What thought experiments teach us about the value of life

We all know of those thought experiments that are supposed to test our moral judgments – for example, would you divert a runaway train from a tunnel where it would crush five people into another tunnel housing just one unfortunate person? Or would you stop the train by pushing someone in front of it? But what do these thought experiments teach us about how we value life? We find out from Julian Baggini writing in Aeon Magazine.