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I remember reading somewhere(I don't really remember where, sorry) that a lightsaber isn't really hot, it just makes atoms vibrate and hence heat is produced in a material the lightsaber comes in contact with.

I am not entirely sure if this is true, but it just got me wondering if a lightsaber comes in contact with an extremely flammable substance(gasoline or gunpowder or any similar thing in the SW universe), would it ignite the substance or not?

Cearon O'Flynn
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mayank budhwani
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    Isn't that the very definition of heat? The transfer of kinetic energy from one particle to another? – Yorik Feb 05 '16 at 16:21
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    I am imagining Luke being careless and starting forest fires all over Endor. – William Jackson Feb 05 '16 at 16:41
  • Related: http://scifi.stackexchange.com/questions/92681/no-endor-wildfires – Wad Cheber Feb 05 '16 at 17:27
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    I read something similar, but took it to mean that the lightsaber itself isn't giving off heat. Meaning if the lightsaber is 0.001 inches from your face, you don't feel "heat" coming from it, but as soon as it makes even the slightest contact, whamo, instant burns. – Geoff Feb 05 '16 at 17:28
  • Related: http://scifi.stackexchange.com/questions/48346/does-a-lightsaber-have-a-cauterizing-effect-when-cutting-off-appendages-or-not – Wad Cheber Feb 05 '16 at 17:28
  • @MishaRosnach Agreed its odd. But its a state of matter that doesn't exist in our world, not plasma, not electricity, not light. I over-exaggerated the distances, but the lightsaber seems different than say holding a white-hot piece of iron an inch from your face. – Geoff Feb 05 '16 at 18:31
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    @Geoff If the lightsaber is .001" away from your face, has the capacity to instantly make substances really hot, and there is air between it and your skin, you're getting a burn. If you mean to say that is isn't giving off microwave, infrared, and ultraviolet radiation, all of which can give you burns, then that's kind of strange: it's clearly giving off visible light radiation, whose spectrum is between ultraviolet and infrared. On the other hand, if a Jedi can do some sci fi woowoo when making a lightsaber, then it's a useful feature for preventing constant burns on the Jedi's hands. – Misha R Feb 05 '16 at 18:31
  • @Geoff sorry re-commented right before you posted :) Although I think the way I re-commented addresses your reply somewhat. If you're ok with fully in-universe sci fi tech woowoo, then I agree, this property is definitely useful and would probably be a requirement for a good lightsaber maker. Otherwise you're gonna burn the skin off your hands every time they get close to the blade. Unless the heat is directional, like a welding torch... Hmm. Yeah I dunno. – Misha R Feb 05 '16 at 18:34
  • Maybe it's a special field that causes electronic excitation. The light comes from air bouncing off the field. You don't get much heat transmission unless the field is in constant contact with something dense. – MackTuesday Feb 05 '16 at 21:49
  • I believe that in Splinter of the Mind's Eye (which is no longer canon, I think), Luke mentions that you could shave with a lightsaber if you were really careful. But it has been a long time since I read the book. – MichaelS Feb 06 '16 at 03:27
  • @Yorik "Transfer of kinetic energy" would be incorrect going by the strict thermodynamics definition. I was going to say it's the transfer of thermal energy, but when double checking, it seems that it's technically defined as any energy transfer that "isn't work." I'm not quite sure what that even means, but W = ∫Fdx = ΔK. So transfer of "kinetic energy" could be work. – jpmc26 Feb 06 '16 at 04:51
  • By the way, even if it can't 'spark' an ignition, it would quickly reach what's called flash point, where the substance reaches a specific temperature and ignites without any spark. @jpmc26 also work is defined as a change in energy so you are correct with that last equation. U=dE –  Feb 06 '16 at 07:30
  • @jpmc26 roughly speaking, heat is energy transfer that goes away if you ignore all the random microscopic motion of individual particles, and work is energy transfer that doesn't. I'm pretty sure we have some Q&A about this on [physics.SE]. – David Z Feb 06 '16 at 12:49
  • @DavidZ Yeah. It took me a bit to grasp it, but I either read or realized something that heat is the energy transfer that affects the internal state of a system. E.g., work might affect the entire system's (object's) overall velocity (its motion through the surrounding space) while heat could only affect temperature or phase of matter (properties of the system). – jpmc26 Feb 06 '16 at 19:24
  • @jpmc26: I was simplifying a bit, but in an ideal gas, 100% of thermal energy is translational kinetic energy (they are synonyms). So I think that you overstated it a little when you said what I said went against the definition of thermodynamics. Also, I said "particle." Since temperature is a statistical phenomenon ( the average translational kinetic energy in a system), it doesn't really have meaning for an individual particle. Generally, however I don't have issue with your explanations. – Yorik Feb 09 '16 at 15:27

4 Answers4

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YES

The lightsaber is shown many times to burn and melt objects.

Such as when Anakin loses his arm against Dooku in Attack of the Clones, you can see his skin and clothes burning.

anakin armless

Or when Darth Maul stabs Qui-Gon you see a burn mark on his clothes in The Phantom Menace

bye qui-gon

Or When Qui-Gon Melts the Trade Federation ship doors in The Phantom Menace

melty door

It may even steam in the rain, as this picture taken from screen shots of Attack of the Clones does show a fuzzier, more jagged looking lightsaber blade when Obi-Wan is in the rain on Kaminio than when he fights Dooku on Geonosis, which could be caused by steam.

steam?

Legends

And depending on the level of canon we are delving into, the game Jedi Outcast 2: Jedi Academy shows definite sparking from rain on the lightsaber.

The clone wars cartoon shows actual steam coming off of both Anakin and Assajj Ventriss' blades.

Heat is therefore produced one way or another.

This heat would transfer to a flammable material and cause ignition.

Even if the lightsaber isn't hot and "...it just makes atoms vibrate and hence heat is produced in a material the lightsaber comes in contact with" (which I have never heard) when a lightsaber blade came into contact with a flammable or combustible material it would make the atoms vibrate in that material, it would then heat up and cause ignition within itself.

It is still creating heat through one mechanism or another.

Cearon O'Flynn
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Yes, simply by heat. Heat exchange from a lightsaber is seen in The Phantom Menace, when Obi-Wan Kenobi and Qui-Gon Jinn use their lightsabers to melt through the doors in the Trade Federation ship. The metal is seen to heat up and glow red while melting.

enter image description here

enter image description here

Wad Cheber
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Escoce
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  • +1, and I added two images of the scene. I hope you don't mind. :) – Wad Cheber Feb 05 '16 at 17:25
  • Holding his hand that close to molten metal why doesn't he get burned? – Erik Feb 05 '16 at 18:38
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    Having worked in a glass shop, molten glass heated to white hot (much hotter than red hot) it's hot while in close proximity (an inch or two) but it quickly drops off to just warm past 3 inches. Doesn't matter whether it's metal or glass red hot is the same regardless of material. It's how much red and infrared light is radiated. – Escoce Feb 05 '16 at 18:42
  • @Erik The Force, yo. – corsiKa Feb 05 '16 at 18:47
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    @corsiKa That is why he looks so intent. He is force pushing the heat away. – Erik Feb 05 '16 at 18:49
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    That makes sense that the heat drops off pretty quickly. I didn't think about it until you mentioned your experience but a more common experience would be putting your hand over a pan to see if it has warmed up yet. I will say that his hand looks much closer to the molten metal than 3 inches away but maybe the glowing metal is making it look like his hand is closer than it really is. On a separate note, before now I thought your avatar was holding a spear. Now I know it is a tube for blowing glass... ;) – Erik Feb 05 '16 at 18:53
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    @Escoce: Red-hot is always the same temperature but different objects will radiate different amounts of heat at the same temperature, due to varying emissivity. http://www.engineeringtoolbox.com/emissivity-coefficients-d_447.html – Dietrich Epp Feb 05 '16 at 20:53
  • I think his hand would be melted by the time he was done (it took a while as I recall), but if we correct for Bad Hollywood, in "reality" he would have just not pushed the lightsaber so far through the door so his hand was further away from the molten metal. – MichaelS Feb 06 '16 at 03:25
4

It could (and has)

In canon, we see a lightsaber start a fire at least once. When Kylo Ren smashes up his instrument panel with his lightsaber, there are a few small fires.

enter image description here

(See in particular the upper left). Clearly, some flammable components were ignited.

This is consistent with the general nature of lightsabers. They seem to create a great deal of heat when they come into contact with objects, being capable of cauterizing wounds and melting metal. On the other hand, it’s not clear exactly how flammable an object must be to start a fire: we see lightsabers cutting through trees, but not producing anything more than localized burning, rather than setting the tree on fire immediately.

enter image description here

But in any case, a lightsaber is certainly capable of setting something on fire.

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Adamant
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4

When Darth Vader was fighting Obi-wan the first time in the Kenobi series, he used his lightsaber to light a big flame and used the Force to throw Obi-wan into the fire. He said "Now you will suffer Obi-wan, your pain has just begun."

DavidW
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