The Fourier transform is also a Gaussian in terms of the wavenumber, the k -vector, (with inverse width, 1 / a = 2 ⟨ ⟨ k ⋅ ⋅ k ⟩ ⟩ / 3 ⟨ ⟨ 1 ⟩ ⟩ = 2 ( Δ Δ p x / ℏ ℏ ) 2 , so that Δ Δ x Δ Δ p x = ℏ ℏ / 2 , i.e., it satisfies the uncertainty relation), ψ ψ ( k , 0 ) = ( 2 π π a ) 3 / 2 e − − a k ⋅ ⋅ k / 2 .