On the other hand, consider a wave function that is a sum of many waves, which we may write as ψ ψ ( x ) ∝ ∝ ∑ ∑ n A n e i p n x / ℏ ℏ , where A n represents the relative contribution of the mode p n to the overall total. The figures to the right show how with the addition of many plane waves, the wave packet can become more localized. We may take this a step further to the continuum limit, where the wave function is an integral over all possible modes ψ ψ ( x ) = 1 2 π π ℏ ℏ ∫ ∫ − − ∞ ∞ ∞ ∞ φ φ ( p ) ⋅ ⋅ e i p x / ℏ ℏ d p , with φ φ ( p ) representing the amplitude of these modes and is called the wave function in momentum space. In mathematical terms, we say that φ φ ( p ) is the Fourier transform of ψ ψ ( x ) and that x and p are conjugate variables. Adding together all of these plane waves comes at a cost, namely the momentum has become less precise, having become a mixture of waves of many different momenta.