Dark Energy and Dark Matter + Expanding Universe

[loser_boy_3]

Well, I've heard about this stuff in the past, but I'm not horribly up to date. Can anyone explain the new understanding of dark matter and dark energy. As well as WHY the universe expands?

 

[rogers_buck]

If you read some of the threads on this board you will find a lot quite a few discussions on these topics.<br /><br />In a nutshell:<br />Dark matter is matter that can only be observed or inferred by its gravitational effect. It might be strange quark matter, ordinary matter we cannot observe, or gravitational shadows of mass in this universe or an adjacent brane universe. Pick any two.<br /><br />Dark energy is the born-again cosmological constant invoked originally to explain a static universe. Dark energy is used to explain why the expansion of the universe might be accelerating. The pressure of the universe should be zero given that gravity cancels mass, so dark energy is thought to inject a negative pressure causing the expansion to speed up. The loss of gravitons from our universe to an adjacent brane universe has been posited as a possible source. Other sources invoke vaccuum energy and even white holes. I'm sure I'm leaving out an important one but I can't think of it at the moment. All the negative pressure...<br /><br />The expanding universe has been known since the days of Hubble (guy not the space craft) looking at red shifts of distant galaxies. By extrapolating everything flying apart back in time there came a theory described as the Big Bang. <br /><br />The best guess for what started the Big Bang is a supercooled Higgs field caught on a potential plataue when a microscopic early irregular universe cooled. The super cooled Higgs field infused space with a constant negative pressure. There are two key differences between a supercooled Higgs field and a cosmological constant:<br />1) Higgs field does not vary with time,<br />2) the energy and negative energy is 10**100 times larger than the cosmologicl constant.<br />I think this is called Guth's theory, I might be wrong. The gun powder for the Big Bang.<br /><br />

 

[loser_boy_3]

Ya, but why does it accelerate?

 

[rogers_buck]

If the lost graviton idea is presumed the cause, then make note that the gravitons are lost to higher dimension branes over vast distances and long time scales. That would make the loss accelerating due to the inverse square.<br />

 

[zenith]

so is there any relation to dark matter and anti matter?<br /><br />also is it "dark" matter cos we cant see it or cos its on the "dark side"...(sounds like a stupid question.. but some of the reasons for things in science are very silly in origion)

 

[loser_boy_3]

The whole idea of gravitons is a wee bit iffy to me.. I mean their particles of gravity basically right? That just doesn't seem plausible. Pass me a link to a nice article dealing with them and we'll see if i change my mind.

 

[silylene old]

I have been seeing some serious (and good) papers being published which are criticising the "dark energy" theory as being founded upon sloppy curve fitting and lack of statistical rigor. <br /><br />Here are a couple of critical papers which have also been published on the web: <br />http://lib.stat.cmu.edu/~genovese/talks/stanford-04.pdf <br />http://www.arxiv.org/PS_cache/astro-ph/pdf/0401/0401198.pdf <br /><br />According to fits of the WMAP data, the universe is made up of: <br />4% "normal" matter <br />23% "dark matter" <br />72% "dark energy" <br /><br />As I understand it, the shape of the CMB is a result of the compressions and rarefactions in the fundamental waves of the early expanding universe. The size/shape of the first big hump gives information about the curvature of the universe. The second hump relates to gravity counteracting sonic motion and thus gives information especially on the amount of matter. The third hump gives information about the amount of dark matter. <br /><br /><br />Here is the fit to the data. The data fit to the second hump is questionable, and the data fit to the third hump sure looks like a fantasy to me and also apparently to some statistical mathematicians. I had never seen the data points earlier. I know if I ever tried publishing a curve fit like this I would've been (rightfully) hooted out by my peers.<br /><br />If the "dark energy" theory gets retracted, this will be humiliating for some. <br /><br />Or am I misunderstanding the debate ? <br /><br /> The graph (waiting for approval) is the observed power spectrum for the cosmic microwave background (CMB). <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>

 

[rogers_buck]

Dark matter is matter that we cannot see but can deduce from its gravitational effects. Ordiany anti-matter doesn't fill the bill for dark matter. Special quark matter might, and special quark anti-matter might as well. Special quark matter interacts only weakly with ordianary matter and anti-speacial quark matter will not anhilate with ordinary matter or anti matter. But it has mass and we can't see it, so it is a candidate.<br /><br />An Indian group calculated what would happen if special quark matter hit the earth. They predicted that there would be two mass extinction events. The first due to a radiation effect I didn't catch the mechanism for, and the second due to massive volcanism. There were several mass extinctions that had an unexplained first die-off followed by volcanism 2000 years latter as predicted.<br /><br />There was another group that decided that if special quark matter hit the earth in a smaller proportion it would have an unexplained shallow earthquake at the ingress point, and a nearly simultaneous event somewhere else on the earths surface as the egress event. They found several such events in the records of uncorrelated earth queakes.<br /><br />None of this is proof of course.<br /><br />