Note: This writeup was orignally a rebuttal to a now-defunct node. The italic quotes are the ghostly remnants of this ethereal prose
I realise that this is a thread of complete speculation and should not be treated with any form of scientific rigour, but I'm afraid rep_movsd's contribution is incorrect even from the standpoint of sci-fi pseudoscience. A big part of making any 'made-up' science sound plausible is making it make logical (or in fact illogical) sense to a human being upon first hearing. This is shown quite aptly in Gene Wolfe's "Book of the New Sun" quartet, in which interstellar travel is accomplished by bouncing light back and forth between perfect mirrors. Eventually, the universe gets into a philosophical debate with itself as to which is the reflected and which is the reflection, and an object (a Fish made of light, as it happens) is spontaneously created at the focus of the mirrors. This makes absolutely no sense whatsoever to a scientist, but to the more fantastical 'common sense' squelchy bit in your brain it is only natural. That's why 'turbolaser' sounds so cool whilst meaning little; more power + modern invention = big shooty death. Following the same reasoning, Gorgonzola has done a superb job with his theory. I have no idea what a spinning meson will do when stretched, but by jingo does his theory sound cool with virtual photons and gluon strings flying off all over the place. Rep_movsd has been slightly less successful, for the following reasons:
The nasty thing about nuclear fusion is that it requires a huge magnetic field to keep it in check, unless your lightsabre is roughly the size of, say, the sun. They may very well have made fusion generators this size, but it'd pull the change out of your pockets and the fillings out of your teeth, which could easily distract you from your cataclysmic duel of fates.
Now this is more like it; gravity and anti-gravity generators are all over the Star Wars universe. Unfortunately, gravity has a habit of tenaciously hanging onto everything around it, such as the lightsabre wielder, his credit card, nearby rocks, migrating birds etc. Two such devices in close contact would inevitably wrench themselves out of their respective owners' hands and skitter around on the floor, chasing one another's handles like a pair of insanely horny ferrets. Not to mention, unless the 'stalk' were very strong indeed the gravitational tidal forces along its length would tend to curl it up into a circle, then crush it into slag. Of course, this all neglects the very human aspect of lightsabres; the immutable coolness of them. The idea of a beam of pure light leaping unbidden from an understated chrome handle is attractive; the idea of a thin metal wire that looks suspiciously like the antenna from a portable radio being at the centre of all that white-hot righteous fury is not.
"This energizes a powerful gravitatonal field generator mounted on a thin long stalk which telescopes out when the sabre is turned on."
This kind of queers the pudding completely, as the gravity generator now has to be powerful enough to bend the path of light itself 180 degrees at the end of the sabre, so it comes back the other way. The only entity in either real life or Star Wars capable of that is a black hole, which I fear may be somewhat ungainly to wave around on the end of a thin 'stalk'. The upside is that you'd have a sword which could quite literally destroy whole planets, but I doubt you'd want to be around when you turned it on. Sort of like a lonely rancor, then. (sorry...)
"Mounted around the stalk are three lasers which shoot out parallel to the stalk and are bent a full 180 degrees by the gravitatonal field generator. The laser photons re-enter the handle and are recycled to emerge again."
Ouch. Just gets worse really. The lightsabre does indeed vaporise just about anything it touches, with the rather notable exception of other lightsabres. Think of Return of the Jedi, or Phantom Menace, where the protagonist and black-clad uber-villain end up in a face-to-face grimace contest either side of squealing lightsabre blades. Not mechanically strong indeed? Piffle. This could however be explained by the aforementioned gravitational effect, and the combatants have instead got their lightsabres inseperably stuck together and are trying really hard to get them apart rather than overpower one another. Yes. Incidentally, no laser beam(not even in Star Wars, wherein both lasers and 'blasters' fire ionised gas blasts) can vaporise to that degree, even with a 1GW fusion generator behind it. Not even three of them.
"The central stalk need not be mechanically strong because it never directly touches anything(The laser vaporizes anything it comes into contact with)."
Can't argue with that, it's stated in almost every Extended Universe book that talks about lightsabres. The only minor problem is that the lightsabre is glowing like a firework the whole time it is active, which means photons are flying off it in great quantity all the time. This also fails to address quite how the lightsabre deflects anything, because photons arent that good at standing their ground.
"Since the laser beams are recycled, the sabre uses minimal energy unless its actually cutting through something."