Only the Shadow Knows

When I was a youngster, I was taught that light goes in straight lines. At some point, I also became aware that light spreads out from a light source such as a light bulb. However, it still seemed to me that I was missing something important. I couldn't figure out why shadows had such blurry edges. If the light goes straight, shouldn't the edge of a shadow be sharp? And what really bothered me was, if the light spreads out—gets bigger in a sense—and we use our pupil to grab a tiny fraction of that light, why can we see the whole object?

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