Where is the border between sky and space? That's what 5-year-old Matthias of Durham, New Hampshire wants to know. Allesandra, 3 of Bella Vista, Arkansas wants to know why we can't hold air. We're going to get scientific, but also philosophical and imaginative with anthropologist Hugh Raffles, astronomer John O'Meara, and, a special treat, cellist Zoë Keating, who scored the episode for us to help us really feel it!

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