 on 2014-01-14. Score: 1

Dark matter is actually matter. Real matter, just that we can not observe it.

Part of it is actually cold hydrogen, and even cold dust.

Other parts of it are actually different particles that may decay. But that does not mean formation of new Hydrogen. To form Hydrogen you need both a proton and an electron to get bound together, and this implies they meeting, which is very difficult in low density regions like those of extragalactic dark matter.

> **Comments:**
> **username_0**: Pure hydrogen and "dust" should be observable, but dark matter is only indirectly observed.  
> **username_1**: Well, protons are ionised hydrogen. And given that IGM is very hot and significantly ionised, protons to contribute to hydrogen.  
> **username_2**: Dark matter behaves the same way as mass does (gravitationally speaking), but it is absolutely not simply dust and gas that we have a hard time seeing. Dust and gas still interact electromagnetically (that is, emit photons; albeit at lower frequencies if cold). Dark matter appears not to interact electromagnetically. They are completely different categories.  
> **username_1**: @astromax, in fact, some part of what is called DM can come from our incomplete knowledge of IGM or even from not so easily observable outer parts of spiral galaxies.  
> **username_2**: So you're saying that part of the "dark matter" that has is out there is matter that we simply cannot see well enough? If so, I couldn't agree with you LESS: http://physics.stackexchange.com/questions/78873/does-the-term-dark-matter-apply-to-nonluminescent-bodies-which-still-interact/78882#78882  
> **username_4**: I agree completely with @astromax. Part (not all, of course, and probably not the main part) of the dark matter is just unobservable ordinary matter that is detected only due to gravitational effects. Hence the name.  
> **username_5**: @astromax is saying that dark matter comes from **non-baryonic** matter. The point is that it isn't ordinary matter we are "missing", it is a new type of matter that doesn't interact the same way that normal (i.e. baryonic) matter interacts.  
> **username_4**: @Aaron this is not how Dark Matter is defined in Astronomy, when we make rotation profiles for galaxies. Dark matter is ordunary matter, but just dark=unobservable.  
> **username_2**: @Envite That is absolutely incorrect. Astronomer's do not define dark matter as cold gas, dust, or the like, which is simply unobservable.  
> **username_4**: https://en.wikipedia.org/wiki/Baryonic_dark_matter  
> **username_5**: From your link: "Both indicate that the amount of baryonic dark matter is much smaller than the total amount of dark matter." Therefore, baryonic dark matter has a very small impact on our understanding of dark matter and while you can mention that there is baryonic matter that we can't observe, it is not the answer to the question.  

---

