6 ms·

> Isn't "heating" a function of regular energy and matter? I'm a bit confused at what made you think this. If there is any way to transfer energy from it to so

> Isn't "heating" a function of regular energy and matter? I'm a bit confused at what made you think this. If there is any way to transfer energy from it to something else (which there must be, else it would be impossible to ever interact with it), then it can heat in exactly the same way as anything else.

andsoitis 3y ago
Thanks. That makes sense. I think the confusing thing for me is that dark matter doesn’t interact with the electromagnetic field so it doesn’t reflect, absorb, or emit electromagnetic radiation. But your explanation makes sense to me.
- Sharlin 3y ago
  As the article says, the proposed mechanism is self-annihilation, which would presumably produce energy in the form of perfectly ordinary photons.
  - AnimalMuppet 3y ago
    That seems wrong. "Dark matter" usually means matter that doesn't interact with photons, not just "matter that is dark because no light is shining on it". But if it emits photons, even in a matter-antimatter reaction, then it couples with photons, and so it can't be dark matter in that sense.
    - Sharlin 3y ago
      Apparently (eg. [1]) there would be a couple of different pathways available for WIMP annihilation, to a W⁺W⁻ boson pair, or to μ⁺μ⁻ muon pair, or a e⁺e⁻ electron-positron pair, so the immediate annihilation products would be charged non-dark matter particles which would either quickly decay or annihilate into photons or simply shed their energy via normal EM interactions. [1] P. Salati, 2014. Dark Matter Annihilation in the Universe. https://arxiv.org/abs/1403.4495 https://arxiv.org/abs/1403.4495
    - simonh 3y ago
      Sure, it’s only called dark matter because we find it hard to observe it.
wyager 3y ago
Conceivably there could be interactions which are sufficiently constrained to prevent the equipartition theorem from coming into play in practice. For example, an interaction with a massive carrier may not be able to support thermal transfer except at very high energies. Gravitational heat transfer would, I assume, work for everything, but it would also be very very slow. We're a little bit spoiled by EM - it makes thermal interactions happen quickly and at all energy scales.
- some_furry 3y ago
  There's also the Unruh effect, where being in a gravity well causes radiation https://en.wikipedia.org/wiki/Unruh_effect https://en.wikipedia.org/wiki/Unruh_effect (I don't know if this is relevant at all! Just an interesting tangent)
idiotsecant 3y ago
[flagged]
- bowsamic 3y ago
  I'm not sure why what I said warranted such an aggressive response. Can you explain more?
- MattPalmer1086 3y ago
  I did not read the parent post as aggressive at all. Maybe you could chill out a bit?
- sebzim4500 3y ago
  For what it's worth your comment reads about ten times more obnoxious than the guy you are replying to.
Beldin 3y ago
Not OP, but: > If there is any way to transfer energy, then it can heat in exactly the same way as anything else. If it could heat up, Dark Matter wouldn't be dark. So yeah, dark matter that heats isn't quite what one would expect.
- bowsamic 3y ago
  > If it could heat up, Dark Matter wouldn't be dark. I don't think this is correct at all. A system doesn't have to interact with EM to be thermodynamic. If you can define a temperature for it and there is the possibility for energy transfer, then it can heat up
  - ninkendo 3y ago
    > there is the possibility for energy transfer I think this is where the debate is. I’m not a physicist but my understanding of the current dark matter models is that it doesn’t interact with itself in a way that could be thought of as “energy transfer” (ie. like particles that collide), but only gravitationally. This would mean there’s no real way for a dark matter “particle” to transfer momentum to another particle, and thus no real way for “heat” to exist as such.
    - bowsamic 3y ago
      Gravity can transfer energy. For example gravitational waves transfer energy. They can be used to boil a kettle of strong enough

andsoitis 3y ago

Thanks. That makes sense. I think the confusing thing for me is that dark matter doesn’t interact with the electromagnetic field so it doesn’t reflect, absorb, or emit electromagnetic radiation. But your explanation makes sense to me.

Sharlin 3y ago
As the article says, the proposed mechanism is self-annihilation, which would presumably produce energy in the form of perfectly ordinary photons.
- AnimalMuppet 3y ago
  That seems wrong. "Dark matter" usually means matter that doesn't interact with photons, not just "matter that is dark because no light is shining on it". But if it emits photons, even in a matter-antimatter reaction, then it couples with photons, and so it can't be dark matter in that sense.
  - Sharlin 3y ago
    Apparently (eg. [1]) there would be a couple of different pathways available for WIMP annihilation, to a W⁺W⁻ boson pair, or to μ⁺μ⁻ muon pair, or a e⁺e⁻ electron-positron pair, so the immediate annihilation products would be charged non-dark matter particles which would either quickly decay or annihilate into photons or simply shed their energy via normal EM interactions. [1] P. Salati, 2014. Dark Matter Annihilation in the Universe. https://arxiv.org/abs/1403.4495 https://arxiv.org/abs/1403.4495
  - simonh 3y ago
    Sure, it’s only called dark matter because we find it hard to observe it.

wyager 3y ago

Conceivably there could be interactions which are sufficiently constrained to prevent the equipartition theorem from coming into play in practice. For example, an interaction with a massive carrier may not be able to support thermal transfer except at very high energies. Gravitational heat transfer would, I assume, work for everything, but it would also be very very slow. We're a little bit spoiled by EM - it makes thermal interactions happen quickly and at all energy scales.

some_furry 3y ago
There's also the Unruh effect, where being in a gravity well causes radiation https://en.wikipedia.org/wiki/Unruh_effect https://en.wikipedia.org/wiki/Unruh_effect (I don't know if this is relevant at all! Just an interesting tangent)

idiotsecant 3y ago

[flagged]

bowsamic 3y ago
I'm not sure why what I said warranted such an aggressive response. Can you explain more?
MattPalmer1086 3y ago
I did not read the parent post as aggressive at all. Maybe you could chill out a bit?
sebzim4500 3y ago
For what it's worth your comment reads about ten times more obnoxious than the guy you are replying to.

Beldin 3y ago

Not OP, but: > If there is any way to transfer energy, then it can heat in exactly the same way as anything else. If it could heat up, Dark Matter wouldn't be dark. So yeah, dark matter that heats isn't quite what one would expect.

bowsamic 3y ago
> If it could heat up, Dark Matter wouldn't be dark. I don't think this is correct at all. A system doesn't have to interact with EM to be thermodynamic. If you can define a temperature for it and there is the possibility for energy transfer, then it can heat up
- ninkendo 3y ago
  > there is the possibility for energy transfer I think this is where the debate is. I’m not a physicist but my understanding of the current dark matter models is that it doesn’t interact with itself in a way that could be thought of as “energy transfer” (ie. like particles that collide), but only gravitationally. This would mean there’s no real way for a dark matter “particle” to transfer momentum to another particle, and thus no real way for “heat” to exist as such.
  - bowsamic 3y ago
    Gravity can transfer energy. For example gravitational waves transfer energy. They can be used to boil a kettle of strong enough