Imagine I place a lightsaber hilt upright on the ground, in a room with a very very low ceiling which is to some extent impervious to lightsabers (or at least which takes some time to be melted into submission). Then I turn on the lightsaber. What happens? Does the lightsaber blade splash over a wider area as it hits the ceiling? Does the hilt experience a downward force exerted by the blade as it is pushed down by the ceiling, like some kind of metallic extending sword would in real life? Does the blade simply shrink?
I would be surprised if this is not dealt with somewhere in the Extended Universe, if nothing else, but I would be most interested in canon events that suggest an answer. For example, Qui-Gon Jinn cutting through the blast door in The Phantom Menace is the kind of event that might be helpful; except in this instance it's not very relevant because it shows only that lightsabers experience force when you try and move them sideways (and he appears to be able to plunge the saber end-on into the blast door with essentially no effort).
I am, of course, not seeking a real-world scientific explanation. Unless there have been large advances in many fields recently that I'm not aware of, lightsabers continue not to exist and continue not to have a plausible real-world physics, however speculative.