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?
1. General Relativity
2. Standard Model of particle physics
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
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
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