The answer is fairly simple the roads were built when

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The answer is fairly simple. The roads were built when the city was tiny, centuries or even millennia ago, to serve that proto-city. Then, as the city grew, it grew around those roads. Buildings went up, and museums and castles and theaters and sewers and all the other stuff of a city. Would you move Big Ben, or tear down the Louvre and start over, to straighten out a winding road? When faced with that choice, people usually keep the old roads. Careful checking will show you that people actually have put a lot of effort into improving the roads over time, moving things, tunneling under or bridging over, adding subways to take off some of the strain, patching and fixing and repairing, spending billions of dollars, but always starting from the existing system rather than starting over. There is a useful analogy here in considering how humans learn things, and in particular how we learn science. I’ve had the joy of watching closely as our two daughters grew from babies to toddlers (and on to remarkable young women), and many of you who read this either have closely observed growing babies, or will. Scientists watch babies, too, and are learning all sorts of things about learning. By the time a baby is a year old, he or she knows quite a lot about the world. The baby knows that some things are inanimate and others animate—rattles don’t walk away, but parents do. Many things are predictable for a baby—a rattle released in midair always falls down, not up, unless grabbed by a mother or father or other living thing. A rattle placed properly on the railing of a crib will stay there. In gaining this knowledge, the baby is putting down “roads” in the brain, wiring in information that later will be called “common sense”. When artificial-intelligence researchers have tried to get computers to do human jobs, perhaps the biggest difficulty has been that the computers lack this “common sense”—teaching the computer all the things that a baby learns proves to be quite difficult, because the baby learns so much. Notice, however, that this “common sense” is often not really correct. For example, babies do not start off with a modern view of the shape of the Earth and the physics of gravity. Whatever a baby does think, a “round, round world”, with people and rattles
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pulled toward the center by the warping of space-time by mass that causes gravity, is not in the original common-sense picture. Careful studies show that, when children are finally told about gravity on the spherical Earth, they initially resist the idea. They may deny it, or they may try to modify it to fit with their “common sense”. (If asked to draw the world, they may add a flat spot or divot just where they live in an otherwise spherical Earth, or they may draw people living inside a sphere.) Often, it takes until age nine or so before children really say that they accept the idea that they are held to a spherical Earth by gravity, and they draw the idea and work with it properly.
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