How close before "touching"? If I slowly lower a book to a table from a height of say 1 m, it is at some point, 0.5m away, then 0.4 m away, etc., until ultimately it rests on the table and I let it lie there. Now i understand (correctly?) that the book is not actually touching the table, there is some sort of photon exchange, but the molecules/electrons of the book never actually 'touch' the molecules/electrons of the table. So my question is, just exactly how close to the book molecules/particles get to the book molecules/particles of the table. Is the answer a.) The Planck Length b.) A silly fraction of a nanometer c.) 0 d.) none of the above I expect the answer is (d), but I'd like an explanation. (I'm not talking about Zeno's paradox). Thanks!