On a holiday a few years ago, my husband and I were driving around purposelessly with some friends, with their son and our daughter sitting in the rearmost seat, chatting away. We pricked up our ears when we heard the children talking about what they wanted to be when they grew up. Their son, who was still short of 10 and about four years younger than our daughter, declared that he’d become an inventor. This is what he said he intended to invent: A machine that would allow a person to speak with loved ones who were dead and gone.

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