Follow Berkeley Talks, a Berkeley News podcast that features lectures and conversations at UC Berkeley. See all Berkeley Talks. When Princeton University Professor Mark Johnston’s daughter was 18 months old, she stood on a beach with what he describes as a “quizzical philosophical look on her face, as if she was thinking, ‘Is this my only life?'” That question is the heart of Johnston’s talk at UC Berkeley this past March, where he revisits a topic he wrote about two decades ago.