Best bleeding-edge physics explanation for lightsabers involves high-temperature superconductors, ultradense energy cells, and far more advanced plasma technology than we have now. To exhibit all the properties seen in the films (blade casts a shadow when a light-source is behind it, blade core is intensely bright but illumination drops off drastically and can't light a room, heat effects in materials the blade comes in contact with, near-microscopic cuts [ROTJ sail barge fight], near-massless but difficult to wield, and so forth), the best guess is:
- High-energy plasma arcing between opposing nodes
- Multiple node pairs arrayed in a circle, cycling on and off
- Something akin to an electron gun below the nodes that distorts the arc out dramatically in the direction of the emitter
- Toroidal electromagnets in said emitter further narrowing the "blade" to near-one-dimensionality
We could build one today, but the blade would be as tenuous as out other contemporary plasma experiments, the emitter housing would be th esize of a small car, and it would require several daisy-chained power plants to keep it running for any amount of time. Throw in thirty thousand years' worth of amplification and miniaturization and the results would be far more impressive -- and portable. A single set of nodes would result in a two-dimensional plasma windo with, basically, a chainsaw edge (from the plasma arcing from one node to the other). This conveniently explains Pre Vizsla's "darksaber". Mounting multiple node pairs, with superconductors allowing them to cycle at near-lightspeed, means the cutting edge faces any/every direction almost simultaneously. The timing of that cycling would be controlled by -- wait for it... crystals. We like quartz here on Earth, but I imagine they found their own preferred properties in kaiber crystals, in-universe.
Also, though almost massless, the blade "rotating" that fast would impart gyroscopic effects, so it would definitely take (Force-enhanced?) strength and skill to use. And depending on how highly-tuned a blade is would make it potentially a more effective weapon, at the trade-off of being harder to control. Kinda like how the best dogfighting aircraft are so unstable, if it weren't for onboard computers constantly tweaking things so they fly straight and level, they'd stall and fall right out of the sky. That instability means they can "fall" any direction at a twitch. Great responsiveness, but at greater risk. The "default" tuning is Luke's ANH silvery-with-a-tinge-of-blue. Jedi who don't have the equipment to tune their blade properly, or for whom combat is less of a priority, would see it shifted toward the green, or even into the yellow. Those who have to make do with substandard materials and makeshift tools would end up with blades all the way down in the red. Very likely if one finds oneself and ones comrades exiled from the Order and on the far side of known space. Meanwhile, Mace is, once again, the ultimate Jedi badass, with his saber tuned all the way up into the violet.
As I mentioned elsewhere, though, because plasma is uncoupled electrons, something with high amounts of free electrons in its atomic structure would be able to resist the blade longer than something that is electron-poor. Plastic? Flesh? Wood? Voop -- right through. Crystalline structures such as metal? Reference Luke's saber bouncing off Vader's shoulder armor in ESB or Qui-Gon's saber taking forever to slag the blast door in TPM. If you then apply a plasma field to a conductor like that, you raise its resistance even more. Like charges repel. And because there's no spinning massless blade, electro-staves or power-tonfas will be easier to wield -- but still dangerous to the wielder. Don't touch the live parts. Flamethrowers and flechettes are probably still better bets.
--Jonah
