Question

What is there that does not shadow?

Answer 1

Answer:

For instance, only charged particles interact with photons, which are the particles which make up light. As a neutrino is an uncharged particle, and doesn't interact with photons at all, a neutrino (or a material made of only neutrinos) would cast no shadow.

Answer 2

Transparent objects don't show shadows as they do not allow the light to pass through them is a straight manner.

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Also the objects which are reactive with with photons make light and the others do not.

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@ Lalitya