Tests of Big Bang Cosmology
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Excerpts from "This Week's Finds in Mathematical Physics (Week 196)"        

  First of all, we only "know" anything about the world on the
  basis of various assumptions. If our assumptions turn out to be
  wrong, our "knowledge" may turn out to be wrong too. Even worse,
  our favorite concepts may turn out to be meaningless, or
  meaningful only under some restrictions.

  So, when we talk about what happened in the first microsecond 
  after the Big Bang, we're not claiming absolute certainty. 
  Instead, we're using various widely accepted assumptions about
  physics to guess what happened. Given these assumptions, the
  concept of "the first microsecond after the Big Bang" makes
  perfect sense. But if these assumptions are wrong, the whole
  question could dissolve into meaninglessness. That's just a risk
  we have to run. What are these assumptions, exactly?

  They include:
  1.  General Relativity
  2.  Standard Model of particle physics
        supplemented by
  3.  Dark Energy
  4.  Dark Matter

  Assumptions 3 and 4 are the ones most people like to worry 
  about, because our only evidence for them comes from cosmological
  observations, and if they're true, they probably require some
  sort of modification of the Standard Model. But if we don't make
  these assumptions, our model of cosmology just doesn't work...
  while if we *do*, it seems to work quite well. In fact, the
  WMAP experiment gives a lot of new evidence that it works
  surprisingly well.

The first second of the Universe

  The history of the Universe after its first second is now tested
  by high quality observations of light element abundances and
  temperature anisotropies of the cosmic microwave background. The
  epoch of the first second itself has not been tested directly
  yet; however, it is constrained by experiments at particle and
  heavy ion accelerators. Here I attempt to describe the epoch
  between the electroweak transition and the primordial

  The most dramatic event in that era is the quark--hadron
  transition at 10 Ás. Quarks and gluons condense to form a gas
  of nucleons and light mesons, the latter decay subsequently. At
  the end of the first second, neutrinos and neutrons decouple from
  the radiation fluid. The quark--hadron transition and dissipative
  processes during the first second prepare the initial conditions
  for the synthesis of the first nuclei. 

  As for the cold dark matter (CDM), WIMPs (weakly interacting
  massive particles) -- the most popular candidates for the CDM --
  decouple from the presently known forms of matter, chemically
  (freeze-out) at 10 ns and kinetically at 1 ms. The chemical
  decoupling fixes their present abundances and dissipative
  processes during and after thermal decoupling set the scale for
  the very first WIMP clouds.

Wilkinson Microwave Anisotropy Probe (WMAP) Results

WMAP Technical Papers

No Center

Also see Ned Wright's Cosmology Tutorial

WMAP: Foundations of the Big Bang theory

WMAP: Tests of Big Bang Cosmology

Science, Religion, and the Big Bang


Interview with Physicist Steven Weinberg

  QUESTION: You have written that the more comprehensible the
  universe becomes the more pointless it seems. Could you explain
  what you mean by that?

  DR. WEINBERG: Years ago I wrote a book about cosmology, and
  near the end I tried to summarize the view of the expanding
  universe and the laws of nature. And I made the remark - I
  guess I was foolish enough to make the remark - that the more
  the universe seems comprehensible the more it seems pointless.
  And that remark has been quoted more than anything else I've
  ever said. It's even in Bartlett's Quotations. I think it's
  been the truth in the past that it was widely hoped that by
  studying nature we will find the sign of a grand plan, in which
  human beings play a particularly distinguished starring role.
  And that has not happened. I think that more and more the
  picture of nature, the outside world, has been one of an
  impersonal world governed by mathematical laws that are not
  particularly concerned with human beings, in which human beings
  appear as a chance phenomenon, not the goal toward which the
  universe is directed. And for some this has no effect on their
  religion. Their religion never looked for any kind of point in
  nature. For others this is appalling, the idea that all of the
  stars and galaxies and atoms are going about their business,
  and it's just by accident that here on this solar system the
  peculiar chemical properties of DNA acting over billions of
  years have produced these people who have been able to talk and
  look around and enjoy life. For some people that picture is
  antithetical to the view of nature and the world that their
  religion had given them.

  QUESTION: Do you believe then there is no overall point to the

  DR. WEINBERG: I believe that there is no point in the universe
  that can be discovered by the methods of science. I believe
  that what we have found so far, an impersonal universe in which
  it is not particularly directed toward human beings is what we
  are going to continue to find. And that when we find the
  ultimate laws of nature they will have a chilling, cold
  impersonal quality about them.

  I don't think this means [however] there's no point to life.
  Usually the remark is quoted just as it stands. But if anyone
  read the next paragraph, they would see that I went on to say
  that if there is no point in the universe that we discover by
  the methods of science, there is a point that we can give the
  universe by the way we live, by loving each other, by
  discovering things about nature, by creating works of art. And
  that -- in a way, although we are not the stars in a cosmic
  drama, if the only drama we're starring in is one that we are
  making up as we go along, it is not entirely ignoble that faced
  with this unloving, impersonal universe we make a little island
  of warmth and love and science and art for ourselves. That's
  not an entirely despicable role for us to play.

Admirers of the Allegretto from Beethoven's 7th