The Men of the Great Assembly had three sayings: "Be patient before reachinga decision; Enable many students to stand on their own; Make a fence around yourteaching."
Ethics of the Fathers 1:1
There are two aspects of cosmology today that make it more alluring than ever.First, there is an enormous amount of data. To give just one example of how rapidlyour knowledge of the structure of the universe is advancing, consider galaxy surveyswhich map the sky. In 1985, the state-of-the-art survey was the one carried out bythe Center for Astrophysics; it consisted of the positions of 1100 galaxies. Today, theSloan Digital Sky Survey and the Two Degree Field between them have recordedthe 3D positions of half a million galaxies.
The other aspect of modern cosmology which distinguishes it from previousefforts to understand the universe is that we have developed a consistent theoret-ical framework which agrees quantitatively with the data. These two features arethe secret of the excitement in modern cosmology: we have a theory which makespredictions, and these predictions can be tested by observations.
Understanding what the theory is and what predictions it makes is not trivial.First, many of the predictions are statistical. We don't predict that there should bea hot spot in the cosmic microwave background (CMB) at RA = 15h, dec= 27~.Rather, predictions are about the distribution and magnitude of hot and cold spots.Second, these predictions, and the theory on which they are based, involve lots ofsteps, many arguments drawn from a broad range of physics. For example, wewill see that the distribution of hot and cold spots in the CMB depends on quan-tum mechanics, general relativity, fluid dynamics, and the interaction of light withmatter. So we will indeed follow the first dictum of the Men of the Great Assem-bly and be patient before coming to judgment. Indeed, the fundamental measuresof structure in the universe--the power spectra of matter and radiation--agreeextraordinary well with the current cosmological theory, but we won't have thetools to understand this agreement completely until Chapters 7 and 8. Sober mindshave always knows that it pays to be patient before pronouncing judgment on ideasas lofty as those necessary to understand our Universe. The modern twist on this"Be patient" theme is that we need to set up the framework (in this case Chapters.