I'm no expert in this stuff, it's just a hobby to me, but I've been reading up on the WIMP theory a bit - layman articles, not published research.

From Wiki on Dark Matter:

It also cannot interact with ordinary matter via electromagnetic forces; in particular, dark matter particles do not carry any electric charge.

But what I've read on WIMP theory is that WIMPs could be made up of Strange Quarks and Neutrons - maybe that's just a theory, not "the theory", but here's my question. Since Strange Quarks have charge, wouldn't WIMPs probobly have charge? and if they don't, what balances out the charge?

Also, and I'm not sure this can be answered in Layman words, but what exactly happens when a particle interacts with Electromagnetic forces. Forget normal matter, lets go back to the early universe when most of the dark matter probobly formed, and there's lots of angry photos flying around and the universe is a bunch of particles - lose protons, neutrons, electrons and stuff. light, as I understand it, passes through dark matter but not lose protons or Neutrons - cause at the time, the universe was opaque. - what exactly happens when a photon hits a proton or an electron that theoretically doesn't happen when the light hits dark matter. I understand what happens when light hits hydrogen for example, well enough, it either passes through or it shoots the electron to a higher orbit.


Strange Quarks and Neutrons are certainly not cadidates for WIMP Dark Matter or even any kind of dark matter at all.

Matter interacting with electromagnetic forces is just that - a force due to its electric charge (or current). Now in particle physics this force is described as the transmission of a (virtual) photon. Also, (real) photons are basically what you call "light".

Ergo, the presence of any charged matter will have an influence on light passing through it. This leads to effects such as diffraction and fluorescence.

If "dark" matter was electrically charged (or made up from electrically charged objects), it would interact with light and show effects like diffraction and fluorescence. Once could therefore use light to see this kind of matter - ergo it is not dark matter, but what we would call dust or interstellar gas.

Now from earth-based experiments we also have strong constraints on whether dark matter can interact via the strong force. This is because we know that we should feel a constant flux of dark matter, since this stuff is also present in the Milky Way. But we've never seen Dark Matter bump into a nucleus, which would happen very often, if is was charged under the strong force.

Therefore, there are only two interactions left that dark matter can participate in: Gravity (which we DO observe) and the Weak force (which we are testing in various experiments right now). The fact that we need particles that interact only though the weak force, but are sufficiently massive to build up in galaxies (actually we think it's the other way round, that galaxies form in blobs of dark matter) leads to the name

W(eakly) I(nteracting) M(assive) P(article).

  • $\begingroup$ Thank you. That's great. Very helpful. Looking at the article I read, seems I'd read it wrong, it's not WIMPs but Macros - which I'd think, would carry a charge but might get away with being unseen dark matter cause they would be heavy enough to be somewhat rare. I'm not saying I believe in Marcos, but it's a curious theory. phys.org/news/… So, follow up question if I may. If Marcos are dark matter, why wouldn't they clump? Maybe we have to prove they exist first to know the answer to that. - thanks again. $\endgroup$ – userLTK Feb 16 '15 at 9:27
  • $\begingroup$ Indeed, Machos have a very different phenomenology. But I think with Machos are highly disfavored, in both astrophysical consideration (e.g. from galaxy cluster collisions) and cosmology (from considerations of BBN and CMB data). $\endgroup$ – Neuneck Feb 16 '15 at 9:32
  • $\begingroup$ Machos. I'm embarrassed that I can't even get a word right. Oops. and Thanks!! $\endgroup$ – userLTK Feb 16 '15 at 11:33

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