The Drunken Philosopher #7: Ri-diddly-doo, just passin' on through...

Walking.  Through.  Walls.

Did I get your attention?  From olden tales and lore of phantoms to the current sci-fi and comics, the rate of occurrences of this phenomenon/ability without any real thought to the specifics of how exactly it would work is almost as amazing as the ability itself.  We know that about 99% of all matter, even of the solid sort, is just empty space, and it's the fields generated by the repulsion forces of those countless subatomic particles that make things seem "solid"... so if there was a way to turn those fields off or without collapsing our own atoms into neutron star matter, or simply align our subatomic particles just right either through magic, SCIENCE!, or some sort of Men Who Stare at Goats -level meditation technique, then that would be awesome... but then, how would we make sure that we'd only be intangible to the walls?
If gravity still acted on us, wouldn't we logically just pass right through the floor from the moment we activated the ability?  I'd think it would rather suck to go from passing through walls one moment, to plummeting to the center of the Earth the next, like some sort of IRL version of a bad clipping glitch in a videogame.  Would we have to jump at the wall, render ourselves intangible, then deactivate the ability immediately thereafter to avoid falling through the floor of the adjoining room?  And further, if we could switch the ability off and on, we'd also run the risk of timing it wrong and ending up fused into the wall like that one guy from the Philadelphia Experiment.  You could argue that you'd just have to reactivate the ability, then pull out of the object, but with the particles having once been solidified together, how would the ability then know which particles were originally yours?  You may just end up stuck that way.

Of course, we must also consider stuff like ghosts and other "actual" phantoms.  They're often shown passing through both walls and floors/ceilings, possessing objects, etc. with nary the slightest regard for the physical laws of this Earth.  But here's the kicker:  if they're absolutely unbound from ANY of the laws of physics, wouldn't that imply that they'd be left behind at their point in the universe as a whole, and thus have to spend an unfathomable amount of effort just to keep up with the Earth's rotation, orbit around the Sun, our solar system's movement around the galactic core, and our galaxy's movement through the cosmos?  If truly unbound from physics, that's already 4 exceedingly painstaking calculations, with even the slightest error meaning a deviation somewhere in the tens of thousands of miles per hour, needed just for the seemingly simple task of haunting one particular room or house.  Ain't nobody with no body got time for that.

All of this said, there's still the angle of magic to consider... but I think I'd rather just leave the magicians their secrets, lest I spoil my enjoyment of their miraculous feats.