Sciency Words: WIMPs (An A to Z Challenge Post)

Today’s post is a special A to Z Challenge edition of Sciency Words, an ongoing series here on Planet Pailly where we take a look at some interesting science or science related term so we can all expand our scientific vocabularies together. In today’s post, W is for:


Approximately 85% of the matter in the universe is invisible; or if it’s not invisible, then it’s doing a really good job hiding from our telescopes. We call this invisible and/or well-hidden matter “dark matter.” We know about its existence only because of its gravitational effects, and also because of its childish taunting.

Scientists love acronyms, especially clever acronyms. There are many possible explanations for the dark matter phenomenon. One of them is a hypothetical subatomic particle called a WIMP: a Weakly Interacting Massive Particle.

Under the current standard model of particle physics, the universe is governed by four fundamental forces: gravity, electromagnetism, the weak nuclear force, and the strong nuclear force. Click here to learn everything you could possibly need to know about these forces.

If WIMPs exist, they interact with some of the fundamental forces, but not others.

  • Gravity: yes.
  • Electromagnetism: no.
  • Weak nuclear force: maybe yes.
  • Strong nuclear force: probably no.

Light is a result of electromagnetism. Since WIMPs don’t interact with the electromagnetic force, that would explain why we can’t see them.

But invisible particles like WIMPs aren’t the only possible answers to the huge question mark of dark matter. What about matter that’s visible but well hidden? Massive Astrophysical Compact Halo Objects (or MACHOs) are massive but faint objects in space, such as brown dwarfs, rogue planets, or black holes—the kinds of objects that would have a lot of gravity but would be difficult to spot with a telescope.

I have to imagine someone worked really hard to come up with MACHO as an acronym, so it would match well with WIMP. While there are other hypotheses out there, somehow the WIMPs vs. MACHOs debate seems to get the most attention. Which hypothesis does the best job explaining the dark matter mystery?

At this point, to the best of my knowledge as of this writing, physicists still cannot prove or disprove the existence of WIMPs. However, a recent astronomical survey seems to have ruled the MACHOs out of consideration. There simply cannot be enough black holes, brown dwarfs, and other stuff out there to account for 85% of the matter in the universe.

So the WIMPs haven’t won (at least not yet), but the MACHOs definitely lost. Big time. The MACHOs are losers. Big, fat losers. Hey, that’s not me saying that; it’s just what the science acronyms are telling us.

Next time on Sciency Words: A to Z, another reason to get mad at the I.A.U.

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