Quote:
Originally Posted by lynnejanet
Is it possible, though? I know that atoms and molecules are always moving, but that movement is miniscule. They are vibrating, but they're not actually moving any great distance, otherwise the wall/window/other solid wouldn't be solid in the first place. I think if you tried to calculate the probability of individual particles in two different solid objects, of different densities, vibrating at just the right frequency to pass next to each other, the probability would be 0.

No, just close to 0 (as KirkMcD wrote). Also, if you actually looked at an atom, most of it is open space. What stops you is not your atoms running into the wall's atoms, but the fields that surround your atoms interacting (and repelling) the fields of the wall's atoms.
Besides, my point was a QM one. There is a mathematical probability, not equal to zero (but really close) that you can walk up to a wall and simply "pop" out the other side. There are actual devices that use this QM principle. One of them is the tunneling electron microscope.