How does a lightsaber behave in a confined space?

Question

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.

Answer 1

I don't believe there's a solid answer in current canon, unfortunately, but there are some facts that might be relevant to your hypothetical scenario.

When Rey and Kylo Ren are fighting the Praetorian Guard in The Last Jedi, the Guards' red armour can resist most blows but a direct thrust will go straight through them. See around 1:37 in this clip, for example. So that might suggest that even if you built your room out of something mostly lightsaber-resistant, the blade from your upright hilt would still go through.

There's also cortosis, which is such a good conductor that a lightsaber striking it has its energy redirected back into the hilt, causing the blade to vanish (apparently without damaging the lightsaber itself). This comes up in the novel Thrawn: Alliances, where cortosis is a major plot point:

"Igniting the lightsaber again, Anakin slashed a second time. Again, the blade disappeared before it could do more than leave a scratch on the droid’s metallic skin."

That might suggest that if you did have a completely lightsaber-resistant material and left the blade no room to extend, it would simply cut out. Which makes sense as a safety feature, if nothing else.