Physics of lightsabers in stories.

[Obese Wan Kenobese]

Feel free to share anything you know about lightsaber physics or design here.

I'm starting with a question my brother in law asked me. Is there anything in the stories that states or demonstrates that the lightsaber has a physical force pushing away from the hilt?

Obviously there's more than just light, as that would not prevent sabers from passing blades. But is there anything that pushes away from the hilt during lock up, for example? What stops someone from pushing toward an opponent's hand, as most lightsabers don't have hilt guards? Is it just a technique not employed for combat skill reasons?

[BurceChuat]

I was interested in this topic too, I had a feeling it had to do with the magnetic fields keeping the blades in check.

https://www.reddit.com/r/AskScienceFiction/comments/2o4a6t/star_wars_do_lightsabers_have_friction/

[Obese Wan Kenobese]

Assuming no friction, vectors of the applied physical force from the opponents AND vectors pushing from the hilts would generate a natural lock up position based on their angles to one another and the effort exerted. Pushing closer toward the hilt would leave them almost running each other straight through as the hilt would push more the closer they get.

No friction AND no hilt repulsion(I just made that phrase up) would leave the two shifting back and forth ever adjusting their positions, pressure and applied angles until someone did slip and lose their hand. Although, I suspect it's somewhat like that anyway with our polycarbonate. Air gives us almost no friction, yet we still control the direction of our swings. We slip around when impacting full speed. Lock up would almost have to be planned without friction. If I swing hard and my opponent goes easy, the impact creates a new direction of our combined vectors. Which leads to a new question. Do lightsabers have inertia/momentum in the blade? As the actors are using dull metal sticks for their duels and stunts, their motion is consistent with some mass like a real sword. Though not particularly heavy.

Anybody wanna slick up their blades and see how it changes the duel when friction is reduced?

[Rapine]

Good question - a poser.

I always considered them as energy fields that simultaneously attract and repel one another (think a mess off ionized gases).  Therefore, the blades would actually be a part of one another, while not at the same time. No slip, but able to easily be separated.

I like the explanation Burce found as well though.

[Vyk]

Do lightsabers have inertia/momentum in the blade? As the actors are using dull metal sticks for their duels and stunts, their motion is consistent with some mass like a real sword. Though not particularly heavy.

They absolutely do!  The "massless blade" assumption is a myth that contradicts canon.  You can tell because a thrown lightsaber doesn't rotate around a point on the hilt, but a point on the blade.  In the case of Vader's throw, this is obviously because the prop that was actually thrown was a heavy hilt with a light (but not massless) blade, and I've heard people assert that it should be interpreted as a limit of special effects.  However, when retaking the Jedi Temple in ROTS, Yoda throws his saber into a Clone Trooper's chest, and his saber also spins around a point on the blade.  A CGI saber thrown by a CGI character at a CGI target can spin any way they want--the animators made a deliberate decision to make lightsabers behave as if the blades have mass. 

Now, in games, we sometimes (but not always) see the sabers rotate around a point on the hilt.  This doesn't necessarily mean the blades are massless--merely that the hilts are more massive relative to the blade.  In KOTOR, for example, they behave like the movies; in TOR, they rotate around a point on the hilt.  It's possible that between KOTOR and TOR saber technology changed; maybe by TOR the standard was to use a heavier power cell, shifting the balance point down.  (The real-world explanation is presumably either that animators assumed the blade should be massless or they just felt it looked cooler--the closer the point of rotation to the pommel, the larger the diameter of the disc traced by the blade.)  Note that most games are explicitly not canon; however, the Old Republic era's canonicity has not yet been decided (last I knew).

What stops someone from pushing toward an opponent's hand, as most lightsabers don't have hilt guards? Is it just a technique not employed for combat skill reasons?

What causes it is unclear, but it seems to be the case that lightsaber blades don't slide on each other.  There are any number of cases where the obvious thing to do would be to slide down the blade and lop somebody's hand off, but to my knowledge (I could have missed something, but I've watched pretty carefully ) you never see blades slide on each other^*.  (This is also what keeps Kylo Ren's saber's design from being stupid--the quillions aren't there to protect a user's hand like on a real-world sword, they serve some other function; therefore it doesn't matter if the emitter sticks out a little.)

Considering who we've seen fight, I don't imagine it's combat-skill reasons.  In even contests between the most powerful Force users known (Yoda vs Dooku, Windu vs Sidious) you don't see it.  In uneven contests (Dooku vs Kenobi and Dooku vs Skywalker in AOTC) you don't see it.  This suggests it's neither a matter of having the right knowledge nor of being sufficiently superior to pull it off--it's a fundamental characteristic of lightsaber design.

^* Actually, I'm aware of one time they do slide (as mentioned in Burce's link).  However, I suspect that was unintentional; contrary to what's said in the link, the blades appear to disengage before Kenobi lops off Grievous's hand.  (You can see the lockup glare vanish.)  It looks like Kenobi's saber slides down a bit and then back up, as if Ewan McGregor tried to correct a mistake (or maybe it's just that the blades are bouncing).  I don't know how that scene was actually filmed; Grievous is CGI, of course, but I have to assume there was a stand-in during the lightsaber combat, because Kenobi's saber certainly behaves like it's hitting something real.  It could be that there are similar occurrences in other fights--I haven't actually watched every lightsaber swing frame-by-frame (yet )--but if so I think they're also errors.

[Vyk]

Another observation on saber physics:

I have previously referred to lightsabers as "glowing blades of instant death".  It took me a while to realize that this isn't true; a saber requires some amount of force to significantly injure the target.  We know this because of the fighting style used.  If all you needed was a quick touch to burn a hole through your opponent, you wouldn't swing--you'd poke.  Watch a modern competitive sword sport, either fencing or kendo, and you'll see that they either use very small swings (saber fencing and kendo) or just lunges (foil and epee fencing); the reason for this is that you just need to touch the opponent to score.  In Star Wars, large swings are used--even by Count Dooku or the Grand Inquisitor, both of whom come closer to fencing than any other lightsaber fighters in canon SW.  (On the rare occasions that you do see thrusts used, they're also very large compared to those used in competitive fencing--more akin to a full-force punch.)  This suggests that sabers need large swings for some reason.

What we don't know from that alone is whether they need the swings for velocity or force.  Fortunately, Qui-Gon and the Trade Federation can answer that for us!  When Qui-Gon is cutting through the doors to the Trade Federation flagship's bridge, he cuts slowly but leans into it some.  (Much to Nute Gunray's dismay.)  This tells us that velocity is not the important factor, and force is; the large swings are to get speed and momentum to deliver significant force with the lightweight (but not massless ) blade.  This makes sense, because otherwise, lockups like we often see would be silly; you wouldn't try to shove your opponent's parry down with brute force if all you'd end up doing was scorching their hair!

This does mean that Ahsoka Tano's icepick grip is not quite as stupid as I'd initially considered it; if she tried to parry an especially heavy blow, she'd merely suffer severe burns and possibly sever her ulna rather than lopping off her forearm entirely.    Still, if I were her, I think I'd either learn to fight with a normal grip or else find myself a phrik vambrace for that arm! 

[Obese Wan Kenobese]

I've been told non force users often cut their own hands off when they use sabers. Suggesting a volatility of some kind. I had guessed the saber's field containing the energy also generated some type of vibration, odd balance or kinetic pull that increased momentum. The heat for cutting a large dense door needs time to build up. If the magnetic field repels the metal door, Qui Gon would need to control the blade as he cuts through.

As far as swinging motions, I'm sure the choreography is intended to entertain. The best martial art moves are not always the showiest. They're quick and effective to end the fight quickly, leaving little for emotional power, music and the realization by the audience that Luke is tempted to the darkside, for example. If Dooku can have a different style, then I don't see why we couldn't see someone show up with fencing style thrusts in the future.

[Vyk]

I've been told non force users often cut their own hands off when they use sabers. Suggesting a volatility of some kind. I had guessed the saber's field containing the energy also generated some type of vibration, odd balance or kinetic pull that increased momentum.

"Non-Force-users can't use lightsabers" is another common idea with no basis in canon.  Han Solo has absolutely no difficulty making a simple, straight cut through a tauntaun's belly while wearing heavy gloves and a parka in freezing temperatures and blowing wind.  At this time, it's unclear whether Finn has any Force sensitivity; if he doesn't, then we've even seen a non-Force-user use a saber in prolonged combat without injuring himself.  (He's a little clumsy with it, but no more so than anybody else using an unfamiliar weapon, to my eyes.)  If lightsabers were dangerous for non-Force-users, either Maz Kanata was very confident that Finn was Force-sensitive or she was perfectly happy sending Finn into combat with a weapon that would probably get him killed!  (General Grievous is also not Force-sensitive, but he is a cyborg; it's plausible that compensates for any tricky characteristics of lightsabers.)

Beyond that, note that the first time Luke, Finn, or Rey handle lightsabers, they have no difficulty controlling them.  (They look pretty much the same as if you hand somebody an Ultrasaber and they start waving it around--no weird gyroscopic effects or whatever.)  Either Force sensitivity is sufficient to let you control it with no other training, or the Force has nothing to do with it and they're actually not that hard to handle.

Personally, I have always interpreted the lack of non-Force-users with lightsabers, and even the assertion that they can't use them, as being because they're kind of stupid to use if you don't have the Force.  Against an enemy with a blaster and more than a few feet away, you're pretty much dead because you're unable to parry blaster bolts.  Against an enemy with a lightsaber and the Force, you're pretty much dead because he can react far more quickly than you can.  (Hence why Finn does a lot of running away against Kylo Ren; Rey does too, for that matter, right up until she opens herself to the Force.)  Proof of this goes back to General Grievous; despite him having four lightsabers, Obi-wan takes him apart (literally!) pretty quickly with only one, including his initial thrust that successfully parries two lightsabers both moving fast enough to be blurs and rotating at different speeds (you can see them go in and out of sync with each other), an ability Obi-wan didn't know Grievous had (he's literally staggered when he sees it).  Overall, Obi-wan seems to have less trouble against a superhuman cyborg with four lightsabers than he does against Dooku or Anakin, each with one, in the same movie.  That, to me, is what is meant by "non-Force-users can't use lightsabers".

As far as swinging motions, I'm sure the choreography is intended to entertain. The best martial art moves are not always the showiest. They're quick and effective to end the fight quickly, leaving little for emotional power, music and the realization by the audience that Luke is tempted to the darkside, for example. If Dooku can have a different style, then I don't see why we couldn't see someone show up with fencing style thrusts in the future.

Well, of course it's intended to entertain.    However, it's also our only clue to the behavior of sabers in SW.  We know as an audience that Christopher Lee still makes large swings because they look flashier than quick cuts and thrusts (actual competitive fencing and kendo move so quickly that they can be boring--you can't really tell what's going on).  However, when we're trying to take what we see on screen and use it to deduce how the weapons behave, we can conclude that Count Dooku making large swings, despite a comparatively fencing-like style, implies that large swings are somehow necessary with lightsabers.

If, instead, you decide to write lightsaber fights off as intended to entertain and impossible to derive meaning from, then you have to write off all of SW that way--after all, that's its whole purpose, entertainment.  If you're willing to put meaning on any of it, then you have to try to find explanations that fit what you see, not write off anything you see that doesn't fit what you want to believe.  It would be a shame to write it off, anyway--SW has an internal consistency that is rare in popular science fiction, and that took a lot of effort on the part of the people who made it.  That's why I'm willing to put in the effort to figure out what it means. 

[Obese Wan Kenobese]

I didn't say they can't. I said I was told they often cut their hands off etc. I'm aware of multiple non force users who do use lightsabers. But, I haven't read every book. A friend who read more told me it's dangerous for non force users.

I didn't write it off, but I'm not going to write it in that they must take big swings. I'm making plausible suggestions addressing the point, not excluding your view.

Lucas originally intended red and blue sabers, but green was used in ROTJ because it looked better on the blue sky on Tattooine. Jackson requested purple. And, many people extrapolated that color meant something, so it LATER became canon that colors had significance in video games and books that Lucas didn't write, but approved.

I started this topic to ask people who knew facts from the story to aid my understanding. Our best guess is welcome, but don't bash another option put forth.

[Obese Wan Kenobese]

Darth Sidious' first kill of the Jedi that come to arrest him with Windu is with a thrust.

https://youtu.be/YBLcxXR1PMw?t=40

Sidious also runs Savage Opress through with two lightsabers.

Maul runs Qui-Gon through.

https://youtu.be/ojXpHwhIqO8?t=37

Han dies run through with an ignition.

Lots of swinging for defense and strike attempts. More stabbing deaths. Or maybe that's just why Sith like pointy sabers. Poke poke.

[Obese Wan Kenobese]

I see references to gyroscopic effect, weightless blades with fast building momentum and variations of those ideas eluding to the danger for an unskilled attempting to fight with it. Cutting or lightly sweeping as we see in film is different than battle. But, I don't see specific reference to stories these ideas come from.

SPOILERS: Heir to the Jedi states plainly that an amethyst lightsaber with 3 kyber crystals belonging to a Jedi Rodian that died was given to Luke. He found it to be slippery regardless of being clean, as if it were trying to escape his hand. It was suggested that his father's saber allowed him to use it, while the Rodian's saber rejected him. But this was all Luke's supposition. He also thought it might be because it was for a Rodian, though he could not find a physical explanation as to this "slipperiness". Luke did still use the saber for a while, before taking it apart. Granted, this is Disney canon.

[Vyk]

I didn't say they can't. I said I was told they often cut their hands off etc. I'm aware of multiple non force users who do use lightsabers. But, I haven't read every book. A friend who read more told me it's dangerous for non force users.

I generally don't address the EU anymore.  It's no longer officially canon, and, bluntly, some EU authors were terrible at thinking things through.  Overall, the EU had poor oversight compared to post-Disney works.  (Because if anybody knows how to be overbearing in the name of protecting their intellectual property, it's Disney. )

Lucas originally intended red and blue sabers, but green was used in ROTJ because it looked better on the blue sky on Tattooine. Jackson requested purple. And, many people extrapolated that color meant something, so it LATER became canon that colors had significance in video games and books that Lucas didn't write, but approved.

I actually find it cool that, at this point, we can still assume color means something, at least in some fashion.  The producer (IIRC) of Rebels stated that Ahsoka's lightsabers are white specifically because of her lack of affiliation.  The Old Republic era hasn't explicitly been made non-canon, so for the time being, we can assume that KOTOR's colors meant something at one point.  (Although they're clearly meaningless by the times of the films or even TOR, and probably KOTOR itself.)  I would really love to see a new color in the new films, though, preferably tied in with a specific meaning.

I started this topic to ask people who knew facts from the story to aid my understanding. Our best guess is welcome, but don't bash another option put forth.

My goal is never to bash.  I've long been interested in deducing what I can about lightsabers from the films, and like to present what I've observed and concluded.  (For some time, I've actually been considering making a thread just for that.)  I don't claim that what I say is the last word; in fact, I love being proven wrong.  However, I demand a fairly high standard of proof, and, in keeping with both old and new canon policy, whatever is seen on screen overrules whatever is written elsewhere.  If a dozen books say lightsaber blades are massless (I'd guess at least that many books say that!) and two throws on-screen, totaling maybe two seconds of screen time, show they aren't, then the blades aren't massless and the books are wrong; and if an opinion put forth is based on those books, I'm going to point out the error.

Darth Sidious' first kill of the Jedi that come to arrest him with Windu is with a thrust.

https://youtu.be/YBLcxXR1PMw?t=40

Sidious also runs Savage Opress through with two lightsabers.

Maul runs Qui-Gon through.

https://youtu.be/ojXpHwhIqO8?t=37

Han dies run through with an ignition.

Lots of swinging for defense and strike attempts. More stabbing deaths. Or maybe that's just why Sith like pointy sabers. Poke poke.

I'm not claiming that people are never killed with thrusts, merely that the thrusts that are done are done with considerable force.  Sidious kills Saesee Tiin with a long, two-handed thrust, implying considerable force.  Maul does a 180-degree spin before stabbing Qui-Gon, which again suggests building up momentum.  I find it hard to follow saber fights in the cartoons, so I generally don't try to draw conclusions like "how much force was he exerting?" from what I see there; still, Sidious's strike is no mild poke but a double behind-the-back icepick stab.

Han's death, on the other hand, is an interesting point.  (No pun intended.)  We're never given reason to believe that igniting sabers exert particularly much force--they don't visibly kick back in people's hands, for example--but clearly Kylo Ren's saber runs Han through easily.  Perhaps it actually was pushing back against Kylo's hands quite hard; perhaps it's due to the unusual nature of Kylo's saber.  (Maybe the unstable blade, at least while extending, acts like an electric carving knife or chainsaw and decreases the force needed?)

You do make the interesting point that Sith kills are largely done by thrusts.  Perhaps Jedi have become so used to swings for attack that they are bad at defending against thrusting attacks, and Sith train for that?  Dooku was Jedi-trained, and indeed he rarely thrusts.  I'll have to watch more carefully to see how often Jedi thrust; we see them on the screen much more often, but largely against battle droids, which are nearly skeletal and wouldn't seem to be great thrusting targets.  Still... an interesting possibility!

I see references to gyroscopic effect, weightless blades with fast building momentum and variations of those ideas eluding to the danger for an unskilled attempting to fight with it. Cutting or lightly sweeping as we see in film is different than battle. But, I don't see specific reference to stories these ideas come from.

Finn and Rey do both use the Graflex saber in battle, and presumably neither was trained with a lightsaber before.  I too remember reading the ideas you mentioned; however, I don't, off the top of my head, remember where.  A quick check of the reference books I have handy show that:
Star Wars Lightsabers: A Guide To Weapons of the Force states that lightsaber blades are weightless.
Jedi vs Sith; The Essential Guide to the Force states that they both have no mass and have a strong gyroscopic effect, and that mastering its handling requires a lifetime of training.  (Which makes one wonder how Luke defeated Vader, or even held up to him at all; some of Vader's training would have been negated by the changes in his body mechanics from his reconstruction, but you're still talking about somebody with decades of lightsaber experience against somebody with whatever brief training Obi-wan and Yoda had given him.)
I didn't see any comment about lightsaber handling characteristics in The Jedi Path or the Book of Sith, but I may have missed it.
I should point out that Jedi vs Sith derives strongly from EU sources; most of the book is based on what is now Legends material, leaving anything said there suspect.  (The other three books mentioned also predate the new canon policy, I believe, and are not authoritative, but aren't EU-influenced to the same extreme; JvS is ostensibly an in-universe book written by a EU character!)

Incidentally, there's a fun way to retcon the "lightsaber blades are weightless" version.  Weight is due to gravitational mass, which, while identical to inertial mass in every case known to modern science, could potentially be different for an exotic material (like a lightsaber blade might be made of).  It's entirely possible that lightsaber blades, although not massless, are weightless, and a stationary saber would balance on a point on the hilt (since gravity would not be acting on the blade).  This shouldn't affect their swinging or throwing characteristics significantly, however.  I wonder...  would a midgrade blade filled with helium or perhaps a vacuum be weightless but not massless? 

SPOILERS: Heir to the Jedi states plainly that an amethyst lightsaber with 3 kyber crystals belonging to a Jedi Rodian that died was given to Luke. He found it to be slippery regardless of being clean, as if it were trying to escape his hand. It was suggested that his father's saber allowed him to use it, while the Rodian's saber rejected him. But this was all Luke's supposition. He also thought it might be because it was for a Rodian, though he could not find a physical explanation as to this "slipperiness". Luke did still use the saber for a while, before taking it apart. Granted, this is Disney canon.

Affinity between a saber and its wielder is something that has been suggested, but that I don't currently know of solid evidence for.  (Luke doesn't either, apparently. )  Still, Anakin's/Luke's saber had some sort of connection with Rey (while Finn doesn't seem to have been affected; no way of knowing if Maz Kanata had been).  Anakin and Obi-wan used "loaner" lightsabers in AOTC; on the other hand, they were also soundly defeated when wielding them against Dooku!  Obi-wan successfully uses Qui-Gon's saber against Maul, but very, very briefly, and they were also master and Padawan, so there's no useful information there.  We also can't really derive anything from Anakin's brief use of Dooku's saber in ROTS.  It's probable that Obi-wan used Anakin's lightsaber for a while at some point before giving it to Luke--the saber changed configuration significantly between ROTS and ANH--but again, they had been closely linked.

It seems likely that we'll get more information about this in Episode VIII; I can't imagine Rey won't ask Luke about her Force vision.

[Vyk]

Immediately after hitting "Post", another possibility occurred to me.

What if all the things said about lightsaber handling apply only to old-style sabers, like Kylo Ren's?  (According to a plaque at Disneyland, "Kylo Ren's unusual lightsaber is an ancient design, although the one he carries is recently constructed.")  Maybe the unstable blade creates odd handling, giving him a handicap, which is why his novice opponents were not more easily defeated.  It might also mean that his desire for the Graflex saber wasn't merely because of what it symbolized but also because it was a superior weapon.  It could be that is why sabers of his style are not in common use by the time of the movies--modern ones are easier to handle, making them more maneuverable for novice and expert alike.  However, the tricky handling of lightsabers is such widespread "common knowledge" that few people are aware that it no longer applies.  (After all, even in the time of the prequels, how many non-Jedi would get the chance to handle a lightsaber and find out for themselves?)

[Obese Wan Kenobese]

Thank you for the book references.

I kinda figured Vader stands his ground as he is the more confident stronger swordsman, but also because he's got metal legs etc. Luke can jump around, but Vader can sense his movements and predict for a strong defense while Luke struggles. Though, Maul seems to keep his acrobatics with metal legs, while Vader plants himself.

One of the Disney books I read stated that Snoke explicitly told Kylo to make an ancient style saber. Though, I can't recall if that was one of Disney's info books or not. I think it was 'Absolutely Everything You Need to Know' or 'Ultimate Star Wars'. Maybe it was even in 'Rebels'.

Helium isn't massless. It is buoyant in general air at sea level yada yada. It could generate upward force like in a balloon, counteracting gravity to try to simulate being weightless. I don't know the numbers, but I doubt we could float a blade just by filling the blade with helium or vacuum. Any material that withstands the outside pressure would be heavy enough to always succumb to the acceleration of gravity. Either way, we wouldn't lose inertia and momentum. In reality, that's physics with a set formula.

This is fantasy and doesn't have to keep technology to strict physics, so if a book approved by Lucas says the blade is weightless, but behaves with inertia and momentum, then that's what I'd follow, even if the special effects and actors struggle to properly simulate the appearance of weightless movement with momentum disproportionate to the actual mass of their props. We can neither make a blade with no friction nor the 'sticky' behavior we think we see on film. We can only choreograph, instruct and perform. Does it take disproportionately more effort to make the saber start moving or disproportionately more effort to make it stop moving or just stop spinning? These ideas could be in the story, but not easily simulated. When I spin my polycarbonate saber, the centrifugal-centripetal forces and momentum are in a set balance. A plasma bolt inside a field won't behave like my polycarbonate or the movie prop.

I was hoping to find out if the books or otherwise stated clearly a reason for lock up. I'd even be satisfied if a skilled swordsman could explain why it would be problematic to attempt sliding blades. "It's simply not done in the movie" could be changed at any time by another movie or book. A new director working with a choreographer who shows him/her something the director likes could blast all our inferences out the window with a different combat style. Did Luke do spins like prequel Obi? Did Vader do what Anakin did? How much of what we see is just Kendo, special effects, neat choreography or just our inferred guess? I'm attempting to be cautious about fiction. Yes, I'm that pathetic.

It sounds like the rules people are going by are just those inferences that vary by individual. A sophisticated form of "I got you!" "No, you didn't! I was in the safe zone!"

[Vivectius]

Here's current canon: http://starwars.wikia.com/wiki/Lightsaber

Here's the more interesting Ledgends info: http://starwars.wikia.com/wiki/Lightsaber/Legends

And a bit on Lightsaber combat:
http://starwars.wikia.com/wiki/Lightsaber_combat/Legends

There are links in all of the above articles to more specific styles, techniques, Lightsaber masters, and variations on the Lightsaber that I encourage everyone to read.

In reference to your specific question on blade lock up:  sliding your blade down your opponent's blade towards their hand, wrist or even forearm is a valid technique.  BUT, it must be done very quickly, as your opponent can perform the same maneuver, including slicing you open straight down from head to groin if they are faster than you are.  In addition, body control and footwork can play a major role.  If your opponent steps to the side, they can have their blade above yours, and you need to try to recover from your downward momentum as they are able to bring their blade up, usually cutting upward from under the chin through the top of the head.  There are other ways to deal with lock up as well, both offensively and defensively, but I'm too tired now to go into them.