What is Dark Matter ?
Posted on: April 7, 2009 - 2:02am
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What is Dark Matter ?
As I was reading this story,Galaxy Mix : No Dark Matter Required www.sciencenews.org/view/generic/id/41011/title/Galaxy_mix_No_dark_matter_required.it made me think about the science freaks at RRS,and I was wondering about their take on this.
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Dark Matter is.... Matter thats Dark
IN B4 PINEAPPLE!!
That's the million dollar question, really.
I believe the current answer is, "We're not sure."
- Leon Trotsky, Last Will & Testament
February 27, 1940
It is matter that does not interact with the electromagnetic/weak force. In other words, it does not interact with light. It doesn't absorb it, it doesn't give it off as radiation. In fact, the only force that we know that it interacts with for sure is gravity. So it is matter (has gravity), but does not interact with light (hence it is 'dark').
Think about it a bit like this. You know of electrons, protons, and neutrons, right? Well, electrons have a negative charge, protons a positive charge, and neutrons no charge. When passing through an electric or magnetic field, the proton and electron will interact with the field and change direction and/or speed. The neutron will just pass on by without being affected by the field.
Dark matter is like the neutron, except that it doesn't seem to interact with any forces except gravity. So, in fact, dark matter can pass right through electrons, protons, and even neutrons without being affected by their electromagnetic charge, or their weak nuclear properties. (I'm not sure about the strong nuclear force. I guess we don't have evidence that dark matter interacts with strong nuclear force either.)
So, it is like the dark matter is there, but it does not interact with other matter except through gravity. And since gravity is a very very weak force, which requires large amounts of matter to be detectable, it is very hard to detect dark matter. And it's also hard to determine what kinds of *other* interactions dark matter might have.
For example, maybe dark matter has some properties that allow it to interact via a force we don't even know about yet, the equivalent of dark-matter-electromagnetism. All we know is that dark matter forms in clumps, but we don't know very much about the detailed structure of these clumps. The clumps are the size of galaxies, as far as we know. We can't detect dark matter with much better resolution than that.
Another interesting thing is that we are probably floating around in a cloud of dark matter right now, and can't sense it, because all of our natural senses are at the level of the electromagnetic force. We can see light, we can touch atoms (also electromagnetic sensing), we can hear vibrations in air (another form of electromagnetic sensing), etc., but we don't have very good gravity senses, and we certainly don't have the kind of resolution to detect dark matter around us.
We are electromagnetic creatures. That's the level at which life as we know it operates. There could be a whole bizarre world 'living' all around us, and we don't even know it, because this dark matter 'world' doesn't interact with electromagnetic force.
But, as far as we know, maybe dark matter is just these big invisible clumps. Imagine massive invisible gravity clouds just floating around. They are attracted to other matter, like stars, planets, and galaxies, and so they form clumps in the approximate size of galaxies. By supplying extra gravity, they help stars to form, and galaxies to keep their shapes. But other than that, we have no idea what else it might do.
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It seems from a recent article in New Scientist magazine, of 7 March 2009, that current hopes for giving further clues to the nature of dark matter are
1. NASA's Fermi satellite which is measuring with high accuracy the energies and quantities of high energy electrons, one of the key decay products from dark matter particle collisions according to some proposed theories;
and
2. the Large Hadron Collider (naturally), particularly in complementing the Fermi observations.
Because of the elusive nature of dark matter, such clues rely on somewhat indirect measurements, such as looking for the mix of detectable particles predicted to be produced by collisions between dark matter particles, which will vary for different models of what they may be.
Favorite oxymorons: Gospel Truth, Rational Supernaturalist, Business Ethics, Christian Morality
"Theology is now little more than a branch of human ignorance. Indeed, it is ignorance with wings." - Sam Harris
The path to Truth lies via careful study of reality, not the dreams of our fallible minds - me
From the sublime to the ridiculous: Science -> Philosophy -> Theology
I remember reading an article within the last week or two that suggested we're getting a bit closer to narrowing it down. This isn't the same source I originally read it from, but it is the same story. I hadn't posted it before because it's not really all that certain to be dark matter in the first place.
http://www.economist.com/science/displaystory.cfm?story_id=13403121
Enlightened Atheist, Gaming God.
There's a certain amount of controversy around dark matter these days. I didn't know it, but there is. Here's an entry from what is going to become one of my favorite blogs.
"Yes, I seriously believe that consciousness is a product of a natural process. I find that the neuroscientists, psychologists, and philosophers who proceed from that premise are the ones who are actually making useful contributions to our understanding of the mind." - PZ Myers
Rather than listen to those stupid scientific and rational explanations, I suggest you heed my explanation for what dark matter is:
God.
Thanks for all of the input about Dark Matter,after reading the article it would seem that any gases floating around in space can fall into a dark matter halo and form a star,is it another star maker ?
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Not exactly. The physics of star formation works without dark matter. Hydrogen alone in enough quantities will ignite a fusion reaction. Adding some dark matter to the mix would just make it easier for the star to form, as it adds more gravity, causing the hydrogen to squeeze together more, and lowering the threshold required to ignite the fusion reaction.
Where dark matter plays a key role, however, is in explaining why our galaxies are so big, why they have so many stars, and why they rotate as quickly as they do. Part of the answer comes from the discovery that most (if not all) galaxies have super-massive black holes in their centres, but that doesn't completely answer the questions. Without dark matter, our galaxies would be much smaller. The majority of mass in most galaxies is dark matter.
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