What is the Universe made of? How old is it?

Abstract

For the past 15 years most astronomers have assumed that 95% of the Universe was in some mysterious form of cold dark matter. They also assumed that the cosmological constant, Omega_Lambda, was Einstein's biggest blunder and could be ignored. However, recent measurements of the cosmic microwave background combined with other cosmological observations strongly suggest that 75% of the Universe is made of cosmological constant (vacuum energy), while only 20% is made of non-baryonic cold dark matter. Normal baryonic matter, the stuff most physicists study, makes up about 5% of the Universe. If these results are correct, an unknown 75% of the Universe has been identified. Estimates of the age of the Universe depend upon what it is made of. Thus, our new inventory gives us a new age for the Universe: 13.4 +/- 1.6 Gyr.