[LeifCarrotson]

I am pretty sure this is satire. But this is the internet, so it is hard to tell.

To be clear: to an astrophysicist, "dark" means "does not interact with electromagnetic radiation except through the curvature of space-time by gravity". It only interacts with normal matter in that it affects gravity. It is otherwise completely transparent.

It does no mean "is not currently reflecting or producing visible light". Your closet does not contain dark matter when you close the door.

[logfromblammo]

Well... it might.

Your closet probably has the same concentration of dark matter in it as everywhere else on the surface of Earth. But that quantity is unmeasurable at our current technology level, because any signal we might get is completely obscured by all the noise from bright matter around here.

Dark matter is not matter that does not emit light. A rogue asteroid far from any star is a dark object, but it is not dark matter. If you aimed a radar beam at it, the signal would bounce off, and you could detect the reflected/absorbed/re-emitted signal when it gets back to you. If you somehow found an aggregation of dark matter, your radar beam would not bounce. It would pass right through, like a flashlight beam shining through a crystal ball. Your beam might refract slightly due to the gravity, but it would not reflect. It would be similar to aiming a neutrino beam at the regular asteroid. Most of the beam just passes straight through without interacting.

Not even black holes are dark matter (or if they ever were, they aren't any more), because they absorb light. If one eclipses a known light source, you can see the black spot, along with the lensing around the outside. They interact with light.

[zuminator]

A couple comments here are somewhat conflating dark matter, in general, with non-baryonic matter, which is what we presume to be the primary component of dark matter. Dark matter theories arose because the Milky Way and other galaxies are much heavier than they appear to be based upon the mass of objects in them that we can detect. Therefore we know there's something else out there that has mass, and is spread fairly evenly throughout the galaxy but is otherwise currently undetectable to us. We don't know enough to definitively say what that stuff is or isn't. Part of that mysterious stuff may be MACHOs (massive compact halo objects), which are just made of normal baryonic matter that's aggregated in bodies too small and dark for us to individually detect through existing means, such as small rocky objects which would be perfectly visible if we could get a spotlight on them, and also black holes, neutron stars, dwarf stars, and other dark objects. However, it's currently thought that the majority of dark matter is non-baryonic, which fits the exotic description of invisible and completely non-interacting except through gravitational attraction. MACHOs have the problem that if they're plentiful enough to account for the missing mass, we really ought to be able to detect them through other means. (And furthermore that if baryonic matter were the primary form of dark matter, it would be too abundant for our well-established theories of structure formation and nucleosynthesis to work.) But the bigger problem is that none of the theories of non-baryonic matter are in any way substantiated either, except for garden variety neutrinos, which don't have enough mass and are too energetic to account for the bulk of dark matter. This leaves the door open to even more exotic speculations such as tweaking the theory of gravitation. In a sense, the real darkness to "dark" matter lies in our understanding more than anything else.

[T0T0R0]

Just going to point out that science is filled with garbage theories, and "Dark Matter" certainly feels like one of them.

Why not just go back to calling it The Æther? Or mayhap a form of non-luminiferous aether, if I may be so bold?

https://en.wikipedia.org/wiki/Aether_theories

  a space-filling substance or field, thought 
  to be necessary as a transmission medium for 
  the propagation of [...] gravitational forces.

You say tomato, I say Tomato. Aether. Why not?

[Retra]

Because that would be the kind of 'garbage theory' that would make you look incompetent rather than clever.

[oldmanjay]

If there's one thing I've learned from the internet, it's that people sure prize the appearance of being clever.

[mikeash]

I thought it just meant that it can't (yet?) be detected with electromagnetic radiation, not that it necessarily doesn't interact. For example, MACHOs have fallen out of favor, but were once a decent theory to explain dark matter, and they're just normal matter in a form and location that makes them hard to see.