If you were to shoot billions of tennis balls through two large slits and observe the pattern they create on a screen placed behind the slits, you would not observe the same interference pattern that is typically seen in the double-slit experiment with particles such as electrons or photons.
The interference pattern in the double-slit experiment arises due to the wave-like nature of particles and their ability to interfere with each other. It is a result of the superposition of different possible paths that the particles can take, leading to constructive and destructive interference at different points on the screen.
Tennis balls, being macroscopic objects, do not exhibit the same wave-like behavior as particles at the quantum level. They are much larger and subject to classical mechanics rather than quantum mechanics. When tennis balls are shot through the slits, they would behave as classical particles and follow well-defined trajectories. The pattern they create on the screen would resemble two distinct clusters corresponding to the slits, rather than an interference pattern of alternating bright and dark regions.
In the double-slit experiment, the wave-particle duality is a characteristic of particles at the quantum level. It does not manifest in the same way for macroscopic objects like tennis balls. The phenomenon of wave-particle duality is specific to particles on the quantum scale, where their behavior is described by wave functions and probabilities rather than classical trajectories.