ABSTRACT
For about 20 years, I had the pleasure of working on cosmic magnetism together with Yakov Borisovich. YaB magnetized me at first glance, when he appeared wearing an ordinary sweater at one of the Moscow PhysTech meetings and, in a very simple and powerful manner, explained that the universe must have been hot at the beginning of its expansion. However, his first response to my desire to work with him was cool. ‘I am not obliged,’ he said, ‘to take every student.’ And then, after a pause, he added: ‘Can you figure out what is going on with muon neutrinos at the beginning of the expansion?’
