Shortly after the Big Bang, the universe was still impenetrable. Its density was so high that a variation of only 50 percent - a coffee bean in a cake batter - would have been enough to produce a black hole immediately. The density was at least variable enough to let grow whole galaxies from the differences later. However, there seem to have been no "coffee beans" at that time - this is revealed today by the rather uniform cosmic background radiation. Nevertheless, so-called promordial black holes could have been formed at that time, just on other ways. They could…