  p-Adic quantum mechanics is constructed from the Dirac-von Neumann axioms
identifying quantum states with square-integrable functions on the
N-dimensional p-adic space. This choice is equivalent to the hypothesis of the
discreteness of the space. The time is assumed to be a real variable. The
p-adic quantum mechanics is motivated by the question: what happens with the
standard quantum mechanics if the space has a discrete nature? The time
evolution of a quantum state is controlled by a nonlocal Schr\"{o}dinger
equation obtained from a p-adic heat equation by a temporal Wick rotation. This
p-adic heat equation describes a particle performing a random motion in the
N-dimensional p-adic space. The Hamiltonian is a nonlocal operator; thus, the
Schr\"{o}dinger equation describes the evolution of a quantum state under
nonlocal interactions. In this framework, the Schr\"{o}dinger equation admits
complex-valued plane wave solutions, which we interpret as p-adic de Broglie
waves. These mathematical waves have all wavelength 1/p. In the p-adic
framework, the double-slit experiment cannot be explained using the
interference of the de Broglie waves. The wavefunctions can be represented as
convergent series in the de Broglie waves, but the p-adic de Broglie waves are
just mathematical objects. Only the square of the modulus of a wave function
has a physical meaning as a time-dependent probability density. These
probability densities exhibit interference patterns similar to the ones
produced by `quantum waves.' In the p-adic framework, in the double-slit
experiment, each particle goes through one slit only.
