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Dark Matter Measurements
ksp0704 writes: "According to this article at space.com, scientists have finally measured the approximately 90% of the universe we can't see (the dark matter)." I'm sure it will continue to be a topic of debate for years, but two independent measurements agreeing is a good sign.
What makes the size of dark matter so important is that it will decide whether the universe continues to expand outward from the big bang, or eventually begins to shrink back to a singularity. Considering the universe started as a singularity, having it end that way may be indicative of another universe after this one. If everything continues to spread out, entropy will come out the clear winner.
Gack. How do they figure an explosion of spacetime is nuclear? There were no nuclei to fuse or split. My cynicism is telling me that the author just though "nuclear" sounded big and bang-y.
Excellent questions. Only problem is that it has no relevance to the "Creation of Normal Matter" the article is talking about.
The "normal matter" they were talking about are baryons (electrons, protons, neutrons etc and their composites). And the "creation" they talk about is "Big Bang Nucleonsynthesis", which is when protons and neutrons and electrons and stuff fuse together to make H, He and Li. The ratio of the production rates of these stuff implies certain "wiggles" in the CMB spectrum, so gives us a gauge (with lots and lots of caveats the scientists don't tell you) to the so-called "baryonic density". (Dark matter, by definition, do not interact with baryons, so it's hard to measure them since all the tools we have are made out of baryons.)
Big Bang Nucleonsynthesis (despite its name) can occur without a Big Bang : we just need the Universe to be Very Hot and Dense at some point.
Your questions about the origins of Big Bang is a much deeper and harder question. While it seems a philosophical argument, it is recently being attacked by some theorists. Most of the time, they just ask the question : do we need a Big Bang that starts from a singularity? The answer, with our current observations, is a BIG NO. But then they have to figure out a better alternative that can give us a very hot and dense Early Universe (so we can have Big Bang Nucleosynthesis, which is a very very very very well observed and constrained theory : i.e. it's fucking correct.)
Mode (3) smart-aleck mode. Press * to return to main menu.
In short, we don't really know. Some speculate that this universe was created from another universe. By this I mean that our universe may have been created in such a way that a bubble gets blown from a wad of chewing gum. But where did that universe come from? Others speculate that our universe started when a quantum particle "came out of nowhere" and then inflated (the big bang) into our universe. Many of the people that beleive this think that our universe will eventually deflate (the big crunch) into nothing once more. At that time, humans maybe able to escape to another more younger universe by traveling through higher dimensional space.
Some good books dealing with these subjects that I've read/currently reading are:
- Hyperspace by Michio Kaku
- In Search of Schrondinger's Cat by John Gribben
- The Elegant Universe by Brian Green
All are very good. Hope that helps.
I sure hope you're Ross Tessien, who posted this article to Usenet!
This slashdot comment also looks like this Usenet post.
This slashdot comment also looks like this Usenet post.
The stars you see are all within our own galaxy, which is "only" about 100,000 light years across, so all the star light is from well after the dinosaurs bit it. There is a lot of light from other galaxies that are over 65 million light years away, but it's relatively faint, so you've probably not really noticed it.
Yes, by seeing farther away objects we can raise the lower bound for the age of the universe. Astronomers are working on that. Yes, we think the universe is expanding, and we have a lot of proof for it too, mostly the red-shift that Hubble (the man, not the telescope) noticed. And yes, maybe the universe had a creation date (you've heard of the big bang theory, right?). (How did this get modded up?)
Okay, top paragraph: distance doesn't stop light, only matter, and there's relatively very little of it in space. Light from far away objects
Your belief that the universe has always been here is unsupported. (Again, big bang theory.) You're belief that it is infinite in all directions is also unsupported.
Yes, they can guess how much dark matter there is. By definition, the part of the universe we can't see is dark matter...it's called that because we can't see it. It's not any different from normal matter (as far as we know), it's just not emiting any light, so we can't see it. And by the calculations for the estimated mass of the universe, and the calculations of the total mass of all the matter we can see, yes, there must be some (up to 90% of the total mass, by the measurements in this article).
(I ask again... why did this get modded up?)
Those who fail to understand communication protocols, are doomed to repeat them over port 80.
You're right that "dark matter" does get used in the sense of things that aren't emmitting enough light for us to see. The article in question however is using it exclusively in the sense of (non-baryonic) matter which does not interact with electromagnetic radiation and thus can never emit light. Things in this category would be exotics such as nuetrinos, WIMPs, and a variety of other things.
For the record the bright objects we see account for about 3-6% of the needed gravity. Dark normal objects are guessed to account for 4-20%. Nuetrinos probably make up around 10%. Anything left over either has to be accounted for either by exotic dark matter or by a serious reaccounting of the above categories.