This relationship is confirmed by Monte Carlo simulations in 1D diffusion (Fig. ). In this control simulation, A (molecular weight MW = 100 kDa) and B (MW = 10 kDa) randomly move left and right on the x-axis with each step length randomly selected from a Gaussian distribution with standard deviation 𝜎 = √2𝐷∆𝑡, where D is calculated using Equation 6 assuming A and B are spheres in water under normal conditions, and Δt is time step 1 ms. Consistency between simulation and theory for Equation 5 and Equation 7 is observed over prolonged simulations steps confirming that the theory and simulation work consistently. To calculate the collision frequency for single-molecule and single-particle diffusion, or Brownian motion, assuming all 3D directions are symmetric and inherit the relative diffusion constant, the probability density function (PDF) is extended from Equation 5 to the 3D diffusion and shown in Fig. ,