# Can there be a wave function that is physically possible but is non differerentiable (maybe even non-continous)?

The definition of a wave function demands continuity and differentiability so that it can satisfy the Schrödinger Equation. My question is whether this assumption is necessary for reality. Does probability density being positive and normalizable demands the wave function to be differentiable or continuous?

We just want $$\int |Ψ(x)|^2\;dx$$

Does all $\Psi(x)$ that satisfy this criterion fall in the differetiable category? A governing differential equation like the Schrödinger Equation lets us predict/understand the full behavior of the system with our knowledge of boundary conditions. Can a system exist without a governing equation like we know it as all differential equations stand with the continuity and differentiablity assumption, otherwise it is useless. Is it possible for a physical system to be governed by something other than a differential equation? Some new mathematical construct that doesn't need this assumptions?

• The mapping of physics onto functions living on metric spaces is an abstraction, so it doesn't exist anywhere but in our textbooks and in our minds, hence the question is exclusively mathematical in nature. For practical purposes (most physics students have limited math skills) we usually teach physics with functions that are at least two times differentiable (and then add a weirdo delta-function in there to deal with localization), but nothing stops you from going all "functional analysis" on the Schroedinger equation and to seek out the weakest Banach space in which you can make sense of it. – CuriousOne Apr 7 '16 at 18:25
• – ACuriousMind Apr 7 '16 at 18:54
• This might help: physicspages.com/2011/01/25/wave-function-borns-conditions – TheQuantumMan Apr 7 '16 at 19:50

What we want us not just $$\int|\Psi (x)|^2\;dx$$
For example $$p=\int Ψ^*(x)(- i \hbar)\; \text{grad} Ψ(x)\;dx$$
If the wave function is not differeciable $\text{grad}$ will come into a terrible result