Nerds Searching for WIMPs

The Hadron Collider in Switzerland

It is absolutely pouring out right now! And if you trust weather prediction, it's supposed to continue for the next week or so. I am at home warm and dry though. I got all my "chores" done early today, so I am shamelessly sporting my most comfortable (and therefore hideous and mismatched) clothes, drinking my 4th (or 5th?) cup of coffee, and planning on relaxing for the rest of the day, and enjoying the rainy weather.

Anyway, I read an article in the January issue of Popular Science that I thought was interesting about what physicists call "dark matter". I think that even if we don't know what term means, most of us have at least heard it before, either on shows like Star Trek, or some or another documentary about space. But if you are anything like me beyond the actual words themselves we are lost. Anyway, the article I read was great in that it didn't overly complicate what is (with certainty) a very complicated subject. (BTW it is the source for most of what I am going to write about.) In essence it dumbed down one of the greatest mysteries in modern physics to a level that my pitiful brain could process. And since I found it so interesting I wanted to pass it along to you. My plan is to give you a quick and dirty rundown on what dark matter is...or isn't actually.

You would think, because so many people (mostly physicists) theorize about dark matter, write articles about it, build machines to detect it, and spend millions (or probably billions) of dollars researching it, that dark matter would actually exist. But it turns out that would be in incorrect assumption. Surprisingly, as of right now, dark matter does NOT technically exist. Isn't that about the weirdest thing you've ever heard?  Not one particle of dark matter has ever been seen or directly measured by man! Not a one!
This begs the obvious question; "Then why do we think they exist in the first place?" At first glance you might be inclined to lump dark matter in the same category as God and Allah. But unlike the later, scientists have a very good reason to believe dark matter exists. And I'll try my best to explain it to you.

OK, so Newton (Sir Issac, not Wayne) came up with his second law of planetary motion 1687 that basically says the bigger (read "more mass") something is the faster it spins. For example the length of our day is 24 hours, while the length of a day on Jupiter is about 10 hours. Jupiter spins faster because it has more mass. There is a relationship between the mass of Jupiter and it's rate of rotation that can be worked out mathematically. That is to say that you can use math to predict (with excellent accuracy) how fast some heavenly body will rotate if you know what it's mass is. Or the other way around.

Well, back in the 1930's while observing a group of galaxies, one Fritz Zwicky realized that the rate of rotation (which can be measured by an objects Doppler Shift) of the galaxies he was looking at didn't add up to the number of stars that he was able to observe. Basically they were turning much faster than they should be. Based on Newtons second law those galaxies were missing a great deal of mass. The conclusion was that there MUST be more mass in those galaxies than science was capable of observing. It had to be there, we just couldn't see it directly. And thus "dark matter" was born.
In a way it's like observing the circular ripples on the surface of a smooth pond, but never having observed the stone that was tossed in that created them. You see the ripples and you know something had to make them. The spin of galaxies, and the way light is bent around certain regions of seemingly empty space are the ripples, and physicists are now looking for the stone, the actual particle of dark matter itself. And that is a daunting task. How do you look for something when you don't know what you are looking for? To continue with the analogy what if it's not a stone? It could be potato, or it could be another drop of water...who knows?

So how do you look for dark matter? Well, here's where it gets tricky. Scientist think that dark matter is really made up of what they call "weakly interacting massive particles" or WIMPs. This means that they barely interact with what we could call "normal" particles, but that they still have a mass (otherwise they couldn't affect the spin of the galaxies remember more mass=faster spin). I think the acronym is a bit ironic because, as Neil deGrasse Tyson says "85% of the gravity comes from something [and] we don't know what it is!" Eight five percent of everything in the universe doesn't seem very wimpy to me. Anyway physicists are taking two approaches to discover these WIMPs. One was is to create a detector that would capture the result of a head on collision of a WIMP and a regular particle. These devices are housed in old mine shafts and under mountains to discourage false readings by normal particles that bombard the earth every millisecond of every day. The other (as is being attempted at the Large Hadron Collider in Switzerland) is to try to make WIPMs ourselves by smashing protons together hard and fast enough. These facilities are also (I believe) underground. Bizarre isn't it?

It may sound like science-fiction to toss around terms like dark matter and WIMPs. It may seem crazy to look for something that as far as we know doesn't exist. But the "ripples" that physicists observe out in space must have been created by something. And I'll bet we discover dark matter before God appears and tells us it was him.

P.S. The title was borrowed from the article. The author read it off a a t-shirt:)