Bowling balls as waves?

If this wave-particle duality seems so readily demonstrated, one might wonder why we don't see more examples of this in our everyday lives. Why, for example, don't we see obvious ``particles'' like bowling balls behaving as waves sometimes. The answer to this lies in the very small size of Planck's constant (6.63 x 10<sup>-34</sup> J-s), which implies that wave-particle duality exists most readily at the atomic scale. However, in principle we could illustrate the wave nature of bowling balls by setting up a suitable diffraction experiment. Recall, though, that for significant diffraction to occur that the width of the slits must be of the order of the wavelength being used. For a bowling ball traveling at 1 m/s, this would mean that we would need slits about 10<sup>-34</sup> m wide, which is far beyond today's technology. One could increase this size by reducing the speed of the bowling ball (recall the wavelength of the de Broglie wave is inversely proportional to the speed of the particle). However, to use a slit of about 10<sup>-5</sup> m in width would imply that the bowling ball would have to travel at about 10<sup>-29</sup> m/s, which would mean that it would take a very long time (longer than the age of the universe) to pass through the slit. The conclusion we draw from this is that in our everyday lives we are protected from ``quantum weirdness'' by the smallness of Planck's constant, but that this does occur readily at small length scales and, at least in principle, also applies at larger scales.