Thirty-five years ago this summer, the Sony Walkman made its debut in North America and all this week we’re saluting the device that changed the way we listen to music. A couple of things made the Walkman so radical. First, it was the first ultra-portable device that allowed people to take music with them wherever they went. You can make an argument that the Walkman was a big part of the fitness craze of the early 80s because for the first time ever, you could go jogging while listening to music that you programmed. A big feature of the Walkman was the headphones which weighed just 50 grams. Given the size and weight of standard headphones of the day—300 to 400 grams—they were nothing short of revolutionary. And third, the Walkman was the thing that allowed people to walk around in public sealed off from the rest of humanity in a bubble of music. Sony executives were so worried about this anti-social behavior that the first Walkmans came with two headphone jacks. That lasted one model.