If I were to keep increasing the mass of particles I throw at a double slit, at what point would it stop creating an interference pattern?

Question

Why don't things like tennis balls create interference patterns when thrown at double slits? Where's the limit where it stops interfering?

Answer 1

The interference pattern appears when the two slits are at a distance of the order of the wavelength of the incoming waves. This is classical wave dynamics, nothing quantum to it. The quantum part is that particles are actually waves, and have an associated de Broglie wavelength, which depends inversely on their mass. Presumably, making your objects heavier also increases their size. So to observe interference, the slits need to get closer and closer, as the objects themselves get bigger - at some point, you obviously reach the limit where the object size becomes larger than the required distance.