A layman's question: In quantum physics, apparently every "particle/wave" is capable of tunneling/passing through material. Why then is there a shadow at all?
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Like all quantum mechanical processes, tunneling is probabilistic: some fraction of particles approaching a barrier will tunnel through, and some will be reflected (or absorbed.) What's more, the probability for a subatomic particle to tunnel through a barrier of human-scale thickness is usually minuscule — as in, you could bombard the barrier with particles for the entire age of the Universe and you'd still never expect to see one pass through. So for all practical purposes, such objects are "opaque" to the incoming particles.
Michael Seifert
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Not only is tunneling unlikely in many cases, even when it happens, issues of reflection, diffusion, and refraction still apply. Consider the double slit experiment where we have dark spots due to destructive interference. Similar considerations will cause light to be blocked even if partially transparent.
R. Romero
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