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How Hot Would a Light Saber Really Be? 410

Posted by Cliff
from the whizzz-vroom dept.
Datagod asks: "Has anyone ever calculated the temperature you would need to be able to slice through steel like it was thin air? How hot would a light saber really need to be? Also, I am assuming that at least some of the metal would be vaporized and the expanding gas would fling bits of molten metal at the saber wielder. Wouldn't your average Jedi be horribly scarred from all this."
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How Hot Would a Light Saber Really Be?

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  • Re:Very hot. (Score:5, Informative)

    by kryten_nl (863119) on Saturday April 01, 2006 @01:54AM (#15040317)
    Very, very cold.

    As the anti-protons move at uniform speed and the temperature is defined by the relative speed of particles wrt the flow.
  • All your answers ... (Score:5, Informative)

    by psergiu (67614) on Saturday April 01, 2006 @01:55AM (#15040322)
    ... are HERE [howstuffworks.com].
  • by xiphoris (839465) on Saturday April 01, 2006 @01:56AM (#15040328) Homepage
    It's an issue of temperature AND power.

    Consider this: how hot does something have to be to melt an ice sculpture? Well, a match would do it, except a match can't provide the power necessary to melt a significant amount of ice.

    You need the temperature necessary to turn steel into a vapor (look that up on a periodic table of elements); you also need the power necessary to turn some mass (per second) of steel into vapor. Anyone with a background in chemistry should be able to look up the required information on a standard periodic table.

    The equation will look like this:

    (Steel's specific heat) * (volume of steel to vaporize per second) * (temperature difference) = power necessary.
  • Re:Wickedlasers (Score:5, Informative)

    by kaan (88626) on Saturday April 01, 2006 @01:58AM (#15040335)
    omg for a second there i thought you posted a url to http://wickedweasel.com [wickedweasel.com].

    *phew* that was close!
  • by Dracos (107777) on Saturday April 01, 2006 @02:03AM (#15040355)

    Light sabers (and all other Star Wars pseudo-science) work because Lucas has no idea how physics works in reality, and he doesn't understand that there is a point where suspension of disbelief can no longer support the premise,especially in an adult audience.

  • by sirwired (27582) on Saturday April 01, 2006 @02:11AM (#15040388)
    Remember boys and girls, a lightsaber can be a dangerous weapon, and improperly used, it can hurt! Here are a few simple tips for Lightsaber Safety...

    http://www.atomfilms.com/af/content/your_lightsabe r [atomfilms.com]

    SirWired
  • by Quaoar (614366) on Saturday April 01, 2006 @02:31AM (#15040440)
    A plasma doesn't behave like a black body, so the blade would not become "whiter" as the plasma got hotter. The plasma of choice would have a couple of visible spectral lines (depending on the gas you ionize), and making the plasma "hotter" would just make those specific colors brighter. You can doubly ionize and even triply ionize the gas, but these transitions typically fall out of the visible range.

    Also, the magnetic field by itself would just constrain the particles to the axis of the saber. There's no guarantee that the stuff you vaporize will fly away from the handle, it could just as easy fly towards the handle. I would guess that there's also an electric potential keeping the plasma from melting your hands.
  • Re:Shadows (Score:5, Informative)

    by Ruie (30480) on Saturday April 01, 2006 @02:46AM (#15040492) Homepage
    I remember getting scolded by some fanboys for suggesting that lightsabers should cast no shadows (apparently they must cast shadows since shadows were present in Episode 4...) because the cutting edge - whether plasma or whatever else - would need to be hairline-thin regardless of temperature in order to slice through things without causing unmanageable explosions of melted and vaporized target material.

    Well, assume for a moment that it works. To melt metal one needs a lot of energy - so it likely comes from a nuclear source.

    1kg of steel has specific heat of 448 joules per degree Kelvin.

    Energy from fusion of hydrogen atoms is at most 8 Mev, the energy stored in Hafnium atom is 3 Mev - let's assume that the agent used has weight of Hafnium but produces 1 Mev per atom.

    Thus 1kg of energy agent stores 9e10 Joules - plenty enough to heat 20e3 tonnes of steel to 10000 degrees - cool !

    So, as long as I am having fun, here is a "complete" light saber design - just so that no one tries to patent something that obvious:

    • Handle - let's separate in two compartments - one contains energy agent and the other initiator that bombards that agent with nuclear particles.
    • In response to bombardment energy agent produces new particles in much greater proportion - this is a sticky point as single pass stimulated emission amplification is likely not that efficient - but then we have power to spare ! In fact this might be a feature as the handle will last very long time - the amplification medium will deplete slowly and from one end.
    • the particles are passed through moderator which limits their mean path in air to desired length.
    • put peltier element around the energy agent and moderator and feed the energy into the initiator.
    • initiator could be made as short pulse laser striking metal foil - these have been tested as tabletop devices already and should be capable to produce 3Mev gamma rays.
    • move the initiator around as energy agent is used up.
    The particle fountain would be very narrow - but it will heat up the air and that would produce the glow. Oh - and plasmas are opaque to light so there will be a shadow.

  • Re:2nd post (Score:5, Informative)

    by cekerr (608293) on Saturday April 01, 2006 @02:58AM (#15040529)
    When I clicked on the link:
    "The House Subcommittee on Modern Intergalactic Weapons Development and Regulation"
    My Firefox browser was hijacked, endless screens opened up and somebody's voice came over the speaker saying I know not what. One of the screens was an unpleasant image.
    OK, I've been April Fooled. But I doubt it was the sort of thing slash.dot approves of and if it does, I'm disapointed.
    Yes, I know all sorts of clever people can hijack my computer via malicious links. But I had hoped for better standards around here.
    I'm now on the 4 hour virus scan/spyware checking cycle on my laptop. Just as well it's Saturday.
  • http://www.starwars.com/databank/technology/lights aber/?id=eu [starwars.com]
    br> Once unleashed, the power channels through a positively charged continuous energy lens at the center of the handle. The beam then arcs circumferentially back to a negatively charged high energy flux aperture. A superconductor transfers the power from the flux aperture to the power cell. As a result, a lightsaber only expends power when its blade cuts through something. So efficient is the blade, that it does not radiate heat unless it comes into contact with something.
  • by Troed (102527) on Saturday April 01, 2006 @04:19AM (#15040781) Homepage Journal
    Steel the common name for the pure form of Iron

    Uh no. Steel is the name given to various Iron alloys. Iron is the name for the pure form of ... Iron. You got it exactly backwards.

    Yes, I'm a Mechanical Engineer.

  • by d_strand (674412) on Saturday April 01, 2006 @04:57AM (#15040866)
    E=(1 * 449 * 2841) + (1 * 247000) + (1 * 6090000) E= 1275609 + 247000 + 6090000 E= 7612609 J
    Power = 7612609/10 = 761 megawatts

    Assuming your numbers are correct, your last conclusion is wrong.
    7612609 J produced over 10 seconds means 761260.9 Watts == 761 KILOwatts, not megawatts. Quite a difference.
  • Re:Very hot. (Score:2, Informative)

    by Vlad2.0 (956796) on Saturday April 01, 2006 @05:34AM (#15040934)
    Cowyboy Neal
  • Exploding Bodies (Score:3, Informative)

    by Detritus (11846) on Saturday April 01, 2006 @11:25AM (#15041736) Homepage
    Considering that the human body is mostly water, wouldn't it flash to steam and blow up when struck by a light saber?
  • Re:2nd post (Score:1, Informative)

    by Anonymous Coward on Saturday April 01, 2006 @02:13PM (#15042430)
    Note the link: http://www.house.gov/htbin/leave_site?ln_url=http: //hagaren.be/&ln_desc=http://slashdot.org/ In essence, you are not going to see what you think you are going to see.

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