An attosecond is a unit of time in the International System of Units equal to 10⁻¹⁸ or ¹⁄₁ ₀₀₀ ₀₀₀ ₀₀₀ ₀₀₀ ₀₀₀ ₀₀₀ of a second. An attosecond is to a second as a second is to about 31.71 billion years. Wikipedia