The 19th letter of the Greek alphabet, represented by the symbol τ; used in science and mathematics.
From Greek 'tau,' ultimately from Semitic languages through Phoenician. The letter name traveled with the Greek alphabet from its origins around 1000 BCE.
Tau (τ) is the constant relating a circle's circumference to its radius, and some mathematicians argue it's more fundamental than pi (π) because it appears more naturally in equations—this decades-long debate shows how even the symbols we use to describe reality have passionate advocates.
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