"The history of cosmology shows that in every age devout people believe
that they have at last discovered the true nature of the Universe."
- E. R. Harrison (1981)
Cosmology is the scientific attempt to answer fundamental questions of mythical proportion: How did the Universe come to be? How did it evolve? How will it end? If humanity goes extinct it will be of some solace to know that just before we went, incredible progress was made in our understanding of the Universe. "The effort to understand the Universe is one of the very few things that lifts human life a little above the level of farce, and gives it some of the grace of tragedy." (Weinberg 1977).
A few decades ago cosmology was laughed at for being the only science with no data. Cosmology was theory-rich but data-poor. It attracted armchair enthusiasts spouting speculations without data to test them. The night sky was calculated to be as bright as the Sun, the Universe was younger than the Galaxy and initial conditions, like animistic gods, were invoked to explain everything. Times have changed. We have entered a new era of precision cosmology. Cosmologists are being flooded with high quality measurements from an army of new instruments. We are observing the Universe at new frequencies, with higher sensitivity, higher spectral resolution and higher spatial resolution. We have so much new data that state-of-the-art computers process and store them with difficulty. Cosmology papers now include error bars - often asymmetric and sometimes even with a distinction made between statistical and systematic error bars. This is progress.
Cosmological observations such as measurements of the cosmic microwave background, and the inflationary ideas used to interpret them, are at the heart of what we know about the origin of the Universe and everything in it. Over the past century cosmological observations have produced the standard hot big bang model describing the evolution of the Universe in sharp mathematical detail. This model provides a consistent framework into which all relevant cosmological data seem to fit, and is the dominant paradigm against which all new ideas are tested. It became the dominant paradigm in 1965 with the discovery of the cosmic microwave. In the 1980's the big bang model was interpretationally upgraded to include an early short period of rapid expansion and a critical density of non-baryonic cold dark matter.
For the past 20 years many astronomers have assumed that 95% of the Universe was clumpy non-baryonic cold dark matter. They also assumed that the cosmological constant, , was Einstein's biggest blunder and could be ignored. However, recent measurements of the cosmic microwave background combined with supernovae and other cosmological observations have given us a new inventory. We now find that 73% of the Universe is made of vacuum energy, while only 23% is made of non-baryonic cold dark matter. Normal baryonic matter, the stuff this paper is made of, makes up about 4% of the Universe. Our new inventory has identified a previously unknown 73% of the Universe! This has forced us to abandon the standard CDM (M = 1) model and replace it with a new hard-to-fathom -dominated CDM model.