"Because the neutrino only interacts weakly, when moving through ordinary matter its chance of interacting with it is very small. It would take a light year of lead to block half the neutrinos flowing through it."

Neutrino, in Wikipedia http://en.wikipedia.org/wiki/Neutrino

"... if all humanity, about 250 million tons, were distributed in a layer of homogeneous thickness on all the emergent lands, the "stature of man" would not be visible to the naked eye; the thickness one would obtain would be around sixteen thousandths of a millimeter."

Primo Levi, in The Periodic Table (1975)

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