Posted on 08/22/2006 11:19:27 AM PDT by LibWhacker
Everyone is scientific circles is abuzz with the big news: there's proof that dark matter exists! The paper from the scientists who made the discovered is here; and a Sean Carroll (no relation) has a very good explanation on his blog, Cosmic Variance. This discovery happens to work as a great example of just why good science needs good math.
As I always say, one of the ways to recognize a crackpot theory in physics is by the lack of math. For an example, you can look at the electric universe folks. They have a theory, and they make predictions: but because there's no math, the predictions are vague, and there's no good way of really testing them, because there's no quantifiable way of making a precise prediction - because there's no math. So they can make predictions like "the stardust experiment will get bigger particles than they expect"; but they can't tell you how big.
The dark matter result is a beautiful example of how to use good math in science.
Here's the basic idea. The theory says that there are two kinds of matter: "dark" matter, and "light" matter. Dark matter only interacts with light matter via gravity; it does not interact with light matter via other forces. But dark matter and light matter generally clump in the same places - because gravity pulls them together. So it's very difficult to really prove that dark matter exists - because you can't see it directly, and it normally only appears with light matter, so you can't really prove that the dark matter is there: any observed effect might be caused by the light matter behaving in a way different than our current theories claim it should.
But what if you could somehow sweep the light matter away?
What the scientists who did this work found is a collision of two galactic clusters. When these clusters collided, the light matter, mostly in the form of gas, interacted very strongly with one another, creating a shock wave pattern. But the dark matter passed through without interacting - the "collision" between the gas clouds didn't affect the dark matter. So the gas clouds were swept back, while the dark matter continued moving. There's a great animation illustrating this; in the animation, the blue is the dark matter; the red is the light matter. As the two clusters pass through each other, the light matter is swept away by the electromagnetic interactions between the gas clouds; the dark matter passes right through:
Here's where the math comes in.
They used a combination of optical and X-ray telescope to produce maps of the gravitational fields of the clusters. This was done by computing the gravitational lensing effect distorting the images of other, more distant galaxies visible behind the collided clusters. By carefully computing the distortion caused by gravitational lensing, they were able to determine the distribution of mass in the collided clusters. And what they found was the bulk of the mass was not in the light matter. It was in the places that the center of gravities of the clusters would have been without the shock-wave effects of the collision. So the bulk of the mass of these two clusters do not appear on our telescope images; but it behaves exactly as the math predicts it would if it were dark matter.
The prediction and the result are both based on very careful computations based on the mathematical predictions of gravity and relativity. They were able to predict precisely what they would expect from the interaction using a mathematical model of the how the gas clouds would interact to be swept away; and how the dark matter would interact gravitationally to predict where the dark matter masses should be. Then they were able, via a separate computation to determine how much mass was in what location based on gravitational lensing. And finally, they were able to compare the two separately computed results to see if the reality matched the prediction.
Now that is both good math and good science! And the science could not have been done without the math.
This is serious. A matter dark indeed.
Technology is made of science. Science is made of math.
interest ping
Math is a figment of your imagination.
Interesting little animation at the source ... but how exactly did they rebuild that sequence of events from what is essentially a snapshot in the process? A galactic collision would take a couple of million years or more in order to be completed.
My math professor was fond of saying "Everyday we live in a world of bi-polar, non-Ecludian geometry, but only a few realize it." He would never provide an explanation but did say that I would be wiser when I figured out what he ment.
It took me a long time to understand.
It's too dark!
Does this mean Col. Jack O'Neill (my dream lover) comes out of retirement and returns to Stargate SGC?
No. Math is a figment of God's imagination and we have discovered part of it.
You do know that Stargate SG-1 has been cancelled, don't you?
HAHA! Einstein was Right!
placemarker
Are you serious? Stargate has been cancelled? Good God, no!
"Are you serious? Stargate has been cancelled? Good God, no!"
The producers of SG-1 say they will be on the air, somewhere, they just don't know where yet. Hope they're right.
I hope so. I love the show. I've been a faithful viewer since the show debuted 10 years ago. Even though I dream of the character of Jack O'Neill, as a woman, I idolize the role of Col. Samantha Carter. If I were a little girl and I could point to someone I'd like to be when I grew up, it would definitely be Col Samantha Carter. And if I were to ever to fall in love and remarry, it would definitely be the character of Col. Jack O'Neill. Sigh!
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