Autumn is a moment of heightened synchronicity, when all the natural world seems to hunker down for the onset of winter. Even fall foliage’s colorful showiness — a brief but brilliant pageant in the face of encroaching cold — is yet another concession to the inevitability of harsher days ahead. As sunlit hours grow shorter and nights become cooler, trees move nutrients from leaves to limbs for storage. Photosynthesis grinds to a halt, and green chlorophylls break down, allowing other pigments — carotenoids and anthocyanins — a fleeting instant to exhibit their fiery oranges, crisp yellows, and deep reds. Finally, the leaves will turn brown and drop. Biologists call the whole process “senescence,” deterioration with age and eventual mortality. But that word — that sentiment — feels inadequate to the phenomenon it describes. Autumn’s kaleidoscopic display will recycle itself next year and the year after, always an outward expression of beauty and renewal at a time when the rest of the world appears to turn inward.