Let us consider transporting particle in the n-dimensional Euclidian space Rn
. It is assumed that a particle originating at a point x∈Rn
moves in a straight line with constant speed c and continues to move until it suffers a collision. The probability that the particle has a collision between t and t + Δ is kΔ + o(Δ), where k is constant. When a particle has a collision, say at y in Rn
, it moves afresh from y with an isotropic choice of direction independent of past history.