The average person does not understand or care how a lizard going one direction and not another, or an energized particle hitting a sensor rather than a rock, matters at all in the grand scheme of things. A scientist, however, knows that initial conditions are everything, and that small differences at the outset make for huge differences in results down the line. The observer and the observed always interact. Everything changes. Send a historian to observe, say, the assassination of Julius Caesar, and their presence changes the scene. There is one more person present at the murder who wasn’t
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