The Nine Numbers Of The Cosmos, Michael Rowan-Robinson, c. 1999

Note: a deceptively titled book, to raise sales, no doubt. It would be much more accurate to have titled it "Nine Concepts Of The Cosmos."

From wiki:

A baryon is a composite subatomic particle made up of three quarks (as distinct from mesons, which comprise one quark and one antiquark). Baryons and mesons belong to the hadron family, which are the quark-based particles. The name "baryon" comes from the Greek word for "heavy" (βαρύς, barys), because, at the time of their naming, most known elementary particles had lower masses than the baryons.

As quark-based particles, baryons participate in the strong interaction, whereas leptons, which are not quark-based, do not. The most familiar baryons are the protons and neutrons that make up most of the mass of the visible matter in the universe. Electrons (the other major component of the atom) are leptons. Each baryon has a corresponding antiparticle (antibaryon) where quarks are replaced by their corresponding antiquarks. For example, a proton is made of two up quarks and one down quark; and its corresponding antiparticle, the antiproton, is made of two up antiquarks and one down antiquark.

First number: baryons 

What are we made of? Protons, neutrons, heavy particles (baryons); and light particles (leptons, electrons). We'll find out later that there are other types of leptons, and that baryons are probably not even fundamental particles but are themselves composite.

Density of baryons in the universe: 2.5 x 10^-28 kg m^-3 which is a very, very low density. The average densities of the earth, the sun, and the human body are all within a factor of a few of 1,000 kg m^-3.

The second number characterizes the smoothness of the universe. We are not in a very special place geographically in the universe. 

The third of the nine numbers: the current rate at which the universe is expanding, which is measured by what is known as the Hubble constant.

The fourth of the nine numbers: the finite age of the universe.

The fifth cosmic number: the temperature of the universe today, as measured by the microwave background radiation.

The sixth cosmic number: the average density of dark matter in the universe. (This dark matter is cold. See next cosmic number.)

The seventh cosmic number: characterizes the missing ingredient required to understand large-scale structure, which could be tilt, strings, or hot dark matter.

The eighth number of the cosmos, the cosmological constant, ^ (lambda), was introduced by Einstein in 1917 in order to permit a static model of the universe.

The ninth cosmic number characterizes the history of galaxy and star formation. It turns out that it may be quite difficult to do this with a single number.