# Position and momentum space | ðŸ—– nosplit | â†‘ parent "Uncertainty principle" | 103, 3, 205

One way to think is: what is the definition of space space? It is a way to write the wave function $Ïˆ_{x}(x)$ such that:And the, what is the definition of momentum space? It is of course a way to write the wave function $Ïˆ_{p}(p)$ such that:

- the position operator is the multiplication by $x$
- the momentum operator is the derivative by $x$

- the momentum operator is the multiplication by $p$

Bibliography:

- https://physics.stackexchange.com/questions/39442/intuitive-explanation-of-why-momentum-is-the-fourier-transform-variable-of-posit/39508#39508 gives the best idea: the Fourier transform writes a function as a (continuous) sum of plane waves, and each plane wave has a fixed momentum.
- https://en.wikipedia.org/wiki/Position_and_momentum_space