Although this book has been available for some time, it is only now appearing in an English edition. This gives me the opportunity of adding a few explanations. I have not struggled to include the very latest, tentative results. I have, instead, concentrated on presenting cosmological ideas to interested non experts. They often encounter considerable difficulties when attempts are made to explain even long-established results in this field, so the aim of this book is to provide them with help. Naturally, I have also tried to include modern findings. To help with the explanation I have made...