What are the theories of Dark Matter and Dark Energy?

How do various non-Big Bang cosmological theories explain CMB?

• There are various re-examinations of the Big Bang theory and/or inflation. http://www.scientificamerican.com/article.cfm?id=the-inflation-summer - SciAm http://www.technologyreview.com/view/419984/big-bang-abandoned-in-new-model-of-the-universe/ - MIT Tech Review Generally their hurdle for being complete is different than the Big Bang and its followup cosmological theories. (Here they need Dark Matter and Energy to explain behavior, without explaining what this stuff is.) A big one is Cosmic Microwave Background Radiation (CMB). Are there theories that have explained this while differing from the Big Bang hyperinflation start of the universe?

• Answer:

  First of all, the first article is a *not* reexamination of the BB cosmology.  At most they are reexaminations of the idea of inflation, which is something different, and it makes it seem like there is more controversy over inflation than there actually is.  It's a pretty terrible article because it doesn't go into why people think there is inflation in the first place (i.e. the horizon problem or the monopole problem).  The Steinhardt-Turok model of the universe doesn't challenge the big bang.  It's a reasonable try to get an alternative to inflation.  Instead of having the universe expand rapidly after the big bang, you smooth things out by rapid expansion before the BB.  The trouble with Steinhardt-Turok is that you have to assume way more things that you do with inflation.  With inflation you just have to assume some scalar field that causes rapid expansion, whereas with Steinhardt-Turok, you have to assume that there are multidimensional branes and you have to make up an entire set of physics for them.  Steinhardt-Turok deals with the CMB by saying that all of the "alternative physics" ends in the first millisecond or so after time zero and then everything after that is standard. Second, if you go back to what was known in the 1960's, it's pretty easy to come up with a microwave background from a non-BB theory.  Proponents of the steady state theory argued that the cosmic microwave background were scattered light from ultra-distant galaxies.  This gives you a cosmic microwave background but it gives you nothing like the current cosmic microwave background.  In particular, if you zoom in on the microwave background you should see the galaxies generating it and you don't. Also Steinhardt-Turok is a odd but "serious" model.  Shu Yi-Wun's model in the second article, I wouldn't consider a "serious" model.  Steinhardt-Turok proposes new physics in areas that we can't observe, and Steinhardt is pretty careful not to create contradictions with known observations.  There are pretty strong limits on how much the speed of light and G can change, and you can't get the acceleration that you see without breaking lots of things.  The calculation on page 17-18 is wrong, once you start changing the speed of light, you not only change redshift but you also have to change the brightness.  The diagram in Fig 3 is terrible.  First there are no error bars, which makes the graph totally useless. The problem is that by plotting mb versus z, you can't really see the difference between alternative models.  If I plot mb versus z, with a non-accelerating universe or with a different set of models, I'm not going to be able to really tell if it is a good fit or not.  If you just plot mb versus z with different models, you'll quickly see that it's impossible from the diagrams to see if it's a good fit or not since the way that the plot scales, everything looks like a good fit. What you really need to do is to plot delta mb (i.e. the difference between the brightness magnitude and a "flat model").  Once you do that then you'll start seeing model differences.  (See Fig 3 here http://www.pnas.org/content/96/8/4224/F3.expansion.html ) for the right way of doing it.  If you plot z versus mb, you all of the lines will bunch up together and you can't see what works and what doesn't. Steinardt has done his homework.  Shu hasn't, and there are about a three *BIG* holes in the Shu paper that I can see.  It's hard for me to take Shu's paper seriously because Steinardt realizes what the issues in his model are, whereas Shu doesn't.