One of Albert Einstein's lesser known achievements is the invention of a household refrigerator. In the 1920s, the gases inside refrigerators were toxic and a crack in an inner seal could lead to leaks, sometimes with deadly results. Einstein designed a safer model, although it never went into production because it was too expensive. Gino Segre, a physics professor, uses this piece of trivia to introduce his exploration of temperature as a key scientific parameter, along with time and distance. Temperature is central to explaining when life first appeared, and it can help us understand how galaxies, stars and planets formed. The concept of absolute zero may yield amazing new technologies from the world of quantum physics. Our bodies maintain a constant temperature of 37 degrees, regardless of whether we live in the Arctic or the Sahara, yet there's no simple reason for this. Nor is there a complete answer to what advantages are offered by fever as a response to infection.