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 \pm 1.6 Gyr .