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Star Wars Prequels Science

Scientists Create New "Lightsaber-Like" Form of Matter 175

Posted by samzenpus
from the may-the-new-matter-be-with-you dept.
First time accepted submitter loftarasa writes "A group of scientists led by Harvard Professor of Physics Mikhail Lukin and MIT Professor of Physics Vladan Vuletic have developed a form of matter by binding massless photons together in a special kind of medium to create 'photonic molecules', effectively bringing us a bit closer to a world with lightsabers. 'The discovery, Lukin said, runs contrary to decades of accepted wisdom about the nature of light. Photons have long been described as massless particles which don't interact with each other – shine two laser beams at each other, he said, and they simply pass through one another. "Photonic molecules," however, behave less like traditional lasers and more like something you might find in science fiction – the light saber.' The work is described in Nature (paywalled)."
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Scientists Create New "Lightsaber-Like" Form of Matter

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  • by Anonymous Coward on Thursday September 26, 2013 @07:15PM (#44965861)

    Street justice can get pretty rough [youtube.com].

  • by ciaohound (118419) on Thursday September 26, 2013 @07:15PM (#44965875)

    Oh yeah.

  • by TwineLogic (1679802) on Thursday September 26, 2013 @07:29PM (#44965983)

    As the photons enter the cloud of cold atoms, Lukin said, its energy excites atoms along its path, causing the photon to slow dramatically. As the photon moves through the cloud, that energy is handed off from atom to atom, and eventually exits the cloud with the photon.

    These are not photons in free space being described. These are photons which have excited electron orbitals in some material.

  • by martyb (196687) on Thursday September 26, 2013 @07:31PM (#44965995)
    Slightly OT question but TFA mentions that photons are massless particles. I've read that elsewhere, too.

    I've also heard that black holes are so massive that the force of gravity does not let anything escape including light.

    So, if photons have no mass, how do black holes keep the photons from escaping?

    • by ChronoReverse (858838) on Thursday September 26, 2013 @07:37PM (#44966033)
      Because it turns out you don't need mass to be affected by gravity.


      A smart guy called Einstein did a lot of explaining about this.
    • by Anonymous Coward on Thursday September 26, 2013 @07:41PM (#44966061)

      I'm no expert.

      But I think it has less to do with gravity directly effecting things, and more to do with the gravity of the singularity simply bending space to the degree that things move into it. Thus, anything traveling through that warped space would be effected.

    • by HornWumpus (783565) on Thursday September 26, 2013 @07:58PM (#44966143)

      Photons have no _rest mass_ or they couldn't go the speed of light. Their mass is their energy which is a function of their frequency.

      • Re: (Score:2, Interesting)

        by martyb (196687)
        Photons have no _rest mass_ or they couldn't go the speed of light. Their mass is their energy which is a function of their frequency.

        Aaaaah! rest mass == massless, but because of their energy, and e=mc^2, there is, effectively, a mass, which the black hole can act upon... got it! Thanks!

        • by ebyrob (165903)

          I think momentum is an important term to remember here. Photons may not have rest mass, but they do have momentum. (in classical physics: p = m * v)

      • by AGMW (594303)
        >Photons have no _rest mass_ or they couldn't go the speed of light.

        So, we keep measuring the speed of light more and more precision, and what if our precision with that measurement simply isn't up to the job, and light actually travels at ever so slightly less than the (theoretical) speed of light.
        Photons at rest could then have a Really (really really ...) small mass ...

        ebyrob> I think momentum is an important term to remember here. Photons may not have rest mass, but they do have momentum. (in

        • Photons at rest could then have a Really (really really ...) small mass ...

          Well, theoretically (and only theoretically) photons could have a gigantive rest mass that is 100% converted to energy when in motion. The problem we normally face is that we cannot convert (or think of how to convert) 100% to 100% energy in a manner required to do that - t0 at rest, t1 in motion, a=c over t0 to t1 and (t1-t0) is nearly zero (e.g. 0.000.....0001 or 1*10^-infinity).

        • In addition to the point about different energies having different speeds.

          If they had _any_ rest mass at all their mass would be approaching infinity as they approached the speed of light.

    • by joe_frisch (1366229) on Thursday September 26, 2013 @08:12PM (#44966235)

      Physicists - please cover your ears, I'm trying to simplify.

      When particle move near the speed of light their mass increases. At the speed of light it becomes infinite. Imagine a very light particle, moving very fast. By making it move near C I can get any mass I want. So now imagine i make the original particle lighter, an keep moving it faster in such a way that its moving mass stays the same. In the limit a particle with zero mass moving at the speed of light can have some moving mass. That is how a photon works.

      Gravity will bend light, but the effect is very weak because light is moving very quickly. Gravity around a black hole is so strong that it will stop even light.

      Real relativity and general relativity changes this a little, but the basic idea is the same. Photons are very light -> massless. They move very fast -> speed of light, so they have mass from their motion. Gravity doesn't bend light much - but black holes have very strong gravity so they do bend light.

      • by justthinkit (954982) <floyd@just-think-it.com> on Thursday September 26, 2013 @08:44PM (#44966411) Homepage Journal
        Gravity around a black hole is so strong that it will stop even light.

        .
        The BH does not stop light. It changes the path light takes so it never leaves the black hole's event horizon.

        • Yes, all timelike curves cross the event horizon and hit the singularity (I think, maybe not for rotating black holes) because of the curvature of space.

            I wanted physicists to cover their ears because I was trying for a vaguely correct explanation that didn't require too much background.

          Even without general relativity you could imagine a concentration of mass what would prevent (newtonian) light from escaping.

      • by Princeofcups (150855) <john@princeofcups.com> on Thursday September 26, 2013 @09:30PM (#44966717) Homepage

        Physicists - please cover your ears, I'm trying to simplify.

        Sorry, but I can't let that go, especially since it's been modded up. Just no. Light does not have mass. There is no such thing as "moving mass."

        General relativity: How does a large mass bend light? Because a large mass bends space around it. Light ends up bending around the object, kind of like a banked roadway. A black hole bends space so tightly that if light gets too close (the event horizon), it gets sucked in. That's why we refer to it as a hole.

        • by joe_frisch (1366229) on Thursday September 26, 2013 @11:35PM (#44967409)

          A photon has mass energy. If I take an empty box made of perfect reflectors and add a photon, it will weigh more (by a tiny bit). It will have more inertia since inertial and gravitational mass are as far as we can tell exactly equivalent (as required if you use a curved space model of gravity).

          In any case, words are a bit fuzzy. A photon has 4-momentum and the mass like term (or time like term if you wish) is non-zero.

          btw- curved spacetime is a perfect model for all existing measurements involving gravity, but is incompatible with quantum mechanics at very (unreachable) high energies.

        • You are wrong, read wikipedia or google for "photon mass".

    • by XiaoMing (1574363) on Thursday September 26, 2013 @08:25PM (#44966309)

      Slightly OT question but TFA mentions that photons are massless particles. I've read that elsewhere, too.

      I've also heard that black holes are so massive that the force of gravity does not let anything escape including light.

      So, if photons have no mass, how do black holes keep the photons from escaping?

      Gravity bends the fabric of space-time itself, which the photons are travelling through.

      • by AGMW (594303)

        Gravity bends the fabric of space-time itself, which the photons are travelling through.

        Yeah, I get that, but I thought that the gravitational attraction was between the relative masses of the two objects. Presumably, therefore, any massless doodah wandering by would be unaffected by the masses of thingamejigs it might pass.
        That being so ...

        A mass-less photon (at speed) whizzing past a superhumongous 'body' would be unaffected by it, gravitationally, regardless of how massive the body was, if it had no mass. Ergo - a photon at speed has mass.

        Where does that mass come from. If it comes fr

        • by ceoyoyo (59147)

          E=mc^2. Rearranged, m = E / c^2.

          A photon has no rest mass (or energy). It does have energy associated with it's motion, and energy is equivalent to mass. You can use that mass/energy as the term in the classical momentum equation, or calculate the non-classical momentum directly based on it's frequency.

        • Your thinking of F = G*m1*m2/r^2
          if m1 is 0 then F would be 0 in newtonian physics. Einstein General Relativity replaces this equation. The theory was proved when Einstein showed that light bent around the sun. (measured during an eclipse)
    • They are massless, but they are still affected by the curvature of space, which according to relativity is the actual 'cause' of gravity. The space at the event horizon is curved such that not even photons can escape.

    • by ultranova (717540)

      So, if photons have no mass, how do black holes keep the photons from escaping?

      Because black holes are undead stars reaching from their graves with claws of gravity, and we all know that if you try to run from the monster you end up running right at it, which is what happens to photons. Then they get eaten and are never seen again.

    • by MickLinux (579158)

      Photons have no rest mass. They do have mass, though. In line with that, I should also note that photons do not exist in their own system, when in transit through high vacuum. That is, within their own system, the time - dilated length of time that they experience (while travelling at the speed of light) approaches zero.

      Of course, photons seldom travel at the speed of light. And their own existence seems to use non-photons as their space.

    • by drkim (1559875)

      So, if photons have no mass, how do black holes keep the photons from escaping?

      They don't. The gravitational field created by the black hole bends space-time.

      Think of a marble rolling around a flat sheet. The marble always moves in a straight line.

      Now imagine the sheet has a big depression in it. The marble still rolls 'straight' but as it follows the dip in the sheet, it 'curves' into the dip.

      Now, to the marble, it feels like it's still going straight.
      To an outside observer it looks like the marble is tracking into the dip.

    • by idji (984038)
      photons travel in "straight lines" at the speed of light. inside a blackhole the "straight lines" are loops or relativistically twisted that a photon would take an eternity to reach the event horizon. From the photon's own perspective all is normal, but not from the observer outside
    • Photons have no "rest mass".
      But as every photon is moving it has 'kinetic' mass, h*v / (c^2).

      • Congratulations, you've taken an extremely shallow knowledge of relativistic mass and assumed it's actually relevant.
        • Pfft ...

          If photons had no mass, something like a photovoltaic cel would not work.

          The one with "shallow" ... or more precisely "no knowledge" about photons is you.

    • by sjames (1099)

      When a particle is said to have no mass, they really mean it has no mass at rest. It still has the mass associated with it's energy and photons have energy.

    • So, if photons have no mass, how do black holes keep the photons from escaping?

      Good question, photons are energy, E(eV) = 1.24 / Î(μm).... the answer is m = E / c^2. Photons are like atoms, individually they are insignificant, because c^2 in is so large.

  • Good thing that lightsaber quote isn't getting out of hand.
  • by Anonymous Coward on Thursday September 26, 2013 @07:33PM (#44966005)
    Science is cool enough without ridiculous hyperbole.
    That is all.
  • ....... the number of accidental amputees is going to skyrocket.
  • by atari2600a (1892574) on Thursday September 26, 2013 @07:54PM (#44966125)
    Everyone knows photons were meant to be shot out of phasers, not for dueling with lasers.
    • by msobkow (48369)

      Phasers are not lasers.

      • by msobkow (48369)

        By that I mean that directed energy weapons are highly unlikely to use photons as the means of deploying their energy bursts. Magnetic bubbles of plasma or streams of electrons or even subatomic particles would be far more likely to be used.

        Lasers, on the other hand, shoot photons.

        • by TheCarp (96830)

          Really? Because of all those things, the only one that is currently actually being used as a directed energy weapon is...in fact, the laser.

          At least so far as "directed energy" doesn't count the acceleration of metal projectiles or explosive shells, which still take the cake for directed energy burst delivery.

        • by cellocgw (617879)

          Lasers, on the other hand, shoot photons.

          Yer a frickin' libral. Everyone knows that lasers don't shoot photons! People with a laser shoot photons.

    • Better to put them in a torpedo....

  • Light Saber? (Score:5, Insightful)

    by OhSoLaMeow (2536022) on Thursday September 26, 2013 @08:03PM (#44966161)
    Hokey religions and ancient weapons are no match for a good blaster at your side, kid.
    • Hokey religions and ancient weapons are no match for a good blaster at your side, kid.

      Of course these light-sabers will be made for a more civilized time...

      (ducks!)

  • While everyone misses the science. Sad state of affairs of the so called 'geek'.

  • by slew (2918) on Thursday September 26, 2013 @08:32PM (#44966361)

    From what I can tell, they are simply creating a system of quantum-mechanically entangled photons, not a "molecule" of photons...

    Apparently trick is that they created a medium (a laser cooled "gas" of rubidium atoms), and excited it with photons from a laser at a frequency that created a condition for the formation of a Rydberg state in the gas. This state is basically kind-of a pseudo-atom (i.e., a group of atoms that behave somewhat like a "scaled-up" atom). The gas made up of the pseudo-atom has a different apparent index of refraction than the unexcited medium looks to the first photon but it can effectively keep a second photon nearby the first photon in a type of quantum entanglement

    This is what is described as a photon "molecule". Of course the energy levels required to create a similar Rydberg state in air (at room-temperature) would be slightly different orders of magnitude because you are pumping in enough energy into the air so that hyper-energized pseudo-molecules of air are resisting your opponent's light sabre... Not so sure you want to be actually holding a device that does that ;^)

  • Lightsaber! (Score:4, Insightful)

    by manu0601 (2221348) on Thursday September 26, 2013 @08:54PM (#44966481)

    The journalist could not say their finding will cure cancer or obesity in several decades, therefore they sold it as a potential path to lightsabers!

    We would probably not accept such bold tactics from politicians, why do we accept it from scientific journalists?

    • by mdielmann (514750)

      The journalist could not say their finding will cure cancer or obesity in several decades, therefore they sold it as a potential path to lightsabers!

      We would probably not accept such bold tactics from politicians, why do we accept it from scientific journalists?

      From what I've seen, we do accept such outrageous tactics from politicians. Journalists seem to have realized that they can do the same.

  • If it wasn't his nickname before.....
  • Holodeck (Score:5, Interesting)

    by Tekoneiric (590239) on Thursday September 26, 2013 @09:45PM (#44966813) Journal
    This is more like holodeck matter from Star Trek or hard light holograms from Red Dwarf rather than a lightsaber.
  • Without Jedi skills, carrying a light-saber is just a good way to get shot.

  • by Anonymous Coward

    What a terrible article summary.

    Light is not self interacting at the tree level. This means there is no scattering of light in the classical sense, only through virtual particles (quantum loop corrections). Did this group of experimenters prove otherwise? No.

    This is the most clear statement from TFA

    "It's a photonic interaction that's mediated by the atomic interaction," Lukin said. "That makes these two photons behave like a molecule, and when they exit the medium they're much more likely to do so togeth

    • by ceoyoyo (59147)

      That's not actually really new either - people have been shooting lasers into super cold rubidium gas for years. What's new here is that these guys shot two photons in and watched them come out again.

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