Neutrinos are fundamental to the construction of the Universe. They are tremendously abundant, outnumbering atoms by about a billion to one. They modulate the reactions that cause massive stars to explode as supernovas. Their properties provide clues about the laws governing particle physics. And yet neutrinos are among the most enigmatic particles, largely due to their reticent nature: they have no electric charge and practically no mass, so they interact only extremely weakly with ordinary matter. Some 65 billion of them stream through every square centimetre of your body – an area the size of a thumbnail – every second, without your ever noticing them. ... The discovery of the neutrino dates back to the 1930s, when the famed Italian physicist Enrico Fermi helped to hammer out the first workable theory of nuclear phenomena such as radioactive decay. ... Neither Fermi nor anyone else at the time thought that such tiny wisps of matter could ever be detected directly. Before long, the spread of fascism in Europe overshadowed any such lofty thoughts. ... In 1938, he managed a Sound-of-Music-like escape, exploiting a trip to Stockholm to accept the Nobel Prize in order to slip out of Europe and head for the United States, where he became one of the early scientific leaders of the Manhattan Project.