Why will your downstairs neighbor live longer than you? What color is the mirror? How much does Thor's hammer weigh? Why can't we travel to the past? How many megapixels does the human eye have? To read this book, you will spend 0.0005% of your life, from 7,200 to 14,400 seconds. Perhaps as much as for Blade Runner 2049 or for the original Star Wars trilogy. But you know that time is something relative, like so many other things. If a long and happy life awaits you, you will live over two billion seconds, although you will sleep for one-third of them. The remaining seconds, after some time on the pillow, you will be awake, you will live them, you will enjoy them. Because they can be wonderful. So think about how you will make the best use of them. In a few years, some of the things you will read in this book, those that are considered certain today, may not make any sense. Nothing remains the same, nothing is stable. "The only constant is change," predicted Heraclitus 2,500 years ago. It is the miracle of science that advances unstoppably day by day. That's why I want this book to be a source of inspiration for you, to help you seek your own answers to all the questions that concern you, and to search for these answers without resorting to standardized knowledge or unscientific myths. A BOOK FOR YOUNG MEN AND WOMEN, FOR THEIR TEACHERS AND PROFESSORS, AND FOR INQUIRING MINDS OF ALL AGES