30 Standard Cosmological Model approaching the so-called Planck scale [(hc 5 /G) 1/2 10 19 GeV], at which quantum mechanics and gravity are expected to be unified. Unfortunately, the exponential expansion of the Universe during inflation erased memory of earlier cosmic epochs, such as the Planck time. 2.7 Most Matter Is Dark Surprisingly, most of the matter in the Universe is not the same ordinary matter that we are made of (see figure 2.4). If it were ordinary matter (which also makes stars and diffuse gas), it would have interacted with light, thereby revealing its existence to observations through telescopes. Instead, observations of many different astrophysical envi- ronments require the existence of some mysterious dark